GCN Circular 36159
Subject
LIGO/Virgo/KAGRA S240413p: X-ray upper limits from EP-WXT for the candidate AGN counterpart
Date
2024-04-18T13:34:02Z (20 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
J. W. Hu, W. Chen, S. Q. Jiang, D. Y. Li, C. C. Jin, Y. Liu, Z. X. Ling, C. Zhang, H. Q. Cheng, C. Z. Cui, D. W. Fan, H. B. Hu, M. H. Huang, T. Y. Lian, H. Y. Liu, M. J. Liu, Z. Z. Lv, X. Mao, H. W. Pan, X. Pan, H. Sun, W. X. Wang, Y. L. Wang, Q. Y. Wu, X. P. Xu, Y. F. Xu, H. N. Yang, W. Yuan, M. Zhang, W. D. Zhang, W. J. Zhang, Z. Zhang, D. H. Zhao (NAOC, CAS), E. Kuulkers, A. Santovincenzo (ESA), P. O'Brien (Univ. of Leicester), K. Nandra, A. Rau (MPE), B. Cordier (CEA), on behalf of the Einstein Probe team
C.R. Bom et al. (GCN 36146) reported a candidate optical counterpart associated with a known AGN for the binary black hole merger S240413p (GCN 36075). The position of this AGN was covered by EP-WXT in four observations from 2024-04-13 to 2024-04-17. No significant X-ray counterpart was detected in these observations, and a flux upper limit at the 90% confidence level is estimated for each of the observations.
The details of these observations are:
No. | Start time (UTC) | End time (UTC) | Exposure (s) | Upper limit (erg/s/cm2)
-------------------------------------------------------------------------------------------
1 | 2024-04-13 20:45:36 | 2024-04-13 21:35:22 | 2986 | 5.2 x 10^-12
2 | 2024-04-15 01:36:51 | 2024-04-15 01:57:31 | 1240 | 2.8 x 10^-11
3 | 2024-04-15 06:25:48 | 2024-04-15 06:37:08 | 680 | 3.4 x 10^-11
4 | 2024-04-15 12:52:24 | 2024-04-15 23:21:34 | 18776 | 4.6 x 10^-12
Furthermore, no X-ray sources were detected in the above observations at the nearby positions mentioned by Antonella Palmese et al. (GCN 36153) with similar upper limits. No new transients were found in these EP-WXT fields, either.
The above observations were made with the WXT instrument during the commissioning phase of EP. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). EP is a mission of the Chinese Academy of Sciences in collaboration with ESA, MPE and CNES.