GRB 250808A

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 250808A ( Fermi GBM team, GCN 41296
Loading...
 
 ) errorbox  18725 sec after notice time and 18749 sec after trigger time at 2025-08-08 23:37:41 UT, with upper limit up to  16.5 mag. The observations began at zenith distance = 79 deg. The sun  altitude  is -22.7 deg. 

The galactic latitude b = -42 deg., longitude l = 211 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=2964051

We obtain a following upper limits.  

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

   18779 | 2025-08-08 23:37:41 |   MASTER-Kislovodsk | (03h 36m 57.03s , -13d 48m 11.9s) |   C |    60 | 15.0 |        
   20676 | 2025-08-09 00:09:18 |   MASTER-Kislovodsk | (03h 54m 25.00s , -15d 41m 27.8s) |   C |    60 | 12.1 |        
   21637 | 2025-08-09 00:25:19 |   MASTER-Kislovodsk | (04h 11m 41.65s , -22d 41m 02.9s) |   C |    60 | 15.0 |        
   21697 | 2025-08-09 00:25:19 |   MASTER-Kislovodsk | (04h 11m 41.66s , -22d 41m 03.0s) |   C |   180 | 15.9 |  Coadd 
   21720 | 2025-08-09 00:26:42 |   MASTER-Kislovodsk | (04h 11m 34.93s , -22d 42m 01.6s) |   C |    60 | 15.3 |        
   21806 | 2025-08-09 00:28:08 |   MASTER-Kislovodsk | (04h 11m 43.16s , -22d 41m 36.9s) |   C |    60 | 15.7 |        
   21889 | 2025-08-09 00:29:31 |   MASTER-Kislovodsk | (04h 11m 39.40s , -22d 40m 19.5s) |   C |    60 | 15.8 |        
   21949 | 2025-08-09 00:29:31 |   MASTER-Kislovodsk | (04h 11m 39.42s , -22d 40m 19.8s) |   C |   180 | 16.4 |  Coadd 
   21979 | 2025-08-09 00:31:01 |   MASTER-Kislovodsk | (04h 11m 39.61s , -22d 41m 49.4s) |   C |    60 | 15.8 |        
   22063 | 2025-08-09 00:32:25 |   MASTER-Kislovodsk | (04h 11m 43.91s , -22d 40m 21.3s) |   C |    60 | 15.7 |        
   22151 | 2025-08-09 00:33:53 |   MASTER-Kislovodsk | (04h 11m 36.12s , -22d 40m 49.1s) |   C |    60 | 15.9 |        
   22211 | 2025-08-09 00:33:53 |   MASTER-Kislovodsk | (04h 11m 36.14s , -22d 40m 49.5s) |   C |   180 | 16.5 |  Coadd 
   22232 | 2025-08-09 00:35:14 |   MASTER-Kislovodsk | (04h 11m 37.37s , -22d 39m 46.9s) |   C |    60 | 15.9 |        
   22315 | 2025-08-09 00:36:37 |   MASTER-Kislovodsk | (04h 11m 43.55s , -22d 40m 44.4s) |   C |    60 | 15.8 |        
   22398 | 2025-08-09 00:38:00 |   MASTER-Kislovodsk | (04h 11m 38.67s , -22d 41m 40.3s) |   C |    60 | 16.0 |        
   22482 | 2025-08-09 00:39:24 |   MASTER-Kislovodsk | (04h 11m 43.85s , -22d 41m 24.6s) |   C |    60 | 15.9 |        
   22752 | 2025-08-09 00:43:54 |   MASTER-Kislovodsk | (04h 11m 43.50s , -22d 39m 33.3s) |   C |    60 | 15.7 |        
   22834 | 2025-08-09 00:45:16 |   MASTER-Kislovodsk | (04h 11m 39.63s , -22d 40m 21.8s) |   C |    60 | 15.7 |        
   22894 | 2025-08-09 00:45:16 |   MASTER-Kislovodsk | (04h 11m 39.63s , -22d 40m 21.9s) |   C |   180 | 16.1 |  Coadd 
   22919 | 2025-08-09 00:46:41 |   MASTER-Kislovodsk | (04h 11m 37.85s , -22d 39m 18.0s) |   C |    60 | 15.7 |        
   23011 | 2025-08-09 00:48:13 |   MASTER-Kislovodsk | (04h 11m 44.98s , -22d 40m 14.4s) |   C |    60 | 15.2 |        
   23093 | 2025-08-09 00:49:35 |   MASTER-Kislovodsk | (04h 11m 39.09s , -22d 41m 10.2s) |   C |    60 | 15.0 |        
   23153 | 2025-08-09 00:49:35 |   MASTER-Kislovodsk | (04h 11m 39.09s , -22d 41m 10.2s) |   C |   180 | 15.9 |  Coadd 
   23199 | 2025-08-09 00:51:21 |   MASTER-Kislovodsk | (04h 11m 44.24s , -22d 40m 39.2s) |   C |    60 | 15.4 |        
   23283 | 2025-08-09 00:52:45 |   MASTER-Kislovodsk | (04h 11m 42.44s , -22d 39m 17.6s) |   C |    60 | 15.4 |        
   23381 | 2025-08-09 00:54:23 |   MASTER-Kislovodsk | (04h 11m 42.54s , -22d 40m 34.8s) |   C |    60 | 15.0 |        
   23467 | 2025-08-09 00:55:49 |   MASTER-Kislovodsk | (04h 11m 45.72s , -22d 38m 58.4s) |   C |    60 | 14.3 |        
   24214 | 2025-08-09 01:08:16 |   MASTER-Kislovodsk | (04h 11m 48.73s , -22d 39m 27.6s) |   C |    60 | 13.7 |        
   24300 | 2025-08-09 01:09:42 |   MASTER-Kislovodsk | (03h 36m 57.33s , -13d 44m 50.9s) |   C |    60 | 12.9 |        
Filter C is a clear (unfiltred) band. 


