Journal Article

The identity and position of X-ray sources in globular clusters: radio emission from NGC6712

Callanan, Paul, McHardy, Ian M., Machin, Graham, Lehto, Harry J.

1990

Overview

NINE globular clusters are known to contain luminous (L x > 10 36 erg s −1 ) X-ray sources, but because the X-ray position error boxes, a few arcseconds in size, contain many stars, optical iden-tification of the sources has not been possible, with the exception of that in NGC7078 (ref. 19). This has prevented detailed investiga-tion of the emitting objects. If the X-ray sources are similar to low-mass X-ray binaries (LMXBs) outside globular clusters, low-level radio emission would be expected 1,2 , and the detection of such radio emission would both strengthen the case that luminous globular cluster X-ray sources are LMXBs and aid optical iden-tification by means of an accurate radio position. We report here the detection of radio emission from the position of the luminous X-ray source A1850–08 (ref. 3) in the globular cluster NGC6712. The centroid of the slightly elongated radio source coincides with a previously suggested 20th magnitude stellar optical counterpart 4 . If the radio emission is synchrotron radiation, the minimum energy requirement and magnetic field strength are similar to what is found in the radio counterparts to other high-luminosity X-ray sources such as Sco X-l and Cyg X-3.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: Astronomy / Astrophysics / Emissions / Humanities and Social Sciences / letter / multidisciplinary / Science / Science (multidisciplinary) / Stars & galaxies