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

We report the identification of seven transient X-ray sources in the nearbyMagellanic-type galaxy NGC 4449 using the archival multi-epoch X-rayobservations conducted with {\it Chandra}, {\it XMM-Newton} and {\it Swift}telescopes over year 2001--2013. Among them, two sources are classified assupersoft X-ray sources (SSSs) because of their soft X-ray color and rest ofthe sources are X-ray binaries (XRBs). Transient SSSs spectra can be fittedwith a blackbody of effective temperature $\sim 80-105$ eV and luminositieswere $\simeq 10^{37} - 10^{38} {\rm~erg\ s}^{-1}$ in 0.3--8 keV. Theseproperties are consistent with the widely accepted model for SSSs, an accretingwhite dwarf with the steady nuclear burning on its surface, while the SSSemission has also been observed in many post-nova systems. Detailed analysis ofone sufficiently bright SSS revealed the strong short-term variability,possibly showing a 2.3 hour periodic modulation, and long-term variability,detectable over 23 years with different X-ray telescopes before year 2003. TheX-ray properties of four other transients are consistent with neutron star orblack hole binaries in their hard state, while the remaining source is mostlikely an XRB with a quasi-soft X-ray spectrum. Analysis of archival {\itHubble Space Telescope} image data was also conducted, and multiple massivestars were found as possible counterparts. We conclude that the X-ray transientproperties in NGC 4449 are similar to those in other Magellanic-type galaxies.

Transient X-ray Sources in the Magellanic-type Galaxy NGC 4449