March 2025 - vsnet-grb-info - ooruri.kusastro.kyoto-u.ac.jp

[vsnet-grb-info 37568] GRB250226A: GRANDMA Optical Observations
by GCN Circulars 03 Mar '25

03 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39554 SUBJECT: GRB250226A: GRANDMA Optical Observations DATE: 25/03/03 04:48:59 GMT FROM: Lydia Nyambane at UMN <nyamb021(a)umn.edu> M. Tanasan (NARIT), L. Nyambane (UMN), H. Muenter (UMN), C. Andrade (UMN), Y. Rajabov (UBAI), F. Magnani (CPPM), M. Masek (FZU), S. Alshamsi (AUS), W. Corradi (LNA), T. Almeida (LNA), K. Noysena (NARIT), L. Fraga (LNA), N. Sasaki (LNA), A. Takey (NRIAG), Y. Hendy (NRIAG), M. Abdelkareem (NRIAG), E. Elhosseiny F. … [View More]Navarete (NOIRLab/SOAR), S. Antier (OCA/IJCLAB), M. Coughlin (UMN), S. Karpov (FZU), P. Hello (IJCLAB), P-A. Duverne (APC), T. Pradier (Unistra/IPHC), N. Guessoum (AUS) on behalf of the GRANDMA and Kilonova-Catcher collaborations: The GRANDMA collaboration imaged the field of a fast X-ray transient GRB 250226A discovered by Fermi GBM (Fermi GBM team, GCN circ. 39479) and EP WXT and FXT (Jiang et al., GCN circ. 39482; Jiang et al., GCN circ. 39513) and detected also by GECAM-B (Zhang et al., GCN circ. 39492) and INTEGRAL SPI-ACS and PICsIT (Thakur et al., GCN circ. 39518). GRANDMA observations were performed at RA = 224.2651, DEC = 20.9756 with the OPD/60cm, TRT-SBO, KAO, Lisnyky/AZT-8 and AbAO-T70 telescopes starting ~0.4 days post T0 in the R and i' bands. We detect the optical afterglow and report some of the observations at the following magnitudes: | T-start (UTC) | Magnitude | UL (5sigma) | Filter | Telescope | | 2025-02-26 17:19:21 | 21.5 +/- 0.2 | 21.5 | R (AB) | TRT-SBO | | 2025-02-27 01:39:46 | 21.15+/-0.15 | 22.6 | i’ (AB) | KAO | | 2025-02-27 05:28:50 | 22.0+/-0.25 | 21.8 | R (AB) | OPD/60cm | Our findings were consistent with the MEPHISTO telescope (Zou et al., GCN 39511), the Xinglong Observatory ( Jiang et al., GCN 39515), and the Las Cumbres Observatory Global Telescope network (LCOGT) (Poidevin et al., GCN 39524). All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). Images obtained in Johnson Cousin filters were calibrated using the Gaia DR3 and PS1 catalog. We use the SkyPortal application (skyportal.io) to monitor our observational campaign (Coughlin et al. 2023). GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (http://kilonovacatcher.in2p3.fr/). View this GCN Circular online at https://gcn.nasa.gov/circulars/39554. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L… [View Less]

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[vsnet-grb-info 37567] EP250302a: Montarrenti Observatory optical detection
by GCN Circulars 02 Mar '25

02 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39553 SUBJECT: EP250302a: Montarrenti Observatory optical detection DATE: 25/03/02 23:05:33 GMT FROM: Simone Leonini at Montarrenti Observatory (Siena, Italy) <s.leonini(a)iol.it> S. Leonini, M. Conti, P. Rosi, L.M. Tinjaca Ramirez (Montarrenti Observatory, Siena, Italy, part of UAI/SSV-GRB section), M.G. Dainotti (National Astronomical Observatory of Japan), Y. Niino (Tokyo University, Institute of Astronomy) and K. Kalinowski (Aarhus University, … [View More]

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[vsnet-grb-info 37566] Fermi GRB 250302A: Global MASTER-Net observations report
by GCN Circulars 02 Mar '25

