- GCN Circular #42799
B.-T. Wang (YNAO), Y.-H. I. Yin (HKU), G. J. Yang (NAOC), H.-Z. Wu (HUST) and W. D. Zhang (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 EP251122a. The transient triggered EP-WXT (ID: 01709248658) at 2025-11-22T13:53:51 (UTC). The WXT position of the source is R.A. = 38.017 deg, DEC = 14.132 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. = 38.0199 deg, DEC = 14.1277 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).
- GCN Circular #42800
Z.-Y. Lin, C. Lachaud (APC), S. Schanne, D. Turpin (CEA/Irfu), T. Maiolino (LUPM), D. Götz (CEA/Irfu), D. B. Malesani (DAWN/NBI and Radboud) report on behalf of the SVOM team:
At 2025-11-22T13:57:08 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 251122A (SVOM burst-id sb25112204), also triggered by EP/WXT as EP251122a (Wang et al., GCN 42799).
The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network.
The burst was only detected by the Image Trigger (IMT), which produced a sequence of 6 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 10.68 in the [5-20] keV energy band over a time window of 327.68 seconds starting at 2025-11-22T13:52:01.
The localization of the best alert is R.A., Dec. 38.1450, 14.0645 degrees (J2000) with a 90% confidence level (C.L.) radius of 7.48 arcmin (including systematic error of 2 arcmin added in quadrature).
SVOM slewed to the burst.
SVOM/MXT began observing the field at 2025-11-22T14:00:05 UTC, 177 seconds after T0. Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec. 38.026, +14.124 degrees:
R.A. (J2000) = 02h32m06s
Dec. (J2000) = +14d07m26s
with a 90% C.L. radius of 75 arcseconds.
This location is 7.8 arcminutes from the ECLAIRs onboard position. This position may be improved as more data is received.
VT began observing the field after the slew. The analysis of the data will be published in a future circular.
The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE.
The Burst Advocate (BA) on shift for this alert is Zheyu Lin: zheyu.lin@apc.in2p3.fr.
Please contact the BA by email if you require additional information.
- GCN Circular #42801
Chao WU (NAOC), Zhe Kang (CHO), Liping Xin(NAOC), Xuhui Han(NAOC), Pinpin Zhang (NAOC), Xiaomeng Lu (NAOC), Zhenwei Li (CHO), You Lv (CHO), Ruosong Zhang (NAOC), Yujie Xiao(NAOC), Yulei Qiu(NAOC), Jing Wang (NAOC), Jinsong Deng(NAOC), Lei Huang(NAOC), Jianyan Wei (NAOC), Z.-Y. Lin, C. Lachaud (APC) report on behalf of the SVOM/C-GFT team:
We observed the field of GRB 251122A detected by EP/WXT(Wang et al., GCN 42799, ID:01709248658) and SVOM/ECLAIRs (Lin et al., GCN 42800, SVOM burst-id sb25112204) with LATIOS on SVOM/C-GFT. Observations started at 2025-11-22T13:59:06 UTC, ~118 seconds after the trigger.
A series of g, r, and i band images were obtained.
No credible candidate was detected within the error box provided by EP/FXT (Wang et al., GCN 42799) and SVOM/MXT (Lin et al., GCN 42800 ) in our images after preliminary processing, the three sigma upper limit is:
| Date-Obs (mid-time) | Mid_t - T0 (s) | Exposure Time (s) | Band | Upper Limit (AB) |
|---------------------|----------------|-------------------|------|------------------|
| 2025-11-22T13:59:45 | 157 | 6×10 | i | 20.05 |
The photometry was calibrated against nearby UCAC4 catalogue and no correction for Galactic dust extinction was applied.
We thank the observation assistants Bowen Li and Hongyan Xue 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 #42802
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-Kislovodsk robotic telescope [1] located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) was pointed to the EP251122a ( EP Team et al., GCN 42799) errorbox 3880 sec after notice time and 5537 sec after trigger time at 2025-11-22 15:26:08 UT, with upper limit up to 19.3 mag. The observations began at zenith distance = 60 deg. The sun altitude is -18.9 deg.
