GRB 240402C

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 240402C (CALET/CGBM detection: trigger no. 1396070722; INTEGRAL/SPI-ACS peak detection at 2024-04-02 ~05:29:48 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 2024-04-02 05:30:53.0 UTC. The T90 duration measured by GRBAlpha is 91.0 s and the overall significance during T90 reaches 11 sigma in the 120-400 keV band.

The light curve obtained by GRBAlpha is available here: https://grbalpha.konkoly.hu/static/share/GRB240402C_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. 

C.C. Cheung, R. Woolf, M. Kerr, J.E. Grove (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge, D. Kocevski (MSFC), and M.S. Briggs (UAH) report:
 
The Glowbug gamma-ray telescope [1,2], operating on the International Space Station, reports the detection of GRB 240402C, which was also detected by GRBAlpha (GCN 36036
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 ), INTEGRAL/SPI-ACS, and CALET/CGBM (Trigger 1396070722). 

Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2024-04-02 05:29:43.544 with a duration of 98.3 s and a total significance of about 16 sigma.  The light curve comprises an initial double-peaked structure from T0 to T0+20s, and a complex multi-peaked structure from T0+60s to T0+80s.

The analysis results presented here are preliminary and use a response function that lacks a detailed characterization of the surrounding passive structure of the ISS.
 
Glowbug is a NASA-funded technology demonstrator for sensitive, low-cost gamma-ray transient telescopes developed, built, and operated by the U.S. Naval Research Laboratory (NRL) with support from the University of Alabama in Huntsville, USRA, and NASA MSFC.  It was launched on 2023 March 15 aboard the Department of Defense Space Test Program’s STP-H9 to the ISS.  The detector comprises 12 large-area (15 cm x 15 cm) CsI:Tl panels covering the surface of a half cube, and two hexagonal (5-cm diameter, 10-cm length) CLLB scintillators, giving it a large field of view (instantaneous FoV ~2/3 sky) over a wide energy band of 50 keV to >2 MeV.
 
[1] Grove, J.E. et al. 2020, Proc. Yamada Conf. LXXI, arXiv:2009.11959
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[2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O
[3] Goldstein, A. et al. 2020, ApJ 895, 40, arXiv :1909.03006
 
Distribution Statement A: Approved for public release.  Distribution is unlimited.

Y. Asaoka (ICRR), A. Yoshida, T. Sakamoto, S. Sugita, Y. Kawakubo (AGU),
K. Yamaoka (Nagoya U), S. Nakahira (JAXA), 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 long GRB 240402C (GRBAlpha detection: Dafcikova et al., GCN Circ. 36036
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 ;
Glowbug gamma-ray detection: Cheung et al., GCN Circ. 36038
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 ) triggered
the CALET Gamma-ray Burst Monitor (CGBM) at 05:30:42.49 UTC on 2 April 2024
(http://cgbm.calet.jp/cgbm_trigger/flight/1396070722/index.html).
The burst signal was seen by all CGBM detectors.

The burst light curve shows a double-peaked structure that starts
at T-62.6 sec, peaks at T+1.6 sec, and ends at T+21.1 sec.
The T90 and T50 durations measured by the SGM data are 76.5 +/- 2.6 sec
and 53.5 +/- 1.0 sec (40-1000 keV), respectively.

The ground-processed light curve is available at

http://cgbm.calet.jp/cgbm_trigger/ground/1396070722/index.html

The CALET data used in this analysis are provided by
the Waseda CALET Operation Center located at Waseda University.