277 research outputs found
Spatially resolved XMM-Newton analysis and a model of the nonthermal emission of MSH 15-52
We present an X-ray analysis and a model of the nonthermal emission of the
pulsar wind nebula (PWN) MSH15-52. We analyzed XMM-Newton data to obtain the
spatially resolved spectral parameters around the pulsar PSRB1509-58. A
steepening of the fitted power-law spectra and decrease in the surface
brightness is observed with increasing distance from the pulsar. In the second
part of this paper, we introduce a model for the nonthermal emission, based on
assuming the ideal magnetohydrodynamic limit. This model is used to constrain
the parameters of the termination shock and the bulk velocity of the leptons in
the PWN. Our model is able to reproduce the spatial variation of the X-ray
spectra. The parameter ranges that we found agree well with the parameter
estimates found by other authors with different approaches. In the last part of
this paper, we calculate the inverse Compton emission from our model and
compare it to the emission detected with the H.E.S.S. telescope system. Our
model is able to reproduce the flux level observed with H.E.S.S., but not the
spectral shape of the observed TeV {\gamma}-ray emission.Comment: Accepted for publication in A&A, 9 pages, 15 figure
Diffusive propagation of cosmic rays from supernova remnants in the Galaxy. I: spectrum and chemical composition
In this paper we investigate the effect of stochasticity in the spatial and
temporal distribution of supernova remnants on the spectrum and chemical
composition of cosmic rays observed at Earth. The calculations are carried out
for different choices of the diffusion coefficient D(E) experienced by cosmic
rays during propagation in the Galaxy. In particular, at high energies we
assume that D(E)\sim E^{\delta}, with and being the
reference scenarios. The large scale distribution of supernova remnants in the
Galaxy is modeled following the distribution of pulsars, with and without
accounting for the spiral structure of the Galaxy. We find that the stochastic
fluctuations induced by the spatial and temporal distribution of supernovae,
together with the effect of spallation of nuclei, lead to mild but sensible
violations of the simple, leaky-box-inspired rule that the spectrum observed at
Earth is with , where
is the slope of the cosmic ray injection spectrum at the sources. Spallation of
nuclei, even with the small rates appropriate for He, may account for slight
differences in spectral slopes between different nuclei, providing a possible
explanation for the recent CREAM observations. For we find that
the slope of the proton and helium spectra are and
respectively at energies above 1 TeV (to be compared with the measured values
of and ). For the hardening of the He
spectra is not observed. We also comment on the effect of time dependence of
the escape of cosmic rays from supernova remnants, and of a possible clustering
of the sources in superbubbles. In a second paper we will discuss the
implications of these different scenarios for the anisotropy of cosmic rays.Comment: 28 pages, To appear in JCA
Time-dependent modeling of pulsar wind nebulae: Study on the impact of the diffusion-loss approximations
In this work, we present a leptonic, time-dependent model of pulsar wind
nebulae (PWNe). The model seeks a solution for the lepton distribution function
considering the full time-energy dependent diffusion-loss equation. The
time-dependent lepton population is balanced by injection, energy losses, and
escape. We include synchrotron, inverse Compton (IC, with the cosmic-microwave
background as well as with IR/optical photon fields), self-synchrotron Compton
(SSC), and bremsstrahlung processes, all devoid of any radiative
approximations. With this model in place we focus on the Crab nebula as an
example and present its time dependent evolution. Afterwards, we analyze the
impact of different approximations made at the level of the diffusion-loss
equation, as can be found in the literature. Whereas previous models ignored
the escape term, e.g., with the diffusion-loss equation becoming advective,
others approximated the losses as catastrophic, so that the equation has only
time derivatives. Additional approximations are also described and computed. We
show which is the impact of these approaches in the determination of the PWN
evolution. In particular, we find the time-dependent deviation of the
multi-wavelength spectrum and the best-fit parameters obtained with the
complete and the approximate models.Comment: In press in MNRA
Indirect signals from light neutralinos in supersymmetric models without gaugino mass unification
We examine indirect signals produced by neutralino self-annihilations, in the
galactic halo or inside celestial bodies, in the frame of an effective MSSM
model without gaugino-mass unification at a grand unification scale. We compare
our theoretical predictions with current experimental data of gamma-rays and
antiprotons in space and of upgoing muons at neutrino telescopes. Results are
presented for a wide range of the neutralino mass, though our discussions are
focused on light neutralinos. We find that only the antiproton signal is
potentially able to set constraints on very low-mass neutralinos, below 20 GeV.
