GRB 250907A
GCN Circular 41762
Subject
GRB 250907A: CALET Gamma-Ray Burst Monitor detection
Date
2025-09-09T07:19:26Z (a month ago)
From
Yuta Kawakubo at Aoyama Gakuin University <kawakubo@phys.aoyama.ac.jp>
Via
Web form
M. L. Cherry (LSU), A. Yoshida, T. Sakamoto, S. Sugita,
Y. Kawakubo (AGU), K. Yamaoka (Nagoya U), S. Nakahira (JAXA),
Y. Asaoka (ICRR), S. Torii, Y. Akaike, K. Kobayashi (Waseda U),
Y. Shimizu, T. Tamura (Kanagawa U), N. Cannady (GSFC/UMBC),
S. Ricciarini (U of Florence), P. S. Marrocchesi (U of Siena),
and the CALET collaboration:
The long GRB 250907A (GECAM-B detection: Wang et al., GCN Circ. 41749)
triggered the CALET Gamma-ray Burst Monitor (CGBM) at 22:00:54.59 UTC on 7 September 2025
(https://cgbm.calet.jp/cgbm_trigger/flight/1441317257/index.html).
The burst signal was seen by all CGBM detectors. Because of a problem with the ground
alert processing script, the GCN notice was not distributed automatically for this event.
The burst light curve shows a single pulse that starts
at T-0.9 sec, peaks at T+0.4 sec, and ends at T+5.9 sec.
The T90 and T50 durations measured by the SGM data are 6.0 +/- 0.6 sec
and 3.0 +/- 0.2 sec (40-1000 keV), respectively.
The ground-processed light curve is available at
https://cgbm.calet.jp/cgbm_trigger/ground/1441317257/
The CALET data used in this analysis are provided by
the Waseda CALET Operation Center located at Waseda University.
GCN Circular 41749
Subject
GRB 250907A: GECAM-B detection
Date
2025-09-08T15:18:41Z (a month ago)
From
Chenwei Wang at IHEP <cwwang@ihep.ac.cn>
Via
Web form
Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team:
GECAM-B was triggered in-flight by a bright long burst GRB 250907A at 2025-09-07T22:00:52.850 UTC (denoted as T0), which is also detected by Konus-Wind. According to the GECAM-B light curves in about 40-6000 keV, this burst mainly consists of multiple pulses with a duration (T90) of 36.5 +0.5/-3.0 s.
The GECAM-B light curve can be found here:
https://www.bursthub.cn//admin/static/gecambgrb250907A.png
GECAM-B localized this burst to the following position (J2000):
Ra: 337.2 deg
Dec: -9.0 deg
Err: 1.3 deg (1-sigma, statistical only)
The time-averaged spectrum from T0-5 s to T0+40 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.08 +0.14/-0.12 and the cutoff energy, parameterized as Epeak, is 535 +192/-129 keV. The event fluence (10-1000 keV) in this time interval is (7.57 +0.51/-0.61)E-05 erg/cm^2. The 'Amati' relation diagram of GRB 250907A is shown at:
https://www.bursthub.cn//admin/static/gecambgrb250907A_amati.png
Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS).