A new search strategy for microquasar candidates using NVSS/2MASS and XMM-Newton data

¹ Departamento de Física (EPS), Universidad de Jaén, Campus Las Lagunillas sn, Ed-A3, 23071 Jaén, Spain e-mail: [jcombi;jmarti]@ujaen.es
² Centro Universitario Regional Zona Atlántica (CURZA), Universidad Nacional del COMAHUE, Monseñor Esandi y Ayacucho, 8500 Viedma (Rio Negro), Argentina e-mail: albacete@fcaglp.unlp.edu.ar
³ Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, Palermo 90141, Italy

Received: 16 July 2007
Accepted: 20 September 2007

Abstract

Aims.Microquasars are ideal natural laboratories for understanding accretion/ejection processes, studying the physics of relativistic jets, and testing gravitational phenomena. Nevertheless, these objects are difficult to find in our Galaxy. The main goal of this work is to increase the number of known systems of this kind, which should allow better testing of high-energy phenomena and more realistic statistical studies of this galactic population to be made.

Methods.We have developed an improved search strategy based on positional cross-identification with very restrictive selection criteria to find new MQs, taking advantage of more sensitive modern X-ray data. To do this, we made combined use of the radio, infrared, and X-ray properties of the sources, using different available catalogs.

Results.We find 86 sources with positional coincidence in the NVSS/XMM catalogs at galactic latitudes ≤ 10°. Among them, 24 are well-known objects and the remaining 62 sources are unidentified. Out of 86 sources, 31 have one or two possible infrared counterparts in the 2MASS catalog. For the fully coincident sources, whenever possible, we analyzed color–color and hardness ratio diagrams and found that at least 3 of them display high-mass X-ray binary characteristics, making them potential microquasar candidates.