GCN Circular 41498
Subject
IPN triangulation of GRB 250821B (long/bright)
Event
Date
2025-08-22T15:46:04Z (a month ago)
From
Dmitry Svinkin at Ioffe Institute <svinkin@mail.ioffe.ru>
Via
Web form
A.S. Kozyrev, D.V. Golovin, M.L. Litvak, I.G. Mitrofanov, and A.B. Sanin
on behalf of the HEND/Mars Odyssey team,
D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia,
and T. Cline on behalf of the Konus-Wind team,
A. Goldstein, M. S. Briggs, C. Wilson-Hodge,
and E. Burns on behalf of the Fermi GBM 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 bright, long-duration GRB 250821B
(Ferm-GBM detection: The Fermi GBM team, GCN 41473;
Smith and Meegan, GCN 41477;
BALROG localization: Preis and Greiner, GCN 41475;
SVOM-GRM detection: Tan et al., GCN 41486)
was detected by Fermi (GBM trigger 777485272), SVOM (GRM),
Konus-Wind, and Mars-Odyssey (HEND), at about 58067 s UT (16:07:47).
We have triangulated it to a preliminary, 3 sigma error box
whose coordinates are:
---------------------------------------------
RA(2000), deg Dec(2000), deg
---------------------------------------------
Center:
29.373 (01h 57m 30s) -82.081 (-82d 04' 51")
Corners:
26.171 (01h 44m 41s) -82.255 (-82d 15' 19")
32.420 (02h 09m 41s) -81.925 (-81d 55' 30")
32.427 (02h 09m 42s) -81.883 (-81d 52' 58")
26.212 (01h 44m 51s) -82.213 (-82d 12' 48")
---------------------------------------------
The error box area is 127 sq. arcmin, and its maximum
dimension is 56 arcmin (the minimum one is 2 arcmin).
The Sun distance was 106 deg.
This localization may be improved.
The IPN localization is consistent with, but reduces the area of,
the Fermi-GBM (GCN 41473) and BALROG (GCN 41475) localizations.
A triangulation map and HEALPix FITS file are posted at
http://www.ioffe.ru/LEA/GRBs/GRB250821_T58069/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.