2,513 research outputs found
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&
Detection of TeV emission from the intriguing composite SNR G327.1-1.1
The shock wave of supernova remnants (SNRs) and the wind termination shock in
pulsar wind nebula (PWNe) are considered as prime candidates to accelerate the
bulk of Galactic cosmic ray (CR) ions and electrons. The SNRs hosting a PWN
(known as composite SNRs) provide excellent laboratories to test these
hypotheses. The SNR G327.1-1.1 belongs to this category and exhibits a shell
and a bright central PWN, both seen in radio and X-rays. Interestingly, the
radio observations of the PWN show an extended blob of emission and a curious
narrow finger structure pointing towards the offset compact X-ray source
indicating a possible fast moving pulsar in the SNR and/or an asymmetric
passage of the reverse shock. We report here on the observations, for a total
of 45 hours, of the SNR G327.1-1.1 with the H.E.S.S. telescope array which
resulted in the detection of TeV gamma-ray emission in spatial coincidence with
the PWN.Comment: Proceeding of the 32nd ICRC, August 11-18 2011, Beijing, Chin
X- and gamma-ray studies of HESS J1731-347 coincident with a newly discovered SNR
In the survey of the Galactic plane conducted with H.E.S.S., many VHE
gamma-ray sources were discovered for which no clear counterpart at other
wavelengths could be identified. HESS J1731-347 initially belonged to this
source class. Recently however, the new shell-type supernova remnant (SNR)
G353.6-0.7 was discovered in radio data, positionally coinciding with the VHE
source. We will present new X-ray observations that cover a fraction of the VHE
source, revealing nonthermal emission that most likely can be interpreted as
synchrotron emission from high-energy electrons. This, along with a larger
H.E.S.S. data set which comprises more than twice the observation time used in
the discovery paper, allows us to test whether the VHE source may indeed be
attributed to shell-type emission from that new SNR. If true, this would make
HESS J1731-347 a new object in the small but growing class of non-thermal
shell-type supernova remnants with VHE emission.Comment: 4 pages, 5 figures, to appear in proceedings of the 31st ICRC, Lodz,
Polan
Sets Represented as the Length-n Factors of a Word
In this paper we consider the following problems: how many different subsets
of Sigma^n can occur as set of all length-n factors of a finite word? If a
subset is representable, how long a word do we need to represent it? How many
such subsets are represented by words of length t? For the first problem, we
give upper and lower bounds of the form alpha^(2^n) in the binary case. For the
second problem, we give a weak upper bound and some experimental data. For the
third problem, we give a closed-form formula in the case where n <= t < 2n.
Algorithmic variants of these problems have previously been studied under the
name "shortest common superstring"
One size does not fit all: Identifying clusters of physical activity, screen time, and sleep behaviour co-development from childhood to adolescence
Purpose
Canada was the first to adopt comprehensive 24-h movement guidelines that include recommendations for physical activity, screen time and sleep to promote health benefits. No studies have investigated the concurrent development of these behaviours in youth. The objectives were to assess adherence to the Canadian 24-h movement guidelines for children and youth and estimate co-development of self-reported moderate-to-vigorous intensity physical activity (MVPA), screen time and sleep during 8-years from childhood to adolescence.
Methods
Nine hundred and twenty three participants of the MATCH study self-reported their MVPA, screen time and sleep duration at least twice over 8 years. MVPA and screen time were measured three times per year (24 cycles), and sleep was measured once per year (8 cycles). Guideline adherence was dichotomised as meeting each specific health behaviour recommendation or not. Multi-group trajectory modeling was used to identify unique trajectories of behavioural co-development. Analyses were stratified by sex.
Results
Between 10 and 39% of youth did not meet any recommendation at the various cycles of data collection. More than half of youth met only one or two recommendation, and roughly 5% of participants met all three recommendations at one or more study cycle throughout the 8 years of follow-up. Four different trajectories of behavioural co-development were identified for boys and for girls. For boys and girls, a complier (good adherence to the guideline recommendations; 12% boys and 9% girls), a decliner (decreasing adherence to the guideline recommendations; 23% boys and 18% girls) and a non-complier group (low adherence to the guideline recommendations; 42% boys and 42% girls) were identified. In boys, a MVPA-complier group (high MVPA-low screen time; 23%) was identified, whereas in girls a screen-complier group (moderate screen time-low MVPA; 30%) was identified.
