GRB 240501B

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 long-duration GRB 240501B. Inspection of INTEGRAL/SPI-ACS data also showed the detection of the burst.

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 2024-05-01 10:43:40.5 UTC. The measured peak count rate associated with the burst is 496 (+47, -49) counts/s above the background in the combined data of three quadrants (out of four), with a total of 3754 (+358, -332) counts. The local mean background count rate was 352 (+2, -4) counts/s. Using cumulative rates, we measure a T90 of 27 (+2, -1) s. 

It 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 2024-05-01 10:43:40.3 UTC. The measured peak count rate is 889 (+87, -51) counts/s above the background in the combined Veto data of all quadrants, with a total of 6798 (+706, -707) counts. The local mean background count rate was 1539 (+5, -6) counts/s. We measure a T90 of 28 (+3, -2) 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 

M. Dafcikova, J. Ripa, M. Kolar (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, 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 240501B (AstroSat/CZTI detection: GCN 36360
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 ; INTEGRAL/SPI-ACS peak detection at 2024-05-01 ~10:43:41 UT) 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 2024-05-01 10:43:31.9 UTC. The T90 duration measured by GRBAlpha is 33.5 s and the overall significance during T90 reaches 30 sigma.

The light curve obtained by GRBAlpha is available here: https://grbalpha.konkoly.hu/static/share/GRB240501B_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. 

A.S. Kozyrev, D.V. Golovin, M.L. Litvak, I.G. Mitrofanov, and A.B. Sanin
on behalf of the HEND/Mars Odyssey team,

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

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

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)
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 long-duration GRB 240501B
(AstroSat CZTI detection: Waratkar et al., GCN 36360
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 ;
GRBAlpha detection: Dafcikova et al., GCN 36374
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 )
was detected by INTEGRAL (SPI-ACS), Konus-Wind,
AstroSat (CZTI), GRBAlpha, and Mars-Odyssey (HEND)
at about 38616 s UT (10:43:36).

We have triangulated it to a preliminary, 3 sigma error box
whose coordinates are:
 ---------------------------------------------
  RA(2000), deg                 Dec(2000), deg
 ---------------------------------------------
 Center:
  265.232 (17h 40m 56s) +27.954 (+27d 57' 15")
 Corners:
  265.021 (17h 40m 05s) +32.390 (+32d 23' 24")
  265.108 (17h 40m 26s) +32.347 (+32d 20' 48")
  265.394 (17h 41m 34s) +23.414 (+23d 24' 51")
  265.314 (17h 41m 15s) +23.466 (+23d 27' 56")
 ---------------------------------------------
The error box area is 2315 sq. arcmin, and its maximum
dimension is 9.0 deg (the minimum one is 4 arcmin).
The Sun distance was 115 deg.

This localization is consistent with the 
GBM-HEND annulus (180.767 1.045 84.864 0.509)
and the Fermi-GBM final localization (The Fermi GBM Team, GCN 36359
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 )
reported for the GRB 240501A (occurred ~660 s after GRB 240501B),
indicating that GRB 240501B and GRB 240501A are likely distinct 
emission episodes of the same ultra-long GRB.

This localization may be improved.

A triangulation map and HEALPix FITS file are posted at
http://www.ioffe.ru/LEA/GRBs/GRB240501_T38616/IPN/

The Konus-Wind time history and spectrum will be given
in a forthcoming GCN Circular.