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  • 1. Ackley, K.
    et al.
    Amati, L.
    Barbieri, C.
    Bauer, F. E.
    Benetti, S.
    Bernardini, M. G.
    Bhirombhakdi, K.
    Botticella, M. T.
    Branchesi, M.
    Brocato, E.
    Bruun, S. H.
    Bulla, Mattia
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Campana, S.
    Cappellaro, E.
    Castro-Tirado, A. J.
    Chambers, K. C.
    Chaty, S.
    Chen, Ting-Wan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Max-Planck-Institut für Extraterrestrische Physik, Germany.
    Ciolfi, R.
    Coleiro, A.
    Copperwheat, C. M.
    Covino, S.
    Cutter, R.
    D'Ammando, F.
    D'Avanzo, P.
    De Cesare, G.
    D'Elia, V.
    Della Valle, M.
    Denneau, L.
    De Pasquale, M.
    Dhillon, V. S.
    Dyer, M. J.
    Elias-Rosa, N.
    Evans, P. A.
    Eyles-Ferris, R. A. J.
    Fiore, A.
    Fraser, M.
    Fruchter, A. S.
    Fynbo, J. P. U.
    Galbany, L.
    Gall, C.
    Galloway, D. K.
    Getman, F.
    Ghirlanda, G.
    Gillanders, J. H.
    Gomboc, A.
    Gompertz, B. P.
    Gonzalez-Fernandez, C.
    Gonzalez-Gaitan, S.
    Grado, A.
    Greco, G.
    Gromadzki, M.
    Groot, P. J.
    Gutierrez, C. P.
    Heikkila, T.
    Heintz, K. E.
    Hjorth, J.
    Hu, Y.-D.
    Huber, M. E.
    Inserra, C.
    Izzo, L.
    Japelj, J.
    Jerkstrand, Anders
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Jin, Z. P.
    Jonker, P. G.
    Kankare, E.
    Kann, D. A.
    Kennedy, M.
    Kim, S.
    Klose, S.
    Kool, Erik C.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kotak, R.
    Kuncarayakti, H.
    Lamb, G. P.
    Leloudas, G.
    Levan, A. J.
    Longo, F.
    Lowe, T. B.
    Lyman, J. D.
    Magnier, E.
    Maguire, K.
    Maiorano, E.
    Mandel, I.
    Mapelli, M.
    Mattila, S.
    McBrien, O. R.
    Melandri, A.
    Michalowski, M. J.
    Milvang-Jensen, B.
    Moran, S.
    Nicastro, L.
    Nicholl, M.
    Nicuesa Guelbenzu, A.
    Nuttal, L.
    Oates, S. R.
    O'Brien, P. T.
    Onori, F.
    Palazzi, E.
    Patricelli, B.
    Perego, A.
    Torres, M. A. P.
    Perley, D. A.
    Pian, E.
    Pignata, G.
    Piranomonte, S.
    Poshyachinda, S.
    Possenti, A.
    Pumo, M. L.
    Quirola-Vasquez, J.
    Ragosta, F.
    Ramsay, G.
    Rau, A.
    Rest, A.
    Reynolds, T. M.
    Rosetti, S. S.
    Rossi, A.
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sabha, N. B.
    Sagués Carracedo, Ana
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Salafia, O. S.
    Salmon, L.
    Salvaterra, R.
    Savaglio, S.
    Sbordone, L.
    Schady, P.
    Schipani, P.
    Schultz, A. S. B.
    Schweyer, Tassilo
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Max-Planck-Institut für Extraterrestrische Physik, Germany.
    Smartt, S. J.
    Smith, K. W.
    Smith, M.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Srivastav, S.
    Stanway, E. R.
    Starling, R. L. C.
    Steeghs, D.
    Stratta, G.
    Stubbs, C. W.
    Tanvir, N. R.
    Testa, V.
    Thrane, E.
    Tonry, J. L.
    Turatto, M.
    Ulaczyk, K.
    van der Horst, A. J.
    Vergani, S. D.
    Walton, N. A.
    Watson, D.
    Wiersema, K.
    Wiik, K.
    Wyrzykowski, L.
    Yang, Sheng
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Yi, S.-X.
    Young, D. R.
    Observational constraints on the optical and near-infrared emission from the neutron star-black hole binary merger candidate S190814bv2020In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 643, article id A113Article in journal (Refereed)
    Abstract [en]

    Context. Gravitational wave (GW) astronomy has rapidly reached maturity, becoming a fundamental observing window for modern astrophysics. The coalescences of a few tens of black hole (BH) binaries have been detected, while the number of events possibly including a neutron star (NS) is still limited to a few. On 2019 August 14, the LIGO and Virgo interferometers detected a high-significance event labelled S190814bv. A preliminary analysis of the GW data suggests that the event was likely due to the merger of a compact binary system formed by a BH and a NS.

    Aims. In this paper, we present our extensive search campaign aimed at uncovering the potential optical and near infrared electromagnetic counterpart of S190814bv. We found no convincing electromagnetic counterpart in our data. We therefore use our non-detection to place limits on the properties of the putative outflows that could have been produced by the binary during and after the merger.

    Methods. Thanks to the three-detector observation of S190814bv, and given the characteristics of the signal, the LIGO and Virgo Collaborations delivered a relatively narrow localisation in low latency - a 50% (90%) credible area of 5 deg(2) (23 deg(2)) - despite the relatively large distance of 26752 Mpc. ElectromagNetic counterparts of GRAvitational wave sources at the VEry Large Telescope collaboration members carried out an intensive multi-epoch, multi-instrument observational campaign to identify the possible optical and near infrared counterpart of the event. In addition, the ATLAS, GOTO, GRAWITA-VST, Pan-STARRS, and VINROUGE projects also carried out a search on this event. In this paper, we describe the combined observational campaign of these groups.

    Results. Our observations allow us to place limits on the presence of any counterpart and discuss the implications for the kilonova (KN), which was possibly generated by this NS-BH merger, and for the strategy of future searches. The typical depth of our wide-field observations, which cover most of the projected sky localisation probability (up to 99.8%, depending on the night and filter considered), is r similar to 22 (resp. K similar to 21) in the optical (resp. near infrared). We reach deeper limits in a subset of our galaxy-targeted observations, which cover a total similar to 50% of the galaxy-mass-weighted localisation probability. Altogether, our observations allow us to exclude a KN with large ejecta mass M greater than or similar to 0.1 M-circle dot to a high (> 90%) confidence, and we can exclude much smaller masses in a sub-sample of our observations. This disfavours the tidal disruption of the neutron star during the merger.

    Conclusions. Despite the sensitive instruments involved in the campaign, given the distance of S190814bv, we could not reach sufficiently deep limits to constrain a KN comparable in luminosity to AT 2017gfo on a large fraction of the localisation probability. This suggests that future (likely common) events at a few hundred megaparsecs will be detected only by large facilities with both a high sensitivity and large field of view. Galaxy-targeted observations can reach the needed depth over a relevant portion of the localisation probability with a smaller investment of resources, but the number of galaxies to be targeted in order to get a fairly complete coverage is large, even in the case of a localisation as good as that of this event.

