High energy processes in microquasars

Microquasars are X-ray binary stars with the capability to generate relativisticjets. It is expected that microquasars are gamma-ray sources, because of the analogy with quasars and because the theoretical models predict emission at such energy range. In addition, from observational arguments, there are two microquasars that appear as the possible counterparts for two unidentified high-energy gamma-ray sources.Comment: Universitat de Barcelona, Departament d'Astronomia i Meteorologia, 12 pages, 5 figures. Invited talk presented at the International Symposium "High-Energy Gamma-Ray Astronomy", 26-30 July 2004, Heidelberg (Germany). To be published by AIP Proceedings Serie

Microquasars as high-energy gamma-ray sources

Galactic microquasars are certainly one of the most recent additions to the field of high energy astrophysics and have attracted increasing interest over the last decade. However, the high energy part of the spectrum of microquasars is the most poorly known, mainly due the lack of sensitive instrumentation in the past. Microquasars are now primary targets for all of the observatories working in the X-ray and gamma-ray domains. They also appear as the possible counterparts for some of the unidentified sources of high-energy gamma-rays detected by the experiment EGRET on board the satellite COMPTON-GRO. This paper provides a general review of the main observational results obtained up to now as well as a summary of the scenarios for production of high-energy gamma-rays at the present moment.Comment: Invited talk presented at the V Microquasar Workshop, Beijing, June 2004. Accepted for publication in the Chinese Journal of Astronomy and Astrophysics. 14 pages, 9 figure

Stellar radio astrophysics

Radio emission has been detected from all the stages of stellar evolution across the HR Diagram. Its presence reveals both astrophysical phenomena and stellar activity which, otherwise, would not be detectable by other means. The development of large, sensitive interferometers has allowed us to resolve the radio structure of several stellar systems, providing insights into the mass transfer process in close binary systems. I review the main characteristics of the radio emission from several kinds of stars, paying special attention to those cases where such an emission originates in relativistic jets.Comment: 20 pages, 6 figures. Talk presented at the JENAM-2003 Symposium, "Radio Astronomy at 70: from Karl Jansky to microjansky", Budapest, Hungary, 27-30 August 2003. To be published by EDP Sciences, eds. L. Gurvits, S. Frey, and S. Rawling

A possible black hole in the gamma-ray microquasar LS 5039

The population of high energy and very high energy gamma-ray sources, detected with EGRET and the new generation of ground-based Cherenkov telescopes, conforms a reduced but physically important sample. Most of these sources are extragalactic (e.g., blazars), while among the galactic ones there are pulsars and SN remnants. The microquasar LS 5039, previously proposed to be associated with an EGRET source by Paredes et al. (2000), has recently been detected at TeV energies, confirming that microquasars should be regarded as a class of high energy gamma-ray sources. To model and understand how the energetic photons are produced and escape from LS 5039 it is crucial to unveil the nature of the compact object, which remains unknown. Here we present new intermediate-dispersion spectroscopy of this source which, combined with values reported in the literature, provides an orbital period of 3.90603+/-0.00017 d, a mass function f(M)=0.0053+/-0.0009 M_sun, and an eccentricity e=0.35+/-0.04. Atmosphere model fitting to the spectrum of the optical companion, together with our new distance estimate of d=2.5+/-0.1 kpc, yields R_opt=9.3+0.7-0.6 R_sun, log (L_opt/L_sun)=5.26+/-0.06, and M_opt=22.9+3.4-2.9 M_sun. These, combined with our dynamical solution and the assumption of pseudo-synchronization, yield an inclination i=24.9+/-2.8 degree and a compact object mass M_X=3.7+1.3-1.0 M_sun. This is above neutron star masses for most of the standard equations of state and, therefore, we propose that the compact object in LS 5039 is a black hole. We finally discuss about the implications of our orbital solution and new parameters of the binary system on the CNO products, the accretion/ejection energetic balance, the SN explosion scenario, and the behaviour of the TeV emission with the new orbital period.Comment: 10 pages, 8 figures. Accepted for publication in MNRAS. Minor changes according to referee repor