EP251202a
GCN Circular 42967
Subject
EP251202a / GRB251202A: AstroSat CZTI detection
Date
2025-12-03T10:02:30Z (2 hours ago)
From
Anuraag Arya at IIT Bombay <aryaanuraag910@gmail.com>
Via
Web form
A. Arya (IITB), A. Goyal (IITB), U. Pathak (IITB), M. Tembhurnikar (IUCAA), S. Salunke (IUCAA), Harsha K. H. (IUCAA), G. Waratkar (Caltech/IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration:
Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of GRB 251202A which was also detected by Fermi/GBM (Fermi GBM Team, GCN Circ. 42933) and is associated with EP251202a detected by Einstein Probe (Zhang et. al., GCN Circ. 42937).
The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2025-12-02 01:51:01.50 UTC. The measured peak count rate associated with the burst is 118 (+37, -21) counts/s above the background in the combined data of all quadrants, with a total of 689 (+148, -156) counts. The local mean background count rate was 341 (+4, -5) counts/s. Using cumulative rates, we measure a T90 of 9.4 (+0.5, -1.3) s.
The source was also faintly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range.
CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project.
CZTI GRB detections are reported regularly on the payload site at:
http://astrosat.iucaa.in/czti/?q=grb
GCN Circular 42964
Subject
EP251202a/GRB 251202A: KAIT optical observations
Date
2025-12-02T20:38:22Z (15 hours ago)
From
Weikang Zheng at UC Berkeley <weikang@berkeley.edu>
Via
email
WeiKang Zheng (UCB), Xuhui Han (NAOC), Pinpin Zhang (NAOC) and
Alexei V. Filippenko (UCB) report on behalf of the KAIT GRB team:
The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at
Lick Observatory, observed the field of EP251202a/GRB 251202A
(Zhang et al., GCN 42937; Liang et al., GCN 42946; Fermi GBM team,
GCN 42933; Bala et al., GCN 42957) from 6.29 to 10.59 hours
after the burst. A set of 60s clear (roughly R) filter images
were obtained. We clearly detected the optical afterglow (Li
et al., GCN 42934; Zhu et al., GCN 42939; O’Neill et al., GCN
42947; Quirola-Vasquez et al., GCN 42948; Kuin et al., GCN 42956)
in our coadd images. We measure its brightness decayed from
18.7 +/- 0.1 mag (Vega; mid time 6.30 hours) to 19.3 +/- 0.2 mag
(mid time of 10.55 hours) with a power-law decay index of 1.07.
GCN Circular 42948
Subject
EP251202a / GRB 251202A: LCO r- and i-band optical detection
Date
2025-12-02T14:00:22Z (a day ago)
From
Jonathan Quirola at Radboud University <jaquirola1990@gmail.com>
Via
Web form
J. Quirola-Vasquez (Radboud), J. Sanchez-Sierras (Radboud), D. B. Malesani (DAWN/NBI and Radboud), G. Corcoran (UCD), A. Martin-Carrillo (UCD), P. G. Jonker (Radboud), A. J. Levan (Radboud and Warwick), J. A. Chacón (PUC), F. E. Bauer (SSI and UTA), J. N. D. van Dalen (Radboud), A. P. C. van Hoof (Radboud) report on behalf of a larger collaboration:
We observed the optical counterpart (Li et al., GCN 42934) of EP251202a (Zhang et al., GCN 42937, Liang et al., GCN 42946) and Fermi GRB 251202A (Fermi GBM team, GCN 42933) with a spectroscopic redshift of z = 2.785 (Zhu et al., GCN 42939) using the Las Cumbres Observatory (LCO) network at the McDonald Observatory, equipped with the SINISTRO camera. Observations were obtained in the r (6x200 s) and i (6x200 s) bands, starting on 2025-12-02 at 09:00:43 UTC (i.e., a mid-time observation of 7.35 and 7.75 hr after the EP/WXT trigger, respectively).
Calibrated to nearby stars from the Pan-STARRS catalog, we measure AB magnitudes r = 19.22 +/- 0.06 and i = 19.12 +/- 0.06, not corrected for Galactic extinction.
