EP251023b
GCN Circular 42418
Subject
EP251023b/GRB 251023B: JinShan optical observation
Date
2025-10-24T08:38:09Z (2 days ago)
From
L. B. He at NAOC <helb@bao.ac.cn>
Via
Web form
L.B. He, J. An, S.Q. Jiang, X. Liu, Z.P. Zhu, D. Xu (NAOC), S.Y. Fu, A.D. Zhu, L. Lei, H.Z. Wu (HUST), J.Z. Liu (XAO) report on behalf of a large collaboration:
We observed the field of EP251023b/GRB 251023B (Kang et al., GCN 42392; Nakahira et al., GCN 42402; Wu et al., GCN 42415) using the 100C telescope of the JinShan project, located at Altay, Xinjiang, China. Observations started at 2025-10-23 16:01:41 UT, i. e. 7.3 hours after the trigger.
The previously reported optical counterpart (Mandarakas et al., GCN 42404) was detected in our stacked z-band frame with a magnitude z~21.4 at a mid-time 9.75 hrs post-burst. The magnitude was callibrated with nearby PanSTARRS1 dr2 catalog without the Galactic extinction correction.
We acknowledge the excellent support from T.Q. Chen and J.F. Zhang for enabling these observations.
GCN Circular 42416
Subject
EP251023b: Global MASTER-Net observations report
Date
2025-10-24T06:18:23Z (2 days ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
email
V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko,
G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU),
O.Gress, N.Budnev (ISU),
C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
A.Sosnovskij (CrAO),
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) was pointed to the EP251023b ( EP Team et al., GCN 42415) errorbox 40434 sec after trigger time at 2025-10-23 20:02:41 UT, with upper limit up to 20.1 mag. The observations began at zenith distance = 38 deg. The sun altitude is -34.7 deg.
The galactic latitude b = -18 deg., longitude l = 187 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=3022366
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
40494 | 2025-10-23 20:02:41 | MASTER-Tunka | (04h 53m 57.12s , +12d 53m 42.1s) | C | 120 | 16.4 |
40494 | 2025-10-23 20:02:41 | MASTER- | (04h 53m 27.18s , +12d 59m 22.7s) | C | 120 | 18.8 |
40627 | 2025-10-23 20:04:54 | MASTER- | (04h 53m 23.22s , +13d 00m 50.4s) | C | 120 | 19.8 |
40628 | 2025-10-23 20:04:54 | MASTER-Tunka | (04h 53m 53.26s , +12d 55m 10.3s) | C | 120 | 16.4 |
40761 | 2025-10-23 20:07:07 | MASTER-Tunka | (04h 53m 53.45s , +12d 53m 31.3s) | C | 120 | 16.9 |
40761 | 2025-10-23 20:07:07 | MASTER- | (04h 53m 23.36s , +12d 59m 11.7s) | C | 120 | 19.9 |
41086 | 2025-10-23 20:13:02 | MASTER-Tunka | (04h 53m 57.11s , +12d 54m 43.4s) | C | 60 | 19.7 |
41176 | 2025-10-23 20:13:02 | MASTER-Tunka | (04h 53m 57.11s , +12d 54m 43.3s) | C | 240 | 20.0 | Coadd
41086 | 2025-10-23 20:13:02 | MASTER- | (04h 53m 26.63s , +13d 00m 28.7s) | C | 60 | 19.7 |
