XMM-Newton observations of H2O maser galaxy NGC 7479

Jin Wang, Jiang-Shui Zhang, Jun-Hui Fan

Abstract


The XMM-Newton observations of H2O megamaser galaxy NGC 7479 are presented. Its smoothed X-ray image clearly shows spiral morphology, which matches well with its optical asymmetric spiral structure. One prominent source can be found at the tip of its northern spiral arm, which is much brighter than its nuclear X-ray source (about a 50% higher count rate). For the nuclear source (a circular region with a radius of 20 ), the spectra show soft excess below 2 keV and a strong iron Kα emission line. The best fitting model includes a partially absorbed model for the hard continuum and one thermal plasma model for the soft scatter component. Both the high column density (NH ∼ 6.88 × 1023 cm-2 ) and strong fluorescent iron line (with an equivalent width of ∼1.5 keV) support the existence of one heavily obscured AGN. For the bright prominent source, its radial profile is consistent with that of a single point-like source. Its spectra are extracted from the circular region around its peak, with a radius of 20´´ and 6´´ respectively and both spectra show no significant difference. Four alternative models for the ultra-luminous X-ray source (ULXs) can reproduce the spectra well: an absorbed power law, thermal bremsstrahlung, multicolor blackbody disk plus another blackbody or power law. Further observations (e.g., the tremendous improvement in the spatial resolution of the Chandra X-ray observations) and studies are desirable for probing the nature of this prominent source. In addition, we also estimate the mass of its central engine to be 1.18×107M and maser disk parameters: the disk radius of ∼0.7 pc and the dimensionless accretion rate (L2-10keV /LEdd ) of 1.2×10-4.



Keywords


masers — galaxies: active — galaxies: nuclei — galaxies: individual (NGC 7479) — X-rays: galaxies

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Print ISSN: 1674-4527

Online ISSN: 2397-6209