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


KEEK L., ARZOUMANIAN Z., Bult P., Cackett E. M., CHAKRABARTY D., Chenevez J., ...More

ASTROPHYSICAL JOURNAL LETTERS, vol.855, no.1, 2018 (SCI-Expanded) identifier identifier

  • Publication Type: Article / Article
  • Volume: 855 Issue: 1
  • Publication Date: 2018
  • Doi Number: 10.3847/2041-8213/aab104
  • Journal Name: ASTROPHYSICAL JOURNAL LETTERS
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Keywords: accretion, accretion disks, stars: individual (Aql X-1), stars: neutron, X-rays: binaries, X-rays: bursts, TIMING-EXPLORER, AQUILA X-1, SPECTRAL EVOLUTION, NEUTRON-STARS, OUTBURST, DISK, CALIBRATION, PERSISTENT, ABSORPTION, EMISSION
  • Istanbul University Affiliated: Yes

Abstract

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