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  • 1. 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.

  • 2. 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.

  • 3. 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).

  • 4. Bellm, Eric C.
    et al.
    Wang, Yuankun
    van Roestel, Jan
    Phillipson, Rebecca A.
    Coughlin, Michael W.
    Tomsick, John A.
    Groom, Steven L.
    Healy, Brian
    Purdum, Josiah
    Rusholme, Ben
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Bealo, Peter
    Lora, Stefano
    Muyllaert, Eddy
    Peretto, Ivo
    Schwendeman, Erik J.
    An Optically Discovered Outburst from XTE J1859+2262023In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 956, no 1, article id 21Article in journal (Refereed)
    Abstract [en]

    Using the Zwicky Transient Facility, in 2021 February we identified the first known outburst of the black hole X-ray transient XTE J1859+226 since its discovery in 1999. The outburst was visible at X-ray, UV, and optical wavelengths for less than 20 days, substantially shorter than its full outburst of 320 days in 1999, and the observed peak luminosity was 2 orders of magnitude lower. Its peak bolometric luminosity was only 2 × 1035 erg s−1, implying an Eddington fraction of about 3 × 10−4. The source remained in the hard spectral state throughout the outburst. From optical spectroscopy measurements we estimate an outer disk radius of 1011 cm. The low observed X-ray luminosity is not sufficient to irradiate the entire disk, but we observe a surprising exponential decline in the X-ray light curve. These observations highlight the potential of optical and infrared synoptic surveys to discover low-luminosity activity from X-ray transients.

  • 5. Coughlin, Michael W.
    et al.
    Antier, Sarah
    Dietrich, Tim
    Foley, Ryan J.
    Heinzel, Jack
    Bulla, Mattia
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Christensen, Nelson
    Coulter, David A.
    Issa, Lina
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita). Université Paris-Saclay, France.
    Khetan, Nandita
    Measuring the Hubble constant with a sample of kilonovae2020In: Nature Communications, E-ISSN 2041-1723, Vol. 11, no 1, article id 4129Article in journal (Refereed)
  • 6. Coughlin, Michael W.
    et al.
    Dietrich, Tim
    Antier, Sarah
    Almualla, Mouza
    Anand, Shreya
    Bulla, Mattia
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Foucart, Francois
    Guessoum, Nidhal
    Hotokezaka, Kenta
    Kumar, Vishwesh
    Raaijmakers, Geert
    Nissanke, Samaya
    Implications of the search for optical counterparts during the second part of the Advanced LIGO's and Advanced Virgo's third observing run: lessons learned for future follow-up observations2020In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 497, no 1, p. 1181-1196Article in journal (Refereed)
    Abstract [en]

    Joint multimessenger observations with gravitational waves and electromagnetic (EM) data offer new insights into the astrophysical studies of compact objects. The third Advanced LIGO and Advanced Virgo observing run began on 2019 April 1; during the 11 months of observation, there have been 14 compact binary systems candidates for which at least one component is potentially a neutron star. Although intensive follow-up campaigns involving tens of ground and space-based observatories searched for counterparts, no EM counterpart has been detected. Following on a previous study of the first six months of the campaign, we present in this paper the next five months of the campaign from 2019 October to 2020 March. We highlight two neutron star-black hole candidates (S191205ah and S200105ae), two binary neutron star candidates (S191213g and S200213t), and a binary merger with a possible neutron star and a `MassGap' component, S200115j. Assuming that the gravitational-wave (GW) candidates are of astrophysical origin and their location was covered by optical telescopes, we derive possible constraints on the matter ejected during the events based on the non-detection of counterparts. We find that the follow-up observations during the second half of the third observing run did not meet the necessary sensitivity to constrain the source properties of the potential GW candidate. Consequently, we suggest that different strategies have to be used to allow a better usage of the available telescope time. We examine different choices for follow-up surveys to optimize sky localization coverage versus observational depth to understand the likelihood of counterpart detection.

