The Nature of the X-Ray Point Source in the Bar of NGC 6822

Details The Nature of the X-Ray Point Source in the Bar of NGC 6822 The Nature of the X-Ray Point Source in the Bar of NGC 6822

May 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997aas...190.0201e&link_type=abstract

American Astronomical Society, 190th AAS Meeting, #02.01; Bulletin of the American Astronomical Society, Vol. 29, p.779

Astronomy and Astrophysics

Astronomy

Scientific paper

We have analysed archival ROSAT PSPC and Einstein HRI data for the x-ray point source in the bar of the Local Group dwarf irregular galaxy NGC 6822. The source decreased in x-ray flux by roughly an order of magnitude in the 13 years between the HRI and PSPC observations. It has a PSPC flux of f_X ~ 8 x 10(-14) erg cm(-2) s(-1) in the 0.2--2 keV band, giving L_X ~ 2.4 x 10(36) erg s(-1) for a distance of 500 kpc. The x-ray position is within the isophotes of the optical emission-line object Ho 12. It is unclear if Ho 12 is an \ion {H} {2} region or a supernova remnant, although the SNR interpretation is better supported by the available optical data. The x-rays are unlikely to be direct emission from an SNR, due to the observed strong x-ray variability. The x-ray spectrum of the source is very soft. Acceptable fits are found for either a Raymond-Smith thermal model with kT~0.56 keV, or a blackbody model with kT~0.06 keV. The latter model would place the source amongst the class of Super-Soft x-ray sources first found in the Magellanic Clouds. If the thermal model is correct, the source appears similar to Galactic and Magellanic Cloud stellar-mass black hole binary candidates. We have identified a list of potential optical counterparts from published photometry. However, for either model discussed above, we expect the apparent magnitude of the optical counterpart to be in the range 21.5 la m_V la 24.0. Thus the optical counterpart may be below the limit of published photometry.

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