English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Tools annual

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Presents the access of premium content as premium feature

Premium Content

Global: Zendy Plus annual

Global: Zendy Free Plan

We present the results of X-ray variability and spectral analysis of a sampleof 15 new candidates for active galactic nuclei with relatively low-mass blackholes (BHs). They are selected from the Second XMM-Newton Serendipitous SourceCatalogue based on strong variability quantified by normalized excessvariances. Their BH masses are estimated to be 1.1-6.6x10^6 M_solar by using acorrelation between excess variance and BH mass. Seven sources have estimatedBH masses smaller than 2x10^6 M_solar, which are in the range forintermediate-mass black holes. Eddington ratios of sources with known redshiftsrange from 0.07 to 0.46 and the mean Eddington ratio is 0.24. These resultsimply that some of our sources are growing supermassive black holes, which areexpected to have relatively low masses with high Eddington ratios. X-ray photonindices of the 15 sources are in the range of ~0.57-2.57, and 5 among them havesteep (>2) photon indices, which are the range for narrow-line Seyfert 1s. SoftX-ray excess is seen in 12 sources, and is expressed by a blackbody model withkT~83-294 eV. We derive a correlation between X-ray photon indices andEddington ratios, and find that the X-ray photon indices of about a half of oursources are flatter than the positive correlation suggested previously.

A New Sample of Candidate Intermediate-Mass Black Holes Selected by X-ray Variability