  • 7. Coughlin, Michael W.
    et al.
    Dietrich, Tim
    Heinzel, Jack
    Khetan, Nandita
    Antier, Sarah
    Bulla, Mattia
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Christensen, Nelson
    Coulter, David A.
    Foley, Ryan J.
    Standardizing kilonovae and their use as standard candles to measure the Hubble constant2020In: Physical Review Research, E-ISSN 2643-1564, Vol. 2, no 2, article id 022006Article in journal (Refereed)
    Abstract [en]

    The detection of GW170817 is revolutionizing many areas of astrophysics with the joint observation of gravitational waves and electromagnetic emissions. These multimessenger events provide a new approach to determine the Hubble constant, thus, they are a promising candidate for mitigating the tension between measurements of type-Ia supernovae via the local distance ladder and the cosmic microwave background. In addition to the “standard siren” provided by the gravitational-wave measurement, the kilonova itself has characteristics that allow one to improve existing measurements or to perform yet another, independent measurement of the Hubble constant without gravitational-wave information. Here, we employ standardization techniques borrowed from the type-Ia community and apply them to kilonovae, not using any information from the gravitational-wave signal. We use two versions of this technique, one derived from direct observables measured from the light curve, and the other based on inferred ejecta parameters, e.g., mass, velocity, and composition, for two different models. These lead to Hubble constant measurements of H0=109+49−35 km s−1 Mpc−1 for the measured analysis, and H0=85+22−17 km s−1 Mpc−1 and H0=79+23−15 km s−1 Mpc−1 for the inferred analyses. This measurement has error bars within ∼2 to the gravitational-wave measurements (H0=74+16−8 km s−1 Mpc−1), showing its promise as an independent constraint on H0.

  • 8. Heinzel, J.
    et al.
    Coughlin, M. W.
    Dietrich, T.
    Bulla, Mattia
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Antier, S.
    Christensen, N.
    Coulter, D. A.
    Foley, R. J.
    Issa, Lina
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita). Université Paris-Saclay, France.
    Khetan, N.
    Comparing inclination-dependent analyses of kilonova transients2021In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 502, no 2, p. 3057-3065Article in journal (Refereed)
    Abstract [en]

    The detection of the optical transient AT2017gfo proved that binary neutron star mergers are progenitors of kilonovae (KNe). Using a combination of numerical-relativity and radiative-transfer simulations, the community has developed sophisticated models for these transients for a wide portion of the expected parameter space. Using these simulations and surrogate models made from them, it has been possible to perform Bayesian inference of the observed signals to infer properties of the ejected matter. It has been pointed out that combining inclination constraints derived from the KN with gravitational-wave measurements increases the accuracy with which binary parameters can be estimated, in particular breaking the distance-inclination degeneracy from gravitational wave inference. To avoid bias from the unknown ejecta geometry, constraints on the inclination angle for AT2017gfo should be insensitive to the employed models. In this work, we compare different assumptions about the ejecta and radiative reprocesses used by the community and we investigate their impact on the parameter inference. While most inferred parameters agree, we find disagreement between posteriors for the inclination angle for different geometries that have been used in the current literature. According to our study, the inclusion of reprocessing of the photons between different ejecta types improves the modeling fits to AT2017gfo and, in some cases, affects the inferred constraints. Our study motivates the inclusion of large similar to 1-mag uncertainties in the KN models employed for Bayesian analysis to capture yet unknown systematics, especially when inferring inclination angles, although smaller uncertainties seem appropriate to capture model systematics for other intrinsic parameters. We can use this method to impose soft constraints on the ejecta geometry of the KN AT2017gfo.

  • 9. Kasliwal, M. M.
    et al.
    Cannella, C.
    Bagdasaryan, A.
    Hung, T.
    Feindt, Ulrich
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Singer, L. P.
    Coughlin, M.
    Fremling, C.
    Walters, R.
    Duev, D.
    Itoh, R.
    Quimby, R. M.
    The GROWTH Marshal: A Dynamic Science Portal for Time-domain Astronomy2019In: Publications of the Astronomical Society of the Pacific, ISSN 0004-6280, E-ISSN 1538-3873, Vol. 131, no 997, article id 038003Article in journal (Refereed)
    Abstract [en]

    We describe a dynamic science portal called the GROWTH Marshal that allows time-domain astronomers to define science programs; program filters to save sources from different discovery streams; coordinate follow-up with various robotic or classical telescopes; analyze the panchromatic follow-up data; and generate summary tables for publication. The GROWTH marshal currently serves 137 scientists, 38 science programs, and 67 telescopes. Every night, in real time, several science programs apply various customized filters to the 105 nightly alerts from the Zwicky Transient Facility. Here, we describe the schematic and explain the functionality of the various components of this international collaborative platform.

  • 10. 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%.

