221 research outputs found
An innovative blazar classification based on radio jet kinematics
Blazars are usually classified following their synchrotron peak frequency
( scale) as high, intermediate, low frequency peaked BL Lacs (HBLs,
IBLs, LBLs), and flat spectrum radio quasars (FSRQs), or, according to their
radio morphology at large scale, FR~I or FR~II. However, the diversity of
blazars is such that these classes seem insufficient to chart the specific
properties of each source. We propose to classify a wide sample of blazars
following the kinematic features of their radio jets seen in very long baseline
interferometry (VLBI). For this purpose we use public data from the MOJAVE
collaboration in which we select a sample of blazars with known redshift and
sufficient monitoring to constrain apparent velocities. We selected 161 blazars
from a sample of 200 sources. We identify three distinct classes of VLBI jets
depending on radio knot kinematics: class I with quasi-stationary knots, class
II with knots in relativistic motion from the radio core, and class I/II,
intermediate, showing quasi-stationary knots at the jet base and relativistic
motions downstream. A notable result is the good overlap of this kinematic
classification with the usual spectral classification; class I corresponds to
HBLs, class II to FSRQs, and class I/II to IBLs/LBLs. We deepen this study by
characterizing the physical parameters of jets from VLBI radio data. Hence we
focus on the singular case of the class I/II by the study of the blazar BL Lac
itself. Finally we show how the interpretation that radio knots are
recollimation shocks is fully appropriate to describe the characteristics of
these three classes.Comment: 12 pages, 13 figures, accepted by A&
The buried Balmer-edge signatures from quasars
In our previous paper, we have reported the detection of a Balmer edge
absorption feature in the polarized flux of one quasar (Ton 202). We have now
found similar Balmer edge features in the polarized flux of four more quasars
(4C09.72, 3C95, B2 1208+32, 3C323.1), and possibly a few more, out of 14 newly
observed with the VLT and Keck telescopes. In addition, we also re-observed Ton
202, but we did not detect such a dramatic feature, apparently due to
polarization variability (the two observations are one-year apart). The
polarization measurements of some quasars are affected by an interstellar
polarization in our Galaxy, but the measurements have been corrected for this
effect reasonably well.
Since the broad emission lines are essentially unpolarized and the
polarization is confined only to the continuum in the five quasars including
Ton 202 in both epochs, the polarized flux is considered to originate interior
to the broad emission line region. The Balmer edge feature seen in the
polarized flux is most simply interpreted as an intrinsic spectral feature of
the quasar UV/optical continuum, or the ``Big Blue Bump'' emission. In this
case, the edge feature seen in absorption indeed indicates the thermal and
optically-thick nature of the continuum emitted. However, we also discuss other
possible interpretations.Comment: Accepted for publication in MNRAS; 31 pages, 38 figures with reduced
resolutions; the paper with a full resolution is at
http://www.roe.ac.uk/~mk/papers/04Ba_vk.ps.g
A mixed lepto-hadronic scenario for PKS 2155-304
The models developed to describe the spectral energy distribution (SED) of
blazars can be divided into leptonic or hadronic scenarios, according to the
particles responsible for the high-energy component. We have developed a new
stationary code which computes all the relevant leptonic and hadronic
processes, permitting the study of both leptonic and hadronic scenarios in a
consistent way. Interestingly, mixed lepto-hadronic scenarios (in which both
components contribute to the high energy emission) naturally arise in this
framework. We present the first application to the well known BL Lac object PKS
2155-304.Comment: 4 pages, 1 figure; to appear in the proceedings of the Gamma 2012
conferenc
IVOA Provenance data model: hints from the CTA Provenance prototype
We present the last developments on the IVOA Provenance data model, mainly
based on the W3C PROV concept. In the context of the Cherenkov astronomy, the
data processing stages imply both assumptions and comparison to dedicated
simulations. As a consequence, Provenance information is crucial to the end
user in order to interpret the high level data products. The Cherenkov
Telescope Array (CTA), currently in preparation, is thus a perfect test case
for the development of an IVOA standard on Provenance information. We describe
general use-cases for the computational Provenance in the CTA production
pipeline and explore the proposed W3C notations like PROV-N formats, as well as
Provenance access solutions.Comment: 4 pages, 3 figures, to appear in ADASS XXV proceedings, edited by N.
