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  • 1. Aartsen, M. G.
    et al.
    Ackermann, M.
    Adams, J.
    Aguilar, J. A.
    Ahlers, M.
    Ahrens, Maryon
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Altmann, D.
    Anderson, T.
    Arguelles, C.
    Arlen, T. C.
    Auffenberg, J.
    Bai, X.
    Barwick, S. W.
    Baum, V.
    Beatty, J. J.
    Tjus, J. Becker
    Becker, K. -H
    BenZvi, S.
    Berghaus, P.
    Berley, D.
    Bernardini, E.
    Bernhard, A.
    Besson, D. Z.
    Binder, G.
    Bindig, D.
    Bissok, M.
    Blaufuss, E.
    Blumenthal, J.
    Boersma, D. J.
    Bohm, Christian
    Stockholm University, Faculty of Science, Department of Physics.
    Bos, F.
    Bose, D.
    Boeser, S.
    Botner, O.
    Brayeur, L.
    Bretz, H. -P
    Brown, A. M.
    Casey, J.
    Casier, M.
    Cheung, E.
    Chirkin, D.
    Christov, A.
    Christy, B.
    Clark, K.
    Classen, L.
    Cleverinann, F.
    Coenders, S.
    Cowen, D. F.
    Silva, A. H. Cruz
    Danninger, Matthias
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Daughhetee, J.
    Davis, J. C.
    Day, M.
    de Andre, J. P. A. M.
    De Clercq, C.
    De Ridder, S.
    Desiati, P.
    de Vries, K. D.
    de With, M.
    DeYoung, T.
    Diaz-Velez, J. C.
    Dunkman, M.
    Eagan, R.
    Eberhardt, B.
    Eichmann, B.
    Eisch, J.
    Euler, S.
    Evenson, P. A.
    Fadiran, O.
    Fazely, A. R.
    Fedynitch, A.
    Feintzeig, J.
    Felde, J.
    Feusels, T.
    Filimonov, K.
    Finley, Chad
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Fischer-Wasels, T.
    Flis, Samuel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Franckowiak, A.
    Frantzen, K.
    Fuchs, T.
    Gaisser, T. K.
    Gaior, R.
    Gallagher, J.
    Gerhardt, L.
    Gier, D.
    Gladstone, L.
    Gluesenkamp, T.
    Goldschmidt, A.
    Golup, G.
    Gonzalez, J. G.
    Goodman, J. A.
    Gora, D.
    Grant, D.
    Gretskov, P.
    Groh, J. C.
    Gross, A.
    Ha, C.
    Haack, C.
    Ismail, A. Haj
    Hallen, P.
    Hallgren, A.
    Halzen, F.
    Hanson, K.
    Hebecker, D.
    Heereman, D.
    Heinen, D.
    Helbing, K.
    Hellauer, R.
    Hellwig, D.
    Hickford, S.
    Hill, G. C.
    Hoffman, K. D.
    Hoffmann, R.
    Homeier, A.
    Hoshina, K.
    Huang, F.
    Huelsnitz, W.
    Hulth, Per Olof
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Hultqvist, Klas
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Hussain, S.
    Ishihara, A.
    Jacobi, E.
    Jacobsen, J.
    Jagielski, K.
    Japaridze, G. S.
    Jero, K.
    Jlelati, O.
    Jurkovic, M.
    Kaminsky, B.
    Kappes, A.
    Karg, T.
    Karle, A.
    Kauer, M.
    Kelley, J. L.
    Kheirandish, A.
    Kiryluk, J.
    Klaes, J.
    Klein, S. R.
    Koehne, J. -H
    Kohnen, G.
    Kolanoski, H.
    Koob, A.
    Koepke, L.
    Kopper, C.
    Kopper, S.
    Koskinen, D. J.
    Kowalski, M.
    Kriesten, A.
    Krings, K.
    Kroll, G.
    Kroll, M.
    Kunnen, J.
    Kurahashi, N.
    Kuwabara, T.
    Labare, M.
    Larsen, D. T.
    Larson, M. J.
    Lesiak-Bzdak, M.
    Leuermann, M.
    Leute, J.
    Luenemann, J.
    Madsen, J.
    Maggi, G.
    Maruyama, R.
    Mase, K.
    Matis, H. S.
    Maunu, R.
    McNally, F.
    Meagher, K.
    Medici, M.
    Meli, A.
    Meures, T.
    Miarecki, S.
    Middell, E.
    Middlemas, E.
    Milke, N.
    Miller, J.
    Mohrmann, L.
    Montaruli, T.
    Morse, R.
    Nahnhauer, R.
    Naumann, U.
    Niederhausen, H.
    Nowicki, S. C.
    Nygren, D. R.
    Obertacke, A.
    Odrowski, S.
    Olivas, A.
    Omairat, A.
    O'Murchadha, A.
    Palczewski, T.
    Paul, L.
    Penek, Oe.
    Pepper, J. A.
    de los Heros, C. Perez
    Pfendner, C.
    Pieloth, D.
    Pinat, E.
    Posselt, J.
    Price, P. B.
    Przybylski, G. T.
    Puetz, J.
    Quinnan, M.
    Raedel, L.
    Rameez, M.
    Rawlins, K.
    Redl, P.
    Rees, I.
    Reimann, R.
    Relich, M.
    Resconi, E.
    Rhode, W.
    Richman, M.
    Riedel, B.
    Robertson, S.
    Rodrigues, Jp.
    Rongen, M.
    Rott, C.
    Ruhe, T.
    Ruzybayev, B.
    Ryckbosch, D.
    Saba, S. M.
    Sander, H. -G
    Sandroos, J.
    Santander, M.
    Sarkar, S.
    Schatto, K.
    Scheriau, F.
    Schmidt, T.
    Schmitz, M.
    Schoenen, S.
    Schoeneberg, S.
    Schoenwald, A.
    Schukraft, A.
    Schulte, L.
    Schulz, O.
    Seckel, D.
    Sestayo, Y.
    Seunarine, S.
    Shanidze, R.
    Smith, M. W. E.
    Soldin, D.
    Spiczak, G. M.
    Spiering, C.
    Stamatikos, M.
    Stanev, T.
    Stanisha, N. A.
    Stasik, A.
    Stezelberger, T.
    Stokstad, R. G.
    Stoessl, A.
    Strahler, E. A.
    Stroem, R.
    Strotjohann, N. L.
    Sullivan, G. W.
    Taavola, H.
    Taboada, I.
    Tamburro, A.
    Tepe, A.
    Ter-Antonyan, S.
    Terliuk, A.
    Tesic, G.
    Tilav, S.
    Toale, P. A.
    Tobin, M. N.
    Tosi, D.
    Tselengidou, M.
    Unger, E.
    Usner, M.
    Vallecorsa, S.
    van Eijndhoven, N.
    Vandenbroucke, J.
    van Santen, J.
    Vehring, M.
    Voge, M.
    Vraeghe, M.
    Walck, Christian
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Wallraff, M.
    Weaver, Ch.
    Wellons, M.
    Wendt, C.
    Westerhoff, S.
    Whelan, B. J.
    Whitehorn, N.
    Wichary, C.
    Wiebe, K.
    Wiebusch, C. H.
    Williams, D. R.
    Wissing, H.
    Wolf, Martin
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Wood, T. R.
    Woschnagg, K.
    Xu, D. L.
    Xu, X. W.
    Yanez, J. P.
    Yodh, G.
    Yoshida, S.
    Zarzhitsky, P.
    Ziemann, J.
    Zierke, S.
    Zoll, Marcel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Searches for small-scale anisotropies from neutrino point sources with three years of IceCube data2015In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 66, p. 39-52Article in journal (Refereed)
    Abstract [en]

    Recently, IceCube found evidence for a diffuse signal of astrophysical neutrinos in an energy range of similar to 60 TeV to the PeV-scale [1]. The origin of those events, being a key to understanding the origin of cosmic rays, is still an unsolved question. So far, analyses have not succeeded to resolve the diffuse signal into point-like sources. Searches including a maximum-likelihood-ratio test, based on the reconstructed directions and energies of the detected down- and up-going neutrino candidates, were also performed on IceCube data leading to the exclusion of bright point sources. In this paper, we present two methods to search for faint neutrino point sources in three years of IceCube data, taken between 2008 and 2011. The first method is an autocorrelation test, applied separately to the northern and southern sky. The second method is a multipole analysis, which expands the measured data in the northern hemisphere into spherical harmonics and uses the resulting expansion coefficients to separate signal from background. With both methods, the results are consistent with the background expectation with a slightly more sparse spatial distribution, corresponding to an underfluctuation. Depending on the assumed number of sources, the resulting upper limit on the flux per source in the northern hemisphere for an E-2 energy spectrum ranges from similar to 1.5. 10(-8) GeV/cm(2) s(-1), in the case of one assumed source, to similar to 4. 10(-10) GeV/cm(2) s(-1), in the case of 3500 assumed sources.

