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Long-term optical variability of the Be/X-ray binary GRO J2058+42
We investigate the long-term optical variability of the Be/X-ray binary GRO J2058+42 and the possible connection with periods of enhanced X-ray activity. We performed an optical spectroscopic and photometric analysis on data collected during about 18 years. We also present the first optical polarime...
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Published in: | arXiv.org 2023-01 |
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Main Authors: | , , , |
Format: | Article |
Language: | English |
Subjects: | |
Online Access: | Get full text |
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Summary: | We investigate the long-term optical variability of the Be/X-ray binary GRO J2058+42 and the possible connection with periods of enhanced X-ray activity. We performed an optical spectroscopic and photometric analysis on data collected during about 18 years. We also present the first optical polarimetric observations of this source. The long-term optical light curves in the \(BVRI\) bands and the evolution of the H\(\alpha\) equivalent width display a sinusoidal pattern with maxima and minima that repeat every \(\sim\)9.5 years. The amplitude of this variability increases as the wavelength increases. The H\(\alpha\) equivalent width varied from about \(-0.3\) to \(-15\) \AA. We found a significant decrease in the polarization degree during the low optical state. The optical maxima occur near periods of enhanced X-ray activity and are followed by a drop in the optical emission. Unlike many other Be/X-ray binaries, GRO 2058+42 does not display \(V/R\) variability. The long-term optical variability agrees with the standard model of a Be/X-ray binary, where the circumstellar disk of the Be star grows and dissipates on timescales of 9--10 years. We find that the dissipation of the disk started after a major X-ray outburst. However, the stability of the H\(\alpha\) line shape as a double-peak profile and the lack of asymmetries suggest the absence of a warped disk and argue against the presence of a highly distorted disk during major X-ray outbursts. |
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ISSN: | 2331-8422 |
DOI: | 10.48550/arxiv.2301.09415 |