The galactic latitude b = -42 deg., longitude l = 157 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=3049413
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
5627 | 2025-11-22 15:26:08 | MASTER-Kislovodsk | (02h 30m 23.79s , +14d 20m 55.2s) | C | 180 | 16.9 |
5628 | 2025-11-22 15:26:08 | MASTER-Kislovodsk | (02h 30m 33.71s , +13d 58m 00.6s) | C | 180 | 17.8 |
7537 | 2025-11-22 15:57:58 | MASTER-Kislovodsk | (02h 30m 49.90s , +14d 17m 52.7s) | C | 180 | 18.7 |
7539 | 2025-11-22 15:58:00 | MASTER-Kislovodsk | (02h 31m 02.20s , +13d 55m 05.3s) | C | 180 | 19.3 |
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 #42803
Y.-C. Cheng (NCU), J.Y.B Choo (UKM), A.N. Garcia (PUP), A.L.A.M. Nasir (UniSZA), J.-L. Yang (NCU) on behalf of the 47th International School for Young Astronomers (ISYA) in Taipei, A. Aryan, T.-W. Chen, Y.-H. Lee, C.-S. Lin (all NCU), S. Yang (HNAS), A. K. H. Kong (NTHU), J. Gillanders, S. J. Smartt (both Oxford), Y. J. Yang (NYUAD), A. Sankar.K, Y.-C. Pan, C.-C. Ngeow, M.-H. Lee, C.-H. Lai, W.-J. Hou, H.-C. Lin, H.-Y. Hsiao, J.-K. Guo (all NCU), 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 EP251122a (Wang et al., GCN 42799) using the 1m LOT at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al., 2025, ApJ, 983, 86, doi:10.3847/1538-4357/adb428). A follow-up observation by SVOM found a temporally and spatially coincident long GRB 251122A (Lin et al. GCN 42800). The first LOT epoch of observations began at 14:13 UTC on the 22nd of November 2025 (MJD 61001.592), 0.31 hr after the EP-WXT trigger.
We used the Kinder pipeline (Yang et al. A&A 646, A22) to stack the images and perform template subtraction with the DESI Legacy Survey (Dey et al. 2019, AJ 157, 168) DR10 image. In the difference image, we find a faint, uncataloged optical counterpart candidate at RA, DEC = 02:32:05.1284, +14:07:43.826; lying within the 20" EP-FXT localization circle. The counterpart candidate is likely associated with the DESI Legacy Survey (DR10) galaxy at RA, Dec = 38.0213, 14.1289, with r = 24.64 mag and a photometric redshift of 1.113 ± 0.368.
We perform PSF photometry on the position of the source with the stacked frames. The details of the observations and measured PSF magnitude (in the AB system) of the proposed counterpart of EP251122a are as follows:
Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass
LOT | r | 61001.592 | 0.31 | 300 * 6 | 23.1 +/- 0.2 | 0".93 | 1.01
We caution that the optical counterpart candidate is detected at a level close to the detection limit (>23.2 mag). Our observation is consistent with Wu et al. (GCN 42801) and deeper than their limits.
The presented magnitude is calibrated using the field stars from the Pan-STARRS1 DR2 and is not corrected for the expected Galactic foreground extinction of A_r = 0.35 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 can be found in Aryan et al. 2025, ApJS, 281, 20, doi:10.3847/1538-4365/adfc69.
- GCN Circular #42804
A. Saccardi (CEA/Irfu), D. B. Malesani (DAWN/NBI and Radboud), L. P. Xin (NAOC), D. Turpin, J. T. Palmerio (CEA/Irfu), C. Wu (NAOC), B. Cordier (CEA/Irfu), Z.-Y. Lin, C. Lachaud (APC),
report on behalf of the SVOM mission team:
We observed the field of GRB 251122A / EP251122a detected by SVOM/ECLAIRs (Lin et al. GCN 42800) and EP/WXT (Wang et al., GCN 42799) with the LCO 1m telescope at the Siding Spring Observatory equipped with the Sinistro instrument.
