47 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&
Noyaux actifs de galaxies en rayons gamma extrêmes: Connexions radio-gamma pour l’étude des blazars intermédiaires
The development of multi-wavelength observations of active galactic nuclei nowadays allows to reach a quasi-full coverage of their emission from radio to the highest reachable energies, in the TeV domain, by the Cherenkov telescopes. Consequently, the emission models of these sources are increasingly constraints, in particular for blazars where standard one zone synchrotron self-Compton (SSC) emission scenarios are regularly disproved by this new information flow. The main subject of this thesis is the in-depth study of blazars called « intermediates » between the two spectral categories identified long-time ago which are BL Lacs and FSRQs (for flat spectrum radio quasars).In a first stage we lead a complete study of the intermediate blazar Ap Librae for which we show that the extended jet basis play a very significant role in the overall source radiation. For this study we present the development of a SSC multi-zones code dealing in a consistent way the radiative interactions between the different components. Thereafter we are focusing on the radio features of the jet, observed by very long baseline interferometry (VLBI), being able to be used to constrain effectively the physical and geometrical parameters of the model. This study allows to deduce a strong link between the observed jet radio knots and the compact zone which emits in gamma-rays.In a second stage we characterize a blazar population by the radio spectra study, which like Ap Librae shows a relatively strong jet compared to the emission of the compact SSC zone. We propose a new blazar classification based on kinematic properties of VLBI jets in a sample of 167 sources selected in the MOJAVE database. A good correlation between VLBI kinematic properties and spectral classes is found and highlight the presence of an intermediate class. Hence we check the consistence of peculiar properties of this class in the general blazar unification scheme.This thesis being also within the H.E.S.S. collaboration, we present the analysis results of recently detected or very promising sources at very high energies. We expose also the last developments of a method which could improve the astrometric accuracy of the H.E.S.S. array by a star tracking on the cameras.Le développement des observations multi-longueurs d'onde des noyaux actifs de galaxies permetaujourd'hui d'atteindre une couverture quasi complète de leur rayonnement depuis la radio jusqu'auxplus hautes énergies accessibles, du domaine du TeV, par les télescopes Tcherenkov.Les modèles d'émissions de ces sources se trouvent de plus en plus contraints, en particulier pourles blazars où les scénarios standards de type Synchrotron Self Compton (SSC) à une zone sontrégulièrement mis en défaut par ce nouveau flot d'informations.Le sujet principal de cette thèse est l'étude approfondie des blazars dits « intermédiaires » entre lesdeux catégories spectrales depuis longtemps identifiées que sont les BL Lacs et les FSRQs (pourflat spectrum radio quasars).En première approche nous menons une étude complète du blazar intermédiaire Ap Librae pourlequel nous montrons que la base du jet étendu joue un rôle très significatif dans le rayonnementglobal de la source. Pour cette étude nous présentons le développement d'un code SSC multi-zonestraitant de manière cohérente les interactions radiatives entre les différentes composantes.Nous nous concentrons ensuite sur les caractéristiques radio observées par « very large baselineinterferometry » (VLBI) du jet pouvant être utilisées pour contraindre efficacement les paramètresphysiques et géométriques du modèle, et déduisons un lien fort entre les nodules radios observésdans le jet et la zone compacte émettant en gamma.En seconde approche nous caractérisons une population de blazars par l'étude des spectres radios,qui à l'instar d'Ap Librae présentent un jet relativement puissant devant l'émission d'une zonecompacte SSC. Nous proposons une classification nouvelle des blazars basée sur les propriétéscinématiques des jets VLBI dans un échantillon de 167 sources sélectionnées dans la base dedonnées de la collaboration MOJAVE. La présence d'une corrélation entre la cinématiqueradio et la classe spectrale met en avant la nature de cette classe intermédiaire, dont nous vérifionspar la suite la cohérence dans un scénario d'unification des blazars.Cette thèse étant également au sein de la collaboration du réseau de télescopes TcherenkovH.E.S.S., nous présentons les résultats d'analyse de sources nouvellement détectées ou trèsprometteuses aux très hautes énergies. Nous exposons aussi les développements récents d'uneméthode d'amélioration de la précision astrométrique du réseau par le suivi d'étoiles sur les caméras
