Optical and infrared observations of the X-ray source 1WGA J1713.4–3949 in the G347.3-0.5 SNR (original) (raw)

The isolated neutron star candidate 2XMM J104608.7-594306

Astronomy & Astrophysics, 2009

Over the last decade, X-ray observations unveiled the existence of several classes of isolated neutron stars (INSs) which are radio-quiet or exhibit radio emission with properties much at variance with those of ordinary radio pulsars. The identification of new sources is crucial in order to understand the relations among the different classes and to compare observational constraints with theoretical expectations. A recent analysis of the 2XMMp catalogue provided less than 30 new thermally emitting INS candidates. Among these, the source 2XMM J104608.7-594306 appears particularly interesting because of the softness of its X-ray spectrum and of the present upper limits in the optical, which imply a logarithmic X-ray-to-optical flux ratio greater than 3.1, corrected for absorption. We present the X-ray and optical properties of 2XMM J104608.7-594306 and discuss its nature in the light of two possible scenarios invoked to explain the X-ray thermal emission from INSs: the release of residual heat in a cooling neutron star, as in the seven radio-quiet ROSAT-discovered INSs, and accretion from the interstellar medium. We find that the present observational picture of 2XMM J104608.7-594306 is consistent with a distant cooling INS with properties in agreement with the most up-to-date expectations of population synthesis models: it is fainter, hotter and more absorbed than the seven ROSAT sources and possibly located in the Carina Nebula, a region likely to harbour unidentified cooling neutron stars. The accretion scenario, although not entirely ruled out by observations, would require a very slow (~10 km/s) INS accreting at the Bondi-Hoyle rate.

The compact central source in the RX J0852-4622 supernova remnant

2001

The central region of the recently discovered supernova remnant RX J0852.0-4622 was observed with the ACIS detector aboard the Chandra X-ray Observatory. We found only one relatively bright source, about 4' north of the SNR center, with a flux of sim2times10−12\sim 2\times 10^{-12}sim2times10−12 erg s$^{-1}$ cm$^{-2}$ in the 0.5--10 keV band. The position of this point-like source, CXOU J085201.4-461753, rules out its association with the two bright stars in the field, HD 76060 and Wray 16-30. Observations of the field with the CTIO 0.9-m telescope show a star ($R\approx 17$, Bapprox19B\approx 19Bapprox19) at about 2\farcs4 from the nominal X-ray position. We consider association of this star with the X-ray source unlikely and estimate a limiting magnitude of the optical counterpart as Bge22.5B \ge 22.5Bge22.5 and Rge21.0R \ge 21.0Rge21.0. Based on the X-ray-to-optical flux ratio, we argue that the X-ray source is likely the compact remnant of the supernova explosion that created the RX J0852.0-4622 SNR. The observed X-ray spectrum of the source is softer than spectra of magnetospheric radiation of rotation-powered pulsars, but it is harder than spectra of cooling neutron stars emitting thermal radiation from the entire surface, similar to the central compact source of the Cas A SNR. We suggest that CXOU J085201.4-461753 belongs to the growing family of radio-quiet compact central sources, presumably neutron stars, recently discovered in a number of SNRs.