  • 2. Ahumada, Tomas
    et al.
    Anand, Shreya
    Coughlin, Michael W.
    Andreoni, Igor
    Kool, Erik C.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kumar, Harsh
    Reusch, Simeon
    Sagués Carracedo, Ana
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Stein, Robert
    Cenko, S. Bradley
    Kasliwal, Mansi M.
    Singer, Leo P.
    Dunwoody, Rachel
    Mangan, Joseph
    Bhalerao, Varun
    Bulla, Mattia
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Burns, Eric
    Graham, Matthew J.
    Kaplan, David L.
    Perley, Daniel
    Almualla, Mouza
    Bloom, Joshua S.
    Cunningham, Virginia
    De, Kishalay
    Gatkine, Pradip
    Ho, Anna Y. Q.
    Karambelkar, Viraj
    Kong, Albert K. H.
    Yao, Yuhan
    Anupama, G. C.
    Barway, Sudhanshu
    Ghosh, Shaon
    Itoh, Ryosuke
    McBreen, Sheila
    Bellm, Eric C.
    Fremling, Christoffer
    Laher, Russ R.
    Mahabal, Ashish A.
    Riddle, Reed L.
    Rosnet, Philippe
    Rusholme, Ben
    Smith, Roger
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Bissaldi, Elisabetta
    Fletcher, Corinne
    Hamburg, Rachel
    Mailyan, Bagrat
    Malacaria, Christian
    Roberts, Oliver
    In Search of Short Gamma-Ray Burst Optical Counterparts with the Zwicky Transient Facility2022In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 932, no 1, article id 40Article in journal (Refereed)
    Abstract [en]

    The Fermi Gamma-ray Burst Monitor (GBM) triggers on-board in response to ∼40 short gamma-ray bursts (SGRBs) per year; however, their large localization regions have made the search for optical counterparts a challenging endeavour. We have developed and executed an extensive program with the wide field of view of the Zwicky Transient Facility (ZTF) camera, mounted on the Palomar 48 inch Oschin telescope (P48), to perform target-of-opportunity (ToO) observations on 10 Fermi-GBM SGRBs during 2018 and 2020–2021. Bridging the large sky areas with small field-of-view optical telescopes in order to track the evolution of potential candidates, we look for the elusive SGRB afterglows and kilonovae (KNe) associated with these high-energy events. No counterpart has yet been found, even though more than 10 ground-based telescopes, part of the Global Relay of Observatories Watching Transients Happen (GROWTH) network, have taken part in these efforts. The candidate selection procedure and the follow-up strategy have shown that ZTF is an efficient instrument for searching for poorly localized SGRBs, retrieving a reasonable number of candidates to follow up and showing promising capabilities as the community approaches the multi-messenger era. Based on the median limiting magnitude of ZTF, our searches would have been able to retrieve a GW170817-like event up to ∼200 Mpc and SGRB afterglows to z = 0.16 or 0.4, depending on the assumed underlying energy model. Future ToOs will expand the horizon to z = 0.2 and 0.7, respectively.

  • 3. Ahumada, Tomas
    et al.
    Singer, Leo P.
    Anand, Shreya
    Coughlin, Michael W.
    Kasliwal, Mansi M.
    Ryan, Geoffrey
    Andreoni, Igor
    Cenko, S. Bradley
    Fremling, Christoffer
    Kumar, Harsh
    Pang, Peter T. H.
    Burns, Eric
    Cunningham, Virginia
    Dichiara, Simone
    Dietrich, Tim
    Svinkin, Dmitry S.
    Almualla, Mouza
    Castro-Tirado, Alberto J.
    De, Kishalay
    Dunwoody, Rachel
    Gatkine, Pradip
    Hammerstein, Erica
    Iyyani, Shabnam
    Mangan, Joseph
    Perley, Dan
    Purkayastha, Sonalika
    Bellm, Eric
    Bhalerao, Varun
    Bolin, Bryce
    Bulla, Mattia
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Cannella, Christopher
    Chandra, Poonam
    Duev, Dmitry A.
    Frederiks, Dmitry
    Gal-Yam, Avishay
    Graham, Matthew
    Ho, Anna Y. Q.
    Hurley, Kevin
    Karambelkar, Viraj
    Kool, Erik C.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kulkarni, S. R.
    Mahabal, Ashish
    Masci, Frank
    McBreen, Sheila
    Pandey, Shashi B.
    Reusch, Simeon
    Ridnaia, Anna
    Rosnet, Philippe
    Rusholme, Benjamin
    Carracedo, A. Sagués
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Smith, Roger
    Soumagnac, Maayane
    Stein, Robert
    Troja, Eleonora
    Tsvetkova, Anastasia
    Walters, Richard
    Valeev, Azamat F.
    Discovery and confirmation of the shortest gamma-ray burst from a collapsar2021In: Nature Astronomy, E-ISSN 2397-3366, Vol. 5, no 9, p. 917-927Article in journal (Refereed)
    Abstract [en]

    Gamma-ray bursts (GRBs) are among the brightest and most energetic events in the Universe. The duration and hardness distribution of GRBs has two clusters(1), now understood to reflect (at least) two different progenitors(2). Short-hard GRBs (SGRBs; T-90 < 2 s) arise from compact binary mergers, and long-soft GRBs (LGRBs; T-90 > 2 s) have been attributed to the collapse of peculiar massive stars (collapsars)(3). The discovery of SN 1998bw/GRB 980425 (ref. (4)) marked the first association of an LGRB with a collapsar, and AT 2017gfo (ref. (5))/GRB 170817A/GW170817 (ref. (6)) marked the first association of an SGRB with a binary neutron star merger, which also produced a gravitational wave. Here, we present the discovery of ZTF20abwysqy (AT2020scz), a fast-fading optical transient in the Fermi satellite and the Interplanetary Network localization regions of GRB 200826A; X-ray and radio emission further confirm that this is the afterglow. Follow-up imaging (at rest-frame 16.5 days) reveals excess emission above the afterglow that cannot be explained as an underlying kilonova, but which is consistent with being the supernova. Although the GRB duration is short (rest-frame T-90 of 0.65 s), our panchromatic follow-up data confirm a collapsar origin. GRB 200826A is the shortest LGRB found with an associated collapsar; it appears to sit on the brink between a successful and a failed collapsar. Our discovery is consistent with the hypothesis that most collapsars fail to produce ultra-relativistic jets.

  • 4. Almualla, Mouza
    et al.
    Anand, Shreya
    Coughlin, Michael W.
    Dietrich, Tim
    Guessoum, Nidhal
    Sagués Carracedo, Ana
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Ahumada, Tomás
    Andreoni, Igor
    Antier, Sarah
    Bellm, Eric C.
    Bulla, Mattia
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita). Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Singer, Leo P.
    Optimizing serendipitous detections of kilonovae: cadence and filter selection2021In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 504, no 2, p. 2822-2831Article in journal (Refereed)
    Abstract [en]

    The rise of multimessenger astronomy has brought with it the need to exploit all available data streams and learn more about the astrophysical objects that fall within its breadth. One possible avenue is the search for serendipitous optical/near-infrared counterparts of gamma-ray bursts (GRBs) and gravitational-wave (GW) signals, known as kilonovae. With surveys such as the Zwicky Transient Facility (ZTF), which observes the sky with a cadence of ∼3 d, the existing counterpart locations are likely to be observed; however, due to the significant amount of sky to explore, it is difficult to search for these fast-evolving candidates. Thus, it is beneficial to optimize the survey cadence for realtime kilonova identification and enable further photometric and spectroscopic observations. We explore how the cadence of wide field-of-view surveys like ZTF can be improved to facilitate such identifications. We show that with improved observational choices, e.g. the adoption of three epochs per night on a ∼ nightly basis, and the prioritization of redder photometric bands, detection efficiencies improve by about a factor of two relative to the nominal cadence. We also provide realistic hypothetical constraints on the kilonova rate as a form of comparison between strategies, assuming that no kilonovae are detected throughout the long-term execution of the respective observing plan. These results demonstrate how an optimal use of ZTF increases the likelihood of kilonova discovery independent of GWs or GRBs, thereby allowing for a sensitive search with less interruption of its nominal cadence through Target of Opportunity programs.

