GRB 260415B
GCN Circular 44371
Subject
GRB 260415B: CALET Gamma-Ray Burst Monitor detection
Date
2026-04-21T09:51:16Z (3 days ago)
From
Yuta Kawakubo at Aoyama Gakuin University <kawakubo@phys.aoyama.ac.jp>
Via
Web form
P. S. Marrocchesi (U of Siena), A. Yoshida, T. Sakamoto, S. Sugita,
Y. Kawakubo (AGU), K. Yamaoka (Nagoya U), S. Nakahira (JAXA),
Y. Asaoka (ICRR), S. Torii, Y. Akaike, K. Kobayashi (Waseda U), Y. Shimizu,
T. Tamura (Kanagawa U), N. Cannady (GSFC), M. L. Cherry (LSU),
S. Ricciarini (U of Florence),
and the CALET collaboration:
The CALET Gamma-ray Burst Monitor (CGBM) detected GRB 260415B
(Fermi GBM Final Real-time Localization: Fermi GBM team, GCN #44300;
NuSTAR detection: Waratkar et al., GCN #44302; Glowbug gamma-ray
detection: Woolf et al., GCN #44313) at 02:28:55.55 UTC on 15 April 2026
(https://cgbm.calet.jp/cgbm_trigger/flight/1460255329/index.html).
The burst signal was seen by all CGBM detectors.
The burst light curve shows a multi-peaked structure starting
at T-2.9 s, peaking at T+22.1 s, and ending at T+124.5 s.
The T90 and T50 durations measured with the SGM data are 111.6 +/- 1.8 s
and 50.7 +/- 1.0 s (40-1000 keV), respectively.
The ground-processed light curve is available at
https://cgbm.calet.jp/cgbm_trigger/ground/1460255329/
The CALET data used in this analysis were provided by
the Waseda CALET Operation Center located at Waseda University.
GCN Circular 44313
Subject
GRB 260415B: Glowbug gamma-ray detection
Date
2026-04-16T13:41:43Z (8 days ago)
From
Richard S. Woolf at US Naval Research Laboratory <richard.s.woolf.civ@us.navy.mil>
Via
Web form
R. Woolf, C.C. Cheung, 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, reports the detection of GRB 260415B, which was also detected by Fermi GBM (GCN 44300), NuSTAR (GCN 44302), and CALET (Trigger ID No. 1460255329).
Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2026-04-15 02:25:27.664 with a duration of 272.2 s and a total significance of about 33.0 sigma. The light curve comprises an initial peak at T0, followed by secondary emission, exhibiting four distinct peaks, spanning from ~T0+200s to ~T0+272s.
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
[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.
GCN Circular 44302
Subject
GRB 260415B: NuSTAR detection of long prompt emission
Date
2026-04-15T22:13:57Z (8 days ago)
From
Gaurav Waratkar at Caltech <gauravwaratkar@iitb.ac.in>
Via
Web form
G. Waratkar (Caltech) and B. Grefenstette (Caltech) report 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-duration GRB 260415B in both the NuSTAR CsI anti-coincidence shields. Details of the search algorithm will be described in a future paper.
The NuSTAR SINGS algorithm, triggered at 2026-04-15T02:28:55.54 UTC, shows a detection of GRB 260415B, also detected by Fermi/GBM (Fermi GBM Team, GCN 44300) and CALET/GBM (Trigger 1460255329).
The NuSTAR CsI shield data are recorded at 1 Hz. We detect a ~30-s burst followed by a ~20-s burst after a ~20-s gap, consistent with CALET/GBM and the broad bright Fermi/GBM peak at ~200 s post-trigger. The peak count rate is ~1500-cps with a baseline rate of ~1000-cps during this time period. We do not see evidence in the signal above 100 keV in the CZT detectors.
The Fermi/GBM localization (GCN 44300) at RA = 229.43, Dec = 24.94 implies an offset from the NuSTAR boresight of 71-deg (i.e. from the side of the instrument) and an offset from the geocenter of 107-deg.
Lightcurves and analysis for this GRB can be found here:
https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2026/260415B
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.
GCN Circular 44300
Subject
GRB 260415B: Fermi GBM Final Localization
Date
2026-04-15T05:51:24Z (9 days ago)
From
Lorenzo Scotton at UAH <lscottongcn@outlook.com>
Via
Web form
The Fermi GBM team reports the detection of a likely LONG GRB
"At 02:25:33.80 UT on 15 April 2026, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 260415B (trigger 797912738/260415101).
The on-ground calculated location, using the Fermi GBM trigger data,
is RA = 229.43, Dec = 24.94 (J2000 degrees, equivalent to J2000 15h 18m, +24d 56'),
with a statistical uncertainty of 9.03 degrees.
The angle from the Fermi LAT boresight is 41 degrees.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260415101/quicklook/glg_skymap_all_bn260415101.png
The HEALPix FITS file, including the estimated localization systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260415101/quicklook/glg_healpix_all_bn260415101.fit
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260415101/quicklook/glg_lc_medres34_bn260415101.gif"