Evidence for intermediate polars as the origin of the Galactic Center hard X-ray emission

Abstract

Recently, unresolved hard (20-40 keV) X-ray emission has been discovered within the central 10 pc of the Galaxy, possibly indicating a large population of intermediate polars (IPs). Chandra and XMM-Newton measurements in the surrounding ~50 pc imply a much lighter population of IPs with $⟨M_{\mathrm{WD}}⟩\approx 0.5M_{\odot }$. Here we use broad-band NuSTAR observations of two IPs: TV Columbae, which has a fairly typical but widely varying reported mass of $M_{\mathrm{WD}}\approx 0.5-1.0M_{\odot }$, and IGR J17303-0601, with a heavy reported mass of $M_{\mathrm{WD}}\approx 1.0-1.2M_{\odot }$. We investigate how varying spectral models and observed energy ranges influence estimated white dwarf mass. Observations of the inner 10 pc can be accounted for by IPs with $⟨M_{\mathrm{WD}}⟩\approx 0.9M_{\odot }$, consistent with that of the CV population in general, and the X-ray observed field IPs in particular. The lower mass derived by Chandra and XMM-Newton appears to be an artifact of narrow energy band fitting. To explain the (unresolved) CHXE by IPs requires an X-ray (2-8 keV) luminosity function (XLF) extending down to at least $5\times 10^{31}$ erg/s. The CHXE XLF, if extended to the surrounding ~50 pc observed by Chandra and XMM-Newton, requires at least ~20-40% of the $\sim$9000 point sources are IPs. If the XLF extends just a factor of a few lower in luminosity, then the vast majority of these sources are IPs. This is in contrast to recent observations of the Galactic ridge, where the bulk of the 2-8 keV emission is ascribed to dwarf novae.

arXiv comment17 pages, accepted for publication in Astrophysical Journal

References in corpus (43)

• On the Absorption of X-rays in the Interstellar Medium
• The Nuclear Spectroscopic Telescope Array (NuSTAR) Mission
• Collisional Plasma Models with APEC/APED: Emission Line Diagnostics of Hydrogen-like and Helium-like Ions
• Atomic Data for Astrophysics. II. New Analytic Fits for Photoionization Cross Sections of Atoms and Ions
• White Dwarf Mass Distribution in the SDSS
• Post-common-envelope binaries from SDSS. XI: The white dwarf mass distributions of CVs and pre-CVs
• The initial-final mass relationship of white dwarfs revisited: effect on the luminosity function and mass distribution
• Discrete sources as the origin of the Galactic X-ray ridge emission
• Binary Star Origin of High Field Magnetic White Dwarfs
• Diffuse X-ray Emission in a Deep Chandra Image of the Galactic Center
• Surface Brightness Profile of the Milky Way's Nuclear Star Cluster
• A Catalog of X-ray Point Sources from Two Megaseconds of Chandra Observations of the Galactic Center
• RXTE Measurement of the Diffuse X-ray Emission From the Galactic Ridge: Implications for the Energetics of the Interstellar Medium
• Spectropolarimetric Survey of Hydrogen-rich White Dwarf Stars
• The open cluster initial-final mass relationship and the high-mass tail of the white dwarf distribution
• The Spectra and Variability of X-ray Sources in a Deep Chandra Observation of the Galactic Center
• Hard X-ray emission from the Galactic ridge
• RXTE broadband X-ray spectra of intermediate polars and white dwarf mass estimates
• 20-100 keV properties of cataclysmic variables detected in the INTEGRAL/IBIS survey
• INTEGRAL hard X-ray spectra of the cosmic X-ray background and Galactic ridge emission
• White dwarf masses in intermediate polars observed with the Suzaku satellite
• Deriving an X-ray luminosity function of dwarf novae based on parallax measurements
• Binary dynamics near a massive black hole
• Constraints on the space density of intermediate polars from the Swift-BAT survey
• Intermediate polars in the Swift/BAT survey: Spectra and white dwarf masses
• Characterization of new hard X-ray Cataclysmic Variables
• Broad-band spectral analysis of the Galactic Ridge X-ray Emission
• NuSTAR Hard X-ray Survey of the Galactic Center Region II: X-ray Point Sources
• A four-year XMM-Newton/Chandra monitoring campaign of the Galactic Centre: analysing the X-ray transients
• The space density of magnetic cataclysmic variables
• INTEGRAL/IBIS and Swift/XRT observations of hard cataclysmic variables
• Fe Line Diagnostics of Cataclysmic Variables and Galactic Ridge X-ray Emission
• A 6.3-h superhump in the cataclysmic variable TV Columbae: the longest yet seen
• Hard X-ray properties of magnetic cataclysmic variables
• Interferometric Astrometry with Hubble Space Telescope Fine Guidance Sensor 3:The Parallax of the Cataclysmic Variable TV Columbae
• X-ray Luminosities of Optically-Selected Cataclysmic Variables and Application to the Galactic Ridge X-ray Emission
• Unambiguous Detection of Reflection in Magnetic Cataclysmic Variables: Joint NuSTAR-XMM-Newton Observations of Three Intermediate Polars
• White dwarf masses in cataclysmic variables
• XMM-Newton observations of the Galactic Centre Region - I: The distribution of low-luminosity X-ray sources
• A large-scale survey of X-ray filaments in the Galactic Centre
• Discovery of a Significant Magnetic CV Population in the Limiting Window
• Spectrum of Relativistic and Subrelativistic Cosmic Rays in the 100 pc Central Region
• Periodicities In The X-Ray Intensity Variations of TV Columbae: An Intermediate Polar