  • 5. Anand, Shreya
    et al.
    Coughlin, Michael W.
    Kasliwal, Mansi M.
    Bulla, Mattia
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Ahumada, Tomás
    Sagués Carracedo, Ana
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Almualla, Mouza
    Andreoni, Igor
    Stein, Robert
    Foucart, Francois
    Singer, Leo P.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Bellm, Eric C.
    Bolin, Bryce
    Caballero-García, M. D.
    Castro-Tirado, Alberto J.
    Cenko, S. Bradley
    De, Kishalay
    Dekany, Richard G.
    Duev, Dmitry A.
    Feeney, Michael
    Fremling, Christoffer
    Goldstein, Daniel A.
    Golkhou, V. Zach
    Graham, Matthew J.
    Guessoum, Nidhal
    Hankins, Matthew J.
    Hu, Youdong
    Kong, Albert K. H.
    Kool, Erik C.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kulkarni, S. R.
    Kumar, Harsh
    Laher, Russ R.
    Masci, Frank J.
    Mróz, Przemek
    Nissanke, Samaya
    Porter, Michael
    Reusch, Simeon
    Riddle, Reed
    Rosnet, Philippe
    Rusholme, Ben
    Serabyn, Eugene
    Sánchez-Ramírez, R.
    Rigault, Mickael
    Shupe, David L.
    Smith, Roger
    Soumagnac, Maayane T.
    Walters, Richard
    Valeev, Azamat F.
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita). California Institute of Technology, USA; Russian Academy of Sciences, Russia.
    Optical follow-up of the neutron star-black hole mergers S200105ae and S200115j2021In: Nature Astronomy, E-ISSN 2397-3366, Vol. 5, p. 46-53Article in journal (Refereed)
    Abstract [en]

    LIGO and Virgo's third observing run revealed the first neutron star-black hole (NSBH) merger candidates in gravitational waves. These events are predicted to synthesize r-process elements(1,2)creating optical/near-infrared 'kilonova' emission. The joint gravitational wave and electromagnetic detection of an NSBH merger could be used to constrain the equation of state of dense nuclear matter(3), and independently measure the local expansion rate of the Universe(4). Here, we present the optical follow-up and analysis of two of the only three high-significance NSBH merger candidates detected to date, S200105ae and S200115j, with the Zwicky Transient Facility(5). The Zwicky Transient Facility observed similar to 48% of S200105ae and similar to 22% of S200115j's localization probabilities, with observations sensitive to kilonovae brighter than -17.5 mag fading at 0.5 mag d(-1)in the g- and r-bands; extensive searches and systematic follow-up of candidates did not yield a viable counterpart. We present state-of-the-art kilonova models tailored to NSBH systems that place constraints on the ejecta properties of these NSBH mergers. We show that with observed depths of apparent magnitude similar to 22 mag, attainable in metre-class, wide-field-of-view survey instruments, strong constraints on ejecta mass are possible, with the potential to rule out low mass ratios, high black hole spins and large neutron star radii.

  • 6. Andreoni, Igor
    et al.
    Coughlin, Michael W.
    Almualla, Mouza
    Bellm, Eric C.
    Bianco, Federica B.
    Bulla, Mattia
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Cucchiara, Antonino
    Dietrich, Tim
    Goobar, Ariel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kool, Erik C.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Li, Xiaolong
    Ragosta, Fabio
    Sagués Carracedo, Ana
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Singer, Leo P.
    Optimizing Cadences with Realistic Light-curve Filtering for Serendipitous Kilonova Discovery with Vera Rubin Observatory2022In: Astrophysical Journal Supplement Series, ISSN 0067-0049, E-ISSN 1538-4365, Vol. 258, no 1, article id 5Article in journal (Refereed)
    Abstract [en]

    Current and future optical and near-infrared wide-field surveys have the potential to find kilonovae, the optical and infrared counterparts to neutron star mergers, independently of gravitational-wave or high-energy gamma-ray burst triggers. The ability to discover fast and faint transients such as kilonovae largely depends on the area observed, the depth of those observations, the number of revisits per field in a given time frame, and the filters adopted by the survey; it also depends on the ability to perform rapid follow-up observations to confirm the nature of the transients. In this work, we assess kilonova detectability in existing simulations of the Legacy Survey of Space and Time strategy for the Vera C. Rubin Wide Fast Deep survey, with focus on comparing rolling to baseline cadences. Although currently available cadences can enable the detection of >300 kilonovae out to ∼1400 Mpc over the 10 year survey, we can expect only 3–32 kilonovae similar to GW170817 to be recognizable as fast-evolving transients. We also explore the detectability of kilonovae over the plausible parameter space, focusing on viewing angle and ejecta masses. We find that observations in redder izy bands are crucial for identification of nearby (within 300 Mpc) kilonovae that could be spectroscopically classified more easily than more distant sources. Rubin's potential for serendipitous kilonova discovery could be increased by gain of efficiency with the employment of individual 30 s exposures (as opposed to 2 × 15 s snap pairs), with the addition of red-band observations coupled with same-night observations in g or r bands, and possibly with further development of a new rolling-cadence strategy.

  • 7. Andreoni, Igor
    et al.
    Coughlin, Michael W.
    Kool, Erik C.
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Astronomy.
    Kasliwal, Mansi M.
    Kumar, Harsh
    Bhalerao, Varun
    Carracedo, Ana Sagués
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics.
    Ho, Anna Y. Q.
    Pang, Peter T. H.
    Saraogi, Divita
    Sharma, Kritti
    Shenoy, Vedant
    Burns, Eric
    Ahumada, Tomás
    Anand, Shreya
    Singer, Leo P.
    Perley, Daniel A.
    De, Kishalay
    Fremling, U. C.
    Bellm, Eric C.
    Bulla, Mattia
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Astronomy.
    Crellin-Quick, Arien
    Dietrich, Tim
    Drake, Andrew
    Duev, Dmitry A.
    Goobar, Ariel
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics.
    Graham, Matthew J.
    Kaplan, David L.
    Kulkarni, S. R.
    Laher, Russ R.
    Mahabal, Ashish A.
    Shupe, David L.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Astronomy.
    Walters, Richard
    Yao, Yuhan
    Fast-transient Searches in Real Time with ZTFReST: Identification of Three Optically Discovered Gamma-Ray Burst Afterglows and New Constraints on the Kilonova Rate2021In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 918, no 2, article id 63Article in journal (Refereed)
    Abstract [en]

    The most common way to discover extragalactic fast transients, which fade within a few nights in the optical, is via follow-up of gamma-ray burst and gravitational-wave triggers. However, wide-field surveys have the potential to identify rapidly fading transients independently of such external triggers. The volumetric survey speed of the Zwicky Transient Facility (ZTF) makes it sensitive to objects as faint and fast fading as kilonovae, the optical counterparts to binary neutron star mergers, out to almost 200 Mpc. We introduce an open-source software infrastructure, the ZTF REaltime Search and Triggering, ZTFReST, designed to identify kilonovae and fast transients in ZTF data. Using the ZTF alert stream combined with forced point-spread-function photometry, we have implemented automated candidate ranking based on their photometric evolution and fitting to kilonova models. Automated triggering, with a human in the loop for monitoring, of follow-up systems has also been implemented. In 13 months of science validation, we found several extragalactic fast transients independently of any external trigger, including two supernovae with post-shock cooling emission, two known afterglows with an associated gamma-ray burst (ZTF20abbiixp, ZTF20abwysqy), two known afterglows without any known gamma-ray counterpart (ZTF20aajnksq, ZTF21aaeyldq), and three new fast-declining sources (ZTF20abtxwfx, ZTF20acozryr, ZTF21aagwbjr) that are likely associated with GRB200817A, GRB201103B, and GRB210204A. However, we have not found any objects that appear to be kilonovae. We constrain the rate of GW170817-like kilonovae to R < 900 Gpc(-3) yr(-1) (95% confidence). A framework such as ZTFReST could become a prime tool for kilonova and fast-transient discovery with the Vera Rubin Observatory.

  • 8. Andreoni, Igor
    et al.
    Kool, Erik C.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sagués Carracedo, Ana
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kasliwal, Mansi M.
    Bulla, Mattia
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Ahumada, Tomás
    Coughlin, Michael W.
    Anand, Shreya
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Goobar, Ariel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kaplan, David L.
    Loveridge, Tegan T.
    Karambelkar, Viraj
    Cooke, Jeff
    Bagdasaryan, Ashot
    Bellm, Eric C.
    Cenko, S. Bradley
    Cook, David O.
    De, Kishalay
    Dekany, Richard
    Delacroix, Alexandre
    Drake, Andrew
    Duev, Dmitry A.
    Fremling, Christoffer
    Golkhou, V. Zach
    Graham, Matthew J.
    Hale, David
    Kulkarni, S. R.
    Kupfer, Thomas
    Laher, Russ R.
    Mahabal, Ashish A.
    Masci, Frank J.
    Rusholme, Ben
    Smith, Roger M.
    Tzanidakis, Anastasios
    Sistine, Angela Van
    Yao, Yuhan
    Constraining the Kilonova Rate with Zwicky Transient Facility Searches Independent of Gravitational Wave and Short Gamma-Ray Burst Triggers2020In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 904, no 2, article id 155Article in journal (Refereed)
    Abstract [en]

