Fe K lines in the nuclear region of M82

Abstract

Abstract We study the spatial distribution of the Fe 6.4 and 6.7 keV lines in the nuclear region of M82 using the Chandra archival data with a total exposure time of 500 ks. The deep exposure provides a significant detection of the Fe 6.4 keV line. Both the Fe 6.4 and 6.7 keV lines are diffuse emissions with similar spatial extent, but their morphology do not exactly follow each other. Assuming a thermal collisional-ionization-equilibrium (CIE) model, the fitted temperatures are around 5–6 keV and the Fe abundances are about 0.4–0.6 solar value. We also report the spectrum of a point source, which shows a strong Fe 6.7 keV line and is likely a supernova remnant or a superbubble. The fitted Fe abundance of the point source is 1.7 solar value. It implies that part of the iron may be depleted from the X-ray emitting gases as the predicted Fe abundance is about 5 times solar value if assuming a complete mixing. If this is a representative case of the Fe enrichment, a mild mass-loading of a factor of 3 will make the Fe abundance of the point source in agreement with that of the hot gas, which then implies that most of the hard X-ray continuum (2–8 keV) of M82 has a thermal origin. In addition, the Fe 6.4 keV line is consistent with the fluorescence emission irradiated by the hard photons from nuclear point sources.