EP260210a
GCN Circular 43773
Subject
EP260210a: Mondy optical upper limits
Date
2026-02-17T15:04:00Z (22 days ago)
From
Alina Volnova at IKI RAS <alinusss@gmail.com>
Via
Web form
A. Volnova (IKI), E. Klunko (ISTP), N. Pankov (IKI), A. Pozanenko (IKI) report on behalf of IKI-GRB-FuN:
We observed the field of the fast X-ray transient EP260210a (Shi et al. GCN 43681) with the AZT-33IK 1.5m telescope of the Mondy observatory on Feb. 10 and 14 taking several 120-seconds frames in the R band. In the refined EP-FXT error circle (Yang et al., GCN 43696) we do not detect any new optical source in the stacked frames of our data. All catalogued sources located inside the refined EP-FXT error circle are detected in our stacked frames and do not exhibit any significant variations between the two epochs. In particular, the only one galaxy is presented within the refined EP-FXT error circle at coordinates of (J2000) 11:19:19.81 +45:23:43.8 in the SDSS catalogue.
Preliminary photometry of the galaxy and observational details are the following:
Date UT start t-T0 Exp. Filter SDSS_galaxy UL Site/Telescope
(mid,days) (n*s) (3sigma)
2026-02-10 15:18:13 0.22584 30*120 R 20.29+/-0.05 22.7 Mondy/AZT-33IK
2026-02-14 20:08:59 4.42816 30*120 R 20.31+/-0.06 22.4 Mondy/AZT-33IK
The photometry is based on nearby SDSS stars (R-magnitudes obtained using the 2005 Lupton transformation equations) and is not corrected for Galactic extinction.
Our results are consistent with other published observations (Kang et al., GCN 43683; Fortin et al., GCN 43684; Li et al., GCN 43687; Aryan et al., GCN 43692; Lipunov et al., GCN 43697).
GCN Circular 43697
Subject
EP260210a: Global MASTER-Net observations report
Date
2026-02-11T15:54:23Z (a month 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 [1] located in Russia (Applied Physics Institute, Irkutsk State University) was pointed to the EP260210a ( EP Team et al., GCN 43681) errorbox 1 days 8970 sec after notice time and 1 days 16089 sec after trigger time at 2026-02-11 14:49:07 UT, with upper limit up to 20.9 mag. The observations began at zenith distance = 41 deg. The sun altitude is -42.1 deg.
The galactic latitude b = 65 deg., longitude l = 162 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=3130129
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
7568 | 2026-02-10 12:25:35 | MASTER- | (11h 18m 01.50s , +46d 01m 48.3s) | C | 180 | 20.1 |
7568 | 2026-02-10 12:25:35 | MASTER- | (11h 19m 42.26s , +45d 29m 04.1s) | C | 180 | 19.9 |
7757 | 2026-02-10 12:28:45 | MASTER- | (11h 18m 02.83s , +46d 02m 53.1s) | C | 180 | 20.0 |
7757 | 2026-02-10 12:28:45 | MASTER- | (11h 19m 43.41s , +45d 30m 08.6s) | C | 180 | 19.8 |
7947 | 2026-02-10 12:31:54 | MASTER- | (11h 18m 09.32s , +46d 01m 59.2s) | C | 180 | 19.9 |
