TITLE:   GCN CIRCULAR
NUMBER:  33843
SUBJECT: IPN triangulation of GRB 230518A (short)
DATE:    23/05/21 13:50:51 GMT
FROM:    Dmitry Svinkin at Ioffe Institute <svinkin@mail.ioffe.ru>

D. Svinkin, D. Frederiks, A. Ridnaia, A. Lysenko,
on behalf of the IPN,

A. Goldstein, M. S. Briggs, C. Wilson-Hodge,
and E. Burns on behalf of the Fermi GBM team,

E. Bozzo and C. Ferrigno, on behalf of the INTEGRAL SPI-ACS GRB team,

and

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


The short-duration GRB 230518A
(Fermi-GBM detection: The Fermi GBM team, GCN Circ. 33822;
Swift-BAT/GUANO detection: Ronchini, GCN Circ. 33825)
has been detected by Fermi (GBM trigger 706142972), Swift (BAT),
and INTEGRAL (SPI-ACS), so far, at about 82168 s UT (22:49:28).
The burst was outside the coded field of view of the BAT.

We have triangulated it to a GBM-SPI-ACS annulus centered at
RA(2000)=19.521 deg (01h 18m 05s) Dec(2000)=-66.594 deg (-66d 35' 40")
whose radius is 88.662 +/- 2.786 deg (3 sigma).

The annulus combined with the Fermi-GBM final position (GCN 33822;
glg_healpix_all_bn230518951_v00) gives 480 sq. deg (3 sigma) localization region.

The localization is inconsistent with the localization of the NSBH merger event candidate S230518h (LVK Collaborations, GCN Circ. 33813, 33816).

A triangulation map and HEALPix FITS file are posted at
http://www.ioffe.ru/LEA/GRBs/GRB230518_T82167/IPN/