TITLE: GCN GRB OBSERVATION REPORT NUMBER: 2584 SUBJECT: GRB and XRF on April 27, 2004. Detection by Konus-Wind and Helicon (Coronas-F) DATE: 04/05/04 00:30:27 GMT FROM: Dmitry Frederiks at Ioffe Institute S. Golenetskii, E. Mazets, V. Pal'shin, and D. Frederiks on behalf of Konus-Wind and Helicon/Coronas-F teams, T. Cline, on behalf of the Konus GRB team, A weak GRB 040427b was detected by Konus-Wind at 20:12:36.251 UT and Helicon-Coronas-F at 20:12:36.871 UT. It had a duration of approximately 12s. In addition, 76.5 s after the GRB a short intense soft X-ray burst of different origin was detected by both instruments. It had a duration ~0.19s, fluence 7x10-7 erg/cm2 and peak flux 6x10-6 erg/(cm2 s), both in 20-100 keV range. Its spectrum can be fitted by power law with approximate photon index -4. The X-Ray burst source is located near ecliptic plane (+/- 15 deg, according to Konus-Wind data) and in anti-solar hemisphere (according to Helicon data). [GCN OPS NOTE: This Circular was delayed 3 days due to a problem caused by a recent security-tightening measure implimented by GSFC network operations. This affects only the Circulars -- the Notices continue to operate. This problem is being worked. While it is expected to be solved soon (Tuesday 04May04), Circular submission can still be processed, albeit manually, if you CC scott@milkyway.gsfc.nasa.gov. My apologies for the inconvenience.]