P. F. Lorente, & K. Shortridge (San Francisco: ASP), ASP Conf. Se
High energy blazars spectroscopy with X-Shooter on the VLT
We present results of observations in the UV to near-IR range for eight
blazars, three of which have been recently discovered at Very High Energies
(VHE) and five appearing as interesting candidates for VHE {\gamma}-ray
detection. We focus in this paper on the search for their redshifts, which are
unknown or considered as uncertain.Comment: 4 pages, 8 figures, to appear in the proceedings of the 5th
International Symposium on High-Energy Gamma-Ray Astronomy (Gamma2012), July
9-13, 2012, Heidelberg, German
ExHaLe-jet: Modeling blazar jets with an extended hadro-leptonic radiation code
Blazars emit across all electromagnetic wavelengths. While the so-called
one-zone model has described well both quiescent and flaring states, it cannot
explain the radio emission and fails in more complex data sets, such as AP
Librae. In order to self-consistently describe the entire electromagnetic
spectrum emitted by the jet, extended radiation models are necessary. Notably,
kinetic descriptions of extended jets can provide the temporal and spatial
evolution of the particle species and the full electromagnetic output. Here, we
present the initial results of a newly developed hadro-leptonic extended-jet
code: ExHaLe-jet. As protons take much longer than electrons to lose their
energy, they can transport energy over much larger distances than electrons and
are therefore essential for the energy transport in the jet. Furthermore,
protons induce injection of additional pairs through pion and Bethe-Heitler
pair production, which can explain a dominant leptonic radiation signal while
still producing neutrinos. In this talk, we discuss the differences between
leptonic and hadronic dominated SED solutions, the SED shapes, evolution along
the jet flow, and jet powers. We also highlight the important role of external
photon fields, such as the accretion disk and the BLR.Comment: Proceedings paper to the GAMMA2022 conference held in Barcelona,
Spain. To appear as PoS(Gamma2022)18
Spectroscopy of High Energy BL Lac Objects with X-shooter on the VLT
Context. The study of BL Lac objects (BLL) detected in gamma-rays gives
insights on the acceleration mechanisms in play in such systems and is also a
valuable tool to constrain the density of the extragalactic background light.
As their spectra are dominated by the non-thermal emission of the jet and the
spectral features are weak and narrow in the optical domain, measuring their
redshift is challenging. However such a measure is fundamental as it allows a
firm determination of the distance and luminosity of the source, and therefore
a consistent model of its emission. Aims. Measurement of the redshift of BLL
detected in gamma-rays and determination of global properties of their host
galaxies. Methods. We observed a sample of eight BLL (KUV 00311-1938, PKS
0447-439, PKS 0301-243, BZB J0238-3116, BZB J0543-5532, BZB J0505+0415, BZB
J0816-1311 and RBS 334) with the X-shooter spectrograph installed at the ESO
Very Large Telescope in order to take advantage of its unprecedented wavelength
coverage and of its resolution about 5 times higher than generally used in such
studies. We extracted UVB to NIR spectra that we then corrected for telluric
absorption and calibrated in flux. We systematically searched for spectral
features. When possible, we determined the contribution of the host galaxy to
the overall emission. Results. Of the eight BLL, we measured the redshift of
five of them and determined lower limits for two through the detection of
intervening systems. All seven of these objects have redshifts greater than
0.2. In two cases, we refuted redshift values reported in other publications.
Through careful modelling, we determined the magnitude of the host galaxies. In
two cases, the detection of emission lines allowed to provide hints on the
overall properties of the gas in the host galaxies.Comment: 19 pages, 10 figures, 7 tables, in press on A&
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