02 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39552 SUBJECT: Fermi GRB 250302A: Global MASTER-Net observations report DATE: 25/03/02 21:33:42 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, N.Tiurina, P.Balanutsa, , D.Vlasenko, I.Panchenko, A.Kuznetsov, G.Antipov, A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta,… [View More] R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity) D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-Tunka robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Applied Physics Institute, Irkutsk State University) started inspect of the Fermi GRB 250302A ( Fermi GBM team, GCN 39548) errorbox 21539 sec after notice time and 21575 sec after trigger time at 2025-03-02 19:46:08 UT, with upper limit up to 20.4 mag. The observations began at zenith distance = 43 deg. The sun altitude is -36.5 deg. MASTER-Kislovodsk robotic telescope located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB 250302A errorbox 22677 sec after notice time and 22713 sec after trigger time at 2025-03-02 20:05:06 UT, with upper limit up to 17.7 mag. The observations began at zenith distance = 77 deg. The sun altitude is -50.2 deg. The galactic latitude b = 46 deg., longitude l = 22 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2796892 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 21605 | 2025-03-02 19:46:08 | MASTER-Tunka | (15h 31m 17.49s , +16d 30m 25.9s) | C | 60 | 19.8 | 21665 | 2025-03-02 19:46:08 | MASTER-Tunka | (15h 31m 17.49s , +16d 30m 25.9s) | C | 180 | 20.3 | Coadd 21678 | 2025-03-02 19:47:20 | MASTER-Tunka | (15h 39m 40.44s , +16d 31m 15.0s) | C | 60 | 19.8 | 21738 | 2025-03-02 19:47:20 | MASTER-Tunka | (15h 39m 40.44s , +16d 31m 14.9s) | C | 180 | 20.3 | Coadd 22064 | 2025-03-02 19:53:47 | MASTER-Tunka | (15h 41m 02.12s , +18d 25m 27.9s) | C | 60 | 19.8 | 22124 | 2025-03-02 19:53:47 | MASTER-Tunka | (15h 41m 02.11s , +18d 25m 27.9s) | C | 180 | 20.4 | Coadd 22137 | 2025-03-02 19:55:00 | MASTER-Tunka | (15h 49m 28.20s , +18d 23m 04.7s) | C | 60 | 19.7 | 22197 | 2025-03-02 19:55:00 | MASTER-Tunka | (15h 49m 28.20s , +18d 23m 04.6s) | C | 180 | 20.3 | Coadd 22210 | 2025-03-02 19:56:13 | MASTER-Tunka | (15h 31m 19.81s , +16d 32m 30.0s) | C | 60 | 19.9 | 22283 | 2025-03-02 19:57:25 | MASTER-Tunka | (15h 39m 34.02s , +16d 30m 56.3s) | C | 60 | 19.9 | 22586 | 2025-03-02 20:02:28 | MASTER-Tunka | (15h 23m 46.12s , +16d 31m 47.0s) | C | 60 | 20.0 | 22646 | 2025-03-02 20:02:28 | MASTER-Tunka | (15h 23m 46.12s , +16d 31m 47.0s) | C | 180 | 20.3 | Coadd 22744 | 2025-03-02 20:05:06 | MASTER-Kislovodsk | (15h 31m 05.90s , +18d 24m 03.2s) | C | 60 | 13.6 | 22820 | 2025-03-02 20:06:23 | MASTER-Tunka | (15h 40m 59.24s , +18d 26m 16.1s) | C | 