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Paper: Microquasars
Volume: 300, Radio Astronomy at the Fringe
Page: 105
Authors: Dhawan, V.
Abstract: Microquasars are here taken to be accreting stars with relativistic jets. The accretion disks emit thermal X-rays of a few keV, often with a power-law tail to higher energies, attributed to Compton up-scattering by relativistic electrons. These electrons in turn may produce synchrotron emission—radio, IR, even X-rays. About a dozen jet sources are now established in the Galaxy, with some 30 more neutron stars and black holes detected in sporadic radio monitoring, out of ∼300 X-ray binaries. Many are found by high-energy satellites, and are essentially transients, though timescales range from days to years.

Selected recent VLBA observations are reviewed. The VLBA provides rapid response to transients, by dynamic scheduling; multi-frequency coverage; and easy phase-referencing, with ∼1 mJy detectability and ∼1 mas astrometry. For a few objects, very rich data sets have resulted from the confluence of radio imaging, X-ray light curves from RXTE, and spectroscopy from Chandra. The time variations of disk, corona, and radio jets show the interplay of accretion and ejection in these systems. Such ‘laboratory quality’ data is more readily had for galactic objects, compared to distant, slowly varying AGN. The problems of imaging time-variable, moving sources await the sensitivity and snapshot coverage of the EVLA, and the New Mexico Array, respectively. SKA users can look forward to the whole iceberg.
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