GCN 45196: Konus-Wind detection of GRB 260721A
2026-07-22T14:58:58.214Z | rev 0
D. Svinkin, D. Frederiks, A. Lysenko, V. Panteleeva,
A. Ridnaia, A. Tsvetkova, M. Ulanov, and T. Cline
on behalf of the Konus-Wind team, report:
The long-duration GRB 260721A
(NuSTAR-ACS detection: Grefenstette and Waratkar, GCN 45192)
triggered Konus-Wind at T0=04620.710 s UT (01:17:00.710).
The burst light curve shows a single pulse
which starts at ~T0-0.6 s and has a total duration of ~33 s (75-1200 keV).
The emission is seen up to ~2 MeV.
The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB260721_T04620/
As observed by Konus-Wind, the burst
had the total fluence of 2.03(-0.14,+0.18)x10^-5 erg/cm2,
and the 64-ms peak flux, measured from T0+1.568 s,
of 2.41(-0.44,+0.45)x10^-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).
The time-averaged spectrum of the burst
(measured from T0 to T0+33.024 s)
is best fit in the 20 keV - 10 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.48(-0.11,+0.14),
the high energy photon index beta = -2.69(-0.22,+0.19),
the peak energy Ep = 161(-11,+10) keV
(chi2 = 93/97 dof).
The spectrum near the maximum count rate
(measured from T0+0.256 to T0+8.448 s)
is best fit in the 20 keV - 10 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = 0.02(-0.15,+0.17),
the high energy photon index beta = -2.76(-0.27,+0.18),
the peak energy Ep = 196(-12,+13) keV
(chi2 = 84/82 dof).
All the quoted errors are at the 68% confidence level.
All the quoted values are preliminary.
GCN 45192: GRB 260721A: NuSTAR detection of prompt emission
2026-07-21T16:36:31.392Z | rev 0
B. Grefenstette (Caltech) and G. Waratkar (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 260721A 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 2026-07-21 01:17:08 UTC, shows a detection of GRB 260721A, also detected by Konus-Wind (Svinkin, priv. Comm & GCN notices).
The NuSTAR CsI shield data are recorded at 1 Hz. We detect a burst lasting for about 10-s. Offline analysis indicates that the burst first appeared in the NuSTAR data 6 to 7-s prior to the trigger time (with a non-barycenter corrected, offline T0 of roughly 2026-07-21T01:17:02). The peak count rate is ~2000-cps with a baseline rate of ~1000-cps during this time period. We do not see any evidence in the signal above 100 keV in the CZT detectors.
Lightcurves and analysis for this GRB can be found here:
https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2026/260721A/
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.