GRB 250202B

M. Dafcikova, J. Ripa (Masaryk U.), A. Pal (Konkoly Observatory), N. Werner  (Masaryk U.), M. Ohno (Hiroshima U.),  L. Meszaros, B. Csak (Konkoly Observatory), H. Takahashi (Hiroshima U.), F. Munz , M. Topinka, F. Hroch, N. Husarikova, J.-P. Breuer (Masaryk U.), J. Hudec, J. Kapus, M. Frajt, M. Rezenov (Spacemanic s.r.o), R. Laszlo (Needronix), G. Galgoczi (Wigner Research Center/Eotvos U.), N. Uchida (ISAS/JAXA), T. Enoto (Kyoto U.), Zs. Frei (Eotvos U.), Y. Fukazawa, K. Hirose, H. Matake (Hiroshima U.), S. Hisadomi (Nagoya U.), Y. Ichinohe (Rikkyo U.), L. L. Kiss (Konkoly Observatory),  T. Mizuno (Hiroshima U.), K. Nakazawa (Nagoya U.), H. Odaka (Univ of Tokyo), K. Torigoe (Hiroshima U.), P. Svoboda, V. Daniel, J. Dudas, M. Junas, J. Gromes (VZLU), I. Vertat (FEL ZCU)  -- the VZLUSAT-2/GRB payload collaboration.

The long-duration GRB 250202B (FERMI/GBM: GCN Circular 39120
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 ; AstroSat/CZTI: GCN Circular 39122
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 ; NuSTAR detection: GCN 39135
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 ; Konus/Wind detection: GCN 39149
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 ; CALET/CGBM detection: trigger no. 1422503847; INTEGRAL/SPI-ACS peak detection at 2025-02-02 ~03:57:20 UTC) was detected by the GRB detector on board of the VZLUSAT-2 3U CubeSat (https://www.vzlusat2.cz/en/).

The data acquisition was performed by the GRB detector unit no. 1. The detection was confirmed at the peak time 2025-02-02 03:57:18 UTC. The T90 duration is 87 s and the significance during T90 reaches 80 sigma.

The light curve obtained by VZLUSAT-2 is available here:
https://vzlusat2.konkoly.hu/static/share/GRB250202B_GCN_VZLUSAT2.pdf

All VZLUSAT-2 detections are listed at: https://monoceros.physics.muni.cz/hea/VZLUSAT-2/
The GRB detectors on VZLUSAT-2 are a demonstration payload for a future CubeSat constellation (Werner et al. Proc. SPIE 2018). Two GRB modules of VZLUSAT-2 are placed in a perpendicular manner and each consists of a 75 x 75 x 5 mm3 CsI scintillator read out by a SiPM array, covering the energy range from ~30 keV to ~1000 keV. VZLUSAT-2 was launched on 2022 January 13 from Cape Canaveral.

D. Frederiks, A.Lysenko, A. Ridnaia, D. Svinkin,
A. Tsvetkova,  M. Ulanov, and T. Cline,
on behalf of the Konus-Wind team, report:

The long GRB 250202B (Fermi-GBM detection: The Fermi GBM team, GCN 39120
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 ;
Bala et al., GCN 39133
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 ; AstroSat-CZTI detection: Srijan et al., GCN 39122
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 ;
NuSTAR-ACS detection: Grefenstette, GCN 39135
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 ; IPN triangulation: Svinkin et al., GCN 39144
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 )
triggered Konus-Wind (KW) at T0=14235.288 s UT (03:57:15.288).

The burst light curve consists of multiple multi-peaked emission pulses.
The total duration of the burst is ~100 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/GRB250202_T14235/

As observed by Konus-Wind, the burst had
a fluence of (2.05 ± 0.07)x10^-4 erg/cm^2 and
a 64-ms peak energy flux, measured from T0 + 2.112 s,
of (1.62 ± 0.10)x10^-5 erg/cm^2/s (both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum (measured from T0 to T0+106.240 s)
is best fit in the 20 keV - 15 MeV range
by a GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -0.87 (-0.05,+0.06),
the high energy photon index beta = -2.67 (-0.12,+0.09),
the peak energy Ep = 273 (-8,+9) keV,
chi2 = 121/97 dof.

The spectrum near the peak count rate (measured from T0 to T0+2.560 s)
is best fit in the 20 keV - 15 MeV range
by a GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -0.38 (-0.07,+0.08),
the high energy photon index beta = -3.40 (-0.72,+0.33),
the peak energy Ep = 413 (-21,+21) keV,
chi2 = 63/60 dof.

All the quoted errors are estimated at the 68% confidence level.
All the presented results are preliminary.

