A second glance at SN 2002ap and the M74 field with XMM-Newton

摘要

We have re-observed the field of M74 in January 2003 with XMM-Newton, 11months after the X-ray detection of SN 2002ap. From a comparison of the twoXMM-Newton observations we obtain more accurate values for the X-ray luminosityand colours of the source five days after the event, and a limit on its declinerate. We compare its X-ray behaviour (prompt soft X-ray emission, relativelylow luminosity) with that of other Type Ic SNe, and speculate that SN 2002apmay share some physical properties (low mass-loss rate and high-velocitystellar wind from the progenitor star) with the candidate hypernova/GRBprogenitor SN 1998bw, but with a lower (non-relativistic) speed of the ejecta.We suggest that the X-ray emission observed in 2002 is likely to come from theradiatively-cooling reverse shock, at a temperature kT ~ 0.8 keV, and that thissoft component was already detected 5 d after the event because the absorbingcolumn density of the cool shell between the forward and reverse shocks wasonly ~ 10^{20} cm^{-2}, ie, the shell was optically thin in the soft X-rayband. The new XMM-Newton data also allowed us to continue monitoring two brightvariable sources in M74 that had reached peak luminosities > 10^{39} erg s^{-1}in previous XMM-Newton and Chandra observations. Finally, we used two Chandraobservations from 2001 to investigate the luminosity and colour distribution ofthe X-ray source population of M74, typical of moderately-active late-typespirals.