113 research outputs found
Stochastic Acceleration in Relativistic Parallel Shocks
(abridged) We present results of test-particle simulations on both the first
and the second order Fermi acceleration at relativistic parallel shock waves.
We consider two scenarios for particle injection: (i) particles injected at the
shock front, then accelerated at the shock by the first order mechanism and
subsequently by the stochastic process in the downstream region; and (ii)
particles injected uniformly throughout the downstream region to the stochastic
process. We show that regardless of the injection scenario, depending on the
magnetic field strength, plasma composition, and the employed turbulence model,
the stochastic mechanism can have considerable effects on the particle spectrum
on temporal and spatial scales too short to be resolved in extragalactic jets.
Stochastic acceleration is shown to be able to produce spectra that are
significantly flatter than the limiting case of particle energy spectral index
-1 of the first order mechanism. Our study also reveals a possibility of
re-acceleration of the stochastically accelerated spectrum at the shock, as
particles at high energies become more and more mobile as their mean free path
increases with energy. Our findings suggest that the role of the second order
mechanism in the turbulent downstream of a relativistic shock with respect to
the first order mechanism at the shock front has been underestimated in the
past, and that the second order mechanism may have significant effects on the
form of the particle spectra and its evolution.Comment: 14 pages, 11 figures (9 black/white and 2 color postscripts). To be
published in the ApJ (accepted 6 Nov 2004
30 years of multi-wavelength observations of 3C 273
We present a wide multi-wavelength database of most observations of the
quasar 3C 273 obtained during the last 30 years. This database is the most
complete set of observations available for an active galactic nucleus (AGN). It
contains nearly 20'000 observations grouped together into 70 light curves
covering 16 orders of magnitude in frequency from the radio to the gamma-ray
domain.
The database is constituted of many previously unpublished observations and
of most publicly available data gathered in the literature and on the World
Wide Web (WWW). It is complete to the best of our knowledge, except in the
optical (UBV) domain where we chose not to add all observations from the
literature. In addition to the photometric data, we present the spectra of 3C
273 obtained by the International Ultraviolet Explorer (IUE) satellite. In the
X-ray domain, we used the spectral fit parameters from the literature to
construct the light curves.
Apart from describing the data, we show the most representative light curves
and the average spectrum of 3C 273. The database is available on the WWW in a
homogeneous and clear form and we wish to update it regularly by adding new
observations.Comment: 12 pages, 6 figures, to be published in A&AS, data available at:
http://obswww.unige.ch/3c273
CIV 1549 as an Eigenvector 1 Parameter for Active Galactic Nuclei
[Abridged] We have been exploring a spectroscopic unification for all known
types of broad line emitting AGN. The 4D Eigenvector 1 (4DE1) parameter space
shows promise as a unification capable of organizing quasar diversity on a
sequence primarily governed by Eddington ratio. This paper considers the role
of CIV 1549 measures with special emphasis on the CIV 1549 line shift as a
principal 4DE1 diagnostic. We use HST archival spectra for 130 sources with S/N
high enough to permit reliable CIV 1549 broad component (BC) measures. We find
a CIV 1549 BC profile blueshift that is strongly concentrated among (largely
radio-quiet: RQ) sources with FWHM(H beta BC) < 4000 km/s (which we call
Population A). Narrow line Seyfert 1 (NLSy1, with FWHM H beta < 2000 km/s)
sources belong to this population but do not emerge as a distinct class. The
systematic blueshift, widely interpreted as arising in a disk wind/outflow, is
not observed in broader lined AGN which we call Population B. We find new
correlations between FWHM(CIV 1549 BC) and CIV 1549 line shift as well as the
equivalent width of CIV 1549. They are seen only in Pop. A sources. CIV 1549
measures enhance the apparent dichotomy at FWHM(Hbeta BC) approx. 4000 \kms\
(Sulentic et al. 2000) suggesting that it has more significance in the context
of Broad Line Region structure than the more commonly discussed RL vs. RQ
dichotomy. Black hole masses computed from FWHM CIV 1549 BC for about 80 AGN
indicate that the CIV 1549 width is a poor virial estimator. Comparison of mass
estimates derived from Hbeta BC and CIV 1549 reveals that the latter show
different and nonlinear offsets for population A and B sources. A significant
number of sources also show narrow line CIV 1549 emission. We present a recipe
for CIV 1549 narrow component extraction.Comment: Accepted for publication in the Astrophysical Journa
INTEGRAL and Swift observations of IGRJ19294+1816 in outburst
IGRJ19294+1816 was discovered by INTEGRAL in 2009 during a bright X-ray
outburst and was classified as a possible Be X-ray binary or supergiant fast
X-ray transient. On 2010 October 28, the source displayed a second X-ray
outburst and a 2 months-long monitoring with Swift was carried out to follow
the evolution of the source X-ray flux during the event. We report on the
INTEGRAL and Swift observations of the second X-ray outburst observed from
IGRJ19294+1816. We detected pulsations in the X-ray emission from the source at
\sim12.5 s up to 50 keV. The source X-ray flux decreased smoothly during the
two months of observation displaying only marginal spectral changes. Due to the
relatively rapid decay of the source X-ray flux, no significant variations of
