652 research outputs found
H.E.S.S. deeper observations on SNR RX J0852.0-4622
Supernova Remnants (SNRs) are believed to be acceleration sites of Galactic
cosmic rays. Therefore, deep studies of these objects are instrumental for an
understanding of the high energy processes in our Galaxy. RX J0852.0-4622, also
known as Vela Junior, is one of the few (4) shell-type SNRs resolved at Very
High Energies (VHE; E > 100 GeV). It is one of the largest known VHE sources (~
1.0 deg radius) and its flux level is comparable to the flux level of the Crab
Nebula in the same energy band. These characteristics allow for a detailed
analysis, shedding further light on the high-energy processes taking place in
the remnant. In this document we present further details on the spatial and
spectral morphology derived with an extended data set. The analysis of the
spectral morphology of the remnant is compatible with a constant power-law
photon index of 2.11 +/- 0.05_stat +/- 0.20_syst from the whole SNR in the
energy range from 0.5 TeV to 7 TeV. The analysis of the spatial morphology
shows an enhanced emission towards the direction of the pulsar PSR J0855-4644,
however as the pulsar is lying on the rim of the SNR, it is difficult to
disentangle both contributions. Therefore, assuming a point source, the upper
limit on the flux of the pulsar wind nebula (PWN) between 1 TeV and 10 TeV, is
estimated to be ~ 2% of the Crab Nebula flux in the same energy range
VHE gamma-ray observations of the young synchrotron-dominated SNRs G1.9+0.3 and G330.2+1.0 with H.E.S.S
Supernova remnants (SNRs) are widely considered to be accelerators of cosmic
rays (CR). They are also expected to produce very-high-energy (VHE;
GeV) gamma rays through interactions of high-energy particles with the
surrounding medium and photon fields. They are, therefore, promising targets
for observations with ground-based imaging atmospheric Cherenkov telescopes
like the H.E.S.S. telescope array. VHE gamma-ray emission has already been
discovered from a number of SNRs, establishing them as a prominent source class
in the VHE domain. Of particular interest are the handful of SNRs whose X-ray
spectra are dominated by non-thermal synchrotron emission, such as the VHE
gamma-ray emitters RX J0852.0-4622 (Vela Jr.) and RX J1713-3946. The shell-type
SNRs G1.9+0.3 and G330.2+1.0 also belong to this subclass and are further
notable for their young ages ( kyr), especially G1.9+0.3, which was
recently determined to be the youngest SNR in the Galaxy ( yr). These
unique characteristics motivated investigations with H.E.S.S. to search for VHE
gamma rays. The results of the H.E.S.S. observations and analyses are
presented, along with implications for potential particle acceleration
scenarios.Comment: ICRC 2011 proceedings, 4 pages, 2 figures, 3 table
HESS J1507-622: an unique unidentified source off the Galactic Plane
Galactic very high energy (VHE, > 100 GeV) gamma ray sources in the inner
Galaxy H.E.S.S. survey tend to cluster within 1 degree in latitude around the
Galactic plane. HESS J1507-622 instead is unique, since it is located at
latitude of ~3.5 degrees. HESS J1507-622 is slightly extended over the PSF of
the instrument and hence its Galactic origin is clear. The search for
counterparts in other wavelength regimes (radio, infrared and X-rays) failed to
show any plausible counterparts; and given its position off the Galactic plane
and hence the absorption almost one order of magnitude lower, it is very
surprising to not see any counterparts especially at X-rays wavelengths (by
ROSAT, XMM Newton and Chandra). Its latitude implies that it is either rather
close, within about 1 kpc, or is located well off the Galactic plane. And also
the models reflect the uniqueness of this object: a leptonic PWN scenario would
place this source due to its quite small extension to multi-kpc distance
whereas a hadronic scenario would preferentially locate this object at
distances of < 1 kpc where the density of target material is higher
New unidentified H.E.S.S. Galactic sources
H.E.S.S. is one of the most sensitive instruments in the very high energy
(VHE; > 100 GeV) gamma-ray domain and has revealed many new sources along the
Galactic Plane. After the successful first VHE Galactic Plane Survey of 2004,
H.E.S.S. has continued and extended that survey in 2005-2008, discovering a
number of new sources, many of which are unidentified. Some of the unidentified
H.E.S.S. sources have several positional counterparts and hence several
different possible scenarios for the origin of the VHE gamma-ray emission;
