Type Ia Supernova Rate in the Galactic Center Region

According to recent analyses of the type-Ia supernova rate as a function of redshift, delayed and prompt type-Ia supernovae (SN Ia) should explode respectively in the Galactic bulge and in the nuclear bulge, a gas rich structure with ongoing star formation, located in the central region of the Milky Way. We estimate the rate of type-Ia supernovae in the Galactic bulge and nuclear bulge. We show that this rate is insufficient by an order of magnitude to explain by positron escape from type-Ia supernovae envelopes alone the large positron injection rate into the Galactic central region, as re-observed recently by the Spectrometer on INTEGRAL, which amounts to 1.25 10^{43} e+ s^{-1} and would require 0.5 SN Ia explosions per century.
Comment: 5 pages, 3 figures. Accepted for publication in ESA SP-622 (Proceedings of the 6th INTEGRAL Workshop, Moscow, 2006 07 03-07)