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

L. Keek*, Z. Arzoumanian, P. Bult, E. M. Cackett, D. Chakrabarty, J. Chenevez, A. C. Fabian, K. C. Gendreau, S. Guillot, T. Güver, J. Homan, G. K. Jaisawal, F. K. Lamb, R. M. Ludlam, S. Mahmoodifar, C. B. Markwardt, J. M. Miller, G. Prigozhin, Y. Soong, T. E. StrohmayerM. T. Wolff

*Corresponding author for this work

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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.
Original languageEnglish
Article numberL4
JournalThe Astrophysical Journal Letters
Issue number1
Number of pages6
Publication statusPublished - 2018

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