Bjet_MCMC: A new tool to automatically fit the broadband SEDs of blazars
Multiwavelength observations are now the norm for studying blazars' various
states of activity, classifying them, and determining possible underlying
physical processes driving their emission. Broadband emission models became
unavoidable tools for testing emission scenarios and setting values to physical
quantities such as the magnetic field strength, Doppler factor, or shape of the
particle distribution of the emission zone(s). We announce here the first
public release of a new tool, Bjet_MCMC, that can automatically fit broadband
spectral energy distributions (SEDs) of blazars. The complete code is available
on GitHub and allows testing leptonic synchrotron self-Compton models (SSC),
with or without external inverse-Compton processes from the thermal environment
of supermassive black holes (accretion disk and broad line region). The code is
designed to be user-friendly and computationally efficient. It contains a core
written in C++ and a fully parallelized SED fitting method. The original
multi-SSC zones model of Bjet is also available on GitHub but is not included
in the MCMC fitting process at the moment. We present the features,
performance, and results of Bjet_MCMC, as well as user advice.Comment: 14 pages, 7 figures, 3 tables, Submitted to Ap
Panoramic SETI: Program Update and High-Energy Astrophysics Applications
Optical SETI (Search for Extraterrestrial Intelligence) instruments that can
explore the very fast time domain, especially with large sky coverage, offer an
opportunity for new discoveries that can complement multimessenger and time
domain astrophysics. The Panoramic SETI experiment (PANOSETI) aims to observe
optical transients with nanosecond to second duration over a wide field-of-view
(2,500 sq.deg.) by using two assemblies of tens of telescopes to
reject spurious signals by coincidence detection. Three PANOSETI telescopes,
connected to a White Rabbit timing network used to synchronize clocks at the
nanosecond level, have been deployed at Lick Observatory on two sites separated
by a distance of 677 meters to distinguish nearby light sources (such as
Cherenkov light from particle showers in the Earth's atmosphere) from
astrophysical sources at large distances. In parallel to this deployment, we
present results obtained during four nights of simultaneous observations with
the four 12-meter VERITAS gamma-ray telescopes and two PANOSETI telescopes at
the Fred Lawrence Whipple Observatory. We report PANOSETI's first detection of
astrophysical gamma rays, comprising three events with energies in the range
between 15 TeV and 50 TeV. These were emitted by the Crab
Nebula, and identified as gamma rays using joint VERITAS observations.Comment: 9 pages, 5 figures, SPIE Astronomical Telescopes + Instrumentation
conference, 2022, Montr\'eal, Qu\'ebec, Canad
A VERITAS/Breakthrough Listen Search for Optical Technosignatures
The Breakthrough Listen Initiative is conducting a program using multiple
telescopes around the world to search for "technosignatures": artificial
transmitters of extraterrestrial origin from beyond our solar system. The
VERITAS Collaboration joined this program in 2018, and provides the capability
to search for one particular technosignature: optical pulses of a few
nanoseconds duration detectable over interstellar distances. We report here on
the analysis and results of dedicated VERITAS observations of Breakthrough
Listen targets conducted in 2019 and 2020 and of archival VERITAS data
collected since 2012. Thirty hours of dedicated observations of 136 targets and
249 archival observations of 140 targets were analyzed and did not reveal any
signals consistent with a technosignature. The results are used to place limits
on the fraction of stars hosting transmitting civilizations. We also discuss
the minimum-pulse sensitivity of our observations and present VERITAS
observations of CALIOP: a space-based pulsed laser onboard the CALIPSO
satellite. The detection of these pulses with VERITAS, using the analysis
techniques developed for our technosignature search, allows a test of our
analysis efficiency and serves as an important proof-of-principle.Comment: 15 pages, 7 figure
VERITAS discovery of very high energy gamma-ray emission from S3 1227+25 and multiwavelength observations
We report the detection of very high energy gamma-ray emission from the
blazar S3 1227+25 (VER J1230+253) with the Very Energetic Radiation Imaging
Telescope Array System (VERITAS). VERITAS observations of the source were
triggered by the detection of a hard-spectrum GeV flare on May 15, 2015 with
