GRB 250620A
GCN Circular 40791
Subject
GRB 250620A: Fermi GBM Final Real-time Localization
Date
2025-06-20T08:15:50Z (5 days ago)
From
Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply@GIOC.nsstc.nasa.gov>
Via
email
The Fermi GBM team reports the detection of a likely SHORT GRB
At 08:05:18 UT on 20 Jun 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250620A (trigger 772099523.9444 / 250620337).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 46.2, Dec = 65.8 (J2000 degrees, equivalent to J2000 03h 04m, 65d 47'), with a statistical uncertainty of 6.2 degrees.
The angle from the Fermi LAT boresight is 164.0 degrees.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250620337/quicklook/glg_skymap_all_bn250620337.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/bn250620337/quicklook/glg_healpix_all_bn250620337.fit
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250620337/quicklook/glg_lc_medres34_bn250620337.gif
GCN Circular 40796
Subject
GRB 250620A: Swift/BAT-GUANO subthreshold detection of a possibly short burst
Date
2025-06-20T19:50:54Z (5 days ago)
From
Jimmy DeLaunay at Penn State <delauj2@gmail.com>
Via
Web form
James DeLaunay (PSU), Rachel Hamburg (USRA), Oindabi Mukherjee (USRA), Samuele Ronchini (PSU), Aaron Tohuvavohu (Caltech), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC), Maia Williams (PSU), Gayathri Raman (PSU) report:
Swift/BAT did not localize GRB 250620A onboard (T0: 2025-06-20T08:05:18.94 UTC, Fermi/GBM trig 772099523)
The Fermi notice, distributed in near real-time, triggered the Swift Mission Operations Center operated Gamma-ray Urgent Archiver for Novel Opportunities (GUANO; Tohuvavohu et al. 2020, ApJ, 900, 1).
Upon trigger by this notice, GUANO sent a command to the Swift Burst Alert Telescope (BAT) to save 200 seconds of BAT event-mode data from [-50,+150] seconds around the time of the burst. All the requested event mode data was delivered to the ground.
The BAT likelihood search, NITRATES (DeLaunay + Tohuvavohu 2022, ApJ, 941, 169), performed on the temporal window [T0-20 s, T0+20 s], detects the burst with a sqrt(TS) of 7.3 in a 0.512 s analysis time bin, starting at T0 + 8.96 s. This corresponds to a FAR ~ 5e-4 Hz.
This is ~9 s after the initial short spike detected by Fermi/GBM, but is temporally coincident with a separate pulse seen in the Fermi/GBM lightcurve.
The initial short spike is also detected by NITRATES, but very weakly with a sqrt(TS) of 6.8 (FAR ~ 2e-3 Hz) in a 0.256 s analysis time bin, starting at T0 - 0.128 s.
Using the NITRATES analysis, parameter estimation was performed to obtain the localization of this burst in the form of a HEALPIX Multi-Order Coverage (MOC) skymap. This localization accounts for both statistical and systematic errors. More details in the creation and calibration of these maps will soon be published (DeLaunay et al. 2025. in prep)
The 90% credible area is 15,094 deg2 and the 50% credible area is 5,333 deg2.
The integrated probability inside the coded field of view is 1%.
The NITRATES skymap is very large but is consistent with the Fermi localization reported in the final position notice (GCN 40791).
A plot of the probability skymap can be viewed here:
[skymap_plot](https://guano.swift.psu.edu/trigger_report?id=772099554/#:~:text=Probability%20Skymap)
The probability skymap file can be downloaded from the link here
[skymap_fits_file](https://guano.swift.psu.edu/files/772099554/0_n_PROBMAP)
[joint_skymap_fits_file](https://guano.swift.psu.edu/files/772099554/0_n_JOINTMAP)
Instructions on how to read and manipulate this map can be found here:
https://guano.swift.psu.edu/documentation
More details about this burst can be found on the trigger report page here:
https://guano.swift.psu.edu/trigger_report?id=772099554
GUANO is a fully autonomous, extremely low latency, spacecraft commanding pipeline designed for targeted recovery of BAT event mode data around the times of compelling astrophysical events to enable more sensitive GRB searches.
