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

¹ Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse, 85741 Garching, Germany e-mail: [pkahabka;fwh]@mpe.mpg.de
² Observatoire de Strasbourg, 11 rue de l'Université, 67000 Strasbourg, France e-mail: pakull@astro.u-strasbg.fr
³ Centre for Astronomy, James Cook University, Townsville, Queensland 4811, Australia
⁴ University of Western Sydney, Locked Bag 1797, Penrith South DC, NSW 1797, Australia

Received: 23 August 2007
Accepted: 16 December 2007

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 ~310³⁷ erg s^-1 and absorbing LMC column of 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.