The gamma-ray signal, both from the galactic center and from high galactic
latitudes, requires significantly steep profiles or substantial clumpiness in
order to reach detectable levels. The up-going muon signal is largely below
experimental sensitivities for the neutrino flux coming from the Sun; for the
flux from the Earth an improvement of about one order of magnitude in
experimental sensitivities (with a low energy threshold) can make accessible
neutralino masses close to O, Si and Mg nuclei masses, for which resonant
capture is operative.Comment: 17 pages, 1 tables and 5 figures, typeset with ReVTeX4. The paper may
also be found at http://www.to.infn.it/~fornengo/papers/indirect04.ps.gz or
through http://www.astroparticle.to.infn.it/. Limit from BR(Bs--> mu+ mu-)
adde
Effectiveness of a Long-term Home-Based Exercise Training Program in Patients With COPD After Pulmonary Rehabilitation: A Multicenter Randomized Controlled Trial
Background: Most patients with COPD do not maintain exercise training after pulmonary rehabilitation (PR).
Research question: Does a 12-month home-based, minimal-equipment strength training program after PR have an effect on dyspnea, exercise capacity, and patient-reported outcomes in patients with COPD?
Study design and methods: In a parallel-arm multicenter study across four Swiss PR clinics, patients with COPD were allocated randomly (1:1 ratio) into an intervention group (IG; home-based strength training program) or control group (CG; usual care). The primary outcome was change in Chronic Respiratory Questionnaire (CRQ) dyspnea scale score from baseline to 12 months. Secondary outcomes were change in exercise capacity (1-min sit-to-stand-test [1MSTST], 6-min walk test [6MWT]), health-related quality of life, exacerbations, and symptoms. We assessed the IG's experience by interviews at study end. Main analyses were based on the intention-to-treat approach, and adjusted linear regression models were used.
Results: One hundred twenty-three patients with COPD (IG, n = 61; CG, n = 62) were randomized, 61 of whom were women and whose mean ± SD age was 66.8 ± 8.1 years and mean ± SD FEV1 was 39.3 ± 15.3% predicted. One hundred four participants completed 12 months of follow-up (IG, n= 53; CG, n= 51). Of the 53 IG participants, 37 participants (70%) conducted the training until study end. We found no difference in change in CRQ dyspnea scale score over 12 months (adjusted mean difference, 0.28; 95% CI, -0.23 to 0.80; P = .27). We found moderate evidence for a difference in 1MSTST repetitions favoring the IG (adjusted mean difference, 2.6; 95% CI, 0.22-5.03; P = .033), but no evidence for an effect in other outcomes. Seventy-nine percent of the IG reported positive effects that they attributed to the training.
Interpretation: The home exercise program had no effect on dyspnea, but improved 1MSTST performance and patient-perceived fitness. The supported program was well accepted by patients with COPD and may facilitate continued exercise training at home.
Trial registry: ClinicalTrials.gov; No.: NCT03461887; URL: www.
Clinicaltrials: gov.
Keywords: COPD; dyspnea; effectiveness; functional exercise capacity; home-based exercise training; long-term maintenance; minimal equipment; pulmonary rehabilitation; quality of life; randomized controlled tria
Jet Tomography in the Forward Direction at RHIC
Hadron production at high- displays a strong suppression pattern in a
wide rapidity region in heavy ion collisions at RHIC energies. This finding
indicates the presence of strong final state effects for both transversally and
longitudinally traveling partons, namely induced energy loss. We have developed
a perturbative QCD based model to describe hadron production in collision,
which can be combined with the Glauber -- Gribov model to describe hadron
production in heavy ion collisions. Investigating and collisions
at energy GeV at mid-rapidity, we find the opacity of the
strongly interacting hot matter to be proportional to the participant nucleon
number. Considering forward rapidities, the suppression pattern indicates the
formation of a longitudinally contracted dense deconfined zone in central heavy
ion collisions. We determine parameters for the initial geometry from the
existing data.Comment: 6 pages for Hot Quarks '06 Conferenc
Photon Production in Hot and Dense Strongly Interacting Matter
This text is meant as an introduction to the theoretical physics of photon
emission in hot and dense strongly interacting matter, the principal
application being relativistic nuclear collisions. We shall cover some of the
results and techniques appropriate for studies at SPS, RHIC, and LHC energiesComment: 35 pages, accepted for publication, Landolt-Boernstein Volume 1-23
