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Abstract: The first supersoft source SSS identification with an optical nova in M 31was based on ROSAT observations. Twenty additional X-ray counterparts mostlyidentified as SSS by their hardness ratios were detected using archival ROSAT,XMM-Newton and Chandra observations obtained before July 2002. Based on theseresults optical novae seem to constitute the major class of SSS in M 31. Ananalysis of archival Chandra HRC-I and ACIS-I observations obtained from July2004 to February 2005 demonstrated that M 31 nova SSS states lasted from monthsto about 10 years. Several novae showed short X-ray outbursts starting within50 d after the optical outburst and lasting only two to three months. Thefraction of novae detected in soft X-rays within a year after the opticaloutburst was more than 30%. Ongoing optical nova monitoring programs, opticalspectral follow-up and an up-to-date nova catalogue are essential for the X-raywork. Re-analysis of archival nova data to improve positions and findadditional nova candidates are urgently needed for secure recurrent novaidentifications. Dedicated XMM-Newton-Chandra monitoring programs for X-rayemission from optical novae covering the center area of M 31 continue toprovide interesting new results e.g. coherent 1105s pulsations in the SSScounterpart of nova M31N 2007-12b. The SSS light curves of novae allow us -together with optical information - to estimate the mass of the white dwarf, ofthe ejecta and the burned mass in the outburst. Observations of the centralarea of M 31 allow us - in contrast to observations in the Galaxy - to monitormany novae simultaneously and proved to be prone to find many interesting SSSand nova types.



Author: W. Pietsch Max-Planck-Institut für extraterrestrische Physik, Garching

Source: https://arxiv.org/



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