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

A. Levan (Radboud U.), D. B. Malesani (DAWN/NBI and Radboud Univ.), I. F. Giudice (INAF/OACn), L. Izzo (INAF/OACn & DARK/NBI), A. L. Thakur (INAF-IAPS), N. R. Tanvir (U. Leicester), G. Corcoran (UCD), A. de Ugarte Postigo (LAM), A. Martin-Carrillo (UCD), A. Saccardi (CEA/Irfu), M. De Pasquale (U. Messina), D. Hartmann (Clemson U.) report on behalf of the Stargate collaboration:

We observed the field of SVOM/ECLAIRs GRB 250808A (Adrien et al., GCN 41297
Loading...
 
 ) using ESO VLT UT3 (Melipal) equipped with the X-shooter instrument, starting at 9 August 08:56 UT, approximately 14.5 hr after the burst trigger. A sequence of 1x120s (r band) and 5x60s (z band) images was obtained with the acquisition camera. Comparison to z-band images obtained with the Legacy Survey shows a new source within the Swift/XRT localisation region (Evans et al., GCN 41300
Loading...
 
 ) at coordinates:

RA(J2000) = 04:14:12.39
Dec(J2000) = -22:49:23.5

The source has an approximate magnitude of z ~ 21.8 mag (AB). We suggest this is the optical counterpart of GRB 250808A. We notice that this source is also detected in the r-band acquisition image.

We also note the presence of a very faint (r = 24.28 mag, z = 23.73 mag) catalogued object in the Legacy Survey DR10 just below the afterglow position. We propose this source to be the host galaxy of GRB 250808A.
 
We acknowledge excellent support from the ESO observing staff in Paranal, in particular Cecilia Bustos, Rodrigo Palominos, and Rob van Holstein.

Antonio de Ugarte Postigo (LAM), Noémie Globus (UNAM), Jean-Grégoire Ducoin (CPPM), Alan M. Watson (UNAM), Jean-Luc Atteia (IRAP), Rosa L. Becerra (U Roma), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Fredd Alvarez (UNAM), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (OCA), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), D. Adrien (CEA) and D. Turpin (CEA):

We imaged the field of the SVOM GRB 250808A (Adrien et al., GCN Circ. 41297
Loading...
 
 ) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-08-09 11:11 to 11:50 UTC (from 16.8 to 17.4 hours after the trigger) and obtained 32x60 s of exposure in the i filter. The observations were carried out mostly during the astronomical twilight and with an average airmass ~ 2.7.

The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction.

Within the full SVOM/ECLAIRs error circle we do not detect any new source down to a 5-sigma limiting magnitude of i > 21.4 mag. More specifically, within the error circle of the XRT afterglow (Evans et al. GCN  Circ. 41300
Loading...
 
 ) we do not detect any significant optical counterpart down to the following 3-sigma limit:

i > 22.0 mag

We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams.

COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico.

A. Holzmann Airasca (UniTrento and INFN Bari), S. Bala (USRA) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 18:25:12.48 UT on 08 August 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 250808A (trigger 776370317/250808768).
which was also detected by SVOM/ECLAIRs (D. Adrien et al. 2025, GCN 41297
Loading...
 
 ).
The Fermi GBM on-ground location is consistent with the SVOM/ECLAIRs position.

The angle from the Fermi LAT boresight is 33 degrees.

The GBM light curve consists of a single variable emission episode with a duration (T90)
of about 49 s (50-300 keV). The time-averaged spectrum
from T0-6.1 to T0+51.2 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -1.1 +/- 0.2 and the cutoff energy,
parameterized as Epeak, is 70 +/- 7 keV.

The event fluence (10-1000 keV) in this time interval is
(2.7 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+45 s in the 10-1000 keV band is 2.5 +/- 0.2 ph/s/cm^2.

