The giant outburst of EXO 2030+375 I: Spectral and pulse profile evolution

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https://doi.org/10.1051/0004-6361/202348594

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https://orcid.org/0000-0002-4656-6881

Date

2024-08-22

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journal articles
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Citation of Original Publication

Thalhammer, P., R. Ballhausen, E. Sokolova-Lapa, J. Stierhof, A. Zainab, R. Staubert, K. Pottschmidt, et al. “The Giant Outburst of EXO 2030+375 - I. Spectral and Pulse Profile Evolution.” Astronomy & Astrophysics 688 (August 1, 2024): A213. https://doi.org/10.1051/0004-6361/202348594.

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This work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.
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Astrophysics - High Energy Astrophysical Phenomena

Abstract

The Be X-ray binary EXO 2030+375 went through its third recorded giant outburst from June 2021 to early 2022. We present the results of both spectral and timing analysis based on NICER monitoring, covering the 2−10 keV flux range from 20 to 310 mCrab. Dense monitoring with observations carried out about every second day and a total exposure time of ∼160 ks allowed us to closely track the source evolution over the outburst. Changes in the spectral shape and pulse profiles showed a stable luminosity dependence during the rise and decline. The same type of dependence has been seen in past outbursts. The pulse profile is characterized by several distinct peaks and dips. The profiles show a clear dependence on luminosity with a stark transition at a luminosity of ∼2 × 10³⁶ erg s−1, indicating a change in the emission pattern. Using relativistic raytracing, we demonstrate how anisotropic beaming of emission from an accretion channel with a constant geometrical configuration can give rise to the observed pulse profiles over a range of luminosities.