  • 11. Kupfer, Thomas
    et al.
    Prince, Thomas A.
    van Roestel, Jan
    Bellm, Eric C.
    Bildsten, Lars
    Coughlin, Michael W.
    Drake, Andrew J.
    Graham, Matthew J.
    Klein, Courtney
    Kulkarni, Shrinivas R.
    Masci, Frank J.
    Walters, Richard
    Andreoni, Igor
    Biswas, Rahul
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Bradshaw, Corey
    Duev, Dmitry A.
    Dekany, Richard
    Guidry, Joseph A.
    Hermes, J. J.
    Laher, Russ R.
    Riddle, Reed
    Year 1 of the ZTF high-cadence Galactic plane survey: strategy, goals, and early results on new single-mode hot subdwarf B-star pulsatos2021In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 505, no 1, p. 1254-1267Article in journal (Refereed)
    Abstract [en]

    We present the goals, strategy, and first results of the high-cadence Galactic plane survey using the Zwicky Transient Facility (ZTF). The goal of the survey is to unveil the Galactic population of short-period variable stars, including short-period binaries, and stellar pulsators with periods less than a few hours. Between 2018 June and 2019 January, we observed 64 ZTF fields resulting in 2990 deg2 of high stellar density in the ZTF-r band along the Galactic plane. Each field was observed continuously for 1.5 to 6 h with a cadence of 40 sec. Most fields have between 200 and 400 observations obtained over 2–3  continuous nights. As part of this survey, we extract a total of ≈230 million individual objects with at least 80 epochs obtained during the high-cadence Galactic plane survey reaching an average depth of ZTF–r ≈ 20.5 mag. For four selected fields with 2–10 million individual objects per field, we calculate different variability statistics and find that ≈1–2  per cent of the objects are astrophysically variable over the observed period. We present a progress report on recent discoveries, including a new class of compact pulsators, the first members of a new class of Roche lobe filling hot subdwarf binaries as well as new ultracompact double white dwarfs and flaring stars. Finally, we present a sample of 12 new single-mode hot subdwarf B-star pulsators with pulsation amplitudes between ZTF–r = 20–76 mmag and pulsation periods between P = 5.8–16 min with a strong cluster of systems with periods ≈6 min. All of the data have now been released in either ZTF Data Release 3 or Data Release 4.

  • 12. Pang, Peter T. H.
    et al.
    Dietrich, Tim
    Coughlin, Michael W.
    Bulla, Mattia
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). University of Ferrara, Italy; INFN, Sezione di Ferrara, Italy; INAF, Osservatorio Astronomico d’Abruzzo, Italy.
    Tews, Ingo
    Almualla, Mouza
    Barna, Tyler
    Weizmann Kiendrebeogo, Ramodgwendé
    Kunert, Nina
    Mansingh, Gargi
    Reed, Brandon
    Sravan, Niharika
    Toivonen, Andrew
    Antier, Sarah
    Vandenberg, Robert O.
    Heinzel, Jack
    Nedora, Vsevolod
    Salehi, Pouyan
    Sharma, Ritwik
    Somasundaram, Rahul
    Van Den Broeck, Chris
    An updated nuclear-physics and multi-messenger astrophysics framework for binary neutron star mergers2023In: Nature Communications, E-ISSN 2041-1723, Vol. 14, no 1, article id 8352Article in journal (Refereed)
    Abstract [en]

    The multi-messenger detection of the gravitational-wave signal GW170817, the corresponding kilonova AT2017gfo and the short gamma-ray burst GRB170817A, as well as the observed afterglow has delivered a scientific breakthrough. For an accurate interpretation of all these different messengers, one requires robust theoretical models that describe the emitted gravitational-wave, the electromagnetic emission, and dense matter reliably. In addition, one needs efficient and accurate computational tools to ensure a correct cross-correlation between the models and the observational data. For this purpose, we have developed the Nuclear-physics and Multi-Messenger Astrophysics framework NMMA. The code allows incorporation of nuclear-physics constraints at low densities as well as X-ray and radio observations of isolated neutron stars. In previous works, the NMMA code has allowed us to constrain the equation of state of supranuclear dense matter, to measure the Hubble constant, and to compare dense-matter physics probed in neutron-star mergers and in heavy-ion collisions, and to classify electromagnetic observations and perform model selection. Here, we show an extension of the NMMA code as a first attempt of analyzing the gravitational-wave signal, the kilonova, and the gamma-ray burst afterglow simultaneously. Incorporating all available information, we estimate the radius of a 1.4M neutron star to be R = 11.98+0.35−0.40 km.

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