  • 2. Abdallah et al., DELPHI Collaboration: J
    et al.
    Moa, Torbjörn
    Stockholm University, Faculty of Science, Department of Physics.
    Study of Multi-Muon Bundles in Cosmic Ray Showers Detected with the DELPHI Detector at LEP2007In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 28, no 3, p. 273-286Article in journal (Refereed)
    Abstract [en]

    The DELPHI detector at LEP has been used to measure multi-muon bundles originating from cosmic ray interactions with air. The cosmic events were recorded in "parasitic mode" between individual e(+)e(-) interactions and the total live time of this data taking is equivalent to 1.6 x 10(6) s. The DELPHI apparatus is located about 100 m underground and the 84 metres rock overburden imposes a cutoff of about 52 GeV/c on muon momenta. The data from the large volume Hadron Calorimeter allowed the muon multiplicity of 54,201 events to be reconstructed. The resulting muon multiplicity distribution is compared with the prediction of the Monte Carlo simulation based on CORSIKA/QGSJETOI. The model fails to describe the abundance of high multiplicity events. The impact of QGSJET internal parameters on the results is also studied.

  • 3. Abdo, A. A.
    et al.
    Ackermann, M.
    Ajello, M.
    Ampe, J.
    Anderson, B.
    Atwood, W. B.
    Axelsson, M.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Bagagli, R.
    Baldini, L.
    Ballet, J.
    Barbiellini, G.
    Bartelt, J.
    Bastieri, D.
    Baughman, B. M.
    Bechtol, K.
    Bédérède, D.
    Bellardi, F.
    Bellazzini, R.
    Belli, F.
    Berenji, B.
    Bisello, D.
    Bissaldi, E.
    Bloom, E. D.
    Bogaert, G.
    Bogart, J. R.
    Bonamente, E.
    Borgland, A. W.
    Bourgeois, P.
    Bouvier, A.
    Bregeon, J.
    Brez, A.
    Brigida, M.
    Bruel, P.
    Burnett, T. H.
    Busetto, G.
    Caliandro, G. A.
    Cameron, R. A.
    Campell, M.
    Caraveo, P. A.
    Carius, S.
    Carlson, P.
    Casandjian, J. M.
    Cavazzuti, E.
    Ceccanti, M.
    Cecchi, C.
    Charles, E.
    Chekhtman, A.
    Cheung, C. C.
    Chiang, J.
    Chipaux, R.
    Cillis, A. N.
    Ciprini, S.
    Claus, R.
    Cohen-Tanugi, J.
    Condamoor, S.
    Conrad, J.
    Stockholm University, Faculty of Science, Department of Physics.
    Corbet, R.
    Cutini, S.
    Davis, D. S.
    Deklotz, M.
    Dermer, C. D.
    de Angelis, A.
    de Palma, F.
    Digel, S. W.
    Dizon, P.
    Dormody, M.
    Do Couto E Silva, E.
    Drell, P. S.
    Dubois, R.
    Dumora, D.
    Edmonds, Y.
    Fabiani, D.
    Farnier, C.
    Favuzzi, C.
    Ferrara, E. C.
    Ferreira, O.
    Fewtrell, Z.
    Flath, D. L.
    Fleury, P.
    Focke, W. B.
    Fouts, K.
    Frailis, M.
    Freytag, D.
    Fukazawa, Y.
    Funk, S.
    Fusco, P.
    Gargano, F.
    Gasparrini, D.
    Gehrels, N.
    Germani, S.
    Giebels, B.
    Giglietto, N.
    Giordano, F.
    Glanzman, T.
    Godfrey, G.
    Goodman, J.
    Grenier, I. A.
    Grondin, M.-H.
    Grove, J. E.
    Guillemot, L.
    Guiriec, S.
    Hakimi, M.
    Haller, G.
    Hanabata, Y.
    Hart, P. A.
    Hascall, P.
    Hays, E.
    Huffer, M.
    Hughes, R. E.
    Jóhannesson, G.
    Johnson, A. S.
    Johnson, R. P.
    Johnson, T. J.
    Johnson, W. N.
    Kamae, T.
    Katagiri, H.
    Kataoka, J.
    Kavelaars, A.
    Kelly, H.
    Kerr, M.
    Klamra, W.
    Knödlseder, J.
    Kocian, M. L.
    Kuehn, F.
    Kuss, M.
    Latronico, L.
    Lavalley, C.
    Leas, B.
    Lee, B.
    Lee, S.-H.
    Lemoine-Goumard, M.
    Longo, F.
    Loparco, F.
    Lott, B.
    Lovellette, M. N.
    Lubrano, P.
    Lung, D. K.
    Madejski, G. M.
    Makeev, A.
    Marangelli, B.
    Marchetti, M.
    Massai, M. M.
    May, D.
    Mazzenga, G.
    Mazziotta, M. N.
    McEnery, J. E.
    McGlynn, S.
    Meurer, C.
    Michelson, P. F.
    Minuti, M.
    Mirizzi, N.
    Mitra, P.
    Mitthumsiri, W.
    Mizuno, T.
    Moiseev, A. A.
    Mongelli, M.
    Monte, C.
    Monzani, M. E.
    Moretti, E.
    Morselli, A.
    Moskalenko, I. V.
    Murgia, S.
    Nelson, D.
    Nilsson, L.
    Nishino, S.
    Nolan, P. L.
    Nuss, E.
    Ohno, M.
    Ohsugi, T.
    Omodei, N.
    Orlando, E.
    Ormes, J. F.
    Ozaki, M.
    Paccagnella, A.
    Paneque, D.
    Panetta, J. H.
    Parent, D.
    Pelassa, V.
    Pepe, M.
    Pesce-Rollins, M.
    Picozza, P.
    Pinchera, M.
    Piron, F.
    Porter, T. A.
    Rainò, S.
    Rando, R.
    Rapposelli, E.
    Raynor, W.
    Razzano, M.
    Reimer, A.
    Reimer, O.
    Reposeur, T.
    Reyes, L. C.
    Ritz, S.
    Robinson, S.
    Rochester, L. S.
    Rodriguez, A. Y.
    Romani, R. W.
    Roth, M.
    Ryde, F.
    Sacchetti, A.
    Sadrozinski, H. F.-W.
    Saggini, N.
    Sanchez, D.
    Sander, A.
    Sapozhnikov, L.
    Saxton, O. H.
    Saz Parkinson, P. M.
    Sellerholm, A.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, Department of Physics.
    Sgrò, C.
    Siskind, E. J.
    Smith, D. A.
    Smith, P. D.
    Spandre, G.
    Spinelli, P.
    Starck, J.-L.
    Stephens, T. E.
    Strickman, M. S.
    Strong, A. W.
    Sugizaki, M.
    Suson, D. J.
    Tajima, H.
    Takahashi, H.
    Takahashi, T.
    Tanaka, T.
    Tenze, A.
    Thayer, J. B.
    Thayer, J. G.
    Thompson, D. J.
    Tibaldo, L.
    Tibolla, O.
    Torres, D. F.
    Tosti, G.
    Tramacere, A.
    Turri, M.
    Usher, T. L.
    Vilchez, N.
    Virmani, N.
    Vitale, V.
    Wai, L. L.
    Waite, A. P.
    Wang, P.
    Winer, B. L.
    Wood, D. L.
    Wood, K. S.
    Yasuda, H.
    Ylinen, T.
    Ziegler, M.
    The on-orbit calibration of the Fermi Large Area Telescope2009In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 32, no 3-4, p. 193-219Article in journal (Refereed)
    Abstract [en]

    The Large Area Telescope (LAT) on-board the Fermi Gamma-ray Space Telescope began its on-orbit operations on June 23, 2008. Calibrations, defined in a generic sense, correspond to synchronization of trigger signals, optimization of delays for latching data, determination of detector thresholds, gains and responses, evaluation of the perimeter of the South Atlantic Anomaly (SAA), measurements of live time, of absolute time, and internal and spacecraft boresight alignments. Here we describe on-orbit calibration results obtained using known astrophysical sources, galactic cosmic rays, and charge injection into the front-end electronics of each detector. Instrument response functions will be described in a separate publication. This paper demonstrates the stability of calibrations and describes minor changes observed since launch. These results have been used to calibrate the LAT datasets to be publicly released in August 2009.