41159 | 2025-10-23 20:14:15 | MASTER-Tunka | (04h 53m 50.19s , +12d 54m 07.5s) | C | 60 | 19.7 |
41159 | 2025-10-23 20:14:15 | MASTER- | (04h 53m 19.72s , +12d 59m 52.6s) | C | 60 | 19.7 |
41263 | 2025-10-23 20:15:30 | MASTER-Tunka | (04h 53m 51.71s , +12d 55m 04.5s) | C | 120 | 19.8 |
41263 | 2025-10-23 20:15:30 | MASTER- | (04h 53m 21.21s , +13d 00m 49.4s) | C | 120 | 19.8 |
41398 | 2025-10-23 20:17:44 | MASTER-Tunka | (04h 53m 57.01s , +12d 54m 00.3s) | C | 120 | 19.8 |
41518 | 2025-10-23 20:17:44 | MASTER-Tunka | (04h 53m 57.02s , +12d 54m 00.4s) | C | 360 | 20.0 | Coadd
41398 | 2025-10-23 20:17:44 | MASTER- | (04h 53m 26.46s , +12d 59m 45.2s) | C | 120 | 19.8 |
41530 | 2025-10-23 20:19:57 | MASTER-Tunka | (04h 53m 50.71s , +12d 52m 55.2s) | C | 120 | 19.7 |
41530 | 2025-10-23 20:19:57 | MASTER- | (04h 53m 20.15s , +12d 58m 40.0s) | C | 120 | 19.7 |
41663 | 2025-10-23 20:22:10 | MASTER-Tunka | (04h 53m 57.82s , +12d 53m 08.0s) | C | 120 | 19.7 |
41663 | 2025-10-23 20:22:10 | MASTER- | (04h 53m 27.32s , +12d 58m 52.6s) | C | 120 | 19.7 |
41796 | 2025-10-23 20:24:22 | MASTER-Tunka | (04h 53m 54.06s , +12d 54m 19.5s) | C | 120 | 19.7 |
41916 | 2025-10-23 20:24:22 | MASTER-Tunka | (04h 53m 54.06s , +12d 54m 19.5s) | C | 360 | 20.1 | Coadd
41796 | 2025-10-23 20:24:22 | MASTER- | (04h 53m 23.57s , +13d 00m 03.9s) | C | 120 | 19.6 |
41929 | 2025-10-23 20:26:35 | MASTER-Tunka | (04h 53m 54.16s , +12d 52m 58.5s) | C | 120 | 19.8 |
41929 | 2025-10-23 20:26:35 | MASTER- | (04h 53m 23.66s , +12d 58m 43.0s) | C | 120 | 19.8 |
42062 | 2025-10-23 20:28:48 | MASTER-Tunka | (04h 53m 57.79s , +12d 54m 17.4s) | C | 120 | 19.9 |
42062 | 2025-10-23 20:28:48 | MASTER- | (04h 53m 27.25s , +13d 00m 01.6s) | C | 120 | 19.9 |
42195 | 2025-10-23 20:31:02 | MASTER-Tunka | (04h 53m 52.11s , +12d 53m 34.1s) | C | 120 | 19.9 |
42315 | 2025-10-23 20:31:02 | MASTER-Tunka | (04h 53m 52.11s , +12d 53m 34.1s) | C | 360 | 20.1 | Coadd
42195 | 2025-10-23 20:31:02 | MASTER- | (04h 53m 21.54s , +12d 59m 18.5s) | C | 120 | 19.9 |
42327 | 2025-10-23 20:33:13 | MASTER-Tunka | (04h 53m 50.56s , +12d 54m 30.9s) | C | 120 | 20.0 |
42327 | 2025-10-23 20:33:13 | MASTER- | (04h 53m 19.95s , +13d 00m 15.1s) | C | 120 | 19.9 |
42460 | 2025-10-23 20:35:27 | MASTER-Tunka | (04h 53m 57.26s , +12d 53m 27.1s) | C | 120 | 19.9 |
42460 | 2025-10-23 20:35:27 | MASTER- | (04h 53m 26.58s , +12d 59m 11.0s) | C | 120 | 19.9 |
42595 | 2025-10-23 20:37:41 | MASTER-Tunka | (04h 53m 52.25s , +12d 52m 22.4s) | C | 120 | 19.9 |
42685 | 2025-10-23 20:37:41 | MASTER-Tunka | (04h 53m 52.25s , +12d 52m 22.4s) | C | 300 | 20.1 | Coadd
42595 | 2025-10-23 20:37:41 | MASTER- | (04h 53m 21.54s , +12d 58m 06.1s) | C | 120 | 19.9 |
42730 | 2025-10-23 20:39:56 | MASTER-Tunka | (04h 53m 57.37s , +12d 52m 45.8s) | C | 120 | 20.0 |
