GRB 250320B
GCN Circular 39792
Subject
GRB 250320B: Fermi GBM Final Real-time Localization
Date
2025-03-20T23:25:50Z (2 months 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 LONG GRB
At 23:15:22 UT on 20 Mar 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250320B (trigger 764205327.02257 / 250320969).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 249.2, Dec = -21.8 (J2000 degrees, equivalent to J2000 16h 36m, -21d 48'), with a statistical uncertainty of 1.0 degrees.
The angle from the Fermi LAT boresight is 31.0 degrees.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250320969/quicklook/glg_skymap_all_bn250320969.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/bn250320969/quicklook/glg_healpix_all_bn250320969.fit
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250320969/quicklook/glg_lc_medres34_bn250320969.gif
GCN Circular 39806
Subject
Fermi GRB 250320B: Global MASTER-Net observations report
Date
2025-03-21T09:16:08Z (2 months ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
email
V.Lipunov, E.Gorbovskoy, N.Tiurina, P.Balanutsa, , D.Vlasenko, I.Panchenko,
A.Kuznetsov, G.Antipov, A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, 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. 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-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) started inspect of the Fermi GRB 250320B ( Fermi GBM team, GCN 39792) errorbox 33041 sec after notice time and 33077 sec after trigger time at 2025-03-21 08:26:39 UT, with upper limit up to 18.4 mag. The observations began at zenith distance = 12 deg. The sun altitude is -28.6 deg.
The galactic latitude b = 16 deg., longitude l = 357 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=2818681
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
33098 | 2025-03-21 08:26:39 | MASTER-OAFA | (16h 26m 20.48s , -22d 13m 22.4s) | C | 40 | 17.1 |
33138 | 2025-03-21 08:26:39 | MASTER-OAFA | (16h 26m 20.49s , -22d 13m 22.3s) | C | 120 | 17.8 | Coadd
33108 | 2025-03-21 08:26:40 | MASTER-OAFA | (16h 36m 11.47s , -21d 49m 19.6s) | C | 60 | 18.3 |
33173 | 2025-03-21 08:27:55 | MASTER-OAFA | (16h 26m 22.64s , -22d 11m 46.3s) | C | 40 | 17.2 |
33184 | 2025-03-21 08:27:55 | MASTER-OAFA | (16h 36m 13.62s , -21d 47m 42.5s) | C | 60 | 18.3 |
33249 | 2025-03-21 08:29:10 | MASTER-OAFA | (16h 26m 17.85s , -22d 12m 32.3s) | C | 40 | 17.2 |
33259 | 2025-03-21 08:29:10 | MASTER-OAFA | (16h 36m 08.92s , -21d 48m 27.6s) | C | 60 | 18.4 |
33354 | 2025-03-21 08:30:25 | MASTER-OAFA | (16h 26m 16.38s , -22d 11m 33.0s) | C | 100 | 17.5 |
33484 | 2025-03-21 08:30:25 | MASTER-OAFA | (16h 26m 16.37s , -22d 11m 32.9s) | C | 360 | 18.2 | Coadd
33364 | 2025-03-21 08:30:26 | MASTER-OAFA | (16h 36m 07.07s , -21d 47m 24.6s) | C | 120 | 15.3 |
33490 | 2025-03-21 08:32:41 | MASTER-OAFA | (16h 26m 23.41s , -22d 12m 34.3s) | C | 100 | 17.5 |
33530 | 2025-03-21 08:32:41 | MASTER-OAFA | (16h 26m 23.41s , -22d 12m 34.3s) | C | 180 | 17.9 | Coadd
33625 | 2025-03-21 08:34:57 | MASTER-OAFA | (16h 26m 17.86s , -22d 13m 34.9s) | C | 100 | 17.5 |
33791 | 2025-03-21 08:37:12 | MASTER-OAFA | (16h 26m 22.80s , -22d 13m 29.4s) | C | 160 | 17.7 |
33928 | 2025-03-21 08:40:29 | MASTER-OAFA | (16h 26m 20.00s , -22d 12m 03.3s) | C | 40 | 17.1 |
33938 | 2025-03-21 08:40:29 | MASTER-OAFA | (16h 36m 11.27s , -21d 47m 56.2s) | C | 60 | 18.3 |
34002 | 2025-03-21 08:41:44 | MASTER-OAFA | (16h 26m 19.86s , -22d 13m 31.8s) | C | 40 | 17.2 |
34013 | 2025-03-21 08:41:44 | MASTER-OAFA | (16h 36m 11.25s , -21d 49m 24.6s) | C | 60 | 18.3 |
34077 | 2025-03-21 08:42:58 | MASTER-OAFA | (16h 26m 22.13s , -22d 11m 55.1s) | C | 40 | 17.1 |
34087 | 2025-03-21 08:42:59 | MASTER-OAFA | (16h 36m 13.43s , -21d 47m 47.9s) | C | 60 | 18.3 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
GCN Circular 39808
Subject
GRB 250320B: AstroSat CZTI detection
Date
2025-03-21T09:26:45Z (2 months ago)
From
Gaurav Waratkar at IIT Bombay <gauravwaratkar@iitb.ac.in>
Via
Web form
J. Joshi (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 a bright long-duration GRB 250320B which was also detected by Fermi/GBM (Fermi GBM Team, GCN Circ. 39792).
