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[vsnet-grb-info 40885] EP251124a: Einstein Probe detection of an X-ray transient
by GCN Circulars 24 Nov '25

24 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42816 SUBJECT: EP251124a: Einstein Probe detection of an X-ray transient DATE: 25/11/24 13:17:56 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> H.Zhou (PMO, CAS), J. -Y. Cao (IHEP), H.-N. Yang, and Z.-X. Ling (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 EP251124a. The transient triggered EP-WXT (ID: 01709248862) at 2025-11-24T11:10:05 (UTC). The WXT position of the source is R.A. = 43.732 deg, DEC = 41.577 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. According to the FXT onboard alert, which provided coordinates calculated autonomously on board the satellite, FXTA detected an X-ray source and FXTB detected two X-ray sources (denoted as FXTB-1 and FXTB-2) within the WXT error circle. Their coordinates (J2000) are: FXTA: R.A. = 43.7117 deg, DEC = 41.5715 deg FXTB-1: R.A. = 43.7188 deg, DEC = 41.5692 deg FXTB-2: R.A. = 43.7061 deg, DEC = 41.6121 deg All FXT localizations are reported with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). FXTB-1 is consistent with the source detected by FXTA. 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). View this GCN Circular online at https://gcn.nasa.gov/circulars/42816. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40884] GRB 251116C: Swift-XRT confirmation of fading
by GCN Circulars 24 Nov '25

24 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42815 SUBJECT: GRB 251116C: Swift-XRT confirmation of fading DATE: 25/11/24 10:30:46 GMT FROM: Matteo Ferro at INAF-OAB <matteo.ferro(a)inaf.it> M. Ferro, M. G. Bernardini, B. Sbarufatti, C. Salvaggio, R. Brivio, A. Mei (INAF-OAB) report on behalf of the Swift-XRT team: Swift-XRT has conducted further observations of the field of the SVOM/ECLAIRs-detected burst GRB 251116C (Pillas et al., GCN 42703). The observations now extend from T0+10 ks to T0+452 ks and have a total exposure time of 6.1 ks. The previously-reported "Source 1" (Evans et al., GCN 42721), is now found to be fading with ~3-sigma significance, and is therefore likely the GRB afterglow. The results of the XRT-team automatic analysis of the source are available at https://www.swift.ac.uk/SVOM/team/SVOM_FIELD00051/Source1.php. The results of the full analysis of the XRT observations are available at https://www.swift.ac.uk/SVOM/SVOM_FIELD00051/. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42815. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40883] GRB 251122A/EP251122a: FTW optical and NIR observations
by GCN Circulars 23 Nov '25

23 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42814 SUBJECT: GRB 251122A/EP251122a: FTW optical and NIR observations DATE: 25/11/23 22:37:25 GMT FROM: Malte Busmann at Ludwig-Maximilians-Universität München <m.busmann(a)physik.lmu.de> 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/42814. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40882] GRB 251122A/EP251122A: 1.3m DFOT optical detection
by GCN Circulars 23 Nov '25

23 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42813 SUBJECT: GRB 251122A/EP251122A: 1.3m DFOT optical detection DATE: 25/11/23 20:02:06 GMT FROM: ANSHIKA GUPTA at ARIES <anshika05180(a)gmail.com> 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/42813. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40881] The EP-WXT trigger 01709248783 is likely a flaring star
by GCN Circulars 23 Nov '25

23 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42812 SUBJECT: The EP-WXT trigger 01709248783 is likely a flaring star DATE: 25/11/23 09:51:43 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> C.-L. Guo (NAO, CAS), J. Yang (ZZU), W.-F. Wen (SZTU), and Z.-X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709248783 at the time of 2025-11-23T09:00:39, is likely a stellar flare associated with a Double or Multiple Star BPS CS 31060-0015. The estimated flux of the flare is around 1e-10 erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 3.8e30 erg/s. 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). View this GCN Circular online at https://gcn.nasa.gov/circulars/42812. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40880] GRB 251122A / EP251122a: Xinglong 2.16m optical observation
by GCN Circulars 23 Nov '25

23 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42811 SUBJECT: GRB 251122A / EP251122a: Xinglong 2.16m optical observation DATE: 25/11/23 08:45:24 GMT FROM: Yinuo Ma <mayn(a)bao.ac.cn> 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/42811. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40879] EP251118A: 3.6m DOT optical afterglow detection
by GCN Circulars 23 Nov '25

