NICER Observes the Effects of an X-Ray Burst on the Accretion Environment in Aql X-1

[摘要] Accretion disks around neutron stars regularly undergo sudden strong irradiation by Type I X-raybursts powered by unstable thermonuclear burning on the stellar surface. We investigate the impacton the disk during one of the first X-ray burst observations with the Neutron Star Interior CompositionExplorer (NICER) on the International Space Station. The burst is seen from Aql X-1 during the hardspectral state. In addition to thermal emission from the neutron star, the burst spectrum exhibits anexcess of soft X-ray photons below 1 keV, where NICER's sensitivity peaks. We interpret the excessas a combination of reprocessing by the strongly photoionized disk and enhancement of the pre-burstpersistent flux, possibly due to Poynting Robertson drag or coronal reprocessing. This is the firstsuch detection for a short sub-Eddington burst. As these bursts are observed frequently, NICER willbe able to study how X-ray bursts affect the disk and corona for a range of accreting neutron starsystems and disk states.

[发布日期] 2018-02-28

[学科分类] 天体物理学

[关键词] ACCRETION DISKS;AUGMENTATION;COMPANION STARS;CORONAS;DOPPLER EFFECT;DRAG;EMISSION SPECTRA;HYDROGEN;IRRADIATION;NEUTRON STARS;PHOTOIONIZATION;RECLAMATION;SPECTRAL THEORY;X RAY BINARIES