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Published February 1, 2021 | Accepted Version + Published
Journal Article Open

Swift Multiwavelength Follow-up of LVC S200224ca and the Implications for Binary Black Hole Mergers


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, q̂ < 1.4 × 10⁻⁴, and an upper limit on the isotropic-equivalent energy of a blast wave E < 4.1 × 10⁵¹ erg (assuming typical GRB parameters).

Additional Information

© 2021. The American Astronomical Society. Received 2020 November 12; revised 2020 December 7; accepted 2020 December 9; published 2021 February 3. This publication is an official product of the Swift GW follow-up team. The authors wish to thank the anonymous referee for helpful comments that enhanced the clarity of the paper. N. J. K. and J. A. K. would like to acknowledge support from NASA Grants 80NSSC19K0408 and 80NSSC20K1104. P. A. E., K. L. P., A. P. B., J. P. O., A. A. B., S. W. K. E., N. P. M. K., and M. J. P. acknowledge funding from the UK Space Agency. P. D. A. acknowledges support from PRIN-MIUR 2017 (grant 20179ZF5KS). M. G. B., G. C., S. C., A. D. A., P. D. A., A. M. and G. T. acknowledge funding from the Italian Space Agency, contract ASI/INAF n. I/004/11/4. The authors would like to acknowledge support from the Italian Ministry of Foreign Affairs and International Cooperation grant MAE0065741. E. T. acknowledges support by the National Aeronautics and Space Administration through grant NNX10AF62G issued through the Astrophysics Data Analysis Program. M. D. P. acknowledges support for this work by the Scientific and Technological Research Council of Turkey (TÜBİTAK), grant No: MFAG-119F073. D. B. M. is supported by research grant 19054 from Villum Fonden. Facility: NASA Neil Gehrels Swift Observatory.

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Published - Klingler_2021_ApJ_907_97.pdf

Accepted Version - 2012.05384.pdf


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Additional details

August 22, 2023
October 23, 2023