A NICER look at thermonuclear X-ray bursts from Aql X-1

Abstract

We present spectral and temporal properties of all the thermonuclear X-ray bursts observed from Aql X-1 by the Neutron Star Interior and Composition Explorer (NICER) between 2017 July and 2021 April. This is the first systematic investigation of a large sample of type I X-ray bursts from Aql X-1 with improved sensitivity at low energies. We detect 22 X-ray bursts including two short recurrence burst events in which the separation was only 451 s and 496 s. We perform time resolved spectroscopy of the bursts using the fixed and scaled background (f_a method) approaches. We show that the use of a scaling factor to the pre-burst emission is the statistically preferred model in about 68% of all the spectra compared to the fixed background approach. Typically the f_a values are clustered around 1-3, but can reach up to 11 in a burst where photospheric radius expansion is observed. Such f_a values indicate a very significant increase in the pre-burst emission especially at around the peak flux moments of the bursts. We show that the use of the f_a factor alters the best fit spectral parameters of the burst emission. Finally, we employed a reflection model instead of scaling the pre-burst emission. We show that reflection models also do fit the spectra and improve the goodness of the fits. In all cases we see that the disc is highly ionized by the burst emission and the fraction of the reprocessed emission to the incident burst flux is typically clustered around 20%.

Accepted for publication in Monthly Notices of the Royal Astronomical Society

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Cited by in corpus (12)

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• A Comprehensive Study of Thermonuclear X-ray Bursts from 4U 1820-30 with NICER: Accretion Disk Interactions and a Candidate Burst Oscillation
• Discovery of a 584.65 Hz Burst Oscillation in the Low Mass X-Ray Binary 4U 1730--22
• The thermonuclear X-ray bursts of 4U 1730-22
• Broadband spectro-temporal investigation of neutron star low-mass X-ray binary GX 349+2
• Insight-HXMT observations on thermonuclear X-ray bursts from 4U~1608--52 in 2022: the accretion rate dependent anisotropy of burst emission
• Radiation Driven Warping of Accretion Discs Due to X-ray Bursts
• Probing thermonuclear bursts and X-ray reflection features in Aql X-1 during 2024 outburst
• NICER observations of type-I X-ray bursts from the ultra-compact X-ray binary M15 X-2
• Tracing the outburst decay of soft X-ray transients Aql X-1 and 4U 1608-52 with XSPECT