Energy-resolved pulse profile changes in V 0332+53: Indications of wings in the cyclotron absorption line profile
arXiv:2412.10907 · doi:10.1051/0004-6361/202451469
Abstract
We aim to investigate the energy-resolved pulse profile changes of the accreting X-ray pulsar V 0332+53, focusing in the cyclotron line energy range, using the full set of available NuSTAR observations. We applied a tailored pipeline to study the energy dependence of the pulse profiles and to build the pulsed fraction spectra (PFS) for the different observations. We studied the profile changes also using cross-correlation and lag spectra. We re-analysed the energy spectra to search for links between the local features observed in the PFS and spectral emission components associated with the shape of the fundamental cyclotron line. In the PFS data, with sufficiently high statistics, we observe a consistent behaviour around the cyclotron line energy. Specifically, two Gaussian-shaped features appear symmetrically on either side of the putative cyclotron line. These features exhibit minimal variation with source luminosity, and their peak positions consistently remain on the left and right of the cyclotron line energy. Associated with the cyclotron line-forming region, we interpret them as evidence for the resonant cyclotron absorption line wings, as predicted by theoretical models of how the cyclotron line profile should appear along the observer's line of sight. A phase-resolved analysis of the pulse in the energy bands surrounding these features enables us to determine both the spectral shape and the intensity of the photons responsible for these peaks in the PFS. Assuming these features correspond to a spectral component, we used their shapes as priors for the corresponding emission components, finding a statistically satisfactory description of the spectra. To explain these results, we propose that our line of sight is close to the direction of the spin axis, while the magnetic axis is likely orthogonal to it.
33 pages, 58 figures. Accepted for publication in A&A
References in corpus (23)
- The Astropy Project: Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package
- Discovery of a flux-related change of the cyclotron line energy in Her X-1
- A model for cyclotron resonance scattering features
- Luminosity dependence of the cyclotron line and evidence for the accretion regime transition in V 0332+53
- Determination of X-ray pulsar geometry with IXPE polarimetry
- Distances to Galactic X-ray Binaries with Gaia DR2
- Luminosity-dependent changes of the cyclotron line energy and spectral hardness in Cep X-4
- On the radiation beaming of bright X-ray pulsars and constraints on neutron star mass-radius relation
- The X-ray polarimetry view of the accreting pulsar Cen X-3
- Transient X-ray pulsar V0332+53: pulse phase-resolved spectroscopy and the reflection model
- X-ray emission from magnetized neutron star atmospheres at low mass accretion rates. I. Phase-averaged spectrum
- X-ray polarimetry of X-ray pulsar X Persei: another orthogonal rotator?
- X-ray pulsar GRO J100857 as an orthogonal rotator
- Radiative Relativistic Magnetohydrodynamic Simulations of Neutron Star Column Accretion in Cartesian Geometry
- Cyclotron line formation by reflection on the surface of a magnetic neutron star
- Energy-resolved pulse profiles of accreting pulsars: Diagnostic tools for spectral features
- Glancing through the accretion column of EXO 2030+375
- Catalog of the Galactic population of X-ray pulsars in High-mass X-ray binary systems
- Pulsating iron spectral features in the emission of X-ray pulsar V0332+53
- Vacuum polarization alters the spectra of accreting X-ray pulsars
- An in-depth analysis of the variable cyclotron lines in GX 3012
- Cyclotron line formation in the radiative shock of an accreting magnetized neutron star
- Observations of V0332+53 during the 2015 Outburst using Fermi/GBM, MAXI, Swift, and INTEGRAL