7947 | 2026-02-10 12:31:54 | MASTER- | (11h 19m 49.66s , +45d 29m 14.2s) | C | 180 | 19.7 |
8137 | 2026-02-10 12:35:04 | MASTER- | (11h 18m 03.97s , +46d 01m 06.6s) | C | 180 | 19.7 |
8137 | 2026-02-10 12:35:04 | MASTER- | (11h 19m 44.15s , +45d 28m 20.7s) | C | 180 | 19.5 |
8327 | 2026-02-10 12:38:14 | MASTER- | (11h 19m 50.14s , +45d 28m 55.2s) | C | 180 | 18.1 |
9693 | 2026-02-10 13:01:01 | MASTER- | (11h 18m 06.50s , +46d 04m 07.7s) | C | 180 | 19.5 |
9693 | 2026-02-10 13:01:01 | MASTER- | (11h 19m 42.80s , +45d 31m 23.3s) | C | 180 | 19.3 |
102519 | 2026-02-11 14:49:07 | MASTER-Tunka | (11h 17m 51.29s , +45d 05m 25.7s) | C | 60 | 20.1 |
102519 | 2026-02-11 14:49:07 | MASTER-Tunka | (11h 17m 17.48s , +45d 11m 57.6s) | C | 60 | 20.1 |
102579 | 2026-02-11 14:49:07 | MASTER-Tunka | (11h 17m 17.48s , +45d 11m 57.6s) | C | 180 | 20.8 | Coadd
102593 | 2026-02-11 14:50:21 | MASTER-Tunka | (11h 17m 48.72s , +45d 07m 01.6s) | C | 60 | 20.1 |
102593 | 2026-02-11 14:50:21 | MASTER-Tunka | (11h 17m 14.82s , +45d 13m 33.5s) | C | 60 | 20.1 |
102675 | 2026-02-11 14:51:42 | MASTER-Tunka | (11h 17m 14.77s , +45d 11m 48.3s) | C | 60 | 20.2 |
102675 | 2026-02-11 14:51:42 | MASTER-Tunka | (11h 17m 48.77s , +45d 05m 16.6s) | C | 60 | 20.1 |
102777 | 2026-02-11 14:52:55 | MASTER-Tunka | (11h 17m 18.23s , +45d 13m 40.4s) | C | 120 | 20.3 |
102897 | 2026-02-11 14:52:55 | MASTER-Tunka | (11h 17m 18.23s , +45d 13m 40.3s) | C | 360 | 20.9 | Coadd
102777 | 2026-02-11 14:52:55 | MASTER-Tunka | (11h 17m 52.48s , +45d 07m 09.3s) | C | 120 | 20.3 |
102911 | 2026-02-11 14:55:08 | MASTER-Tunka | (11h 17m 11.60s , +45d 12m 39.5s) | C | 120 | 20.4 |
102911 | 2026-02-11 14:55:08 | MASTER-Tunka | (11h 17m 46.09s , +45d 06m 09.1s) | C | 120 | 20.4 |
103052 | 2026-02-11 14:57:30 | MASTER-Tunka | (11h 17m 46.28s , +45d 07m 08.1s) | C | 120 | 20.4 |
103052 | 2026-02-11 14:57:30 | MASTER-Tunka | (11h 17m 11.47s , +45d 13m 37.9s) | C | 120 | 20.4 |
103185 | 2026-02-11 14:59:43 | MASTER-Tunka | (11h 17m 52.89s , +45d 06m 06.4s) | C | 120 | 20.3 |
103185 | 2026-02-11 14:59:43 | MASTER-Tunka | (11h 17m 17.88s , +45d 12m 35.6s) | C | 120 | 20.4 |
103349 | 2026-02-11 15:02:26 | MASTER-Tunka | (11h 16m 48.88s , +46d 09m 10.4s) | C | 120 | 20.4 |
103349 | 2026-02-11 15:02:26 | MASTER-Tunka | (11h 17m 28.36s , +46d 01m 15.6s) | C | 120 | 20.3 |
103469 | 2026-02-11 15:02:26 | MASTER-Tunka | (11h 17m 28.35s , +46d 01m 15.6s) | C | 360 | 20.8 | Coadd
103485 | 2026-02-11 15:04:42 | MASTER-Tunka | (11h 16m 55.90s , +46d 09m 20.0s) | C | 120 | 20.4 |
103485 | 2026-02-11 15:04:42 | MASTER-Tunka | (11h 17m 35.59s , +46d 01m 25.7s) | C | 120 | 20.4 |
103618 | 2026-02-11 15:06:56 | MASTER-Tunka | (11h 16m 51.63s , +46d 10m 48.7s) | C | 120 | 20.4 |
103618 | 2026-02-11 15:06:56 | MASTER-Tunka | (11h 17m 31.57s , +46d 02m 54.6s) | C | 120 | 20.3 |
