TITLE:   GCN CIRCULAR
NUMBER:  39652
SUBJECT: IPN triangulation of GRB 250309B
DATE:    25/03/10 13:17:34 GMT
FROM:    Dmitry Svinkin at Ioffe Institute <svinkin@mail.ioffe.ru>

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 long-duration GRB 250309B
(Fermi-GBM BALROG localization: Preis and Greiner, GCN 39629;
Fermi-GBM detection: The Fermi GBM team, GCN 39635;
McDermott et al., GCN 39642;
GECAM-B detection: Wang et al., GCN 39648)
was detected by Fermi (GBM trigger 763198715), Konus-Wind,
Mars-Odyssey (HEND), and GECAM-B at about 27510 s UT (07:38:30).

We have triangulated it to a preliminary, 3 sigma error box
whose coordinates are:
-------------------------------
  RA(2000), deg  Dec(2000), deg
 ------------------------------
 Center:
  208.8101       -12.9141
 Corners:
  204.1541       -23.3442
  204.3621       -23.0319
  213.4312        -2.9483
  213.5345        -2.5970
 -------------------------------
The error box area is 1.3 sq. deg, and its maximum
dimension is 23 deg (the minimum one is 3.5 arcmin).
The Sun distance was 135 deg.

This localization may be improved.

The IPN localization is consistent with, but reduces the area of,
the final Fermi-GBM (GCN 39635) and BALROG (GCN 39629) localizations.

A triangulation map and HEALPix FITS file are posted at
http://www.ioffe.ru/LEA/GRBs/GRB250309_T27513/IPN/
The HEALPix triangulation map is the multi-order HEALPix in units of
probability density.

The localization of IceCube-250309A (IceCube Collaboration, GCN 39631) is inconsistent with the IPN localization. The optical transient ZTF25aaitvjt/AT2025dws (Stein  et al., GCN 39639) is inside the IPN box, which further strengthen the interpretation of transient as the burst afterglow.

The Konus-Wind time history and spectrum will be given
in a forthcoming GCN Circular.