  • 4. Abramowski, A.
    et al.
    Acero, F.
    Aharonian, F.
    Akhperjanian, A. G.
    Anton, G.
    Barnacka, A.
    de Almeida, U. Barres
    Bazer-Bachi, A. R.
    Becherini, Y.
    Becker, J.
    Behera, B.
    Bernloehr, K.
    Bochow, A.
    Boisson, C.
    Bolmont, J.
    Bordas, P.
    Borrel, V.
    Brucker, J.
    Brun, F.
    Brun, P.
    Buehler, R.
    Bulik, T.
    Buesching, I.
    Carrigan, S.
    Casanova, S.
    Cerruti, M.
    Chadwick, P. M.
    Charbonnier, A.
    Chaves, R. C. G.
    Cheesebrough, A.
    Chounet, L. -M
    Clapson, A. C.
    Coignet, G.
    Conrad, Jan
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Dalton, M.
    Daniel, M. K.
    Davids, I. D.
    Degrange, B.
    Deil, C.
    Dickinson, Hugh J.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Djannati-Atai, A.
    Domainko, W.
    Drury, L. O 'C.
    Dubois, F.
    Dubus, G.
    Dyks, J.
    Dyrda, M.
    Egberts, K.
    Eger, P.
    Espigat, P.
    Fallon, L.
    Farnier, C.
    Fegan, S.
    Feinstein, F.
    Fernandes, M. V.
    Fiasson, A.
    Fontaine, G.
    Foerster, A.
    Fuessling, M.
    Gabici, S.
    Gallant, Y. A.
    Gast, H.
    Gerard, L.
    Gerbig, D.
    Giebels, B.
    Glicenstein, J. F.
    Glueck, B.
    Goret, P.
    Goering, D.
    Hague, J. D.
    Hampf, D.
    Hauser, M.
    Heinz, S.
    Heinzelmann, G.
    Henri, G.
    Hermann, G.
    Hinton, J. A.
    Hoffmann, A.
    Hofmann, W.
    Hofverberg, P.
    Horns, D.
    Jacholkowska, A.
    de Jager, O. C.
    Jahn, C.
    Jamrozy, M.
    Jung, I.
    Kastendieck, M. A.
    Katarzynski, K.
    Katz, U.
    Kaufmann, S.
    Keogh, D.
    Kerschhaggl, M.
    Khangulyan, D.
    Khelifi, B.
    Klochkov, D.
    Kluzniak, W.
    Kneiske, T.
    Komin, Nu.
    Kosack, K.
    Kossakowski, R.
    Laffon, H.
    Lamanna, G.
    Lenain, J. -P
    Lennarz, D.
    Lohse, T.
    Lopatin, A.
    Lu, C. -C
    Marandon, V.
    Marcowith, A.
    Masbou, J.
    Maurin, D.
    Maxted, N.
    McComb, T. J. L.
    Medina, M. C.
    Mehault, J.
    Moderski, R.
    Moulin, E.
    Naumann, C. L.
    Naumann-Godo, M.
    de Naurois, M.
    Nedbal, D.
    Nekrassov, D.
    Nguyen, N.
    Nicholas, B.
    Niemiec, J.
    Nolan, S. J.
    Ohm, S.
    Olive, J-F
    Wilhelmi, E. de Ona
    Opitz, B.
    Ostrowski, M.
    Panter, M.
    Arribas, M. Paz
    Pedaletti, G.
    Pelletier, G.
    Petrucci, P. -O
    Pita, S.
    Puehlhofer, G.
    Punch, M.
    Quirrenbach, A.
    Raue, M.
    Rayner, S. M.
    Reimer, A.
    Reimer, O.
    Renaud, M.
    de los Reyes, R.
    Rieger, F.
    Ripken, Joachim
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Rob, L.
    Rosier-Lees, S.
    Rowell, G.
    Rudak, B.
    Rulten, C. B.
    Ruppel, J.
    Ryde, F.
    Sahakian, V.
    Santangelo, A.
    Schlickeiser, R.
    Schoeck, F. M.
    Schoenwald, A.
    Schwanke, U.
    Schwarzburg, S.
    Schwemmer, S.
    Shalchi, A.
    Sikora, M.
    Skilton, J. L.
    Sol, H.
    Spengler, G.
    Stawarz, L.
    Steenkamp, R.
    Stegmann, C.
    Stinzing, F.
    Sushch, I.
    Szostek, A.
    Tam, P. H.
    Tavernet, J. -P
    Terrier, R.
    Tibolla, O.
    Tluczykont, M.
    Valerius, K.
    van Eldik, C.
    Vasileiadis, G.
    Venter, C.
    Vialle, J. P.
    Viana, A.
    Vincent, P.
    Vivier, M.
    Voelk, H. J.
    Volpe, F.
    Vorobiov, S.
    Vorster, M.
    Wagner, S. J.
    Ward, M.
    Wierzcholska, A.
    Zajczyk, A.
    Zdziarski, A. A.
    Zech, A.
    Zechlin, H. -S
    Search for Lorentz Invariance breaking with a likelihood fit of the PKS 2155-304 flare data taken on MJD 539442011In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 34, no 9, p. 738-747Article in journal (Refereed)
    Abstract [en]

    Several models of Quantum Gravity predict Lorentz Symmetry breaking at energy scales approaching the Planck scale (similar to 10(19) GeV). With present photon data from the observations of distant astrophysical sources, it is possible to constrain the Lorentz Symmetry breaking linear term in the standard photon dispersion relations. Gamma Ray Bursts (GRB) and flaring Active Galactic Nuclei (AGN) are complementary to each other for this purpose, since they are observed at different distances in different energy ranges and with different levels of variability. Following a previous publication of the High Energy Stereoscopic System (H.E.S.S.) collaboration [1], a more sensitive event-by-event method consisting of a likelihood fit is applied to PKS 2155-304 flare data of MJD 53944 (July 28, 2006) as used in the previous publication. The previous limit on the linear term is improved by a factor of similar to 3 up to M(QG)(1), > 2.1 X 10(1B) GeV and is currently the best result obtained with blazars. The sensitivity to the quadratic term is lower and provides a limit of M(QG)(q) > 6.4 x 10(10) GeV, which is the best value obtained so far with an AGN and similar to the best limits obtained with GRB.

  • 5. Abramowski, A.
    et al.
    Acero, F.
    Aharonian, F.
    Akhperjanian, A. G.
    Anton, G.
    Barnacka, A.
    de Almeida, U. Barres
    Bazer-Bachi, A. R.
    Becherini, Y.
    Becker, J.
    Behera, B.
    Bernloehr, K.
    Bochow, A.
    Boisson, C.
    Bolmontr, J.
    Bordas, P.
    Borrel, V.
    Brucker, J.
    Brun, F.
    Brun, P.
    Bulik, T.
    Buesching, I.
    Carrigan, S.
    Casanova, S.
    Cerruti, M.
    Chadwick, P. M.
    Charbonnier, A.
    Chaves, R. C. G.
    Cheesebrough, A.
    Chounet, L. -M
    Clapson, A. C.
    Coignet, G.
    Conrad, Jan
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Dalton, M.
    Daniel, M. K.
    Davids, I. D.
    Degrange, B.
    Deil, C.
    Dickinson, Hugh J.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Djannati-Atai, A.
    Domainko, W.
    Drury, L. O. C.
    Dubois, F.
    Dubus, G.
    Dyks, J.
    Dyrda, M.
    Egberts, K.
    Eger, P.
    Espigat, P.
    Fallon, L.
    Farnier, C.
    Fegan, S.
    Feinstein, F.
    Fernandes, M. V.
    Fiasson, A.
    Fontaine, G.
    Foerster, A.
    Fuessling, M.
    Gallant, Y. A.
    Gast, H.
    Gerard, L.
    Gerbig, D.
    Giebels, B.
    Glicenstein, J. F.
    Glueck, B.
    Goret, P.
    Goering, D.
    Hague, J. D.
    Hampf, D.
    Hauser, M.
    Heinz, S.
    Heinzelmann, G.
    Henri, G.
    Hermann, G.
    Hinton, J. A.
    Hoffmann, A.
    Hofmann, W.
    Hofverberg, P.
    Horns, D.
    Jacholkowska, A.
    de Jager, O. C.
    Jahn, C.
    Jamrozy, M.
    Jung, I.
    Kastendieck, M. A.
    Katarzynski, K.
    Katz, U.
    Kaufmann, S.
    Keogh, D.
    Kerschhaggl, M.
    Khangulyan, D.
    Khelifi, B.
    Klochkov, D.
    Kluzniak, W.
    Kneiske, T.
    Komin, Nu
    Kosack, K.
    Kossakowski, R.
    Laffon, H.
    Lamanna, G.
    Lennarz, D.
    Lohse, T.
    Lopatin, A.
    Lu, C. -C
    Marandon, V.
    Marcowith, A.
    Masbou, J.
    Maurin, D.
    Maxted, N.
    McComb, T. J. L.
    Medina, M. C.
    Mehault, J.
    Moderski, R.
    Moulin, E.
    Naumann, C. L.
    Naumann-Godo, M.
    de Naurois, M.
    Nedbal, D.
    Nekrassov, D.
    Nguyen, N.
    Nicholas, B.
    Niemiec, J.
    Nolan, S. J.
    Ohm, S.
    Olive, J. -F
    Wilhelmi, E. de Ona
    Opitz, B.
    Ostrowski, M.
    Panter, M.
    Arribas, M. Paz
    Pedaletti, G.
    Pelletier, G.
    Petrucci, P. -O
    Pita, S.
    Puehlhofer, G.
    Punch, M.
    Quirrenbach, A.
    Raue, M.
    Rayner, S. M.
    Reimer, A.
    Reimer, O.
    Renaud, M.
    de los Reyes, R.
    Rieger, F.
    Ripken, Joachim
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Rob, L.
    Rosier-Lees, S.
    Rowell, G.
    Rudak, B.
    Rulten, C. B.
    Ruppel, J.
    Ryde, F.
    Sahakian, V.
    Santangelo, A.
    Schlickeiser, R.
    Schoeck, F. M.
    Schoenwald, A.
    Schwanke, U.
    Schwarzburg, S.
    Schwemmer, S.
    Shalchi, A.
    Sikora, M.
    Skilton, J. L.
    Sol, H.
    Spengler, G.
    Stawarz, L.
    Steenkamp, R.
    Stegmann, C.
    Stinzing, F.
    Sushch, I.
    Szostek, A.
    Tavernet, J. -P
    Terrier, R.
    Tibolla, O.
    Tluczykont, M.
    Valerius, K.
    van Eldik, C.
    Vasileiadis, G.
    Venter, C.
    Vialle, J. P.
    Viana, A.
    Vincent, P.
    Vivier, M.
    Voelk, H. J.
    Volpe, F.
    Vorobiov, S.
    Vorster, M.
    Wagner, S. J.
    Ward, M.
    Wierzcholska, A.
    Zajczyk, A.
    Zdziarski, A. A.
    Zech, A.
    Zechlin, H. -S
    HESS constraints on dark matter annihilations towards the sculptor and carina dwarf galaxies2011In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 34, no 8, p. 608-616Article in journal (Refereed)
    Abstract [en]

