GRB 250819A

M. Tembhurnikar (IUCAA), G. Waratkar (IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration:

Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of GRB 250819A which was also detected by Insight-HXMT (Wang et. al., GCN Circ. 41457
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 ), and SVOM/GRM (SVOM team, GCN Circ. 41458
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 ).

The source was clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2025-08-19 17:49:46.59 UTC. The measured peak count rate associated with the burst is 396 (+68, -65) counts/s above the background in the combined data of all quadrants, with a total of 1066 (+262, -291) counts. The local mean background count rate was 1300 (+10, -12) counts/s. We measure a T90 of 3.3 (+1.8, -1.0) s from the cumulative Veto light curve.

The source was also faintly detected in the CZT detectors in the 20-200 keV energy range. 

CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project.

CZTI GRB detections are reported regularly on the payload site at:
http://astrosat.iucaa.in/czti/?q=grb

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

SVOM/ECLAIRs team: Tais Maiolino (LUPM), Stéphane Schanne (CEA)

Report on behalf of the SVOM team:

SVOM/GRM was triggered in-flight by a burst GRB 250819A (SVOM trigger reference: sb25081903) at 2025-08-19T17:49:46.000 UTC (T0), which is also detected by Insight-HXMT/HE (Wang et al., GCN#41457
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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 multi-pulses with a T90 of 7.4 +3.2/-2.0 s in the 15-5000 keV band.

The SVOM/GRM light curve can be found here:
https://www.bursthub.cn//admin/static/svgrb250819A.png

The SVOM/GRM on-ground localization of this burst is (J2000):
RA: 354.6 deg
DEC: -18.8 deg
Error: 12.6 deg (1sigma, statistical only)
We caution that the calibration of SVOM/GRM is undergoing and this localization is subject to systematic errors. 

In addition, the position of this burst, as determined by GRM, is located at about 32 degrees from the SVOM optical axis, which is inside the ECLAIRs field of view and consistent with a sub-threshold detection of ECLAIRs. The preliminary ECLAIRs localization is RA: 338.3 deg, DEC: -19.8 deg, with an error estimated as 30 arcmin, close to the edge of ECLAIRs field of view.

With the localization from ECLAIRs, the time-averaged spectrum from T0-1.5 to T0+8.0 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.98 +0.13/-0.10 and the cutoff energy, parameterized as Epeak, is 1740 +1250/-750 keV. The event fluence (10-1000 keV) in this time interval is (4.11 +0.35/-0.34)E-06 erg/cm^2. 

Thus GRB 250819A is well consistent with Type I GRBs in the 'Amati' relation diagram, as shown at:  
https://www.bursthub.cn//admin/static/grb250819A_amati.png

Based on the location of this GRB in 'Amati' relation diagram, a possible merger origin is suggested. A SVOM ToO has been programmed. Follow-up observations are strongly encouraged.

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)

Chen-Wei Wang, Wen-Jun Tan, Yue Huang, Shao-Lin Xiong, and Chao Zheng report on behalf of the Insight-HXMT team:

At 2025-08-19T17:49:46.000 (T0), Insight-HXMT/HE detected an intermedium duration burst GRB 250819A.

The Insight-HXMT/HE light curve mainly consists of multi-pulses with a T90 of 7.5 +3.2/-2.9 s. The 1s peak rate, measured from T0-0.25 s, is 1153 cnts/sec. The total counts from this burst is 4769 counts.

The HXMT/HE light curve can be found here:
https://www.bursthub.cn//admin/static/hxmtgrb250819A.png

All measurements above are made with the CsI detectors operating in the regular mode with the energy range of about 60-900 keV (deposited energy). Only gamma-rays with energy greater than about 200 keV can penetrate the spacecraft and leave signals in the CsI detectors installed inside of the telescope. 

Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://www.hxmt.or