Abstract
Abstract On 2020 February 24, during their third observing run (“O3”), the Laser Interferometer Gravitational-wave Observatory and Virgo Collaboration detected S200224ca: a candidate gravitational wave (GW) event produced by a binary black hole (BBH) merger. This event was one of the best-localized compact binary coalescences detected in O3 (with 50%/90% error regions of 13/72 deg2), and so the Neil Gehrels Swift Observatory performed rapid near-UV/X-ray follow-up observations. Swift-XRT and UVOT covered approximately 79.2% and 62.4% (respectively) of the GW error region, making S200224ca the BBH event most thoroughly followed-up in near-UV (u-band) and X-ray to date. No likely EM counterparts to the GW event were found by the Swift BAT, XRT, or UVOT, nor by other observatories. Here, we report on the results of our searches for an EM counterpart, both in the BAT data near the time of the merger, and in follow-up UVOT/XRT observations. We also discuss the upper limits we can place on EM radiation from S200224ca, as well as the implications these limits have on the physics of BBH mergers. Namely, we place a shallow upper limit on the dimensionless BH charge, , and an upper limit on the isotropic-equivalent energy of a blast wave E < 4.1 × 1051 erg (assuming typical GRB parameters).
Highlights
On 2015 September 12 the advanced Laser Interferometer Gravitational-wave Observatory began its first observing run (“O1”; LIGO Scientific Collaboration et al 2015), which ran until 2016 January 19. aLIGO consists of two interferometers located in Hanford, Washington, and Livingston, Louisiana, whose unprecedented sensitivity can detect a differential strain of less than one ten-thousandth the charge diameter of a proton
In August, aLIGO was augmented by the addition of the Advanced Virgo detector (a 3 km long interferometer located in Cascina, Italy (Acernese et al 2015)), which collectively formed the LIGO/ Virgo Collaboration (LVC)
In panel (c), we show the integrated LVC localization probability that is outside the Burst Alert Telescope (BAT) field of view (FOV) but above the Earth limb
Summary
On 2015 September 12 the advanced Laser Interferometer Gravitational-wave Observatory (aLIGO) began its first observing run (“O1”; LIGO Scientific Collaboration et al 2015), which ran until 2016 January 19. aLIGO consists of two interferometers located in Hanford, Washington, and Livingston, Louisiana, whose unprecedented sensitivity can detect a differential strain (over a 4 km length) of less than one ten-thousandth the charge diameter of a proton. During O1, aLIGO made the first direct detections of gravitational wave (GW) signals of astrophysical origin: GW150914, GW151226, and LVT151012 (Abbott et al 2016a, 2016b, 2016c), marking the beginning of a new era in GW astronomy These signals originated from the merging of binary black holes (BBHs), and served as an observational test of general relativity in the very strong field limit (in which no deviations from theory were seen). LVC began promptly announcing GW triggers to some observatories under a memorandum of understanding, which allowed rapid followup searches During this run, eight more GW events were detected: seven BBH mergers and a binary neutron star (BNS) merger (Abbott et al 2019a).
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