27 research outputs found
Variability of the extreme z=4.72 blazar, GB 1428+4217
We report X-ray and radio variability of GB 1428+4217 which confirm its
blazar nature. IR observations reveal a powerful optical-UV component, not
obscured by dust, which is suggestive of the presence of a billion solar mass
black hole, already formed by z ~ 5. A detailed comparison of the broad band
spectral properties of GB 1428+4217 with those of nearby blazars shows it to be
extreme, but nevertheless consistent with the trend found for nearby sources.Comment: MNRAS, in press - 5 pages, 5 figure
Fish Oil Intake During Gestation and Lactation Attenuated STZ-Induced Diabetes inMale Offspring via Activation of Brown Fat and Modulating Oxylipin Profile
Fish oil (FO) has been demonstrated to activate brown thermogenesis and attenuate inflammation in the brown adipose tissue (BAT). Previously, we have reported thatmaternal FO supplementation promotes BAT activity of the weaned mice pups. However, whether maternal FO intake could confer sustainable metabolic benefits to offspring remains uncovered. Therefore, this study aimed to determine the differential impact of maternal FO during pregnancy versus lactation on BAT transcriptome and evaluate the role of bioactive lipid metabolites derived from maternal FO supplementation on the extended metabolic benefits of older pups in the context of type 1 diabetes (T1D).
Conclusions: Our results suggested that maternal FO intake in pregnancy and lactation, at least partly, protects against the risk of T1D of the offspring through augmented BAT function and antiinflammatory oxylipin production
On the kinematics of the neutron star low mass X-ray binary Cen X-4
We present the first determination of the proper motion of the neutron star
low mass X-ray binary {Cen X-4} measured from relative astrometry of the
secondary star using optical images at different epochs. We determine the
Galactic space velocity components of the system and find them to be
significantly different from the mean values that characterize the kinematics
of stars belonging to the halo, and the thin and the thick disc of the Galaxy.
The high metallicity of the secondary star of the system rules out a halo
origin and indicates that the system probably originated in the Galactic disc.
A statistical analysis of the galactocentric motion revealed that this binary
moves in a highly eccentric () orbit with an inclination of
to the Galactic plane. The large Galactic space velocity
components strongly support that a high natal kick as a result of a supernova
explosion could have propelled the system into such an orbit from a birth place
in the Galactic disc. The high Li abundance in the secondary, comparable to
that of stars in star forming regions and young stellar clusters like the
Pleiades, may suggest a relatively recent formation of the system. Following
the orbit backwards in time, we found that the system could have been in the
inner regions of the Galactic disc 100--200 Myr ago. The neutron star
might have formed at that moment. However, we cannot rule out the possibility
that the system formed at a much earlier time if a Li production mechanism
exists in this LMXB.Comment: 6 pages, 4 figures, accepted for publication in A&
The quiescent light curve and evolutionary state of GRO J1655-40
We present ellipsoidal light-curve fits to the quiescent B, V, R and I light
curves of GRO J1655-40 (Nova Scorpii 1994). The fits are based on a simple
model consisting of a Roche-lobe filling secondary and an accretion disc around
the black-hole primary. Unlike previous studies, no assumptions are made about
the interstellar extinction or the distance to the source; instead these are
determined self-consistently from the observed light curves. In order to obtain
tighter limits on the model parameters, we used the distance determination from
the kinematics of the radio jet as an additional constraint. We obtain a value
for the extinction that is lower than was assumed previously; this leads to
lower masses for both the black hole and the secondary star of 5.4 +/- 0.3 Msun
and 1.45 +/- 0.35 Msun, respectively. The errors in the determination of the
model parameters are dominated by systematic errors, in particular due to
uncertainties in the modeling of the disk structure and uncertainties in the
atmosphere model for the chemically anomalous secondary in the system. A lower
mass of the secondary naturally explains the transient nature of the system if
it is either in a late case A or early case B mass-transfer phase.Comment: 12 pages, 4 figures, submitted to MNRA
Energetic constraints to chemo-photometric evolution of spiral galaxies
The problem of chemo-photometric evolution of late-type galaxies is dealt
with relying on prime physical arguments of energetic self-consistency between
chemical enhancement of galaxy mass, through nuclear processing inside stars,
and luminosity evolution of the system. Chemical enhancement is assessed in
terms of the so-called "yield metallicity", that is the metal abundance of
processed mass inside stars, as constrained by the galaxy photometric history.Comment: Ready to appear in the MNRAS. A total of 24 pages with 17 figures & 6
tables. Further info at author's web site (see
http://www.bo.astro.it/~eps/home.html
The stellar content of the XMM-Newton Bright Serendipitous Survey
Context: The comparison of observed counts in a given sky direction with
predictions by Galactic models yields constraints to the spatial distribution
and the stellar birthrate of young stellar populations. In this work we present
the results of the analysis of the stellar content of the XMM-Newton Bright
Serendipitous Survey (XBSS). This unbiased survey includes a total of 58
stellar sources selected in the 0.5 -- 4.5 keV energy band, having a limiting
sensitivity of cnt s and covering an area of 28.10 sq. deg.