103751 | 2026-02-11 15:09:09 | MASTER-Tunka | (11h 16m 51.33s , +46d 09m 05.5s) | C | 120 | 20.3 |
103751 | 2026-02-11 15:09:09 | MASTER-Tunka | (11h 17m 31.48s , +46d 01m 11.8s) | C | 120 | 20.3 |
103871 | 2026-02-11 15:09:09 | MASTER-Tunka | (11h 17m 31.47s , +46d 01m 11.8s) | C | 360 | 20.7 | Coadd
103885 | 2026-02-11 15:11:23 | MASTER-Tunka | (11h 17m 34.65s , +46d 02m 45.1s) | C | 120 | 20.3 |
103885 | 2026-02-11 15:11:23 | MASTER-Tunka | (11h 16m 54.22s , +46d 10m 39.3s) | C | 120 | 20.3 |
104023 | 2026-02-11 15:13:41 | MASTER-Tunka | (11h 17m 29.15s , +46d 02m 05.1s) | C | 120 | 20.3 |
104023 | 2026-02-11 15:13:41 | MASTER-Tunka | (11h 16m 48.47s , +46d 09m 59.3s) | C | 120 | 20.3 |
104159 | 2026-02-11 15:15:56 | MASTER-Tunka | (11h 17m 27.69s , +46d 03m 03.6s) | C | 120 | 20.3 |
104279 | 2026-02-11 15:15:56 | MASTER-Tunka | (11h 17m 27.68s , +46d 03m 03.7s) | C | 360 | 20.7 | Coadd
104159 | 2026-02-11 15:15:56 | MASTER-Tunka | (11h 16m 46.62s , +46d 10m 57.7s) | C | 120 | 20.3 |
104292 | 2026-02-11 15:18:10 | MASTER-Tunka | (11h 16m 53.54s , +46d 09m 55.8s) | C | 120 | 20.3 |
104292 | 2026-02-11 15:18:10 | MASTER-Tunka | (11h 17m 34.89s , +46d 02m 02.3s) | C | 120 | 20.2 |
104425 | 2026-02-11 15:20:23 | MASTER-Tunka | (11h 16m 46.28s , +46d 08m 53.8s) | C | 120 | 20.3 |
104425 | 2026-02-11 15:20:23 | MASTER-Tunka | (11h 17m 27.96s , +46d 01m 00.0s) | C | 120 | 20.3 |
104559 | 2026-02-11 15:22:36 | MASTER-Tunka | (11h 16m 53.19s , +46d 09m 18.6s) | C | 120 | 20.3 |
104559 | 2026-02-11 15:22:36 | MASTER-Tunka | (11h 17m 35.15s , +46d 01m 24.7s) | C | 120 | 20.3 |
104679 | 2026-02-11 15:22:36 | MASTER-Tunka | (11h 17m 35.15s , +46d 01m 24.6s) | C | 360 | 20.7 | Coadd
104693 | 2026-02-11 15:24:50 | MASTER-Tunka | (11h 16m 48.89s , +46d 10m 36.4s) | C | 120 | 20.2 |
104693 | 2026-02-11 15:24:50 | MASTER-Tunka | (11h 17m 31.14s , +46d 02m 42.6s) | C | 120 | 20.2 |
104826 | 2026-02-11 15:27:04 | MASTER-Tunka | (11h 16m 48.61s , +46d 08m 57.8s) | C | 120 | 20.2 |
104826 | 2026-02-11 15:27:04 | MASTER-Tunka | (11h 17m 31.07s , +46d 01m 04.0s) | C | 120 | 20.0 |
104964 | 2026-02-11 15:29:21 | MASTER-Tunka | (11h 16m 51.20s , +46d 10m 29.3s) | C | 120 | 20.2 |
104964 | 2026-02-11 15:29:21 | MASTER-Tunka | (11h 17m 33.89s , +46d 02m 34.8s) | C | 120 | 20.0 |
105084 | 2026-02-11 15:29:21 | MASTER-Tunka | (11h 17m 33.89s , +46d 02m 34.8s) | C | 360 | 20.6 | Coadd
105098 | 2026-02-11 15:31:35 | MASTER-Tunka | (11h 16m 44.36s , +46d 09m 44.7s) | C | 120 | 20.2 |
105098 | 2026-02-11 15:31:35 | MASTER-Tunka | (11h 17m 27.28s , +46d 01m 49.9s) | C | 120 | 20.2 |
105231 | 2026-02-11 15:33:48 | MASTER-Tunka | (11h 16m 43.65s , +46d 10m 43.2s) | C | 120 | 20.2 |
105231 | 2026-02-11 15:33:48 | MASTER-Tunka | (11h 17m 26.90s , +46d 02m 48.1s) | C | 120 | 20.2 |
