GRB 250322B

M. Tembhurnikar (IUCAA), 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 250322B.

The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2025-03-22 20:08:27.0 UTC. The measured peak count rate associated with the burst is 183 (+9, -10) counts/s above the background in the combined data of two quadrants (out of four), with a total of 9235 (+367, -313) counts. The local mean background count rate was 148 (+1, -1) counts/s. Using cumulative rates, we measure a T90 of 73 (+2, -2) s.

The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2025-03-22 20:08:19.9 UTC. The lightcurve shows a small precursor peak around 50 s before the main burst, which itself consists of multiple peaks. This initial feature is absent from the CZT data due to data quality issues. Due to the low intensity of the precursor, it does not impact T90 duration measurements in the Veto detector. The measured peak count rate associated with the burst is 3634 (+111, -117) counts/s above the background in the combined data of all quadrants, with a total of 150040 (+1345, -1413) counts. The local mean background count rate was 1238 (+3, -3) counts/s. We measure a T90 of 75 (+1, -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

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 250322B 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 2025-03-22 20:08:06.000 with a resolution ~5-seconds. This is consistent with the detection by AstroSat CZT (Waratkar et al., GCN circ. 39848
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 ). The NuSTAR CsI shield data are recorded at 1 Hz.

The GRB appears to be a complex, broad burst with peak count rates near 4,000 cps over a baseline of ~1,000 cps. The burst lasts for over 100-s above background. We see clear evidence for correlated >100 keV X-rays in both CdZnTe focal planes for at least one of the multiple peaks in the burst. 

Offline analysis of the CsI lightcurve shows complex features, including at least four quasi-periodic “dips” in the emission with intervals of roughly 20-s between the dips. A more detailed analysis of these features will follow.

Discovery report and a preliminary lightcurve for this GRB showing the dips can be found here:

https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2025/250322B/

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. 

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,

E. Burns on behalf of the IPN,

S. Barthelmy, J. Cummings, H. Krimm, D. Palmer, A. Tohuvavohu,
and J. DeLaunay on behalf of the Swift-BAT team,

G. Waratkar, J.Joshi, V. Bhalerao, D. Bhattacharya,
and S. Vadawale, on behalf of the Astrosat-CZTI team,

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 bright, long-duration GRB 250322B
(AstroSat-CZTI detection: Tembhurnikar et al., GCN 39848
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 ;
NuSTAR CsI shield detection: Grefenstette et al., GCN 39857
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 )
was detected by AstroSat (CZTI), NuSTAR (CsI shield),
Konus-Wind, Swift (BAT), and Mars-Odyssey (HEND)
at about 72435 s UT (20:07:15).
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:
  319.668 (21h 18m 40s) -24.964 (-24d 57' 51")
 Corners:
  319.574 (21h 18m 18s) -23.375 (-23d 22' 29")
  319.886 (21h 19m 33s) -26.698 (-26d 41' 53")
  319.642 (21h 18m 34s) -26.204 (-26d 12' 13")
  319.155 (21h 16m 37s) -22.325 (-22d 19' 29")
 ---------------------------------------------
The error box area is 2638 sq. arcmin, and its maximum
dimension is 4.4 deg (the minimum one is 12.2 arcmin).
The Sun distance was 48 deg.

This localization may be improved.

A triangulation map and HEALPix FITS file are posted at
http://www.ioffe.ru/LEA/GRBs/GRB250322_T72435/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. 

Tilak Katoch, H. M. Antia and Parag Shah from TIFR, Mumbai, India report for the LAXPC onboard AstroSat.

AstroSat LAXPC data analysis revealed the presence of a strong long duration multiple peaks complex GRB 250322B. The GRB burst profile shows that it was triggered at T0 = 20h 08m 05s UT on 22 Mar 2025, when the satellite was in a normal operating mode and well before and after the SAA region.

This multiple peak complex burst profile has been recorded by both LAXPC instruments (LAXPC10 and LAXPC20) in their respective lightcurves. The burst profile observed in these lightcurves lasted for T90 ~ 97 sec. The strongest peak measured has a count rate 526 +/- 28 count/sec in LAXPC10 above the background and 1110 +/- 36 count/sec in LAXPC20 at T0+12 sec. A precursor peak is observed by both LAXPC10 and LAXPC20 at T0-50 sec.

LAXPC20 has a nominal energy range of 3-100 keV, but due to the lower gain in LAXPC10, the energy range is approximately 15-400 keV. The background subtracted lightcurves of the LAXPC instruments with 1 sec time bin is available at the website:
https://www.tifr.res.in/~astrosat_laxpc/grb250322b.jpg

LAXPC was built by TIFR in collaboration with the Indian Space Research Organisation. The Indian Space Research Organisation funded, managed and facilitated the project.

M. Kolar, 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, L. Szakszonova, M. Duriskova, 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 250322B (AstroSat/CZTI: GCN Circular 39848
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 , NuSTAR: GCN Circular 39857
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 ) 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 2025-03-22 20:08:19 UTC . The T90 duration measured by GRBAlpha is 77.5 s and the overall significance during T90 reaches 132 sigma.

The light curve obtained by GRBAlpha is available here:
https://grbalpha.konkoly.hu/static/share/GRB250322B_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.