184 research outputs found
Reanalysis of Data Taken by the CANGAROO 3.8 Meter Imaging Atmospheric Cherenkov Telescope: PSR B1706-44, SN 1006, and Vela
We have reanalyzed data from observations of PSR B1706-44, SN 1006, and the
Vela pulsar region made with the CANGAROO 3.8 m imaging atmospheric Cherenkov
telescope between 1993 and 1998 in response to the results reported for these
sources by the H.E.S.S. collaboration. In our reanalysis, in which gamma-ray
selection criteria have been determined exclusively using gamma-ray simulations
and OFF-source data as background samples, no significant TeV gamma-ray signals
have been detected from compact regions around PSR B1706-44 or within the
northeast rim of SN 1006. We discuss reasons why the original analyses gave the
source detections. The reanalysis did result in a TeV gamma-ray signal from the
Vela pulsar region at the 4.5 sigma level using 1993, 1994, and 1995 data. The
excess was located at the same position, 0.13 deg. to the southeast of the Vela
pulsar, as that reported in the original analysis. We have investigated the
effect of the acceptance distribution in the field of view of the 3.8 m
telescope, which rapidly decreases toward the edge of the field of the camera,
on the detected gamma-ray morphology. The expected excess distribution for the
3.8 m telescope has been obtained by reweighting the distribution of HESS
J0835-455 measured by H.E.S.S. with the acceptance of the 3.8 m telescope. The
result is morphologically comparable to the CANGAROO excess distribution,
although the profile of the acceptance-reweighted H.E.S.S. distribution is more
diffuse than that of CANGAROO. The integral gamma-ray flux from HESS J0835-455
has been estimated for the same region as defined by H.E.S.S. from the
1993-1995 data of CANGAROO to be F(> 4.0 +/- 1.6 TeV) = (3.28 +/- 0.92) x
10^{-12} photons cm^{-2} s^{-1}, which is statistically consistent with the
integral flux obtained by H.E.S.S.Comment: Published in ApJ, minor improvement
Very High Energy Gamma Rays from PSR1706-44
We have obtained evidence of gamma-ray emission above 1 TeV from PSR1706-44,
using a ground-based telescope of the atmospheric \v{C}erenkov imaging type
located near Woomera, South Australia. This object, a -ray source
discovered by the COS B satellite (2CG342-02), was identified with the radio
pulsar through the discovery of a 102 ms pulsed signal with the EGRET
instrument of the Compton Gamma Ray Observatory. The flux of the present
observation above a threshold of 1 TeV is 1 10
photons cm s, which is two orders of magnitude smaller than the
extrapolation from GeV energies. The analysis is not restricted to a search for
emission modulated with the 102 ms period, and the reported flux is for all
-rays from PSR1706-44, pulsed and unpulsed. The energy output in the
TeV region corresponds to about 10 of the spin down energy loss rate of
the neutron star.Comment: 13 pages, latex format (article), 2 figures include
Observations of the supernova remnant W28 at TeV energies
The atmospheric Cerenkov imaging technique has been used to search for
point-like and diffuse TeV gamma-ray emission from the southern supernova
remnant, W28, and surrounding region. The search, made with the CANGAROO 3.8m
telescope, encompasses a number of interesting features, the supernova remnant
itself, the EGRET source 3EG J1800-2338, the pulsar PSR J1801-23, strong 1720
MHz OH masers and molecular clouds on the north and east boundaries of the
remnant. An analysis tailored to extended and off-axis point sources was used,
and no evidence for TeV gamma-ray emission from any of the features described
above was found in data taken over the 1994 and 1995 seasons. Our upper limit
(E>1.5 TeV) for a diffuse source of radius 0.25deg encompassing both molecular
clouds was calculated at 6.64e-12 photons cm^-2 s^-1 (from 1994 data), and
interpreted within the framework of a model predicting TeV gamma-rays from
shocked-accelerated hadrons. Our upper limit suggests the need for some cutoff
in the parent spectrum of accelerated hadrons and/or slightly steeper parent
spectra than that used here (-2.1). As to the nature of 3EG J1800-2338, it
possibly does not result entirely from pi-zero decay, a conclusion also
consistent with its location in relation to W28.Comment: 11 pages, 5 figures. Accepted for publication in Astronomy and
Astrophysic
TeV Gamma Ray Emission from Southern Sky Objects and CANGAROO Project
We report recent results of the CANGAROO Collaboration on very high energy
gamma ray emission from pulsars, their nebulae, SNR and AGN in the southern
sky. Observations are made in South Australia using the imaging technique of
detecting atmospheric Cerenkov light from gamma rays higher than about 1 TeV.
The detected gamma rays are most likely produced by the inverse Compton process
by electrons which also radiate synchrotron X-rays. Together with information
from longer wavelengths, our results can be used to infer the strength of
magnetic field in the emission region of gamma rays as well as the energy of
the progenitor electrons. A description of the CANGAROO project is also given,
as well as details of the new telescope of 7 m diameter which is scheduled to
be in operation within two years.Comment: 5 pages, 1 figure, LaTeX 2.09 with aipproc.sty & epsfig.sty, to
appear in proceedings of the 4th Compton Symposium, Williamsburg, 199
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