the source spin period across the event could be measured. This prevented a
firm confirmation of the previously suggested orbital period of the source at
117 d. This periodicity was also searched by using archival Swift /BAT data. We
detected a marginally significant peak in the periodogram and determined the
best period at 116.2\pm0.6 days (estimated chance probability of a spurious
detection 1%). The smooth decline of the source X-ray flux across the two
months of observations after the onset of the second outburst, together with
its relatively low value of the spin period and the absence of remarkable
changes in the spectral parameters (i.e., the absorption column density),
suggests that IGRJ19294+1816 is most likely another member of the Be X-ray
binaries discovered by INTEGRAL and not a supergiant fast X-ray transient.Comment: Accepted for publication in A&A. 7 pages, 10 figure
Scientific Performance of the ISDC Quick Look Analysis
The INTEGRAL Science Data Centre (ISDC) routinely monitors the Near Real Time
data (NRT) from the INTEGRAL satellite. A first scientific analysis is made in
order to check for the detection of new, transient or highly variable sources
in the data. Of primary importance for this work is the Interactive Quick Look
Analysis (IQLA), which produces JEM-X and ISGRI images and monitors them for
interesting astrophysical eventsComment: 4 pages, 3 figures. Proceedings of 5th INTEGRAL Workshop: The
INTEGRAL Universe, Munich, 16-20 February 2004. Accepted for publication in
European Space Agency Special Publication 552. See paper for institute
affiliation
A kinematic study of the compact jet in quasar B3 1633+382
We present a study of the motion of compact jet components in quasar B3
1633+382. Through analyzing 14 epochs of VLBI observations of three components
(B1, B2, and B3) at 22 GHz, we find two different possibilities of component
classification. Thus two corresponding kinematical models can be adopted to
explain the evolutionary track of components. One is a linear motion, while
another is a helical model. Future observations are needed to provide new
kinematical constraints for the motion of these components in this source.Comment: 7 pages, 3 figures; Accepted for publication in A&
Survival of Chondrocytes in Rabbit Septal Cartilage After Electromechanical Reshaping
Electromechanical reshaping (EMR) has been recently described as an alternative method for reshaping facial cartilage without the need for incisions or sutures. This study focuses on determining the short- and long-term viability of chondrocytes following EMR in cartilage grafts maintained in tissue culture. Flat rabbit nasal septal cartilage specimens were bent into semi-cylindrical shapes by an aluminum jig while a constant electric voltage was applied across the concave and convex surfaces. After EMR, specimens were maintained in culture media for 64Â days. Over this time period, specimens were serially biopsied and then stained with a fluorescent liveâdead assay system and imaged using laser scanning confocal microscopy. In addition, the fraction of viable chondrocytes was measured, correlated with voltage, voltage application time, electric field configuration, and examined serially. The fraction of viable chondrocytes decreased with voltage and application time. High local electric field intensity and proximity to the positive electrode also focally reduced chondrocyte viability. The density of viable chondrocytes decreased over time and reached a steady state after 2â4Â weeks. Viable cells were concentrated within the central region of the specimen. Approximately 20% of original chondrocytes remained viable after reshaping with optimal voltage and application time parameters and compared favorably with conventional surgical shape change techniques such as morselization
The spectral energy distribution of the central parsecs of the nearest AGN
Spectral energy distributions (SEDs) of the central few tens of parsec region
of some of the nearest, most well studied, active galactic nuclei (AGN) are
presented. These genuine AGN-core SEDs, mostly from Seyfert galaxies, are
characterised by two main features: an IR bump with the maximum in the 2-10
micron range, and an increasing X-ray spectrum in the 1 to ~200 keV region.
These dominant features are common to Seyfert type 1 and 2 objects alike. Type
2 AGN exhibit a sharp drop shortward of 2 micron, with the optical to UV region
being fully absorbed, while type 1s show instead a gentle 2 micron drop ensued
by a secondary, partially-absorbed optical to UV emission bump. Assuming the
bulk of optical to UV photons generated in these AGN are reprocessed by dust
and re-emitted in the IR in an isotropic manner, the IR bump luminosity
represents >70% of the total energy output in these objects while the high
energies above 20 keV are the second energetically important contribution.
Galaxies selected by their warm IR colours, i.e. presenting a relatively-flat
flux distribution in the 12 to 60 micron range have often being classified as
AGN. The results from these high spatial resolution SEDs question this
criterion as a general rule. It is found that the intrinsic shape of the IR SED
of an AGN and inferred bolometric luminosity largely depart from those derived
from large aperture data. AGN luminosities can be overestimated by up to two
orders of magnitude if relying on IR satellite data. We find these differences
to be critical for AGN luminosities below or about 10^{44} erg/s. Above this
limit, AGNs tend to dominate the light of their host galaxy regardless of the
aperture size used. We tentatively mark this luminosity as a threshold to
identify galaxy-light- vs AGN- dominated objects.Comment: 50 pages, 14 figures. Accepted for publication in MNRA
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