A Hard Tail in the Broad Band Spectrum of the Dipper XB 1254-690

Abstract

We report on the results of spectral analysis of the dipping source XB 1254-690 observed by the BeppoSAX satellite. We find that the X-ray dips are not present during the BeppoSAX observation, in line with recent RXTE results. The broad band (0.1-100 keV) energy spectrum is well fitted by a three-component model consisting of a multicolor disk blackbody with an inner disk temperature of ~0.85 keV, a comptonized spectrum with an electron temperature of ~2 keV, and a bremsstrahlung at a temperature of ~20 keV. Adopting a distance of 10 kpc and taking into account a spectral hardening factor of ~1.7 (because of electron scattering which modifies the blackbody spectrum emitted by the disk) we estimated that the inner disk radius is $R_{\mathrm{in}}\sqrt{\cos i}\sim 11$ km, where i is the inclination angle of the system with respect to the line of sight. The comptonized component could originate in a spherical corona or boundary layer, surrounding the neutron star, with optical depth ~19. The bremsstrahlung emission, contributing ~4% of the total luminosity, probably originates in an extended accretion disk corona with radius $\sim 10^{10}$ cm. In this scenario we calculated that the optical depth of this region is ~0.71 and its mean electron density is $N_e\sim 2.7\times 10^{14}$ cm${}^{-3}$. This last component might also be present in other low mass X-ray binaries, but, because of its low intrinsic luminosity, it is not easily observable. We also find an absorption edge at ~1.27 keV with an optical depth of ~0.15. Its energy could correspond to the L-edge of Fe XVII, or K-edge of Ne X or neutral Mg.

13 pages, 3 figures, Accepted by ApJ

References in corpus (4)

• On the interpretation of the multicolour disc model for black hole candidates
• Hard X-ray Emission From Low Mass X-ray Binaries
• The Broad Band Spectrum of MXB 1728-34 Observed by BeppoSAX
• A Cessation of X-ray Dipping Activity in X1254-690

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• Discovery of narrow X-ray absorption features from the low-mass X-ray binary X 1254-690 with XMM-Newton
• X-ray observations of RX J0822-4300 and Puppis-A
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• Variations in the dip properties of the low-mass X-ray binary XB 1254-69 observed with XMM-Newton and INTEGRAL
• Disc-Jet coupling in the LMXB 4U1636-53 from INTEGRAL
• Spectral states evolution of 4U 1728-34 observed by INTEGRAL and RXTE: non-thermal component detection
• A re-analysis of the NuSTAR and XMM-Newton broad-band spectrum of Ser~X-1
• Chandra Observation of the Dipping Source XB 1254-690
• On the disc reflection spectroscopy of NS LMXB Serpens~X-1: analysis of a recent NuSTAR observation
• Suzaku Observation of the High-Inclination Binary EXO 0748-676 in the Hard State
• Reflection component in the Bright Atoll Source GX 9+9
• Kinematical Studies of the Low Mass X-Ray Binary GR Mus (XB1254-690)
• X-ray Bursts in Neutron Star and Black Hole Binaries from USA and RXTE Data: Detections and Upper Limits
• The origin of the tilted disk in the low mass X-ray binary GR Mus (XB 1254-690)
• Renewed activity from the X-ray transient SAXJ 1810.8-2609 with INTEGRAL
• Broad-band spectral analysis of LMXB XTE J1710-281 with Suzaku
• Updating the orbital ephemeris of the dipping source XB 1254-690 and the distance to the source
• Discovery of X-ray absorption lines from the low-mass X-ray binaries 4U 1916-053 and X 1254-069 with XMM-Newton
• Timing and spectral study of XB 1254-690 using new RXTE PCA data