GRB 251201A

Yue Wang, Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team:

GECAM-B was triggered on-ground by GRB 251201A, at 2025-12-01T04:37:04.100 UTC (denoted as T0), which is also detected by MAXI/GSC (MAXI team, GCN #42913
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 ) and SVOM/GRM (Yue Wang et al., GCN #42932
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 ). 

According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of multiple pulses followed by a possible flare with a total T90 of 47.7 +/-15.6 s.

The GECAM-B light curve can be found here:
https://www.bursthub.cn//admin/static/gecambgrb251201A.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).

SVOM/GRM team: Yue Wang, Chen-Wei Wang, Wen-Jun Tan, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP)

SVOM/ECLAIRs team: Maria Grazia BERNARDINI (INAF-OAB, LUPM)

Report on behalf of the SVOM team:

SVOM/GRM was triggered in-flight by GRB 251201A (SVOM trigger reference: sb25120107) at 2025-12-01T04:37:04.500 (T0), which is also detected by MAXI/GSC (MAXI team, GCN #42913
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 ) and GECAM-B. 

With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a multi-pulses followed by a possible flare with a total T90 of 39.3 +5.1/-1.8 s in the 15-5000 keV band, the T90 of the main emission is 4.1 +0.4/-0.2 s.

The SVOM/GRM light curve can be found here:
https://www.bursthub.cn//admin/static/svgrb251201A.png

In addition, the position of this burst, as determined by MAXI/GSC (RA=309.032, DEC=30.413, GCN #42913
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 ), is located at about 59 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. 

With this localization, the time-averaged spectrum from T0-3 to T0+40 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.55 +0.15/-0.11 and the cutoff energy, parameterized as Epeak, is 352 +308/-144 keV. The event fluence (10-1000 keV) in this time interval is (5.32 +0.54/-0.58)E-06 erg/cm^2.  

The 1s peak spectrum, measured from T0-0.3 to T0+0.7 s, if fitted by a power law function with an exponential high-energy cutoff, the power law index is -0.51 +0.11/-0.12 and the cutoff energy, parameterized as Epeak, is 154 +11/-9 keV. The flux (10-1000 keV) in this time interval is (1.71 +0.08/-0.07)E-06 erg/cm^2/s.

The localization of GRB 251201A in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb251201A_amati.png
The localization of GRB 251201A in the 'Yonetoku' relation diagram is shown at: 
https://www.bursthub.cn//admin/static/svgrb251201A_yonetoku.png

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. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS.

The SVOM/GRM point of contact for this burst is: Yue Wang (IHEP) (yuewang@ihep.ac.cn)

D. Iijima, Y. Kawakubo (AGU), M. Nakajima (Nihon U.),
H. Negoro, K. Takagi, H. Takahashi, H. Nishio (Nihon U.),
T. Mihara, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN),
T. Sakamoto, M. Serino, S. Sugita, H. Hiramatsu, Y. Kondo, A. Yoshida (AGU),
Y. Tsuboi, H. Sugai, N. Nagashima, Y. Ishihara (Chuo U.),
M. Shidatsu, C. Kang, T. Nakamoto, M. Uenishi, T. Usuki, S. Yatsuzuka (Ehime U.),
I. Takahashi, Y. Yatsu (Science Tokyo),
S. Nakahira, S. Ueno, H. Tomida, M. Ishikawa, S. Ogawa, M. Kurihara (JAXA),
Y. Ueda, K. Fujiwara (Kyoto U.),
M. Yamauchi, M. Nishio, C. Hiraizumi (Miyazaki U.),
K. Yamaoka (Nagoya U.),
M. Sugizaki (Kanazawa U.),
W. Iwakiri (Chiba U.),
T. Kawamuro (Osaka U.),
S. Yamada (Tohoku U)
report on behalf of the MAXI team:

The MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient source at 04:36:59 UT on December 1, 2025.
Assuming that the source flux was constant over the transit,
we obtain the source position at
(R.A., Dec) = (309.032 deg, 30.413 deg) = (20 36 07, +30 24 46) (J2000)
with a statistical 90% C.L. elliptical error region
with long and short radii of 0.20 deg and 0.16 deg, respectively.
The roll angle of long axis from the north direction is 14.0 deg counterclockwise.
There is an additional systematic uncertainty of 0.1 deg (90% containment radius).
The X-ray flux averaged over the scan was 327 +- 36 mCrab
(4.0-10.0keV, 1 sigma error).
Without assumptions on the source constancy, we obtain a rectangular error
box for the transient source with the following corners:
(R.A., Dec) = (307.993, 30.840) deg = (20 31 58, +30 50 23) (J2000)
(R.A., Dec) = (307.875, 30.457) deg = (20 31 29, +30 27 25) (J2000)
(R.A., Dec) = (310.227, 29.897) deg = (20 40 54, +29 53 49) (J2000)
(R.A., Dec) = (310.354, 30.278) deg = (20 41 24, +30 16 40) (J2000)
There was no significant excess flux in the previous transit at 03:04 UT.