Related papers: The time-lag -- photon-index correlation in GX 339…
Recently, we reported an observational correlation between a) the time-lag of the hard (9 - 15 keV) with respect to the soft (2 - 5 keV) X-ray photons in black-hole X-ray binaries (BHXRBs) and b) the power-law photon index $\Gamma$ of the…
We have performed a timing and spectral analysis of a set of black-hole binaries to study the correlation between the photon index and the time lag of the hard photons with respect to the soft ones. We provide further evidence that the…
Some recent observational results impose significant constraints on all the models that have been proposed to explain the Galactic black-hole X-ray sources in the hard state. In particular, it has been found that during the hard state of…
we propose a jet model for the low/hard state of black-hole X-ray sources which explains a) the X-ray spectra, b) the timelag spectra, c) the increase in the amplitude (QPO and high frequency) with increasing photon energy, and d) the…
Galactic black-hole X-ray binaries (BHBs) emit a compact, optically thick, mildly relativistic radio jet when they are in the hard and hard-intermediate states. In these states, BHBs exhibit a correlation between the time lag of hard…
We present a detailed analysis of the X-ray/IR fast variability of the Black-Hole Transient GX 339-4 during its low/hard state in August 2008. Thanks to simultaneous high time-resolution observations made with the VLT and RXTE, we performed…
The X-ray variations of hard state black hole X-ray binaries above 2 keV show 'hard lags', in that the variations at harder energies follow variations at softer energies, with a time-lag \tau depending on frequency \nu approximately as \tau…
We present the discovery of fast infrared/X-ray correlated variability in the black-hole transient GX 339-4. The source was observed with sub-second time resolution simultaneously with VLT/ISAAC and RXTE/PCA in August 2008, during its…
Most, probably all, accreting binaries that are believed to contain a black-hole emit radio waves when they are in the low/hard state. Whenever this radio emission has been resolved, a jet-like structure has become apparent. We propose that…
Here we present timing analysis of a set of eight Rossi X-ray Timing Explorer (RXTE) observations of the black hole candidate GX 339-4 that were taken during its hard/low state. On long time scales, the RXTE All Sky Monitor data reveal…
A rapid timing analysis of VLT/ULTRACAM and RXTE observations of the black hole binary GX 339-4 in its 2007 low/hard state is presented. The optical light curves in the r', g' and u' filters show slow (~20 s) quasi-periodic variability.…
We present the discovery of optical/X-ray flux correlations on rapid timescales in the low/hard state of the Galactic black hole GX 339-4. The source had recently emerged from outburst and was associated with a relatively-faint counterpart…
Owing to the frequency and reproducibility of its outbursts, the black-hole candidate GX 339-4 has become the standard against which the outbursts of other black-hole candidate are matched up. Here we present the first systematic study of…
We present a spectro-timing analysis of the black hole X-ray transient GX 339-4 using simultaneous observations from Astrosat and NICER during the 2021 outburst period. The combined spectrum obtained from NICER, LAXPC, and SXT data is…
We carried out a systematic analysis of time lags between X-ray energy bands in a large sample (32 sources) of unabsorbed, radio quiet active galactic nuclei (AGN), observed by XMM-Newton. The analysis of X-ray lags (up to the…
We report the few hundred second anti-correlated soft lags between soft and hard energy bands in the source GX 339-4 using RXTE observations. In one observation, anti-correlated soft lags were observed using the ISGRI/INTEGRAL hard energy…
We investigate the observed correlation between the 2--10 keV X-ray luminosity (in unit of the Eddington luminosity; $l_X \equiv L_X/L_{Edd}$) and the photon index ($\Gamma$) of the X-ray spectrum for both black hole X-ray binaries (BHBs)…
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…
Most black hole candidate X-ray binaries show Fourier time lags between softer and harder X-rays. The hard photons seem to arrive up to a few ms after the soft for a given Fourier frequency of the perturbation. The energy dependence of the…
We report results obtained from a systematic analysis of X-ray lags in a sample of black hole X-ray binaries, with the aim of assessing the presence of reverberation lags and studying their evolution during outburst. We used XMM-Newton and…