A live reporting of Swift/BAT event data recovered by GUANO can be found at:
https://www.swift.psu.edu/guano/
GCN Circular 40805
Subject
GRB250620A: Fermi GBM Observation
Date
2025-06-21T23:52:54Z (4 days ago)
From
rhamburg@usra.edu
Via
Web form
R. Hamburg (USRA) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:
"At 08:05:18.94 UT on 20 June 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 250620A (trigger 772099523/250620337) which was
also detected by Swift/BAT-GUANO (DeLaunay et al. 2025, GCN 40796).
The angle from the Fermi LAT boresight is 164 degrees.
The GBM light curve two pulses with a duration (T90)
of about 12 s (50-300 keV). The time-averaged spectrum
from T0-0.3 to T0+10 s is best fit by a simple power law
function with index -1.6 +/- 0.2.
The event fluence (10-1000 keV) in this time interval is
(1.1 +/- 1.3)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+3.8 s in the 10-1000 keV band is 9 +/- 2 ph/s/cm^2.
A Band function fits the spectrum equally well with
Epeak = 2000 +/- 200 keV, alpha = -1.08 +/- 0.03 and beta = -2.44 +/- 0.09.
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/"
GCN Circular 40806
Subject
GRB 250620A: SVOM/GRM observation of a short burst
Date
2025-06-22T05:55:18Z (3 days ago)
From
Chenwei Wang at IHEP <cwwang@ihep.ac.cn>
Via
Web form
SVOM/GRM team: Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP)
SVOM/ECLAIRs team: Ulysse Jacob (LUPM)
Report on behalf of the SVOM team:
SVOM/GRM was triggered in-flight by a bright burst GRB 250620A (SVOM trigger reference: sb25062002) at 2025-06-20T08:05:19 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN#40791) and Swift/BAT (James DeLaunay et al., GCN#40796).
With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a narrow spike with a T90 of 0.15 +/-0.05 s in the 15-5000 keV band.
The SVOM/GRM light curve can be found here:
https://www.bursthub.cn//admin/static/svgrb250620A.png
In addition, the position of this burst, as determined by Fermi/GBM (RA= 46.2, DEC= 65.8, GCN#40791), is located at about 111 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view.
With this localization, the time-averaged spectrum from T0-0.2 to T0 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.64 +0.25/-0.19 and the cutoff energy, parameterized as Epeak, is 1310 +1780/-780 keV. The event fluence (10-1000 keV) in this time interval is (8.36 +0.89/-0.87)E-07 erg/cm^2.
The localization of GRB 250620A in the 'Amati' relation diagram is shown at:
https://www.bursthub.cn//admin/static/grb250620A_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)
GCN Circular 40822
Subject
GRB 250620A: AstroSat CZTI detection
Date
2025-06-25T11:52:12Z (2 hours ago)
From
Gaurav Waratkar at IIT Bombay <gauravwaratkar@iitb.ac.in>
Via
Web form
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 250620A which was also detected by Fermi/GBM (Fermi GBM Team, GCN Circ. 40791), Swift/BAT-GUANO (DeLaunay et al., GCN Circ. 40796), and SVOM/GRM (Wang et al., GCN Circ. 40806).
The source was clearly detected in the CZT detectors in the 20-200 keV energy range. We see only the initial short duration spike in the CZT detector data. The light curve peaks at 2025-06-20 08:05:18.89 UTC. The measured peak count rate associated with the burst is 853 (+613, -193) counts/s above the background in the combined data of three quadrants (out of four), with a total of 45 (+31, -13) counts. The local mean background count rate was 118 (+14, -102) counts/s. Using cumulative rates, we measure a T90 of 0.11 (+0.03, -0.03) s for the first spike.
The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. We see both episodes in Veto detectors, separated by about 10 s. The light curve, showing two burst episodes, peaks at 2025-06-20 08:05:27.70 UTC. The measured peak count rate associated with the burst is 368 (+65, -69) counts/s above the background in the combined data of all quadrants, with a total of 821 (+368, -375) counts. The local mean background count rate was 1184 (+7, -8) counts/s. We measure a T90 of 12 (+2, -10) s from the cumulative Veto light curve. The large negative uncertainty arises from the relatively weak detection of the first spike.
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