    The Sculptor and Carina dwarf spheroidal galaxies were observed with the H.E.S.S. Cherenkov telescope array between January 2008 and December 2009. The data sets consist of a total of 11.8 h and 14.811 of high quality data, respectively. No gamma-ray signal was detected at the nominal positions of these galaxies above 220 GeV and 320 GeV, respectively. Upper limits on the gamma-ray fluxes at 95% CL assuming two forms for the spectral energy distribution (a power law shape and one derived from dark matter annihilation) are obtained at the level of 10(-13)-10(-12) cm(-2) s(-1) in the TeV range. Constraints on the velocity weighted dark matter particle annihilation cross section for both Sculptor and Carina dwarf galaxies range from <sigma v > 10(-21) cm(3) s(-1) down to <sigma v > similar to 10(-2)2 cm(3) s(-1) on the dark matter halo model used. Possible enhancements of the gamma-ray flux are studied: the Sommerfeld effect, which is found to exclude some dark matter particle masses, the internal Bremsstrahlung and clumps in the dark-matter halo distributions.

  • 6. Ackermann, M.
    et al.
    Ajello, M.
    Allafort, A.
    Atwood, W. B.
    Axelsson, Magnus
    Stockholm University, Faculty of Science, Department of Astronomy.
    Baldini, L.
    Barbiellini, G.
    Bastieri, D.
    Bechtol, K.
    Bellazzini, R.
    Berenji, B.
    Bloom, E. D.
    Bonamente, E.
    Borgland, A. W.
    Bouvier, A.
    Bregeon, J.
    Brez, A.
    Brigida, M.
    Bruel, P.
    Buehler, R.
    Buson, S.
    Caliandro, G. A.
    Cameron, R. A.
    Caraveo, P. A.
    Casandjian, J. M.
    Cecchi, C.
    Charles, E.
    Chekhtman, A.
    Chiang, J.
    Ciprini, S.
    Claus, R.
    Cohen-Tanugi, J.
    Cutini, S.
    de Palma, F.
    Dermer, C. D.
    Digel, S. W.
    do Couto e Silva, E.
    Drell, P. S.
    Drlica-Wagner, A.
    Dubois, R.
    Enoto, T.
    Falletti, L.
    Favuzzi, C.
    Fegan, S. J.
    Focke, W. B.
    Fortin, P.
    Fukazawa, Y.
    Funk, S.
    Fusco, P.
    Gargano, F.
    Gehrels, N.
    Germani, S.
    Giglietto, N.
    Giordano, F.
    Giroletti, M.
    Glanzman, T.
    Godfrey, G.
    Grenier, I. A.
    Grove, J. E.
    Guiriec, S.
    Hadasch, D.
    Hayashida, M.
    Hays, E.
    Hughes, R. E.
    Johannesson, G.
    Johnson, A. S.
    Johnson, T. J.
    Kamae, T.
    Katagiri, H.
    Kataoka, J.
    Knoedlseder, J.
    Kuss, M.
    Lande, J.
    Latronico, L.
    Lee, S. -H
    Longo, F.
    Loparco, F.
    Lovellette, M. N.
    Lubrano, P.
    Madejski, G. M.
    Mazziotta, M. N.
    McEnery, J. E.
    Michelson, P. F.
    Mizuno, T.
    Moiseev, A. A.
    Monte, C.
    Monzani, M. E.
    Morselli, A.
    Moskalenko, I. V.
    Murgia, S.
    Nakamori, T.
    Naumann-Godo, M.
    Nolan, P. L.
    Norris, J. P.
    Nuss, E.
    Ohsugi, T.
    Okumura, A.
    Omodei, N.
    Orlando, E.
    Ormes, J. F.
    Ozaki, M.
    Paneque, D.
    Panetta, J. H.
    Parent, D.
    Pesce-Rollins, M.
    Pierbattista, M.
    Piron, F.
    Raino, S.
    Rando, R.
    Razzano, M.
    Reimer, A.
    Reimer, O.
    Reposeur, T.
    Ritz, S.
    Rochester, L. S.
    Sgro, C.
    Siskind, E. J.
    Smith, P. D.
    Spandre, G.
    Spinelli, P.
    Suson, D. J.
    Takahashi, H.
    Tanaka, T.
    Thayer, J. G.
    Thayer, J. B.
    Thompson, D. J.
    Tibaldo, L.
    Tosti, G.
    Troja, E.
    Usher, T. L.
    Vandenbroucke, J.
    Vasileiou, V.
    Vianello, G.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Vilchez, N.
    Vitale, V.
    Waite, A. P.
    Wang, P.
    Winer, B. L.
    Wood, K. S.
    Yang, Z.
    Zimmer, Stephan
    Stockholm University, Faculty of Science, Department of Physics.
    In-flight measurement of the absolute energy scale of the Fermi Large Area Telescope2012In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 35, no 6, p. 346-353Article in journal (Refereed)
    Abstract [en]

    The Large Area Telescope (LAT) on-board the Fermi Gamma-ray Space Telescope is a pair-conversion telescope designed to survey the gamma-ray sky from 20 MeV to several hundreds of GeV. In this energy band there are no astronomical sources with sufficiently well known and sharp spectral features to allow an absolute calibration of the LAT energy scale. However, the geomagnetic cutoff in the cosmic ray electron-plus-positron (CRE) spectrum in low Earth orbit does provide such a spectral feature. The energy and spectral shape of this cutoff can be calculated with the aid of a numerical code tracing charged particles in the Earth's magnetic field. By comparing the cutoff value with that measured by the LAT in different geomagnetic positions, we have obtained several calibration points between similar to 6 and similar to 13 GeV with an estimated uncertainty of similar to 2%. An energy calibration with such high accuracy reduces the systematic uncertainty in LAT measurements of, for example, the spectral cutoff in the emission from gamma ray pulsars.

