1,068 research outputs found
Highlight results from the MAGIC telescopes
The MAGIC telescopes are a couple of IACT (Imaging Atmospheric Cherenkov Telescopes) located in the Canary island of La Palma. The first telescope, named MAGIC I, has operated since 2004, while the second telescope, MAGIC II,
was inaugurated in September 2009. Since then the two instruments have worked simultaneously and have taken data in stereoscopic mode. The telescopes are characterized by a reflective surface of 17 meters of diameter and by an ultra-fast electronics. A key feature of MAGIC is the energy threshold of ∼ 50 GeV, the lowest among the existing IACT. This peculiar threshold allows a superposition of the energy
spectra observed by MAGIC with those obtained with gamma-ray satellites, observing up to several hundred GeV. In this contribution we present the main scientific achievements recently obtained by MAGIC in the observation of both galactic and extragalactic objects. The future perspectives are also discussed
Very high-energy constraints on the infrared extragalactic background light
Context. Measurements of the Extragalactic Background Light (EBL) are a
fundamental source of information on the collective emission of cosmic sources.
Aims. At infrared wavelengths, however, these measurements are precluded by
the overwhelming dominance from Interplanetary Dust emission and the Galactic
infrared foreground. Only at m, where the foregrounds are
minimal, has the Infrared EBL (IR EBL) been inferred from analysis of the COBE
maps. The present paper aims to assess the possibility of evaluating the IR EBL
from a few m up to the peak of the emission at >100 m using an
indirect method that avoids the foreground problem.
Methods. To this purpose we exploit the effect of pair-production from
gamma-gamma interaction by considering the highest energy photons emitted by
extragalactic sources and their interaction with the IR EBL photons. We
simulate observations of a variety of low redshift emitters with the
forthcoming Imaging Atmospheric Cherenkov Telescope (IACT) arrays (CTA in
particular) and water Cherenkov observatories (LHAASO, HAWC, SWGO) to assess
their suitability to constrain the EBL at such long wavelengths.
Results. We find that, even under the most extremely favorable conditions of
huge emission flares, extremely high-energy emitting blazars are not very
useful for our purpose because they are much too distant (>100 Mpc the nearest
ones, MKN 501 and MKN 421). Observations of more local Very High Energy (VHE)
emitting AGNs, like low-redshift radio galaxies (M87, IC 310, Centaurus A), are
better suited and will potentially allow us to constrain the EBL up to m
Predicting particle quality attributes of organic crystalline materials using Particle Informatics
In this work, a novel quercetin solvate of dimethylformamide (QDMF) was studied. The crystal structure was solved using single crystal X-ray diffraction and analysed using synthon analysis and other particle informatics tools (e.g., solvate analyser). The thermal behaviour and thermodynamic stability of QDMF were studied experimentally using Raman spectroscopy, ATR-FTIR spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. A clear relationship between the two-step desolvation behaviour of QDMF and the type, strength, and directionality of the main bulk synthons characterizing the QDMF structure was observed. Additionally, the attachment energy model was used to predict the QDMF morphology, together with facet-specific topology and chemical nature of each of the dominant {001}, {110}, and {200} facets. The {200} facet was found to be significantly rougher than the other two; whereas, the {110} was characterized by a higher percentage of exposed DMF molecules compared to the other two facets. Specific scanning electron microscopy and contact angle measurements were used to experimentally detect differences among the three facets and validate the modelling results
Constraining blazar distances with combined Fermi and TeV data: an empirical approach
We discuss a method to constrain the distance of blazars with unknown
redshift using combined observations in the GeV and TeV regimes. We assume that
the VHE spectrum corrected for the absorption through the interaction with the
Extragalactic Background Light can not be harder than the spectrum in the
Fermi/LAT band. Starting from the observed VHE spectral data we derive the
EBL-corrected spectra as a function of the redshift z and fit them with power
laws to be compared with power law fits to the LAT data. We apply the method to
all TeV blazars detected by LAT with known distance and derive an empirical law
describing the relation between the upper limits and the true redshifts that
can be used to estimate the distance of unknown redshift blazars. Using
different EBL models leads to systematic changes in the derived upper limits.
Finally, we use this relation to infer the distance of the unknown redshift
blazar PKS 1424+240.Comment: 5 pages, 4 figures, accepted for publication in MNRAS, minor revisio
Discovery of very high energy gamma-rays from the flat spectrum radio quasar 3C 279 with the MAGIC telescope
3C 279 is one of the best studied flat spectrum radio quasars located at a
comparatively large redshift of z = 0.536. Observations in the very high energy
band of such distant sources were impossible until recently due to the expected
steep energy spectrum and the strong gamma-ray attenuation by the extragalactic
background light photon field, which conspire to make the source visible only
with a low energy threshold. Here the detection of a significant gamma-ray
signal from 3C 279 at very high energies (E > 75 GeV) during a flare in early
2006 is reported. Implications of its energy spectrum on the current
understanding of the extragalactic background light and very high energy
gamma-ray emission mechanism models are discussed.Comment: 4 pages, 6 figures, submitted to proceedings of "4th Heidelberg
International Symposium on High Energy Gamma-Ray Astronomy 2008
Extreme & High Synchrotron Peaked Blazars at the limit of Fermi-LAT detectability: the -ray spectrum of 1BIGB sources
We present the 1-100 GeV spectral energy distribution for a population of 148
high-synchrotron-peaked blazars (HSPs) recently detected with Fermi-LAT as part
of the First Brazil-ICRANet Gamma-ray Blazar catalogue (1BIGB). Most of the
1BIGB sources do not appear in previous Fermi-LAT catalogues and their
gamma-ray spectral properties are presented here for the first time,
representing a significant new extension of the gamma-ray blazar population.
Since our sample was originally selected from an excess signal in the 0.3-500
GeV band, the sources stand out as promising TeV blazar candidates, potentially
in reach of the forthcoming very-high-energy (VHE) gamma-ray observatory, CTA.
The flux estimates presented here are derived considering PASS8 data,
integrating over more than 9 years of Fermi-LAT observations. We also review
the full broadband fit between 0.3-500 GeV presented in the original 1BIGB
paper for all sources, updating the power-law parameters with currently
available Fermi-LAT dataset. The importance of these sources in the context of
VHE population studies with both current instruments and the future CTA is
evaluated. To do so, we select a subsample of 1BIGB sources and extrapolate
their gamma-ray SEDs to the highest energies, properly accounting for
absorption due to the extragalactic background light. We compare those
extrapolations to the published CTA sensitivity curves and estimate their
detectability by CTA. Two notable sources from our sample, namely 1BIGB
J224910.6-130002 and 1BIGB J194356.2+211821, are discussed in greater detail.
All gamma-ray SEDs, which are shown here for the first time, are made publicly
available via the Brazilian Science Data Center (BSDC) service, maintained at
CBPF, in Rio de Janeiro.Comment: 13 pages, 6 figure
- …