TITLE:   GCN CIRCULAR
NUMBER:  40506
SUBJECT: IPN triangulation of GRB 250516B
DATE:    25/05/20 21:24:50 GMT
FROM:    Dmitry Svinkin at Ioffe Institute <svinkin@mail.ioffe.ru>

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

E. Burns on behalf of the IPN,

S. Barthelmy, J. Cummings, H. Krimm, D. Palmer, and A. Tohuvavohu
on behalf of the Swift-BAT team,

C. Wang, S. Xiong, S. Zheng and Y. Zhang,
on behalf of the Insight-HXMT and GECAM team,

and 

M. Dafcikova, J. Ripa (Masaryk U.), A. Pal (Konkoly Observatory), 
N. Werner (Masaryk U.), M. Ohno, H. Takahashi (Hiroshima U.), 
L. Meszaros, B. Csak (Konkoly Observatory), F. Munz (Masaryk U.),
on behalf of the GRBAlpha team,

report:

The bright, long-duration GRB 250516B
(GECAM-B detection: Wang et al., GCN 40469;
NuSTAR-ACS detection: Grefenstette et al., GCN 40484;
Insight-HXMT-HE detection: Wang et al., GCN 40489;
GRBAlpha detection: Dafcikova et al., GCN 40496)
was detected by GECAM-B, GECAM-A, Konus-Wind, NuSTAR (ACS),
Insight-HXMT (HE), Swift (BAT), and GRBAlpha
at about 23492 s UT (06:31:32).
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:
  143.08          21.29
 Corners:
  144.27          24.01
  143.64          24.28
  141.81          18.37
  142.40          18.15
 -------------------------------
The error box area is 4.2 sq. deg, and its maximum
dimension is 6.3 deg (the minimum one is 41 arcmin).
The Sun distance was 82 deg.

This localization may be improved.

A triangulation map and HEALPix FITS file are posted at
http://www.ioffe.ru/LEA/GRBs/GRB250516_T23492/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.