1,580 research outputs found
Linking radio and gamma ray emission in Ap Librae
Ap Lib is one of the rare Low Synchrotron Peaked blazars detected so far at
TeV energies. This type of source is not properly modelled by standard one-zone
leptonic Synchrotron-self-Compton (SSC) emission scenarios. The aim of this
paper is to study the relevance of additional components which should naturally
occur in a SSC scenario for a better understanding of the emission mechanisms,
especially at very high energies (VHE). Methods. We use simultaneous data from
a multi-wavelength campaign of Planck, Swift-UVOT and Swift-XRT telescopes
carried out in February 2010, as well as quasi-simultaneous data of WISE, Fermi
and H.E.S.S. taken in 2010. The multi-lambda emission of Ap Lib is modelled by
a blob-in-jet SSC scenario including the contribution of the base of the VLBI
extended jet, the radiative blob-jet interaction, the accretion disk and its
associated external photon field. We show that signatures of a strong
parsec-scale jet and of an accretion disk emission are present in the SED. We
can link the observationnal VLBI jet features from MOJAVE to parameters
expected for a VHE emitting blob accelerated near the jet base. The VHE
emission appears to be dominated by the inverse-Compton effect of the blob
relativistic electrons interacting with the jet synchrotron radiation. In such
scenario Ap Lib appears as an intermediate source between BL Lac objects and
Flat Spectrum Radio Quasars. Ap Lib could be a bright representative of a
specific class of blazars, in which the parsec-scale jet luminosity is no more
negligible compared to the blob and contributes to the high energy emission via
inverse Compton processes.Comment: 12 pages, 7 figures, Accepted for publication in A&
La survie religieuse des communautés protestantes du centre de la France et du Bassin parisien de la Révocation de l’édit de Nantes à l’édit de tolérance (1685-1787)
Le protestantisme du Nord de la France aux XVIIe et XVIIIe siècles se caractérise par sa grande dispersion ainsi que par sa très faible importance numérique. Pourtant, malgré le choc de la Révocation, les conversions et les départs, des communautés vivantes traversent le dernier siècle de l\u27Ancien Régime. Du point de vue religieux, des signes montrent que, tout au long de cette période, les protestants conservent une foi vivante: des assemblées se tiennent dès les premiers mois de l\u27édit de Fontainebleau, des «nouveaux convertis» attaquent le dogme et la discipline de l\u27Église catholique, ou refusent l\u27intervention du curé dans les grands moments de leur vie. Les formes de résistance et les rythmes de persécution sont cependant variables d\u27une communauté, voire d\u27une époque à l\u27autre. Certaines églises, en particulier celles de Picardie, profitent de la proximité de la frontière avec les Pays-Bas autrichiens, ainsi que de la présence des pasteurs qui accompagnent les garnisons de la Barrière. D\u27autres, plus isolées, trouvent dans la capitale un lieu d\u27accueil et leurs membres fréquentent les chapelles d\u27ambassades des pays protestants. Ce n\u27est pourtant que tardivement, et non sans mal, que les structures ecclésiastiques se réorganisent, à partir du milieu des années 1760. L\u27édit de tolérance permet à ces communautés affaiblies démographiquement de reparaître au grand jour, là où elles ont survécu
Host galaxies of AGN
The relationship of an AGN to its host galaxy is a crucial question in the study of galaxy evolution. We perform stellar population synthesis in the central regions of galaxies of different activity levels. A large number of stellar features are measured both in the optical and near-infrared. We find the nuclear stellar population to be related to the level of activity. These differences are no more conspicuous further away in the bulge of the galaxy
Shocks in relativistic transverse stratified jets, a new paradigm for radio-loud AGN
The transverse stratification of active galactic nuclei (AGN) jets is
suggested by observations and theoretical arguments, as a consequence of
intrinsic properties of the central engine (accretion disc + black hole) and
external medium. On the other hand, the one-component jet approaches are
heavily challenged by the various observed properties of plasmoids in radio
jets (knots), often associated with internal shocks. Given that such a
transverse stratification plays an important role on the jets acceleration,
stability, and interaction with the external medium, it should also induce
internal shocks with various strengths and configurations, able to describe the
observed knots behaviours. By establishing a relation between the transverse
stratification of the jets, the internal shock properties, and the multiple
observed AGN jet morphologies and behaviours, our aim is to provide a
consistent global scheme of the various AGN jet structures. Working on a large
sample of AGN radio jets monitored in very long baseline interferometry (VLBI)
by the MOJAVE collaboration, we determined the consistency of a systematic
association of the multiple knots with successive re-collimation shocks. We
then investigated the re-collimation shock formation and the influence of
different transverse stratified structures by parametrically exploring the two
relativistic outflow components with the specific relativistic hydrodynamic
(SRHD) code AMRVAC. We were able to link the different spectral classes of AGN
with specific stratified jet characteristics, in good accordance with their
VLBI radio properties and their accretion regimes.Comment: 16 pages, 12 figures, accepted for publication in A&
A synchrotron self-Compton model for the VHE gamma-ray emission from Cen A
The H.E.S.S. experiment has reported the detection of very high energy (VHE:
E>100 GeV) gamma-ray emission from the well-known radio-galaxy Cen A. Following
this discovery, we refine the previous multi-blob synchrotron self-Compton
(SSC) model applied to the multi-wavelength emission from this source using the
new H.E.S.S. data. The prediction of the VHE gamma-ray level of emission for
Cen A presented in Lenain et al. paper agrees very well in the view of this
recent data. Further VHE observations of Cen A might detect variability, which
would comfort our inner jet modeling. The next generation of imaging
atmospheric Cherenkov telescopes, will help to reveal possible multiple sources
of VHE emission in the complex structure of Cen A.Comment: 4 pages, 1 figure; contribution to the 31st ICRC, Lodz, Poland, July
200
H.E.S.S. discovery of very-high-energy gamma-ray emission of PKS 1440-389
Blazars are the most abundant class of known extragalactic very-high-energy
(VHE, E>100 GeV) gamma-ray sources. However, one of the biggest difficulties in
investigating their VHE emission resides in their limited number, since less
than 60 of them are known by now. In this contribution we report on H.E.S.S.