105363 | 2026-02-11 15:36:01 | MASTER-Tunka | (11h 16m 49.86s , +46d 09m 40.6s) | C | 120 | 20.2 |
105363 | 2026-02-11 15:36:01 | MASTER-Tunka | (11h 17m 33.35s , +46d 01m 46.0s) | C | 120 | 20.2 |
105513 | 2026-02-11 15:36:01 | MASTER-Tunka | (11h 17m 33.35s , +46d 01m 46.1s) | C | 420 | 20.6 | Coadd
105496 | 2026-02-11 15:38:13 | MASTER-Tunka | (11h 16m 44.46s , +46d 08m 38.1s) | C | 120 | 19.8 |
105496 | 2026-02-11 15:38:13 | MASTER-Tunka | (11h 17m 28.25s , +46d 00m 43.9s) | C | 120 | 19.9 |
105659 | 2026-02-11 15:40:27 | MASTER-Tunka | (11h 16m 48.73s , +46d 08m 57.2s) | C | 180 | 20.1 |
105659 | 2026-02-11 15:40:27 | MASTER-Tunka | (11h 17m 32.92s , +46d 01m 02.1s) | C | 180 | 20.1 |
105853 | 2026-02-11 15:43:40 | MASTER-Tunka | (11h 16m 46.04s , +46d 10m 05.2s) | C | 180 | 20.1 |
105853 | 2026-02-11 15:43:40 | MASTER-Tunka | (11h 17m 30.80s , +46d 02m 10.3s) | C | 180 | 20.1 |
106045 | 2026-02-11 15:46:53 | MASTER-Tunka | (11h 17m 30.87s , +46d 00m 58.4s) | C | 180 | 20.0 |
106045 | 2026-02-11 15:46:53 | MASTER-Tunka | (11h 16m 45.59s , +46d 08m 52.7s) | C | 180 | 20.0 |
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 43696
Subject
EP260210a: refined analysis of the EP-FXT observation
Date
2026-02-11T14:20:01Z (a month ago)
Edited On
2026-02-12T13:46:40Z (a month 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
Z. H. Yang, R. Shi (PMO), Q. C. Zhao (IHEP), G. Y. Zhao (SYSU), Y. J. Zhang (THU) and Z. X. Ling (NAOC) on behalf of the Einstein Probe (EP) team:
The fast X-ray transient EP260210a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Shi et al., GCN 43681). The refined analysis of the WXT data shows that the event started at T0=2026-02-10T10:20:58.53 (UTC), and lasted for approximately 220 seconds. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 1.6×10^20 cm^-2, and a photon index of 1.57 (-0.4/+0.4). The derived average unabsorbed 0.5-4 keV flux is 1.5 (-0.3/+0.4) × 10^(-10) erg/s/cm^2.
The Follow-up X-ray Telescope (FXT) on board EP autonomously observed this source a few minutes after the on board trigger. The FXT observation started at 2026-02-10T10:24:57 (UTC, T0+238 s). The effective exposure time of the observation is around 5 ks. On-ground analysis of the FXT data found an uncatalogued source at R.A. = 169.8314, DEC = 45.3949 (J2000) with an uncertainty of 10 arcsec in radius (90% C.L. statistical and systematic). The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 1.6 × 10^20 cm^-2, and a photon index of 2.7 (-0.1/+0.1). The derived average unabsorbed 0.5-10 keV flux is 6.4 (-1.0/+1.0) ×10^(-13) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.
Further FXT follow-up observations have been arranged.
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).
