What causes the absence of pulsations in Central Compact Objects in supernova remnants?

Most young neutron stars belonging to the class of Central Compact Objects(CCOs)in supernova remnants do not have known periodicities.We investigated seven such CCOs to understand the common reasons for the absence of detected pulsations.Making use of XMM-Newton,Chandra,and NICER observations,we perform a systematic timing and spectral analysis to derive updated sensitivity limits for both periodic signals and multi-temperature spectral components that could be associated with radiation from hotspots on the neutron star surface.Based on these limits,we then investigated for each target the allowed viewing geometry that could explain the lack of pulsations.We find that it is unlikely(<10-6)to attribute that we do not see pulsations to an unfavorable viewing geometry for five considered sources.Alternatively,the carbon atmosphere model,which assumes homogeneous temperature distribution on the surface,describes the spectra equally well and provides a reasonable interpretation for the absence of detected periodicities within current limits.The unusual properties of CCOs with respect to other young neutron stars could suggest a different evolutionary path,as that proposed for sources experiencing episodes of significant fallback accretion after the supernova event.

The orbital phase resolved spectroscopy of X-ray binary 4U 1822–371 with Suzaku

4U 1822-371 is a typical edge-on eclipsing low mass X-ray binary and the prototype of accre- tion disk coronal sources. We report on the results of a spectral analysis over the energy range 0.5-45 keV observed by Suzaku in 2006. We extract spectra from five orbital phases. The spectra can be equally well described by various previously proposed models： an optically thick model described by a partially cov- ered cutoff power law and an optically thin model described by a blackbody plus a cutoff power law. The optically thick model requires a covering fraction of about 55%, while the optically thin model requires a temperature of the central source of about 0.16 keV. The spectrum in the optically thick model also shows the previously detected cyclotron line feature at ~30 keV with the same Suzaku observation. This fea- ture confirms the presence of a strong magnetic field. The Fe Ks fluorescent line strengths as well as the detected Fe xxvI strengths are similar to previous Chandra and XMM-Newton detections in our phased spectral analysis; however, we also observe strong Fe xxvI during the eclipse, which indicates a slightly larger central corona.