Faint super-soft X-ray sources in XMM-Newton Large Magellanic Cloud fields

Abstract

Aims: We report the discovery of three faint, super-soft X-ray sources in LMC fields observed with XMM-Newton.
Methods: We analyse the three new sources together with RX J0537.7-7034 and RX J0507.1-6743, both known since ROSAT.
Results: We identify XMMU J050803.1-684017 with the LMC planetary nebula LHA 120-N 102 = LMC SMP 29. The EPIC-pn spectrum of XMMU J050803.1-684017 can be fitted with a blackbody spectrum with an effective temperature of ~(26-51) eV and a bolometric luminosity of (0.1-30)×10³⁶ erg s^-1, depending on the assumed absorption. The source is consistent with the nucleus of a planetary nebula. The EPIC-pn spectrum of XMMU J052530.5-671501 is characterized by a blackbody temperature of ~(38-120) eV, a best-fit bolometric luminosity of ~3×10³⁷ erg s^-1 and absorbing LMC column of ∼8⁺²_-8×10²¹ cm^-2. This most likely highly-absorbed super-soft source resembles the LMC super-soft source CAL 87. The EPIC-pn spectrum of XMMU J052215.0-701658 yields a blackbody temperature of ~(24-83) eV, but there are only about 40 source counts and the spectral parameters of the source are not well constrained. We observe RX J0537.7-7034 with EPIC-pn to be about a factor of 15 fainter compared to the ROSAT observation 11 years earlier. RX J0507.1-6743 is observed as an absorbed super-soft source by XMM-Newton and the improved X-ray position coincides with a MACHO star which is consistent with a symbiotic star.