GRB 250516B
GCN Circular 40469
Subject
GRB 250516B: GECAM-B detection of a bright long burst
Date
2025-05-16T19:33:50Z (13 days ago)
From
Chenwei Wang at IHEP <cwwang@ihep.ac.cn>
Via
Web form
Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team:
GECAM-B was triggered in-flight by a bright long burst GRB 250516B at 2025-05-16T06:31:34.7 UTC (denoted as T0). According to the GECAM-B light curves in about 40-6000 keV, this burst mainly consists of multiple pulses with a duration (T90) of 40.6 +0.9/-0.7 s.
The GECAM-B light curve can be found here:
https://www.bursthub.cn//admin/static/gecamgrb250516B.png
GECAM-B localized this burst to the following position (J2000):
Ra: 137.5 deg
Dec: 41.4 deg
Err: 7.0 deg (1-sigma, statistical only)
The time-averaged spectrum from T0-5 s to T0+75 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.00 +/-0.07 and the cutoff energy, parameterized as Epeak, is 367 +46/-36 keV. The event fluence (10-1000 keV) in this time interval is (2.3 +/-0.1)E-04 erg/cm^2. Thus GRB 250516B is consistent with Type II GRBs in the 'Amati' relation diagram, as shown at:
https://www.bursthub.cn//admin/static/grb250516B_amati.png
Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS).
GCN Circular 40484
Subject
GRB 250516B: NuSTAR Detection of the Prompt Emission
Date
2025-05-17T19:08:14Z (12 days 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 250516B 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 2025-05-16 06:31:39 with a resolution ~5-seconds. This is consistent with the GECAM-B reported time of 2025-05-16T06:31:34.7 (Wang et al., GCN circ. 40469).
The GRB is a broad burst with multiples peaks. The brightest has a peak count rates in the anti-coincidence shields near 4,000 cps over a baseline of ~1,000 cps. The burst is also clearly seen in the CdZnTe detectors.
Discovery report and a preliminary lightcurves for this GRB can be found here:
https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2025/250516B/
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 40489
Subject
GRB 250516B: Insight-HXMT detection
Date
2025-05-19T12:37:22Z (10 days ago)
From
Chenwei Wang at IHEP <cwwang@ihep.ac.cn>
Via
Web form
Chen-Wei Wang, Shao-Lin Xiong, and Jin-Peng Zhang report on behalf of the Insight-HXMT team:
At 2025-05-16T06:31:34.7 (T0), Insight-HXMT/HE detected the bright long burst GRB 250516B, which is also detected by GECAM-B (Wang et al., GCN #40469), NuSTAR (B. Grefenstette et al., GCN #40484) and Konus-Wind.
The Insight-HXMT/HE light curve mainly consists of multiple pulses with a T90 of 39.6 +0.3/-0.2 s.
The 1s peak rate, measured from T0+13.1 s, is 27175 cnts/sec.
The total counts from this burst is 423316 counts.
The HXMT/HE light curve can be found here:
https://www.bursthub.cn//admin/static/hxmtgrb250516B.png
All measurements above are made with the CsI detectors operating in the regular mode with the energy range of about 30-1000 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.org.
GCN Circular 40496
Subject
GRB 250516B: GRBAlpha detection
Date
2025-05-20T08:49:07Z (9 days ago)
From
Marianna Dafčíková at Masaryk University <500025@mail.muni.cz>
Via
Web form
M. Dafcikova, J. Ripa (Masaryk U.), A. Pal (Konkoly Observatory), N. Werner (Masaryk U.), M. Ohno, H. Takahashi (Hiroshima U.), L. Meszaros, B. Csak (Konkoly Observatory), N. Husarikova, F. Munz , M. Topinka, M. Duriskova, M. Kolar, L. Szakszonova, J.-P. Breuer, F. Hroch (Masaryk U.), T. Urbanec, M. Kasal, A. Povalac (Brno U. of Technology), J. Hudec, J. Kapus, M. Frajt (Spacemanic s.r.o), R. Laszlo, M. Koleda (Needronix s.r.o), M. Smelko, P. Hanak, P. Lipovsky (Technical U. of Kosice), G. Galgoczi (Wigner Research Center/Eotvos U.), Y. Uchida, H. Poon, H. Matake (Hiroshima U.), N. Uchida (ISAS/JAXA), T. Bozoki (Eotvos U.), G. Dalya (Eotvos U.), T. Enoto (Kyoto U.), Zs. Frei (Eotvos U.), G. Friss (Eotvos U.), Y. Fukazawa, K. Hirose (Hiroshima U.), S. Hisadomi (Nagoya U.), Y. Ichinohe (Rikkyo U.), K. Kapas (Eotvos U.), L. L. Kiss (Konkoly Observatory), T. Mizuno (Hiroshima U.), K. Nakazawa (Nagoya U.), H. Odaka (Univ of Tokyo), J. Takatsy (Eotvos U.), K. Torigoe (Hiroshima U.), N. Kogiso, M. Yoneyama (Osaka Metropolitan U.), M. Moritaki (U. Tokyo), T. Kano (U. Michigan) -- the GRBAlpha collaboration.
