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

ULX-7, in the northern spiral arm of M51, demonstrates unusual behaviour foran ultraluminous X-ray source, with a hard X-ray spectrum but very highshort-term variability. This suggests that it is not in a typical ultraluminousstate. We analyse the source using archival data from XMM-Newton, Chandra andNuSTAR, and by examining optical and radio data from HST and VLA. Our X-rayspectral analysis shows that the source has a hard power-law spectral shapewith a photon index Gamma~1.5, which persists despite the source's X-rayluminosity varying by over an order of magnitude. The power spectrum of thesource features a break at 6.5^{+0.5}_{-1.1}x10^-3 Hz, from a low-frequencyspectral index of alpha_1=-0.1^{+0.5}_{-0.2} to a high-frequency spectral indexof alpha_2=0.65^{+0.05}_{-0.14}, making it analogous to the low-frequency breakfound in the power spectra of low/hard state black holes (BHs). We can take alower frequency limit for a corresponding high-frequency break to calculate aBH mass upper limit of 1.6x10^3 solar masses. Using the X-ray/radio fundamentalplane we calculate another upper limit to the BH mass of 3.5x10^4 solar massesfor a BH in the low/hard state. The hard spectrum, high rms variability andmass limits are consistent with ULX-7 being an intermediate-mass BH; however wecannot exclude other interpretations of this source's interesting behaviour,most notably a neutron star with an extreme accretion rate.

A variable ULX and possible IMBH candidate in M51a