    The first binary neutron star merger, GW170817, was accompanied by a radioactivity-powered optical/infrared transient called a kilonova. To date, no compelling kilonova has been found in all-sky optical surveys, independently of short gamma-ray burst and gravitational-wave triggers. In this work, we searched the first 23 months of the Zwicky Transient Facility (ZTF) data stream for candidate kilonovae in the form of rapidly evolving transients. We combined ZTF alert queries with forced point-spread-function photometry and nightly flux stacking to increase our sensitivity to faint and fast transients. Automatic queries yielded >11,200 candidates, 24 of which passed quality checks and selection criteria based on a grid of kilonova models tailored for both binary neutron star and neutron star-black hole mergers. None of the candidates in our sample was deemed a possible kilonova after thorough vetting. The sources that passed our selection criteria are dominated by Galactic cataclysmic variables. We identified two fast transients at high Galactic latitude, one of which is the confirmed afterglow of long-duration GRB.190106A, the other is a possible cosmological afterglow. Using a survey simulation code, we constrained the kilonova rate for a range of models including top-hat, linearly decaying light curves, and synthetic light curves obtained with radiative transfer simulations. For prototypical GW170817-like kilonovae, we constrain the rate to be R < 1775 Gpc(-3) yr(-1) (95% confidence). By assuming a population of kilonovae with the same geometry and composition of GW170817 observed under a uniform viewing angle distribution, we obtained a constraint on the rate of R.<.4029 Gpc(-3) yr(-1).

  • 9. Andreoni, Igor
    et al.
    Margutti, Raffaella
    Salafia, Om Sharan
    Parazin, B.
    Villar, V. Ashley
    Coughlin, Michael W.
    Yoachim, Peter
    Mortensen, Kris
    Brethauer, Daniel
    Smartt, S. J.
    Kasliwal, Mansi M.
    Alexander, Kate D.
    Anand, Shreya
    Berger, E.
    Bernardini, Maria Grazia
    Bianco, Federica B.
    Blanchard, Peter K.
    Bloom, Joshua S.
    Brocato, Enzo
    Bulla, Mattia
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Cartier, Regis
    Cenko, S. Bradley
    Chornock, Ryan
    Copperwheat, Christopher M.
    Corsi, Alessandra
    D'Ammando, Filippo
    D'Avanzo, Paolo
    Datrier, Laurence Elise Helene
    Foley, Ryan J.
    Ghirlanda, Giancarlo
    Goobar, Ariel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Grindlay, Jonathan
    Hajela, Aprajita
    Holz, Daniel E.
    Karambelkar, Viraj
    Kool, Erik C.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Lamb, Gavin P.
    Laskar, Tanmoy
    Levan, Andrew
    Maguire, Kate
    May, Morgan
    Melandri, Andrea
    Milisavljevic, Dan
    Miller, A. A.
    Nicholl, Matt
    Nissanke, Samaya M.
    Palmese, Antonella
    Piranomonte, Silvia
    Rest, Armin
    Sagués Carracedo, Ana
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Siellez, Karelle
    Singer, Leo P.
    Smith, Mathew
    Steeghs, D.
    Tanvir, Nial
    Target-of-opportunity Observations of Gravitational-wave Events with Vera C. Rubin Observatory2022In: Astrophysical Journal Supplement Series, ISSN 0067-0049, E-ISSN 1538-4365, Vol. 260, no 1, article id 18Article in journal (Refereed)
    Abstract [en]

    The discovery of the electromagnetic counterpart to the binary neutron star (NS) merger GW170817 has opened the era of gravitational-wave multimessenger astronomy. Rapid identification of the optical/infrared kilonova enabled a precise localization of the source, which paved the way to deep multiwavelength follow-up and its myriad of related science results. Fully exploiting this new territory of exploration requires the acquisition of electromagnetic data from samples of NS mergers and other gravitational-wave sources. After GW170817, the frontier is now to map the diversity of kilonova properties and provide more stringent constraints on the Hubble constant, and enable new tests of fundamental physics. The Vera C. Rubin Observatory's Legacy Survey of Space and Time can play a key role in this field in the 2020s, when an improved network of gravitational-wave detectors is expected to reach a sensitivity that will enable the discovery of a high rate of merger events involving NSs (∼tens per year) out to distances of several hundred megaparsecs. We design comprehensive target-of-opportunity observing strategies for follow-up of gravitational-wave triggers that will make the Rubin Observatory the premier instrument for discovery and early characterization of NS and other compact-object mergers, and yet unknown classes of gravitational-wave events.

  • 10. Andreoni, Igor
    et al.
    Sagués Carracedo, Ana
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Schulze, Steve
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Bulla, Mattia
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kool, Erik C.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Zhang, Jielai
    A very luminous jet from the disruption of a star by a massive black hole2022In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 612, no 7940, p. 430-434Article in journal (Refereed)
    Abstract [en]

    Tidal disruption events (TDEs) are bursts of electromagnetic energy that are released when supermassive black holes at the centres of galaxies violently disrupt a star that passes too close1. TDEs provide a window through which to study accretion onto supermassive black holes; in some rare cases, this accretion leads to launching of a relativistic jet2,3,4,5,6,7,8,9, but the necessary conditions are not fully understood. The best-studied jetted TDE so far is Swift J1644+57, which was discovered in γ-rays, but was too obscured by dust to be seen at optical wavelengths. Here we report the optical detection of AT2022cmc, a rapidly fading source at cosmological distance (redshift z = 1.19325) the unique light curve of which transitioned into a luminous plateau within days. Observations of a bright counterpart at other wavelengths, including X-ray, submillimetre and radio, supports the interpretation of AT2022cmc as a jetted TDE containing a synchrotron ‘afterglow’, probably launched by a supermassive black hole with spin greater than approximately 0.3. Using four years of Zwicky Transient Facility10 survey data, we calculate a rate of 0.02+0.04−0.01 Gpc−3 yr−1 for on-axis jetted TDEs on the basis of the luminous, fast-fading red component, thus providing a measurement complementary to the rates derived from X-ray and radio observations11. Correcting for the beaming angle effects, this rate confirms that approximately 1 per cent of TDEs have relativistic jets. Optical surveys can use AT2022cmc as a prototype to unveil a population of jetted TDEs.

  • 11. Cai, Y.-Z.
    et al.
    Pastorello, A.
    Fraser, M.
    Botticella, M.T.
    Elias-Rosa, N.
    Wang, L.-Z.
    Kotak, R.
    Benetti, S.
    Cappellaro, E.
    Turatto, M.
    Reguitti, A.
    Mattila, S.
    Smartt, S.J.
    Ashall, C.
    Benitez, S.
    Chen, Ting-Wan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Harutyunyan, A.
    Kankare, E.
    Lundqvist, Peter
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Mazzali, P.A.
    Morales-Garoffolo, A.
    Ochner, P.
    Pignata, G.
    Prentice, S.J.
    Reynolds, T.M.
    Shu, X.-W.
    Stritzinger, M. D.
    Tartaglia, L.
    Terreran, G.
    Tomasella, L.
    Valenti, S.
    Valerin, G.
    Wang, G.-J.
    Wang, X.-F.
    Borsato, L.
    Callis, E.
    Cannizzaro, G.
    Chen, S.
    Congiu, E.
    Ergon, Mattias
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Galbany, L.
    Gal-Yam, A.
    Gao, X.
    Gromadzki, M.
    Holmbo, S.
    Huang, F.
    Inserra, C.
    Itagaki, K.
    Kostrzewa-Rutkowska, Z.
    Maguire, K.
    Margheim, S.
    Moran, S.
    Onori, F.
    Sagués Carracedo, Ana
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Smith, K.W.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Somero, A.
    Wang, B.
    Young, D.R.
    Intermediate-luminosity red transients: Spectrophotometric properties and connection to electron-capture supernova explosions2021In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 654, article id A157Article in journal (Refereed)
    Abstract [en]

    We present the spectroscopic and photometric study of five intermediate-luminosity red transients (ILRTs), namely AT 2010dn, AT 2012jc, AT 2013la, AT 2013lb, and AT 2018aes. They share common observational properties and belong to a family of objects similar to the prototypical ILRT SN 2008S. These events have a rise time that is less than 15 days and absolute peak magnitudes of between −11.5 and −14.5 mag. Their pseudo-bolometric light curves peak in the range 0.5–9.0 × 1040 erg s−1 and their total radiated energies are on the order of (0.3–3) × 1047 erg. After maximum brightness, the light curves show a monotonic decline or a plateau, resembling those of faint supernovae IIL or IIP, respectively. At late phases, the light curves flatten, roughly following the slope of the 56Co decay. If the late-time power source is indeed radioactive decay, these transients produce 56Ni masses on the order of 10−4 to 10−3M. The spectral energy distribution of our ILRT sample, extending from the optical to the mid-infrared (MIR) domain, reveals a clear IR excess soon after explosion and non-negligible MIR emission at very late phases. The spectra show prominent H lines in emission with a typical velocity of a few hundred km s−1, along with Ca II features. In particular, the [Ca II] λ7291,7324 doublet is visible at all times, which is a characteristic feature for this family of transients. The identified progenitor of SN 2008S, which is luminous in archival Spitzer MIR images, suggests an intermediate-mass precursor star embedded in a dusty cocoon. We propose the explosion of a super-asymptotic giant branch star forming an electron-capture supernova as a plausible explanation for these events.