42730 | 2025-10-23 20:39:56 | MASTER- | (04h 53m 26.63s , +12d 58m 29.3s) | C | 120 | 20.0 |
42833 | 2025-10-23 20:42:09 | MASTER-Tunka | (04h 53m 54.47s , +12d 53m 48.3s) | C | 60 | 19.9 |
42833 | 2025-10-23 20:42:09 | MASTER- | (04h 53m 23.67s , +12d 59m 31.7s) | C | 60 | 19.9 |
42907 | 2025-10-23 20:43:24 | MASTER-Tunka | (04h 53m 54.53s , +12d 52m 27.5s) | C | 60 | 19.8 |
42967 | 2025-10-23 20:43:24 | MASTER-Tunka | (04h 53m 54.54s , +12d 52m 27.5s) | C | 180 | 20.0 | Coadd
42907 | 2025-10-23 20:43:24 | MASTER- | (04h 53m 23.70s , +12d 58m 10.7s) | C | 60 | 19.8 |
42980 | 2025-10-23 20:44:36 | MASTER-Tunka | (04h 53m 56.90s , +12d 54m 01.3s) | C | 60 | 19.7 |
42980 | 2025-10-23 20:44:36 | MASTER- | (04h 53m 26.04s , +12d 59m 44.2s) | C | 60 | 19.7 |
43052 | 2025-10-23 20:45:49 | MASTER-Tunka | (04h 53m 52.30s , +12d 53m 09.6s) | C | 60 | 19.5 |
43052 | 2025-10-23 20:45:49 | MASTER- | (04h 53m 21.42s , +12d 58m 52.8s) | C | 60 | 19.5 |
43134 | 2025-10-23 20:47:11 | MASTER-Tunka | (04h 53m 51.00s , +12d 54m 07.5s) | C | 60 | 19.2 |
43194 | 2025-10-23 20:47:11 | MASTER-Tunka | (04h 53m 50.99s , +12d 54m 07.5s) | C | 180 | 19.7 | Coadd
43135 | 2025-10-23 20:47:11 | MASTER- | (04h 53m 20.10s , +12d 59m 50.4s) | C | 60 | 19.1 |
43208 | 2025-10-23 20:48:25 | MASTER-Tunka | (04h 53m 58.03s , +12d 53m 05.4s) | C | 60 | 19.2 |
43208 | 2025-10-23 20:48:25 | MASTER- | (04h 53m 27.12s , +12d 58m 48.7s) | C | 60 | 19.1 |
43284 | 2025-10-23 20:49:41 | MASTER-Tunka | (04h 53m 50.96s , +12d 52m 02.9s) | C | 60 | 19.0 |
43284 | 2025-10-23 20:49:41 | MASTER- | (04h 53m 20.05s , +12d 57m 45.8s) | C | 60 | 19.0 |
43358 | 2025-10-23 20:50:54 | MASTER-Tunka | (04h 53m 58.58s , +12d 52m 08.7s) | C | 60 | 18.8 |
43418 | 2025-10-23 20:50:54 | MASTER-Tunka | (04h 53m 58.58s , +12d 52m 08.7s) | C | 180 | 19.3 | Coadd
43358 | 2025-10-23 20:50:54 | MASTER- | (04h 53m 27.65s , +12d 57m 51.3s) | C | 60 | 18.7 |
43435 | 2025-10-23 20:52:12 | MASTER-Tunka | (04h 53m 54.73s , +12d 53m 32.9s) | C | 60 | 18.7 |
43435 | 2025-10-23 20:52:12 | MASTER- | (04h 53m 23.76s , +12d 59m 15.7s) | C | 60 | 18.7 |
43507 | 2025-10-23 20:53:24 | MASTER-Tunka | (04h 53m 54.77s , +12d 52m 13.3s) | C | 60 | 18.3 |
43507 | 2025-10-23 20:53:24 | MASTER- | (04h 53m 23.79s , +12d 57m 56.2s) | C | 60 | 18.2 |
43579 | 2025-10-23 20:54:36 | MASTER-Tunka | (04h 53m 57.61s , +12d 53m 34.0s) | C | 60 | 18.7 |
43639 | 2025-10-23 20:54:36 | MASTER-Tunka | (04h 53m 57.62s , +12d 53m 34.0s) | C | 180 | 19.9 | Coadd
43579 | 2025-10-23 20:54:36 | MASTER- | (04h 53m 26.61s , +12d 59m 16.6s) | C | 60 | 18.7 |
43654 | 2025-10-23 20:55:50 | MASTER-Tunka | (04h 53m 52.49s , +12d 52m 52.2s) | C | 60 | 19.6 |
43654 | 2025-10-23 20:55:50 | MASTER- | (04h 53m 21.48s , +12d 58m 34.6s) | C | 60 | 19.5 |
