Letter to the Editor

AGILE detection of delayed gamma-ray emission from GRB 080514B

¹ INAF/IASF - Milano, via E. Bassini 15, 20133 Milano, Italy e-mail: giuliani@iasf-milano.inaf.it
² INAF/IASF - Roma, via del Fosso del Cavaliere 100, 00133 Roma, Italy
³ INAF/IASF - Bologna, via Gobetti 101, 40129 Bologna, Italy
⁴ INFN - Pavia, via Bassi 6, 27100 Pavia, Italy
⁵ Dip. di Fisica Nucleare e Teorica, Univ. degli Studi di Pavia, via A. Bassi 6, 27100, Pavia, Italy
⁶ Dip. di Fisica, Univ. “Tor Vergata”, via della Ricerca Scientifica 1, 00133 Roma, Italy
⁷ Dip. di Fisica and INFN Trieste, via Valerio 2, 34127 Trieste, Italy
⁸ CIFS–Torino, Viale Settimio Severo 63, 10133 Torino, Italy
⁹ ENEA, via Martiri di Monte Sole 4, 40129 Bologna, Italy
¹⁰ INFN - Roma “La Sapienza”, Piazzale A. Moro 2, 00185 Roma, Italy
¹¹ INFN - Roma “Tor Vergata”, via della Ricerca Scientifica 1, 00133 Roma, Italy
¹² Dip. di Fisica, Univ. dell'Insubria, via Valleggio 11, 22100 Como, Italy
¹³ ENEA - Roma, via E. Fermi 45, 00044 Frascati (Roma), Italy
¹⁴ ASI, Viale Liegi 26, 00198 Roma, Italy
¹⁵ ASI - ASDC, via G. Galilei, 00044 Frascati (Roma), Italy
¹⁶ NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
¹⁷ Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK
¹⁸ Department of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802, USA
¹⁹ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
²⁰ University of California, Berkeley, Space Sciences Lab, 7 Gauss Way, Berkeley, CA 94720, USA
²¹ Institute for Space Research, Profsojuznaja 84/32, Moscow 117997, Russia
²² Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA

Received: 1 August 2008
Accepted: 8 September 2008

Abstract

GRB 080514B  is the first gamma ray burst (GRB), since the time of EGRET, for which individual photons of energy above several tens of MeV have been detected with a pair-conversion tracker telescope. This burst was discovered with the Italian AGILE gamma-ray satellite. The GRB was localized by a cooperation between AGILE and the interplanetary network (IPN). The gamma-ray imager (GRID) estimate of the position, obtained before the SuperAGILE-IPN localization, is found to be consistent with the burst position. The hard X-ray emission observed by SuperAGILE lasted about 7 s, while there is evidence that the emission above 30 MeV extends for a longer duration (at least 13 s). Similar behavior has been seen from a few other GRBs observed with EGRET. However, during the brightest phases, the latter measurements were affected by instrumental dead time effects, resulting in only lower limits to the burst intensity. Thanks to the small dead time of the AGILE/GRID we could assess that in the case of GRB 080514B the gamma-ray to X-ray flux ratio changes significantly between the prompt and extended emission phase.