Our observation started at 2025-11-22T14:56:27 (UTC) about 1 hour after the trigger. We obtained 3x200 s exposures in each of the SDSS r and Pan-STARRS z filters. The r-band images are unfortunately trailed, which reduces our sensitivity. In the stacked images, we do not detect any new optical source within the EP/FXT and SVOM/MXT error circles.
We measure the following 3-sigma upper limits calibrated against the Pan-STARRS catalog, and not corrected for Galactic extinction:
r > 20.8 AB (mid time 80 min after the SVOM T0);
z > 20.4 AB (mid time 63 min after the SVOM T0).
Our results are consistent with the limits reported by Wu et al. (GCN 42801). We do not detect the candidate counterpart reported by Cheng et al. (GCN 42803), which is fainter and reported at an earlier epoch than our observations.
This project is funded by the SVOM collaboration.
- GCN Circular #42805
L. Cotter, G. Corcoran (UCD), J. A. Chacon (PUC), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), P. G. Jonker (Radboud), report on behalf of a larger collaboration:
We observed the field of the transient event GRB 251122A / EP251122a detected by EP/WXT (Wang et al., GCN 42799) and by SVOM/ECLAIR (Lin et al., GCN 42800) with the Las Cumbres Observatory (LCO) network. We acquired six 300 s exposures in the r band starting on 2025-11-22 at 15:20:01 UTC (86 min after the EP/EXTtrigger).
No new source is detected within the error circle provided by EP/FXT (Wang et al., GCN 42799) and SVOM/MXT (Lin et al., GCN 42800). From the stacked r-band images we obtained a three sigma upper limit of r > 22.4 mag (AB), calibrated against the Pan-STARRS catalog and is not corrected for Galactic extinction.
We do not detect the candidate counterpart reported by Cheng et al. (GCN 42803), which was however fainter than our limit and observed at an earlier epoch. Our non-detection is also consistent with previous reports (Wu et al., GCN 42801; Lipunov et al., GCN 42802; Saccardi et al., GCN 42804).
- GCN Circular #42806
H.L. Li, C. Wu (NAOC), J. T. Palmerio (CEA), L.P. Xin, Y. L. Qiu (NAOC), Z.-Y. Lin, C. Lachaud (APC) report on behalf of the SVOM team.
SVOM/VT performed an automatic slew on the burst of GRB 251122A/EP251122a (sb25112204) triggered by SVOM/ECLAIRs (Lin et al., GCN 42800) and EP/WXT(Wang et al., GCN 42799). SVOM/VT began observing the field automatically at 2025-11-22T14:02:17 UTC, ~5.15 minutes after the T0 (SVOM trigger time:2025-11-22T13:57:08), with the slew of the platform triggered on-board, in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
We confirm the detection of the source reported by Cheng et al. (GCN 42803) in the VT_R band of sequence 1 and 3 with the downlinked VHF data.
The AB magnitude was derived as follows:
--------------------------------------------
(T-T0)mid exptime band mag
7.65 min 300 sec VT_R 21.82 +/-0.12
88.30 min 300 sec VT_R 21.96 +/-0.15
No correction for Galactic extinction was applied to the photometry.
This result is consistent with the report by Wu et al.(GCN 42801), Lipunov et al.(GCN 42802), Saccardi
et al.(GCN 42804), Cotter et al.(GCN 42805).
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 #42807
Tian-Rui Sun, Yan-Long Hua (PMO), Chao Wu (NAOC), Jin-Jun Geng, Xue-Feng Wu, Jun-Jie Wei,, Yi-Fang Liang, Ding-Fang Hu, Guan-Xiao Li, Yuan-Tai Yang, Xu Kong, Ji-An Jiang report on behalf of the WFST team:
Following the detection of GRB 251122A / EP251122a by SVOM/ECLAIRs (Lin et al., GCN 42800) and by the Einstein Probe (Wang et al., GCN 42799), we conducted follow-up observations with the Wide Field Survey Telescope (WFST Collaboration; arXiv:2306.07590) at the Lenghu Astronomical Observation Base in Qinghai Province, China.
