1,552 research outputs found
Exploring the bulk of the BL Lac object population:1. parsec-scale radio structures
Context. The advent of Fermi is changing our understanding on the radio and
gamma-ray emission in Active Galactic Nuclei. Contrary to pre-Fermi ideas, BL
Lac objects are found to be the most abundant emitters in the gamma-ray band.
However, since they are relatively weak radio sources, most of their
parsec-scale structure and their multi-frequency properties are poorly
understood and/or have not been investigated in a systematically fashion. Aims.
Our main goal is to analyze the radio and gamma-ray emission properties of a
sample of 42 BL Lacs selected, for the first time in the literature, with no
constraint on their radio and gamma-ray flux densities/emission. Methods.
Thanks to new Very Long Baseline Array observations at 8 and 15 GHz for the
whole sample, we present here fundamental parameters such as radio flux
densities, spectral index information, and parsec-scale structure. Moreover, we
search for gamma-ray counterparts using data reported in the Second Catalog of
Fermi Gamma-ray sources. Results. Parsec-scale radio emission is observed in
the majority of the sources at both frequencies. Gamma-ray counterparts are
found for 14/42 sources. Conclusions. The comparison between our results in
radio and gamma-ray bands points out the presence of a large number of faint BL
Lacs showing "non classical" properties such as low source compactness, core
dominance, no gamma-ray emission and steep radio spectral indexes. A deeper
multiwavelength analysis will be needed.Comment: 19 pages, 6 figures, 6 tables, accepted for publication in A&
Oocyte quality assessment in marine invertebrates: a novel approach by fluorescence spectroscopy
Background: The assessment of oocyte quality is, nowadays, a major challenge in aquaculture, oocyte cryopreservation, and environmental science. Oocyte quality is a determining factor in fertilization and embryo development; however, there is still a lack of rapid and sensitive cellular markers for its assessment. Currently, its estimation is predominantly based on morphological analysis, which is subjective and does not consistently reflect the developmental competence of the oocytes. Despite several recent studies investigating molecular markers related to oocyte quality, methods currently available for their determination pose various technical challenges and limitations. In this study, we developed a novel approach based on fluorescence spectroscopy to assess different intrinsic physiological parameters that can be employed to evaluate egg quality in marine invertebrates that are widely used as animal models such as sea urchins and mussels. Results: Different physiological parameters, such as viability, mitochondrial activity, intracellular ROS levels, plasma membrane lipid peroxidation, and intracellular pH, for egg quality evaluation have been successfully assessed in sea urchins and mussels by using specific fluorescent dyes and detecting the fluorescent signals in eggs through fluorescence spectroscopy. Conclusions: Based on our findings, we propose these physiological markers as useful predictors of egg quality in marine invertebrates; they can be estimated rapidly, selectively, and sensitively by employing this novel approach, which, due to the speed of analysis, the low cost, and easy use can be considered a powerful analytical tool for the egg quality assessment
Hints of the existence of Axion-Like-Particles from the gamma-ray spectra of cosmological sources
Axion Like Particles (ALPs) are predicted to couple with photons in the
presence of magnetic fields. This effect may lead to a significant change in
the observed spectra of gamma-ray sources such as AGNs. Here we carry out a
detailed study that for the first time simultaneously considers in the same
framework both the photon/axion mixing that takes place in the gamma-ray source
and that one expected to occur in the intergalactic magnetic fields. An
efficient photon/axion mixing in the source always means an attenuation in the
photon flux, whereas the mixing in the intergalactic medium may result in a
decrement and/or enhancement of the photon flux, depending on the distance of
the source and the energy considered. Interestingly, we find that decreasing
the value of the intergalactic magnetic field strength, which decreases the
probability for photon/axion mixing, could result in an increase of the
expected photon flux at Earth if the source is far enough. We also find a 30%
attenuation in the intensity spectrum of distant sources, which occurs at an
energy that only depends on the properties of the ALPs and the intensity of the
intergalactic magnetic field, and thus independent of the AGN source being
observed. Moreover, we show that this mechanism can easily explain recent
puzzles in the spectra of distant gamma-ray sources... [ABRIDGED] The
consequences that come from this work are testable with the current generation
of gamma-ray instruments, namely Fermi (formerly known as GLAST) and imaging
atmospheric Cherenkov telescopes like CANGAROO, HESS, MAGIC and VERITAS.Comment: 16 pages, 7 figures. Replaced to match the published version in Phys.
Rev. D. Minor changes with respect to v
Variability Modes of Blazars from Intensive Optical Monitoring
We report the main results of our six year long intensive optical monitoring
on blazars ON 231 (W Com), BL Lac, and 3C 273. Intensive optical monitoring is
an indispensable tool to obtain well sampled light curves and thus to
understand the correlation with the variability in other bands and to
discriminate among the proposed emission models. The curves based on our work
show different variability modes: intermittent mode, quasi-regular mode and
mixed mode. It is not clear if different variability modes can be present, at
various times, in the life of an object suggesting that their occurrence can be
related to the evolution of blazars. An optimized and nearly continuous optical
monitoring is the only way to know the activity status of the sources and to
retrieve useful information on their physical dynamics. Also, the rapid
availability of information about the luminosity of a source is very important
to trigger space based observations and to activate large multifrequency
collaborations. We stress that a significant sample of blazars can be observed
with small size telescopes (0.35-0.80 cm) equipped with CCD cameras. A
world-wide network of several instruments in different countries, is very
useful to increase the time coverage and to reduce the number of nights lost
for bad meteorological conditions.Comment: Paper submitted to the AIP Conference Proceedings "High Energy
Gamma-Ray Astronomy" - Conf. Proc. of the gamma-2000 symposium held in
Heidelberg. 4 pages, doc format source (AIP Proc.), 1 gif figur
Refining the associations of the Fermi Large Area Telescope Source Catalogs
The Fermi-Large Area Telescope (LAT) First Source Catalog (1FGL) was released
in February 2010 and the Fermi-LAT 2-Year Source Catalog (2FGL) appeared in
April 2012, based on data from 24 months of operation. Since their releases,
many follow up observations of unidentified gamma-ray sources (UGSs) were
performed and new procedures to associate gamma-ray sources with potential
counterparts at other wavelengths were developed. Here we review and
characterize all the associations as published in the 1FGL and 2FGL catalog on
the basis of multifrequency archival observations. In particular we located 177
spectra for the low-energy counterparts that were not listed in the previous
Fermi catalogs, and in addition we present new spectroscopic observations of 8
gamma-ray blazar candidates. Based on our investigations, we introduce a new
counterpart category of "candidate associations" and propose a refined
classification for the candidate low-energy counterparts of the Fermi sources.
We compare the 1FGL-assigned counterparts with those listed in the 2FGL to
determine which unassociated sources became associated in later releases of the
Fermi catalogs. We also search for potential counterparts to all the remaining
unassociated Fermi sources. Finally, we prepare a refined and merged list of
all the associations of the 1FGL plus 2FGL catalogs that includes 2219 unique
Fermi objects. This is the most comprehensive and systematic study of all the
associations collected for the gamma-ray sources available to date. We conclude
that 80% of the Fermi sources have at least one known plausible gamma-ray
emitter within their positional uncertainty regions.Comment: 26 pages, 24 figures, 7 tables, ApJS accepted for publication
(pre-proof version uploaded
- …