1,924 research outputs found
Jet-Disc coupling in the accreting black hole XTEJ1118+480
We interpret the rapid correlated UV/optical/ X-ray variability of
XTEJ1118+480 as a signature of the coupling between the X-ray corona and a jet
emitting synchrotron radiation in the optical band.We propose a scenario in
which the jet and the X-ray corona are fed by the same energy reservoir where
large amounts of accretion power are stored before being channelled into either
the jet or the high energy radiation. This time dependent model reproduces the
main features of the rapid multi-wavelength variability of XTEJ1118+480. A
strong requirement of the model is that the total jet power should be at least
a few times larger than the observed X-ray luminosity. This would be consistent
with the overall low radiative efficiency of the source. We present independent
arguments showing that the jet probably dominates the energetic output of all
accreting black holes in the low-hard state.Comment: 8 pages, 1 figure, to appear in the proceedings of "From X-ray
binaries to quasars: Black hole accretion on all mass scales, (Amsterdam,
July 2004)", Eds. T. Maccarone, R. Fender, L. H
Implications of very rapid TeV variability in blazars
We discuss the implications of rapid (few-minute) variability in the TeV flux
of blazars, which has been observed recently with the HESS and MAGIC
telescopes. The variability timescales seen in PKS 2155-304 and Mrk 501 are
much shorter than inferred light-crossing times at the black hole horizon,
suggesting that the variability involves enhanced emission in a small region
within an outflowing jet. The enhancement could be triggered by dissipation in
part of the black hole's magnetosphere at the base of the outflow, or else by
instabilities in the jet itself. By considering the energetics of the observed
flares, along with the requirement that TeV photons escape without producing
pairs, we deduce that the bulk Lorentz factors in the jets must be >50. The
distance of the emission region from the central black hole is less
well-constrained. We discuss possible consequences for multi-wavelength
observations.Comment: 5 pages, no figures, accepted for publication in Monthly Notices of
the Royal Astronomical Society Letter
X-ray observations of the galaxy cluster PKS 0745-191: To the virial radius, and beyond
We measure X-ray emission from the outskirts of the cluster of galaxies PKS
0745-191 with Suzaku, determining radial profiles of density, temperature,
entropy, gas fraction, and mass. These measurements extend beyond the virial
radius for the first time, providing new information about cluster assembly and
the diffuse intracluster medium out to ~1.5 r_200, (r_200 ~ 1.7 Mpc ~ 15'). The
temperature is found to decrease by roughly 70 per cent from 0.3-1 r_200. We
also see a flattening of the entropy profile near the virial radius and
consider the implications this has for the assumption of hydrostatic
equilibrium when deriving mass estimates. We place these observations in the
context of simulations and analytical models to develop a better understanding
of non-gravitational physics in the outskirts of the cluster.Comment: 10 pages, 11 figures, accepted to MNRAS; expanded discussion of
analysis and uncertainties, results qualitatively unchange
Allan Variance Analysis as Useful Tool to Determine Noise in Various Single-Molecule Setups
One limitation on the performance of optical traps is the noise inherently
present in every setup. Therefore, it is the desire of most experimentalists to
minimize and possibly eliminate noise from their optical trapping experiments.
A step in this direction is to quantify the actual noise in the system and to
evaluate how much each particular component contributes to the overall noise.
For this purpose we present Allan variance analysis as a straightforward
method. In particular, it allows for judging the impact of drift which gives
rise to low-frequency noise, which is extremely difficult to pinpoint by other
methods. We show how to determine the optimal sampling time for calibration,
the optimal number of data points for a desired experiment, and we provide
measurements of how much accuracy is gained by acquiring additional data
points. Allan variances of both micrometer-sized spheres and asymmetric
nanometer-sized rods are considered.Comment: 14 pages, 6 figures, presented at SPIE Optics+Photonics 2009 in San
Diego, CA, US
The Ultra-Fast Outflow of WKK 4438: Suzaku and NuSTAR X-ray Spectral Analysis
Previous X-ray spectral analysis has revealed an increasing number of AGNs
with high accretion rates where an outflow with a mildly relativistic velocity
originates from the inner accretion disk. Here we report the detection of a new
ultra-fast outflow (UFO) with a velocity of in addition to a relativistic disk reflection
component in a poorly studied NLS1 WKK~4438, based on archival \nustar and
\suzaku observations. The spectra of both \suzaku and \nustar observations show
an Fe~\textsc{xxvi} absorption feature and the \suzaku data also show evidence
for an Ar~\textsc{xviii} with the same blueshift. A super-solar argon abundance
() and a slight iron over-abundance
() are found in our spectral
modelling. Based on Monte-Carlo simulations, the detection of the UFO is
estimated to be around at 3 significance. The fast wind most likely
arises from a radius of away from the central black hole. The disk
is accreting at a high Eddington ratio (). The
mass outflow rate of the UFO is comparable with the disk mass inflow rate
(), assuming a maximum covering factor.
The kinetic power of the wind might not be high enough to have influence in AGN
feedback () due to a relatively
small column density (~cm). However note that
both the inferred velocity and the column density could be lower limits owing
to the low viewing angle ().Comment: 7 pages, 3 figures, accepted by MNRA
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