The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2025-03-20 23:15:29.50 UTC. The measured peak count rate associated with the burst is 350 (+38, -29) counts/s above the background in the combined data of three quadrants (out of four), with a total of 5456 (+403, -388) counts. The local mean background count rate was 207 (+2, -2) counts/s. Using cumulative rates, we measure a T90 of 85 (+3, -4) s. In the preliminary analysis, we find 997 Compton events associated with this event.
The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2025-03-20 23:15:28.37 UTC. The measured peak count rate associated with the burst is 2028 (+97, -71) counts/s above the background in the combined data of all quadrants, with a total of 27352 (+899, -1147) counts. The local mean background count rate was 1278 (+4, -4) counts/s. We measure a T90 of 81 (+3, -1) s from the cumulative Veto light curve.
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
GCN Circular 39813
Subject
GRB 250320B: SVOM/GRM observation of a long burst
Date
2025-03-21T13:20:50Z (2 months ago)
From
wenlongzhang2018@163.com
Via
Web form
SVOM/GRM team: Wen-Long Zhang, Wen-Jun Tan, Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP)
SVOM/ECLAIRs team: Nicolas Dagoneau (CEA), Maria-Grazia Bernardini (INAF-OAB), Jean-Luc Atteia (IRAP), Frédéric Piron (LUPM)
Report on behalf of the SVOM team:
SVOM/GRM was triggered in-flight by GRB 250320B (SVOM trigger reference: sb25032001) at 2025-03-20T23:15:23.000 (T0), which was also observed by Fermi/GBM (Fermi GBM team, GCN #39792) and AstroSat CZTI (J. Joshi et al., GCN 39808).
With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multi-peaks with a T90 of 86.5 +0.5/-1.0 s in the 15-5000 keV band.
The SVOM/GRM light curve can be found here:
https://www.bursthub.cn//admin/static/svgrb250320B.png
In addition, the position of this burst, as determined by Fermi/GBM (Fermi GBM Team, GCN #39792), is located at about 53.9 degrees (with a few degrees of statistical and systematic errors) from the SVOM optical axis. This burst was detected by the Count-Rate Trigger onboard ECLAIRs, as an increase in counts over background, but it was not localized by the coded-mask imaging process, which confirms that the burst occurred outside the ECLAIRs field of view.
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/GRM point of contact for this burst is: Wen-Long Zhang (IHEP) (zhangwl@ihep.ac.cn)
GCN Circular 39819
Subject
GRB 250320B: Fermi-LAT detection
Date
2025-03-21T18:05:59Z (2 months ago)
From
A. Holzmann Airasca at University of Trento and INFN Bari <a.holzmannairasca@unitn.it>
Via
Web form
A. Holzmann Airasca (UniTrento and INFN Bari), S. Lopez (CNRS / IN2P3), P. Monti-Guarnieri (University and INFN, Trieste), N. Di Lalla (Stanford Univ.), F. Longo (University and INFN, Trieste) and R. Gupta (NASA GSFC) report on behalf of the Fermi-LAT Collaboration:
On March 20, 2025, Fermi-LAT detected high-energy emission from GRB 250320B, which was also detected by Fermi-GBM (trigger 764205327 / 250320969, GCN 39792), AstroSat CZTI (GCN 39808) and SVOM/GRM (GCN 39813).
The best LAT on-ground location is found to be:
RA, Dec = 244.66, -30.37 (J2000)
with an error radius of 0.3 deg (90 % containment, statistical error only).
This was 40 deg from the LAT boresight at the time of the GBM trigger (T0 = 23:15:22.02 UT).
The data from the Fermi-LAT shows a significant increase in the event rate that is spatially and temporally correlated with the GBM emission with high significance. The photon flux above 100 MeV in the time interval 0 - 1400 s after the GBM trigger is (3.6 ± 1.1) E-6 ph/cm2/s. The estimated photon index above 100 MeV is -2.35 ± 0.31.
The highest-energy photon is a 1.9 GeV event which is observed ~ 245 seconds after the GBM trigger.
A Swift ToO has been requested for this burst.
The Fermi-LAT point of contact for this burst is Aldana Holzmann Airasca (aldana.holzmannairasca@ba.infn.it).
The Fermi-LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.
GCN Circular 39823
Subject
GRB 250320B: Fermi GBM Observation
Date
2025-03-21T21:09:51Z (2 months ago)
From
eliza.neights@gmail.com
Via
Web form
E. Neights (GWU, NASA/GSFC), R. Hamburg (UAH), C. Meegan (UAH) and O.J. Roberts (USRA) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:
"At 23:15:22.02 UT on 20 March 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 250320B (trigger 764205327/250320969).
which was also detected by AstroSat CZTI (Joshi et al. 2025, GCN 39808), SVOM/GRM (Zhang et al. 2025, GCN 39813), and Fermi LAT (Holzmann Airasca et al. 2025, GCN 39819).
