70 research outputs found
The Fate of Dead Radio-loud Active Galactic Nuclei: A New Prediction of Long-lived Shell Emission
We examine the fate of a dead radio source in which jet injection from the
central engine has stopped at an early stage of its evolution ( yr). To this aim, we theoretically evaluate the evolution of the
emission from both the lobe and the shell, which are composed of shocked jet
matter and a shocked ambient medium, respectively. Based on a simple dynamical
model of expanding lobe and shell, we clarify how the broadband spectrum of
each component evolves before and after the cessation of the jet activity. It
is shown that the spectrum is strongly dominated by the lobe emission while the
jet is active (). On the other hand, once the jet activity has
ceased (), the lobe emission fades out rapidly, since fresh electrons
are no longer supplied from the jet. Meanwhile, shell emission only shows a
gradual decrease, since accelerated electrons are continuously supplied from
the bow shock that is propagating into the ambient medium. As a result, overall
emission from the shell overwhelms that from the lobe at wide range of
frequencies from radio up to gamma-ray soon after the jet activity has ceased.
Our result predicts a new class of dead radio sources that are dominated by
shell emission. We suggest that the emission from the shell can be probed in
particular at a radio wavelengths with the Square Kilometer Array (SKA) phase
1.Comment: 9 pages, 3 figures, accepted for publication in Ap
The extragalactic gamma-ray sky: A view on the most powerful phenomena in the universe
The gamma-ray sky provides a look into the most energetic and violent processes of the universe. In the last years, gamma-ray satellites are scanning the sky for understanding the physics governing the gamma-ray emission. A wealth of information on the physics of the gamma-ray sky has been obtained by gamma-ray satellites orbiting around the Earth. So far, roughly three thousands sources have been detected in gamma-rays, and this number is going to increase as the gamma-ray missions continue to survey the sky. The high energy sky is dominated by extragalactic objects. A large fraction of the detected sources has no obvious counterpart in catalogs at other wavelengths, leaving their nature under debate. This contribution will focus on the extragalactic gamma-ray sky, its properties and processes at work with the aim of discussing the main issues highly debated in the astrophysical community
Observing the Time Evolution of the Multi-Component Nucleus of 3C\,84
The advent of global mm-band Very Long Baseline Interferometry (VLBI) in
recent years has finally revealed the morphology of the base of the two most
prominent nearby, bright, extragalactic radio jets in M\,87 and 3C\,84. The
images are quite surprising considering the predictions of jet theory and
current numerical modeling. The jet bases are extremely wide compared to
expectations and the nucleus of 3C\,84 is very complicated. It appears as a
double in 86\,GHz observations with 50\,as resolution and a triple nucleus
with 30\,as resolution with space-based VLBI by RadioAstron at 22\,GHz.
What is even odder is that the double and triple are arranged along an
east-west line that is approximately orthogonal to the north-south large scale
jet on 150\,as 4\,mas scales. We explore the emergence of an
(east-west) double nucleus in the lower resolution 43\,GHz Very Long Baseline
Array (VLBA) imaging from August 2018 to April 2020. The double is marginally
resolved. We exploit the east-west resolution associated with the longest
baselines, \,mas, to track a predominantly east-west separation
speed of \,c. We estimate that the observed mildly
relativistic speed persists over a de-projected distance of
times the central, supermassive black hole, gravitational radius (\,lt-yrs) from the point of origin.Comment: To appear in Ap
Uncovering the host galaxy of the -ray-emitting narrow-line Seyfert 1 galaxy FBQS J1644+2619
The discovery of -ray emission from radio-loud narrow-line Seyfert 1
(NLSy1) galaxies has questioned the need for large black hole masses (> 10
M) to launch relativistic jets. We present near-infrared data of the
-ray-emitting NLSy1 FBQS J1644+2619 that were collected using the
camera CIRCE (Canarias InfraRed Camera Experiment) at the 10.4-m Gran
Telescopio Canarias to investigate the structural properties of its host galaxy
and to infer the black hole mass. The 2D surface brightness profile is modelled
by the combination of a nuclear and a bulge component with a S\'ersic profile
with index = 3.7, indicative of an elliptical galaxy. The structural
parameters of the host are consistent with the correlations of effective radius
and surface brightness against absolute magnitude measured for elliptical
