218 research outputs found
The x-ray corona and jet of cygnus x-1
Evidence is presented indicating that in the hard state of Cygnus X-1, the
coronal mag- netic field might be below equipartition with radiation
(suggesting that the corona is not powered by magnetic field dissipation) and
that the ion temperature in the corona is significantly lower than what
predicted by ADAF like models. It is also shown that the current estimates of
the jet power set interesting contraints on the jet velocity (which is at least
mildly relativistic), the accretion efficiency (which is large in both spectral
states), and the nature of the X-ray emitting region (which is unlikely to be
the jet).Comment: 8 pages, 1 figure. Accepted for publication in Journal of Modern
Physics D, Proceedings of HEPRO II conference, Buenos Aires, Argentina,
October 26-30, 200
Using infrared/X-ray flare statistics to probe the emission regions near the event horizon of Sgr A*
The supermassive black hole at the centre of the Galaxy flares at least daily
in the infrared (IR) and X-ray bands, yet the process driving these flares is
still unknown. So far detailed analysis has only been performed on a few bright
flares. In particular, the broadband spectral modelling suffers from a strong
lack of simultaneous data. However, new monitoring campaigns now provide data
on thousands of flaring events, allowing a statistical analysis of the flare
properties. In this paper, we investigate the X-ray and IR flux distributions
of the flare events. Using a self-consistent calculation of the particle
distribution, we model the statistical properties of the flares. Based on a
previous work on single flares, we consider two families of models: pure
synchrotron models and synchrotron self-Compton (SSC) models. We investigate
the effect of fluctuations in some relevant parameters (e.g. acceleration
properties, density, magnetic field) on the flux distributions. The
distribution of these parameters is readily derived from the flux distributions
observed at different wavelengths. In both scenarios, we find that fluctuations
of the power injected in accelerated particles plays a major role. This must be
distributed as a power-law (with different indices in each model). In the
synchrotron dominated scenario, we derive the most extreme values of the
acceleration power required to reproduce the brightest flares. In that model,
the distribution of the acceleration slope fluctuations is constrained and in
the SSC scenario we constrain the distributions of the correlated magnetic
field and flow density variations.Comment: 9 pages, 3 tables, 6 figures, MNRAS, June 201
Thermal instability as a constraint for warm X-ray corona in AGN
Context. Warm corona is a possible explanation for Soft X-ray Excess in
Active Galactic Nuclei (AGN). This paper contains self consistent modeling of
both: accretion disk with optically thick corona, where the gas is heated by
magneto-rotational instability dynamo (MRI), and cooled by radiation which
undergoes free-free absorption and Compton scattering. Aims. We determine the
parameters of warm corona in AGN using disk-corona structure model that takes
into account magnetic and radiation pressure. We aim to show the role of
thermal instability (TI) as a constraint for warm, optically thick X-ray corona
in AGN. Methods. With the use of relaxation code, the vertical solution of the
disk driven by MRI together with radiative transfer in hydrostatic and
radiative equilibrium is calculated, which allows us to point out how TI
affects the corona for wide range of global parameters. Results. We show that
magnetic heating is strong enough to heat upper layers of the accretion disk
atmosphere, which form the warm corona covering the disk. Magnetic pressure
does not remove TI caused by radiative processes operating in X-ray emitting
plasma. TI disappears only in case of accretion rates higher than 0.2 of
Eddington, and high magnetic field parameter > 0.1.
Conclusions. TI plays the major role in the formation of the warm corona above
magnetically driven accretion disk in AGN. The warm, Compton cooled corona,
responsible for soft X-ray excess, resulted from our model has typical
temperature in the range of 0.01 - 2 keV and optical depth even up to 50, which
agrees with recent observations
Energetics of a black hole: constraints on the jet velocity and the nature of the X-ray emitting region in Cyg X-1
We investigate the energetics of the jet and X-ray corona of Cyg X-1. We show
that the current estimates of the jet power obtained from Halpha and [O III]
measurements of the optical nebula surrounding the X-ray source allow one to
constrain the bulk velocity of the jet. It is definitely relativistic (v >0.1c)
and most probably in the range (0.3-0.8)c. The exact value of the velocity
depends on the accretion efficiency. These constraints are obtained
independently of, and are consistent with, previous estimates of the jet bulk
velocity based on radio measurements. We then show that the X-ray emission does
not originate in the jet. Indeed, the energy budget does not allow the corona
to be ejected to infinity at relativistic speed. Rather, either a small
fraction of the corona escapes to infinity, or the ejection velocity of the
corona is vanishingly low. Although the corona could constitute the jet
launching region, it cannot be identified with the jet itself. We discuss the
consequences for various X-ray emission models.Comment: 9 pages, 4 figures, to appear in MNRA
Absorption lines from magnetically driven winds in X-ray binaries II: high resolution observational signatures expected from future X-ray observatories
In our self-similar, analytical, magneto-hydrodynamic (MHD)
accretion-ejection solution, the density at the base of the outflow is
explicitly dependent on the disk accretion rate - a unique property of this
class of solutions. We had earlier found that the ejection index is a key MHD parameter that decides if the flow
can cause absorption lines in the high resolution X-ray spectra of black hole
binaries. Here we choose 3 dense warm solutions with and
carefully develop a methodology to generate spectra which are convolved with
the Athena and XRISM response functions to predict what they will observe
seeing through such MHD outflows. In this paper two other external parameters
were varied - extent of the disk, , and the angle of the line of sight, .
