GRB 250308A
GCN Circular 39632
Subject
GRB 250308A: SVOM/GRM observation of a bright short burst
Date
2025-03-09T12:40:35Z (3 months ago)
Edited On
2025-03-09T19:31:47Z (3 months ago)
From
Chenwei Wang at IHEP <cwwang@ihep.ac.cn>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Chenwei Wang at IHEP <cwwang@ihep.ac.cn>
Via
Web form
SVOM/GRM team: Chen-Wei Wang, Zheng-Hang Yu, 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 250308A (SVOM trigger reference: sb25030804) at 2025-03-08T18:06:30.9 (T0), which is also detected by CALTE/GBM (TRIGGER ID: 1425492335) and Konus-Wind.
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 1.9 +0.9/-0.8 s in the 15-5000 keV band.
The SVOM/GRM light curve can be found here:
https://www.bursthub.cn//admin/static/svgrb250308A.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/GRM point of contact for this burst is: Chen-Wei Wang (IHEP) (cwwang@ihep.ac.cn)
GCN Circular 39636
Subject
GRB 250308A: SVOM/GRM detection of QPO in the tail emission
Date
2025-03-09T16:00:23Z (3 months ago)
From
Chenwei Wang at IHEP <cwwang@ihep.ac.cn>
Via
Web form
SVOM/GRM team: Chen-Wei Wang, Wen-Jun Tan, Zheng-Hang Yu, 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:
The bright short burst, GRB 250308A (GCN #39632), consists of a narrow spike followed by a short tail emission (from T0-0.15 to T0+0.15 s), which shows a feature of QPO, with a center frequency at approximately 31 Hz.
The on-ground localization of this burst is (J2000):
RA: 170.9 deg
DEC: 25.6 deg
Error: 5.2 deg (1sigma, statistical only)
We caution that the calibration of SVOM/GRM is undergoing and this localization is subject to systematic errors.
With this localization, the time-averaged spectrum from T0-0.3 to T0+0.2 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.28 +/- 0.04 and the cutoff energy, parameterized as Epeak, is 452 +/- 56 keV. The event fluence (10-1000 keV) in this time interval is (4.9 +/- 0.2)E-06 erg/cm^2.
The feature of QPO in the tail emission and the spectrum parameters are consistent with the scenario of magnetar giant flare. Follow-up observations are strongly encouraged.
We note that these results are preliminary. Refined analysis will be reported later.
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: Chen-Wei Wang (IHEP) (cwwang@ihep.ac.cn)
GCN Circular 39653
Subject
IPN triangulation of GRB 250308A (short)
Date
2025-03-10T16:02:51Z (3 months ago)
From
Dmitry Svinkin at Ioffe Institute <svinkin@mail.ioffe.ru>
Via
Web form
A.S. Kozyrev, D.V. Golovin, M.L. Litvak, I.G. Mitrofanov, and A.B. Sanin
on behalf of the HEND/Mars Odyssey team,
D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia,
and T. Cline on behalf of the Konus-Wind team,
Y. Zhang, C. Wang, S. Xiong, J. Wei, and B. Cordier
on behalf of the SVOM-GRM team,
S. Barthelmy, J. Cummings, H. Krimm, D. Palmer, and A. Tohuvavohu
on behalf of the Swift-BAT team,
E. Burns on behalf of the IPN,
and
W. Boynton, C. Fellows, K. Harshman, H. Enos, R. Starr,
and A.S. Gardner on on behalf of the GRS-Odyssey GRB team,
report:
The short-duration GRB 250308A
(SVOM-GRM detection: Wang et al., GCN 39632, 39636)
was detected by SVOM (GRM), Konus-Wind, Swift (BAT), CALET (GBM),
and Mars-Odyssey (HEND) at about 65191 s UT (18:06:31).
The burst was outside the coded field of view of the BAT.
We have triangulated it to a preliminary, 3 sigma error box
whose coordinates are:
---------------------------------------------
RA(2000), deg Dec(2000), deg
---------------------------------------------
Center:
160.761 (10h 43m 03s) +23.741 (+23d 44' 26")
Corners:
160.858 (10h 43m 26s) +24.405 (+24d 24' 18")
160.981 (10h 43m 55s) +24.338 (+24d 20' 15")
160.655 (10h 42m 37s) +23.074 (+23d 04' 27")
160.536 (10h 42m 09s) +23.145 (+23d 08' 43")
---------------------------------------------
The error box area is 578 sq. arcmin, and its maximum
dimension is 1.3 deg (the minimum one is 7.4 arcmin).
The Sun distance was 159 deg.
This localization may be improved.
The distance between the center of SVOM (GRM) localization (GCN 39636)
and the IPN box center is 9.4 deg.
