2012/05/02 by Naoya Kamizasa, Yuichi Terashima, Hisamitsu Awaki · 1 citation
Physics and Astronomy · #Active galactic nucleus #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Black-body radiation #Galaxies: Formation, Evolution, Phenomena #Optical depth #Photon #Range (aeronautics) #Spectral line #Supermassive black hole #astro-ph.HE
paper · pdf · doi:10.1088/0004-637x/751/1/39
To Appear in ApJ, 14 pages, 5 figures
openalex publication_date 2012/05/02 · arxiv created 2012/05/12 · arxiv updated 2015/06/05 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We present the results of X-ray variability and spectral analysis of a sample of 15 new candidates for active galactic nuclei with relatively low-mass black holes (BHs). They are selected from the Second XMM-Newton Serendipitous Source Catalogue based on strong variability quantified by normalized excess variances. Their BH masses are estimated to be (1.1–6.6) × 10 6 M ☉ by using a correlation between excess variance and BH mass. Seven sources have estimated BH masses smaller than 2 × 10 6 M ☉ , which are in the range for intermediate-mass black holes. Eddington ratios of sources with known redshifts range from 0.07 to 0.46 and the mean Eddington ratio is 0.24. These results imply that some of our sources are growing supermassive black holes, which are expected to have relatively low masses with high Eddington ratios. X-ray photon indices of the 15 sources are in the range of ≈0.57–2.57 and 5 among them have steep (>2) photon indices, which are the range for narrow-line Seyfert 1s. Soft X-ray excess is seen in 12 sources and is expressed by a blackbody model with kT ≈ 83–294 eV. We derive a correlation between X-ray photon indices and Eddington ratios, and find that the X-ray photon indices of about a half of our sources are flatter than the positive correlation suggested previously.