Kilonova Luminosity Function Constraints Based on Zwicky Transient Facility Searches for 13 Neutron Star Merger Triggers during O3

Kasliwal, Mansi M. and Anand, Shreya and Ahumada, Tomás and Stein, Robert and Carracedo, Ana Sagués and Andreoni, Igor and Coughlin, Michael W. and Singer, Leo P. and Kool, Erik C. and De, Kishalay and Kumar, Harsh and AlMualla, Mouza and Yao, Yuhan and Bulla, Mattia and Dobie, Dougal and Reusch, Simeon and Perley, Daniel A. and Cenko, S. Bradley and Bhalerao, Varun and Kaplan, David L. and Sollerman, Jesper and Goobar, Ariel and Copperwheat, Christopher M. and Bellm, Eric C. and Anupama, G. C. and Corsi, Alessandra and Nissanke, Samaya and Agudo, Iván and Bagdasaryan, Ashot and Barway, Sudhanshu and Belicki, Justin and Bloom, Joshua S. and Bolin, Bryce and Buckley, David A. H. and Burdge, Kevin B. and Burruss, Rick and Caballero-García, Maria D. and Cannella, Chris and Castro-Tirado, Alberto J. and Cook, David O. and Cooke, Jeff and Cunningham, Virginia and Dahiwale, Aishwarya and Deshmukh, Kunal and Dichiara, Simone and Duev, Dmitry A. and Dutta, Anirban and Feeney, Michael and Franckowiak, Anna and Frederick, Sara and Fremling, Christoffer and Gal-Yam, Avishay and Gatkine, Pradip and Ghosh, Shaon and Goldstein, Daniel A. and Golkhou, V. Zach and Graham, Matthew J. and Graham, Melissa L. and Hankins, Matthew J. and Helou, George and Hu, Youdong and Ip, Wing-Huen and Jaodand, Amruta and Karambelkar, Viraj and Kong, Albert K. H. and Kowalski, Marek and Khandagale, Maitreya and Kulkarni, S. R. and Kumar, Brajesh and Laher, Russ R. and Li, K. L. and Mahabal, Ashish and Masci, Frank J. and Miller, Adam A. and Mogotsi, Moses and Mohite, Siddharth and Mooley, Kunal and Mroz, Przemek and Newman, Jeffrey A. and Ngeow, Chow-Choong and Oates, Samantha R. and Patil, Atharva Sunil and Pandey, Shashi B. and Pavana, M. and Pian, Elena and Riddle, Reed and Sánchez-Ramírez, Rubén and Sharma, Yashvi and Singh, Avinash and Smith, Roger and Soumagnac, Maayane T. and Taggart, Kirsty and Tan, Hanjie and Tzanidakis, Anastasios and Troja, Eleonora and Valeev, Azamat F. and Walters, Richard and Waratkar, Gaurav and Webb, Sara and Yu, Po-Chieh and Zhang, Bin-Bin and Zhou, Rongpu and Zolkower, Jeffry (2020) Kilonova Luminosity Function Constraints Based on Zwicky Transient Facility Searches for 13 Neutron Star Merger Triggers during O3. The Astrophysical Journal, 905 (2): 145. ISSN 0004-637X

Abstract

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 deg2, 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 Mej < 0.03 M⊙, Xlan > 10-4, or φ > 30° 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%....