374 research outputs found
Two-sided radio emission in ON231 (W Comae)
Recent radio images of the BL Lac object ON231 (W Com, 1219+285) show
remarkable new features in the source structure compared to those previously
published. The images were obtained from observations made with the European
VLBI Network plus MERLIN at 1.6 GHz and 5 GHz after the exceptional optical
outburst occurred in Spring 1998. The up-to-date B band historic light curve of
ON231 is also presented together with the R band luminosity evolution in the
period 1994--1999. We identify the source core in the radio images with the
brightest component having the flattest spectrum. A consequence of this
assumption is the existence of a two--sided emission in ON231 not detected in
previous VLBI images. A further new feature is a large bend in the jet at about
10 mas from the core. The emission extends for about 20 mas after the bend,
which might be due to strong interaction with the environment surrounding the
nucleus. We suggest some possible interpretations to relate the changes in the
source structure with the optical and radio flux density variation in the frame
of the unification model.Comment: 8 pages, 8 figure
Inflammation, Mitochondria and Natural Compounds Together in the Circle of Trust
Human diseases are characterized by the perpetuation of an inflammatory condition in which the levels of Reactive Oxygen Species (ROS) are quite high. Excessive ROS production leads to DNA damage, protein carbonylation and lipid peroxidation, conditions that lead to a worsening of inflammatory disorders. In particular, compromised mitochondria sustain a stressful condition in the cell, such that mitochondrial dysfunctions become pathogenic, causing human disorders related to inflammatory reactions. Indeed, the triggered inflammation loses its beneficial properties and turns harmful if dysregulation and dysfunctions are not addressed. Thus, reducing oxidative stress with ROS scavenger compounds has proven to be a successful approach to reducing inflammation. Among these, natural compounds, in particular, polyphenols, alkaloids and coenzyme Q10, thanks to their antioxidant properties, are capable of inhibiting the activation of NF-κB and the expression of target genes, including those involved in inflammation. Even more, clinical trials, and in vivo and in vitro studies have demonstrated the antioxidant and anti-inflammatory effects of phytosomes, which are capable of increasing the bioavailability and effectiveness of natural compounds, and have long been considered an effective non-pharmacological therapy. Therefore, in this review, we wanted to highlight the relationship between inflammation, altered mitochondrial oxidative activity in pathological conditions, and the beneficial effects of phytosomes. To this end, a PubMed literature search was conducted with a focus on various in vitro and in vivo studies and clinical trials from 2014 to 2022
The Long Term Optical Variability of the BL Lac object S5 0716+714: Evidence for a Precessing Jet
We present the historic light curve of the BL Lac object S5 0716+714,
spanning the time interval from 1953 to 2003, built using Asiago archive plates
and our recent CCD observations, together with literature data. The source
shows an evident long term variability, over which well known short term
variations are superposed. In particular, in the period from 1961 to 1983 the
mean brightness of S5 0716+714 remained significantly fainter than that
observed after 1994. Assuming a constant variation rate of the mean magnitude
we can estimate a value of about 0.11 magnitude/year. The simultaneous
occurrence of decreasing ejection velocities of superluminal moving components
in the jet reported by Bach et al. (2005) suggests that both phenomena are
related to the change of the direction of the jet to the line of sight from
about 5 to 0.7 degrees for an approximately constant bulk Lorentz factor of
about 12. A simple explanation is that of a precessing relativistic jet, which
should presently be close to the smallest orientation angle. One can therefore
expect in the next ten years a decrease of the mean brightness of about 1
magnitude.Comment: to appear on The Astronomical Journal, 17 pages, 7 figures. Fig.2 is
given as a separated jpg fil
The BeppoSAX view of the hot cluster Abell 2319
We present results from a BeppoSAX observation of the rich cluster Abell
2319. The broad band spectrum (2-50 keV) of the cluster can be adequately
represented by an optically thin thermal emission model with a temperature of
9.6+/-0.3 keV and a metal abundance of 0.25+/-0.03 in solar units, and with no
evidence of a hard X-ray excess in the PDS spectrum. From the upper limit to
the hard tail component we derive a lower limit of ~0.04 \muG for the
volume-averaged intracluster magnetic field. By performing spatially resolved
spectroscopy in the medium energy band (2-10 keV), we find that the projected
radial temperature and metal abundance profiles are constant out to a radius of
16 arcmin (1.4 Mpc). A reduction of the temperature of 1/3, when going from the
cluster core out to 16 arcmin, can be excluded in the present data at the 99%
confidence level. From the analysis of the temperature and abundance maps we
find evidence of a temperature enhancement and of an abundance decrement in a
region localized 6 arcmin--8 arcmin NE of the core, where a merger event may be
taking place. Finally, the temperature map indicates that the subcluster
located NW of the main cluster may be somewhat cooler than the rest of the
cluster.Comment: To appear in ApJ-Letter
S5 1803+78 Revisited
We report on our optical monitoring of the BL Lac object S5 1803+78 from 1996 to 2011. The source showed no clear periodicity, but a time scale of about 1 300 days between major flares is possibly present. No systematic trend of the color index with flux variations is evident, at variance with other BL Lacs. In one flare, however, the source was bluer in the rising phase and redder in the falling one. Two ?-ray flares were detected by Fermi-GST during our monitoring: on the occasion of only one of them we found simultaneous optical brightening. A one-zone Synchrotron Self Compton (SSC) model appears too simple to explain the source behavior
Optical and Radio monitoring of S5 1803+74
The optical (BVRI) and radio (8.4 GHz) light curves of S5 1803+784 on a time
span of nearly 6 years are presented and discussed. The optical light curve
showed an overall variation greater than 3 mag, and the largest changes occured
in three strong flares. No periodicity was found in the light curve on time
scales up to a year. The variability in the radio band is very different, and
shows moderate oscillations around an average constant flux density rather than
relevant flares, with a maximum amplitude of 30%, without a simultaneous
correspondence between optical and radio luminosity. The optical spectral
energy distribution was always well fitted by a power law. The spectral index
shows small variations and there is indication of a positive correlation with
the source luminosity. Possible explanations of the source behaviour are
discussed in the framework of current models.Comment: 25 pages, 12 figure
The Intra-Night Optical Variability of the bright BL Lac object S5 0716+714
We address the topic of the Intra-Night Optical Variability of the BL Lac
object S5 0716+714. To this purpose a long term observational campaign was
performed, from 1996 to 2003, which allowed the collection of a very large data
set, containing 10,675 photometric measurements obtained in 102 nights. The
source brightness varied in a range of about 2 mag, although the majority of
observations were performed when it was in the range 13.0 < R < 13.75.
