GRB 260424B

M. Tembhurnikar (IUCAA), Harsha K. H. (IUCAA), S. Salunke (IUCAA), A. Goyal (IITB), A. Arya (IITB), U. Pathak (IITB), G. Waratkar (Caltech/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 short GRB 260424B which was also detected by SVOM/GRM (Wang et al., GCN Circ. 44410
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 ), IPN triangulation (Kozyrev et al., GCN Circ. 44411
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 ), Konus-Wind (Ridnaia et al., 44416), and Glowbug (Cheung et al., 44418).

The source was clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2026-04-24 23:37:24.97 UTC. The measured peak count rate associated with the burst is 646 (+75, -82) counts/s above the background in the combined data of all quadrants, with a total of 685 (+158, -170) counts. The local mean background count rate was 1368 (+14, -15) counts/s.  Due to the intrinsic 1 s binning of veto data, we cannot reliably estimate a T90 for our detection.

The source was also faintly detected in the CZT detectors in the 20-200 keV energy range.

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 data products like interactive and downloadable light curves for this GRB can be found at:
https://astrosat.iucaa.in/cift/cift_products/514769843.98/S514769843.98_details.html

CZTI GRB detections are reported regularly on the payload site at: http://astrosat.iucaa.in/czti/?q=grb

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 [1,2,3], operating on the International Space Station, confirms the detection of the short burst GRB 260424B, which was detected by SVOM/GRM (GCN 44410
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 ), Konus-Wind (GCN 44416
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 ), Mars-Odyssey (HEND), with an IPN triangulation (GCN 44411
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 ).

The burst onset is at 2026-04-24 23:37:24.0 with a burst duration of ~0.6.  The lightcurve comprises a double-peaked structure.

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 and operated until 2024 April when it was put in safe storage on orbit. Glowbug was removed from storage and resumed operation on 2025 September 12.

[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] Woolf, R.S. et al. 2024, Proc. SPIE, 13151, id. 1315108

Distribution Statement A: Approved for public release.  Distribution is unlimited.

Massimiliano Lincetto (CPPM), Fredd Sánchez Álvarez (UNAM), Rosa L. Becerra (UNAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM) report:

We imaged the field of GRB 260424B (SVOM/GRM Team et al., GCN Circ. 44410
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 ; Kozyrev et al., GCN Circ. 44411
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 ; Fermi GBM Team GCN Circ. 44413
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 ; Ridnaia et al., GCN Circ. 44416
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 ) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-04-28 10:43 to 11:45 UTC (from 3.80 to 3.84 days after the trigger) and obtained 48 minutes of simultaneous exposure in the i/z filters.

The data were reduced and coadded with COLIBRÍ ASU pipeline and analysed in STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction.

In the stacked image, and after performing image subtraction against PanSTARRS DR1 templates, we do not detect any new source at the IPN region (Kozyrev et al., GCN Circ. 44411
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 ) down to the following 5-sigma limits:

i > 22.6
z > 21.9

Our images also include the bright galaxy PSO J348.1125+41.2291, centered at RA, Dec = 348.1125, 41.2290, with reported magnitudes of g=17.03, r=16.25, i=15.90, and z=15.61. This galaxy is just outside the IPN region. However, in image-subtraction analysis, we find no evidence for any additional component in the galaxy.

We thank Chenwei Wang (SVOM/GRM) for the helpful communication, and the IPN team for their rapid analysis and prompt release of a refined position, which facilitated the observations of the region.

We thank the staff of the Observatorio Astronómico Nacional at Sierra de San Pedro Mártir, as well as the technical and engineering teams at CEA, CPPM, IRAP, LAM, OHP, OSU Pytheas, and UNAM.

COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico.

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

The short-duration GRB 260424B
(SVOM/GRM detection: Wang et al., GCN Circ. 44410
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 ;
IPN triangulation: Kozyrev et al., GCN Circ. 44411
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 )
triggered Konus-Wind at T0=85042.824 s UT (23:37:22.824).

The burst light curve shows a multipeaked structure 
which starts at ~T0-0.1 s and has a total duration of ~0.6 s.
The emission is seen up to ~3 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB260424_T85042/

As observed by Konus-Wind, the burst
had a fluence of 3.02(-0.30,+0.33)x10^-6 erg/cm2,
and a 16-ms peak flux, measured from T0+0.198 s,
of 1.89(-0.35,+0.38)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+0.256 s)
is best fit in the 20 keV - 10 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -0.67(-0.14,+0.16)
and Ep = 756(-131,+170) keV (chi2 = 25/41 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.0
(chi2 = 24/40 dof).

All the quoted errors are at the 68% confidence level.
All the quoted values are preliminary.

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

E. Burns on behalf of the IPN,

C. Wang (IHEP), S. Xiong (IHEP), S. Zhang (IHEP),
J. Wei (NAOC),  B. Cordier (CEA) on behalf of the SVOM-GRM 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 short-duration GRB 260424B
(SVOM/GRM detection: Wang et al., GCN Circ. 44410
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 )
was detected by Konus-Wind, SVOM (GRM), and
Mars-Odyssey (HEND) at about 85042 s UT (23:37:22).

We have triangulated it to a preliminary, 3 sigma error box
whose coordinates are:
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  RA(2000), deg                 Dec(2000), deg
 ---------------------------------------------
 Center:
  348.155 (23h 12m 37s) +41.208 (+41d 12' 30")
 Corners:
  348.267 (23h 13m 04s) +41.301 (+41d 18' 04")
  348.022 (23h 12m 05s) +41.176 (+41d 10' 32")
  348.027 (23h 12m 06s) +41.107 (+41d 06' 24")
  348.272 (23h 13m 05s) +41.232 (+41d 13' 56")
 ---------------------------------------------
The error box area is 47 sq. arcmin, and its maximum
dimension is 16 arcmin (the minimum one is 3.5 arcmin).
The Sun distance was 48 deg.

A triangulation map and HEALPix FITS file are posted at
http://www.ioffe.ru/LEA/GRBs/GRB260424_T85042/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.

SVOM/GRM team: Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP)
SVOM/ECLAIRs team: Frédéric Daigne (IAP)
Report on behalf of the SVOM team:

SVOM/GRM was triggered in-flight by a short burst GRB 260424B (SVOM trigger reference: sb26042404) at 2026-04-24T23:37:25.500 UTC (T0), which is also detected by Konus-Wind. 

With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a weak soft precursor followed by main emission with a T90 of 1.4 +0.6/-0.5 s in the 15-5000 keV band. 

The SVOM/GRM light curve can be found here:
https://www.bursthub.cn//admin/static/svgrb260424B.png

The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS.

The SVOM point of contact for this burst is: Chen-Wei Wang (IHEP)(cwwang@ihep.ac.cn)