The Fermi GBM on-ground location is consistent with the LAT position.
The angle from the Fermi LAT boresight is 40 degrees.
The GBM light curve consists of multiple emission episodes with a duration (T90)
of about 86 s (50-300 keV). The time-averaged spectrum
from T0-2.0 to T0+107.5 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -1.16 +/- 0.01 and the cutoff energy,
parameterized as Epeak, is 570 +/- 20 keV.
The event fluence (10-1000 keV) in this time interval is
(9.02 +/- 0.07)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+75 s in the 10-1000 keV band is 21.6 +/- 0.4 ph/s/cm^2.
A Band function fits the spectrum equally well
with Epeak = 547 +/- 22 keV, alpha = -1.16 +/- 0.01 and beta = -2.7 +/- 0.2.
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 39826
Subject
GRB 250320B: NuSTAR detection of the prompt emission from two broad bursts and preliminary analysis
Date
2025-03-21T21:58:08Z (2 months ago)
From
Brian Grefenstette at Caltech/NuSTAR <bwgref@srl.caltech.edu>
Via
Web form
B. Grefenstette (Caltech) reports on behalf of the NuSTAR Search for INteresting Gamma-ray Signals (SINGS) working group:
The NuSTAR SINGS working group reports the detection of prompt emission from the Long GRB 250320B in both the NuSTAR CsI anti-coincidence shields and in the CdZnTe detectors. This GRB was identified through a blind search using the CsI shield rates. Details of the search algorithm will be described in a future paper.
The NuSTAR SINGS algorithm triggered at 2025-03-20 23:16:29.000 on the second of two bright, broad bursts (with a resolution ~5-seconds). This is consistent with the detections by the Fermi LAT (Airasca et al, GCN circ. 39819), Fermi GBM (Neights et al., GCN circ. 39823), AstroSat CZT (Waratkar et al., GCN circ. 39808) and SVOM/GRM (Zhang et al., GCN circ. 39813).
The NuSTAR CsI shield data are recorded at 1 Hz. The GRB appears to be composed of two, broad bursts, each strongly detected above background with peak count rates near 3,000 cps over a baseline of ~1,000 cps. We see clear evidence for correlated >100 keV X-rays in both CdZnTe focal planes for both bursts at the time of the GRB.
Using the localization from Fermi LAT at RA = 244.66, Dec = -30.37 implies an offset from the NuSTAR boresight of only 60.49 (e.g., through the side of the instrument) and the offset from the geocenter of 143.51-deg.
Discovery report and preliminary reports for this GRB can be found here:
https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2025/250320B/
Additional analysis will follow.
Information on NuSTAR SINGS can be found here:
https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/
NuSTAR is a NASA Small Explorer mission led by Caltech and managed by JPL for NASA’s Science Mission Directorate in Washington.
GCN Circular 40131
Subject
GRB 250320B: cubesat Avion detection
Date
2025-04-10T08:46:40Z (2 months ago)
From
Andrey Bogomolov at Moscow State University <aabboogg@srd.sinp.msu.ru>
Via
Web form
A. Bogomolov, V. Bogomolov, A. Iyudin, S. Svertilov, N. Vasiliev
on behalf of the MSU “Sozvezdie-270” team, report:
At 2025-03-20 ~23:15:22 UT the long-duration GRB 250320B (Fermi GBM detection: GCN #39792; SVOM detection: GCN #39813, AstroSat CZTI detection: GCN #39808) was detected by the DeCoR-1 instrument on the cubesat Avion of the Moscow University project “Constellation-270” [1].
Total amount of photons detected by Avion is 1350 (energy band 40-500 keV), it corresponds to a fluence of ~6*10^(-6) erg/cm^2 in the range 40-500 keV.
LC in the energy range of 40-500 keV has two main episodes with a maximum flux of ~5.8 phot/(cm^2*s) in the 1st peak with a duration of ~13 s, and ~5.2 phot/(cm^2*s) in the 2nd peak with a duration of ~11 s.
А total duration (T90) of the burst is ~78 s.
The light curve obtained by Avion is available here:
https://swx.sinp.msu.ru/models/grb_cat/data/pictures/GRB20250320_Avion_DeCoR1_s.png
Parameters of GRB 250320B as well as other GRBs detected by Moscow University cubesats are listed at: https://swx.sinp.msu.ru/models/grb_cat/grb.php?lang=en
Avion is one of 5 cubesats of the Moscow University project “Constellation-270” [1] launched on 2023 June 27. The payload of Avion is a set of scintillation gamma-ray detectors DeCoR [2], the energy range is >30 keV, the time resolution is 0.5s.
[1] Svertilov et al. 2023 https://link.springer.com/chapter/10.1007/978-3-031-50248-4_21
[2] Bogomolov et al. 2022 Universe 8, 282 https://www.mdpi.com/2218-1997/8/5/282