Broad-band X-ray measurements of the black hole candidate XTE J1908+094

Abstract

XTE J1908+094 is an X-ray transient that went into outburst in February 2002. After two months it reached a 2-250 keV peak flux of 1 to 2 X 10-8 erg/s/cm2. Circumstantial evidence points to an accreting galactic black hole as the origin of the the X-radiation: pulsations nor thermonuclear flashes were detected that would identify a neutron star and the spectrum was unusually hard for a neutron star at the outburst onset. We report on BeppoSAX and RXTE All Sky Monitor observations of the broad-band spectrum of XTE J1908+094. The spectrum is consistent with a model consisting of a Comptonization component by a ~40 keV plasma (between 2 and 60 keV this component can be approximated by a power law with a photon index of 1.9 to 2.1), a multicolor accretion disk blackbody component with a temperature just below 1 keV and a broad emission line at about 6 keV. The spectrum is heavily absorbed by cold interstellar matter with an equivalent hydrogen column density of 2.5 X 10+22 cm-2, which makes it difficult to study the black body component in detail. The black body component exhibits strong evolution about 6 weeks into the outburst. Two weeks later this is followed by a swift decay of the power law component. The broadness of the 6 keV feature may be due to relativistic broadening or Compton scattering of a narrow Fe-K line.

Accepted for publication in Astronomy & Astrophysics

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• Large Torque Variations in Two Soft Gamma Repeaters
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• WATCHDOG: A Comprehensive All-Sky Database of Galactic Black Hole X-ray Binaries
• Stellar-mass Black Hole Spin Constraints from Disk Reflection and Continuum Modeling
• Magnetars as persistent hard X-ray sources: INTEGRAL discovery of a hard tail in SGR 1900+14
• Investigating state transition luminosities of Galactic black hole transients in the outburst decay
• Resolved, expanding jets in the Galactic black hole candidate XTE J1908+094
• The hard to soft spectral transition in LMXBs - affected by recondensation of gas into an inner disk
• Radio and X-ray observations during the outburst decay of the Black Hole Candidate XTE J1908+094
• Five years of SGR 1900+14 observations with BeppoSAX
• First results from TOO observations of the Aql X-1 field with INTEGRAL
• A Short Review of Relativistic Iron Lines from Stellar-Mass Black Holes
• Long Term Spectral and Timing Behavior of the Black Hole Candidate XTE J1908+094
• Disk-jet coupling changes as a possible indicator for outbursts from GX 339-4 remaining within the X-ray hard state
• A closer look at the X-ray transient XTE J1908+094: identification of two new near-infrared candidate counterparts
• NuSTAR and Swift observations of the black hole candidate XTE J1908+094 during its 2013 outburst
• A Dependable Distance Estimator to Black Hole Low-Mass X-ray Binaries
• Properties of Faint X-ray Activity of XTE J1908+094 in 2019
• An improvement of the BeppoSAX LECS and MECS positioning accuracy
• Long term spectral variability in the Soft Gamma-ray Repeater SGR 1900+14
• Long term spectral variability in the soft gamma ray repeater SGR 1900+14
• The Spin and Orientation of the Black Hole in XTE J1908$+$094