  • 12. Cai, Y.-Z.
    et al.
    Pastorello, A.
    Fraser, M.
    Prentice, S. J.
    Reynolds, T. M.
    Cappellaro, E.
    Benetti, S.
    Morales-Garoffolo, A.
    Reguitti, A.
    Elias-Rosa, N.
    Brennan, S.
    Callis, E.
    Cannizzaro, G.
    Fiore, A.
    Gromadzki, M.
    Galindo-Guil, F. J.
    Gall, C.
    Heikkila, T.
    Mason, E.
    Moran, S.
    Onori, F.
    Sagués Carracedo, Ana
    Stockholm University, Faculty of Science, Department of Physics.
    Valerin, G.
    The transitional gap transient AT 2018hso: new insights into the luminous red nova phenomenon2019In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 632, article id L6Article in journal (Refereed)
    Abstract [en]

    Context. The absolute magnitudes of luminous red novae (LRNe) are intermediate between those of novae and supernovae (SNe), and show a relatively homogeneous spectro-photometric evolution. Although they were thought to derive from core instabilities in single stars, there is growing support for the idea that they are triggered by binary interaction that possibly ends with the merging of the two stars.

    Aims. AT 2018hso is a new transient showing transitional properties between those of LRNe and the class of intermediate-luminosity red transients (ILRTs) similar to SN 2008S. Through the detailed analysis of the observed parameters, our study supports that it actually belongs to the LRN class and was likely produced by the coalescence of two massive stars.

    Methods. We obtained ten months of optical and near-infrared photometric monitoring, and 11 epochs of low-resolution optical spectroscopy of AT 2018hso. We compared its observed properties with those of other ILRTs and LRNe. We also inspected the archival Hubble Space Telescope (HST) images obtained about 15 years ago to constrain the progenitor properties.

    Results. The light curves of AT 2018hso show a first sharp peak (reddening-corrected M-r = -13.93 mag), followed by a broader and shallower second peak that resembles a plateau in the optical bands. The spectra dramatically change with time. Early-time spectra show prominent Balmer emission lines and a weak [Ca II] doublet, which is usually observed in ILRTs. However, the strong decrease in the continuum temperature, the appearance of narrow metal absorption lines, the great change in the H alpha strength and profile, and the emergence of molecular bands support an LRN classification. The possible detection of a M-I similar to -8 mag source at the position of AT 2018hso in HST archive images is consistent with expectations for a pre-merger massive binary, similar to the precursor of the 2015 LRN in M101.

    Conclusions. We provide reasonable arguments to support an LRN classification for AT 2018hso. This study reveals growing heterogeneity in the observables of LRNe than has been thought previously, which is a challenge for distinguishing between LRNe and ILRTs. This suggests that the entire evolution of gap transients needs to be monitored to avoid misclassifications.

  • 13.
    Dhawan, Suhail
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Bulla, Mattia
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Goobar, Ariel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sagués Carracedo, Ana
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Setzer, Christian N.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Constraining the Observer Angle of the Kilonova AT2017gfo Associated with GW170817: Implications for the Hubble Constant2020In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 888, no 2, article id 67Article in journal (Refereed)
    Abstract [en]

    There is a strong degeneracy between the luminosity distance (D-L) and the observer viewing angle (<italic(obs); hereafter viewing angle) of the gravitational wave (GW) source with an electromagnetic counterpart, GW170817. Here, for the first time, we present independent constraints on from broadband photometry of the kilonova (kN) AT2017gfo associated with GW170817. These constraints are consistent with independent results presented in the literature using the associated gamma-ray burst GRB 170817A. Combining the constraints on (obs) with the GW data, we find an improvement of 24% on H-0. The observer angle constraints are insensitive to other model parameters, e.g., the ejecta mass, the half-opening angle of the lanthanide-rich region and the temperature. A broad wavelength coverage extending to the near-infrared is helpful to robustly constrain (obs). While the improvement on H-0 presented here is smaller than the one from high angular resolution imaging of the radio counterpart of GW170817, kN observations are significantly more feasible at the typical distances of such events from current and future LIGO-Virgo collaboration observing runs (D-L similar to 100 Mpc). Our results are insensitive to the assumption of the peculiar velocity of the kN host galaxy.

  • 14.
    Goobar, Ariel
    et al.
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics.
    Pearson Johansson, Joel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Schulze, Steve
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics.
    Arendse, Nikki
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sagués Carracedo, Ana
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Dhawan, Suhail
    Mörtsell, Edvard
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Fremling, Christoffer
    Yan, Lin
    Perley, Daniel
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Joseph, Rémy
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics.
    Hinds, K-Ryan
    Meynardie, William
    Andreoni, Igor
    Bellm, Eric
    Bloom, Josh
    Collett, Thomas E.
    Drake, Andrew
    Graham, Matthew
    Kasliwal, Mansi
    Kulkarni, Shri R.
    Lemon, Cameron
    Miller, Adam A.
    Neill, James D.
    Nordin, Jakob
    Pierel, Justin
    Richard, Johan
    Riddle, Reed
    Rigault, Mickael
    Rusholme, Ben
    Sharma, Yashvi
    Stein, Robert
    Stewart, Gabrielle
    Townsend, Alice
    Vinko, Jozsef
    Wheeler, J. Craig
    Wold, Avery
    Uncovering a population of gravitational lens galaxies with magnified standard candle SN Zwicky2023In: Nature Astronomy, E-ISSN 2397-3366, Vol. 7, no 9, p. 1098-1107Article in journal (Refereed)
    Abstract [en]

    Detecting gravitationally lensed supernovae is among the biggest challenges in astronomy. It involves a combination of two very rare phenomena: catching the transient signal of a stellar explosion in a distant galaxy and observing it through a nearly perfectly aligned foreground galaxy that deflects light towards the observer. Here we describe how high-cadence optical observations with the Zwicky Transient Facility, with its unparalleled large field of view, led to the detection of a multiply imaged type Ia supernova, SN Zwicky, also known as SN 2022qmx. Magnified nearly 25-fold, the system was found thanks to the standard candle nature of type Ia supernovae. High-spatial-resolution imaging with the Keck telescope resolved four images of the supernova with very small angular separation, corresponding to an Einstein radius of only θE = 0.167″ and almost identical arrival times. The small θE and faintness of the lensing galaxy are very unusual, highlighting the importance of supernovae to fully characterize the properties of galaxy-scale gravitational lenses, including the impact of galaxy substructures.