GCN Circular 43692
Subject
EP260210a: Optical upper limits with Kinder observations
Date
2026-02-11T08:35:06Z (a month ago)
From
Amar Aryan at National Central University, Institute of Astronomy (NCUIA) <amararyan941@gmail.com>
Via
Web form
A. Aryan, C.-S. Lin, T.-W. Chen (all NCU), A. K. H. Kong (NTHU), J. H. Gillanders, S. J. Smartt (both Oxford), Y. J. Yang (NYUAD), Y.-H. Lee, A. Sankar.K, M.-H. Lee, C.-H. Lai, Y.-C. Pan, C.-C. Ngeow, W.-J. Hou, H.-Y. Hsiao, H.-C. Lin, J.-K. Guo (all NCU), S. Yang, Z. N. Wang, L. L. Fan, G. H. Sun (all HNAS), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, T. Moore, K. W. Smith, C. Angus, A. Aamer (all QUB), A. Schultz and M. Huber (both IfA, Hawaii) report:
We observed the field of the fast X-ray transient EP260210a (Shi et al. GCN 43681) using the 40cm SLT and 1m LOT at the Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al. 2025, ApJ, 983, 86, doi:10.3847/1538-4357/adb428). The first SLT epoch of observations in r-band started at 13:57 UTC on 10th of February 2026 (MJD 61081.582), 3.57 hr after the EP-WXT trigger.
We utilized the astroalign (Beroiz et al. 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al. 2022, ApJ, 935, 167) packages to align and stack the individual frames. We utilized the Python-based package AutoPhOT (Brennan & Fraser 2022, A&A, 667, A62) to perform template subtraction with the DESI Legacy Survey (Dey et al. 2019, AJ 157, 168) DR10 image (for r-band) and Pan-STARRS1 3Pi (Chambers et al. 2016, arXiv:1612.05560) archive image (for i-band) using the 'SFFT' (Hu et al. 2022, ApJ, 936, 157) algorithm.
Moreover, we used AutoPhOT to perform PSF photometry. We do not detect any new or uncataloged sources within the 20" EP-FXT localization circle. The details of the observations and the measured 3-sigma upper limits (in the AB system) are as follows:
Telescope | Filter | MJD (start)| t-t0 (hr) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass
SLT | r | 61081.582 | 3.57 | 300 * 12 | >22.0 | 1".5 | 1.47
LOT | r | 61081.584 | 3.62 | 300 * 6 | >22.9 | 1".3 | 1.54
SLT | i | 61081.628 | 4.69 | 300 * 20 | >21.6 | 1".4 | 1.18
The non-detections in our observations are consistent with those reported by Kang et al. (GCN 43683), Fortin et al. (GCN 43684), and Li et al. (GCN 43687).
The presented magnitude is calibrated using the field stars from the ATLAS-RefCat2 catalog from MAST (Tonry J. L. et al. 2018, ApJ, 867, 105) and is not corrected for the expected Galactic foreground extinction of A_r = 0.034 mag and A_i = 0.026 mag in the direction of the transient (Schlafly & Finkbeiner 2011). The methodology, details on the Lulin observatory telescopes, and a compilation of our optical follow-up campaign for FXTs discovered within the first year of operation of the Einstein-Probe mission are presented in Aryan et al. 2025, ApJS, 281, 20, doi:10.3847/1538-4365/adfc69.
GCN Circular 43687
Subject
EP260210a: SVOM/VT optical upper limit
Date
2026-02-10T17:33:25Z (a month ago)
From
Huali Li at at NAOC, SVOM <lhl@nao.cas.cn>
Via
Web form
H. L. Li, Y. N. Ma, L. P. Xin, Y. L. Qiu, C. Wu, Z. H. Yao, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. R. Xu, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA) report on behalf of the SVOM/VT team.