Cited by in corpus (42)

• X-ray Emissions from Accreting White Dwarfs: a Review
• Magnetic fields in isolated and interacting white dwarfs
• Hard X-ray view on intermediate polars in the Gaia era
• Observatory science with eXTP
• Birth, life, and death of black hole binaries around supermassive black holes: dynamical evolution of gravitational wave sources
• An Ultra-deep Chandra Catalog of X-ray Point Sources in the Galactic Center Star Cluster
• Hard X-ray Cataclysmic Variables
• Measuring the masses of magnetic white dwarfs: A NuSTAR Legacy Survey
• Gamma-ray and X-ray emission from the Galactic Centre: hints on the nuclear star cluster formation history
• Broad-band characteristics of seven new hard X-ray selected cataclysmic variables
• The X-ray binary population in the Galactic Center revealed through multi-decade observations
• Sagittarius A* High Energy X-ray Flare Properties During NuSTAR Monitoring of the Galactic Center from 2012 to 2015
• INTEGRAL view on Cataclysmic Variables and Symbiotic Binaries
• Measuring the masses of Intermediate Polars with NuSTAR: V709 Cas, NY Lup and V1223 Sgr
• Discovery of Two Polars from a Crossmatch of ZTF and the SRG/eFEDS X-ray Catalog
• A population of compact radio variables and transients in the radio bright zone at the Galactic center observed with the Jansky Very Large Array
• The Galactic Bulge Diffuse Emission in Broad-Band X-rays with NuSTAR
• The NuSTAR Hard X-ray Survey of the Norma Arm Region
• Hard X-ray luminosity functions of cataclysmic variables: Joint Swift/BAT and Gaia data
• NuSTAR and Chandra observations of new X-ray transients in the central parsec of the Galaxy
• An Empirical Correlation of $T_{\max }$ - $M_{\mathrm{WD}}$ of Dwarf Novae and The Average White Dwarf Mass in Cataclysmic Variables in the Galactic Bulge
• Developing the physical understanding of intermediate polars: an X-ray study of TV Col and V2731 Oph
• Massive White Dwarfs in the Galactic Center: A Chandra X-ray Spectroscopy of Cataclysmic Variables
• Classifying IGR J18007-4146 as an intermediate polar using XMM and NuSTAR
• Application of a new X-ray reflection model to V1223 Sagittarii
• Galactic Center constraints on self-interacting sterile neutrinos from fermionic dark matter ("ino") models
• New Constraints on Cosmic Particle Populations at the Galactic Center using X-ray Observations of the Molecular Cloud Sagittarius B2
• Discovery of periodicities in two highly variable intermediate polars towards the Galactic Center
• NuSTAR Hard X-ray Observation of the Gamma-ray Binary Candidate HESS J1832-093
• Chandra, NuSTAR, and Optical Observations of the Cataclysmic Variables IGR J17528-2022 and IGR J20063+3641
• An intermediate polar candidate toward the Galactic plane
• Periodicity from X-ray sources within the inner Galactic disk
• Classifying IGR J15038-6021 as a magnetic CV with a massive white dwarf
• Periodic X-ray Sources in the Galactic Bulge: Application of the Gregory-Loredo Algorithm
• New transient Galactic bulge intermediate polar candidate XMMU J175035.2-293557
• Broad Observational Perspectives Achieved by the Accreting White Dwarf Sciences in the XMM-Newton and Chandra Eras
• Optical Identification of Four Hard X-ray Sources from the INTEGRAL Sky Surveys
• Fluorescent Fe K line emission of gamma Cas stars II. Predictions for magnetic interactions and white-dwarf accretion scenarios
• X-ray emission mechanisms in accreting white dwarfs
• UGPS J194310+183851: an Unusual Optical and X-ray Faint Cataclysmic Variable?
• Origin of X-ray and gamma-ray emission from the Galactic central region
• High Energy Emission from the Galactic Center