GRB 250101B

The Fermi GBM team reports the detection of a likely LONG GRB

At 23:14:12 UT on 1 Jan 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250101B (trigger 757466057.652354 / 250101968).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 70.9, Dec = -3.2 (J2000 degrees, equivalent to J2000 04h 43m, -3d 12'), with a statistical uncertainty of 3.3 degrees.

The angle from the Fermi LAT boresight is 49.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250101968/quicklook/glg_skymap_all_bn250101968.png

The HEALPix FITS file, including the estimated localization systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250101968/quicklook/glg_healpix_all_bn250101968.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250101968/quicklook/glg_lc_medres34_bn250101968.gif

V.Lipunov, E.Gorbovskoy, N.Tiurina,  P.Balanutsa, , D.Vlasenko, I.Panchenko,
A.Kuznetsov,  G.Antipov,  A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, 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. 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-SAAO robotic telescope  (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L)  located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB 250101B ( Fermi GBM team, GCN 38766
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 ) errorbox  30 sec after notice time and 72 sec after trigger time at 2025-01-01 23:15:25 UT, with upper limit up to  17.9 mag. The observations began at zenith distance = 46 deg. The sun  altitude  is -34.5 deg. 

The galactic latitude b = -29 deg., longitude l = 201 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=2730742

We obtain a following upper limits.  

Tmid-T0  |      Date Time      |          Site       |             Coord (J2000)          |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________

      78 | 2025-01-01 23:15:25 |         MASTER-SAAO | (04h 55m 50.35s , -02d 10m 31.1s) |   C |    10 | 17.9 |        
Filter C is a clear (unfiltred) band. 


The observation and reduction will continue. 
The message may be cited.

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

report on behalf of the SVOM team:

During the commissioning phase, SVOM/GRM detected GRB 250101B at 2025-01-01T23:14:12 UT (T0), which was also observed by Fermi/GBM (Fermi GBM Team, GCN 38766
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 ).

With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of two main pulses with a T90 of 5.27 +/-1.24 s.

This burst is located (from Fermi/GBM) at about 96.02 degrees from the SVOM optical axis, and outside the ECLAIRs field of view.

The GRM light curve can be found here:
https://www.bursthub.cn//admin/static/svgrb250101B.png


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


The SVOM point of contact for this burst is: Wen-Long Zhang (IHEP)(zhangwl@ihep.ac.cn)

O. Mukherjee (USRA), S. Bala (USRA) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 23:14:12.65 UT on 01 January 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 250101B (trigger 757466057/250101968).
which was also detected by SVOM/GRM (Zhang et al. 2025, GCN 38793
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 ).

The on-ground calculated location, using the Fermi GBM trigger data,
is RA = 70.87, Dec = -3.25 (J2000 degrees, equivalent to
J2000 4h 43m, -3d 15'), with a statistical uncertainty of 3.29 degrees.
(radius, 1-sigma containment, statistical only; there is additionally a
systematic error which we have characterized as a mixture of two Gaussians,
one with a radius of 1.8 degrees (52% contribution) and one with a radius
of 4.1 degrees (47% contribution) [A. Goldstein et al. 2020, ApJ, 895, 1]).

The angle from the Fermi LAT boresight is 49 degrees.

The GBM light curve consists of a single emission episode with two distinct peaks with a duration (T90)
of about 4.5 s (50-300 keV). The time-averaged spectrum
from T0-1.0 to T0+5.1 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -0.34 +/- 0.09 and the cutoff energy,
parameterized as Epeak, is 146 +/- 7 keV.

The event fluence (10-1000 keV) in this time interval is
(2.418 +/- 0.8)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+0.77 s in the 10-1000 keV band is 5 +/- 0.2 ph/s/cm^2.

The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog:
https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html

For Fermi GBM data and info, please visit the official Fermi GBM Support Page:
https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/"