SVOM/VT performed a Target of Opportunity observation of EP260210a detected by Einstein Probe (Shi et al., GCN 43681). The observation started at 2026-02-10T10:56:57 UTC, 34.52 minutes after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
No uncatalogued sources are detected in single or stacked images within the error box of EP-FXT (Shi et al., GCN 43681), which is compatible with the earlier upper limits from SVOM/C-GFT (Kang et al., GCN 43683) and COLIBRÍ (Fortin et al, GCN 43684). The 3 sigma limit magnitudes are derived as below:
Mid time | Band | Exposure Time | 3 sigma limit magnitude
2.316 hour VT_B 42*50 sec > 23.2 mag
1.535 hour VT_R 39*50 sec > 22.9 mag
Our photometry was not corrected for Galactic extinction.
The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS.
GCN Circular 43684
Subject
EP260210a: COLIBRÍ optical upper limit
Date
2026-02-10T14:47:40Z (a month ago)
From
F. Fortin at IRAP <ffortin.sci.edu@gmail.com>
Via
Web form
Francis Fortin (IRAP), Edilberto Aguilar-Ruiz (UNAM), Jean-Grégoire Ducoin (CPPM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Asuka Kuwata (UNAM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM) report:
We imaged the field of the EP260210a (Shi et al., GCN Circ. 43681) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-02-10 11:13:20 to 13:11:12 UTC (from 0.83 to 2.80 hours after the trigger) and obtained 85 minutes of simultaneous exposure in the r and z filters.
The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction.
In the stacked image, we do not detect any new source at the FXT source position (Shi et al., GCN Circ. 43681) down to the following 5-sigma limit:
r > 23.59
z > 22.15
Our upper limits are compatible with the earlier upper limits of Kang et al. (GCN Circ. 43683).
We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams.
COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico.
GCN Circular 43683
Subject
EP260210a: SVOM/C-GFT upper limit
Date
2026-02-10T13:35:22Z (a month ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
Z. Kang (CHO), C. Wu, L.P. Xin, X.H. Han, P.P. Zhang, X.M. Lu (NAOC), Z.W. Li, Y. Lv (CHO), R.S. Zhang, Y.J. Xiao, Y.L. Qiu, J. Wang, J.S. Deng, L. Huang, J.Y. Wei (NAOC) report on behalf of the SVOM/C-GFT team:
We observed the field of EP260210a detected by EP/WXT (Shi et al., GCN 43681) with LATIOS on SVOM/C-GFT. Observations started at 2026-02-10T10:32:54 UTC, ~ 9.88 min after the trigger.
We obtained g, r, and i-band follow-up imaging. After preliminary analysis，no credible candidate was detected within the error box provided by EP/FXT (Shi et al., GCN 43681) in our images. The 3-sigma upper limits are:
| Mid_T - T0 (min) | Exposure Time (s) | Band | Upper Limit (AB) |
|---|---|---|---|
| 36.13 | 10×60 | i | 20.02 |
| 47.01 | 10×60 | g | 20.15 |
| 59.39 | 10×60 | r | 20.23 |
The photometry was calibrated against UCAC4 catalogue and no correction for Galactic dust extinction was applied.
We thank the observation assistants Chun-Lei Guo and Yin-Huai Hao at Jilin observatory for their excellent support.
The Chinese Ground Follow-up Telescope (C-GFT) for the SVOM mission is located at Jilin Station, Changchun Observatory, National Astronomical Observatories, CAS. It features two instruments: (1) CATCH at the Cassegrain focus with a 21 arcsec x 21 arcsec FOV for simultaneous g/r/i-band imaging, and (2) LATIOS, a 4k x 4k CMOS camera at the prime focus with a 1.28 deg x 1.28 deg FOV that images in g, r, and i bands via filter switching.
GCN Circular 43681
Subject
EP260210a: Einstein Probe detection of an X-ray transient
Date
2026-02-10T12:13:39Z (a month ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
R. Shi (PMO), Z. H. Yang, Q. C. Zhao (IHEP), G. Y. Zhao (SYSU), Y. J. Zhang (THU) and Z. X. Ling (NAOC) on behalf of the Einstein Probe (EP) team:
We report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP260210a. The transient triggered EP-WXT (ID: 01709257873) at 2026-02-10T10:23:01 (UTC). The WXT position of the source is R.A. = 169.840 deg, DEC = 45.408 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic).
A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 169.8314 deg, DEC = 45.3949 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic).
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).