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

GK Per, a classical nova of 1901, is thought to undergo variable massaccretion on to a magnetized white dwarf (WD) in an intermediate polar system(IP). We organized a multi-mission observational campaign in the X-ray andultraviolet (UV) energy ranges during its dwarf nova (DN) outburst in 2015March-April. Comparing data from quiescence and near outburst, we have foundthat the maximum plasma temperature decreased from about 26 to 16.2+/-0.4 keV.This is consistent with the previously proposed scenario of increase in massaccretion rate while the inner radius of the magnetically disrupted accretiondisc shrinks, thereby lowering the shock temperature. A NuSTAR observation alsorevealed a high-amplitude WD spin modulation of the very hard X-rays with asingle-peaked profile, suggesting an obscuration of the lower accretion poleand an extended shock region on the WD surface. The X-ray spectrum of GK Permeasured with the Swift X-Ray Telescope varied on time-scales of days and alsoshowed a gradual increase of the soft X-ray flux below 2 keV, accompanied by adecrease of the hard flux above 2 keV. In the Chandra observation with the HighEnergy Transmission Gratings, we detected prominent emission lines, especiallyof Ne, Mg and Si, where the ratios of H-like to He-like transition for eachelement indicate a much lower temperature than the underlying continuum. Wesuggest that the X-ray emission in the 0.8-2 keV range originates from themagnetospheric boundary.

Multi-mission observations of the old nova GK Per during the 2015 outburst