On the Soft Excess in the X-ray Spectrum of Cir X-1: Revisitation of the Distance to Cir X-1

Abstract

We report on a 300 ks BeppoSAX (0.12-200 keV) observation of Circinus X-1 (Cir X-1) at phases between 0.62 and 0.84 and on a 90 ks BeppoSAX observation of Cir X--1 at phases 0.11-0.16. Using the canonical model adopted until now to fit the energy spectrum of this source large residuals appear below 1 keV. These are well fitted using an equivalent hydrogen column of $0.66\times 10^{22}$ cm${}^{-2}$, adding absorption edges of O VII, O VIII and Ne IX in the spectra extracted from the observation at phases 0.62-0.84 and adding absorption edges of O VII, O VIII, Mg XI and Mg XII and absorption lines of O VIII and Mg XII in the spectra extracted from the observation at phases 0.11-0.16. During the observation at phases 0.62--0.84 the electron density associated to the ionized matter is $\sim 10^{13}$ cm${}^{-3}$ remaining quit constant going away from the compact object. During the observation at phases 0.11-0.16 the electron density profile varies along the distance going from $\sim 6\times 10^{13}$ cm${}^{-3}$ at $\sim 10^{11}$ cm to $\sim 9\times 10^{10}$ cm${}^{-3}$ at $\sim 10^{13}$ cm. The equivalent hydrogen column towards Cir X-1 is thre times lower than the value obtained from previous models. This low value would imply that Cir X-1 is at a distance of 4.1 kpc.

arXiv comment30 pages, 11 figures, accepted by ApJ

References in corpus (25)

• Atomic Data for Astrophysics. II. New Analytic Fits for Photoionization Cross Sections of Atoms and Ions
• A New $\Sigma -D$ Relation and Its Application to the Galactic Supernova Remnant Distribution
• Atomic data for astrophysics. I. Radiative recombination rates for H-like, He-like, Li-like and Na-like ions over a broad range of temperature
• Galactic Kinematics of Cepheids from Hipparcos Proper Motions
• An ultra-relativistic outflow from a neutron star accreting gas from a companion
• Warm absorbers in active galactic nuclei
• The Discovery of a State Dependent Hard Tail in the X-ray Spectrum of the Luminous Z-source GX 17+2
• Refining the Oort and Galactic constants
• Detection of a Hard Tail in the X-ray Spectrum of the Z Source GX 349+2
• The Discovery of Broad P Cygni X-ray Lines from Circinus X-1 with the Chandra High Energy Transmission Grating Spectrometer
• On the Spectral Evolution of Cygnus X-2 along its Color-Color Diagram
• A measurement of the broad-band spectrum of XTE J1118+480 with BeppoSAX and its astrophysical implications
• Variability of the X-ray P Cygni Line Profiles from Circinus X-1 Near Zero Phase
• Circinus X-1: survivor of a highly asymmetric supernova
• The Complete "Z" Track of Circinus X-1
• High resolution optical and infrared spectroscopic observations of Cir X-1
• ASCA observations of the iron K complex of Circinus X-1 near zero phase: spectral evidence for partial covering
• The Composite Broad Band Spectrum of Cir X-1 at the Periastron: a Peculiar Z-source
• Long-term X-ray Variability of Circinus X-1
• Disappearance of Hard X-ray Emission in the Last BeppoSAX Observation of the Z Source GX 349+2
• X-ray behaviour of Circinus X-1 - I: X-ray Dips as a diagnostic of periodic behaviour
• Spectral Evolution of Circinus X-1 Along its Orbit
• Study of the Cir X--1 Broad Band Spectrum at Orbital Phases Close to the Apoastron
• HST observations rule out the association between Cir X-1 and SNR G321.9-0.3
• Evolution of Hard X-Ray Spectra Along the Branches in Cir X-1

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