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Register a new userLuminosity dependence of the electron temperature in the bright hard state of the black hole candidate GX 339--4
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We have analyzed 200 Rossi X-ray Timing Explorer observations of the black hole candidate GX 339--4, all from the bright hard state periods between 1996 and 2005. Purpose of our study is to investigate the radiation mechanisms in the hard state of GX 339--4. The broadband 3--200 keV spectra were successfully modeled by a simple analytic model, power--law with an exponential cut-off modified with a smeared edge. The obtained energy cut-off ($E_{rm{cut}}$) was distributed over 50--200 keV, and the photon index over 1.4--1.7. We found a clear anti-correlation ($E_{rm{cut}} propto L^{-0.70pm0.06}$) between the X-ray luminosity ($L$) in 2--200 keV and $E_{rm{cut}}$, when $L$ is larger than $7 times 10^{37}$ erg s$^{-1}$ (assuming a distance of 8 kpc), while $E_{rm{cut}}$ is roughly constant at around 200 keV when $L$ is smaller than $7 times 10^{37}$ erg s$^{-1}$. This anti-correlation remained unchanged by adopting a more physical thermal Comptonization model, which resulted in the anti-correlation that can be expressed as $kT_{rm{e}} propto L^{-0.24pm0.06}$. These anti-correlations can be quantitatively explained by a picture in which the energy-flow rate from protons to electrons balances with the inverse Compton cooling.
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GX 339-4 has been observed by BeppoSAX twice in spring 1997 as part of a longer monitoring program. The source was close to the highest levels (50 mCrab) of the extended low state (as measured by the XTE ASM during the last 2 years). Its spectrum was quite hard, similar to the Exosat 1984 off state, but 40 times stronger. The source is detected up to more than 120 keV, enabling the possibility to study its high energy spectrum
We use simultaneous Swift and RXTE observations of the black hole binary GX 339-4 to measure the inner radius of its accretion disk in the hard state down to 0.4% L_{Edd} via modeling of the thermal disk emission and the relativistically broadened iron line. For the luminosity range covered in this work, our results rule out a significantly truncated disk at 100-1000 R_g as predicted by the advection-dominated accretion flow paradigm. The measurements depend strongly on the assumed emission geometry, with most results providing no clear picture of radius evolution. If the inclination is constrained to roughly 20 degrees, however, the measurements based on the thermal disk emission suggest a mildly receding disk at a luminosity of 0.4% L_{Edd}. The iron abundance varies between roughly 1-2 solar abundances, with the i=20 degrees results indicating a negative correlation with luminosity, though this is likely due to a change in disk illumination geometry.
We discuss a series of observations of the black hole candidate GX 339-4 in low luminosity, spectrally hard states. We present spectral analysis of three separate archival Advanced Satellite for Cosmology and Astrophysics (ASCA) data sets and eight separate Rossi X-ray Timing Explorer (RXTE) data sets. Three of the RXTE observations were strictly simultaneous with 843 MHz and 8.3-9.1 GHz radio observations. All of these observations have (3-9 keV) flux approximately < 10^{-9} ergs s^{-1} cm^{-2}. The ASCA data show evidence for an 6.4 keV Fe line with equivalent width 40 eV, as well as evidence for a soft excess that is well-modeled by a power law plus a multicolor blackbody spectrum with peak temperature 150-200 eV. The RXTE data sets also show evidence of an Fe line with equivalent widths 20-140 eV. Reflection models show a hardening of the RXTE spectra with decreasing X-ray flux; however, these models do not exhibit evidence of a correlation between the photon index of the incident power law flux and the solid angle subtended by the reflector. `Sphere+disk Comptonization models and Advection Dominated Accretion Flow (ADAF) models also provide reasonable descriptions of the RXTE data. The former models yield coronal temperatures in the range 20-50 keV and optical depths of tau ~ 3. The model fits to the X-ray data, however, do not simultaneously explain the observed radio properties. The most likely source of the radio flux is synchrotron emission from an extended outflow of size greater than O(10^7 GM/c^2).
Galactic black hole binaries produce powerful outflows with emit over almost the entire electromagnetic spectrum. Here, we report the first detection with the Herschel observatory of a variable far-infrared source associated with the compact jets of the black hole transient GX 339-4 during the decay of its recent 2010-2011 outburst, after the transition to the hard state. We also outline the results of very sensitive radio observations conducted with the Australia Telescope Compact Array, along with a series of near-infrared, optical (OIR) and X-ray observations, allowing for the first time the re-ignition of the compact jets to be observed over a wide range of wavelengths. The compact jets first turn on at radio frequencies with an optically thin spectrum that later evolves to optically thick synchrotron emission. An OIR reflare is observed about ten days after the onset of radio and hard X-ray emission, likely reflecting the necessary time to build up enough density, as well as to have acceleration (e.g. through shocks) along an extended region in the jets. The Herschel measurements are consistent with an extrapolation of the radio inverted power-law spectrum, but they highlight a more complex radio to OIR spectral energy distribution for the jets.
We report BeppoSAX and optical observations of the black hole candidate GX 339-4 during its X-ray `off state in 1999. The broad-band (0.8-50 keV) X-ray emission can be fitted by a single power law with spectral index, alpha ~1.6. The observed luminosity is 6.6e33 erg s^{-1} in the 0.5-10 keV band, which is at the higher end of the flux distribution of black hole soft X-ray transients in quiescence, comparable to that seen in GS 2023+338 and 4U 1630-47. An optical observation just before the BeppoSAX observation shows the source to be very faint at these wavelengths as well (B=20.1, V=19.2). By comparing with previously reported `off and low states (LS), we conclude that the `off state is actually an extension of the LS, i.e. a LS at lower intensities. We propose that accretion models such as the advection-dominated accretion flows are able to explain the observed properties in such a state.
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