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 Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

The NuSTAR Legacy program 'Unidentified INTEGRAL sources' targeted faint hardX-ray sources revealed by INTEGRAL in the Galactic plane in order to provideconclusive identification of their nature and insights on the population offaint hard X-ray sources. The NuSTAR and Swift/XRT observations obtained in2015-2017 contributed to the successful identification of five persistentsources. Here, we report on the spectral and variability analyses which helpedto consolidate the classifications of IGR J10447-6027, IGR J16181-5407 and IGRJ20569+4940 as active galactic nuclei, and IGR J17402-3656 as an intermediatepolar. An optical spectrum of the blazar IGR J20569+4940 is also presented.Combining these results with successful identifications of other such faint andpersistent INTEGRAL sources reported in the literature, we investigate possibleimplications for the population of persistent high mass X-ray binaries (HMXBs)below the identification completion limit of the INTEGRAL survey. The currenttrend hints at a deficit of persistent HMXBs below $F_{\rm 17-60keV} =10^{-11}$ erg cm$^{-2}$ s$^{-1}$, but additional efforts dedicated toclassifying faint hard X-ray sources are needed before we can draw solidconclusions.

NuSTAR observations of the unidentified INTEGRAL sources: constraints on the Galactic population of HMXBs