TITLE:   GCN CIRCULAR
NUMBER:  29997
SUBJECT: IPN triangulation of GRB 210427A
DATE:    21/05/11 22:57:01 GMT
FROM:    Dmitry Svinkin at Ioffe Institute  <svinkin@mail.ioffe.ru>

K. Hurley, on behalf of the IPN,

I. G. Mitrofanov, D. V. Golovin, A. S. Kozyrev, M. L. Litvak,
and A. B. Sanin, on behalf of the HEND-Odyssey GRB team,

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

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

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

W. Boynton, C. Fellows, K. Harshman, H. Enos, and R. Starr,
on behalf of the GRS-Odyssey GRB team, report:

The long-duration GRB 210427A
(Fermi-GBM detection: The Fermi GBM team, GCN Circ. 29903;
BALROG localization: Biltzinger et al., GCN Circ. 29905;
GECAM detection: Xie et al., GCN Circ. 29906)
was detected by Fermi (GBM trigger 641192237), Konus-Wind,
Swift (BAT), outside the coded FoV, Mars-Odyssey (HEND),
and GECAM-B at about 17832 s UT (04:57:12).

We have triangulated it to a preliminary, 3 sigma error box
whose coordinates are:
  ---------------------------------------------
   RA(2000), deg                 Dec(2000), deg
  ---------------------------------------------
  Center:
   177.792 (11h 51m 10s) -52.866 (-52d 51' 57")
  Corners:
   176.862 (11h 47m 27s) -54.591 (-54d 35' 28")
   176.750 (11h 47m 00s) -54.533 (-54d 31' 59")
   178.678 (11h 54m 43s) -51.138 (-51d 08' 18")
   178.782 (11h 55m 08s) -51.196 (-51d 11' 46")
  ---------------------------------------------
The error box area is 1036 sq. arcmin, and its maximum
dimension is 3.6 deg (the minimum one is 4.8 arcmin).
The Sun distance was 93 deg.

This box may be improved.

The IPN localization is consistent with, but reduces the area of, the
Fermi RoboBA and BALROG localizations (GCN Circ. 29903 and 29905).
It was inside the Transiting Exoplanet Survey Satellite (TESS)
field of view.

We thank Robert Wilson for pointing out the TESS/IPN coincidence.

A triangulation map is posted at
http://www.ioffe.ru/LEA/GRBs/GRB210427_T17835/IPN/

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