Open AccessSimultaneous radio and X‐ray observations of Galactic Centre low‐mass X‐ray binaries
Author(s) -
Berendsen Stephan G. H.,
Fender Robert,
Kuulkers Erik,
Heise J.,
Van Der Klis M.
Publication year - 2000
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2000.03850.x
Subject(s) - physics , astrophysics , astronomy , astrometry , x ray , telescope , on board , stars , remote sensing , optics , geology
We have performed simultaneous X‐ray and radio observations of 13 Galactic Centre low‐mass X‐ray binaries in 1998 April using the Wide Field Cameras on board BeppoSAX and the Australia Telescope Compact Array, the latter simultaneously at 4.8 and 8.64 GHz. We detect two Z sources, GX 17+2 and GX 5−1, and the unusual ‘hybrid’ source GX 13+1. Upper limits, which are significantly deeper than previous non‐detections, are placed on the radio emission from two more Z sources and seven atoll sources. Hardness–intensity diagrams constructed from the Wide Field Camera data reveal GX 17+2 and GX 5−1 to have been on the lower part of the horizontal branch and/or the upper part of the normal branch at the time of the observations, and the two non‐detected Z sources, GX 340+0 and GX 349+2, to have been on the lower part of the normal branch. This is consistent with the previous empirically determined relation between radio and X‐ray emission from Z sources, in which radio emission is strongest on the horizontal branch and weakest on the flaring branch. For the first time we have information on the X‐ray state of atoll sources, which are clearly radio‐quiet relative to the Z sources, during periods of observed radio upper limits. We place limits on the linear polarization from the three detected sources, and use accurate radio astrometry of GX 17+2 to confirm that it is probably not associated with the optical star NP Ser. Additionally we place strong upper limits on the radio emission from the X‐ray binary 2S 0921−630, disagreeing with suggestions that it is a Z‐source viewed edge‐on.