EP261111a
GCN Circular 46237
Pu Lin, Jin-Ji Li, Zhi-Xiang Tan, Zhong-Nan Dong, Yun Shi, Rui-Chen Gao, Jia-Qi Lin, Hao-Nan Yang, Hao-Ran Zhang, Jian-Hong Cao, Shu-Quan Bai, Si-Rui Huang, Jing-Kai Sun, Lu-Yao Wen, P. H. Thomas Tam, Rong-Feng Shen, and Bin Ma (Sun Yat-sen University) report on behalf of the SYSU 80cm infrared telescope team:
We observed the field of EP261111a detected by the Einstein Probe (G. L. Huang et al., GCN 46226 and Z. X. Li et al., GCN 46235) with the Sun Yat-sen University 80cm infrared telescope in the K and J bands. The observations were carried out in the K band on 2026-11-11 from 15:02:09 to 15:41:58 UT (1.62 - 2.28 hr after the EP/WXT trigger) using stacked images (113 x 20s, 2260 s total exposure), and in the J band on 2026-11-11 from 16:40:41 to 17:41:30 UT (3.26 - 4.27 hr after the EP/WXT trigger) using stacked images (172 x 20s, 3440 s total exposure).
We do not detect any new source within the localization (RA = 43.1193 deg, Dec = +44.4351 deg, J2000; 10 arcsec uncertainty; reported by Einstein Probe, Z. X. Li et al., GCN 46235) in our stacked images, and obtain 5-sigma upper limits of K = 17.83 mag (Vega) and J = 19.83 mag (Vega).
The photometry was calibrated against nearby stars from the 2MASS catalog and is reported in the Vega system, without correction for Galactic extinction.
The SYSU 80cm infrared telescope is operated and managed by the Department of Astronomy, Sun Yat-sen University.
GCN Circular 46236
R. A. J. Eyles-Ferris (Leicester), J. Chácon (PUC), P. G. Jonker (Radboud), D. B. Malesani (DAWN/NBI and Radboud) and A. A. Chrimes (Radboud) report on behalf of a larger collaboration:
We observed the field of the fast X-ray transient EP261111a detected by Einstein Probe (Huang et al., GCN 46226; Li et al., GCN 46235) with LCO 1-m telescopes located at McDonald Observatory (USA) and equipped with SINISTRO instruments. Observations consisted of a sequence of 6 x 300 s exposures in each of the SDSS r and z bands starting at 2026-11-12 01:59:08 UT (~12.4 h post trigger) and 2026-11-12 08:12:07 UT (~18.8 h post trigger), respectively.
We performed image subtraction using PanSTARRS template images and compared the stacked and templates manually. We do not detect any new source inside the Einstein Probe Follow-up X-ray Telescope uncertainty region (Li et al., GCN 46235) to 3-sigma limiting magnitudes of r > 22.7 and z > 22.3 in either our stacked images or the subtractions. Our non-detections are consistent with those of Jin et al. (GCN 46227) and Buckley et al. (GCN 46230).
Our upper limits are in AB magnitudes, calibrated using nearby stars from the PanSTARRS catalogue, and are not corrected for Galactic extinction.
GCN Circular 46235
Z.X. Li, G. L. Huang (IHEP, CAS), Y. J. Zhang (THU), W. D. Zhang (NAO, CAS) on behalf of the Einstein Probe (EP) team:
The fast X-ray transient EP261111a triggered the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission at 2026-11-11T13:25:10 (UTC) (Huang et al., GCN 46226). Subsequent optical follow-up observations were reported by Jin et al. (GCN 46227) and Buckley et al. (GCN 46230).
The refined analysis of the WXT data shows that the event started at T0 = 2026-11-11T13:24:09 (UTC), and lasted for approximately 60 seconds, after which the WXT light curve was interrupted due to the autonomous follow-up observation. During the flare, the average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density (NH) of 1.10×10^21 cm^-2, and a photon index of 1.23 (-0.64/+0.67). The derived average unabsorbed 0.5-4 keV flux is 1.30 (-0.43/+0.65) ×10^(-9) erg/s/cm^2.
The Follow-up X-ray Telescope (FXT) on board EP observed this source autonomously at 2026-11-11T13:28:25 (UTC, T0+256s). The exposure time of this observation is 3150 s. On-ground analysis of the FXT data found an uncatalogued source at R.A. = 43.1193, DEC = 44.4351 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic) within the WXT error circle. The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 1.10×10^21 cm^-2 and a photon index of 1.90 (-0.14/+0.15). The derived average unabsorbed 0.5-10 keV flux is 3.15 (-0.36/+0.41)×10^(-12) erg/s/cm^2. All uncertainties are reported at the 90% confidence interval.
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 46230
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 EP261111a ( EP Team at NAOC/CAS <ep_ta@bao.ac.cn> et al., GCN 46226) errorbox 25131 sec after notice time and 25446 sec after trigger time at 2026-11-11 20:29:16 UT, with upper limit up to 17.8 mag. The observations began at zenith distance = 79 deg. The sun altitude is -33.6 deg.
