575 research outputs found
Broadband Study of Gamma-Ray Blazars at Redshifts
High redshift blazars are among the most powerful non-explosive sources in
the Universe and play a crucial role in understanding the evolution of
relativistic jets. To understand these bright objects, we performed a detailed
investigation of the multiwavelength properties of 79 -ray blazars with
redshifts ranging from z = 2.0 to 2.5, using data from Fermi LAT, Swift
XRT/UVOT, and NuSTAR observations. In the -ray band, the spectral
analysis revealed a wide range of flux and photon indices, from to photons cm s and from 1.66 to
3.15, respectively, highlighting the diverse nature of these sources. The
detailed temporal analysis showed that flaring activities were observed in 31
sources. Sources such as 4C+71.07, PKS 1329-049, and 4C+01.02, demonstrated
significant increase in the -ray luminosity and flux variations,
reaching peak luminosity exceeding erg s. The temporal
analysis extended to X-ray and optical/UV bands, showed clear flux changes in
some sources in different observations. The time-averaged properties of high
redshift blazars were derived through modeling the spectral energy
distributions with a one-zone leptonic scenario, assuming the emission region
is within the broad-line region (BLR) and the X-ray and -ray emissions
are due to inverse Compton scattering of synchrotron and BLR-reflected photons.
This modeling allowed us to constrain the emitting particle distribution,
estimate the magnetic field inside the jet, and evaluate the jet luminosity,
which is discussed in comparison with the disk luminosity derived from fitting
the excess in the UV band.Comment: Accepted for publication in MNRA
The creation of quasigeoid model by local method in the territory of the Republic of Armenia
The structure of the State altitude network of the Republic of Armenia, the adjusted observational data, as well as the obtained results of the accuracy assessment have been studied. Taking into account the available geodetic data, equipments, financial capabilities and professional skills of specialists in the country, it was accepted to create a quasigeoid model by local method. In 2008 a quasigeoid model of the territory of the Republic of Armenia has been created with the accepted method. 2015- 2017 in order to update the model, the altitude points of quasigeoid were condensed. As a result, an updated model of quasigeoid was obtained. The value of estimated accuracy is up to 6 cm. Taking into account the current geopolitical situation of the Republic of Armenia, as well as the requirements of the instruction, it is proposed to make changes to the structure of the State altitude network of the RA and reobserve the I class levelling network according to the new project. This will provide basic geodetic altitude data, necessary for the development of the country's economy
Distributed demand side management with battery storage for smart home energy scheduling
Abstract: The role of Demand Side Management (DSM) with Distributed Energy Storage (DES) has been gaining attention in recent studies due to the impact of the latter on energy management in the smart grid. In this work, an Energy Scheduling and Distributed Storage (ESDS) algorithm is proposed to be installed into the smart meters of Time-of-Use (TOU) pricing consumers possessing in-home energy storage devices. Source of energy supply to the smart home appliances was optimized between the utility grid and the DES device depending on energy tariff and consumer demand satisfaction information. This is to minimize consumer energy expenditure and maximize demand satisfaction simultaneously. The ESDS algorithm was found to offer consumer-friendly and utility-friendly enhancements to the DSM program such as energy, financial, and investment savings, reduced/eliminated consumer dissatisfaction even at peak periods, Peak-to-Average-Ratio (PAR) demand reduction, grid energy sustainability, socio-economic benefits, and other associated benefits such as environmental-friendliness
Moderately Luminous type II Supernovae
Core-collapse Supernovae (CC-SNe) descend from progenitors more massive than
about 8 Msun. Because of the young age of the progenitors, the ejecta may
eventually interact with the circumstellar medium (CSM) via highly energetic
processes detectable in the radio, X-ray, ultraviolet (UV) and, sometimes, in
the optical domains. In this paper we present ultraviolet, optical and near
infrared observations of five type II SNe, namely SNe 2009dd, 2007pk, 2010aj,
1995ad, and 1996W. Together with few other SNe they form a group of moderately
luminous type II events. We collected photometry and spectroscopy with several
telescopes in order to construct well-sampled light curves and spectral
evolutions from the photospheric to the nebular phases. Both photometry and
spectroscopy indicate a degree of heterogeneity in this sample. The light
curves have luminous peak magnitudes (). The ejected
masses of ^56\ni for three SNe span a wide range of values
(MsunM(\ni)Msun), while for a fourth
(SN2010aj) we could determine a stringent upper limit (Msun).