A Band function fits the spectrum equally well
with Epeak= 55 +/- 9 keV, alpha = -0.7 +/- 0.3 and beta = -2.5 +/- 0.3.

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/"

P.A. Evans (U. Leicester), J.A. Kennea (PSU), E. Ambrosi  (INAF-IASFPA) , A.P.
Beardmore (U. Leicester), M.G. Bernardini (INAF-OAB), R. Brivio (INAF-OAB), D.N.
Burrows (PSU), S. Campana (INAF-OAB), M. Capalbi (INAF-OAR), A. D'Ai (INAF-IASFPA),
P. D'Avanzo (INAF-OAB), V. D'Elia (SSDC & INAF-OAR), S. Dichiara (PSU), M. Ferro
(INAF-OAB), A. Melandri (INAF-OAR), J.P. Osborne (U. Leicester), K.L. Page (U.
Leicester), M. Perri (SSDC & INAF-OAR), C. Salvaggio (INAF-OAB), T. Sbarrato
(INAF-OAB), B. Sbarufatti (INAF-OAB), M.A. Williams (PSU) report on behalf of the
Swift-XRT team:

Swift-XRT has performed follow-up observations of the SVOM/ECLAIRs-detected source
GRB 250808A, collecting 1.7 ks of Photon Counting (PC) mode data between T0+3.7 ks
and T0+5.6 ks after the trigger. A candidate counterpart has been found. The details
of this source are:

  Source 1 (SWIFT J041412.2-224923):
  ==================================
    RA (J2000.0):   63.5510  =	04h 14m 12.24s
    Dec (J2000.0):  -22.8231  =  -22d 49' 23.2"
    Error:	    3.9 (arcsec, radius, 90% confidence).
    Detect flag:    GOOD
    Distance:	    4.9 arcmin from the SVOM/ECLAIRs position.
    Mean rate:	    0.140 +/- 0.013 ct s^-1
    Mean flux:	    (4.58 +/- 0.43)e-12 erg cm^-2 s^-1
    Peak rate:	    0.204 +/- 0.046 ct s^-1
    Peak flux:	    (6.7 +/- 1.5)e-12 erg cm^-2 s^-1
    ECF:	    3.27e-11 erg cm^-2 ct^-1
		      assuming NH=1.35e+21 cm^-2, gamma=2.07
		      determined from a spectral fit.
    XMM UL:	    2.2e-12 erg cm^-2 s^-1, (0.3-10 keV)
		      so the source is 3.0-sigma above this 3-sigma upper limit.
    The source may be fading, at the 2.1-sigma level.


All fluxes are 0.3-10 keV, observed. For all flux conversions and comparisons with
catalogues and upper limits  from other missions, we assumed a power-law spectrum
with NH=3x10^20 cm^-2 and photon index (Gamma)=1.7 unless otherwise stated.

The results of the XRT-team automatic analysis of the XRT observations, including a
position-specific upper limit calculator, are available at
https://www.swift.ac.uk/SVOM/SVOM_FIELD00027.

This circular is an official product of the Swift-XRT team.

D. Adrien, D. Turpin, N. Dagoneau (CEA), S. Guillot (IRAP), report on behalf of the SVOM mission team:

At 2025-08-08T18:25:49 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 250808A (SVOM burst-id sb25080803).

The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network.

The burst was only detected by the Image Trigger (IMT), which produced a sequence of 2 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 7.44 in the [5-20] keV energy band over a time window of 163.84 seconds starting at 2025-08-08T18:23:46.

The localization of the best alert is R.A., Dec. 63.5525, -22.9041 degrees:
R.A. (J2000) = 4h14m12.61s
Dec. (J2000) = -22d54m14.75s
 with a 90% confidence level (C.L.) radius of 10.55 arcmin (including systematic error of 2 arcmin added in quadrature).

The time and position are consistent with the Fermi/GBM GRB 250808A (Fermi GBM, GCN 41296
Loading...
 
 ).

This burst was also detected by SVOM/GRM with a significance of 8.20.
Due to the detection significance being below the slew threshold, no immediate slew was performed on this burst.
No X-ray observation could be performed by SVOM/MXT for the time being.No optical observation could be performed by SVOM/VT for the time being.


The Space-based multi-band astronomical 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. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE.

The Burst Advocate (BA) on shift for this alert is Dylan ADRIEN: dylan.adrien@cea.fr.
Please contact the BA by email if you require additional information.

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

At 18:25:12 UT on 8 Aug 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250808A (trigger 776370317.484496 / 250808768).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 62.8, Dec = -16.8 (J2000 degrees, equivalent to J2000 04h 11m, -16d 48'), with a statistical uncertainty of 7.1 degrees.

The angle from the Fermi LAT boresight is 33.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250808768/quicklook/glg_skymap_all_bn250808768.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/bn250808768/quicklook/glg_healpix_all_bn250808768.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250808768/quicklook/glg_lc_medres34_bn250808768.gif