Variability time scales were estimated from the rates of magnitude variation,
which were found to have a distribution function well fitted by an exponential
law with a mean value of 0.027 mag/h, corresponding to an e-folding time scale
of the flux tau_F = 37.6 h. The highest rates of magnitude variation were
around 0.10--0.12 mag/h and lasted less than 2 h. These rates were observed
only when the source had an R magnitude < 13.4, but this finding cannot be
considered significant because of the low statistical occurrence. The
distribution of tau_F has a well defined modal value at 19 h. Assuming the
recent estimate of the beaming factor delta about 20, we derived a typical size
of the emitting region of about 5 times 10^{16}/(1 + z) cm. The possibility to
search for a possible correlation between the mean magnitude variation rate and
the long term changes of the velocity of superluminal components in the jet is
discussed.Comment: 12 pages, 10 figures, accepted for Astronomy and Astrophysic
GR 290 (Romano's Star): 2. Light history and evolutionary state
We have built the historical light curve of the luminous variable GR 290 back
to 1901, from old observations of the star found in several archival plates of
M 33. These old recordings together with published and new data show that for
at least half a century the star was in a low luminosity state, with B ~18.
After 1960, five large variability cycles of visual luminosity were recorded.
The amplitude of the oscillations was seen increasing towards the 1992-1994
maximum, then decreasing during the last maxima. The recent light curve
indicates that the photometric variations have been quite similar in all the
bands, and that the B-V color index has been constant within +/-0.1 m despite
the 1.5m change of the visual luminosity. The spectrum of GR 290 at the large
maximum of 1992-94, was equivalent to late-B type, while, during 2002-2014, it
has varied between WN10h-11h near the visual maxima to WN8h-9h at the
luminosity minima. We have detected, during this same period, a clear
anti-correlation between the visual luminosity, the strength of the HeII 4686 A
emission line, the strength of the 4600-4700 A lines blend and the spectral
type. From a model analysis of the spectra collected during the whole 2002-2014
period we find that the Rosseland radius R_{2/3}, changed between the minimum
and maximum luminosity phases by a factor of 3, while T_eff varied between
about 33,000 K and 23,000 K. The bolometric luminosity of the star was not
constant, but increased by a factor of ~1.5 between minimum and maximum
luminosity, in phase with the apparent luminosity variations. In the light of
current evolutionary models of very massive stars, we find that GR 290 has
evolved from a ~60 M_Sun progenitor star and should have an age of about 4
million years. We argue that it has left the LBV stage and is moving to a
Wolf-Rayet stage of late nitrogen spectral type.Comment: Accepted on The Astronomical Journal, 10 figures. Replaced because
the previous uploaded file was that without the final small corrections
requested by the refere
The BL Lac objects OQ 530 and S5 0716+714. Simultaneous observations in the X-rays, radio, optical and TeV bands
We present the results of the BeppoSAX observations of two BL Lacs, OQ 530
and S5 0716+714, as part of a ToO program for the simultaneous observation at
radio, optical, X-ray and TeV energies. Both sources are detected in the LECS
and MECS, with S5 0716+714 visible also in the PDS band, up to about 60 keV.
The X-ray spectra of both sources are better fitted by a double power-law
model, with a steep soft X-ray component flattening at harder energies, with
breaks at 0.3 and 1.5 keV, respectively. The concave shape of the spectra in
both objects is consistent with soft X-rays being produced by the synchrotron
and harder X-rays by the inverse Compton processes. Also the X-ray variability
properties confirm this scenario, in particular for S5 0716+714 our observation
shows variations by about a factor 3 over one hour below 3 keV and no
variability above. Their simultaneous broad band energy spectral distributions
can be successfully interpreted within the frame of a homogeneous synchrotron
and inverse Compton model, including a possible contribution from an external
source of seed photons with the different spectral states of S5 0716+714 being
reproduced by changing the injected power. The resulting parameters are fully
consistent with the two sources being intermediate objects within the
"sequence" scenario proposed for blazars.Comment: 10 pages, 8 figures, accepted by A&
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
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