WFST began i-band imaging at 2025-11-22T15:45:51 UTC, approximately 1.85 hours after the trigger.
The afterglow is clearly detected in the i band, with a preliminary magnitude derived from 10 × 150 s exposures:
i = 21.89 ± 0.12 (AB)
The photometric calibration was performed using nearby stars from the ATLAS-REFCAT2 catalog, in the AB magnitude system.
The reported magnitude is not corrected for Galactic extinction.
We thank the staff of WFST and the Lenghu observation station for supporting these observations.
- GCN Circular #42808
Y.-H. I. Yin (HKU), B.-T. Wang (YNAO), G. J. Yang (NAOC), H.-Z. Wu (HUST) and W. D. Zhang (NAOC) on behalf of the Einstein Probe (EP) team:
The fast X-ray transient EP251122a triggered the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Wang et al., GCN 42799) and SVOM/ECLAIRs as GRB 251122A (Lin et al, 42800), and followed by several optical telescopes (Wu et al., GCN 42801, Lipunov et al., GCN 412802, Cheng et al., GCN 42803, Saccardi et al., GCN 42804, Cotter et al., GCN 42805, Li et al., GCN 42806, Sun et al., GCN 42807). The refined analysis of the WXT data shows that the event started at T0=2025-11-22T13:53:43 (UTC) and lasted for 10 s with a single pulse, before the observation was interrupted by the autonomous follow-up observation. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 1.33 x 10^21 cm^-2 and a photon index of 1.26 (-0.58/+0.59). The derived average unabsorbed 0.5-4 keV flux is 2.07 (-0.67/+0.77) x 10^(-9) erg/s/cm^2.
The autonomous observation by the Follow-up X-ray Telescope (FXT) was performed at 2025-11-22T13:57:19 (UTC), about 4 minutes after T0. The exposure time of this observation is 6029 s. The on-ground analysis shows that an uncatalogued source was detected at R.A., Dec. = 38.0220, 14.1283 deg (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic). The light curve displays two pulses structure lasting for around 400 s. The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power law with a fixed Galactic equivalent hydrogen column density of 1.33 x 10^21 cm^-2 and a photon index of 1.74 (-0.05/+0.04). The derived average unabsorbed 0.5-10 keV flux is 7.66 (-0.30/+0.33) x 10^(-11) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.
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 #42809
B.-T. Wang (YNAO), Y.-H. I. Yin (HKU), G. J. Yang (NAOC), H.-Z. Wu (HUST) and W. D. Zhang (NAOC) on behalf of the Einstein Probe (EP) team:
EP-FXT performed a follow-up observation of the SVOM/ECLAIRs-detected burst GRB 251122A (SVOM/sb25112204, Lin et al., GCN 42800), also triggered by EP/WXT as EP251122a (Wang et al., GCN 42799) at 2025-11-22T17:08:09 (UTC), about 3.2 hours after the SVOM/ECLAIRs trigger, with an exposure time of 1719 s. One uncatalogued source is detected within the ECLAIRs error circle, and the source is spatially consistent with the counterpart reported in optical and X-ray bands, including detections (Cheng et al., GCN 42803; Li et al., GCN 42806; Sun et al., GCN 42807; Yin et al., GCN 42808) and several upper limits (Wu et al., GCN 42801; Lipunov et al., GCN 42802; Saccardi et al., GCN 42804; Cotter et al., GCN 42805). Preliminary analysis on this source are automatically conducted, and details are listed as follows.
Source 1: EPF_J023205.2+140740
RA (J2000): 38.0226
Dec (J2000): 14.1282
Flux: 5.27 x 10^-13 erg/s/cm2 (observed, 0.5-10 keV)
Flux_err: 1.04 x 10^-13 erg/s/cm2 (1 sigma)
The position uncertainty of the source is about 10 arcsec in radius (90% C.L. statistical and systematic).
