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

Fitting the thermal X-ray spectra of neutron stars (NSs) in quiescent X-raybinaries can constrain the masses and radii of NSs. The effect of undetectedhot spots on the spectrum, and thus on the inferred NS mass and radius, has notyet been explored for appropriate atmospheres and spectra. A hot spot wouldharden the observed spectrum, so that spectral modeling tends to infer radiithat are too small. However, a hot spot may also produce detectable pulsations.  We simulated the effects of a hot spot on the pulsed fraction and spectrum ofthe quiescent NSs X5 and X7 in the globular cluster 47 Tucanae, usingappropriate spectra and beaming for hydrogen atmosphere models, incorporatingspecial and general relativistic effects, and sampling a range of systemangles. We searched for pulsations in archival Chandra HRC-S observations of X5and X7, placing 90\% confidence upper limits on their pulsed fractions below16\%. We use these pulsation limits to constrain the temperature differentialof any hot spots, and to then constrain the effects of possible hot spots onthe X-ray spectrum and the inferred radius from spectral fitting. We find thathot spots below our pulsation limit could bias the spectroscopically inferredradius downward by up to 28\%. For Cen X-4 (which has deeper publishedpulsation searches), an undetected hot spot could bias its inferred radiusdownward by up to 10\%. Improving constraints on pulsations from quiescentLMXBs may be essential for progress in constraining their radii.

The impact of surface temperature inhomogeneities on quiescent neutron star radius measurements