Self-consistent computation of gamma-ray spectra due to proton-proton interactions in black hole systems

In the inner regions of an accretion disk around a black hole, relativistic protons can interact with ambient matter to produce electrons, positrons and $\gamma$-rays. The resultant steady state electron and positron particle distributions are self-consistently computed taking into account Coulomb and Compton cooling, $e^-e^+$ pair production (due to $\gamma-\gamma$ annihilation) and pair annihilation. While earlier works used the diffusion approximation to obtain the particle distributions, here we solve a more general integro-differential equation that correctly takes into account the large change in particle energy that occur when the leptons Compton scatter off hard X-rays. Thus this formalism can also be applied to the hard state of black hole systems, where the dominant ambient photons are hard X-rays. The corresponding photon energy spectrum is calculated and compared with broadband data of black hole binaries in different spectral states. The results indicate that the $\gamma$-ray spectra ($E > 0.8$ MeV) of both the soft and hard spectral states and the entire hard X-ray/$\gamma$-ray spectrum of the ultra-soft state, could be due to $p-p$ interactions. These results are consistent with the hypothesis that there always exists in these systems a $\gamma$-ray spectral component due to $p-p$ interactions which can contribute between 0.5 to 10% of the total bolometric luminosty. The model predicts that {\it GLAST} would be able to detect black hole binaries and provide evidence for the presence of non-thermal protons which in turn would give insight into the energy dissipation process and jet formation in these systems.Comment: Accepted for publication in MNRA

Corona, Jet, and Relativistic Line Models for Suzaku/RXTE/Chandra-HETG Observations of the Cygnus X-1 Hard State

Using Suzaku and the Rossi X-ray Timing Explorer, we have conducted a series of four simultaneous observations of the galactic black hole candidate Cyg X-1 in what were historically faint and spectrally hard low states. Additionally, all of these observations occurred near superior conjunction with our line of sight to the X-ray source passing through the dense phases of the focused wind from the mass donating secondary. One of our observations was also simultaneous with observations by the Chandra-High Energy Transmission Grating. These latter spectra are crucial for revealing the ionized absorption due to the secondary's focused wind. Such absorption is present and must be accounted for in all four spectra. These simultaneous data give an unprecedented view of the 0.8-300 keV spectrum of Cyg X-1, and hence bear upon both corona and X-ray emitting jet models of black hole hard states. Three models fit the spectra well: coronae with thermal or mixed thermal/non-thermal electron populations, and jets. All three models require a soft component that we fit with a low temperature disk spectrum with an inner radius of only a few tens of GM/c^2. All three models also agree that the known spectral break at 10\,keV is not solely due to the presence of reflection, but each gives a different underlying explanation for the augmentation of this break. Thus whereas all three models require that there is a relativistically broadened Fe line, the strength and inner radius of such a line is dependent upon the specific model, {thus making premature line-based estimates of the black hole spin in the Cyg X-1 system. We look at the relativistic line in detail, accounting for the narrow Fe emission and ionized absorption detected by HETG. Although the specific relativistic parameters of the line are continuum-dependent, none of the broad line fits allow for an inner disk radius that is >40 GM/c^2.Comment: 22 pages, 16 figures. Uses emulateapj style. Final three tables inserted as a figure to avoid issues with astro-ph's version of latex mangling the use of lscape. To be published in the Astrophysical Journal, January, 201

Tracing the jet contribution to the mid-IR over the 2005 outburst of GRO J1655-40 via broadband spectral modeling

We present new results from a multi-wavelength (radio/infrared/optical/X-ray) study of the black hole X-ray binary GRO J1655-40 during its 2005 outburst. We detected, for the first time, mid-infrared emission at 24 um from the compact jet of a black hole X-ray binary during its hard state, when the source shows emission from a radio compact jet as well as a strong non-thermal hard X-ray component. These detections strongly constrain the optically thick part of the synchrotron spectrum of the compact jet, which is consistent with being flat over four orders of magnitude in frequency. Moreover, using this unprecedented coverage, and especially thanks to the new Spitzer observations, we can test broadband disk and jet models during the hard state. Two of the hard state broadband spectra are reasonably well fitted using a jet model with parameters overall similar to those previously found for Cyg X-1 and GX 339-4. Differences are also present; most notably, the jet power in GRO J1655-40 appears to be a factor of at least ~3-5 higher (depending on the distance) than that of Cyg X-1 and GX 339-4 at comparable disk luminosities. Furthermore, a few discrepancies between the model and the data, previously not found for the other two black hole systems for which there was no mid-IR/IR and optical coverage, are evident, and will help to constrain and refine theoretical models.Comment: accepted for publication in Ap