60 | 19.8 | 22823 | 2025-03-02 20:06:26 | MASTER-Kislovodsk | (15h 20m 24.78s , +14d 35m 08.1s) | C | 60 | 14.4 | 22893 | 2025-03-02 20:07:36 | MASTER-Tunka | (15h 49m 30.08s , +18d 24m 37.9s) | C | 60 | 19.8 | 22904 | 2025-03-02 20:07:46 | MASTER-Kislovodsk | (15h 28m 43.31s , +14d 36m 18.2s) | C | 60 | 13.6 | 22967 | 2025-03-02 20:08:49 | MASTER-Tunka | (15h 31m 14.39s , +16d 31m 14.0s) | C | 60 | 19.8 | 23042 | 2025-03-02 20:10:04 | MASTER-Tunka | (15h 39m 39.86s , +16d 31m 01.5s) | C | 60 | 19.7 | 23160 | 2025-03-02 20:12:03 | MASTER-Kislovodsk | (15h 36m 12.34s , +14d 34m 34.1s) | C | 60 | 15.6 | 23240 | 2025-03-02 20:13:23 | MASTER-Kislovodsk | (15h 44m 23.73s , +14d 35m 43.7s) | C | 60 | 14.7 | 23337 | 2025-03-02 20:14:59 | MASTER-Tunka | (15h 23m 42.86s , +16d 33m 11.8s) | C | 60 | 19.9 | 23413 | 2025-03-02 20:16:15 | MASTER-Tunka | (15h 30m 58.44s , +12d 44m 41.7s) | C | 60 | 19.8 | 23473 | 2025-03-02 20:16:15 | MASTER-Tunka | (15h 30m 58.44s , +12d 44m 41.7s) | C | 180 | 20.1 | Coadd 23480 | 2025-03-02 20:17:22 | MASTER-Kislovodsk | (15h 31m 02.91s , +18d 23m 56.7s) | C | 60 | 16.9 | 23486 | 2025-03-02 20:17:29 | MASTER-Tunka | (15h 39m 05.45s , +12d 43m 05.6s) | C | 60 | 19.7 | 23546 | 2025-03-02 20:17:29 | MASTER-Tunka | (15h 39m 05.45s , +12d 43m 05.5s) | C | 180 | 20.1 | Coadd 23560 | 2025-03-02 20:18:42 | MASTER-Kislovodsk | (15h 20m 23.76s , +14d 37m 26.2s) | C | 60 | 17.0 | 23561 | 2025-03-02 20:18:43 | MASTER-Tunka | (15h 41m 05.86s , +18d 25m 13.1s) | C | 60 | 19.8 | 23637 | 2025-03-02 20:19:59 | MASTER-Tunka | (15h 49m 27.79s , +18d 25m 54.4s) | C | 60 | 19.7 | 23639 | 2025-03-02 20:20:02 | MASTER-Kislovodsk | (15h 28m 43.11s , +14d 36m 08.7s) | C | 60 | 16.8 | 23712 | 2025-03-02 20:21:15 | MASTER-Tunka | (15h 31m 16.75s , +16d 31m 55.3s) | C | 60 | 19.9 | 23772 | 2025-03-02 20:21:15 | MASTER-Tunka | (15h 31m 16.75s , +16d 31m 55.1s) | C | 180 | 19.8 | Coadd 23785 | 2025-03-02 20:22:27 | MASTER-Tunka | (15h 39m 40.80s , +16d 32m 51.7s) | C | 60 | 19.8 | 23799 | 2025-03-02 20:22:42 | MASTER-Kislovodsk | (15h 21m 17.81s , +12d 41m 36.6s) | C | 60 | 17.1 | 23959 | 2025-03-02 20:25:22 | MASTER-Kislovodsk | (15h 36m 07.19s , +14d 35m 28.8s) | C | 60 | 17.1 | 24039 | 2025-03-02 20:26:41 | MASTER-Kislovodsk | (15h 44m 26.50s , +14d 36m 37.5s) | C | 60 | 17.0 | 24080 | 2025-03-02 20:27:23 | MASTER-Tunka | (15h 23m 42.84s , +16d 32m 51.8s) | C | 60 | 19.9 | 24154 | 2025-03-02 20:28:37 | MASTER-Tunka | (15h 30m 58.25s , +12d 44m 31.8s) | C | 60 | 19.7 | 24230 | 2025-03-02 20:29:53 | MASTER-Tunka | (15h 39m 07.48s , +12d 45m 31.1s) | C | 60 | 19.7 | 24278 | 2025-03-02 20:30:40 | MASTER-Kislovodsk | (15h 31m 07.61s , +18d 24m 25.8s) | C | 60 | 17.4 | 24305 | 2025-03-02 20:31:07 | MASTER-Tunka | (15h 41m 01.62s , +18d 25m 42.8s) | C | 60 | 19.8 | 24365 | 2025-03-02 20:31:07 | MASTER-Tunka | (15h 41m 01.62s , +18d 25m 42.8s) | C | 180 | 20.2 | Coadd 24749 | 2025-03-02 20:38:31 | MASTER-Tunka | (15h 30m 53.25s , +16d 35m 14.6s) | C | 60 | 19.9 | 24939 | 2025-03-02 20:41:41 | MASTER-Kislovodsk | (15h 21m 11.94s , +12d 41m 22.0s) | C | 60 | 17.7 | 25098 | 2025-03-02 20:44:21 | MASTER-Kislovodsk | (15h 36m 07.54s , +14d 36m 59.1s) | C | 60 | 17.5 | 25178 | 2025-03-02 20:45:41 | MASTER-Kislovodsk | (15h 44m 23.92s , +14d 35m 10.2s) | C | 60 | 17.4 | 25423 | 2025-03-02 20:49:46 | MASTER-Tunka | (15h 23m 44.45s , +16d 35m 47.7s) | C | 60 | 20.0 | 25497 | 2025-03-02 20:50:59 | MASTER-Tunka | (15h 30m 54.18s , +12d 45m 40.7s) | C | 60 | 19.9 | 25569 | 2025-03-02 20:52:11 | MASTER-Tunka | (15h 39m 10.58s , +12d 46m 23.3s) | C | 60 | 19.8 | 25643 | 2025-03-02 20:53:25 | MASTER-Tunka | (15h 40m 57.76s , +18d 27m 42.0s) | C | 60 | 20.0 | 25715 | 2025-03-02 20:54:38 | MASTER-Tunka | (15h 49m 22.96s , +18d 28m 04.2s) | C | 60 | 19.8 | 25788 | 2025-03-02 20:55:51 | MASTER-Tunka | (15h 31m 18.68s , +16d 34m 38.3s) | C | 60 | 19.8 | 25861 | 2025-03-02 20:57:04 | MASTER-Tunka | (15h 39m 32.28s , +16d 33m 01.3s) | C | 60 | 19.8 | 26164 | 2025-03-02 21:02:06 | MASTER-Tunka | (15h 23m 47.97s , +16d 36m 20.0s) | C | 60 | 19.7 | 26237 | 2025-03-02 21:03:20 | MASTER-Tunka | (15h 30m 50.25s , +12d 47m 05.1s) | C | 60 | 19.6 | 26311 | 2025-03-02 21:04:33 | MASTER-Tunka | (15h 39m 02.80s , +12d 47m 29.2s) | C | 60 | 19.5 | 26385 | 2025-03-02 21:05:48 | MASTER-Tunka | (15h 41m 03.56s , +18d 28m 19.9s) | C | 60 | 18.6 | 26460 | 2025-03-02 21:07:03 | MASTER-Tunka | (15h 46m 29.50s , +12d 46m 38.1s) | C | 60 | 19.8 | 26537 | 2025-03-02 21:08:19 | MASTER-Tunka | (15h 54m 41.53s , +12d 44m 47.4s) | C | 60 | 19.8 | 26838 | 2025-03-02 21:13:21 | MASTER-Tunka | (15h 23m 46.02s , +16d 36m 09.2s) | C | 60 | 20.1 | 26914 | 2025-03-02 21:14:37 | MASTER-Tunka | (15h 30m 49.86s , +12d 46m 41.0s) | C | 60 | 20.0 | 27078 | 2025-03-02 21:17:20 | MASTER-Tunka | (15h 39m 08.10s , +12d 47m 46.3s) | C | 60 | 20.0 | 27150 | 2025-03-02 21:18:33 | MASTER-Tunka | (15h 46m 26.15s , +12d 46m 38.9s) | C | 60 | 20.0 | 27222 | 2025-03-02 21:19:44 | MASTER-Tunka | (15h 54m 37.57s , +12d 47m 02.5s) | C | 60 | 20.0 | 27300 | 2025-03-02 21:21:02 | MASTER-Tunka | (15h 38m 21.62s , +14d 40m 25.5s) | C | 60 | 20.1 | 27373 | 2025-03-02 21:22:15 | MASTER-Tunka | (15h 46m 43.50s , +14d 39m 54.8s) | C | 60 | 20.1 | 27442 | 2025-03-02 21:23:24 | MASTER-Tunka | (15h 55m 28.03s , +10d 51m 13.2s) | C | 60 | 20.0 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/39552. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L… [View Less]