  • 15. Izzo, L.
    et al.
    de Ugarte Postigo, A.
    Maeda, K.
    Thone, C. C.
    Kann, D. A.
    Della Valle, M.
    Sagués Carracedo, Ana
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Michalowski, M. J.
    Schady, P.
    Schmidl, S.
    Selsing, J.
    Starling, R. L. C.
    Suzuki, A.
    Bensch, K.
    Bolmer, J.
    Campana, S.
    Cano, Z.
    Covino, S.
    Fynbo, J. P. U.
    Hartmann, D. H.
    Heintz, K. E.
    Hjorth, J.
    Japelj, J.
    Kaminski, K.
    Kaper, L.
    Kouveliotou, C.
    Kruzynski, M.
    Kwiatkowski, T.
    Leloudas, G.
    Levan, A. J.
    Malesani, D. B.
    Michalowski, T.
    Piranomonte, S.
    Pugliese, G.
    Rossi, A.
    Sanchez-Ramirez, R.
    Schulze, S.
    Steeghs, D.
    Tanvir, N. R.
    Ulaczyk, K.
    Vergani, S. D.
    Wiersema, K.
    Signatures of a jet cocoon in early spectra of a supernova associated with a γ-ray burst2019In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 565, no 7739, p. 324-+Article in journal (Refereed)
    Abstract [en]

    Long gamma-ray bursts are associated with energetic, broad-lined, stripped-envelope supernovae(1,2) and as such mark the death of massive stars. The scarcity of such events nearby and the brightness of the gamma-ray burst afterglow, which dominates the emission in the first few days after the burst, have so far prevented the study of the very early evolution of supernovae associated with gamma-ray bursts(3). In hydrogen-stripped supernovae that are not associated with gamma-ray bursts, an excess of high-velocity (roughly 30,000 kilometres per second) material has been interpreted as a signature of a choked jet, which did not emerge from the progenitor star and instead deposited all of its energy in a thermal cocoon(4). Here we report multi-epoch spectroscopic observations of the supernova SN 2017iuk, which is associated with the gamma-ray burst GRB 171205A. Our spectra display features at extremely high expansion velocities (around 115,000 kilometres per second) within the first day after the burst(5,6). Using spectral synthesis models developed for SN 2017iuk, we show that these features are characterized by chemical abundances that differ from those observed in the ejecta of SN 2017iuk at later times. We further show that the high-velocity features originate from the mildly relativistic hot cocoon that is generated by an ultra-relativistic jet within the gamma-ray burst expanding and decelerating into the medium that surrounds the progenitor star(7,8). This cocoon rapidly becomes transparent(9) and is outshone by the supernova emission, which starts to dominate the emission three days after the burst.

  • 16.
    Johansson, Joel
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Uppsala University, Sweden.
    Goobar, Ariel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Price, S. H.
    Carracedo, A. Sagués
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Della Bruna, Lorenza
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Nugent, P. E.
    Dhawan, Suhail
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Mörtsell, Edvard
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Papadogiannakis, Seméli
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Amanullah, Rahman
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Goldstein, D.
    Cenko, S. B.
    De, K.
    Dugas, A.
    Kasliwal, M. M.
    Kulkarni, S. R.
    Lunnan, Ragnhild
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Spectroscopy of the first resolved strongly lensed Type Ia supernova iPTF16geu2021In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 502, no 1, p. 510-520Article in journal (Refereed)
    Abstract [en]

    We report the results from spectroscopic observations of the multiple images of the strongly lensed Type Ia supernova (SN Ia), iPTF16geu, obtained with ground-based telescopes and the Hubble Space Telescope (HST). From a single epoch of slitless spectroscopy with HST, we resolve spectra of individual lensed supernova images for the first time. This allows us to perform an independent measurement of the time-delay between the two brightest images, Delta t = 1.4 +/- 5.0 d, which is consistent with the time-delay measured from the light curves. We also present measurements of narrow emission and absorption lines characterizing the interstellar medium in the SN Ia host galaxy at z = 0.4087, as well as in the foreground lensing galaxy at z = 0.2163. We detect strong Naid absorption in the host galaxy, indicating that iPTF16geu belongs to a subclass of SNe Ia displaying 'anomalously' large Naid column densities compared to dust extinction derived from light curves. For the lens galaxy, we refine the measurement of the velocity dispersion, sigma = 129 +/- 4 kms(-1), which significantly constrains the lens model. We use ground-based spectroscopy, boosted by a factor similar to 70 from lensing magnification, to study the properties of a high-z SN Ia with unprecedented signal-to-noise ratio. The spectral properties of the supernova, such as pseudo-Equivalent widths of several absorption features and velocities of the Si II-line, indicate that iPTF16geu is a normal SN Ia. We do not detect any significant deviations of the SN spectral energy distribution from microlensing of the SN photosphere by stars and compact objects in the lensing galaxy.

  • 17. Kasliwal, Mansi M.
    et al.
    Anand, Shreya
    Ahumada, Tomás
    Stein, Robert
    Sagués Carracedo, Ana
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Andreoni, Igor
    Coughlin, Michael W.
    Singer, Leo P.
    Kool, Erik C.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    De, Kishalay
    Kumar, Harsh
    AlMualla, Mouza
    Yao, Yuhan
    Bulla, Mattia
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Dobie, Dougal
    Reusch, Simeon
    Perley, Daniel A.
    Cenko, S. Bradley
    Bhalerao, Varun
    Kaplan, David L.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Goobar, Ariel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Copperwheat, Christopher M.
    Bellm, Eric C.
    Anupama, G. C.
    Corsi, Alessandra
    Nissanke, Samaya
    Agudo, Iván
    Bagdasaryan, Ashot
    Barway, Sudhanshu
    Belicki, Justin
    Bloom, Joshua S.
    Bolin, Bryce
    Buckley, David A. H.
    Burdge, Kevin B.
    Burruss, Rick
    Caballero-García, Maria D.
    Cannella, Chris
    Castro-Tirado, Alberto J.
    Cook, David O.
    Cooke, Jeff
    Cunningham, Virginia
    Dahiwale, Aishwarya
    Deshmukh, Kunal
    Dichiara, Simone
    Duev, Dmitry A.
    Dutta, Anirban
    Feeney, Michael
    Franckowiak, Anna
    Frederick, Sara
    Fremling, Christoffer
    Gal-Yam, Avishay
    Gatkine, Pradip
    Ghosh, Shaon
    Goldstein, Daniel A.
    Golkhou, V. Zach
    Graham, Matthew J.
    Graham, Melissa L.
    Hankins, Matthew J.
    Helou, George
    Hu, Youdong
    Ip, Wing-Huen
    Jaodand, Amruta
    Karambelkar, Viraj
    Kong, Albert K. H.
    Kowalski, Marek
    Khandagale, Maitreya
    Kulkarni, S. R.
    Kumar, Brajesh
    Laher, Russ R.
    Li, K. L.
    Mahabal, Ashish
    Masci, Frank J.
    Miller, Adam A.
    Mogotsi, Moses
    Mohite, Siddharth
    Mooley, Kunal
    Mroz, Przemek
    Newman, Jeffrey A.
    Ngeow, Chow-Choong
    Oates, Samantha R.
    Patil, Atharva Sunil
    Pandey, Shashi B.
    Pavana, M.
    Pian, Elena
    Riddle, Reed
    Sánchez-Ramírez, Rubén
    Sharma, Yashvi
    Singh, Avinash
    Smith, Roger
    Soumagnac, Maayane T.
    Taggart, Kirsty
    Tan, Hanjie
    Tzanidakis, Anastasios
    Troja, Eleonora
    Valeev, Azamat F.
    Walters, Richard
    Waratkar, Gaurav
    Webb, Sara
    Yu, Po-Chieh
    Zhang, Bin-Bin
    Zhou, Rongpu
    Zolkower, Jeffry
    Kilonova Luminosity Function Constraints Based on Zwicky Transient Facility Searches for 13 Neutron Star Merger Triggers during O32020In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 905, no 2, article id 145Article in journal (Refereed)
    Abstract [en]

