1,167 research outputs found
Measurement of the EBL through a combined likelihood analysis of gamma-ray observations of blazars with the MAGIC telescopes
The extragalactic background light (EBL) is the radiation accumulated through
the history of the Universe in the wavelength range from the ultraviolet to the
far infrared. Local foregrounds make the direct measurement of the diffuse EBL
notoriously difficult, while robust lower limits have been obtained by adding
up the contributions of all the discrete sources resolved in deep infrared and
optical galaxy observations. Gamma-ray astronomy has emerged in the past few
years as a powerful tool for the study of the EBL: very-high-energy (VHE)
photons traversing cosmological distances can interact with EBL photons to
produce ee pairs, resulting in an energy-dependent depletion of the
gamma-ray flux of distant sources that can be used to set constraints on the
EBL density. The study of the EBL is one of the key scientific programs
currently carried out by the MAGIC collaboration. We present here the results
of the analysis of 32 VHE spectra of 12 blazars in the redshift range 0.03 -
0.94, obtained with over 300 hours of observations with the MAGIC telescopes
between 2010 and 2016. A combined likelihood maximization approach is used to
evaluate the density and spectrum of the EBL most consistent with the MAGIC
observations. The results are compatible with state-of-the-art EBL models, and
constrain the EBL density to be roughly within of the nominal
value in such models. The study reveals no anomalies in gamma-ray propagation
in the large optical depth regime - contrary to some claims based on
meta-analyses of published VHE spectra.Comment: Proceedings of the 35th International Cosmic Ray Conference (ICRC
2017), Bexco, Busan, Korea (arXiv:1708.05153
Gravitational waves from self-ordering scalar fields
Gravitational waves were copiously produced in the early Universe whenever
the processes taking place were sufficiently violent. The spectra of several of
these gravitational wave backgrounds on subhorizon scales have been extensively
studied in the literature. In this paper we analyze the shape and amplitude of
the gravitational wave spectrum on scales which are superhorizon at the time of
production. Such gravitational waves are expected from the self ordering of
randomly oriented scalar fields which can be present during a thermal phase
transition or during preheating after hybrid inflation. We find that, if the
gravitational wave source acts only during a small fraction of the Hubble time,
the gravitational wave spectrum at frequencies lower than the expansion rate at
the time of production behaves as with an
amplitude much too small to be observable by gravitational wave observatories
like LIGO, LISA or BBO. On the other hand, if the source is active for a much
longer time, until a given mode which is initially superhorizon (), enters the horizon, for , we find that the gravitational
wave energy density is frequency independent, i.e. scale invariant. Moreover,
its amplitude for a GUT scale scenario turns out to be within the range and
sensitivity of BBO and marginally detectable by LIGO and LISA. This new
gravitational wave background can compete with the one generated during
inflation, and distinguishing both may require extra information.Comment: 21 pages, 2 figures, added discussion about numerical integration and
a new figure to illustrate the scale-invariance of the GW power spectrum,
conclusions unchange
Orbit optimization for ASTROD-GW and its time delay interferometry with two arms using CGC ephemeris
ASTROD-GW (ASTROD [Astrodynamical Space Test of Relativity using Optical
Devices] optimized for Gravitation Wave detection) is an optimization of ASTROD
to focus on the goal of detection of gravitation waves. The detection
sensitivity is shifted 52 times toward larger wavelength compared to that of
LISA. The mission orbits of the 3 spacecraft forming a nearly equilateral
