Continuum, cyclotron line, and absorption variability in the high-mass X-ray binary Vela X-1
Diez CM, Grinberg , Fuerst F, Sokolova-Lapa E, Santangelo A, Wilms J, Pottschmidt K, Martinez-Nunez S, Malacaria C, Kretschmar P (2022)
Publication Type: Journal article
Publication year: 2022
Journal
Book Volume: 660
DOI: 10.1051/0004-6361/202141751
Abstract
Because of its complex clumpy wind, prominent cyclotron resonant scattering features, intrinsic variability, and convenient physical parameters (close distance, high inclination, and small orbital separation), which facilitate the observation and analysis of the system, Vela X-1 is one of the key systems for understanding accretion processes in high-mass X-ray binaries on all scales. We revisit Vela X-1 with two new observations taken with NuSTAR at orbital phases similar to 0.68-0.78 and similar to 0.36-0.52, which show a plethora of variability and allow us to study the accretion geometry and stellar wind properties of the system. We follow the evolution of spectral parameters down to the pulse period timescale using a partially covered power law continuum with a Fermi-Dirac cutoff to model the continuum and local absorption. We are able to confirm anti-correlations between the photon index and the luminosity and, for low fluxes, between the folding energy and the luminosity, implying a change of properties in the Comptonising plasma. We were not able to confirm a previously seen correlation between the cyclotron line energy and the luminosity of the source in the overall observation, but we observed a drop in the cyclotron line energy following a strong flare. We see strong variability in absorption between the two observations and within one observation (for the similar to 0.36-0.52 orbital phases) that can be explained by the presence of a large-scale structure, such as accretion and photoionisation wakes in the system, and our variable line of sight through this structure.
Authors with CRIS profile
Ekaterina Sokolova-Lapa
Dr.Karl-Remeis-Sternwarte Bamberg, Astronomisches Institut
Jörn Wilms
Lehrstuhl für Astronomie und Astrophysik
Involved external institutions
Eberhard Karls Universität Tübingen
Germany (DE)
European Space Astronomy Centre (ESAC)
Spain (ES)
University of Maryland, Baltimore County (UMBC)
United States (USA) (US)
Universidad de Cantabria (UC)
Spain (ES)
Universities Space Research Association (USRA)
United States (USA) (US)
Germany (DE)
European Space Astronomy Centre (ESAC)
Spain (ES)
University of Maryland, Baltimore County (UMBC)
United States (USA) (US)
Universidad de Cantabria (UC)
Spain (ES)
Universities Space Research Association (USRA)
United States (USA) (US)
How to cite
APA:
Diez, C.M., Grinberg, ., Fuerst, F., Sokolova-Lapa, E., Santangelo, A., Wilms, J.,... Kretschmar, P. (2022). Continuum, cyclotron line, and absorption variability in the high-mass X-ray binary Vela X-1. Astronomy & Astrophysics, 660. https://doi.org/10.1051/0004-6361/202141751
MLA:
Diez, C. M., et al. "Continuum, cyclotron line, and absorption variability in the high-mass X-ray binary Vela X-1." Astronomy & Astrophysics 660 (2022).
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