2 research outputs found
CANGAROO-III observation of TeV gamma rays from the unidentified gamma-ray source HESS J1614-518
We report the detection, with the CANGAROO-III imaging atmospheric Cherenkov
telescope array, of a very high energy gamma-ray signal from the unidentified
gamma-ray source HESS J1614-518, which was discovered in the H.E.S.S. Galactic
plane survey. Diffuse gamma-ray emission was detected above 760 GeV at the 8.9
sigma level during an effective exposure of 54 hr from 2008 May to August. The
spectrum can be represented by a power-law:
8.2+-2.2_{stat}+-2.5_{sys}x10^{-12}x (E/1TeV)^{-Gamma} cm^{-2} s^{-1} TeV^{-1}
with a photon index Gamma of 2.4+-0.3_{stat}+-0.2_{sys}, which is compatible
with that of the H.E.S.S. observations. By combining our result with
multi-wavelength data, we discuss the possible counterparts for HESS J1614-518
and consider radiation mechanisms based on hadronic and leptonic processes for
a supernova remnant, stellar winds from massive stars, and a pulsar wind
nebula. Although a leptonic origin from a pulsar wind nebula driven by an
unknown pulsar remains possible, hadronic-origin emission from an unknown
supernova remnant is preferred.Comment: 9 pages, 7 figures, accepted for publication in Ap
VERITAS 2008-2009 monitoring of the variable gamma-ray source M87
M87 is a nearby radio galaxy that is detected at energies ranging from radio
to VHE gamma-rays. Its proximity and its jet, misaligned from our
line-of-sight, enable detailed morphological studies and extensive modeling at
radio, optical, and X-ray energies. Flaring activity was observed at all
energies, and multi-wavelength correlations would help clarify the origin of
the VHE emission. In this paper, we describe a detailed temporal and spectral
analysis of the VERITAS VHE gamma-ray observations of M87 in 2008 and 2009. In
the 2008 observing season, VERITAS detected an excess with a statistical
significance of 7.2 sigma from M87 during a joint multi-wavelength monitoring
campaign conducted by three major VHE experiments along with the Chandra X-ray
Observatory. In February 2008, VERITAS observed a VHE flare from M87 occurring
over a 4-day timespan. The peak nightly flux above 250GeV was 7.7% of the Crab
Nebula flux. M87 was marginally detected before this 4-day flare period, and
was not detected afterwards. Spectral analysis of the VERITAS observations
showed no significant change in the photon index between the flare and
pre-flare states. Shortly after the VHE flare seen by VERITAS, the Chandra
X-ray Observatory detected the flux from the core of M87 at a historical
maximum, while the flux from the nearby knot HST-1 remained quiescent. Acciari
et al. (2009) presented the 2008 contemporaneous VHE gamma-ray, Chandra X-ray,
and VLBA radio observations which suggest the core as the most likely source of
VHE emission, in contrast to the 2005 VHE flare that was simultaneous with an
X-ray flare in the HST-1 knot. In 2009, VERITAS continued its monitoring of M87
and marginally detected a 4.2 sigma excess corresponding to a flux of ~1% of
the Crab Nebula. No VHE flaring activity was observed in 2009.Comment: 17 pages, 5 figures, accepted for publication in Ap