observations of the BL Lac object PKS 1440-389. This source has been selected
as target for H.E.S.S. based on its high-energy gamma-ray properties measured
by Fermi-LAT. The extrapolation of this bright, hard-spectrum gamma-ray blazar
into the VHE regime made a detection on a relatively short time scale very
likely, despite its uncertain redshift. H.E.S.S. observations were carried out
with the 4-telescope array from February to May 2012 and resulted in a clear
detection of the source. Contemporaneous multi-wavelength data are used to
construct the spectral energy distribution of PKS 1440-389 which can be
described by a simple one-zone synchrotron-self Compton model.Comment: In Proceedings of the 34th International Cosmic Ray Conference
(ICRC2015), The Hague, The Netherland
Inertial waves and modes excited by the libration of a rotating cube
We report experimental measurements of the flow in a cubic container
submitted to a longitudinal libration, i.e. a rotation modulated in time.
Velocity fields in a vertical and a horizontal plane are measured in the
librating frame using a corotating particle image velocimetry system. When the
libration frequency is smaller than twice the mean rotation rate
, inertial waves can propagate in the interior of the fluid. At
arbitrary excitation frequencies , the oscillating flow
shows two contributions: (i) a basic flow induced by the libration motion, and
(ii) inertial wave beams propagating obliquely upward and downward from the
horizontal edges of the cube. In addition to these two contributions, inertial
modes may also be excited at some specific resonant frequencies. We
characterize in particular the resonance of the mode of lowest order compatible
with the symmetries of the forcing, noted [2,1,+]. By comparing the measured
flow fields to the expected inviscid inertial modes computed numerically
[L.R.M. Maas, Fluid Dyn. Res. \textbf{33}, 373 (2003)], we show that only a
subset of inertial modes, matching the symmetries of the forcing, can be
excited by the libration.Comment: Phys. Fluids (in press
Redshift measurement of Fermi Blazars for the Cherenkov Telescope Array
Blazars are active galactic nuclei, and the most numerous High Energy (HE)
and Very High Energy (VHE) gamma-ray emitters. Their optical emission is often
dominated by non-thermal, and, in the case of BL Lacs, featureless continuum
radiation. This renders the determination of their redshift extremely
difficult. Indeed, as of today only about 50 % of gamma-ray blazars have a
measured spectroscopic redshift. The knowledge of redshift is fundamental
because it allows the precise modeling of the VHE emission and also of its
interaction with the extragalactic background light (EBL). The beginning of the
Cherenkov Telescope Array (CTA) operations in the near future will allow the
detection of several hundreds of new BL Lacs. Using the first Fermi catalogue
of sources above 10 GeV (1FHL), we performed simulations which demonstrate that
at least half of the 1FHL BL Lacs detectable by CTA will not have a measured
redshift. Indeed the organization of observing campaigns to measure the
redshift of these blazars has been recognized as a necessary support for the
AGN Key Science Project of CTA. Taking advantage of the recent success of an
X-shooter GTO observing campaign, we thus devised an observing campaign to
measure the redshifts of as many as possible of these candidates. The main
characteristic of this campaign with respect to previous ones will be the use
of higher resolution spectrographs and of 8 meter class telescopes. We are
starting submitting proposals for these observations. In this paper we will
briefly describe the selection of the candidates, the characteristics of these
observation and the expected results.Comment: 8 pages, 2 figures, In Proceedings of the 34th International Cosmic
Ray Conference (ICRC2015), The Hague, The Netherlands. All CTA contributions
at arXiv:1508.0589
- …