GCN Circular 42403

Subject
IPN triangulation of GRB 251016B
Event
GRB 251016B
Date
2025-10-23T16:17:46Z (2 days 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 MGNS/BepiColombo and HEND/Mars Odyssey teams,

J. Benkhoff on behalf of the BepiColombo 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,

S. Barthelmy, J. Cummings, H. Krimm, D. Palmer, A. Tohuvavohu,
and J. DeLaunay on behalf of the Swift-BAT 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 long-duration GRB 251016B
(Ferm-GBM detection: The Fermi GBM team, GCN 42316Loading...
 
 ;
Godwin et al., GCN 42383Loading...
 
 ;
CALET-GBM detection: Yamaoka et al., GCN 42320Loading...
 
 ;
AstroSat-CZTI detection: Harsha et al., GCN 42324Loading...
 
 )
was detected by Fermi (GBM trigger 782351945), CALET (GBM),
AstroSat (CZTI), Konus-Wind, Swift (BAT), Mars-Odyssey (HEND), and
BepiColombo (MGNS), at about 86340 s UT (23:59:00).
The burst was outside the coded field of view of the BAT.

We have triangulated it to a preliminary, 3 sigma error box
whose coordinates are:
 ---------------------------------------------
  RA(2000), deg                 Dec(2000), deg
 ---------------------------------------------
 Center:
  180.582 (12h 02m 20s) +57.856 (+57d 51' 21")
 Corners:
  173.603 (11h 34m 25s) +54.048 (+54d 02' 53")
  182.331 (12h 09m 19s) +58.703 (+58d 42' 09")
  191.445 (12h 45m 47s) +61.827 (+61d 49' 37")
  178.988 (11h 55m 57s) +57.018 (+57d 01' 07")
 ---------------------------------------------
The error box area is 2295 sq. arcmin, and its maximum
dimension is 12.186 deg (the minimum one is 5 arcmin).
The Sun distance was 69 deg.

This localization may be improved.

A triangulation map and HEALPix FITS file are posted at
http://www.ioffe.ru/LEA/GRBs/GRB251016_T86340/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.