GRB 250814B

V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, 
G.Antipov,  A.Sankovich, Yu.Tselik, 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.Sosnovskij (CrAO),
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-Kislovodsk robotic telescope  (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L)  located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB 250814B ( Fermi GBM team, GCN 41366
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 ) errorbox  47497 sec after notice time and 47527 sec after trigger time at 2025-08-14 23:34:17 UT, with upper limit up to  16.5 mag. The observations began at zenith distance = 119 deg. The sun  altitude  is -74.1 deg. 

The galactic latitude b = -6 deg., longitude l = 181 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=2968279

We obtain a following upper limits.  

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

   47557 | 2025-08-14 23:34:17 |             MASTER- | (05h 18m 51.95s , +23d 45m 27.2s) |   C |    60 | 14.0 |        
   47557 | 2025-08-14 23:34:17 |   MASTER-Kislovodsk | (05h 14m 32.17s , +24d 08m 32.4s) |   C |    60 | 16.5 |        
Filter C is a clear (unfiltred) band. 


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

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

SVOM/ECLAIRs team: Hui Yang (IRAP), Stéphane Schanne (CEA)

Report on behalf of the SVOM team:

SVOM/GRM was triggered on-ground by GRB 250814B at 2025-08-14T10:22:10.500 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN #41366
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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 a single pulse with a T90 of 9.0 +2.0/-3.0 s in the 15-5000 keV band.

The SVOM/GRM light curve can be found here:
https://www.bursthub.cn//admin/static/svgrb250814B.png

The SVOM/GRM on-ground localization of this burst is (J2000):
RA: 73.9 deg
DEC: 22.2 deg
Error: 7.1 deg (1sigma, statistical only)
We caution that the calibration of SVOM/GRM is undergoing and this localization is subject to systematic errors. The SVOM/GRM on-ground localization is consistent with Fermi/GBM (Fermi GBM Team, GCN #41366
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 )

In addition, the position of this burst, as determined by SVOM/GRM, is located at about 71 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view, and is consistent with no indication for subthreshold targets either from CRT and IMT of ECLAIRs.

With this localization, the time-averaged spectrum from T0-5 to T0+7 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.46 +0.16/-0.22 and the cutoff energy, parameterized as Epeak, is 250 +395/-91 keV. The event fluence (10-1000 keV) in this time interval is (2.99 +0.43/-0.41)E-06 erg/cm^2. Thus GRB 250814B is consistent with Type II GRBs in the 'Amati' relation diagram, as shown at:  
https://www.bursthub.cn//admin/static/grb250814B_amati.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 point of contact for this burst is: Chen-Wei Wang (IHEP)(cwwang@ihep.ac.cn)

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

At 10:22:10 UT on 14 Aug 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250814B (trigger 776859735.510984 / 250814432).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 80.1, Dec = 24.6 (J2000 degrees, equivalent to J2000 05h 20m, 24d 36'), with a statistical uncertainty of 4.6 degrees.

The angle from the Fermi LAT boresight is 132.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250814432/quicklook/glg_skymap_all_bn250814432.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/bn250814432/quicklook/glg_healpix_all_bn250814432.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250814432/quicklook/glg_lc_medres34_bn250814432.gif