triangular array are chosen to be near the Sun-Earth Lagrange points L3, L4 and
L5. The 3 spacecraft range interferometrically with one another with arm length
about 260 million kilometers. In order to attain the requisite sensitivity for
ASTROD-GW, laser frequency noise must be suppressed below the secondary noises
such as the optical path noise, acceleration noise etc. For suppressing laser
frequency noise, we need to use time delay interferometry (TDI) to match the
two different optical paths (times of travel). Since planets and other
solar-system bodies perturb the orbits of ASTROD-GW spacecraft and affect the
(TDI), we simulate the time delay numerically using CGC 2.7 ephemeris
framework. To conform to the ASTROD-GW planning, we work out a set of 20-year
optimized mission orbits of ASTROD-GW spacecraft starting at June 21, 2028, and
calculate the residual optical path differences in the first and second
generation TDI for one-detector case. In our optimized mission orbits for 20
years, changes of arm length are less than 0.0003 AU; the relative Doppler
velocities are less than 3m/s. All the second generation TDI for one-detector
case satisfies the ASTROD-GW requirement.Comment: 17 pages, 7 figures, 1 tabl
TeV Particle Astrophysics II: Summary comments
A unifying theme of this conference was the use of different approaches to
understand astrophysical sources of energetic particles in the TeV range and
above. In this summary I review how gamma-ray astronomy, neutrino astronomy and
(to some extent) gravitational wave astronomy provide complementary avenues to
understanding the origin and role of high-energy particles in energetic
astrophysical sources.Comment: 6 pages, 4 figures; Conference summary talk for "TeV Particle
Astrophysics II" at University of Wisconsin, Madison, 28-31 August 200
Science with the space-based interferometer eLISA. III: probing the expansion of the universe using gravitational wave standard sirens
We investigate the capability of various configurations of the space interferometer eLISA to probe the late-time background expansion of the universe using gravitational wave standard sirens. We simulate catalogues of standard sirens composed by massive black hole binaries whose gravitational radiation is detectable by eLISA, and which are likely to produce an electromagnetic counterpart observable by future surveys. The main issue for the identification of a counterpart resides in the capability of obtaining an accurate enough sky localisation with eLISA. This seriously challenges the capability of four-link (2 arm) configurations to successfully constrain the cosmological parameters. Conversely, six-link (3 arm) configurations have the potential to provide a test of the expansion of the universe up to z similar to 8 which is complementary to other cosmological probes based on electromagnetic observations only. In particular, in the most favourable scenarios, they can provide a significant constraint on Ho at the level of 0.5%. Furthermore, (Omega(M), Omega(A)) can be constrained to a level competitive with present SNIa results. On the other hand, the lack of massive black hole binary standard sirens at low redshift allows to constrain dark energy only at the level of few percent
CASCADE protocol: exploring current viral and host characteristics, measuring clinical and patient-reported outcomes, and understanding the lived experiences and needs of individuals with recently acquired HIV infection through a multicentre mixed-methods observational study in Europe and Canada
Introduction: Despite the availability of pre-exposure prophylaxis (PrEP) and antiretroviral therapy (ART), 21 793 people were newly diagnosed with HIV in Europe in 2019. The Concerted action on seroconversion to AIDS and death in Europe study aims to understand current drivers of the HIV epidemic; factors associated with access to, and uptake of prevention methods and ART initiation; and the experiences, needs and outcomes of people with recently acquired HIV.
