The radio counterpart of the likely TeV binary HESS J0632+057

J L Skilton,G Dubus,J Brucker,A Marcowith,M Pandey-Pommier,F A Aharonian,Y Gallant,O Reimer,J A Hinton,C C Cheung,S Funk,A Fiasson

doi:10.1111/j.1365-2966.2009.15272.x

Abstract

The few known gamma-ray binary systems are all associated with variable radio and X-ray emission. The TeV source HESS J0632+057, apparently associated with the Be star MWC148, is plausibly a new member of this class. Following the identification of a variable X-ray counterpart to the TeV source we conducted GMRT and VLA observations in June-September 2008 to search for the radio counterpart of this object. A point-like radio source at the position of the star is detected in both 1280 MHz GMRT and 5 GHz VLA observations, with an average spectral index, alpha, of ~0.6. In the VLA data there is significant flux variability on ~month timescales around the mean flux density of ~0.3 mJy. These radio properties (and the overall spectral energy distribution) are consistent with an interpretation of HESS J0632+057 as a lower power analogue of the established gamma-ray binary systems.

Highlights

There are three firmly established >GeV emitting binaries: PSR B1259−63 (Aharonian et al 2005b), LS 5039 (Aharonian et al 2005a) and LS I+61303 (Albert et al 2006), all systems composed of a compact object and a high-mass star
One of the field sources shows significant variability both on the ∼month separation time-scale of these observations and on shorter (∼hour) time-scales. This source is located at 06h33m06s.59 ± 0.3, +05◦53 39.24 ± 0.3, and is visible both in the National Radio Astronomy Observatories (NRAO) Very Large Array (VLA) Sky Survey (NVSS) archive (1.4 GHz; Condon et al 1998) with a flux of ∼15 mJy and in the XMM–Newton image of this field
The new Giant Metrewave Radio Telescope (GMRT) data provide the best constraint on the size of the radioemitting region in MWC 148

Summary

INTRODUCTION

There are three firmly established >GeV emitting binaries: PSR B1259−63 (Aharonian et al 2005b), LS 5039 (Aharonian et al 2005a) and LS I+61303 (Albert et al 2006), all systems composed of a compact object and a high-mass star. The point-like TeV source HESS J0632+057 (Aharonian et al 2007) has been suggested as a new member of this class of objects This suggestion was based on associations with the massive star MWC 148 (HD 259440) and the unidentified ROSAT and EGRET sources 1RXS J063258.3+054857 and 3EG J0634+0521, and would imply that MWC 148 has a hidden compact companion. Significant variability was detected on time-scales of a few hours The association of this X-ray source with the TeV source (and both sources with MWC 148) seems highly likely and the spectral properties of the X-ray/γ -ray source are consistent with the known γ -ray binaries. We present new radio observations resulting in a detection of the system with both the Very Large Array (VLA) and the Giant Metrewave Radio Telescope (GMRT)

VLA data

GMRT data

DISCUSSION