GRB 250816A

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

At 01:30:10 UT on 16 Aug 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250816A (trigger 777000615.453666 / 250816063).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 156.7, Dec = 58.9 (J2000 degrees, equivalent to J2000 10h 26m, 58d 53'), with a statistical uncertainty of 3.0 degrees.

The angle from the Fermi LAT boresight is 40.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250816063/quicklook/glg_skymap_all_bn250816063.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/bn250816063/quicklook/glg_healpix_all_bn250816063.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250816063/quicklook/glg_lc_medres34_bn250816063.gif

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

SVOM/ECLAIRs team: Olivier GODET (IRAP)

Report on behalf of the SVOM team:

SVOM/GRM was triggered in-flight by a short burst GRB 250816A (SVOM trigger reference: sb25081601) at 2025-08-16T01:30:10.600 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN #41397
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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 0.9 +0.5/-0.4 s in the 15-5000 keV band.

The SVOM/GRM light curve can be found here:
https://www.bursthub.cn//admin/static/svgrb250816A.png

In addition, the position of this burst, as determined by Fermi/GBM (RA= 156.7, DEC= 58.9, GCN #41397
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 ), is located at about 115 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. ECLAIRs was not collecting data at the time of this burst.

With this localization, the time-averaged spectrum from T0-0.3 to T0+0.2 s is best fitted by a power law function. The power law index is -2.17 +/-0.15. The event fluence (10-1000 keV) in this time interval is (1.97 +/-0.24)E-06 erg/cm^2. 

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)

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 250816A ( Fermi GBM team, GCN 41397
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 ) errorbox  16 sec after notice time and 43 sec after trigger time at 2025-08-16 01:30:54 UT, with upper limit up to  12.5 mag. Observations started at twilight.  The observations began at zenith distance = 68 deg. The sun  altitude  is -8.5 deg. 

The galactic latitude b = 50 deg., longitude l = 151 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=2969505

We obtain a following upper limits.  

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

      49 | 2025-08-16 01:30:54 |   MASTER-Kislovodsk | (10h 24m 32.65s , +60d 44m 23.8s) |   C |    10 | 12.5 |        
Filter C is a clear (unfiltred) band. 


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

D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia,
and T. Cline on behalf of the Konus-Wind team,

A. Goldstein, M. S. Briggs, C. Wilson-Hodge,
and E. Burns on behalf of the Fermi GBM team,
report:

The short-duration GRB 250816A
(Fermi-GBM detection: The Fermi GBM team, GCN 41397
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 ;
SVOM-GRM detection: Wang et al., GCN 41400
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 )
was detected by Fermi (GBM trigger 777000615), SVOM (GRM),
and Konus-Wind at about 5410 s UT (01:30:10).
The burst was outside the coded field of view of the BAT.

We have triangulated it to a preliminary, 3 sigma error box
whose area is 7.8 sq. deg, and its maximum
dimension is 32.2 deg (the minimum one is 18.7 arcmin).
The Sun distance was ~46 deg.

This localization may be improved.

A triangulation map and HEALPix FITS file are posted at
http://www.ioffe.ru/LEA/GRBs/GRB250816_T05407/IPN
The HEALPix triangulation map is the multi-order HEALPix in units of
probability density.

The Konus-Wind time history and spectrum will be given
in a forthcoming GCN Circular.