XMM-Newton observation of the brightest X-ray flare detected so far from SgrA*

We report the high S/N observation on October 3, 2002 with XMM-Newton of the brightest X-ray flare detected so far from SgrA* with a duration shorter than one hour (~ 2.7 ks). The light curve is almost symmetrical with respect to the peak flare, and no significant difference between the soft and hard X-ray range is detected. The overall flare spectrum is well represented by an absorbed power-law with a soft photon spectral index of Gamma=2.5+/-0.3, and a peak 2-10 keV luminosity of 3.6 (+0.3-0.4) x 10^35 erg/s, i.e. a factor 160 higher than the Sgr A* quiescent value. No significant spectral change during the flare is observed. This X-ray flare is very different from other bright flares reported so far: it is much brighter and softer. The present accurate determination of the flare characteristics challenge the current interpretation of the physical processes occuring inside the very close environment of SgrA* by bringing very strong constraints for the theoretical flare models.Comment: Accepted for publication in A&A Letters. 4 pages, 2 figures, 1 table

Dissecting X-ray-emitting Gas around the Center of our Galaxy

Most supermassive black holes (SMBHs) are accreting at very low levels and are difficult to distinguish from the galaxy centers where they reside. Our own Galaxy's SMBH provides a uniquely instructive exception, and we present a close-up view of its quiescent X-ray emission based on 3 mega-second of Chandra observations. Although the X-ray emission is elongated and aligns well with a surrounding disk of massive stars, we can rule out a concentration of low-mass coronally active stars as the origin of the emission based on the lack of predicted Fe Kalpha emission. The extremely weak H-like Fe Kalpha line further suggests the presence of an outflow from the accretion flow onto the SMBH. These results provide important constraints for models of the prevalent radiatively inefficient accretion state.Comment: 18 pages, 5 PDF figures, pdflatex format; Final version, published in Scienc

Coordinated NIR/mm observations of flare emission from Sagittarius A*

We report on a successful, simultaneous observation and modelling of the millimeter (mm) to near-infrared (NIR) flare emission of the Sgr A* counterpart associated with the supermassive black hole at the Galactic centre (GC). We present a mm/sub-mm light curve of Sgr A* with one of the highest quality continuous time coverages and study and model the physical processes giving rise to the variable emission of Sgr A*.Comment: 14 pages, 16 figure

As Above, So Below: Exploiting Mass Scaling in Black Hole Accretion to Break Degeneracies in Spectral Interpretation

Over the past decade, evidence has mounted that several aspects of black hole (BH) accretion physics proceed in a mass-invariant way. One of the best examples of this scaling is the empirical "fundamental plane of BH accretion" relation linking mass, radio, and X-ray luminosity over eight orders of magnitude in BH mass. The currently favored theoretical interpretation of this relation is that the physics governing power output in weakly accreting BHs depends more on relative accretion rate than on mass. In order to test this theory, we explore whether a mass-invariant approach can simultaneously explain the broadband spectral energy distributions from two BHs at opposite ends of the mass scale but that are at similar Eddington accretion fractions. We find that the same model, with the same value of several fitted physical parameters expressed in mass-scaling units to enforce self-similarity, can provide a good description of two data sets from V404 Cyg and M81*, a stellar and supermassive BH, respectively. Furthermore, only one of several potential emission scenarios for the X-ray band is successful, suggesting it is the dominant process driving the fundamental plane relation at this accretion rate. This approach thus holds promise for breaking current degeneracies in the interpretation of BH high-energy spectra and for constructing better prescriptions of BH accretion for use in various local and cosmological feedback applications. © 2015. The American Astronomical Society. All rights reserved

A Suzaku Observation of NGC 4593: Illuminating the Truncated Disk

We report results from a 2007 Suzaku observation of the Seyfert 1 AGN NGC 4593. The narrow Fe K alpha emission line has a FWHM width ~4000 km/s, indicating emission from >~ 5000 Rg. There is no evidence for a relativistically broadened Fe K line, consistent with the presence of a radiatively efficient outer disk which is truncated or transitions to an interior radiatively inefficient flow. The Suzaku observation caught the source in a low-flux state; compared to a 2002 XMM observation, the hard X-ray flux decreased by 3.6, while the Fe K alpha line intensity and width each roughly halved. Two model-dependent explanations for the changes in Fe line profile are explored. In one, the Fe line width has decreased from ~10000 to ~4000 km/s from 2002 to 2007, suggesting that the thin disk truncation/transition radius has increased from 1000-2000 to >~5000 Rg. However, there are indications from other compact accreting systems that such truncation radii tend to be associated only with accretion rates relative to Eddington much lower than that of NGC 4593. In the second (preferred) model, the line profile in the XMM observation consists of a time-invariant narrow component plus a broad component originating from the inner part of the truncated disk (~300 Rg) which has responded to the drop in continuum flux. The Compton reflection component strength R is ~1.1, consistent with the measured Fe K alpha line total EQW with an Fe abundance 1.7 times solar. The modest soft excess has fallen by a factor of ~20 from 2002 to 2007, ruling out emission from a region 5 lt-yr in size.Comment: Accepted for publication in The Astrophysical Journal. 17 pages, 10 figure