  • 7.
    Ahrens, Maryon
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Bohm, Christian
    Stockholm University, Faculty of Science, Department of Physics.
    Dumm, Jonathan P.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Finley, Chad
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Flis, Samuel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Hulth, Per Olof
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Hultqvist, Klas
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Walck, Christian
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Wolf, Martin
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Zoll, Marcel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Characterization of the atmospheric muon flux in IceCube2016In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 78, p. 1-27Article in journal (Refereed)
    Abstract [en]

    Muons produced in atmospheric cosmic ray showers account for the by far dominant part of the event yield in large-volume underground particle detectors. The IceCube detector, with an instrumented volume of about a cubic kilometer, has the potential to conduct unique investigations on atmospheric muons by exploiting the large collection area and the possibility to track particles over a long distance. Through detailed reconstruction of energy deposition along the tracks, the characteristics of muon bundles can be quantified, and individual particles of exceptionally high energy identified. The data can then be used to constrain the cosmic ray primary flux and the contribution to atmospheric lepton fluxes from prompt decays of short-lived hadrons. In this paper, techniques for the extraction of physical measurements from atmospheric muon events are described and first results are presented. The multiplicity spectrum of TeV muons in cosmic ray air showers for primaries in the energy range from the knee to the ankle is derived and found to be consistent with recent results from surface detectors. The single muon energy spectrum is determined up to PeV energies and shows a clear indication for the emergence of a distinct spectral component from prompt decays of short-lived hadrons. The magnitude of the prompt flux, which should include a substantial contribution from light vector meson di-muon decays, is consistent with current theoretical predictions. The variety of measurements and high event statistics can also be exploited for the evaluation of systematic effects. In the course of this study, internal inconsistencies in the zenith angle distribution of events were found which indicate the presence of an unexplained effect outside the currently applied range of detector systematics. The underlying cause could be related to the hadronic interaction models used to describe muon production in air showers.

  • 8.
    Ahrens, Maryon
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Bohm, Christian
    Stockholm University, Faculty of Science, Department of Physics.
    Dumm, Jonathan P.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Finley, Chad
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Flis, Samuel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Hultqvist, Klas
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Walck, Christian
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Wolf, Martin
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Zoll, Marcel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    The IceCube realtime alert system2017In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 92, p. 30-41Article in journal (Refereed)
    Abstract [en]

    Although high-energy astrophysical neutrinos were discovered in 2013, their origin is still unknown. Aiming for the identification of an electromagnetic counterpart of a rapidly fading source, we have implemented a realtime analysis framework for the IceCube neutrino observatory. Several analyses selecting neutrinos of astrophysical origin are now operating in realtime at the detector site in Antarctica and are producing alerts for the community to enable rapid follow-up observations. The goal of these observations is to locate the astrophysical objects responsible for these neutrino signals. This paper highlights the infrastructure in place both at the South Pole site and at IceCube facilities in the north that have enabled this fast follow-up program to be implemented. Additionally, this paper presents the first realtime analyses to be activated within this framework, highlights their sensitivities to astrophysical neutrinos and background event rates, and presents an outlook for future discoveries.

  • 9.
    Bergström, Lars
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Dark matter and imaging air Cherenkov arrays2013In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 43, p. 44-49Article in journal (Refereed)
    Abstract [en]

    The CIA will mean a significant increase of the potential for dark matter detection, compared to present-day detectors like MAGIC, HESS and VERITAS. In particular, if - as it might be indicated from early LHC results - the dark matter sector is heavy, perhaps in the TeV mass range, imaging air Cherenkov arrays have a good opportunity to detect gamma-rays from dark matter annihilation in the galactic halo, the galactic center, dwarf galaxies, or galaxy clusters. A review of the present situation is given and a few of the miracles that may enhance chances for detection in CTA are discussed, such as Sommerfeld enhancement and internal bremsstrahlung radiation. A few templates for dark matter are studied, and the importance of the acceptance of the detector at low energies is pointed out. Finally, the idea of a complement to CIA in the form of a high-altitude, low energy threshold dedicated dark matter array, DMA, is discussed.

  • 10. Bernloehr, K.
    et al.
    Barnacka, A.
    Becherini, Y.
    Blanch Bigas, O.
    Carmona, E.
    Colin, P.
    Decerprit, G.
    Di Pierro, F.
    Dubois, F.
    Farnier, Christian
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Funk, S.
    Hermann, G.
    Hinton, J. A.
    Humensky, T. B.
    Khelifi, B.
    Kihm, T.
    Komin, N.
    Lenain, J-P
    Maier, G.
    Mazin, D.
    Medina, M. C.
    Moralejo, A.
    Nolan, S. J.
    Ohm, S.
    Wilhelmi, E. de Ona
    Parsons, R. D.
    Arribas, M. Paz
    Pedaletti, G.
    Pita, S.
    Prokoph, H.
    Rulten, C. B.
    Schwanke, U.
    Shayduk, M.
    Stamatescu, V.
    Vallania, P.
    Vorobiov, S.
    Wischnewski, R.
    Yoshikoshi, T.
    Zech, A.
    Monte Carlo design studies for the Cherenkov Telescope Array2013In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 43, p. 171-188Article in journal (Refereed)
    Abstract [en]

    The Cherenkov Telescopes Array (CTA) is planned as the future instrument for very-high-energy (VHE) gamma-ray astronomy with a wide energy range of four orders of magnitude and an improvement in sensitivity compared to current instruments of about an order of magnitude. Monte Carlo simulations are a crucial tool in the design of CTA. The ultimate goal of these simulations is to find the most cost-effective solution for given physics goals and thus sensitivity goals or to find, for a given cost, the solution best suited for different types of targets with CTA. Apart from uncertain component cost estimates, the main problem in this procedure is the dependence on a huge number of configuration parameters, both in specifications of individual telescope types and in the array layout. This is addressed by simulation of a huge array intended as a superset of many different realistic array layouts, and also by simulation of array subsets for different telescope parameters. Different analysis methods - in use with current installations and extended (or developed specifically) for CTA - are applied to the simulated data sets for deriving the expected sensitivity of CTA. In this paper we describe the current status of this iterative approach to optimize the CTA design and layout.

  • 11.
    Bohm, Christian
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Danninger, Matthias
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Finley, Chad
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics.
    Flis, Samuel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Hulth, Per-Olof
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Hultqvist, Klas
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Johansson, Henrik A. B.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Seo, Seon Hee
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Walck, Christian
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Wolf, Martin
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Zoll, Marcel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    All-particle cosmic ray energy spectrum measured with 26 IceTop stations2013In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 44, p. 40-58Article in journal (Refereed)
    Abstract [en]

    We report on a measurement of the cosmic ray energy spectrum with the IceTop air shower array, the surface component of the IceCube Neutrino Observatory at the South Pole. The data used in this analysis were taken between June and October, 2007, with 26 surface stations operational at that time, corresponding to about one third of the final array. The fiducial area used in this analysis was 0.122 km(2). The analysis investigated the energy spectrum from 1 to 100 PeV measured for three different zenith angle ranges between 0 degrees and 46 degrees. Because of the isotropy of cosmic rays in this energy range the spectra from all zenith angle intervals have to agree. The cosmic-ray energy spectrum was determined under different assumptions on the primary mass composition. Good agreement of spectra in the three zenith angle ranges was found for the assumption of pure proton and a simple two-component model. For zenith angles theta < 30 degrees, where the mass dependence is smallest, the knee in the cosmic ray energy spectrum was observed at about 4 PeV, with a spectral index above the knee of about -3.1. Moreover, an indication of a flattening of the spectrum above 22 PeV was observed.

  • 12.
    Bohm, Christian
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Danninger, Matthias
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Finley, Chad G.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Flis, Samuel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Hulth, Per-Olof
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Hultqvist, Klas
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Johansson, Henrik
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Seo, Seon-Hee
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Walck, Christian
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Wolf, Martin
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Zoll, Marcel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Cosmic ray composition and energy spectrum from 1-30 PeV using the 40-string configuration of IceTop and IceCube2013In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 42, p. 15-32Article in journal (Refereed)
    Abstract [en]

    The mass composition of high energy cosmic rays depends on their production, acceleration, and propagation. The study of cosmic ray composition can therefore reveal hints of the origin of these particles. At the South Pole, the IceCube Neutrino Observatory is capable of measuring two components of cosmic ray air showers in coincidence: the electromagnetic component at high altitude (2835 m) using the IceTop surface array, and the muonic component above similar to 1 TeV using the IceCube array. This unique detector arrangement provides an opportunity for precision measurements of the cosmic ray energy spectrum and composition in the region of the knee and beyond. We present the results of a neural network analysis technique to study the cosmic ray composition and the energy spectrum from 1 PeV to 30 PeV using data recorded using the 40-string/40-station configuration of the IceCube Neutrino Observatory.

