Diagnostic of the spectral properties of Aquila X-1 by Insight-HXMT snapshots during the early propeller phase

TL;DR

This paper analyzes the spectral properties of Aquila X-1 during its 2018 outburst, focusing on the weak propeller stage, using MAXI and Insight-HXMT data to identify spectral components and accretion behavior.

Contribution

It presents the first spectral analysis of Aquila X-1 during the weak propeller stage using Insight-HXMT data, highlighting the need for a Comptonization component.

Findings

Detection of a Comptonization component in the spectra.

Evidence of partial accretion during the weak propeller stage.

Spectral characteristics consistent with transition to the weak propeller regime.

Abstract

We study the 2018 outburst of Aql X-1 via the monitor of all sky X-ray image (MAXI) data. We show that the outburst starting in February 2018 is a member of short-low class in the frame of outburst duration and the peak count rate although the outburst morphology is slightly different from the other fast-rise-exponential-decay (FRED) type outbursts with a milder rising stage. We study the partial accretion in the weak propeller stage of Aql X-1 via the MAXI data of the 2018 outburst. We report on the spectral analysis of 3 observations of Aquila X-1 obtained by Insight - hard X-ray modulation telescope (Insight-HXMT) during the late decay stage of the 2018 outburst. We discuss that the data taken by Insight-HXMT is just after the transition to the weak propeller stage. Our analysis shows the necessity of a comptonization component to take into account the existence of an electron cloud resulting photons partly up-scattered.