EP261030a
GCN Circular 46125
Subject
EP261030a: EP-FXT follow-up observation
Date
2026-11-01T15:35:36Z (4 hours ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
H.-H. Zhang, C.-Y. Dai (NJU), Y.-L. Wang (ICE, CSIC) and Y. Liu (NAOC) on behalf of the Einstein Probe (EP) team:
The X-ray transient EP261030a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Zhang et al., GCN 46121) at 2026-10-30T17:15:19 (UTC). No optical counterpart was detected in follow-up observations with MASTER-SAAO (Buckley et al., GCN 46122) or the GROWTH-India Telescope (Sarkar et al., GCN 46124).
Follow-up observation by the Follow-up X-ray Telescope (FXT) on board EP was performed at 2026-10-31 23:08:47(UTC), ~30 hours after the WXT detection. The exposure time of the observation is around 4 ks. On-ground analysis of the FXT data revealed an X-ray source within the WXT error circle of EP261030a. The source is located at R.A. = 23.6760 deg and Dec. = -11.6749 deg (J2000), with an uncertainty radius of 10 arcsec (90% confidence level, including both statistical and systematic errors). The source lies within the WXT error circle of EP261030a.
The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 2.4E20 cm-2 and a photon index of 1.4(-0.77, +0.84). The derived flux in 0.5-10 keV is 1.6(-0.9, +2.2)E-13 erg/s/cm2. The uncertainties are at the 90% confidence level for the above parameters.
Launched on January 9, 2024, EP is a space-based X-ray observatory designed to monitor the soft X-ray sky and perform X-ray follow-up observations (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).
GCN Circular 46124
Subject
EP261030a: GROWTH-India Telescope Upper Limit
Date
2026-11-01T10:47:50Z (9 hours ago)
From
Aditya Pawan Saikia at IIT Bombay <adityaps@iitb.ac.in>
Via
Web form
A. Sarkar (IITB), V. Vijaykumar (IITB), T. Mohan (IITB), J. Basu (IITB), A.P. Saikia (IITB), S. Patil (IITB), V. Swain (IITB), V. Bhalerao (IITB), G.C. Anupama (IIA), S. Barway (IIA) and K. Angail (IAO) report on behalf of the GIT team:
We observed the field of EP261030a within the localization region of EP-FXT (Zhang et al., GCN 46121), with 0.7m GROWTH-India Telescope (GIT). We started the observation at 2026-10-31 14:29:55 UT, i.e., 21.243 hours after the WXT trigger, and obtained multiple exposures in the SDSS r' filter. We do not detect any optical counterpart in our stacked images at the position reported by the Einstein Probe. The photometric results are as follows:
| MJD (mid) | Filter | tmid-t0 (hours) | Exposure Time (sec) | Upper Limit (5-sigma) |
|---|---|---|---|---|
| 61344.614525 | r' | 21.493 | 5x360 | 21.28 |
The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction.
Our results are consistent with other optical observations (Lipunov et al. GCN 46122)
The GROWTH India Telescope (GIT; Kumar et al. 2022) is a 70-cm telescope with a 0.7-degree field of view, set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. It is located at the Indian Astronomical Observatory (Hanle), operated by IIA. We acknowledge funding by the IITB alumni batch of 1994, which partially supports the operations of the telescope. Telescope technical details are available at https://sites.google.com/view/growthindia/.
GCN Circular 46122
Subject
EP261030a: Global MASTER-Net observations report
Date
2026-10-31T22:09:49Z (a day ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
email
D.Buckley (SAAO),
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 (Lomonosov MSU)
A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity)
A.Sosnovskij (Lomonosov MSU)
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory)
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,
A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory)
R.Rebolo (The Instituto de Astrofisica de Canarias)
O.Gress, N.Budnev(ISU)
M. Segura, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA)
MASTER-SAAO robotic telescope [1] located in South Africa (South African Astronomical Observatory) was pointed to the EP261030a ( EP Team at NAOC/CAS <ep_ta@bao.ac.cn> et al., GCN 46121) errorbox 37209 sec after notice time and 1 days 16553 sec after trigger time at 2026-10-31 21:51:12 UT, with upper limit up to 19.7 mag. The observations began at zenith distance = 21 deg. The sun altitude is -42.9 deg.