  • 13.
    Bohm, Christian
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Danninger, Matthias
    Stockholm University, Faculty of Science, Department of Physics.
    Finley, Chad
    Stockholm University, Faculty of Science, Department of Physics.
    Hulth, Per Olof
    Stockholm University, Faculty of Science, Department of Physics.
    Hultqvist, Klas
    Stockholm University, Faculty of Science, Department of Physics.
    Johansson, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Nygren, David
    Stockholm University, Faculty of Science, Department of Physics.
    Seo, Seon-Hee
    Stockholm University, Faculty of Science, Department of Physics.
    Walck, Christian
    Stockholm University, Faculty of Science, Department of Physics.
    Wikström, Gustav
    Stockholm University, Faculty of Science, Department of Physics.
    The Energy Spectrum of Atmospheric Neutrinos between 2 and 200 TeV with the AMANDA-II Detector2010In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 34, p. 48-58Article in journal (Refereed)
  • 14.
    Bohm, Christian
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Danninger, Matthias
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Finley, Chad
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Hulth, Per Olof
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Hultqvist, Klas
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Johansson, Henrik
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Seo, Seon-Hee
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Walck, Christian
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Background Studies for Acoustic Neutrino Detection at the South Pole2012In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 35, p. 312-324Article in journal (Refereed)
    Abstract [en]

    The detection of acoustic signals from ultra-high energy neutrino interactions is a promising method to measure the flux of cosmogenic neutrinos expected on Earth. The energy threshold for this process depends strongly on the absolute noise level in the target material. The South Pole Acoustic Test Setup (SPATS), deployed in the upper part of four boreholes of the IceCube Neutrino Observatory, has monitored the noise in Antarctic ice at the geographic South Pole for more than two years down to 500 m depth. The noise is very stable and Gaussian distributed. Lacking an in situ calibration up to now, laboratory measurements have been used to estimate the absolute noise level in the 10–50 kHz frequency range to be smaller than 20 mPa. Using a threshold trigger, sensors of the South Pole Acoustic Test Setup registered acoustic events in the IceCube detector volume and its vicinity. Acoustic signals from refreezing IceCube holes and from anthropogenic sources have been used to test the localization of acoustic events. An upper limit on the neutrino flux at energies Eν > 1011 GeV is derived from acoustic data taken over eight months.

  • 15.
    Bohm, Christian
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Danninger, Matthias
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Finley, Chad
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Hulth, Per Olof
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Hultqvist, Klas
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Johansson, Henrik
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Seo, Seon-Hee
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Walck, Christian
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Wikström, Gustav
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Measurement of Acoustic Attenuation in South Pole Ice2011In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 34, no 6, p. 382-393Article in journal (Refereed)
    Abstract [en]

    Using the South Pole Acoustic Test Setup (SPATS) and a retrievable transmitter deployed in holes drilled for the IceCube experiment, we have measured the attenuation of acoustic signals by South Pole ice at depths between 190 m and 500 m. Three data sets, using different acoustic sources, have been analyzed and give consistent results. The method with the smallest systematic uncertainties yields an amplitude attenuation coefficient α = 3.20 ± 0.57 km−1 between 10 and 30 kHz, considerably larger than previous theoretical estimates. Expressed as an attenuation length, the analyses give a consistent result for λ ≡ 1/α of ∼300 m with 20% uncertainty. No significant depth or frequency dependence has been found.

  • 16.
    Bohm, Christian
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Danninger, Matthias
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Finley, Chad
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Hulth, Per Olof
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Hultqvist, Klas
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Johansson, Henrik
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Seo, Seon-Hee
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Walck, Christian
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Wikström, Gustav
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Search for Neutrino-Induced Cascades with Five Years of AMANDA Data2011In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 34, no 6, p. 420-430Article in journal (Refereed)
    Abstract [en]

    We report on the search for electromagnetic and hadronic showers ("cascades") produced by a diffuse flux of extraterrestrial neutrinos in the AMANDA neutrino telescope. Data for this analysis were recorded during 1001 days of detector livetime in the years 2000-2004. The observed event rates are consistent with the background expectation from atmospheric neutrinos and muons. An upper limit is derived for the diffuse flux of neutrinos of all flavors assuming a flavor ratio of v(e):v(mu):v(tau) = 1:1:1 at the detection site. The all-flavor flux of neutrinos with an energy spectrum Phi proportional to E(-2) is less than 5.0 x 10(-7) GeV s(-1) sr(-1) cm(-2) at a 90% C.L. Here, 90% of the simulated signal would fall within the energy range 40 TeV to 9 PeV. We discuss flux limits in the context of several specific models of extraterrestrial and prompt atmospheric neutrino production.

  • 17.
    Bohm, Christian
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Danninger, Matthias
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Finley, Chad
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Hulth, Per-Olof
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Hultqvist, Klas
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Johansson, Henrik
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Seo, Seon Hee
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Walck, Christian
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Zoll, Marcel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    The design and performance of icecube deepcore2012In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 35, no 10, p. 615-624Article in journal (Refereed)
    Abstract [en]

    The IceCube neutrino observatory in operation at the South Pole, Antarctica, comprises three distinct components: a large buried array for ultrahigh energy neutrino detection, a surface air shower array, and a new buried component called DeepCore. DeepCore was designed to lower the IceCube neutrino energy threshold by over an order of magnitude, to energies as low as about 10 GeV. DeepCore is situated primarily 2100 m below the surface of the icecap at the South Pole, at the bottom center of the existing IceCube array, and began taking physics data in May 2010. Its location takes advantage of the exceptionally clear ice at those depths and allows it to use the surrounding IceCube detector as a highly efficient active veto against the principal background of downward-going muons produced in cosmic-ray air showers. DeepCore has a module density roughly five times higher than that of the standard IceCube array, and uses photomultiplier tubes with a new photocathode featuring a quantum efficiency about 35% higher than standard IceCube PMTs. Taken together, these features of DeepCore will increase IceCube's sensitivity to neutrinos from WIMP dark matter annihilations, atmospheric neutrino oscillations, galactic supernova neutrinos, and point sources of neutrinos in the northern and southern skies. In this paper we describe the design and initial performance of DeepCore.

  • 18.
    Bohm, Christian
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Danninger, Matthias
    Stockholm University, Faculty of Science, Department of Physics.
    Hulth, Per Olof
    Stockholm University, Faculty of Science, Department of Physics.
    Hultqvist, Klas
    Stockholm University, Faculty of Science, Department of Physics.
    Johansson, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Nygren, David
    Stockholm University, Faculty of Science, Department of Physics.
    Seo, Seon-Hee
    Stockholm University, Faculty of Science, Department of Physics.
    Walck, Christian
    Stockholm University, Faculty of Science, Department of Physics.
    Wikström, Gustav
    Stockholm University, Faculty of Science, Department of Physics.
    Measurement of Sound Speed vs Depth in South Pole Ice for Neutrino Astronomy2010In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 33, p. 277-286Article in journal (Refereed)
    Abstract [en]

    We have measured the speed of both pressure waves and shear waves as a function of depth between 80 and 500 m depth in South Pole ice with better than 1% precision. The measurements were made using the South Pole Acoustic Test Setup (SPATS), an array of transmitters and sensors deployed in the ice at the South Pole in order to measure the acoustic properties relevant to acoustic detection of astrophysical neutrinos. The transmitters and sensors use piezoceramics operating at 5–25 kHz. Between 200 m and 500 m depth, the measured profile is consistent with zero variation of the sound speed with depth, resulting in zero refraction, for both pressure and shear waves. We also performed a complementary study featuring an explosive signal propagating vertically from 50 to 2250 m depth, from which we determined a value for the pressure wave speed consistent with that determined for shallower depths, higher frequencies, and horizontal propagation with the SPATS sensors. The sound speed profile presented here can be used to achieve good acoustic source position and emission time reconstruction in general, and neutrino direction and energy reconstruction in particular. The reconstructed quantities could also help separate neutrino signals from background.

  • 19. Borriello, Enrico
    et al.
    Maccione, Luca
    Cuoco, Alessandro
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Dark matter electron anisotropy: A universal upper limit2012In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 35, no 8, p. 537-546Article in journal (Refereed)
    Abstract [en]

    We study the dipole anisotropy in the arrival directions of high energy CR electrons and positrons (CRE) of dark matter (DM) origin. We show that this quantity is very weakly model dependent and offers a viable criterion to discriminate among CRE from DM or from local discrete sources, like e.g. pulsars. In particular, we find that the maximum anisotropy which DM can provide is to a very good approximation a universal quantity and, as a consequence, if a larger anisotropy is detected, this would constitute a strong evidence for the presence of astrophysical local discrete CRE sources, whose anisotropy, instead, can be naturally larger than the DM upper limit. We further find that the main source of anisotropy from DM is given by the fluctuation in the number density of DM sub-structures in the vicinity of the observer and we thus devote special attention to the study of the variance in the sub-structures realization implementing a dedicated Montecarlo simulation. Such scenarios will be probed in the next years by Fermi-LAT, providing new hints, or constraints, about the nature of DM.