D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia,
and T. Cline on behalf of the Konus-Wind team,

A. Goldstein, M. S. Briggs, C. Wilson-Hodge,
and E. Burns on behalf of the Fermi GBM team,

E. Bozzo and C. Ferrigno, on behalf of the INTEGRAL SPI-ACS GRB team,

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

and

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

The bright long-duration GRB 250202B
(Fermi-GBM detection: The Fermi GBM team, GCN 39120
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 ;
Bala et al., GCN 39133
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 ;
AstroSat-CZTI detection: Srijan et al., GCN 39122
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 ;
NuSTAR-ACS detection: Grefenstette, GCN 39135
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 )
was detected by Fermi (GBM trigger 760161442), AstroSat (CZTI),
Swift (BAT), Konus-Wind, and INTEGRAL (SPI-ACS)
at about 14237 s UT (03:57:17).
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:
  344.999 (22h 60m 00s) +19.593 (+19d 35' 35")
 Corners:
  343.557 (22h 54m 14s) +22.051 (+22d 03' 04")
  347.168 (23h 08m 40s) +17.149 (+17d 08' 56")
  346.317 (23h 05m 16s) +17.129 (+17d 07' 44")
  342.644 (22h 50m 34s) +22.024 (+22d 01' 27")
 ---------------------------------------------
The error box area is 4.1 sq. deg, and its maximum
dimension is 6.5 deg (the minimum one is 41.5 arcmin).
The Sun distance was 45 deg.

This localization may be improved.

The IPN localization is consistent with, but reduces the area of,
the Fermi-GBM (GCN 39120
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 ) localization.

A triangulation map and HEALPix FITS file are posted at
http://www.ioffe.ru/LEA/GRBs/GRB250202_T14235/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. 

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 250202B in both the NuSTAR CsI anti-coincidence shields. 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 2025-02-02 03:57:12.000 (with a resolution ~5-seconds). This is consistent with the detections by Fermi (Fermi GBM Team, GCN circ. 39120
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 , 39133
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 ) and the Astrosat CTZI detection (Waratkar et al, GCN circ. 39122
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 ). The NuSTAR CsI shield data are recorded at 1 Hz. The GRB appears to be composed of multiple, significantly-detected peaks, including a second significant set of bursts roughly 90-s after the initial trigger. The total duration for the event is at least 100-s. The largest individual burst peaks at 5,000 cps, with other bursts between 2,000 and 3,000 cps. The baseline rate is a ~1,000 cps during this time period. We do not see a clear signal in the CdZnTe detectors.

Using the localization from Fermi at RA = 347.8, Dec = 16.5 implies an offset from the NuSTAR boresight of 115 deg (e.g., through the side of the instrument) and the offset from the geocenter of 114-deg

Lightcurves and analysis for this GRB can be found here:

https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2025/250202B/

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. 

S. Bala (USRA) reports on behalf of the Fermi Gamma-ray Burst Monitor Team:

"At 03:57:17.32 UT on 02 February 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 250202B (trigger 760161442/250202165).

The on-ground calculated location, using the Fermi GBM trigger data,
is RA = 347.80, Dec = 16.48 (J2000 degrees, equivalent to
J2000 23h 11m, +16d 29'), with a statistical uncertainty of 1.43 degrees.
(radius, 1-sigma containment, statistical only; there is additionally a
systematic error which we have characterized as a mixture of two Gaussians,
one with a radius of 1.8 degrees (52% contribution) and one with a radius
of 4.1 degrees (47% contribution) [A. Goldstein et al. 2020, ApJ, 895, 1]).

The angle from the Fermi LAT boresight is 128 degrees.

The GBM light curve consists of many bright peaks with a duration (T90)
of about 89 s (50-300 keV). The time-averaged spectrum
from T0-0.1 to T0+109.4 s is best fit by
a Band function with Epeak = 252 +/- 5 keV,
alpha = -0.81 +/- 0.01, and beta = -2.56 +/- 0.05.

The event fluence (10-1000 keV) in this time interval is
(1.77 +/- 0.01)E-04 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+1.7 s in the 10-1000 keV band is 43.4 +/- 0.7 ph/s/cm^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/"

S. Srijan (IITB), G. Waratkar (IITB), J. Joshi (IUCAA), 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 GRB 250202B which was also detected by Fermi/GBM (Fermi-GBM Team, GCN Circ. 39120
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 ). 

The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2025-02-02 03:57:18.0 UTC. The measured peak count rate associated with the burst is 485 (+14, -15) counts/s above the background in the combined data of all quadrants, with a total of 21162 (+462, -483) counts. The local mean background count rate was 262 (+2, -2) counts/s. Using cumulative rates, we measure a T90 of 91 (+2, -2) s. In the preliminary analysis, we find 2474 Compton events associated with this event.

It was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2025-02-02 03:57:24.5 UTC. The measured peak count rate is 750 (+7, -8) counts/s above the background in the combined Veto data of all quadrants, with a total of 30918 (+312, -410) counts. The local mean background count rate was 1195 (+1, -1) counts/s. We measure a T90 of 90 (+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

The Fermi GBM team reports the detection of a likely LONG GRB

At 03:57:17 UT on 2 Feb 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250202B (trigger 760161442.322744 / 250202165).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 347.8, Dec = 16.5 (J2000 degrees, equivalent to J2000 23h 11m, 16d 30'), with a statistical uncertainty of 1.4 degrees.

The angle from the Fermi LAT boresight is 128.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250202165/quicklook/glg_skymap_all_bn250202165.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/bn250202165/quicklook/glg_healpix_all_bn250202165.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250202165/quicklook/glg_lc_medres34_bn250202165.gif