the Fermi-Large Area Telescope (LAT). A combined five-hour VERITAS exposure on
May 16th and May 18th resulted in a strong 13 detection with a
differential photon spectral index, = 3.8 0.4, and a flux level
at 9% of the Crab Nebula above 120 GeV. This also triggered target of
opportunity observations with Swift, optical photometry, polarimetry and radio
measurements, also presented in this work, in addition to the VERITAS and
Fermi-LAT data. A temporal analysis of the gamma-ray flux during this period
finds evidence of a shortest variability timescale of = 6.2
0.9 hours, indicating emission from compact regions within the jet, and the
combined gamma-ray spectrum shows no strong evidence of a spectral cut-off. An
investigation into correlations between the multiwavelength observations found
evidence of optical and gamma-ray correlations, suggesting a single-zone model
of emission. Finally, the multiwavelength spectral energy distribution is well
described by a simple one-zone leptonic synchrotron self-Compton radiation
model.Comment: 18 pages, 6 figures. Accepted for publication in the Astrophysical
Journal (ApJ
The SuperCam Instrument Suite on the Mars 2020 Rover: Science Objectives and Mast-Unit Description
On the NASA 2020 rover mission to Jezero crater, the remote determination of the texture, mineralogy and chemistry of rocks is essential to quickly and thoroughly characterize an area and to optimize the selection of samples for return to Earth. As part of the Perseverance payload, SuperCam is a suite of five techniques that provide critical and complementary observations via Laser-Induced Breakdown Spectroscopy (LIBS), Time-Resolved Raman and Luminescence (TRR/L), visible and near-infrared spectroscopy (VISIR), high-resolution color imaging (RMI), and acoustic recording (MIC). SuperCam operates at remote distances, primarily 2-7 m, while providing data at sub-mm to mm scales. We report on SuperCam's science objectives in the context of the Mars 2020 mission goals and ways the different techniques can address these questions. The instrument is made up of three separate subsystems: the Mast Unit is designed and built in France; the Body Unit is provided by the United States; the calibration target holder is contributed by Spain, and the targets themselves by the entire science team. This publication focuses on the design, development, and tests of the Mast Unit; companion papers describe the other units. The goal of this work is to provide an understanding of the technical choices made, the constraints that were imposed, and ultimately the validated performance of the flight model as it leaves Earth, and it will serve as the foundation for Mars operations and future processing of the data.In France was provided by the Centre National d'Etudes Spatiales (CNES). Human resources were provided in part by the Centre National de la Recherche Scientifique (CNRS) and universities. Funding was provided in the US by NASA's Mars Exploration Program. Some funding of data analyses at Los Alamos National Laboratory (LANL) was provided by laboratory-directed research and development funds
Broadband Multi-wavelength Properties of M87 during the 2017 Event Horizon Telescope Campaign
Abstract: In 2017, the Event Horizon Telescope (EHT) Collaboration succeeded in capturing the first direct image of the center of the M87 galaxy. The asymmetric ring morphology and size are consistent with theoretical expectations for a weakly accreting supermassive black hole of mass ∼6.5 × 109 M ⊙. The EHTC also partnered with several international facilities in space and on the ground, to arrange an extensive, quasi-simultaneous multi-wavelength campaign. This Letter presents the results and analysis of this campaign, as well as the multi-wavelength data as a legacy data repository. We captured M87 in a historically low state, and the core flux dominates over HST-1 at high energies, making it possible to combine core flux constraints with the more spatially precise very long baseline interferometry data. We present the most complete simultaneous multi-wavelength spectrum of the active nucleus to date, and discuss the complexity and caveats of combining data from different spatial scales into one broadband spectrum. We apply two heuristic, isotropic leptonic single-zone models to provide insight into the basic source properties, but conclude that a structured jet is necessary to explain M87’s spectrum. We can exclude that the simultaneous γ-ray emission is produced via inverse Compton emission in the same region producing the EHT mm-band emission, and further conclude that the γ-rays can only be produced in the inner jets (inward of HST-1) if there are strongly particle-dominated regions. Direct synchrotron emission from accelerated protons and secondaries cannot yet be excluded