EDP Sciences
Free access
Volume 397, Number 2, January II 2003
Page(s) 635 - 643
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20021527

A&A 397, 635-643 (2003)
DOI: 10.1051/0004-6361:20021527

Models for the positive latitude e -e + annihilation feature

P. von Ballmoos1, N. Guessoum2, P. Jean1 and J. Knödlseder1

1  Centre d'Étude Spatiale des Rayonnements, 9 Av. du Colonel Roche, 31028 Toulouse Cedex, France
2  American University of Sharjah, College of Arts & Sciences, Physics Unit, Sharjah, UAE

(Received 2 August 2002 / Accepted 10 October 2002)

Galactic maps of e -e + annihilation radiation based on CGRO-OSSE, SMM and TGRS data have indicated the existence of an extended component at positive Galactic latitudes ( $l\approx -2 ^{\circ}$, $b\approx 7 ^{\circ}$), in addition to the emission from the galactic bulge and disk (Purcell et al. 1997; Cheng et al. 1997; Milne et al. 2000; Milne et al. 2001). This Positive Latitude Enhancement (PLE) was first attributed to an "annihilation fountain" in the Galactic center (Dermer & Skibo 1997) but has since been the object of several models.

After discussing the observational evidence for the PLE, we investigate various models for the PLE: besides the scenarios proposed in the literature, we have introduced a number of models requiring relatively modest positron rates due to a local origin of the e -e + emission (local galactic-, solar system-, earth- and spacecraft-environment origins). The various scenarios for the PLE are constrained in the light of the latest OSSE-SMM-TGRS data analysis results: we have looked at the possible positron production mechanisms as well as the annihilation conditions in the different physical environments (temperature and dust grain content) proposed for the positive-latitude region. By constraining those parameters, based on the recent limits for the line width and the positronium fraction, we found that some of the models can essentially be discarded. A number of other scenarios will have to await further measurements and maps, such as will be possible with INTEGRAL's SPI and IBIS instruments. We present a table/checklist of model-falsification criteria.

Key words: elementary particles -- ISM: bubbles -- ISM: clouds -- ISM: supernova remnants

Offprint request: P. von Ballmoos, pvb@cesr.fr

SIMBAD Objects

© ESO 2003