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 #42811
Y. N. Ma, L. P. Xin, Y. L. Qiu, C. Wu, J. Wang, X. H. Han, P. P. Zhang, H. L. Li, Z. H. Yao, J. Zheng, J. Y. Wei (NAOC) report on behalf of SVOM follow-up team:
We observed the field of GRB 251122A triggered by SVOM/ECLAIRs (Lin et al., GCN 42800) and EP/WXT (Wang et al., GCN 42799; Yin et al., GCN 42808; Wang et al., GCN 42809) using the 2.16m telescope located at Xinglong observatory, China, equipped with the BFOSC camera. We obtained 7*200s frames in R-band, starting at 14:17:55 UT on 2025-11-22, about 20.8 minutes after the trigger.
The optical counterpart (Wu et al., GCN 42801; Lipunov et al., GCN 42802; Cheng et al., GCN 42803; Saccardi et al., GCN 42804; Cotter et al., GCN 42805; Li et al., GCN 42806; Sun et al., GCN 42807) was detected in the stacked image in R band. The magnitude is:
mid time (min) | exposure time (s) | band | mag | mag err
---------------|-------------------|------|--------|--------
32.9 | 7*200 | R | 22.7 | 0.1
The photometry calibration was performed with nearby USNO-B1.0 1040-0024912 as the reference star. Our photometry was not corrected for Galactic extinction.
We thank the staff at Xinglong observatory for their excellent support.
- GCN Circular #42813
Anshika Gupta, Debalina Kar, Pankaj Pawar, Divyanshu Janghel, Dhruv Jain, and Kuntal Misra (ARIES) report:
We observed the field of GRB251122A/ EP251122A detected by Einstein Probe (Wang et al. 2025, GCN 42799) and SVOM (Lin et al. 2025, GCN 42800) with the 1.3m Devasthal Fast Optical Telescope (DFOT), located at the Devasthal Observatory of the Aryabhatta Research Institute of Observational Sciences (ARIES), India. The observations were started on 2025-11-22 at 16:03:25 UT, i.e., ~ 2.15 hours after the EP trigger. We have taken multiple frames with an exposure time of 300s in the R filter. We stacked the images after the alignment. We detect a faint optical afterglow in our stacked image within the error box of EP/FXT (Wang et al. 2025, GCN 42799, 42809) and SVOM/ECLAIRs (Lin et al. 2025, GCN 42800). We obtain the following preliminary magnitude in the stacked image:
Date Start_UT T_start-T0 (hour) Filter Exp time (s) Magnitude
===============================================================
2025-11-22 16:03:25 ~2.15 R 300s*19 22.37 +/-0.04
The optical detection of the burst is consistent with WU et al. 2025 (GCN 42801); Lipunov et al. 2025 (GCN 42802); Cheng et al. 2025 (GCN 42803); Saccardi et al. 2025 (GCN 42804); Cotter et al. 2025 (GCN 42805); Li et al. 2025 (GCN 42806); Sun et al. 2025 (GCN 42807); Ma et al. 2025 (GCN 42811) .
The magnitude is not corrected for the Galactic extinction in the direction of the burst.
Photometric calibration is performed using the standard stars from the USNO-B1.0 catalogue.
- GCN Circular #42814
Malte Busmann (LMU), Xander J. Hall (CMU), Brendan O’Connor (CMU), Daniel Gruen (LMU), and Antonella Palmese (CMU) report:
We observed the FXT localization of GRB 251122A/EP251122a (Wang et al., GCN 42779; Lin et al., GCN 42800; Yin et al., GCN 42808; Wang et al., GCN 42809) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i, and J bands simultaneously for 40 x 180 s starting at 2025-11-23T00:06:12 UT (0.43 days after the trigger). We used r-band templates from the DESI Legacy Survey for difference imaging and did not detect the source identified by Cheng et al. (GCN 42803), Li et al. (GCN 42806), Sun et al. (GCN 42807), Ma et al. (GCN 42811), and Gupta et al. (GCN 42813) at a 3-sigma depth of
r > 24 AB mag.