The galactic latitude b = -71 deg., longitude l = 160 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=3532176
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
103013 | 2026-10-31 21:51:12 | MASTER-SAAO | (01h 32m 47.13s , -12d 01m 38.8s) | C | 120 | 19.2 |
103133 | 2026-10-31 21:51:12 | MASTER-SAAO | (01h 32m 47.13s , -12d 01m 38.8s) | C | 360 | 19.7 | Coadd
103013 | 2026-10-31 21:51:12 | MASTER-SAAO | (01h 30m 53.63s , -11d 45m 59.2s) | C | 120 | 19.1 |
103133 | 2026-10-31 21:51:12 | MASTER-SAAO | (01h 30m 53.63s , -11d 45m 59.2s) | C | 360 | 19.6 | Coadd
103166 | 2026-10-31 21:53:45 | MASTER-SAAO | (01h 32m 41.39s , -12d 02m 16.3s) | C | 120 | 19.0 |
103166 | 2026-10-31 21:53:45 | MASTER-SAAO | (01h 30m 47.87s , -11d 46m 35.7s) | C | 120 | 18.9 |
103319 | 2026-10-31 21:56:17 | MASTER-SAAO | (01h 30m 49.67s , -11d 45m 28.6s) | C | 120 | 19.0 |
103319 | 2026-10-31 21:56:17 | MASTER-SAAO | (01h 32m 43.18s , -12d 01m 09.7s) | C | 120 | 19.0 |
103471 | 2026-10-31 21:58:50 | MASTER-SAAO | (01h 32m 47.69s , -12d 02m 03.8s) | C | 120 | 19.0 |
103471 | 2026-10-31 21:58:50 | MASTER-SAAO | (01h 30m 54.16s , -11d 46m 22.4s) | C | 120 | 19.2 |
103623 | 2026-10-31 22:01:22 | MASTER-SAAO | (01h 32m 41.94s , -12d 02m 58.8s) | C | 120 | 19.7 |
103623 | 2026-10-31 22:01:22 | MASTER-SAAO | (01h 30m 48.39s , -11d 47m 17.2s) | C | 120 | 19.7 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
[1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp.
http : // www.pereplet.ru/lipunov/625.html
GCN Circular 46121
Subject
EP261030a: Einstein Probe detection of a fast X-ray transient
Date
2026-10-31T11:29:56Z (a day ago)
Edited On
2026-10-31T14:58:34Z (a day ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
H.-H. Zhang, C.-Y. Dai (NJU), Y.-L. Wang (ICE, CSIC) and Y. Liu (NAOC) on behalf of the Einstein Probe (EP) team:
We report on the detection of a fast X-ray transient, designated EP261030a, identified in the downlinked data from the Wide-field X-ray Telescope (WXT) aboard the Einstein Probe (EP) mission. The WXT light curve of the transient began at about 2026-10-30T17:15:19 UTC and lasted for about 100 s. The WXT position of the source is R.A. = 23.663 deg, DEC = -11.691 deg (J2000) with an uncertainty of 3.2 arcmin in radius (90% C.L. statistical and systematic).
The 0.5-4 keV WXT spectrum can be fitted by an absorbed power-law model with a fixed Galactic column density of 2.4 x 10^20 cm^-2 and a photon index of 1.0 (-0.4,+0.4). The derived 0.5-4 keV unabsorbed flux is 3.6 (-0.9/+1.1) x 10^-10 erg/cm^2/s.
A follow-up observation with the Follow-up X-ray Telescope (FXT) on board EP has been scheduled. Further information will be updated when the telemetry data is received.
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).