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 Plus annual

Presents the access of premium content as premium feature

Premium Content

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 Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

During the June 2015 outburst of the black hole binary V404 Cyg, rapidchanges in the X-ray brightness and spectra were common. The INTEGRALmonitoring campaign detected spectacular Eddington-limited X-ray flares, butalso rapid variations at much lower flux levels. On 2015 June 21 at 20 h 50min, the 3-10 keV JEM-X data as well as simultaneous optical data started todisplay a gradual brightening from one of these low-flux states. This wasfollowed 15 min later by an order-of-magnitude increase of flux in the 20-40keV IBIS/ISGRI light curve in just 15 s. The best-fitting model for both thepre- and post-transition spectra required a Compton-thick partially coveringabsorber. The absorber parameters remained constant, but the spectral slopevaried significantly during the event, with the photon index decreasing from$\Gamma \approx 3.7$ to $\Gamma \approx 2.3$. We propose that the rapid 20-40keV flux increase was either caused by a spectral state transition that washidden from our direct view, or that there was a sudden reduction in the amountof Compton down-scattering of the primary X-ray emission in the disk outflow.

Rapid spectral transition of the black hole binary V404 Cyg