Conclusions
There is a need to recognise that variations from general trends of decreasing MVPA, increasing screen time and decreasing sleep exist. Specifically, we found that although it is uncommon for youth to adhere to the Canadian 24-h movement guidelines, some youth displayed a high likelihood of attaining one or multiple of the behavioural recommendations. Further, patterns of adherence to the guidelines can differ across different sub-groups of youth
Arg615Cys Substitution in Pig Skeletal Ryanodine Receptors Increases Activation of Single Channels by a Segment of the Skeletal DHPR II-III Loop
AbstractThe effect of peptides, corresponding to sequences in the skeletal muscle dihydropyridine receptor II-III loop, on Ca2+ release from sarcoplasmic reticulum (SR) and on ryanodine receptor (RyR) calcium release channels have been compared in preparations from normal and malignant hyperthermia (MH)-susceptible pigs. Peptide A (Thr671-Leu690; 36μM) enhanced the rate of Ca2+ release from normal SR (SRN) and from SR of MH-susceptible muscle (SRMH) by 10±3.2 nmole/mg/min and 76±9.7 nmole/mg/min, respectively. Ca 2+ release from SRN or SRMH was not increased by control peptide NB (Gly689-Lys708). AS (scrambled A sequence; 36μM) did not alter Ca 2+ release from SRN, but increased release from SRMH by 29±4.9 nmoles/mg/min. RyR channels from MH-susceptible muscle (RyRMH) were up to about fourfold more strongly activated by peptide A (≥1 nM) than normal RyR channels (RyRN) at −40mV. Neither NB or AS activated RyRN. RyRMH showed an ∼1.8-fold increase in mean current with 30μM AS. Inhibition at +40mV was stronger in RyRMH and seen with peptide A (≥0.6μM) and AS (≥0.6μM), but not NB. These results show that the Arg615Cys substitution in RyRMH has multiple effects on RyRs. We speculate that enhanced DHPR activation of RyRs may contribute to increased Ca2+ release from SR in MH-susceptible muscle
Detection of thermal X-ray emission in the halo of the plerionic supernova remnant G21.5-0.9
The detection of a soft thermal X-ray component in the spectrum of a bright
knot in the halo of the plerion G21.5-0.9 is reported. Using a collisional
ionization equilibrium model for an hot optically thin plasma, a temperature
kev, a mass of 0.3--1.0 M and a density of 1.6-6
cm is derived. The spectral analysis suggests a possible overabundance
of Silicon with respect to the solar value in the knot; if this will be
confirmed this object may be a clump of shocked ejecta.Comment: 6 pages, 4 figures, Adv.Sp.Res. in press, proc of COSPAR Session E1.4
"Young Neutron Stars and Supernova Remnants",
http://www.astropa.unipa.it/Library/OAPA_preprints/ns.ps.g
Gamma-ray signatures of cosmic ray acceleration, propagation, and confinement in the era of CTA
Galactic cosmic rays are commonly believed to be accelerated at supernova
remnants via diffusive shock acceleration. Despite the popularity of this idea,
a conclusive proof for its validity is still missing. Gamma-ray astronomy
provides us with a powerful tool to tackle this problem, because gamma rays are
produced during cosmic ray interactions with the ambient gas. The detection of
gamma rays from several supernova remnants is encouraging, but still does not
constitute a proof of the scenario, the main problem being the difficulty in
disentangling the hadronic and leptonic contributions to the emission. Once
released by their sources, cosmic rays diffuse in the interstellar medium, and
finally escape from the Galaxy. The diffuse gamma-ray emission from the
Galactic disk, as well as the gamma-ray emission detected from a few galaxies
is largely due to the interactions of cosmic rays in the interstellar medium.
On much larger scales, cosmic rays are also expected to permeate the
intracluster medium, since they can be confined and accumulated within clusters
of galaxies for cosmological times. Thus, the detection of gamma rays from
clusters of galaxies, or even upper limits on their emission, will allow us to
constrain the cosmic ray output of the sources they contain, such as normal
galaxies, AGNs, and cosmological shocks. In this paper, we describe the impact
that the Cherenkov Telescope Array, a future ground-based facility for
very-high energy gamma-ray astronomy, is expected to have in this field of
research.Comment: accepted to Astroparticle Physics, special issue on Physics with the
Cherenkov Telescope Arra
- …