GRBs and the 511 keV emission of the Galactic bulge

E. Parizot (1) , M. Cassé (2, 3) , R. Lehoucq (2) , J. C. Paul (2, 4)

1 IPNO - Institut de Physique Nucléaire d'Orsay
2 DAPNIA - Département d'Astrophysique, de physique des Particules, de physique Nucléaire et de l'Instrumentation Associée
3 IAP - Institut d'Astrophysique de Paris
4 APC (UMR_7164) - AstroParticule et Cosmologie

We consider the phenomenology of the 511 keV emission in the Galactic bulge, as recently observed by INTEGRAL, and propose a model is which the positrons are produced by gamma-ray bursts (GRB) associated with mini starbursts in the central molecular zone (CMZ). We show that the positrons can easily diffuse across the bulge on timescales of about 10^7 yr, and that their injection rate by GRBs is compatible with the observed fluxes if the mean time between two GRBs in the bulge is about 8 10^4 yr x E_GRB_51. We also explain the low disk-to-bulge emission ratio by noting that positrons from GRBs in the Galactic disk should annihilate on timescales of < 10^4 yr in the dense shell of the underlying supernova remnant, after the radiative transition, while the remnants of GRBs occurring in the hot, low-density medium produced by recurrent starbursts in the CMZ become subsonic before they can form a radiative shell, allowing the positrons to escape and fill the whole Galactic bulge. If the mean time between GRBs is smaller than 10^4 E_51 yr, INTEGRAL should be able to detect the (localized) 511 keV emission associated with one or a few GRB explosions in the disk.

Mots clés: gamma rays; bursts -Galaxy; bulge

Domaines: Cosmologie et astrophysique extra-galactique [astro-ph.CO]; Astrophysique [astro-ph]

E. Parizot, M. Cassé, R. Lehoucq, J. C. Paul. GRBs and the 511 keV emission of the Galactic bulge. Astronomy and Astrophysics - A&A, 2005, 432, pp.889-894. ⟨10.1051/0004-6361:20042215⟩. ⟨in2p3-00023426⟩