  • 20. Braun, Jim
    et al.
    Baker, Mike
    Dumm, Jon
    Finley, Chad
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Karle, Albrecht
    Montaruli, Teresa
    Time-dependent point source search methods in high energy neutrino astronomy2010In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 33, no 3, p. 175-181Article in journal (Refereed)
    Abstract [en]

    We present maximum-likelihood search methods for time-dependent fluxes from point sources, such as flares or periodic emissions We describe a method for the case when the time dependence of the flux can be assumed a anon from other observations, and we additionally describe a method to search for bursts with an unknown rime dependence In the context of high energy neutrino astronomy, we simulate one year of data from a cubic kilometer scale neutrino detector and characterize these methods and equivalent binned methods with respect to the duration of neutrino emission Compared to standard time-integrated searches, we find that up to an order of magnitude fewer events are needed to discover bursts with short durations, even when the burst rime and duration are not known a priori.

  • 21.
    Conrad, Jan
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Imperial College London, UK.
    Statistical issues in astrophysical searches for particle dark matter2015In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 62, p. 165-177Article, review/survey (Refereed)
    Abstract [en]

    In this review statistical issues appearing in astrophysical searches for particle dark matter, i.e. indirect detection (dark matter annihilating into standard model particles) or direct detection (dark matter particles scattering in deep underground detectors) are discussed. One particular aspect of these searches is the presence of very large uncertainties in nuisance parameters (astrophysical factors) that are degenerate with parameters of interest (mass and annihilation/decay cross sections for the particles). The likelihood approach has become the most powerful tool, offering at least one well motivated method for incorporation of nuisance parameters and increasing the sensitivity of experiments by allowing a combination of targets superior to the more traditional data stacking. Other statistical challenges appearing in astrophysical searches are to large extent similar to any new physics search, for example at colliders, a prime example being the calculation of trial factors. Frequentist methods prevail for hypothesis testing and interval estimation, Bayesian methods are used for assessment of nuisance parameters and parameter estimation in complex parameter spaces. The basic statistical concepts will be exposed, illustrated with concrete examples from experimental searches and caveats will be pointed out.

  • 22.
    Conrad, Jan
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Dickinson, Hugh J.
    Stockholm University, Faculty of Science, Department of Physics.
    Farnier, Christian
    Stockholm University, Faculty of Science, Department of Physics. University of Geneva, Switzerland.
    Finley, Chad
    Stockholm University, Faculty of Science, Department of Physics.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy.
    Ripken, Joachim
    Stockholm University, Faculty of Science, Department of Physics.
    Introducing the CTA concept2013In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 43, p. 3-18Article in journal (Refereed)
    Abstract [en]

    The Cherenkov Telescope Array (CTA) is a new observatory for very high-energy (VHE) gamma rays. CTA has ambitions science goals, for which it is necessary to achieve full-sky coverage, to improve the sensitivity by about an order of magnitude, to span about four decades of energy, from a few tens of GeV to above 100 TeV with enhanced angular and energy resolutions over existing VHE gamma-ray observatories. An international collaboration has formed with more than 1000 members from 27 countries in Europe, Asia, Africa and North and South America. In 2010 the CTA Consortium completed a Design Study and started a three-year Preparatory Phase which leads to production readiness of CTA in 2014. In this paper we introduce the science goals and the concept of CTA, and provide an overview of the project.

  • 23. De Franco, Andrea
    et al.
    Inoue, Yoshiyuki
    Sánchez-Conde, Miguel A.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Universidad Autónoma de Madrid, Spain.
    Cotter, Garret
    Cherenkov telescope array extragalactic survey discovery potential and the impact of axion-like particles and secondary gamma rays2017In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 93, p. 8-16Article in journal (Refereed)
    Abstract [en]

    The Cherenkov Telescope Array (CTA) is about to enter construction phase and one of its main key science projects is to perform an unbiased survey in search of extragalactic sources. We make use of both the latest blazar gamma-ray luminosity function and spectral energy distribution to derive the expected number of detectable sources for both the planned Northern and Southern arrays of the CTA observatory. We find that a shallow, wide survey of about 0.5 hour per field of view would lead to the highest number of blazar detections. Furthermore, we investigate the effect of axion-like particles and secondary gamma rays from propagating cosmic rays on the source count distribution, since these processes predict different spectral shape from standard extragalactic background light attenuation. We can generally expect more distant objects in the secondary gamma-ray scenario, while axion-like particles do not significantly alter the expected distribution. Yet, we find that, these results strongly depend on the assumed magnetic field strength during the propagation. We also provide source count predictions for the High Altitude Water Cherenkov observatory (HAWC), the Large High Altitude Air Shower Observatory (LHAASO) and a novel proposal of a hybrid detector.

  • 24.
    Dickinson, Hugh
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Conrad, Jan
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Handling systematic uncertainties and combined source analyses for Atmospheric Cherenkov Telescopes2013In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 41, p. 17-30Article in journal (Refereed)
    Abstract [en]

    In response to an increasing availability of statistically rich observational data sets, the performance and applicability of traditional Atmospheric Cherenkov Telescope analyses in the regime of systematically dominated measurement uncertainties is examined. In particular, the effect of systematic uncertainties affecting the relative normalisation of fiducial ON and OFF-source sampling regions - often denoted as alpha - is investigated using combined source analysis as a representative example case. The traditional summation of accumulated ON and OFF-source event counts is found to perform sub-optimally in the studied contexts and requires careful calibration to correct for unexpected and potentially misleading statistical behaviour. More specifically, failure to recognise and correct for erroneous estimates of alpha is found to produce substantial overestimates of the combined population significance which worsen with increasing target multiplicity. An alternative joint likelihood technique is introduced, which is designed to treat systematic uncertainties in a uniform and statistically robust manner. This alternate method is shown to yield dramatically enhanced performance and reliability with respect to the more traditional approach.

  • 25. Doro, M.
    et al.
    Conrad, Jan
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Emmanoulopoulos, D.
    Sanchez-Conde, M. A.
    Barrio, J. A.
    Birsin, E.
    Bolmont, J.
    Brun, P.
    Colafrancesco, S.
    Connell, S. H.
    Contreras, J. L.
    Daniel, M. K.
    Fornasa, M.
    Gaug, M.
    Glicenstein, J. F.
    Gonzalez-Munoz, A.
    Hassan, T.
    Horns, D.
    Jacholkowska, A.
    Jahn, C.
    Mazini, R.
    Mirabal, N.
    Moralejo, A.
    Moulin, E.
    Nieto, D.
    Ripken, Joachim
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sandaker, H.
    Schwanke, U.
    Spengler, G.
    Stamerra, A.
    Viana, A.
    Zechlin, H. -S
    Zimmer, Stephan
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Dark matter and fundamental physics with the Cherenkov Telescope Array2013In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 43, p. 189-214Article in journal (Refereed)
    Abstract [en]

    The Cherenkov Telescope Array (CTA) is a project for a next-generation observatory for very high energy (GeV-TeV) ground-based gamma-ray astronomy, currently in its design phase, and foreseen to be operative a few years from now. Several tens of telescopes of 2-3 different sizes, distributed over a large area, will allow for a sensitivity about a factor 10 better than current instruments such as H.E.S.S, MAGIC and VERITAS, an energy coverage from a few tens of GeV to several tens of TeV, and a field of view of up to 10 degrees. In the following study, we investigate the prospects for CIA to study several science questions that can profoundly influence our current knowledge of fundamental physics. Based on conservative assumptions for the performance of the different CTA telescope configurations currently under discussion, we employ a Monte Carlo based approach to evaluate the prospects for detection and characterisation of new physics with the array. First, we discuss cm prospects for cold dark matter searches, following different observational strategies: in dwarf satellite galaxies of the Milky Way, which are virtually void of astrophysical background and have a relatively well known dark matter density; in the region close to the Galactic Centre, where the dark matter density is expected to be large while the astrophysical background due to the Galactic Centre can be excluded; and in clusters of galaxies, where the intrinsic flux may be boosted significantly by the large number of halo substructures. The possible search for spatial signatures, facilitated by the larger field of view of CIA, is also discussed. Next we consider searches for axion-like particles which, besides being possible candidates for dark matter may also explain the unexpectedly low absorption by extragalactic background light of gamma-rays from very distant blazars. We establish the axion mass range CIA could probe through observation of long-lasting flares in distant sources. Simulated light-curves of flaring sources are also used to determine the sensitivity to violations of Lorentz invariance by detection of the possible delay between the arrival times of photons at different energies. Finally, we mention searches for other exotic physics with CTA.

