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تسجيل مستخدم جديدCorrelations between radio and bolometric fluxes in GX 339-4 and H1743-322
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Compact radio jets are ubiquitous in stellar-mass black-hole binaries in their hard spectral state. Empirical relations between the radio and narrow-band X-ray fluxes have been used to understand the connection between their accretion discs and jets. However, a narrow-band (e.g., 1--10 or 3--9 keV) X-ray flux can be a poor proxy for either the bolometric luminosity or the mass accretion rate. Here, we study correlations between the radio and unabsorbed broad-band X-ray fluxes, the latter providing good estimates of the bolometric flux. We consider GX 339--4, the benchmark object for the main branch of the correlation, and H1743--322, the first source found to be an outlier of the correlation. The obtained power-law dependencies of the radio flux on the bolometric flux have significantly different indices from those found for the narrow X-ray bands. Also, the radio/bolometric flux correlations for the rise of the outbursts are found to be significantly different from those for the outburst decline. This points to a possible existence of a jet hysteresis in the radio/X-ray source evolution, in addition to that seen in the hardness/flux diagram of low-mass X-ray binaries. The correlation during the rise of the outbursts is similar for both GX 339--4 and H1743--322. The correlation for the decline of the outbursts for H1743--322 lies below that of GX 339--4 at intermediate X-ray fluxes, whereas it approaches the standard correlation at lower X-ray luminosities. We also compare these correlations to those for the high-mass X-ray binaries Cyg X-1 and Cyg X-3.
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The radio:X-ray correlation that characterises accreting black holes at all mass scales - from stellar mass black holes in binary systems to super-massive black holes powering Active Galactic Nuclei - is one of the most important pieces of observatio
nal evidence supporting the existence of a connection between the accretion process and the generation of collimated outflows - or jets - in accreting systems. Although recent studies suggest that the correlation extends down to low luminosities, only a handful of stellar mass black holes have been clearly detected, and in general only upper limits (especially at radio wavelengths) can be obtained during quiescence. We recently obtained detections of the black hole X-ray binary GX 339--4 in quiescence using the MeerKAT radio telescope and Swift X-ray Telescope instrument onboard the Neil Gehrels Swift Observatory, probing the lower end of the radio:X-ray correlation. We present the properties of accretion and of the connected generation of jets in the poorly studied low-accretion rate regime for this canonical black hole XRB system.
We analyze seven NICER and NuSTAR epochs of the black hole X-ray binary GX 339-4 in the hard state during its two most recent hard-only outbursts in 2017 and 2019. These observations cover the 1-100 keV unabsorbed luminosities between 0.3% and 2.1% o
f the Eddington limit. With NICERs negligible pile-up, high count rate and unprecedented time resolution, we perform a spectral-timing analysis and spectral modeling using relativistic and distant reflection models. Our spectral fitting shows that as the inner disk radius moves inwards, the thermal disk emission increases in flux and temperature, the disk becomes more highly ionized and the reflection fraction increases. This coincides with the inner disk increasing its radiative efficiency around ~1% Eddington. We see a hint of hysteresis effect at ~0.3% of Eddington: the inner radius is significantly truncated during the rise ($>49R_{g}$), while only a mild truncation ($sim5R_g$) is found during the decay. At higher frequencies ($2-7$~Hz) in the highest luminosity epoch, a soft lag is present, whose energy dependence reveals a thermal reverberation lag, with an amplitude similar to previous findings for this source. We also discuss the plausibility of the hysteresis effect and the debate of the disk truncation problem in the hard state.
The X-ray binary, black hole candidate, and microquasar H1743-322 exhibited a series of X-ray outbursts between 2003 and 2008. We took optical/infrared (OIR) observations with the ESO/NTT telescope during 3 of these outbursts (2003, 2004, and 2008),
to study its spectral energy distribution (SED). We detect rapid flares of duration ~5 mn in the high time-resolution IR lightcurve. We identify H and He emission lines in the IR spectra, coming from the accretion disk. The IR SED exhibits the spectral index typically associated with the X-ray high, soft state in our observations taken during the 2003 and 2004 outbursts, while the index changes to one that is typical of the X-ray low, hard state during the 2008 outburst. During this last outburst, we detected a change of slope in the NIR spectrum between the J and Ks bands, where the JH part is characteristic of an optically thick disk emission, while the HKs part is typical of optically thin synchrotron emission. Furthermore, the comparison of our IR data with radio and X-ray data shows that H1743-322 exhibits a faint jet both in radio and NIR domains. Finally, we suggest that the companion star is a late-type main sequence star located in the Galactic bulge. These OIR photometric and spectroscopic observations of the microquasar H1743-322, the first of this source to be published in a broad multiwavelength context, allow us to unambiguously identify two spectra of different origins in the OIR domain, evolving from optically thick thermal emission to optically thin synchrotron emission toward longer wavelengths. Comparing these OIR observations with other black hole candidates suggests that H1743-322 behaves like a radio-quiet and NIR-dim black hole in the low, hard state. This study will be useful when quantitatively comparing the overall contribution of the compact jet and accretion flow in the energy budget of microquasars.
We report on a campaign of X-ray and soft gamma-ray observations of the black hole candidate H 1743-322 (also named IGR J17464-3213), performed with the RXTE, INTEGRAL and Swift satellites. The source was observed during a short outburst between 2008
October 03 and 2008 November 16. The evolution of the hardness-intensity diagram throughout the outburst is peculiar, in that it does not follow the canonical pattern through all the spectral states (the so called q-track pattern) seen during the outburst of black-hole transients. On the contrary, the source only makes a transition from the Hard State to the Hard-Intermediate State. After this transition, the source decreases in luminosity and its spectrum hardens again. This behaviour is confirmed both by spectral and timing analysis. This kind of outburst has been rarely observed before in a transient black hole candidate.
Black-hole transients exhibit a correlation between the time lag of hard photons with respect to softer ones and the photon index of the hard X-ray power law. The correlation is not very tight and therefore it is necessary to examine it source by sou
rce. The objective of the present work is to investigate in detail the time-lag -- photon-index correlation in GX 339-4. We have obtained RXTE energy spectra and light curves and have computed the photon index and the time lag of the $9 - 15$ keV photons with respect to the $2 - 6$ keV ones. The observations cover the first stages of the hard state, the pure hard state, and the hard-intermediate state. At low $Gamma$, the correlation is positive and it becomes negative at large $Gamma$. By assuming that the hard X-ray power law index $Gamma$ is produced by inverse Compton scattering of soft disk photons in the jet, we have reproduced the entire correlation by varying two parameters in the jet: the radius of the jet at its base $R_0$ and the Thomson optical depth along the jet $tau_parallel$. We have found that, as the luminosity of the source increases, $R_0$ initially increases and then decreases. This behavior is expected in the context of the Cosmic Battery. As a further test of our model, we predict the break frequency in the radio spectrum as a function of the photon index during the rising part of an outburst.
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