422 research outputs found
Observation of extragalactic sources of very high energy gamma-rays with the MAGIC telescope
MAGIC is currently the largest single dish ground-based imaging air Cherenkov
telescope in operation. During its first cycle of observations more than 20
extragalactic objects have been observed, and very high energy gamma-ray
signals have been detected in several of them. The results of this observations
are presented, together with a discussion of the spectral characteristics and
the flux variability of the detected sources.Comment: 6 pages, 3 figures, to appear in the proceedings of the International
School of Cosmics Ray Astrophysics (ISCRA) 15th Course: Astrophysics at
Ultra-High Energies, Erice, Sicily, Italy, 20-27 Jun 200
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
Gamma-Ray Emission from Two Blazars Behind the Galactic Plane: B2013+370 & B2023+336
B2013+370 and B2023+336 are two blazars at low-galactic latitude that were
previously proposed to be the counterparts for the EGRET unidentified sources,
3EG J2016+3657 and 3EG J2027+3429. Gamma-ray emission associated with the EGRET
sources has been detected by the Fermi Gamma-ray Space Telescope, and the two
sources, 1FGL J2015.7+3708 and 1FGL J2027.6+3335, have been classified as
unidentified in the 1-year catalog. This analysis of the Fermi-LAT data
collected during 31 months reveals that the 1FGL sources are spatially
compatible with the blazars, and are significantly variable, supporting the
hypothesis of extragalactic origin for the gamma-ray emission. The gamma-ray
light curves are compared with 15 GHz radio light curves from the 40-m
telescope at the Owens Valley Radio Observatory (OVRO). Simultaneous
variability is seen in both bands for the two blazar candidates. The study is
completed with the X-ray analysis of 1FGL J2015.7+3708 using Swift observations
that were triggered in August 2010 by a Fermi-detected flare. The resulting
spectral energy distribution shows a two-component structure typical of
blazars. We also identify a second source in the field of view of 1FGL
J2027.6+3335 with similar characteristics to the known LAT pulsars. This study
gives solid evidence favoring blazar counterparts for these two unidentified
EGRET and Fermi sources, supporting the hypothesis that a number of
unidentified gamma-ray sources at low galactic latitudes are indeed of
extragalactic origin.Comment: 10 pages, 7 figures, 6 tables, accepted for publication in The
Astrophysical Journa
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