23 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42810 SUBJECT: EP251118A: 3.6m DOT optical afterglow detection DATE: 25/11/23 04:45:13 GMT FROM: ANSHIKA GUPTA at ARIES <anshika05180(a)gmail.com> Anshika Gupta, Pankaj Pawar, Dhruv Jain, Debolina Kar, and Kuntal Misra (ARIES) report: We observed the field of EP251118A detected by Einstein Probe( Jiang et al. 2025, GCN 42749) with the 3.6m Devasthal Optical Telescope (DOT), located at the Devasthal Observatory of the Aryabhatta Research Institute of Observational Sciences (ARIES), India. The observations were started on 2025-11-22 at 04:57:21.74 UT, i.e., ~84.24 hours after the Einstein Probe trigger. We have taken multiple frames with an exposure time of 120 s in the r filter. We stacked the images after the alignment. We detect the optical counterpart in our stacked image within the error box of NOT (Malesani et al. 2025, GCN 42751). 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 04:57:21.74 ~ 84.24 r 120s*9 22.33 +/- 0.18 Our detection is consistent with Malesani et al. 2025 (GCN 42751); Belkin et al. 2025 (GCN 42758); Yadav et al. 2025 (GCN 42760); Busmann et al. 2025 (GCN 42763); Francile et al. 2025 (GCN 42767); Rodríguez et al. 2025 (GCN 42773); Li et al. 2025 (GCN 42776); Lee et al. 2025 (GCN 42780); Moskvitin et al. 2025 (GCN 42785); Gupta et al. 2025 (GCN 42787); Liu et al. 2025 (GCN 42793); Aryan et al. 2025 (GCN 42798). 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 Gaia catalog. View this GCN Circular online at https://gcn.nasa.gov/circulars/42810. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40878] GRB 251122A / EP251122a: EP-FXT counterpart detection
by GCN Circulars 23 Nov '25

23 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42809 SUBJECT: GRB 251122A / EP251122a: EP-FXT counterpart detection DATE: 25/11/23 03:57:25 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> 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). View this GCN Circular online at https://gcn.nasa.gov/circulars/42809. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40877] EP251122a: refined analysis of the EP-WXT and EP-FXT observations
by GCN Circulars 23 Nov '25

23 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42808 SUBJECT: EP251122a: refined analysis of the EP-WXT and EP-FXT observations DATE: 25/11/23 03:13:31 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> 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). View this GCN Circular online at https://gcn.nasa.gov/circulars/42808. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40876] LIGO/Virgo/KAGRA S251105aj: SVOM/ECLAIRs detection of a high-energy transient SVOM J2320.0-2901 through targeted search
by GCN Circulars 22 Nov '25

22 Nov '25

TITLE: GCN CIRCULAR NUMBER: 42797 SUBJECT: LIGO/Virgo/KAGRA S251105aj: SVOM/ECLAIRs detection of a high-energy transient SVOM J2320.0-2901 through targeted search DATE: 25/11/22 10:00:14 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> H. Yang, O. Godet, J.-L. Atteia, M. Brunet, S. Guillot (IRAP), M. Pillas (IAP), L. P. Xin, Y. N. Ma (NAOC) Using the event-by-event data downloaded through the X-band ground stations, we report on the identification of a faint SVOM/ECLAIRs transient SVOM J2320.0-2901 detected at 2025-11-05T13:00:48.34 UTC (T0), 88.4 s after the compact binary merger candidate S251105aj (The LIGO-Virgo-Kagra Collaboration, GCN 42587). This transient was detected through an offline targeted search for possible counterparts of the GW event S251105aj. SVOM J2320.0-2901 was detected with a timescale of 82 s and below 60 keV, with a best signal-to-noise ratio of 6.1 starting at T0. The localization of SVOM J2320.0-2901 is RA, Dec = 349.998, -29.022 degrees: RA (J2000) = 23h20m00s Dec (J2000) = -29d01m19s with a 90% C.L. radius of 13.9 arcmin (including a systematic error of 6 arcmin added in quadrature). This position is about 2 degrees outside the 99% area contour of the Bilby.multiorder.fits skymap of S251105aj. At the time of the GW trigger, ECLAIRs was covering 88% of the skymap 99% area. The time-averaged spectrum from T0 to T0+82 s in the energy range of 5-60 keV is well fitted by a blackbody (BB) model, with a measured temperature of 7.8 (+1.5/-1.2) keV. With this model, the total 4-120 keV flux is (3.6+/-0.8)e-9 erg/cm^2/s. Assuming a distance of 2071 Mpc (z=0.374) for the source, this corresponds to a luminosity of 1.8e48 erg/s and a BB emission radius of 1.9e6 cm. A broken power-law model is also tested, providing a comparable fit, though with less well-constrained parameters of photon index 1 around -0.5, break energy of 22 (+21/-10) keV, and photon index 2 around 2.9. At this stage, the nature of SVOM J2320.0-2901 is unknown. We conducted SVOM/VT and EP/FXT follow-up observations on this field. The results will be published in dedicated circulars. All the quoted errors are at the 68% confidence level. 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. ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. The SVOM/ECLAIRs point of contact for this source is: Hui Yang (IRAP) (hui.yang(a)irap.omp.eu) View this GCN Circular online at https://gcn.nasa.gov/circulars/42797. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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