1,268 research outputs found
Blazar Flaring Patterns (B-FlaP): Classifying Blazar Candidates of Uncertain type in the third Fermi-LAT catalog by Artificial Neural Networks
The Fermi Large Area Telescope (LAT) is currently the most important facility
for investigating the GeV -ray sky. With Fermi LAT more than three
thousand -ray sources have been discovered so far. 1144 () of
the sources are active galaxies of the blazar class, and 573 () are
listed as Blazar Candidate of Uncertain type (BCU), or sources without a
conclusive classification. We use the Empirical Cumulative Distribution
Functions (ECDF) and the Artificial Neural Networks (ANN) for a fast method of
screening and classification for BCUs based on data collected at -ray
energies only, when rigorous multiwavelength analysis is not available. Based
on our method, we classify 342 BCUs as BL Lacs and 154 as FSRQs, while 77
objects remain uncertain. Moreover, radio analysis and direct observations in
ground-based optical observatories are used as counterparts to the statistical
classifications to validate the method. This approach is of interest because of
the increasing number of unclassified sources in Fermi catalogs and because
blazars and in particular their subclass High Synchrotron Peak (HSP) objects
are the main targets of atmospheric Cherenkov telescopes.Comment: 18 pages, 17 figures, accepted for publication on MNRA
Optical counterparts of undetermined type -ray Active Galactic Nuclei with blazar-like Spectral Energy Distributions
During its first four years of scientific observations, the Fermi Large Area
Telescope (Fermi-LAT) detected 3033 -ray sources above a 4
significance level. Although most of the extra-Galactic sources are active
galactic nuclei (AGN) of the blazar class, other families of AGNs are observed
too, while a still high fraction of detections () remains with
uncertain association or classification. According to the currently accepted
interpretation, the AGN -ray emission arises from inverse Compton (IC)
scattering of low energy photons by relativistic particles confined in a jet
that, in the case of blazars, is oriented very close to our line of sight.
Taking advantage of data from radio and X-ray wavelengths, which we expect to
be produced together with -rays, providing a much better source
localization potential, we focused our attention on a sample of -ray
Blazar Candidates of Undetermined Type (BCUs), starting a campaign of optical
spectroscopic observations. The main aims of our investigation include a census
of the AGN families that contribute to -ray emission and a study of
their redshift distribution, with the subsequent implications on the intrinsic
source power. We furthermore analyze which -ray properties can better
constrain the nature of the source, thus helping in the study of objects not
yet associated with a reliable low frequency counterpart. In this communication
we report on the instruments and techniques used to identify the optical
counterparts of -ray sources, we give an overview on the status of our
work, and we discuss the implications of a large scale study of -ray
emitting AGNs.Comment: 9 pages, 2 figures, proceedings of the 10th Serbian Conference on
Spectral Line Shapes in Astrophysics. JOAA, accepte
A spectroscopic analysis of a sample of narrow-line Seyfert 1 galaxies selected from the Sloan Digital Sky Survey
We revisited the spectroscopic characteristics of narrow-line Seyfert 1
galaxies (NLS1s) by analysing a homogeneous sample of 296 NLS1s at redshift
between 0.028 and 0.345, extracted from the Sloan Digital Sky Survey (SDSS-DR7)
public archive. We confirm that NLS1s are mostly characterized by Balmer lines
with Lorentzian profiles, lower black hole masses and higher Eddington ratios
than classic broad-line Seyfert 1 (BLS1s), but they also appear to be active
galactic nuclei (AGNs) contiguous with BLS1s and sharing with them common
properties. Strong Fe II emission does not seem to be a distinctive property of
NLS1s, as low values of Fe II/H are equally observed in these AGNs. Our
data indicate that Fe II and Ca II kinematics are consistent with the one of
H. On the contrary, O I 8446 seems to be systematically
narrower and it is likely emitted by gas of the broad-line region more distant
from the ionizing source and showing different physical properties. Finally,
almost all NLS1s of our sample show radial motions of the narrow-line region
highly-ionised gas. The mechanism responsible for this effect is not yet clear,
but there are hints that very fast outflows require high continuum luminosities
(> erg/s) or high Eddington ratios (log(L/L)
> -0.1).Comment: 27 pages, 31 figures, 4 tables, accepted for publication in MNRA
[O III] line properties in two samples of radio-emitting narrow-line Seyfert 1 galaxies
The [O III] 4959,5007 lines are a useful proxy to test the
kinematic of the narrow-line region (NLR) in active galactic nuclei (AGN). In
AGN, and particularly in narrow-line Seyfert 1 galaxies (NLS1s) these lines
often show few peculiar features, such as blue wings, often interpreted as
outflowing component, and a shift typically toward lower wavelengths of
the whole spectroscopic feature in some exceptional sources, the so-called blue
outliers, which are often associated to strong winds. We investigated the
incidence of these peculiarities in two samples of radio-emitting NLS1s, one
radio-loud and one radio-quiet. We also studied a few correlations between the
observational properties of the [O III] lines and those of the AGN. Our aim was
