1,122 research outputs found
The First Fermi-LAT SNR Catalog SNR and Cosmic Ray Implications
Galactic cosmic ray (CRs) sources, classically proposed to be Supernova
Remnants (SNRs), must meet the energetic particle content required by direct
measurements of high energy CRs. Indirect gamma-ray measurements of SNRs with
the Fermi Large Area Telescope (LAT) have now shown directly that at least
three SNRs accelerate protons. With the first Fermi LAT SNR Catalog, we have
systematically characterized the GeV gamma-rays emitted by 279 SNRs known
primarily from radio surveys. We present these sources in a multiwavelength
context, including studies of correlations between GeV and radio size, flux,
and index, TeV index, and age and environment tracers, in order to better
understand effects of evolution and environment on the GeV emission. We show
that previously sufficient models of SNRs' GeV emission no longer adequately
describe the data. To address the question of CR origins, we also examine the
SNRs' maximal CR contribution assuming the GeV emission arises solely from
proton interactions. Improved breadth and quality of multiwavelength data,
including distances and local densities, and more, higher resolution gamma-ray
data with correspondingly improved Galactic diffuse models will strengthen this
constraint.Comment: 8 pages, 10 figures; in Proceedings of the 34th International Cosmic
Ray Conference (ICRC 2015), The Hague (The Netherlands
OVII and OVIII line emission in the diffuse soft X-ray background: heliospheric and galactic contributions
We study the 0.57 keV (O VII triplet) and 0.65 keV (O VIII) diffuse emission
generated by charge transfer collisions between solar wind (SW) oxygen ions and
interstellar H and He neutral atoms in the inner Heliosphere. These lines which
dominate the 0.3-1.0 keV energy interval are also produced by hot gas in the
galactic halo (GH) and possibly the Local Interstellar Bubble (LB). We
developed a time-dependent model of the SW Charge-Exchange (SWCX) X-ray
emission, based on the localization of the SW Parker spiral at each instant. We
include input SW conditions affecting three selected fields, as well as
shadowing targets observed with XMM-Newton, Chandra and Suzaku and calculate
X-ray emission fot O VII and O VIII lines. We determine SWCX contamination and
residual emission to attribute to the galactic soft X-ray background. We obtain
ground level intensities and/or simulated lightcurves for each target and
compare to X-ray data. The local 3/4 keV emission (O VII and O VIII) detected
in front of shadowing clouds is found to be entirely explained by the CX
heliospheric emission. No emission from the LB is needed at these energies.
Using the model predictions we subtract the heliospheric contribution to the
measured emission and derive the halo contribution. We also correct for an
error in the preliminary analysis of the Hubble Deep Field North (HDFN).Comment: 21 pages (3 on-line), 10 figures (4 on-line), accepted for
publication in Astronomy and Astrophysic
A new nearby pulsar wind nebula overlapping the RX J0852.0-4622 supernova remnant
Energetic pulsars can be embedded in a nebula of relativistic leptons which
is powered by the dissipation of the rotational energy of the pulsar. The
object PSR J0855-4644 is an energetic and fast-spinning pulsar (Edot =
1.1x10^36 erg/s, P=65 ms) discovered near the South-East rim of the supernova
remnant (SNR) RX J0852.0-4622 (aka Vela Jr) by the Parkes multibeam survey. The
position of the pulsar is in spatial coincidence with an enhancement in X-rays
and TeV gamma-rays, which could be due to its putative pulsar wind nebula
(PWN).
The purpose of this study is to search for diffuse non-thermal X-ray emission
around PSR J0855-4644 to test for the presence of a PWN and to estimate the
distance to the pulsar. An X-ray observation was carried out with the
XMM-Newton satellite to constrain the properties of the pulsar and its nebula.
The absorption column density derived in X-rays from the pulsar and from
different regions of the rim of the SNR was compared with the absorption
derived from the atomic (HI) and molecular (12CO) gas distribution along the
corresponding lines of sight to estimate the distance of the pulsar and of the
SNR.
The observation has revealed the X-ray counterpart of the pulsar together
with surrounding extended emission thus confirming the existence of a PWN. The
comparison of column densities provided an upper limit to the distance of the
pulsar PSR J0855-4644 and the SNR RX J0852.0-4622 (d<900 pc). Although both
objects are at compatible distances, we rule out that the pulsar and the SNR
are associated. With this revised distance, PSR J0855-4644 is the second most
energetic pulsar, after the Vela pulsar, within a radius of 1 kpc and could
therefore contribute to the local cosmic-ray e-/e+ spectrum.Comment: 10 pages, 9 Figures. Accepted for publication in A&
Disentangling hadronic from leptonic emission in the composite SNR G326.31.8
G326.31.8 (also known as MSH 1556) has been detected in radio as a
middle-aged composite supernova remnant (SNR) consisting of an SNR shell and a
pulsar wind nebula (PWN), which has been crushed by the SNR's reverse shock.
Previous -ray studies of SNR G326.31.8 revealed bright and extended
emission with uncertain origin. Understanding the nature of the -ray
emission allows probing the population of high-energy particles (leptons or
hadrons) but can be challenging for sources of small angular extent. With the
recent Large Area Telescope data release Pass 8, we
investigate the morphology of this SNR to disentangle the PWN from the SNR
contribution. We perform a morphological and spectral analysis from 300 MeV to
300 GeV. We use the reconstructed events with the best angular resolution to
separately investigate the PWN and the SNR emissions, which is crucial to
accurately determine the spectral properties of G326.31.8 and understand its
nature. The centroid of the -ray emission evolves with energy and is
spatially coincident with the radio PWN at high energies (E 3 GeV). The
morphological analysis reveals that a model considering two contributions from
the SNR and the PWN reproduces the -ray data better than a
single-component model. The associated spectral analysis using power laws shows
two distinct spectral features, a softer spectrum for the remnant ( =
2.17 0.06) and a harder spectrum for the PWN ( = 1.79
0.12), consistent with hadronic and leptonic origin for the SNR and the PWN
respectively. Focusing on the SNR spectrum, we use one-zone models to derive
some physical properties and, in particular, we find that the emission is best
explained with a hadronic scenario in which the large target density is
provided by radiative shocks in HI clouds struck by the SNR
Influence of high precision telescopic instrument characterization on multilateration points accuracy
Currently accuracy of manufacturing machines is a must. Verification is the main way to obtain it; highlighting the volumetric verification as the best technique to improve machine tool position accuracy along all its workspace in the shortest time possible. In this way, different measurements based on multilateration techniques like laser tracker and laser tracer are used. This paper studies how characteristics of a new high precision telescopic system consisting in three lines, with measuring principle based on simultaneous laser affect multilateration accuracy to obtain 3D coordinates. The paper analyses instrument characterising both the design, the components and their operation. Moreover, tests carried out study how instruments behavior affect to the accuracy of data capture using analytical and optimization techniques, proving an error estimation depending on the technique used
- …