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[vsnet-grb-info 37565] EP250302a: FTW optical and NIR detection
by GCN Circulars 02 Mar '25

02 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39551 SUBJECT: EP250302a: FTW optical and NIR detection DATE: 25/03/02 20:56:16 GMT FROM: Brendan O'Connor at Carnegie Mellon University <boconno2(a)andrew.cmu.edu> Malte Busmann (LMU), Brendan O’Connor (Carnegie Mellon U.), Daniel Gruen (LMU) and Antonella Palmese (Carnegie Mellon U.) report: We observed location of EP250302a (Trigger ID: 01709132186; Zhu et al., GCN 39550) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at … [View More]

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[vsnet-grb-info 37564] EP250302a: Nanshan/HMT optical counterpart detection
by GCN Circulars 02 Mar '25

02 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39550 SUBJECT: EP250302a: Nanshan/HMT optical counterpart detection DATE: 25/03/02 18:16:00 GMT FROM: Dong Xu at NAOC/CAS <dxu(a)nao.cas.cn> Z.P. Zhu, S.Q. Jiang, X. Liu, J. An, S.Y. Fu, D. Xu (NAOC), X. Gao (Urumqi No.1 Senior High School), J.Z. Liu (XAO) report on behalf of a large collaboration: We observed the field of EP250302a detected by Einstein Probe (Trigger ID: 01709132186), using the HMT-0.5m telescope located at Nanshan, Xinjiang, China. … [View More]

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[vsnet-grb-info 37563] IceCube-250302A - IceCube observation of a high-energy neutrino candidate track-like event
by GCN Circulars 02 Mar '25

02 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39549 SUBJECT: IceCube-250302A - IceCube observation of a high-energy neutrino candidate track-like event DATE: 25/03/02 16:04:00 GMT FROM: A. Zegarelli at Ruhr University Bochum <azegarelli(a)icecube.wisc.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: On 2025-03-02 at 03:20:52.90 UT IceCube detected a track-like event with a high probability of being of astrophysical origin. The event was selected by the ICECUBE_Astrotrack_GOLD … [View More]

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[vsnet-grb-info 37562] GRB 250302A: Fermi GBM Final Real-time Localization
by GCN Circulars 02 Mar '25

02 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39548 SUBJECT: GRB 250302A: Fermi GBM Final Real-time Localization DATE: 25/03/02 13:57:01 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 13:46:32 UT on 2 Mar 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250302A (trigger 762615997.991246 / 250302574). The on-ground calculated location, using the Fermi GBM trigger data, is RA = … [View More]

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[vsnet-grb-info 37561] GRB 250228A: Fermi GBM Final Localization
by GCN Circulars 02 Mar '25

02 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39547 SUBJECT: GRB 250228A: Fermi GBM Final Localization DATE: 25/03/02 09:43:31 GMT FROM: Marianna Dafčíková at Masaryk University <500025(a)mail.muni.cz> The Fermi GBM team reports the detection of a likely SHORT GRB "At 07:23:46.16 UT on 28 February 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250228A (trigger 762420231/250228308). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 94.90, Dec = … [View More]

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[vsnet-grb-info 37560] The EP-WXT trigger 01709132140 is likely a flaring star
by GCN Circulars 02 Mar '25

02 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39546 SUBJECT: The EP-WXT trigger 01709132140 is likely a flaring star DATE: 25/03/02 04:53:52 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> X. Mao, S. X. Wen (NAOC, CAS), Y. Q. Zhao (USTC, PRIC), C. Y. Dai (NJU), W. Yuan (NAOC, CAS) report on behalf of the Einstein Probe team: The EP-WXT trigger (ID: 001709132140) on 2025-03-02 01:37:56(UTC) is likely a stellar flare associated with a High Proper Motion Star LP 378-313. Launched on January 9, … [View More]

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[vsnet-grb-info 37559] LIGO/Virgo/KAGRA S250206dm: early X-ray upper limits from Einstein Probe WXT and preliminary results of FXT observations
by GCN Circulars 02 Mar '25

