94 research outputs found
A New Analysis Method for Reconstructing the Arrival Direction of TeV Gamma-rays Using a Single Imaging Atmospheric Cherenkov Telescope
We present a method of atmospheric Cherenkov imaging which reconstructs the
unique arrival direction of TeV gamma rays using a single telescope. The method
is derived empirically and utilizes several features of gamma-ray induced air
showers which determine, to a precision of 0.12 degrees, the arrival direction
of photons, on an event-by-event basis. Data from the Whipple Observatory's 10
m gamma-ray telescope is utilized to test selection methods based on source
location. The results compare these selection methods with traditional
techniques and three different camera fields of view. The method will be
discussed in the context of a search for a gamma-ray signal from a point source
located anywhere within the field of view and from regions of extended
emission.Comment: 24 pages, 16 figures, accepted for publication in Astroparticle
Physics May 11, 200
Towards micro-arcsecond spatial resolution with Air Cherenkov Telescope arrays as optical intensity interferometers
In this poster contribution we highlight the equivalence between an Imaging
Air Cherenkov Telescope (IACT) array and an Intensity Interferometer for a
range of technical requirements. We touch on the differences between a
Michelson and an Intensity Interferometer and give a brief overview of the
current IACT arrays, their upgrades and next generation concepts (CTA, AGIS,
completion 2015). The latter are foreseen to include 30-90 telescopes that will
provide 400-4000 different baselines that range in length between 50m and a
kilometre. Intensity interferometry with such arrays of telescopes attains 50
micro-arcseconds resolution for a limiting V magnitude of ~8.5. This technique
opens the possibility of a wide range of studies, amongst others, probing the
stellar surface activity and the dynamic AU scale circumstellar environment of
stars in various crucial evolutionary stages. Here we discuss possibilities for
using IACT arrays as optical Intensity Interferometers.Comment: Appeared in the proceedings of "The Universe under the Microscope -
Astrophysics at High Angular Resolution", Journal of Physics:Conference
Series (IOP; http://www.iop.org/EJ/toc/1742-6596/131/1
Detection Techniques of Microsecond Gamma-Ray Bursts using Ground-Based Telescopes
Gamma-ray observations above 200 MeV are conventionally made by
satellite-based detectors. The EGRET detector on the Compton Gamma Ray
Observatory (CGRO) has provided good sensitivity for the detection of bursts
lasting for more than 200 ms. Theoretical predictions of high-energy gamma-ray
bursts produced by quantum-mechanical decay of primordial black holes (Hawking
1971) suggest the emission of bursts on shorter time scales. The final stage of
a primordial black hole results in a burst of gamma-rays, peaking around 250
MeV and lasting for a tenth of a microsecond or longer depending on particle
physics. In this work we show that there is an observational window using
ground-based imaging Cherenkov detectors to measure gamma-ray burst emission at
energies E greater than 200 MeV. This technique, with a sensitivity for bursts
lasting nanoseconds to several microseconds, is based on the detection of
multi-photon-initiated air showers.Comment: accepted for publication in the Astrophysical Journa
SGARFACE: A Novel Detector For Microsecond Gamma Ray Bursts
The Short GAmma Ray Front Air Cherenkov Experiment (SGARFACE) is operated at
the Whipple Observatory utilizing the Whipple 10m gamma-ray telescope. SGARFACE
is sensitive to gamma-ray bursts of more than 100MeV with durations from 100ns
to 35us and provides a fluence sensitivity as low as 0.8 gamma-rays per m^2
above 200MeV (0.05 gamma-rays per m^2 above 2GeV) and allows to record the
burst time structure.Comment: 29 pages, 14 figures, accepted for publication in Astroparticle
Physic
New Astrophysical Opportunities Exploiting Spatio-Temporal Optical Correlations
The space-time correlations of streams of photons can provide fundamentally
new channels of information about the Universe. Today's astronomical
observations essentially measure certain amplitude coherence functions produced
by a source. The spatial correlations of wave fields has traditionally been
exploited in Michelson-style amplitude interferometry. However the technology
of the past was largely incapable of fine timing resolution and recording
multiple beams. When time and space correlations are combined it is possible to
achieve spectacular measurements that are impossible by any other means.
Stellar intensity interferometry is ripe for development and is one of the few
unexploited mechanisms to obtain potentially revolutionary new information in
astronomy. As we discuss below, the modern use of stellar intensity
interferometry can yield unprecedented measures of stellar diameters, binary
stars, distance measures including Cepheids, rapidly rotating stars, pulsating
stars, and short-time scale fluctuations that have never been measured before.Comment: Science white paper prepared for the Astro2010 Decadal Revie
Search for TeV Gamma-Rays from Shell-Type Supernova Remnants
If cosmic rays with energies <100 TeV originate in the galaxy and are
accelerated in shock waves in shell-type supernova remnants (SNRs), gamma-rays
will be produced as the result of proton and electron interactions with the
local interstellar medium, and by inverse Compton emission from electrons
scattering soft photon fields. We report on observations of two supernova
remnants with the Whipple Observatory's 10 m gamma-ray telescope. No
significant detections have been made and upper limits on the >500 GeV flux are
reported. Non-thermal X-ray emission detected from one of these remnants
(Cassiopeia A) has been interpreted as synchrotron emission from electrons in
the ambient magnetic fields. Gamma-ray emission detected from the
Monoceros/Rosette Nebula region has been interpreted as evidence of cosmic-ray
acceleration. We interpret our results in the context of these observations.Comment: 4 pages, 2 figures, to appear in the proceedings of 26th
International Cosmic Ray Conference (Salt Lake City, 1999
Very High Energy Gamma-ray spectral properties of Mrk 501 from CAT Cerenkov telescope observations in 1997
The BL Lac object Mrk 501 went into a very high state of activity during
1997, both in VHE gamma-rays and X-rays. We present here results from
observations at energies above 250 GeV carried out between March and October
1997 with the CAT Cerenkov imaging Telescope. The average differential spectrum
between 30 GeV and 13 TeV shows significant curvature and is well represented
by phi_0 * E_TeV^{-(alpha + beta*log10(E_TeV))}, with: phi_0 = 5.19 +/- 0.13
{stat} +/- 0.12 {sys-MC} +1.66/-1.04 {sys-atm} * 10^-11 /cm^2/s/TeV alpha =
2.24 +/- 0.04 {stat} +/- 0.05 {sys} beta = 0.50 +/- 0.07 {stat} (negligible
systematics). The TeV spectral energy distribution of Mrk 501 clearly peaks in
the range 500 GeV-1 TeV. Investigation of spectral variations shows a
significant hardness-intensity correlation with no measurable effect on the
curvature. This can be described as an increase of the peak TeV emission energy
with intensity. Simultaneous and quasi-simultaneous CAT VHE gamma-ray and
BeppoSAX hard X-ray detections for the highest recorded flare on 16th April and
for lower-activity states of the same period show correlated variability with a
higher luminosity in X-rays than in gamma-rays. The observed spectral energy
distribution and the correlated variability between X-rays and gamma-rays, both
in amplitude and in hardening of spectra, favour a two-component emission
scheme where the low and high energy components are attributed to synchrotron
and inverse Compton (IC) radiation, respectively.Comment: Submitted to Astronomy and Astrophysics, 8 pages including 6 figures.
Published with minor change
- …