The galactic latitude b = -13 deg., longitude l = 145 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=3532562
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
25477 | 2026-11-11 20:29:16 | MASTER-SAAO | (02h 50m 17.51s , +44d 06m 21.7s) | C | 60 | 17.6 |
25477 | 2026-11-11 20:29:16 | MASTER-SAAO | (02h 47m 56.22s , +44d 22m 23.8s) | C | 60 | 17.2 |
25571 | 2026-11-11 20:30:50 | MASTER-SAAO | (02h 50m 17.70s , +44d 04m 58.3s) | C | 60 | 17.7 |
25571 | 2026-11-11 20:30:50 | MASTER-SAAO | (02h 47m 56.63s , +44d 21m 02.2s) | C | 60 | 17.1 |
25665 | 2026-11-11 20:32:24 | MASTER-SAAO | (02h 50m 20.39s , +44d 06m 06.3s) | C | 60 | 17.6 |
25665 | 2026-11-11 20:32:24 | MASTER-SAAO | (02h 47m 59.41s , +44d 22m 10.9s) | C | 60 | 17.1 |
25758 | 2026-11-11 20:33:57 | MASTER-SAAO | (02h 50m 15.64s , +44d 05m 36.6s) | C | 60 | 17.8 |
25758 | 2026-11-11 20:33:57 | MASTER-SAAO | (02h 47m 54.73s , +44d 21m 42.2s) | C | 60 | 17.2 |
25850 | 2026-11-11 20:35:30 | MASTER-SAAO | (02h 50m 15.34s , +44d 06m 39.1s) | C | 60 | 17.7 |
25850 | 2026-11-11 20:35:30 | MASTER-SAAO | (02h 47m 54.41s , +44d 22m 45.1s) | C | 60 | 17.1 |
25944 | 2026-11-11 20:37:04 | MASTER-SAAO | (02h 50m 20.97s , +44d 05m 41.0s) | C | 60 | 17.7 |
25944 | 2026-11-11 20:37:04 | MASTER-SAAO | (02h 48m 00.22s , +44d 21m 47.7s) | C | 60 | 17.1 |
26037 | 2026-11-11 20:38:37 | MASTER-SAAO | (02h 50m 15.43s , +44d 04m 42.8s) | C | 60 | 17.7 |
26037 | 2026-11-11 20:38:37 | MASTER-SAAO | (02h 47m 54.78s , +44d 20m 49.9s) | C | 60 | 17.0 |
26130 | 2026-11-11 20:40:10 | MASTER-SAAO | (02h 50m 22.09s , +44d 04m 57.4s) | C | 60 | 17.8 |
26130 | 2026-11-11 20:40:10 | MASTER-SAAO | (02h 48m 01.41s , +44d 21m 05.0s) | C | 60 | 17.0 |
26224 | 2026-11-11 20:41:43 | MASTER-SAAO | (02h 50m 19.54s , +44d 06m 25.2s) | C | 60 | 17.7 |
26224 | 2026-11-11 20:41:43 | MASTER-SAAO | (02h 47m 58.82s , +44d 22m 33.1s) | C | 60 | 17.1 |
26316 | 2026-11-11 20:43:16 | MASTER-SAAO | (02h 50m 19.87s , +44d 05m 17.1s) | C | 60 | 17.7 |
26316 | 2026-11-11 20:43:16 | MASTER-SAAO | (02h 47m 59.19s , +44d 21m 25.6s) | C | 60 | 16.9 |
26410 | 2026-11-11 20:44:49 | MASTER-SAAO | (02h 50m 23.15s , +44d 06m 29.1s) | C | 60 | 17.7 |
26410 | 2026-11-11 20:44:49 | MASTER-SAAO | (02h 48m 02.51s , +44d 22m 37.8s) | C | 60 | 17.0 |
26503 | 2026-11-11 20:46:23 | MASTER-SAAO | (02h 50m 16.81s , +44d 05m 52.1s) | C | 60 | 17.7 |
26503 | 2026-11-11 20:46:23 | MASTER-SAAO | (02h 47m 56.21s , +44d 22m 01.3s) | C | 60 | 16.9 |
26596 | 2026-11-11 20:47:56 | MASTER-SAAO | (02h 50m 17.38s , +44d 06m 54.2s) | C | 60 | 17.7 |
26596 | 2026-11-11 20:47:56 | MASTER-SAAO | (02h 47m 56.82s , +44d 23m 03.8s) | C | 60 | 16.9 |
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 46227
Junjie-Jin (NAOC), Qi-Zhao (NAOC), Dong-Xu (NAOC), Yue-Sun (NAOC), Haiyang-Mu (NAOC), Yu-Zhang (NAOC), Pengliang-Du (NAOC), Zhou-Fan (NAOC), Hong-Wu (NAOC) report on behalf of a large collaboration:
The Wide-field X-ray Telescope on Einstein Probe detected the X-ray transient EP261111a (Huang et al., GCN 46226).
We performed optical observations of the field of EP261111a at Xinglong Observatory. Our measurements are summarized below.
Inspection of the stacked science images and the archival-image comparison revealed no candidate optical counterpart within the EP/WXT localization region (3 arcmin radius). The representative 5-sigma point-source limiting magnitudes are listed below.
Time offsets are measured from the EP/WXT trigger at 2026-11-11T13:25:10Z (GCN 46226).
Mid-time (UTC) | Hours after trigger | Exposure (s) | Filter | 5-sigma limiting magnitude | System | Telescope 2026-11-11T13:48:38.264 | 0.391 | 6 x 300 | g | > 20.955 | PS1-AB-calibrated | Tsinghua-NAOC 0.8-m telescope (TNT)
The tabulated times are exposure-weighted mid-times in UTC. The representative depths were estimated from the background noise in the observed stacked images.
Photometry was calibrated using field stars from the BEST catalog (Xiao et al. 2026) on the PS1 photometric system.
References: GCN 46226 · EP261111a: Einstein Probe detection of an X-ray transient — https://gcn.nasa.gov/circulars/46226
GCN Circular 46226
G. L. Huang, Z. X. Li (IHEP, CAS), Y. J. Zhang (THU), W. D. Zhang (NAO, CAS) 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 EP261111a. The transient triggered EP-WXT (ID: 01709322401) at 2026-11-11T13:25:10 (UTC). The WXT position of the source is R.A. = 43.118 deg, DEC = 44.444 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. = 43.1202 deg, DEC = 44.4365 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).