Protons with energies up to ~ 10 15 eV are the main component 1 of cosmic rays, but evidence for the specific locations where they could have been accelerated to these energies has been lacking 2 . Electrons are known to be accelerated to cosmic-ray energies in supernova remnants 3,4 , and the shock waves associated with such remnants, when they hit the surrounding interstellar medium, could also provide the energy to accelerate protons. The signature of such a process would be the decay of pions (π 0 ), which are generated when the protons collide with atoms and molecules in an interstellar cloud: pion decay results in γ-rays with a particular spectral-energy distribution 5,6 . Here we report the observation of cascade showers of optical photons resulting fromγ-rays at energies of ~ 10 12 eV hitting Earth's upper atmosphere, in the direction of the supernova remnant RX J1713.7-3946. The spectrum is a good match to that predicted by pion decay, and cannot be explained by other mechanisms.
In this Letter we report the discovery of TeV gamma-ray emission from a supernova remnant made with the CANGAROO 3.8 m telescope. TeV gamma rays were detected at the sky position and extension coincident with the northeast rim of shell-type supernova remnant (SNR) SN 1006 (Type Ia). SN 1006 has been a most likely candidate for an extended TeV gamma-ray source, since the clear synchrotron X-ray emission from the rims was recently observed by ASCA (Koyama et al.), which is strong evidence for the existence of very high energy (up to hundreds of TeV) electrons in the SNR. The observed TeV gamma-ray flux was (2.4 ע 0.0.7 [systematic]) # 10 3.0 ע 0.9 (4.6 ע 0.6 ע 1.4) # 10 1.7 ע 0.5 from the 1996 and 1997 observations, respectively. Also, we set an upper limit on the TeV gamma-ray emission from the southwest rim, which is estimated to be cm Ϫ2 s Ϫ1 (≥ TeV, 95% confidence level) Ϫ12
We have detected sub-TeV gamma-ray emission from the direction of the Galactic center (GC) using the CANGAROO-II Imaging Atmospheric Cerenkov Telescope. We detected a statistically significant excess at energies greater than 250 GeV. The flux was 1 order of magnitude lower than that of the Crab Nebula at 1 TeV with a soft spectrum proportional to . The signal centroid is consistent with the GC direction, and the
Ϫ4.65.0עE observed profile is consistent with a pointlike source. Our data suggest that the GeV source 3EG J1746Ϫ2851 is identical to this TeV source, and we study the combined spectra to determine the possible origin of the gammaray emission. We also obtain an upper limit on the cold dark matter density in the Galactic halo.
We have observed the Vela pulsar region at TeV energies using the 3.8 m
imaging Cherenkov telescope near Woomera, South Australia between January 1993
and March 1995. Evidence of an unpulsed gamma-ray signal has been detected at
the 5.8 sigma level. The detected gamma-ray flux is (2.9 +/- 0.5 +/- 0.4) x
10^-12 photons cm^-2 sec^-1 above 2.5 +/- 1.0 TeV and the signal is consistent
with steady emission over the two years. The gamma-ray emission region is
offset from the Vela pulsar position to the southeast by about 0.13 deg. No
pulsed emission modulated with the pulsar period has been detected and the 95 %
confidence flux upper limit to the pulsed emission from the pulsar is (3.7 +/-
0.7) x 10^-13 photons cm^-2 sec^-1 above 2.5 +/- 1.0 TeV.Comment: 18 pages, 3 figures, LaTeX with AASTeX, accepted for publication in
ApJ Letter
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