    We present a systematic search for optical counterparts to 13 gravitational wave (GW) triggers involving at least one neutron star during LIGO/Virgo's third observing run (O3). We searched binary neutron star (BNS) and neutron star black hole (NSBH) merger localizations with the Zwicky Transient Facility (ZTF) and undertook follow-up with the Global Relay of Observatories Watching Transients Happen (GROWTH) collaboration. The GW triggers had a median localization area of 4480 deg(2), a median distance of 267 Mpc, and false-alarm rates ranging from 1.5 to 10(-25) yr(-1). The ZTF coverage in the g and r bands had a median enclosed probability of 39%, median depth of 20.8 mag, and median time lag between merger and the start of observations of 1.5 hr. The O3 follow-up by the GROWTH team comprised 340 UltraViolet/Optical/InfraRed (UVOIR) photometric points, 64 OIR spectra, and three radio images using 17 different telescopes. We find no promising kilonovae (radioactivity-powered counterparts), and we show how to convert the upper limits to constrain the underlying kilonova luminosity function. Initially, we assume that all GW triggers are bona fide astrophysical events regardless of false-alarm rate and that kilonovae accompanying BNS and NSBH mergers are drawn from a common population; later, we relax these assumptions. Assuming that all kilonovae are at least as luminous as the discovery magnitude of GW170817 (-16.1 mag), we calculate that our joint probability of detecting zero kilonovae is only 4.2%. If we assume that all kilonovae are brighter than -16.6 mag (the extrapolated peak magnitude of GW170817) and fade at a rate of 1 mag day(-1) (similar to GW170817), the joint probability of zero detections is 7%. If we separate the NSBH and BNS populations based on the online classifications, the joint probability of zero detections, assuming all kilonovae are brighter than -16.6 mag, is 9.7% for NSBH and 7.9% for BNS mergers. Moreover, no more than <57% (<89%) of putative kilonovae could be brighter than -16.6 mag assuming flat evolution (fading by 1 mag day(-1)) at the 90% confidence level. If we further take into account the online terrestrial probability for each GW trigger, we find that no more than <68% of putative kilonovae could be brighter than -16.6 mag. Comparing to model grids, we find that some kilonovae must have M-ej M, X-lan > 10(-4), or > 30 degrees to be consistent with our limits. We look forward to searches in the fourth GW observing run; even 17 neutron star mergers with only 50% coverage to a depth of -16 mag would constrain the maximum fraction of bright kilonovae to <25%.

  • 18. Mohite, Siddharth R.
    et al.
    Rajkumar, Priyadarshini
    Anand, Shreya
    Kaplan, David L.
    Coughlin, Michael W.
    Sagués Carracedo, Ana
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Saleem, Muhammed
    Creighton, Jolien
    Brady, Patrick R.
    Ahumada, Tomás
    Almualla, Mouza
    Andreoni, Igor
    Bulla, Mattia
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Graham, Matthew J.
    Kasliwal, Mansi M.
    Kaye, Stephen
    Laher, Russ R.
    Shin, Kyung Min
    Shupe, David L.
    Singer, Leo P.
    Inferring Kilonova Population Properties with a Hierarchical Bayesian Framework. I. Nondetection Methodology and Single-event Analyses2022In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 925, no 1, article id 58Article in journal (Refereed)
    Abstract [en]

    We present nimbus: a hierarchical Bayesian framework to infer the intrinsic luminosity parameters of kilonovae (KNe) associated with gravitational-wave (GW) events, based purely on nondetections. This framework makes use of GW 3D distance information and electromagnetic upper limits from multiple surveys for multiple events and self-consistently accounts for the finite sky coverage and probability of astrophysical origin. The framework is agnostic to the brightness evolution assumed and can account for multiple electromagnetic passbands simultaneously. Our analyses highlight the importance of accounting for model selection effects, especially in the context of nondetections. We show our methodology using a simple, two-parameter linear brightness model, taking the follow-up of GW190425 with the Zwicky Transient Facility as a single-event test case for two different prior choices of model parameters: (i) uniform/uninformative priors and (ii) astrophysical priors based on surrogate models of Monte Carlo radiative-transfer simulations of KNe. We present results under the assumption that the KN is within the searched region to demonstrate functionality and the importance of prior choice. Our results show consistency with simsurvey-an astronomical survey simulation tool used previously in the literature to constrain the population of KNe. While our results based on uniform priors strongly constrain the parameter space, those based on astrophysical priors are largely uninformative, highlighting the need for deeper constraints. Future studies with multiple events having electromagnetic follow-up from multiple surveys should make it possible to constrain the KN population further.

  • 19. Pastorello, A.
    et al.
    Chen, T. -W.
    Cai, Y. -Z.
    Morales-Garoffolo, A.
    Cano, Z.
    Mason, E.
    Barsukova, E. A.
    Benetti, S.
    Berton, M.
    Bose, S.
    Bufano, F.
    Callis, E.
    Cannizzaro, G.
    Cartier, R.
    Chen, Ping
    Dong, Subo
    Dyrbye, S.
    Elias-Rosa, N.
    Floers, A.
    Fraser, M.
    Geier, S.
    Goranskij, V. P.
    Kann, D. A.
    Kuncarayakti, H.
    Onori, F.
    Reguitti, A.
    Reynolds, T.
    Rivero Losada, Illa
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Sagués Carracedo, Ana
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Schweyer, T.
    Smartt, S. J.
    Tatarnikov, A. M.
    Valeev, A. F.
    Vogl, C.
    Wevers, T.
    de Ugarte Postigo, A.
    Izzo, L.
    Inserra, C.
    Kankare, E.
    Maguire, K.
    Smith, K. W.
    Stalder, B.
    Tartaglia, L.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Thone, C. C.
    Valerin, G.
    Young, D. R.
    The evolution of luminous red nova AT 2017jfs in NGC 44702019In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 625, article id L8Article in journal (Refereed)
    Abstract [en]

    We present the results of our photometric and spectroscopic follow-up of the intermediate-luminosity optical transient AT 2017jfs. At peak, the object reaches an absolute magnitude of M-g = 15.46 +/- 0.15 mag and a bolometric luminosity of 5.5 x 10(41) erg s(-1). Its light curve has the double-peak shape typical of luminous red novae (LRNe), with a narrow first peak bright in the blue bands, while the second peak is longer-lasting and more luminous in the red and near-infrared (NIR) bands. During the first peak, the spectrum shows a blue continuum with narrow emission lines of H and Fe II. During the second peak, the spectrum becomes cooler, resembling that of a K-type star, and the emission lines are replaced by a forest of narrow lines in absorption. About 5 months later, while the optical light curves are characterized by a fast linear decline, the NIR ones show a moderate rebrightening, observed until the transient disappears in solar conjunction. At these late epochs, the spectrum becomes reminiscent of that of M-type stars, with prominent molecular absorption bands. The late-time properties suggest the formation of some dust in the expanding common envelope or an IR echo from foreground pre-existing dust. We propose that the object is a common-envelope transient, possibly the outcome of a merging event in a massive binary, similar to NGC4490-2011OT1.

  • 20. Pérez-García, M. A.
    et al.
    Izzo, L.
    Barba-González, D.
    Bulla, Mattia
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sagués-Carracedo, Ana
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Pérez, E.
    Albertus, C.
    Dhawan, S.
    Prada, F.
    Agnello, A.
    Angus, C. R.
    Bruun, S. H.
    del Burgo, C.
    Dominguez-Tagle, C.
    Gall, C.
    Goobar, Ariel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Hjorth, J.
    Jones, D.
    López-Sánchez, A. R.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Hubble constant and nuclear equation of state from kilonova spectro-photometric light curves2022In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 666, article id A67Article in journal (Refereed)
    Abstract [en]

    The merger of two compact objects of which at least one is a neutron star is signalled by transient electromagnetic emission in a kilonova (KN). This event is accompanied by gravitational waves and possibly other radiation messengers such as neutrinos or cosmic rays. The electromagnetic emission arises from the radioactive decay of heavy r-process elements synthesized in the material ejected during and after the merger. In this paper we show that the analysis of KNe light curves can provide cosmological distance measurements and constrain the properties of the ejecta. In this respect, MAAT, the new Integral Field Unit in the OSIRIS spectrograph on the 10.4 m Gran Telescopio CANARIAS (GTC), is well suited for the study of KNe by performing absolute spectro-photometry over the entire 3600 − 10 000 Å spectral range. Here, we study the most representative cases regarding the scientific interest of KNe from binary neutron stars, and we evaluate the observational prospects and performance of MAAT on the GTC to do the following: (a) study the impact of the equation of state on the KN light curve, and determine to what extent bounds on neutron star (NS) radii or compactness deriving from KN peak magnitudes can be identified and (b) measure the Hubble constant, H0, with precision improved by up to 40%, when both gravitational wave data and photometric-light curves are used. In this context we discuss how the equation of state, the viewing angle, and the distance affect the precision and estimated value of H0.

