30 research outputs found
Spectrum and Variability of Mrk501 as observed by the CAT Imaging Telescope
The CAT Imaging Telescope has observed the BL Lac object Markarian 501
between March and August 1997. We report here on the variability over this time
including several large flares. We present also preliminary spectra for all
these data, for the low emission state, and for the largest flare.Comment: 4 pages, 4 figures, Late
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
Detection of Vhe Gamma-Rays from MRK 501 with the Cat Imaging Telescope
The CAT imaging telescope on the site on the former solar plant Themis has
been observing gamma-rays from Mrk501 above 220 GeV in March and April 1997.
This source is shown to be highly variable and the light curve is presented.
The detected gamma-ray rate for the most intense flare is in excess of 10 per
minute.Comment: 5 pages, 4 figures, Tex, contribution to 25th ICRC Durba
Observation of the Crab Nebula Gamma-Ray Emission Above 220 Gev by the Cat Cherenkov Imaging Telescope
The CAT imaging telescope, recently built on the site of the former solar
plant Themis (French Pyrenees), observed gamma-rays from the Crab nebula from
October 1996 to March 1997. This steady source, often considered as the
standard candle of very-high-energy gamma-ray astronomy, is used as a test-beam
to probe the performances of the new telescope, particularly its energy
threshold (220 GeV at 20 degrees zenith angle) and the stability of its
response. Due to the fine-grain camera, an accurate analysis of the
longitudinal profiles of shower images is performed, yielding the source
position in two dimensions for each individual shower.Comment: 5 pages, 3 figures, Tex, contribution to 25th ICRC Durba
The CAT Imaging Telescope for Very-High-Energy Gamma-Ray Astronomy
The CAT (Cherenkov Array at Themis) imaging telescope, equipped with a
very-high-definition camera (546 fast phototubes with 0.12 degrees spacing
surrounded by 54 larger tubes in two guard rings) started operation in Autumn
1996 on the site of the former solar plant Themis (France). Using the
atmospheric Cherenkov technique, it detects and identifies very high energy
gamma-rays in the range 250 GeV to a few tens of TeV. The instrument, which has
detected three sources (Crab nebula, Mrk 421 and Mrk 501), is described in
detail.Comment: 24 pages, 15 figures. submitted to Elsevier Preprin
The CAT Imaging Telescope
The VHE gamma-ray imaging telescope CAT started taking data in October 1996. Located at the Themis solar site in southern France, it features a 17.7 m^2 Davies-Cotton mirror equipped with 600 PMT camera at the focal plane. The mechanics and optics, the PMTs and the electronics are presented. The performance, based on the first 7 months of operation, is described
A new analysis method for very high definition Imaging Atmospheric Cherenkov Telescopes as applied to the CAT telescope
A new method of shower-image analysis is presented which appears very
powerful as applied to those Cherenkov Imaging Telescopes with very high
definition imaging capability. It provides hadron rejection on the basis of a
single cut on the image shape, and simultaneously determines the energy of the
electromagnetic shower and the position of the shower axis with respect to the
detector. The source location is also reconstructed for each individual
gamma-ray shower, even with one single telescope, so for a point source the
hadron rejection can be further improved. As an example, this new method is
applied to data from the CAT (Cherenkov Array at Themis) imaging telescope,
which has been operational since Autumn, 1996.Comment: 22 pages. submitted to Elsevier Preprin
Spectrum of TeV Gamma-Rays From The Crab Nebula By The CAT Cherenkov Imaging Telescope
The standard candle for Very High Energy (VHE) gamma-ray astronomy, the Crab Nebula, has been observed by the CAT Telescope in 1996 and 1997. We report here detector studies carried out with this source. We present its energy spectrum as measured by CAT. Introduction The Crab Nebula has become the standard candle of Very-High-Energy (VHE) gamma ray astronomy using the atmospheric Cherenkov technique. This steady galactic source has been seen by every experiment in this field and is the beststudied source of VHE fl-rays (Vacanti et al. 1991; Weekes et al. 1989). As its flux in this energy range does not vary significantly with time, this source is now a very powerful test-beam to calibrate the detector and to test the analysis of the data. In particular, it is useful to check the stability of the detector response and to characterize its energy threshold. We report here the results we have obtained on this source using the CAT detector during the year 1996-1997. First, we briefly recap..