their identification remains unclear. Others have so far no counterparts at any
other wavelength. Particularly, the lack of an X-ray counterpart puts serious
constraints on emission models. Several newly discovered and still unidentified
VHE sources are reported here.Comment: ICRC 2009 proceeding
Self-propelled particles with fluctuating speed and direction of motion
We study general aspects of active motion with fluctuations in the speed and
the direction of motion in two dimensions. We consider the case in which
fluctuations in the speed are not correlated to fluctuations in the direction
of motion, and assume that both processes can be described by independent
characteristic time-scales. We show the occurrence of a complex transient that
can exhibit a series of alternating regimes of motion, for two different
angular dynamics which correspond to persistent and directed random walks. We
also show additive corrections to the diffusion coefficient. The characteristic
time-scales are also exposed in the velocity autocorrelation, which is a sum of
exponential forms.Comment: to appear in Phys. Rev. Let
Young star clusters as gamma ray emitters and their detection with Cherenkov Telescopes
Young massive star clusters as sites of strong stellar winds and supernova explosions may accelerate charged particles at high energies and produce gamma-rays. These sources may also contribute to the production of cosmic rays in our galaxy. At TeV energies several candidates have already been detected: Cygnus OB2, Westerlund 1 \& 2, W43, Pismis 22 and W49A. Our study addresses the issue of very young star clusters where no supernova has occurred yet. During the lifetime of a massive star (M), supersonic stellar winds do indeed release as much energy as a supernova explosion. As supernova remnants are already known as gamma-ray emitters our purpose is to avoid any ambiguity on the origin of a possible gamma ray emission and to fully assume a stellar wind contribution. In this work we first present a catalogue of potential gamma-ray emitting clusters and discuss the criteria used to built the catalogue. We hence model the expected energetic particle spectrum including escapes and losses. We deduce gamma-ray luminosities produced by Inverse Compton and pion decay emission of each cluster and their associated HII regions. We finally compare these gamma-ray luminosities with HESS-II and CTA Cherenkov telescopes sensitivities
Pulsar Wind Nebula candidates recently discovered by H.E.S.S
H.E.S.S. is currently the most sensitive instrument in the very-high-energy
gamma-ray domain and has revealed many new sources along the Galactic Plane, a
significant fraction of which seems to be associated with energetic pulsars.
HESS J1825-137 and Vela X are considered to be the prototypes of such sources
in which the large VHE nebula results from the whole history of the pulsar wind
and the supernova remnant host, both evolving in a complex interstellar medium.
These nebulae are seen to be offset from the pulsar position and, for HESS
J1825-137, a spectral steepening at increasing distance from the pulsar has
been measured. In this context, updated H.E.S.S. results on two previously
published sources, namely HESS J1809-193 and HESS J1912+101, and preliminary
results on the newly discovered HESS J1356-645, are presented. These extended
VHE sources are thought to be associated with the energetic pulsars PSR
J1809-1917, PSR J1913+1011 and PSR J1357-6429, respectively. Properties of each
source in the VHE regime, together with those measured in the radio and X-ray
domains, are discussed.Comment: 4 pages, 6 figures, Submitted to Proceedings of "4th Heidelberg
International Symposium on High Energy Gamma-Ray Astronomy 2008
Collective motion of active Brownian particles in one dimension
We analyze a model of active Brownian particles with non-linear friction and
velocity coupling in one spatial dimension. The model exhibits two modes of
motion observed in biological swarms: A disordered phase with vanishing mean
velocity and an ordered phase with finite mean velocity. Starting from the
microscopic Langevin equations, we derive mean-field equations of the
collective dynamics. We identify the fixed points of the mean-field equations
corresponding to the two modes and analyze their stability with respect to the
model parameters. Finally, we compare our analytical findings with numerical
simulations of the microscopic model.Comment: submitted to Eur. Phys J. Special Topic
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