A Multiwavelength Study of 1WGA J1346.5−6255: A New γ Cas Analog Unrelated to the Background Supernova Remnant G309.2−00.6

Abstract

1WGA J1346.5-6255 is a ROSAT X-ray source found within the radio lobes of the supernova remnant (SNR) G309.2-00.6. It appears to coincide with the bright and early-type star HD 119682, in the galactic open cluster NGC 5281. Its radio morphology, consisting of two brightened and distorted arcs of emission on opposite sides of the 1WGA J1346.5-6255 source and of a jetlike feature and break in the shell, suggest that lWGA J1346.5-6255/G309.2-00.6 is a young analog of the microquasar powering the W50 nebula SS 433. This motivated us to study this source at X-ray and optical wavelengths. We present new Chandra observations of lWGA J1346.5-6255, archival XMM-Newton observations of G309.2-00.6, and optical spectroscopic observations of HD 119682, to search for X-ray jets from 1WGA J1346.5-6255, study its association with the SNR, and test for whether HD 119682 represents its optical counterpart. We find no evidence for jets from 1WGA J1346.5-6255 down to an unabsorbed flux of 2.6 × 10-13 ergs cm-2 s (0.5-7.5 keV), we rule out its association with G309.2-00.6, and we confirm that HD 119682 is its optical counterpart. We derive a distance of 1.2 ± 0.3 kpc, consistent with the distance estimate to NGC 5281 (1.3 ± 0.3 kpc), and much smaller than the distance derived to G309.2-00.6. We discuss the nature of the source, unveil that HD 119682 is a Be star, and suggest it is a new member of the recently proposed group of Cas analogs. The Chandra and XMM-Newton X-ray light curves show variability on timescales of hundreds of seconds, and the presence of a possible period of ∼500 s that could be the rotational period of an accreting neutron star or white dwarf in this γ Cas analog. © 2007. The American Astronomical Society. All rights reserved.