The long-duration GRB 250516B (GECAM-B detection: GCN 40469; NuSTAR detection: GCN 40484; Insight-HXMT/HE detection: GCN 40489; Wind/Konus detection trigger at 2025-05-16 06:31:32.766 UTC) was observed by the GRBAlpha 1U CubeSat (Pal et al. 2023, A&A, 677, 40; https://ui.adsabs.harvard.edu/abs/2023A%26A...677A..40P/abstract).
The detection was confirmed at the peak time 2025-05-16 06:31:54.3 UTC. The T90 duration measured by GRBAlpha is 40 s and the overall significance during T90 reaches 83 sigma.
The light curve obtained by GRBAlpha is available here: https://grbalpha.konkoly.hu/static/share/GRB250516B_GCN.pdf
All GRBAlpha detections are listed at: https://monoceros.physics.muni.cz/hea/GRBAlpha/
GRBAlpha, launched on 2021 March 22, is a demonstration mission for a future CubeSat constellation (Werner et al. Proc. SPIE 2018). The detector of GRBAlpha consists of a 75 x 75 x 5 mm3 CsI scintillator read out by a SiPM array, covering the energy range from ~50 keV to ~1000 keV. To increase the duty cycle and the downlink rate, the upgrade of the on-board data acquisition software stack is in progress. The ground segment is also supported by the radio amateur community and it takes advantage of the SatNOGS network for increased data downlink volume.
GCN Circular 40506
Subject
IPN triangulation of GRB 250516B
Date
2025-05-20T21:24:50Z (9 days ago)
From
Dmitry Svinkin at Ioffe Institute <svinkin@mail.ioffe.ru>
Via
Web form
D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia,
and T. Cline on behalf of the Konus-Wind team,
E. Burns on behalf of the IPN,
S. Barthelmy, J. Cummings, H. Krimm, D. Palmer, and A. Tohuvavohu
on behalf of the Swift-BAT team,
C. Wang, S. Xiong, S. Zheng and Y. Zhang,
on behalf of the Insight-HXMT and GECAM team,
and
M. Dafcikova, J. Ripa (Masaryk U.), A. Pal (Konkoly Observatory),
N. Werner (Masaryk U.), M. Ohno, H. Takahashi (Hiroshima U.),
L. Meszaros, B. Csak (Konkoly Observatory), F. Munz (Masaryk U.),
on behalf of the GRBAlpha team,
report:
The bright, long-duration GRB 250516B
(GECAM-B detection: Wang et al., GCN 40469;
NuSTAR-ACS detection: Grefenstette et al., GCN 40484;
Insight-HXMT-HE detection: Wang et al., GCN 40489;
GRBAlpha detection: Dafcikova et al., GCN 40496)
was detected by GECAM-B, GECAM-A, Konus-Wind, NuSTAR (ACS),
Insight-HXMT (HE), Swift (BAT), and GRBAlpha
at about 23492 s UT (06:31:32).
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:
143.08 21.29
Corners:
144.27 24.01
143.64 24.28
141.81 18.37
142.40 18.15
-------------------------------
The error box area is 4.2 sq. deg, and its maximum
dimension is 6.3 deg (the minimum one is 41 arcmin).
The Sun distance was 82 deg.
This localization may be improved.
A triangulation map and HEALPix FITS file are posted at
http://www.ioffe.ru/LEA/GRBs/GRB250516_T23492/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 40507
Subject
Konus-Wind detection of GRB 250516B
Date
2025-05-20T21:30:43Z (9 days 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 bright, long-duration GRB 250516B
(GECAM-B detection: Wang et al., GCN 40469;
NuSTAR-ACS detection: Grefenstette et al., GCN 40484;
Insight-HXMT-HE detection: Wang et al., GCN 40489;
GRBAlpha detection: Dafcikova et al., GCN 40496;
IPN triangulation: Svinkin et al., GCN 40506)
triggered Konus-Wind at T0=23492.766 s UT (06:31:32.766).
The burst light curve shows multi-peaked structure
which starts at ~T0-0.5 s and has a total duration of ~56 s.
The emission is seen up to ~10 MeV.
The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB250516_T23492/
As observed by Konus-Wind, the burst
had a fluence of 3.00(-0.07,+0.07)x10^-4 erg/cm2,
and a 64-ms peak flux, measured from T0+19.232 s,
of 2.16(-0.19,+0.19)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+60.416 s)
is best fit in the 20 keV - 15 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.80(-0.03,+0.03),
the high energy photon index beta = -2.52(-0.07,+0.06),
the peak energy Ep = 356(-10,+11) keV
(chi2 = 124/97 dof).
The spectrum near the maximum count rate
(measured from T0+18.688 to T0+19.712 s)
is best fit in the 20 keV - 15 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.82(-0.07,+0.07),
the high energy photon index beta = -2.92(-0.50,+0.26),
the peak energy Ep = 482(-37,+41) keV
(chi2 = 46/53 dof).
All the quoted errors are at the 68% confidence level.
All the quoted values are preliminary.