galaxies. From the bulge luminosity, we estimated a black hole mass of
(2.10.2) 10 M, consistent with the values
characterizing radio-loud active galactic nuclei.Comment: 5 pages, 3 figures, 1 table. Monthly Notices of the Royal
Astronomical Society Letter, Vol. 469, L11-L1
The radio/gamma-ray connection from 120 MHz to 230 GHz
Radio loud active galactic nuclei are composed of different spatial features, each one characterized by different spectral properties in the radio band. Among them, blazars are the most common class of sources detected at gamma-rays by Fermi, and their radio emission is dominated by the flat spectrum compact core. In this contribution, we explore the connection between emission at high energy revealed by Fermi and at radio frequencies. Taking as a reference the strong and very highly significant correlation found between gamma rays and cm-λ radio emission, we explore the different behaviours found as we change the energy range in gamma rays and in radio, therefore changing the physical parameters of the zones involved in the emitted radiation. We find that the correlation weakens when we consider (1) gamma rays of energy above 10 GeV (except for high synchrotron peaked blazars) or (2) low frequency radio data taken by the Murchison Widefield Array; on the other hand, the correlation strengthens when we consider mm-λ data taken by Atacama Large Millimeter Array (ALMA)
High-Sensitivity 86GHz (3.5mm) VLBI Observations of M87: Deep Imaging of the Jet Base at a 10 Schwarzschild-Radius Resolution
We report on results from new high-sensitivity, high-resolution 86GHz (3.5
millimeter) observations of the jet base in the nearby radio galaxy M87,
obtained by the Very Long Baseline Array in conjunction with the Green Bank
Telescope. The resulting image has a dynamic range exceeding 1500 to 1, the
highest ever achieved for this jet at this frequency, resolving and imaging a
detailed jet formation/collimation structure down to ~10 Schwarzschild radii
(Rs). The obtained 86GHz image clearly confirms some important jet features
known at lower frequencies, i.e., a wide-opening angle jet base, a
limb-brightened intensity profile, a parabola-shape collimation profile and a
counter jet. The limb-brightened structure is already well developed at <
0.2mas (< 28Rs, projected) from the core, where the corresponding apparent
opening angle becomes as wide as ~100 degrees. The subsequent jet collimation
near the black hole evolves in a complicated manner; there is a "constricted"
structure at tens Rs from the core, where the jet cross section is locally
shrinking. We suggest that an external pressure support from the inner part of
radiatively-inefficient accretion flow may be dynamically important in
shaping/confining the footprint of the magnetized jet. We also present the
first VLBI 86GHz polarimetric experiment for this source, where a highly
polarized (~20%) feature is detected near the jet base, indicating the presence
of a well-ordered magnetic field. As a by-product, we additionally report a
43/86 GHz polarimetric result for our calibrator 3C 273 suggesting an extreme
rotation measure near the core.Comment: Accepted for publication in ApJ. 39 pages, 11 figures, 3 table
The Fermi-LAT view of young radio sources
Compact Symmetric Objects (CSO) are considered to be the young version of Fanaroff-Riley type I and type II radio galaxies, with typical sizes smaller than 1 kpc and ages of the order of a few thousand years. Before the launch of the Fermi satellite, young radio sources were predicted to emerge as a possible new γ-ray emitting population detectable by the Large Area Telescope (LAT). After more than 6 years of Fermi operation, the question of young radio sources as γ-ray emitting objects still remains open. In this contribution, we discuss candidate γ-ray emitting CSO and future perspective for detecting young radio sources with Fermi-LAT
VERA monitoring of the radio jet 3C 84 during 2007--2013: detection of non-linear motion
We present a kinematic study of the subparsec-scale radio jet of the radio
galaxy 3C 84/NGC 1275 with the VLBI Exploration of Radio Astrometry (VERA)
array at 22 GHz for 80 epochs from 2007 October to 2013 December. The averaged
radial velocity of the bright component "C3" with reference to the radio core
is found to be between 2007 October and 2013 December. This
constant velocity of C3 is naturally explained by the advancing motion of the
head of the mini-radio lobe. We also find a non-linear component in the motion
of C3 with respect to the radio core. We briefly discuss possible origins of
this non-linear motion.Comment: 11 pages, 7 figures, 8 tables (table 1 - 5 are supplementaries),
accepted for publication on PAS
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