8 research outputs found
Stereo Imaging of the VHE Gamma-Rays with HEGRA and H.E.S.S
At present, the ground-based astronomy of very high energy (VHE) (E>100 GeV)
gamma-rays experiences the challenging transition phase caused by the
substantial upgrading of its observational instrumentation. Recently the HEGRA
collaboration has evidently demonstrated the power of arrays of imaging
atmospheric Cherenkov telescopes and initiated a number of complementary
projects, such as H.E.S.S., CANGAROO IV, VERITAS. The common philosophy of
those projects is based on the stereoscopic observations of air showers with a
number of imaging telescopes simultaneously. Such observations allow to reduce
substantially the effective energy threshold of detected gamma-ray showers; to
improve the angular and energy resolution for individual gamma-rays; to gain in
suppression of the cosmic ray background. In my talk I have summarized the
general advantages and achieved sensitivity of the stereoscopic observations
using the HEGRA data taken with an array of 5 imaging telescopes having the
energy threshold of 500 GeV. These results completed with the relevant
simulations may be extrapolated on a firm ground towards the future H.E.S.S.
(phase I) array of four 12 m imaging telescopes with the estimated energy
threshold below 100 GeV. Here I discuss in short the anticipated performance of
such an array.Comment: 5 pages, 2 figures, to appear in proc. of ``Heidelberg International
Symposium on High Energy Gamma-Ray Astronomy'' edited by F. Aharonian and H.
Voelk, AIP Conf. Pro
On design studies for the future 50 GeV arrays of imaging air Cherenkov telescopes
Arrays of imaging air Cherenkov telescopes (IACTs) like VERITAS, HESS have
been recently proposed as the instruments of the next generation for ground
based very high energy gamma-ray astronomy invading into 50-100 GeV energy
range. Here we present results of design studies for the future IACT arrays
which have been performed by means of Monte Carlo simulations. We studied
different trigger strategies, abilities of cosmic ray rejection for arrays of 4
and 16 telescopes with 10 m reflectors, equipped with cameras comprising 271
and 721 pixels of 0.25 and 0.15 degree, respectively. The comparative analysis
of the performance of such telescope arrays has been done for both camera
options, providing almost the same field of view of 4.3 degree. An important
issue is the choice of the optimum spacing between the telescopes in such an
array. In order to maximize the signal-to-noise ratio in observations at the
small zenith angles of 20 degree as well as at large zenith angles of 60
degree, different arrangements of IACT array have been examined. Finally, we
present a major recommendations regarding the optimum configuration.Comment: 5 pages, presented at the VERITAS Workshop on TeV Astrophysics of
Extragalactic Sources, eds. M. Catanese, J. Quinn, and T. Weekes, to be
published in Astroparticle Physic
Evidence for Intergalactic Absorption in the TeV Gamma-Ray Spectrum of Mkn 501
The recent HEGRA observations of the blazar Mkn 501 show strong curvature in
the very high energy gamma-ray spectrum. Applying the gamma-ray opacity derived
from an empirically based model of the intergalactic infrared background
radiation field (IIRF), to these observations, we find that the intrinsic
spectrum of this source is consistent with a power-law: dN/dE~ E^-alpha with
alpha=2.00 +/- 0.03 over the range 500 GeV - 20 TeV. Within current synchrotron
self-Compton scenarios, the fact that the TeV spectral energy distribution of
Mkn 501 does not vary with luminosity, combined with the correlated, spectrally
variable emission in X-rays, as observed by the BeppoSAX and RXTE instruments,
also independently implies that the intrinsic spectrum must be close to
alpha=2. Thus, the observed curvature in the spectrum is most easily understood
as resulting from intergalactic absorption.Comment: 7 pages, 1 figure, accepted in ApJ Letters 1999 April
Multiwavelength Observations of LS I +61 303 with VERITAS, Swift and RXTE
We present results from a long-term monitoring campaign on the TeV binary LSI
+61 303 with VERITAS at energies above 500 GeV, and in the 2-10 keV hard X-ray
bands with RXTE and Swift, sampling nine 26.5 day orbital cycles between
September 2006 and February 2008. The binary was observed by VERITAS to be
variable, with all integrated observations resulting in a detection at the 8.8
sigma (2006/2007) and 7.3 sigma (2007/2008) significance level for emission
above 500 GeV. The source was detected during active periods with flux values
ranging from 5 to 20% of the Crab Nebula, varying over the course of a single
orbital cycle. Additionally, the observations conducted in the 2007-2008
observing season show marginal evidence (at the 3.6 sigma significance level)
for TeV emission outside of the apastron passage of the compact object around
the Be star. Contemporaneous hard X-ray observations with RXTE and Swift show
large variability with flux values typically varying between 0.5 and 3.0*10^-11
ergs cm^-2 s^-1 over a single orbital cycle. The contemporaneous X-ray and TeV
data are examined and it is shown that the TeV sampling is not dense enough to
detect a correlation between the two bands.Comment: 30 pages, 5 figures, 2 table, Accepted for publication in The
Astrophysical Journa
Quantum Spacetime Phenomenology
I review the current status of phenomenological programs inspired by
quantum-spacetime research. I stress in particular the significance of results
establishing that certain data analyses provide sensitivity to effects
introduced genuinely at the Planck scale. And my main focus is on
phenomenological programs that managed to affect the directions taken by
studies of quantum-spacetime theories.Comment: 125 pages, LaTex. This V2 is updated and more detailed than the V1,
particularly for quantum-spacetime phenomenology. The main text of this V2 is
about 25% more than the main text of the V1. Reference list roughly double