Clues of interaction, such as the presence of high velocity (HV) features of
the Balmer lines, are visible in the photospheric spectra of SNe 2009dd and
1996W. For SN2007pk we observe a spectral transition from a type IIn to a
standard type II SN. Modelling the observations of SNe 2009dd, 2010aj and
1995ad with radiation hydrodynamics codes, we infer kinetic plus thermal
energies of about 0.2-0.5 foe, initial radii of 2-5 cm and
ejected masses of 5.0-9.5 Msun. These values suggest moderate-mass,
super-asymptotic giant branch (SAGB) or red super-giants (RSG) stars as SN
precursors, in analogy with other luminous type IIP SNe 2007od and 2009bw.Comment: 28 pages, 27 fig, accepted by A&A, 3 pages of online material,
abstract abridged. revised significantly with respect to the previous versio
SN 2006gy: was it really extra-ordinary?
We present an optical photometric and spectroscopic study of the very
luminous type IIn SN 2006gy for a time period spanning more than one year. In
photometry, a broad, bright (M_R~-21.7) peak characterizes all BVRI light
curves. Afterwards, a rapid luminosity fading is followed by a phase of slow
luminosity decline between day ~170 and ~237. At late phases (>237 days),
because of the large luminosity drop (>3 mag), only upper visibility limits are
obtained in the B, R and I bands. In the near-infrared, two K-band detections
on days 411 and 510 open new issues about dust formation or IR echoes
scenarios. At all epochs the spectra are characterized by the absence of broad
P-Cygni profiles and a multicomponent Halpha profile, which are the typical
signatures of type IIn SNe. After maximum, spectroscopic and photometric
similarities are found between SN 2006gy and bright, interaction-dominated SNe
(e.g. SN 1997cy, SN 1999E and SN 2002ic). This suggests that ejecta-CSM
interaction plays a key role in SN 2006gy about 6 to 8 months after maximum,
sustaining the late-time-light curve. Alternatively, the late luminosity may be
related to the radioactive decay of ~3M_sun of 56Ni. Models of the light curve
in the first 170 days suggest that the progenitor was a compact star (R~6-8
10^(12)cm, M_ej~5-14M_sun), and that the SN ejecta collided with massive
(6-10M_sun), opaque clumps of previously ejected material. These clumps do not
completely obscure the SN photosphere, so that at its peak the luminosity is
due both to the decay of 56Ni and to interaction with CSM. A supermassive star
is not required to explain the observational data, nor is an extra-ordinarily
large explosion energy.Comment: 33 pages, 8 figures. Accepted by ApJ. Paper with high-resolution
figures available at
http://web.oapd.inaf.it/supern/sn2006gy_astroph/agnoletto_2006gy.pd
Recent outburst of the young star V1180 Cas
We report on the ongoing outburst of the young variable V1180 Cas, which is
known to display characteristics in common with EXor eruptive variables. We
present results that support the scenario of an accretion-driven nature of the
brightness variations of the object and provide the first evidence of jet
structures around the source. We monitored the recent flux variations of the
target in the Rc, J, H, and K bands. New optical and near-IR spectra taken
during the current high state of V1180 Cas are presented, in conjunction with
H2 narrow-band imaging of the source. Observed near-IR colour variations are
analogous to those observed in EXors and consistent with excess emission
originating from an accretion event. The spectra show numerous emission lines,
which indicates accretion, ejection of matter, and an active disc. Using
optical and near-IR emission features we derive a mass accretion rate of ~3 E-8
Msun/yr, which is an order of magnitude lower than previous estimates. In
addition, a mass loss rate of ~4 E-9 and ~4 E-10 Msun/yr are estimated from
atomic forbidden lines and H2, respectively. Our H2 imaging reveals two bright
knots of emission around the source and the nearby optically invisible star
V1180 Cas B, clearly indicative of mass-loss phenomena. Higher resolution
observations of the detected jet will help to clarify whether V1180 Cas is the
driving source and to determine the relation between the observed knots.Comment: Accepted as Letter in A&A; 4 pages, 3 figure
Abundance trend with condensation temperature for stars with different Galactic birth places
During the past decade, several studies reported a correlation between
chemical abundances of stars and condensation temperature (also known as Tc
trend). However, the real astrophysical nature of this correlation is still
debated. The main goal of this work is to explore the possible dependence of
the Tc trend on stellar Galactocentric distances, Rmean. We used high-quality
spectra of about 40 stars observed with the HARPS and UVES spectrographs to
derive precise stellar parameters, chemical abundances, and stellar ages. A
differential line-by-line analysis was applied to achieve the highest possible
precision in the chemical abundances. We confirm previous results that [X/Fe]
abundance ratios depend on stellar age and that for a given age, some elements
also show a dependence on Rmean. When using the whole sample of stars, we
observe a weak hint that the Tc trend depends on Rmean. The observed dependence
is very complex and disappears when only stars with similar ages are
considered. To conclude on the possible dependence of the Tc trend on the
formation place of stars, a larger sample of stars with very similar
atmospheric parameters and stellar ages observed at different Galactocentric
distances is neededComment: Accepted by A&
- …