TITLE: GCN CIRCULAR NUMBER: 38056 SUBJECT: LIGO/Virgo/KAGRA S241102br: EP-WXT X-ray follow-up and flux limits DATE: 24/11/03 10:19:11 GMT FROM: EP Team at NAOC/CAS ep_ta@bao.ac.cn

Q. Y. Wu (NAO, CAS), J. Mao(YNAO, CAS), Y. F. Liang (PMO, CAS), Q. C. Liu (THU), R. D. Liang, D. H. Zhao, H. N. Yang, W. Yuan (NAO, CAS) report on behalf of the Einstein Probe team:

Following on the trigger of the detection of the gravitational-wave (GW) event S241102br (LVK Collaboration, GCN 38043), we carried out a target-of-opportunity observation of the GW sky region with the Wide-field X-ray telescope(WXT) on board the Einstein Probe (EP). The observation started at 2024-11-02 15:44:04 (UTC), about 3 hours after the trigger of the GW event, lasting for around 5 hours. The 90% credible region of the event was fully covered by the large field-of-view of WXT, centering at the nominal GW source position at (RA=23h00m, Dec=+40d28m). The total effective exposure time is about 8 ks within the source credible region. No new X-ray source is found in this observation. This observation sets upper limits on the 0.5-4 keV flux in the source credible region to be approximately 2.42 x 10^(-12) erg/cm^2/s (90%. C.L.). Furthermore, we derived upper limits (see the Table below) for the top 20 galaxies from the galaxy list within the 90% volume reported by Cook et al. (GCN 38044). For queries on more information about this observation and the upper limits, please contact Qinyu Wu at the EP science center (ep_ta@nao.cas.cn).

galaxy name | ra | dec | flux upper limit (0.5-4 keV) | deg | deg | ergs/cm^2/s -------------------------------------------------------------------------------------------------- WISEAJ225919.78+394535.0 | 344.83242 | 39.75972 | 1.42E-12 WISEAJ225952.51+442917.7 | 344.96871 | 44.48825 | 1.51E-12 WISEAJ230520.33+400018.8 | 346.33458 | 40.00514 | 1.88E-12 WISEAJ230012.95+415343.7 | 345.05417 | 41.89553 | 1.86E-12 WISEAJ225938.70+415648.8 | 344.91125 | 41.94689 | 1.51E-12 WISEAJ230201.05+423126.9 | 345.50446 | 42.52411 | 1.09E-12 WISEAJ225743.15+404134.4 | 344.42971 | 40.69286 | 1.19E-12 WISEAJ225708.96+394204.3 | 344.28733 | 39.70117 | 2.25E-12 WISEAJ225745.81+373140.1 | 344.44088 | 37.52783 | 1.63E-12 WISEAJ230533.61+424929.5 | 346.39000 | 42.82489 | 1.91E-12 WISEAJ230113.12+354411.0 | 345.30462 | 35.73639 | 1.65E-12 WISEAJ230419.52+423037.8 | 346.08129 | 42.51047 | 1.07E-12 WISEAJ230200.39+415916.5 | 345.50162 | 41.98792 | 1.35E-12 WISEAJ225832.97+415012.0 | 344.63725 | 41.83658 | 1.95E-12 WISEAJ230133.36+394404.8 | 345.38892 | 39.73472 | 1.13E-12 WISEAJ230257.02+393909.0 | 345.73754 | 39.65240 | 1.99E-12 WISEAJ225902.80+411053.6 | 344.76171 | 41.18158 | 1.49E-12 WISEAJ225942.19+421403.0 | 344.92588 | 42.23417 | 1.17E-12 WISEAJ230431.87+440856.3 | 346.13275 | 44.14900 | 1.77E-12 WISEAJ230530.98+394323.1 | 346.37912 | 39.72308 | 1.73E-12 --------------------------------------------------------------------------------------------------

Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with onboard X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). EP is an international collaborative mission led by the Chinese Academy of Sciences (CAS) and participated by the European Space Agency (ESA), the Max-Planck Institute for Extraterrestrial Physics (MPE) in Germany and the Centre National d’Etudes Spatiales (CNES) in France.

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