Optical and X-ray variations during 5 outbursts of Aql X-1 in 3.6 years from 2016
Masafumi Niwano, Katsuhiro L. Murata, Naohiro Ito, Yoichi Yatsu,, Nobuyuki Kawai

TL;DR
This study analyzed optical and X-ray light curves of Aql X-1 over 3.6 years, revealing five outbursts with different state transitions and linking optical spectral features to X-ray luminosity and disk geometry.
Contribution
It provides new insights into the electromagnetic radiation mechanisms during outbursts of Aql X-1, especially the optical spectral behavior in different X-ray states.
Findings
Confirmed 5 outbursts with 3 undergoing state transitions
Optical spectrum in High-Soft state matches irradiated disk model
Optical variations explained by X-ray luminosity and disk geometry
Abstract
We analyzed optical/X-ray quasi-simultaneous light curves of Aql X-1, obtained by MAXI (Monitor of All-sky X-ray Image), ZTF (Zwicky Transient Facility) and LCO (Las Cumbres Observatory) in about 3.6 years from 2016, for understanding electromagnetic radiation mechanisms during its outbursts. As a result, we confirmed that 5 outbursts had detected in the epoch, and that 3 outbursts underwent the X-ray state transition across Low-Hard, In-Transition, and High-Soft state while remaining 2 outbursts stayed in the Low-Hard state. We found that the optical spectral energy distribution in the High-Soft state is consistent with a simplified irradiated disk model, and that the optical color/magnitude variation can be explained by variations in the X-ray luminosity and the disk geometrical thickness.
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Taxonomy
TopicsAstrophysical Phenomena and Observations · Gamma-ray bursts and supernovae · Astronomical Observations and Instrumentation
