XMM-Newton observations of SN 1987 A

摘要

Context. We report on XMM-Newton observations of SN 1987 A in the Large Magellanic Cloud. Aims. The large collecting area telescopes together with the European Photon Imaging Cameras ( EPIC) provide X-ray spectra with unprecedented statistical quality and make it possible to investigate the spectral evolution during the brightening observed since the discovery in X-rays. High resolution spectra from the Reflection Grating Spectrometers yield a complementary view and allow us to perform more detailed investigations of prominent emission lines. Methods. The X-ray spectra were modeled with two-temperature emission components from a hot plasma in collisional ionization equilibrium and in non-equilibrium (NEI). Results. We find a temperature for the equilibrium component of 0.24 +/- 0.02 keV in January 2000 and April 2001 which increased to 0.30 +/- 0.02 keV in May 2003 and also an indication for a temperature increase in the hot NEI component from similar to 2 keV to similar to 3 keV. Emission line ratios inferred from the RGS spectra suggest temperatures as low as 100 eV and an increase in the ionization state of oxygen and neon consistent with the observed temperature increases. The fast readout of the EPIC-pn instrument yields X-ray fluxes free of CCD pile-up effects which we used to normalize pile-up corrections for the published Chandra fluxes. The corrected X-ray light curve of SN1987 A in the 0.5-2.0 keV energy band is best represented by a linear increase up to about day 4000 after the explosion and an exponential rise afterwards until the last published Chandra observation on day 6716. Modeling the light curve by emission from the inner ring which is approximated by a circular torus a central density n(H) = 1.15 x 10(4) cm(-3) is found. In this model the forward shock has just passed the center of the torus. Conclusions. SN1987A continues to brighten exponentially in soft X-rays. The X-ray spectra can be represented by pure thermal emission without significant contribution from a compact object yet.