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Methods and analysis: This longitudinal observational study is recruiting participants aged ≥16 years with documented laboratory evidence of HIV seroconversion from clinics in Canada and six European countries. We will analyse data from medical records, self-administered questionnaires, semistructured interviews and participatory photography. We will assess temporal trends in transmitted drug resistance and viral subtype and examine outcomes following early ART initiation. We will investigate patient-reported outcomes, well-being, and experiences of, knowledge of, and attitudes to HIV preventions, including PrEP. We will analyse qualitative data thematically and triangulate quantitative and qualitative findings. As patient public involvement is central to this work, we have convened a community advisory board (CAB) comprising people living with HIV. /
Ethics and dissemination: All respective research ethics committees have approval for data to contribute to international collaborations. Written informed consent is required to take part. A dissemination strategy will be developed in collaboration with CAB and the scientific committee. It will include peer-reviewed publications, conference presentations and accessible summaries of findings on the study’s website, social media and via community organisations
Quasi-periodic modulation observed in the gamma-ray blazar PG 1553+113 and the MAGIC campaign 2015-2017
A gamma-ray nearly-periodic oscillation was observed from the well-known GeV/TeV BL Lac object PG 1553+113 by the Fermi Large Area Telescope (LAT). The quasi-periodicity in the gamma-ray flux (E>100 MeV and E>1 GeV), reported for the first time in an active galactic nucleus, is significant with a 100 GeV) gamma rays and will cover the next maximum of activity, expected between the end of 2016 and beginning of 2017. The MWL data collected during this campaign, coupled with the gamma-ray ones form MAGIC, will be the key to determine the nature of the periodicity to disentangle the processes driving the periodic modulation from flaring activity typical in blazar objects
The Quiescent Intracluster Medium in the Core of the Perseus Cluster
Clusters of galaxies are the most massive gravitationally-bound objects in
the Universe and are still forming. They are thus important probes of
cosmological parameters and a host of astrophysical processes. Knowledge of the
dynamics of the pervasive hot gas, which dominates in mass over stars in a
cluster, is a crucial missing ingredient. It can enable new insights into
mechanical energy injection by the central supermassive black hole and the use
of hydrostatic equilibrium for the determination of cluster masses. X-rays from
the core of the Perseus cluster are emitted by the 50 million K diffuse hot
plasma filling its gravitational potential well. The Active Galactic Nucleus of
the central galaxy NGC1275 is pumping jetted energy into the surrounding
intracluster medium, creating buoyant bubbles filled with relativistic plasma.
These likely induce motions in the intracluster medium and heat the inner gas
preventing runaway radiative cooling; a process known as Active Galactic
Nucleus Feedback. Here we report on Hitomi X-ray observations of the Perseus
cluster core, which reveal a remarkably quiescent atmosphere where the gas has
a line-of-sight velocity dispersion of 164+/-10 km/s in a region 30-60 kpc from
the central nucleus. A gradient in the line-of-sight velocity of 150+/-70 km/s
is found across the 60 kpc image of the cluster core. Turbulent pressure
support in the gas is 4% or less of the thermodynamic pressure, with large
scale shear at most doubling that estimate. We infer that total cluster masses
determined from hydrostatic equilibrium in the central regions need little
correction for turbulent pressure.Comment: 31 pages, 11 Figs, published in Nature July
A registry for Dravet syndrome: The Italian experience
Objectives: We describe the Residras registry, dedicated to Dravet syndrome (DS) and to other phenotypes related to SCN1A mutations, as a paradigm of registry for rare and complex epilepsies. Our primary objectives are to present the tools and framework of the integrative platform, the main characteristics emerging from the patient cohort included in the registry, with emphasis on demographic, clinical outcome, and mortality. / Methods: Standardized data of enrolled pediatric and adult patients were collected in 24 Italian expert centers and regularly updated at least on a yearly basis. Patients were prospectively enrolled, at registry starting, but historical retrospective data were also included. / Results: At present, 281 individuals with DS and a confirmed SCN1A mutation are included. Most patients have data available on epilepsy (n = 263) and their overall neurological condition (n = 255), based on at least one follow-up update. Median age at first clinical assessment was 2 years (IQR 0–9) while at last follow-up was 11 years (IQR 5–18.5). During the 7-year activity of the registry, five patients died resulting in a mortality rate of 1.84 per 1000-person-years. When analyzing clinical changes over the first 5-year follow-up, we observed a significant difference in cognitive function (P < 0.001), an increased prevalence of behavioral disorders including attention deficit (P < 0.001), a significant worsening of language (P = 0.001), and intellectual disability (P < 0.001). / Significance: The Residras registry represents a large collection of standardized national data for the DS population. The registry platform relies on a shareable and interoperable framework, which promotes multicenter high-quality data collection. In the future, such integrated platform may represent an invaluable asset for easing access to cohorts of patients that may benefit from clinical trials with emerging novel therapies, for drug safety monitoring, and for delineating natural history. Its framework makes it improvable based on growing experience with its use and easily adaptable to other rare and complex epilepsy syndromes
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