  • 21.
    Sagués Carracedo, Ana
    Stockholm University, Faculty of Science, Department of Physics.
    Chasing Cosmic Rarities: Kilonovae and Gravitationally Lensed Supernovae in Optical Surveys2024Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis focuses on two important topics in astrophysics: the detection of kilonovae (KNe) and gravitationally lensed supernovae (glSNe) in optical surveys. In the first part, the study quantifies the impact of survey depth and choice of filters on the detection probability of KNe. The results highlight the importance of accounting for asymmetries expected for KNe, and despite several search campaigns, no KNe were detected by the Zwicky Transient Facility (ZTF). Nonetheless, non-detection studies provided meaningful constraints on the luminosity function and on the rates of KNe. The findings contribute to advancing our understanding of these rare, fast, and faint transients. I also discuss the improvements in measuring the Hubble constant with follow-up data of KNe, including broadband photometry and spectrophotometric data from the upcoming IFU instrument MAAT. 

    The second part of the thesis focuses on gravitationally lensed supernovae. The ZTF survey was expected to detect more than one strongly lensed supernova per year, but only one was identified in the first five years. The study presents simulations of lightcurves for lensed supernovae and new rates based on realistic survey simulations for ZTF. Optimal cuts to distinguish lensed supernovae from normal unlensed supernovae are also provided. The thesis discusses time delay and lightcurve modeling for the one event found during ZTF, SN Zwicky, and the lessons learned from it.

    The techniques developed in this thesis can be applied to future surveys to increase the detection rate of KNe and glSNe. These events and their underlying physics provide valuable insights in cosmology.

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  • 22.
    Sagués Carracedo, Ana
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kilonova signatures and observations with Zwicky Transient Facility2022Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    On 17 August 2017, the advanced LIGO and Virgo collaboration detected the first gravitational wave event produced by the merger of a pair of inspiraling binary neutron stars (BNS). This event, named GW170817, was associated with a short gamma-ray burst and the kilonova (KN) AT2017gfo that was followed-up over the following days and weeks over the electromagnetic spectrum from ultraviolet to near infrared frequencies. The merger was localized in a nearby galaxy, NGC 4993 at a distance of 40 Mpc. The close proximity and the orientation of the merger was favourable for studying its properties and evolution with time. 

    This unique discovery gave rise to a new era in multimessenger astronomy and showed the relevance of these events in astrophysics, cosmology, and nuclear physics. Today, we aim at detecting samples of kilonovae to answer the many open questions related to BNS mergers and their use as physics laboratories. However, the observations of kilonovae are generally challenging as these are rare, fast and faint transients.

    In this licentiate thesis, I present the observational difficulties and study the detectability of kilonovae using survey simulations. I quantify the effect of survey depth and choice of filters to optimize detection probability. I highlight the importance of accounting for the asymmetries expected for kilonovae (KNe). One conclusion of this licentiate thesis is that it is unlikely to detect a new KN under the same conditions as AT2017gfo. Even if the intrinsic properties were similar, the orientation of the KN would significantly affect the detection feasibility. 

    We have performed several search campaigns for KN candidates within the Zwicky Transient Facility (ZTF),  the Global Relay of Observatories Watching Transients Happen (GROWTH) and the Electromagnetic counterparts of gravitational wave sources at the Very Large Telescope (ENGRAVE) collaborations. We can distinguish targeted searches after GW triggers and archival searches for serendipitous KN detections. Both kinds of investigations have so far failed to detect KNe with ZTF. Nevertheless, non-detection studies provided meaningful constraints on the luminosity function and the rates of KNe. 

  • 23.
    Sagués Carracedo, Ana
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Bulla, Mattia
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita). Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics.
    Feindt, Ulrich
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Goobar, Ariel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Detectability of kilonovae in optical surveys: post-mortem examination of the LVC O3 run follow-up2021In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 504, no 1, p. 1294-1303Article in journal (Refereed)
    Abstract [en]

    The detection of the binary neutron star (BNS) merger GW170817 and the associated electromagnetic (EM) counterpart, the ‘kilonova’ (kN) AT2017gfo, opened a new era in multimessenger astronomy. However, despite many efforts, it has been proven very difficult to find additional kNe, even though LIGO/Virgo has reported at least one BNS event during their latest run, O3. The focus of this work is the exploration of the sensitivity of the adopted optical surveys searching for kNe during O3. We propose ways to optimize the choices of filters and survey depth to boost the detection efficiency for these faint and fast-evolving transients in the future. In particular, we use kN models to explore the dependence on ejecta mass, geometry, viewing angle, wavelength coverage, and source distance. We find that the kN detection efficiency has a strong viewing-angle dependence, especially for filters blueward of i-band. This loss of sensitivity can be mitigated by early, deep, observations. Efficient gri counterpart searches for kNe at ∼200 Mpc would require reaching a limiting magnitude mlim = 23 mag, to ensure good sensitivity over a wide range of the model phase-space. We conclude that kN searches during O3 were generally too shallow to detect BNS optical counterparts, even under optimistic assumptions.

  • 24. Sagués Carracedo, Ana
    et al.
    Goobar, Ariel
    Mörtsell, Edvard
    Arendse, Nikki
    Johansson, Joel
    Townsend, Alice
    Dhawan, Suhail
    Nordin, Jakob
    Schulze, Steve
    Detectability and Characterisation of Strongly Lensed Supernova Light Curves in the Zwicky Transient FacilityManuscript (preprint) (Other academic)
  • 25.
    Tartaglia, Leonardo
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Pastorello, A.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Mattila, S.
    Fraser, M.
    Taddia, Francesco
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Tomasella, L.
    Turatto, M.
    Morales-Garoffolo, A.
    Elias-Rosa, N.
    Lundqvist, Peter
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Harmanen, J.
    Reynolds, T.
    Cappellaro, E.
    Barbarino, Cristina
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Nyholm, Anders
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kool, Erik
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Ofek, E.
    Gao, X.
    Jin, Z.
    Tan, H.
    Sand, D. J.
    Ciabattari, F.
    Wang, X.
    Zhang, J.
    Huang, F.
    Li, W.
    Mo, J.
    Rui, L.
    Xiang, D.
    Zhang, T.
    Hosseinzadeh, G.
    Howell, D. A.
    McCully, C.
    Valenti, S.
    Benetti, S.
    Callis, E.
    Sagués Carracedo, Ana
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Fremling, C.
    Kangas, T.
    Rubin, A.
    Somero, A.
    Terreran, G.
    The long-lived Type IIn SN 2015da: Infrared echoes and strong interaction within an extended massive shell star star star2020In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 635, article id A39Article in journal (Refereed)
    Abstract [en]

    In this paper we report the results of the first similar to four years of spectroscopic and photometric monitoring of the Type IIn supernova SN 2015da (also known as PSN J13522411+3941286, or iPTF16tu). The supernova exploded in the nearby spiral galaxy NGC 5337 in a relatively highly extinguished environment. The transient showed prominent narrow Balmer lines in emission at all times and a slow rise to maximum in all bands. In addition, early observations performed by amateur astronomers give a very well-constrained explosion epoch. The observables are consistent with continuous interaction between the supernova ejecta and a dense and extended H-rich circumstellar medium. The presence of such an extended and dense medium is difficult to reconcile with standard stellar evolution models, since the metallicity at the position of SN 2015da seems to be slightly subsolar. Interaction is likely the mechanism powering the light curve, as confirmed by the analysis of the pseudo bolometric light curve, which gives a total radiated energy greater than or similar to 10(51) erg. Modeling the light curve in the context of a supernova shock breakout through a dense circumstellar medium allowed us to infer the mass of the prexisting gas to be similar or equal to 8 M-circle dot, with an extreme mass-loss rate for the progenitor star similar or equal to 0.6 M-circle dot yr(-1), suggesting that most of the circumstellar gas was produced during multiple eruptive events. Near- and mid-infrared observations reveal a fluxexcess in these domains, similar to those observed in SN 2010jl and other interacting transients, likely due to preexisting radiatively heated dust surrounding the supernova. By modeling the infrared excess, we infer a mass greater than or similar to 0.4 x 10(-3) M-circle dot for the dust.

1 - 25 of 25
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