  • 26. Dravins, Dainis
    et al.
    LeBohec, Stephan
    Jensen, Hannes
    Stockholm University, Faculty of Science, Department of Astronomy. Lunds universitet.
    Nunez, Paul D.
    Optical intensity interferometry with the Cherenkov Telescope Array2013In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 43, p. 331-347Article in journal (Refereed)
    Abstract [en]

    With its unprecedented light-collecting area for night-sky observations, the Cherenkov Telescope Array (CTA) holds great potential for also optical stellar astronomy, in particular as a multi-element intensity interferometer for realizing imaging with sub-milliarcsecond angular resolution. Such an order-of-magnitude increase of the spatial resolution achieved in optical astronomy will reveal the surfaces of rotationally flattened stars with structures in their circumstellar disks and winds, or the gas flows between close binaries. Image reconstruction is feasible from the second-order coherence of light, measured as the temporal correlations of arrival times between photons recorded in different telescopes. This technique (once pioneered by Hanbury Brown and Twiss) connects telescopes only with electronic signals and is practically insensitive to atmospheric turbulence and to imperfections in telescope optics. Detector and telescope requirements are very similar to those for imaging air Cherenkov observatories, the main difference being the signal processing (calculating cross correlations between single camera pixels in pairs of telescopes). Observations of brighter stars are not limited by sky brightness, permitting efficient CTA use during also bright-Moon periods. While other concepts have been proposed to realize kilometer-scale optical interferometers of conventional amplitude (phase-) type, both in space and on the ground, their complexity places them much further into the future than CTA, which thus could become the first kilometer-scale optical imager in astronomy.

  • 27.
    Finley, Chad
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Bounding the Time Delay between High-energy Neutrinos and Gravitational-wave Transients from Gamma-ray Bursts2011In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 35, no 1, p. 1-7Article in journal (Refereed)
    Abstract [en]

    We derive a conservative coincidence time window for joint searches of gravitational-wave (GW) transients and high-energy neutrinos (HENs, with energies ≳100 GeV), emitted by gamma-ray bursts (GRBs). The last are among the most interesting astrophysical sources for coincident detections with current and near-future detectors. We take into account a broad range of emission mechanisms. We take the upper limit of GRB durations as the 95% quantile of the T90’s of GRBs observed by BATSE, obtaining a GRB duration upper limit of ∼150 s. Using published results on high-energy (>100 MeV) photon light curves for 8 GRBs detected by Fermi LAT, we verify that most high-energy photons are expected to be observed within the first ∼150 s of the GRB. Taking into account the breakout-time of the relativistic jet produced by the central engine, we allow GW and HEN emission to begin up to 100 s before the onset of observable gamma photon production. Using published precursor time differences, we calculate a time upper bound for precursor activity, obtaining that 95% of precursors occur within ∼250 s prior to the onset of the GRB. Taking the above different processes into account, we arrive at a time window of tHENtGW ∈ [−500 s, +500 s]. Considering the above processes, an upper bound can also be determined for the expected time window of GW and/or HEN signals coincident with a detected GRB, tGWtGRBtHENtGRB ∈ [−350 s, +150 s]. These upper bounds can be used to limit the coincidence time window in multimessenger searches, as well as aiding the interpretation of the times of arrival of measured signals.

  • 28. Kamae, Tuneyoshi
    et al.
    Andersson, Viktor
    Arimoto, Makoto
    Axelsson, Magnus
    Stockholm University, Faculty of Science, Department of Astronomy.
    Bettolo, Cecilia Marini
    Björnsson, Claes-Ingvar
    Stockholm University, Faculty of Science, Department of Astronomy.
    Bogaert, Gilles
    Carlson, Per
    Craig, William
    Ekeberg, Tomas
    Engdegdrd, Olle
    Fukazawa, Yasushi
    Gunji, Shuichi
    Hjalmarsdotter, Linnea
    Stockholm University, Faculty of Science, Department of Astronomy.
    Iwan, Bianca
    Kanai, Yoshikazu
    Kataoka, Jun
    Kawai, Nobuyuki
    Kazejev, Jaroslav
    Kiss, Mozsi
    Klamra, Wlodzimierz
    Larsson, Stefan
    Stockholm University, Faculty of Science, Department of Astronomy.
    Madejski, Grzegorz
    Mizuno, Tsunefumi
    Ng, Johnny
    Pearce, Mark
    Ryde, Felix
    Suhonen, Markus
    TaJima, Hiroyasu
    Takahashi, Hiromitsu
    Takahashi, Tadayuki
    Tanaka, Takuya
    Thurston, Timothy
    Ueno, Masaru
    Varneri, Gary
    Yamamoto, Kazuhide
    Yamashita, Yuichiro
    Ylinen, Tomi
    Yoshida, Hiroaki
    PoGOLite - A high sensitivity balloon-borne soft gamma-ray polarimeter2008In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 30, no 2, p. 72-84Article in journal (Refereed)
    Abstract [en]

    We describe a new balloon-borne instrument (PoGOLite) capable of detecting 10% polarisation from 200 mCrab point-like sources between 25 and 80 keV in one 6-h flight. Polarisation measurements in the soft gamma-ray band are expected to provide a powerful probe into high energy emission mechanisms as well as the distribution of magnetic fields, radiation fields and interstellar matter. Synchrotron radiation, inverse Compton scattering and propagation through high magnetic fields are likely to produce high degrees of polarisation in the energy band of the instrument. We demonstrate, through tests at accelerators, with radioactive sources and through computer simulations, that PoGOLite will be able to detect degrees of polarisation as predicted by models for several classes of high energy sources. At present, only exploratory polarisation measurements have been carried out in the soft gamma-ray band. Reduction of the large background produced by cosmic-ray particles while securing a large effective area has been the greatest challenge. PoGOLite uses Compton scattering and photo-absorption in an array of 217 well-type phoswich detector cells made of plastic and BGO scintillators surrounded by a BGO anticoincidence shield and a thick polyethylene neutron shield. The narrow Held of view (FWHM = 1.25 msr, 2.0 deg x 2.0 deg) obtained with detector cells and the use of thick background shields warrant a large effective area for polarisation measurements (similar to 228 cm(2) at E = 40 keV) without sacrificing the signal-to-noise ratio. Simulation studies for an atmospheric overburden of 3-4 g/cm(2) indicate that neutrons and gamma-rays entering the PDC assembly through the shields are dominant backgrounds. Off-line event selection based on recorded phototube waveforms and Compton kinematics reduce the background to that expected for a similar to 100 mCrab source between 25 and 50 keV. A 6-h observation of the Crab pulsar will differentiate between the Polar Cap/Slot Gap, Outer Gap, and Caustic models with greater than 5 sigma significance; and also cleanly identify the Compton reflection component in the Cygnus X-1 hard state. Long-duration flights will measure the dependence of the polarisation across the cyclotron absorption line in Hercules X-1. A scaled-down instrument will be flown as a pathfinder mission from the north of Sweden in 2010. The first science flight is planned to take place shortly thereafter. 

  • 29.
    Spengler, Gerrit
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Significance in gamma ray astronomy with systematic errors2015In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 67, p. 70-74Article in journal (Refereed)
    Abstract [en]

    The influence of systematic errors on the calculation of the statistical significance of a gamma-ray signal with the frequently invoked Li and Ma method is investigated. A simple criterion is derived to decide whether the Li and Ma method can be applied in the presence of systematic errors. An alternative method is discussed for cases where systematic errors are too large for the application of the original Li and Ma method. This alternative method reduces to the Li and Ma method when systematic errors are negligible. Finally, it is shown that the consideration of systematic errors will be important in many analyses of data from the planned Cherenkov Telescope Array.

  • 30. Wood, M.
    et al.
    Jogler, T.
    Dumm, Jonathan
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Funk, S.
    Monte Carlo studies of medium-size telescope designs for the Cherenkov Telescope Array2016In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 72, p. 11-31Article in journal (Refereed)
    Abstract [en]

    We present studies for optimizing the next generation of ground-based imaging atmospheric Cherenkov telescopes (IACTs). Results focus on mid-sized telescopes (MSTs) for CTA, detecting very high energy gamma rays in the energy range from a few hundred GeV to a few tens of TeV. We describe a novel, flexible detector Monte Carlo package, FAST (FAst Simulation for imaging air cherenkov Telescopes), that we use to simulate different array and telescope designs. The simulation is somewhat simplified to allow for efficient exploration over a large telescope design parameter space. We investigate a wide range of telescope performance parameters including optical resolution, camera pixel size, and light collection area. In order to ensure a comparison of the arrays at their maximum sensitivity, we analyze the simulations with the most sensitive techniques used in the field, such as maximum likelihood template reconstruction and boosted decision trees for background rejection. Choosing telescope design parameters representative of the proposed Davies-Cotton (DC) and Schwarzchild-Couder (SC) MST designs, we compare the performance of the arrays by examining the gamma-ray angular resolution and differential point-source sensitivity. We-further investigate the array performance under a wide range of conditions, determining the impact of the number of telescopes, telescope separation, night sky background, and geomagnetic field. We find a 30-40% improvement in the gamma-ray angular resolution at all energies when comparing arrays with an equal number of SC and DC telescopes, significantly enhancing point-source sensitivity in the MST energy range. We attribute the increase in point-source sensitivity to the improved optical point-spread function and smaller pixel size of the SC telescope design.

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