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Title: Radio detections of the neutron star X-ray binaries 4U 1820 - 30 and Ser X-1 in soft X-ray states
Author: Migliari, Simone
Fender, R. P.
Rupen, M.
Wachter, S.
Jonker, P. G.
Homan, J.
Van der Klis, M.
Keywords: Estels binaris de raigs X
Estels de neutrons
Astronomia de raigs X
X-ray binaries
Neutron stars
X-ray astronomy
Issue Date: Jun-2004
Publisher: Royal Astronomical Society
Abstract: We present the analysis of simultaneous X-ray (RXTE) and radio (VLA) observations of two atoll-type neutron star X-ray binaries: 4U 1820 - 30 and Ser X-1. Both sources were steadily in the soft (`banana') X-ray state during the observations. We have detected the radio counterpart of 4U 1820 - 30 at 4.86 and 8.46 GHz at a flux density of ~0.1 mJy. This radio source is positionally coincident with the radio pulsar PSR 1820 - 30A. However, the radio emission of the pulsar falls rapidly with frequency (~ν-3), and we argue that the radio emission of the X-ray binary is dominant above ~2 GHz. Supporting this interpretation, comparison with previous observations reveals variability at the higher radio frequencies that is likely to be due to the X-ray binary. We have detected for the first time the radio counterpart of Ser X-1 at 8.46 GHz, also at a flux density of ~0.1 mJy. The position of the radio counterpart has allowed us to identify its optical counterpart unambiguously. We briefly discuss similarities and differences between the disc-jet coupling in neutron star and black hole X-ray binaries. In particular, we draw attention to the fact that, contrary to other states, neutron star X-ray binaries seem to be more radio-loud than persistent black hole candidates when the emission is `quenched' in the soft state.
Note: Reproducció del document publicat a:
It is part of: Monthly Notices of the Royal Astronomical Society, 2004, vol. 351, num. 1, p. 186-192
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ISSN: 0035-8711
Appears in Collections:Articles publicats en revistes (Física Quàntica i Astrofísica)

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