to understand the difference between radio-quiet and radio-loud NLS1s, which
may in turn provide useful information on the jet formation mechanism. We find
that the NLR gas is much more perturbed in radio-loud than in radio-quiet
NLS1s. In particular the NLR dynamics in -ray emitting NLS1s appears to
be highly disturbed, and this might be a consequence of interaction with the
relativistic jet. The less frequently perturbed NLR in radio-quiet NLS1s
suggests instead that these sources likely do not harbor a fully developed
relativistic jet. Nonetheless blue-outliers in radio-quiet NLS1s are observed,
and we interpret them as a product of strong winds.Comment: 16 pages, 13 figures, 7 tables, accepted for publication on Astronomy
& Astrophysic
High resolution spectroscopy of the extended narrow-line region of IC 5063 and NGC 7212
We studied the properties of the gas of the extended narrow line region
(ENLR) of two Seyfert 2 galaxies: IC 5063 and NGC 7212. We analysed high
resolution spectra to investigate how the main properties of this region depend
on the gas velocity. We divided the emission lines in velocity bins and we
calculated several line ratios. Diagnostic diagrams and SUMA composite models
(photo-ionization + shocks), show that in both galaxies there might be evidence
of shocks significantly contributing in the gas ionization at high |V|, even
though photo-ionization from the active nucleus remains the main ionization
mechanism. In IC 5063 the ionization parameter depends on V and its trend might
be explained assuming an hollow bi-conical shape for the ENLR, with one of the
edges aligned with the galaxy disk. On the other hand, NGC 7212 does not show
any kind of dependence. The models show that solar O/H relative abundances
reproduce the observed spectra in all the analysed regions. They also revealed
an high fragmentation of the gas clouds, suggesting that the complex kinematics
observed in these two objects might be caused by interaction between the ISM
and high velocity components, such as jets.Comment: 29 pages, 32 figures, accepted for publication in MNRA
Parent population of flat-spectrum radio-loud narrow-line Seyfert 1 galaxies
Flat-spectrum radio-loud Narrow-Line Seyfert 1 galaxies (NLS1s) are a
recently discovered class of -ray emitting Active Galactic Nuclei
(AGN), that exhibit some blazar-like properties which are explained with the
presence of a relativistic jet viewed at small angles. When blazars are
observed at larger angles they appear as radio-galaxies, and we expect to
observe an analogue parent population for beamed NLS1s. However, the number of
known NLS1s with the jet viewed at large angles is not enough. Therefore, we
tried to understand the origin of this deficit. Current hypotheses about the
nature of parent sources are steep-spectrum radio-loud NLS1s, radio-quiet NLS1s
and disk-hosted radio-galaxies. To test these hypotheses we built three samples
of candidate sources plus a control sample, and calculated their black hole
mass and Eddington ratio using their optical spectra. We then performed a
Kolmogorov-Smirnov statistical test to investigate the compatibility of our
different samples with a beamed population. Our results indicate that, when the
inclination angle increases, a beamed source appears as a steep-spectrum
radio-loud NLS1, or possibly even as a disk-hosted radio-galaxy with low black
hole mass and high Eddington ratio. Further investigations, involving larger
complete samples and observations at radio frequency, are needed to understand
the incidence of disk-hosted radio-galaxies in the parent population, and to
assess whether radio-quiet NLS1s can play a role, as well.Comment: 12 pages, 6 figures, accepted for publication by Astronomy and
Astrophysic
Observers of quantum systems cannot agree to disagree
Is the world quantum? An active research line in quantum foundations is
devoted to exploring what constraints can rule out the postquantum theories
that are consistent with experimentally observed results. We explore this
question in the context of epistemics, and ask whether agreement between
observers can serve as a physical principle that must hold for any theory of
the world. Aumann's seminal Agreement Theorem states that two observers (of
classical systems) cannot agree to disagree. We propose an extension of this
theorem to no-signaling settings. In particular, we establish an Agreement
Theorem for observers of quantum systems, while we construct examples of
(postquantum) no-signaling boxes where observers can agree to disagree. The PR
box is an extremal instance of this phenomenon. These results make it plausible
that agreement between observers might be a physical principle, while they also
establish links between the fields of epistemics and quantum information that
seem worthy of further exploration.Comment: Close to published versio
Exploring the parent population of beamed NLS1s: from the black hole to the jet
The aim of this work is to understand the nature of the parent population of
beamed narrow-line Seyfert 1 galaxies (NLS1s), by studying the physical
properties of three parent candidates samples: steep-spectrum radio-loud NLS1s,
radio-quiet NLS1s and disk-hosted radio-galaxies. In particular, we focused on
the black hole mass and Eddington ratio distribution and on the interactions
between the jet and the narrow-line region.Comment: 6 pages, 2 figures, to appear in Proceedings of High Energy Phenomena
in Relativistic Outflows (HEPRO) V, Workshop Series of the Argentinian
Astronomical Societ
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