2,036 research outputs found
Discovery of VHE and HE emission from the blazar 1ES 0414+009 with H.E.S.S and Fermi-LAT
The high energy peaked BL Lac (HBL) object 1ES 0414+009 (z=0.287) is a
distant very high-energy (VHE, E > 100 GeV) blazars with well-determined
redshift. This source was detected with the High Energy Stereoscopic System
(H.E.S.S.) between October 2005 and September 2009. It was also detected with
the Fermi Large Area Telescope (LAT) in 21 months of data. The combined high
energy (HE) and VHE spectra, once corrected for gamma-gamma absorption on the
extragalactic background light (EBL), indicate a Compton peak located above few
TeV, among the highest in the BL Lac class.Comment: proceeding from the 25th Texas Symposium on Relativistic Astrophysics
(Heidelberg, Germany, 2010
Late movement of basin-edge lobate scarps on Mercury
Basin-edge lobate scarps are a sub-type of tectonic shortening structure on the surface of Mercury that have formed at the edge of volcanic units that fill or partly fill impact basins. We have performed a global survey of these features and find that they are widespread in basins across the planet. We obtained model ages from crater size–frequency distribution analysis for a subset of our surveyed basins, for both the smooth plains infill and for the last resolvable tectonic activity on the associated basin-edge scarps. Our results indicate that some of these lobate scarps were still accumulating strain in the late Mansurian (approximately 1 Ga). From a photogeological assessment, we find that the orientations of these basin-edge lobate scarps are similar to those reported for the global population of lobate scarps in earlier studies, appearing to align ∼north–south at low latitudes and ∼east–west at higher latitudes. However, reassessing these landforms’ orientation with artificially illuminated topographic data does not allow us to rule out the effect of illumination bias. We propose that these landforms, the result of crustal shortening in response to global contraction, formed along the interface between the basin floor and the smooth plains unit, which acted as a mechanical discontinuity along which shortening strains were concentrated
VHE observations of unidentified EGRET sources
Observations of unidentified EGRET sources were made with the Whipple 10m
imaging atmospheric Cherenkov telescope between Fall 1999 and Spring 2001.
During this period, a high resolution 490 pixel camera with 4 degree field of
view was present on the telescope. Characterization of the off-axis response of
this instrument was done using observations of the Crab Nebula. No significant
emission was detected from the eight unidentified EGRET sources observed and
upper limits are presented as a function of position.Comment: 5 pages, 3 figures, to appear in Proc. Gamma 2001, High-Energy
Astrophysics Symposium, Gehrels, Shrader, Ritz (eds.), April 2001, Baltimor
Evidence for a cosmological effect in \gamma-ray spectra of BL Lacs
We update the list of GeV-TeV extragalactic \gamma-ray sources using the
2-year catalog from the Fermi-LAT and recent results ground-based \gamma-ray
telescopes. Breaks in the spectra between the high energy (100 MeV <E< 300 GeV)
and the very high energy (E> 200 GeV) ranges, and their dependence on distance,
are discussed in the context of absorption on the extragalactic background
light (EBL). We calculate the size of the expected break using a model for the
EBL and compare it to the data taking into account systematic uncertainties in
the measurements. We develop a novel Bayeasian model to describe this dataset
and use it to constrain two simple models for the EBL-induced breaks.Comment: accepted for publication in A&
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