C. Sanchez-Fernandez

The black hole binary V404 Cygni: a highly accreting obscured AGN analogue

Typical black hole binaries in outburst show spectral states and transitions, characterized by a clear connection between the inflow onto the black hole and outflow from its vicinity. The transient stellar mass black hole binary V404 Cyg apparently does not fit in this picture. Its outbursts are characterized by intense flares and intermittent low-flux states, with a dynamical range of several orders of magnitude on timescales of hours. During the 2015 June-July X-ray outburst a joint Swift and INTEGRAL observing campaign captured V404 Cyg in one of these low-flux states. The simultaneous Swift/XRT and INTEGRAL/JEM-X/ISGRI spectrum is reminiscent of that of obscured/absorbed AGN. It can be modeled as a Comptonization spectrum, heavily absorbed by a partial covering, high-column density material (

DETECTION OF VERY LOW-FREQUENCY, QUASI-PERIODIC OSCILLATIONS IN THE 2015 OUTBURST OF V404 CYGNI

N_\textrm{H} \approx 1.4\times10^{24}\,\textrm{cm}^{-2}

V404 Cyg: an INTEGRAL and Swift X-ray view of an obscured microquasar

), and a dominant reflection component, including a narrow Iron-K

A hard X-ray transient in the direction of Terzan 5 detected by INTEGRAL

\alpha

A new outburst of the recurrent neutron star transient SAX J1747.0-2853

line. Such spectral distribution can be produced by a geometrically thick accretion flow able to launch a clumpy mass outflow, likely responsible for both the high intrinsic absorption and the intense reflection emission observed. Similarly to what happens in certain obscured AGN, the low-flux states might not be solely related to a decrease in the intrinsic luminosity, but could instead be caused by an almost complete obscuration of the inner accretion flow.

Two active X-ray transients in the Galactic Center region as seen by INTEGRAL

In 2015 June, the black hole X-ray binary (BHXRB) V404 Cygni went into outburst for the first time since 1989. Here, we present a comprehensive search for quasi-periodic oscillations (QPOs) of V404 Cygni during its recent outburst, utilizing data from six instruments on board five different X-ray missions: Swift/XRT, Fermi/GBM, Chandra/ACIS, INTEGRALs IBIS/ISGRI and JEM-X, and NuSTAR. We report the detection of a QPO at 18 mHz simultaneously with both Fermi/GBM and Swift/XRT, another example of a rare but slowly growing new class of mHz-QPOs in BHXRBs linked to sources with a high orbital inclination. Additionally, we find a duo of QPOs in a Chandra/ACIS observation at 73 mHz and 1.03 Hz, as well as a QPO at 136 mHz in a single Swift/XRT observation that can be interpreted as standard Type-C QPOs. Aside from the detected QPOs, there is significant structure in the broadband power, with a strong feature observable in the Chandra observations between 0.1 and 1 Hz. We discuss our results in the context of current models for QPO formation.

IGR J17453-2853 = Granat 1741.9-2853?

The black hole X-ray binary V404 Cyg entered an outburst phase on 2015 June 15 after 26 years of X-ray quiescence. Its activity was monitored at all wavelengths by virtually all the ground and space based facilities that could observe the source. This produced the largest multi-wavelength dataset on an active black hole X-ray transient. Here we focus on the X-ray monitoring campaign we carried out with the INTEGRAL and Swift satellites. We briefly summarise the results that we obtained from the observation of the most active phase of the outburst and we will describe our understanding of the source in the context of what it is known about accreting stellar mass and super-massive black holes. The results of time-resolved spectroscopy revealed that while the soft X-ray spectra extracted from Swift data reveal the effects of very variable, high column-density material obscuring the source, the hard X-ray spectra extracted from INTEGRAL are most sensitive the the source intrinsic (i.e. accretion driven) changes. Our results suggest that the inner part of the accretion flow in V404 Cyg is inflated into a so-called slim disk that hides the innermost regions of the flow, but also produces a cold, inhomogeneous, high-density outflow that introduces the high-absorption and fast spectral variability. We argue that the black hole in V404 Cyg might have been accreting erratically or even continuously at Eddington/Super-Eddington rates, while being partly or completely obscured. We therefore conclude that the part or even all of the flaring behaviour of the source might have not been accretion-driven, but rather the result of the covering/unveiling of the extremely bright source hidden within the system.