Aims: Our main goal is to understand the recent star formation history of the
Galaxy in the vicinity of the Sun. Methods: We compare the observations with
the predictions obtained with XCOUNT, a model of the stellar X-ray content of
the Galaxy. The model predicts the number and properties of the stars to be
observed in terms of magnitude, colour, population and
ratio distributions of the coronal sources detected
with a given instrument and sensitivity in a specific sky direction. Results:
As in other shallow surveys, we observe an excess of stars not predicted by our
Galaxy model. Comparing the colours of the identified infrared counterparts
with the model predictions, we observe that this excess is produced by yellow
(G+K) stars. The study of the X-ray spectrum of each source reveals a main
population of stars with coronal temperature stratification typical of
intermediate-age stars. As no assumptions have been made for the selection of
the sample, our results must be representative of the entire Solar
Neighbourhood. Some stars show excess circumstellar absorption indicative of
youth.Comment: Accepted for publication in Astronomy and Astrophysics: 02/10/200
The Updated BaSTI Stellar Evolution Models and Isochrones: I. Solar Scaled Calculations
We present an updated release of the BaSTI (a Bag of Stellar Tracks and Isochrones) stellar model and isochrone library for a solar scaled heavy element distribution. The main input physics changed from the previous BaSTI release include the solar metal mixture, electron conduction opacities, a few nuclear reaction rates, bolometric corrections, and the treatment of the overshooting efficiency for shrinking convective cores. The new model calculations cover a mass range between 0.1 and 15 Msun, 22 initial chemical compositions between [Fe/H]=-3.20 and +0.45, with helium to metal enrichment ratio dY /dZ=1.31. The isochrones cover an age range between 20 Myr and 14.5 Gyr, take consistently into account the pre-main sequence phase, and have been translated to a large number of popular photometric systems. Asteroseismic properties of the theoretical models have also been calculated. We compare our isochrones with results from independent databases and with several sets of observations, to test the accuracy of the calculations. All stellar evolution tracks, asteroseismic properties and isochrones are made available through a dedicated Web site
Multi-messenger observations of a binary neutron star merger
On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ~1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of 40+8-8 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 Mo. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ~40 Mpc) less than 11 hours after the merger by the One- Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ~10 days. Following early non-detections, X-ray and radio emission were discovered at the transientâs position ~9 and ~16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta
Multi-messenger Observations of a Binary Neutron Star Merger
On 2017 August 17 a binary neutron star coalescence candidate (later
designated GW170817) with merger time 12:41:04 UTC was observed through
gravitational waves by the Advanced LIGO and Advanced Virgo detectors.
The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray
burst (GRB 170817A) with a time delay of ⌠1.7 {{s}} with respect to
the merger time. From the gravitational-wave signal, the source was
initially localized to a sky region of 31 deg2 at a
luminosity distance of {40}-8+8 Mpc and with
component masses consistent with neutron stars. The component masses
were later measured to be in the range 0.86 to 2.26 {M}ÈŻ
. An extensive observing campaign was launched across the
electromagnetic spectrum leading to the discovery of a bright optical
transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC
4993 (at ⌠40 {{Mpc}}) less than 11 hours after the merger by the
One-Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The
optical transient was independently detected by multiple teams within an
hour. Subsequent observations targeted the object and its environment.
Early ultraviolet observations revealed a blue transient that faded
within 48 hours. Optical and infrared observations showed a redward
evolution over âŒ10 days. Following early non-detections, X-ray and
radio emission were discovered at the transientâs position ⌠9
and ⌠16 days, respectively, after the merger. Both the X-ray and
radio emission likely arise from a physical process that is distinct
from the one that generates the UV/optical/near-infrared emission. No
ultra-high-energy gamma-rays and no neutrino candidates consistent with
the source were found in follow-up searches. These observations support
the hypothesis that GW170817 was produced by the merger of two neutron
stars in NGC 4993 followed by a short gamma-ray burst (GRB 170817A) and
a kilonova/macronova powered by the radioactive decay of r-process
nuclei synthesized in the ejecta.</p