Resultant absorption lines (H and He-like Fe, Ca, Ar) change in strength and
their profiles manifest varying degrees of asymmetry. We checked if a) the
lines and ii) the line asymmetries are detected, in our suit of synthetic
Athena and XRISM spectra. Our analysis shows that Athena should detect the
lines and their asymmetries for a standard 100 ksec observation of a 100 mCrab
source - lines with equivalent width as low as a few eV should be detected if
the 6-8 keV counts are larger than even for the least favourable
simulated cases.Comment: 18 pages, 13 figures in the main body and 3 figures in the appendix.
Accepted for publication in MNRA
A jet model for the fast IR variability of the black hole X-ray binary GX 339-4
Using the simultaneous Infra-Red (IR) and X-ray light curves obtained by Kalamkar et al., we perform a Fourier analysis of the IR/X-ray timing correlations of the black hole X-ray binary (BHB) GX 339-4. The resulting IR vs X-ray Fourier coherence and lag spectra are similar to those obtained in previous studies of GX 339-4 using optical light curves. In particular, above 1 Hz, the lag spectrum features an approximately constant IR lag of about 100 ms. We model simultaneously the radio to IR Spectral Energy Distribution (SED), the IR Power Spectral Density (PSD), and the coherence and lag spectra using the jet internal shock model ISHEM assuming that the fluctuations of the jet Lorentz factor are driven by the accretion flow. It turns out that most of the spectral and timing features, including the 100-ms lag, are remarkably well-reproduced by this model. The 100-ms time-scale is then associated with the travel time from the accretion flow to the IR emitting zone. Our exploration of the parameter space favours a jet which is at most mildly relativistic (ÂŻ < 3), and a linear and positive relation between the jet Lorentz factor and X-ray light curve i.e. (t) â 1âLX(t). The presence of a strong Low-Frequency Quasi-Periodic Oscillation (LFQPO) in the IR light curve could be caused by jet precession driven by LenseâThirring precession of the jet-emitting accretion flow. Our simulations confirm that this mechanism can produce an IR LFQPO similar to that observed in GX 339-4
Combined dark matter searches towards dwarf spheroidal galaxies with Fermi-LAT, HAWC, H.E.S.S., MAGIC, and VERITAS
Cosmological and astrophysical observations suggest that 85% of the total matter of the Universe is made of Dark Matter (DM). However, its nature remains one of the most challenging and fundamental open questions of particle physics. Assuming particle DM, this exotic form of matter cannot consist of Standard Model (SM) particles. Many models have been developed to attempt unraveling the nature of DM such as Weakly Interacting Massive Particles (WIMPs), the most favored particle candidates. WIMP annihilations and decay could produce SM particles which in turn hadronize and decay to give SM secondaries such as high energy \u1d6fe rays. In the framework of indirect DM search, observations of promising targets are used to search for signatures of DM annihilation. Among these, the dwarf spheroidal galaxies (dSphs) are commonly favored owing to their expected high DM content and negligible astrophysical background. In this work, we present the very first combination of 20 dSph observations, performed by the Fermi-LAT, HAWC, H.E.S.S., MAGIC, and VERITAS collaborations in order to maximize the sensitivity of DM searches and improve the current results. We use a joint maximum likelihood approach combining each experimentâs individual analysis to derive more constraining upper limits on the WIMP DM self-annihilation cross-section as a function of DM particle mass. We present new DM constraints over the widest mass range ever reported, extending from 5 GeV to 100 TeV thanks to the combination of these five different \u1d6fe-ray instruments
- âŠ