Discovery and study of the microquasar LS 5039 and a search for new microquasars

Details Discovery and study of the microquasar LS 5039 and a search for new microquasars Discovery and study of the microquasar LS 5039 and a search for new microquasars

Nov 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002phdt.........8r&link_type=abstract

Ph. D. Thesis, Universitat de Barcelona

Computer Science

Databases

21

Microquasars, X-Rays: Binaries, Radio Continuum: Stars, Stars Individual: Ls 5039, Rx J1826.2-1450, 3Eg J1824-1514, Gamma-Rays: Observations

Scientific paper

Microquasars are X-ray binaries displaying relativistic radio jets. There are only around 15 known microquasars in our galaxy, and each one of them has allowed to gain knowledge on the accretion/ejection processes that take place near compact objects. These two facts motivated this thesis, which was focused on the discovery of new microquasars.
In the first part of the thesis we explain how we discovered the microquasar LS 5039, and the follow-up study that we conducted. The technique we used to discover this microquasar was innovative, and consisted on the search of radio counterparts of X-ray binaries in already existing catalogs. Once we had discovered the radio emission from LS 5039 we conducted interferometric radio observations with the VLA, and very long baseline interferometric observations with the VLBA, which showed the presence of relativistic jets in the system. This fact allowed us to include LS 5039 in the reduced group of known microquasars. We conducted then a multiwavelength study of the system. In the radio domain we confirmed the persistent nature of the relativistic jets in this microquasar thanks to EVN and MERLIN observations. In the optical we carried out observations with the 1.5 m OAN telescope and with the 2.5 m INT telescope, and analyzed already existing observations, which allowed us to obtain a distance to the binary system and confirm some of the orbital parameters proposed by other authors. In the X-ray domain we studied its spectrum using our observations with RXTE and BeppoSAX, and we showed that the system does not display X-ray eclipses. Finally, we discovered a possible counterpart in the high-energy gamma-ray domain, among the unidentified sources within the Third EGRET Catalog. Using all these data we have proposed a scenario and a model to explain the multiwavelength behavior of LS 5039. On the other hand, we have studied the space velocity of the binary system, which has allowed us to compute its galactic orbit in the past and discuss on the supernova explosion that originated the compact object in this microquasar.
In the second part of the thesis we explain the technique we developed to discover new microquasars, consisting in the systematic cross-identification of catalogs at different wavelengths (X-ray, radio, optical). In concrete, we used the ROSAT All Sky Bright Source Catalog in X-rays, the NRAO VLA Sky Survey in the radio, the Digitized Sky Survey in the optical and the SIMBAD and NED databases. In particular, we carried out a search of objects in the range between -5 and +5 degrees of galactic latitude, and with a declination higher than -40 degrees. At the end of this process we obtained a sample of 17 objects, of which 4 were already known microquasars. Among the remaining 13 objects, 8 were considered as high priority targets, and we conducted observations of 6 of them. In concrete, we obtained accurate positions with the VLA that allowed to find optical counterparts to all of them with the 2.2 m CAHA telescope, as well as radio spectra, which allowed to gain knowledge on each one of the sources. Finally, we observed these 6 sources using very long baseline interferometry with the EVN and MERLIN, aimed at revealing their structure at milliarcsecond scales. At the end of this study we conclude that two of these sources are good microquasar candidates in our galaxy, three are weak microquasar candidates and the remaining one is a quasar.
The microquasar phenomenon may not be as rare as it seemed before this work.

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