43727 | 2025-10-23 20:57:04 | MASTER-Tunka | (04h 53m 51.37s , +12d 53m 50.1s) | C | 60 | 19.5 |
43727 | 2025-10-23 20:57:04 | MASTER- | (04h 53m 20.37s , +12d 59m 32.4s) | C | 60 | 19.4 |
43800 | 2025-10-23 20:58:16 | MASTER-Tunka | (04h 53m 57.11s , +12d 52m 48.1s) | C | 60 | 19.6 |
43890 | 2025-10-23 20:58:16 | MASTER-Tunka | (04h 53m 57.11s , +12d 52m 48.2s) | C | 240 | 20.0 | Coadd
43800 | 2025-10-23 20:58:16 | MASTER- | (04h 53m 26.13s , +12d 58m 30.3s) | C | 60 | 19.6 |
43873 | 2025-10-23 20:59:30 | MASTER-Tunka | (04h 53m 52.86s , +12d 51m 46.0s) | C | 60 | 19.6 |
43873 | 2025-10-23 20:59:30 | MASTER- | (04h 53m 21.87s , +12d 57m 27.9s) | C | 60 | 19.5 |
43984 | 2025-10-23 21:00:51 | MASTER-Tunka | (04h 53m 58.73s , +12d 51m 48.7s) | C | 120 | 19.2 |
43984 | 2025-10-23 21:00:51 | MASTER- | (04h 53m 27.73s , +12d 57m 30.8s) | C | 120 | 19.2 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
GCN Circular 42415
Subject
EP251023b/GRB 251023B : Einstein Probe detection of a fast X-ray transient
Date
2025-10-24T05:39:45Z (2 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Y. Wu (NJU), D. F. Hu (PMO, CAS), H. N. Yang, T. Zhao, W. D. Zhang (NAO, CAS), on behalf of the Einstein Probe (EP) team:
We report on the detection of a fast X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP251023b. The transient triggered EP-WXT (ID: 01709247298) at 2025-10-23T08:48:47 (UTC). The refined analysis of the WXT data shows that the event started at T0=2025-10-23T08:46:06 (UTC) and lasted for ~160 s. The WXT position of the source is R.A. = 73.502 deg, Dec. = 12.648 deg (J2000) with an uncertainty of 2.2 arcmin in radius (90% C.L. statistical and systematic). The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 2.69 x 10^(21) cm^-2 and a photon index of 1.66（-/+0.25）. The derived average unabsorbed 0.5-4 keV flux is 3.9 (-/+0.5) x 10^(-9) erg/s/cm^2.
We performed a Target-of-Opportunity observation with the Follow-up X-ray Telescope on board EP. The observation began at 2025-10-23T14:40:06 (UTC).An uncatalogued X-ray source was detected within the WXT error circle at R.A. = 73.5021 deg, Dec. = 12.6574 deg (J2000), with a positional uncertainty of 10 arcsec in radius (90% confidence level, including both statistical and systematic uncertainties). The FXT 0.5-10 keV spectrum can be fitted with an absorbed power law with the same fixed Galactic hydrogen column density value and a photon index of 2.16 (-/+0.21). The derived average unabsorbed 0.5-10 keV flux is 2.03 (-0.29/+0.34) x 10^(-12) erg/s/cm^2. The source is spatially consistent with the counterpart reported (Kang et al. GCN 42392, Evans et al. GCN 42401, Nakahira et al. GCN 42402, Mandarakas et al. GCN 42404, Cheung et al. GCN 42407).
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).