A Soft X-Ray Study of the Large Magellanic Cloud

Abstract

A survey of the Large Magellanic Cloud (LMC) has been carried out with the imaging X-ray telescope aboard the Einstein Observatory. Ninety-seven sources were detected. On statistical grounds, we estimate that less than 25 of these are likely to be either foreground stars or background quasars. The remaining 75 sources which are in the LMC have luminosities ranging from 1 × 10³⁵ to 2 × 10³⁸ erg s⁻¹ and are heavily concentrated around the HI complex surrounding the 30 Doradus nebula. At least 25 of the sources are supernova remnants (SNR), including six nebulae that had not been previously recognized as such. Of the remaining 50 sources, about half appear to be extended and are also likely to be SNR. High resolution observations of selected remnants indicate that SNR diameters in the LMC have been consistently underestimated by radio and optical observers, an effect that reduces previous estimates of the SNR rate. However, the X-ray observations also demonstrate that previous catalogs of LMC remnants suffer considerably from incompleteness. When both effects are considered, we derive a SN rate in the LMC of 1 per 110 to 340 years. The identity of the remaining survey sources is unclear. If they are not SNR, as well, they represent a class of objects heretofore unrecognized in the galaxy — point X-ray sources with luminosities between 10³⁵ and 10³⁶ erg s⁻¹.

Work supported by NASA under contract NAS 8-30753