First detection of a VHE gamma-ray spectral maximum from a Cosmic source: H.E.S.S. discovery of the Vela X nebula
The Vela supernova remnant (SNR) is a complex region containing a number of
sources of non-thermal radiation. The inner section of this SNR, within 2
degrees of the pulsar PSR B0833-45, has been observed by the H.E.S.S. gamma-ray
atmospheric Cherenkov detector in 2004 and 2005. A strong signal is seen from
an extended region to the south of the pulsar, within an integration region of
radius 0.8 deg. around the position (RA = 08h 35m 00s, dec = -45 deg. 36'
J2000.0). The excess coincides with a region of hard X-ray emission seen by the
ROSAT and ASCA satellites. The observed energy spectrum of the source between
550 GeV and 65 TeV is well fit by a power law function with photon index = 1.45
+/- 0.09(stat) +/- 0.2(sys) and an exponential cutoff at an energy of 13.8 +/-
2.3(stat) +/- 4.1(sys) TeV. The integral flux above 1 TeV is (1.28 +/- 0.17
(stat) +/- 0.38(sys)) x 10^{-11} cm^{-2} s^{-1}. This result is the first clear
measurement of a peak in the spectral energy distribution from a VHE gamma-ray
source, likely related to inverse Compton emission. A fit of an Inverse Compton
model to the H.E.S.S. spectral energy distribution gives a total energy in
non-thermal electrons of ~2 x 10^{45} erg between 5 TeV and 100 TeV, assuming a
distance of 290 parsec to the pulsar. The best fit electron power law index is
2.0, with a spectral break at 67 TeV.Comment: 5 pages, 4 figures, accepted for publication in Astronomy and
Astrophysics letter
H.E.S.S. observations of gamma-ray bursts in 2003-2007
Very-high-energy (VHE; >~100 GeV) gamma-rays are expected from gamma-ray
bursts (GRBs) in some scenarios. Exploring this photon energy regime is
necessary for understanding the energetics and properties of GRBs. GRBs have
been one of the prime targets for the H.E.S.S. experiment, which makes use of
four Imaging Atmospheric Cherenkov Telescopes (IACTs) to detect VHE gamma-rays.
Dedicated observations of 32 GRB positions were made in the years 2003-2007 and
a search for VHE gamma-ray counterparts of these GRBs was made. Depending on
the visibility and observing conditions, the observations mostly start minutes
to hours after the burst and typically last two hours. Results from
observations of 22 GRB positions are presented and evidence of a VHE signal was
found neither in observations of any individual GRBs, nor from stacking data
from subsets of GRBs with higher expected VHE flux according to a
model-independent ranking scheme. Upper limits for the VHE gamma-ray flux from
the GRB positions were derived. For those GRBs with measured redshifts,
differential upper limits at the energy threshold after correcting for
absorption due to extra-galactic background light are also presented.Comment: 9 pages, 4 tables, 3 figure
Discovery of VHE gamma-rays from the high-frequency-peaked BL Lac object RGB J0152+017
Aims: The BL Lac object RGB J0152+017 (z=0.080) was predicted to be a very
high-energy (VHE; > 100 GeV) gamma-ray source, due to its high X-ray and radio
fluxes. Our aim is to understand the radiative processes by investigating the
observed emission and its production mechanism using the High Energy
Stereoscopic System (H.E.S.S.) experiment. Methods: We report recent
observations of the BL Lac source RGB J0152+017 made in late October and
November 2007 with the H.E.S.S. array consisting of four imaging atmospheric
Cherenkov telescopes. Contemporaneous observations were made in X-rays by the
Swift and RXTE satellites, in the optical band with the ATOM telescope, and in
the radio band with the Nancay Radio Telescope. Results: A signal of 173
gamma-ray photons corresponding to a statistical significance of 6.6 sigma was
found in the data. The energy spectrum of the source can be described by a
powerlaw with a spectral index of 2.95+/-0.36stat+/-0.20syst. The integral flux
above 300 GeV corresponds to ~2% of the flux of the Crab nebula. The source
spectral energy distribution (SED) can be described using a two-component
non-thermal synchrotron self-Compton (SSC) leptonic model, except in the
optical band, which is dominated by a thermal host galaxy component. The
parameters that are found are very close to those found in similar SSC studies
in TeV blazars. Conclusions: RGB J0152+017 is discovered as a source of VHE
gamma-rays by H.E.S.S. The location of its synchrotron peak, as derived from
the SED in Swift data, allows clearly classification it as a
high-frequency-peaked BL Lac (HBL).Comment: Accepted for publication in A&A Letters (5 pages, 4 figures
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