The magnitude is calibrated against the PS1 catalog and not corrected for Galactic extinction.
We thank Christoph Ries from the Wendelstein Observatory for obtaining these observations.
- GCN Circular #42950
A. A. Volnova (IKI), V. V. Rumyantsev (CrAO), A. S. Pozanenko (IKI), N. S. Pankov (IKI) report on behalf of IKI GRB-FuN collaboration:
We observed the FXT localization of GRB 251122A/EP251122a (Wang et al., GCN 42779; Lin et al., GCN 42800; Yin et al., GCN 42808; Wang et al., GCN 42809) with the ZTSH telescope of CrAO starting on 2025-11-11 (UT) 21:37:17 UT and taking several 120s exposures in R-band. The optical counterpart (Cheng et al., GCN 42803; Li et al., GCN 42806; Sun et al., GCN 42807; Ma et al., GCN 42811; Gupta et al., GCN 42813; Busmann et al., GCN 42814) is detected in the stacked frame. Preliminary photometry is the following:
Date UT start t-T0 Exp. Filter OT Err. UL Site/Instrum
(mid,days) (n*s) (3sigma)
2025-11-22 21:37:17 0.34097 20*120 R 22.36 0.25 22.8 CrAO/ZTSh
The photometry is based on nearby stars from the USNO-B1 catalogue (R2 magnitudes) and is not corrected for the Galactic extinction.
- GCN Circular #43490
B. Schneider (LAM), A. Saccardi (CEA/Irfu), J. T. Palmerio (CEA/Irfu), S. D. Vergani (LUX-Paris Obs.), D. B. Malesani (DAWN/NBI and Radboud), M. Ferro (INAF/OAB), G. Corcoran (UCD), C. Lachaud (APC), Z.-Y. Lin (APC), report on behalf of the Stargate collaboration:
At the position of the optical counterpart (Cheng et al., GCN 42803; Li et al., GCN 42806; Sun et al., GCN 42807; Ma et al., GCN 42811; Gupta et al., GCN 42813; Busman et al., GCN 42814; Volnova et al., GCN 42950) of the high-energy transient GRB 251122A / EP251122a (Wang et al., GCN 42799; Lin et al., GCN 42800), a galaxy is visible in the Legacy survey, with magnitude r ~ 24.6, which is also detected in archival images from the Hyper Suprime-Cam Legacy Archive (Tanaka et al. 2021, doi:10.1093/pasj/psab034)
A spectrum of this object was secured using the ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph. The spectrum covers the wavelength range 3000-25000 AA, and consists of 4 exposures of 1200 s each. The observation mid time is 2025 Dec 23.08 UT (30.5 days after the GRB).
A single, very clear emission line is detected at 18140 Å. We discuss its interpretation below.
- At the X-shooter resolution we would expect to resolve it if it was the [O II] 3727/3729 doublet (at z = 3.87). While the line is indeed resolved in wavelength space, it does not show a doublet profile; there is also no hint of Lyalpha nor [O III] 5008 in emission at this redshift.
- The line cannot be [O III] 5008 (at z = 2.62), otherwise we would also detect [O III] 4959, which is expected from first principles to be ~1/3 as intense, and is excluded by our data. We also do not detect Halpha in the K band, a region clean of atmospheric absorption.
- The line is however consistent with Halpha at z = 1.765; at this redshift, both Hbeta and [O III] fall at observed wavelengths with poor atmospheric transmission, and their non-detection is thus not unexpected. The [O II] doublet is not detected at this redshift, although it falls in a noisy region of the spectrum (at the interface between the X-shooter VIS and NIR arms). Dust extinction could also contribute to the faintness of this line.
We conclude that z = 1.765 is most likely the redshift of GRB 251122A / EP251122a.
We acknowledge excellent support from the observing staff at Paranal, in particular Claudia Cid, Florian Rodler, Jonathan Smoker and Thomas Rivinius. The analysis of this spectrum was carried out with the help of the zHunter tool (https://doi.org/10.5281/zenodo.15189495).
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