EDP Sciences
Free access
Volume 432, Number 3, March IV 2005
Page(s) 889 - 894
Section Galactic structure, stellar clusters and populations
DOI http://dx.doi.org/10.1051/0004-6361:20042215

A&A 432, 889-894 (2005)
DOI: 10.1051/0004-6361:20042215

GRBs and the 511 keV emission of the Galactic bulge

E. Parizot1, M. Cassé2, 3, R. Lehoucq2 and J. Paul2, 4

1  Institut de Physique Nucléaire d'Orsay, IN2P3-CNRS/Université Paris-Sud, 91406 Orsay Cedex, France
    e-mail: parizot@ipno.in2p3.fr
2  DAPNIA/Service d'astrophysique, CEA-Saclay, 91191 Gif-sur-Yvette, France
3  Institut d'Astrophysique de Paris, 98bis Bd Arago, 75014 Paris, France
4  Fédération de Recherche, Astroparticule et Cosmologie, Univ. Paris 7, Collège de France, 75231 Paris Cedex 05, France

(Received 20 October 2004 / Accepted 23 November 2004)

We consider the phenomenology of the 511 keV emission in the Galactic bulge, as recently observed by INTEGRAL, and propose a model in 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 $\sim $107 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 $\sim $ $8\times 10^4$ yr $\times (E_{{\rm GRB}}/10^{51}\,{\rm erg})$. We also explain the low disk-to-bulge emission ratio by noting that positrons from GRBs in the Galactic disk should be annihilated on timescales of $\la$104 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.

Key words: gamma rays: bursts -- Galaxy: bulge

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