02 Mar '25

TITLE: GCN CIRCULAR NUMBER: 39545 SUBJECT: LIGO/Virgo/KAGRA S250206dm: early X-ray upper limits from Einstein Probe WXT and preliminary results of FXT observations DATE: 25/03/02 03:55:41 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> D. Y. Li, J. W. Hu, Q. Y. Wu, M. J. Liu, R. D. Liang, H. Sun (NAOC, CAS), A. Li (BNU), C. Q. Shui (IHEP, CAS), M. H. Zhang, X. P. Xu, W. X. Wang, H. Q. Cheng, H. N. Yang, D. H. Zhao, X. Pan, Y. F. Xu, M. Zhang (NAOC, CAS), X. Y. Zhou (PRIC), Y. … [View More]C. Fu (BNU), S. F. Zhu (CSTU), Y. J. Zhang (THU), H. L. Peng (NJNU), G. Y. Zhao (SYU), C. Zhou (HUST), T. C. Zheng (PMO, CAS), Y. Chen, J. Guan, C. K. Li, S. M. Jia, H. S. Zhao, J. Zhang, M. Y. Ge, W. W. Cui, H. Feng, W. Li, C. Z. Liu, F. J. Lu, L. M. Song, J. Wang, J. J. Xu, D. W. Han, S. N. Zhang, X. F. Zhao (IHEP, CAS), Y. Liu, W. D. Zhang, Z. X. Ling, C. C. Jin, H. W. Pan, C. Zhang, W. Yuan (NAOC), B. Zhang (UNLV), L. Piro (INAF), V. Burwitz, P. Friedrich, N. Meidinger, K. Nandra, A. Rau (MPE), E. Kuulkers, A. Santovincenzo (ESA), P. O'Brien (Univ. of Leicester), B. Cordier (CEA) report on behalf of the Einstein Probe team: We report on preliminary results of the observations targeting the sky regions of the LIGO/Virgo/KAGRA NS-BH gravitational-wave event S250206dm (The LIGO-Virgo-KAGRA Collaboration, GCN 39175) to search for any potentially associated X-ray source with the Einstein Probe (EP). Two rounds of observations were carried out with the Wide-field X-ray Telescope (WXT) and Follow-up X-ray Telescope (FXT) on board EP between Feb. 7th and 18th 2025. No promising X-ray transient candidates have been found. The information on the sky coverage and observations can be found at the web page https://ep.bao.ac.cn/ep/cms/article/view?id=185. First, two early WXT observations were performed, starting at 2025-02-07T02:55:12.000Z and 2025-02-07T03:40:22.000Z, about 4.5 hours and 6 hours after the GW event, respectively, each with an exposure time of 2400s. These observations covered 302 square degrees within (55% of) the 90% credible region of the updated LVK sky localization (The LIGO-Virgo-KAGRA Collaboration, GCN 39231). No new X-ray sources were detected. The 0.5-4 keV flux limits over the covered regions are set to be approximately 1.0 x 10^-11 erg/s/cm2 at the 90% confidence level in general. Then, 100 pointed FXT observations were carried out during Feb. 7th and 8th, each with a 300s-exposure, targeting galaxies located within the 90% credible region and the distance uncertainty range of S250206dm. The targets are among the top 500 galaxies that were selected from the GLADE+ catalog and prioritized based on their location, mass, and visibility to FXT. These observations covered 32 (24) square degree in the 90% (50%) credible region, setting 0.5-10 keV flux limits of generally 3e-13 erg/s/cm2 at the 90% confidence level. From Feb. 11th to 18th, 2025, the second round of observations consisted of tiling observations with FXT, covering 34 square degrees in (89% of) the 50% credible region of S250206dm. There were 59 observations performed, each with an exposure of 2000s, setting the average flux limits of approximately 5e-14 erg/s/cm2 at the 90% confidence level. We searched for transient or variable candidates in the FXT data which are apparently associated with the galaxies in the NED-LVS sample in the credible region and distance range of S250206dm (Cook et al. GCN 39235) within a radius of 30 arcsec. Two uncatalogued sources were found to exhibit significant flux decay from the FXT observations, whose details are listed in the table below. The fluxes are in the 0.5-10 keV band and estimated from spectral fitting with an absorbed powerlaw model. EPF J022731.1+551813 was not detected in the second observation, and an upper limit at the 90% confidence level is provided. We note that, however, a stellar flare origin of these two sources cannot be ruled out. ------------------------------------------------------------------------------------------------------ | Source Name | Obs_Time (UTC) | RA | DEC | Flux(erg/s/cm2) | Flux_err | ------------------------------------------------------------------------------------------------------ |EPF J022731.1+551813| 2025-02-13 08:35:07 | 36.8797 | 55.3037 | 5.28e-13 | 2.27e-14 | | | 2025-02-15 13:24:47 | | | <7.0e-14 | | ------------------------------------------------------------------------------------------------------ |EPF J022842.7+542051| 2025-02-08 07:59:43 | 37.1780 | 54.3475 | 6.61e-13 | 1.94e-14 | | | 2025-02-11 18:44:27 | 37.1839 | 54.3466 | 1.09e-13 | 4.27e-14 | | | 2025-02-15 10:12:36 | 37.1795 | 54.3469 | 1.07e-13 | 2.81e-14 | ------------------------------------------------------------------------------------------------------ Follow-up observations are encouraged to identify the nature of these two variable sources. 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). View this GCN Circular online at https://gcn.nasa.gov/circulars/39545. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L… [View Less]

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vsnet-grb-info March 2025