A triangulation map and HEALPix FITS file are posted at
http://www.ioffe.ru/LEA/GRBs/GRB250308_T65194/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.
GCN Circular 39663
Subject
GRB 250308A: CALET Gamma-Ray Burst Monitor detection
Date
2025-03-11T09:19:04Z (3 months ago)
From
Yuta Kawakubo at Aoyama Gakuin University <kawakubo@phys.aoyama.ac.jp>
Via
Web form
Y. Kawakubo, A. Yoshida, T. Sakamoto, S. Sugita (AGU),
K. Yamaoka (Nagoya U), S. Nakahira (JAXA), Y. Asaoka (ICRR), S. Torii,
Y. Akaike, K. Kobayashi (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U),
N. Cannady (GSFC/UMBC), M. L. Cherry (LSU), S. Ricciarini (U of Florence),
P. S. Marrocchesi (U of Siena),
and the CALET collaboration:
The short GRB 250308A (SVOM/GRM observation: the SVOM team, GCN
Circ. 39632, 39636; IPN triangulation: Kozyrev et al., GCN Circ. 39653)
triggered the CALET Gamma-ray Burst Monitor (CGBM) at 18:06:30.72
UTC on 8 March 2025
(https://cgbm.calet.jp/cgbm_trigger/flight/1425492335/index.html).
The burst signal was seen by SGM and HXM2.
The burst light curve shows a single pulse that starts
at T-0.1 sec, peaks at T+0.1 sec, and ends at T+0.3 sec.
The T90 and T50 durations measured by the SGM data are 0.4 +/- 0.2 sec
and 0.2 +/- 0.1 sec (40-1000 keV), respectively.
The ground-processed light curve is available at
https://cgbm.calet.jp/cgbm_trigger/ground/1425492335/
The CALET data used in this analysis are provided by
the Waseda CALET Operation Center located at Waseda University.
GCN Circular 39676
Subject
GRB 250308A: Swift/BAT-GUANO localization skymap of a short burst
Date
2025-03-11T20:10:54Z (3 months ago)
From
Samuele Ronchini at PSU <sjs8171@psu.edu>
Via
Web form
James DeLaunay (PSU), Samuele Ronchini (PSU), Aaron Tohuvavohu (Caltech), Gayathri Raman (PSU), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC) report:
Swift/BAT did not localize GRB 250308A onboard (T0: 2025-03-08T18:06:30.72 UTC, CALET/GBM trig 1425492335 GCN 39663, SVOM/GRM GCN 39632)
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 90 seconds of BAT event-mode data from [-45,+45] 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 32.5 in a 0.256 s analysis time bin, starting at T0 - 0.064 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 2,693 deg2 and the 50% credible area is 785 deg2.
The integrated probability inside the coded field of view is <1%.
The NITRATES skymap is consistent with the SVOM/GRM (GCN 39636) and IPN (GCN 39653) localizations.
A plot of the probability skymap can be viewed here:
[skymap_plot](https://guano.swift.psu.edu/trigger_report?id=763150025/#:~:text=Probability%20Skymap)
The probability skymap file can be downloaded from the link here
[skymap_fits_file](https://guano.swift.psu.edu/files/763150025/0_n_PROBMAP)
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=763150025
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 39720
Subject
Konus-Wind detection of GRB 250308A
Date
2025-03-14T15:54:17Z (3 months ago)
From
Dmitry Svinkin at Ioffe Institute <svinkin@mail.ioffe.ru>
Via
Web form
D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia,
A. Tsvetkova, M. Ulanov, and T. Cline
on behalf of the Konus-Wind team, report:
The short-duration GRB 250308A
(SVOM-GRM detection: Wang et al., GCNs 39632, 39636;
IPN triangulation: Kozyrev et al., GCN 39653;
CALET-GBM detection: Kawakubo et al., GCN 39663;
Swift-BAT/GUANO detection: DeLaunay et al., GCN 39676)
triggered Konus-Wind at T0=65194.997 s UT (18:06:34.997).
The burst light curve shows a multipeaked structure
which starts at ~T0-40 ms and has a total duration of ~0.4 s.
The emission is seen up to ~5 MeV.
The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB250308_T65194/
As observed by Konus-Wind, the burst
had a fluence of 8.23(-0.52,+0.54)x10^-6 erg/cm2,
and a 16-ms peak flux, measured from T0-6 ms,
of 5.24(-0.69,+0.70)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).
The time-averaged spectrum of the burst
(measured from T0 to T0+0.256 s)
is best fit in the 20 keV - 5 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with alpha = -0.41(-0.12,+0.13)
and Ep = 1176(-109,+125) keV (chi2 = 60/52 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.9
(chi2 = 60/51 dof).
All the quoted errors are at the 68% confidence level.
All the quoted values are preliminary.