GCN Circular 42946
Subject
EP251202a/GRB 251202A: refined analysis of the EP-WXT observations
Date
2025-12-02T12:20:05Z (a day ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
R. D. Liang (NAOC) Z. M. Wang (BNU), Y. Wu (NJU), Y. J. Zhang (THU), H. N. Yang, H. Sun (NAOC) on behalf of the Einstein Probe (EP) team:
The fast X-ray transient EP251202a triggered the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Zhang et al., GCN 42937), and was followed by several telescopes (Li et al., GCN 42934, Lipunov et al., GCN 42938 and Zhu et al., GCN 42939, Sbarufatti et al. GCN 42943). The refined analysis of the WXT data shows that the event started at T0=2025-12-02T01:48:23.9 (UTC) and lasted for ~400 s. Three peaks are detected in the lightcurve, whose spectra are characterized by photon indice of 2.33 (-0.90/+1.02), 1.12 (-0.48/+0.60) and 1.19 (-0.51/+1.1), respectively. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 6.48 x 10^20 cm^-2 and a photon index of 1.23 (-0.19/+0.19). The derived average unabsorbed 0.5-4 keV flux is 5.40 (-0.63/+0.70) x 10^(-10) erg/s/cm^2.
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 42939
Subject
EP251202a / GRB 251202A: NOT spectroscopic redshift z = 2.785
Date
2025-12-02T06:18:17Z (a day ago)
From
Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani@nbi.ku.dk>
Via
Web form
Z.P. Zhu (NAOC), D. B. Malesani (DAWN/NBI and Radboud), L. Izzo (INAF/OACN and DARK/NBI), A. de Ugarte Postigo (LAM), D. Xu, X. Liu, S.Q. Jiang, J. An, L.B. He (NAOC), A. Saccardi (CEA/Irfu), R. H. Rasmussen (NOT and Aarhus) report on behalf of a large collaboration:
We observed the optical counterpart (Li et al., GCN 42934) of EP251202a (Zhang et al., GCN 42937), which is likely the same event of Fermi GRB 251202A (Fermi GBM team, GCN 42933), using the Nordic Optical Telescope (NOT), equipped with the ALFOSC camera and spectrograph.
We obtained 10x120 s and 9x120 s exposures in the r and z bands, respectively, starting on 2025 Dec 2 at 02:51:32 UT. The afterglow is clearly detected in single images, with an AB magnitude of r = 17.27 +/- 0.01 at a mid time of 1.05 hr after the trigger.
A sequence of 3 spectra by 1200 s each was then acquired using grism #4, covering the wavelength range 3500-9500 AA. Our first spectrum started on 2025 Dec 2.156 UT (1.93 hr after the EP/WXT trigger). Continuum is detected across the whole wavelength range. A spectral break is detected around 4610 AA, and the onset of the forest is seen blueward of this wavelength. We match existing features to a low-column density Lyman alpha and C IV (unresolved) at z = 2.785, which we believe to be the redshift of the burst. Intervening systems are also seen in Lyman alpha and C IV at z = 2.450 and 2.356.
We acknowledge the use of the grbspec.eu tool to analyse this spectrum.
GCN Circular 42937
Subject
EP251202a/GRB 251202A: Einstein Probe detection of an X-ray transient
Date
2025-12-02T03:28:01Z (a day ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Y. J. Zhang (THU), R. D. Liang (NAOC) Z. M. Wang (BNU), Y. Wu (NJU), H. N. Yang, H. Sun (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 EP251202a. The transient triggered EP-WXT (ID: 01709249064) at 2025-12-02T01:49:15 (UTC). The WXT position of the source is R.A. = 122.121 deg, DEC = 40.600 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). The trigger time and the position of the transient is consistent with that of GRB 251202A detected by Fermi/GBM (GCN 42933).
We performed a follow-up observation with the Follow-up X-ray Telescope (FXT), starting at 2025-12-02T02:09:51 (UTC), about 20 minutes after the trigger. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 122.1190 deg, DEC = 40.6125 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). The position is 12 arcsec from the optical counterpart reported by Las Cumbres Observatory (Li et al., GCN 42934). 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).