1,344 research outputs found
Integrative analysis of the colorectal cancer proteome : potential clinical impact
Peer reviewedPostprin
Fermi Large Area Telescope Observations of the Cygnus Loop Supernova Remnant
We present an analysis of the gamma-ray measurements by the Large Area
Telescope(LAT) onboard the \textit{Fermi Gamma-ray Space Telescope} in the
region of the supernova remnant(SNR) Cygnus Loop(G74.08.5). We detect
significant gamma-ray emission associated with the SNR in the energy band
0.2--100 GeV. The gamma-ray spectrum shows a break in the range 2--3 GeV. The
gamma-ray luminosity is erg s between 1--100
GeV, much lower than those of other GeV-emitting SNRs. The morphology is best
represented by a ring shape, with inner/outer radii 0.7
0.1 and 1.6 0.1. Given the association among
X-ray rims, \halpha filaments and gamma-ray emission, we argue that gamma rays
originate in interactions between particles accelerated in the SNR and
interstellar gas or radiation fields adjacent to the shock regions. The decay
of neutral pions produced in nucleon-nucleon interactions between accelerated
hadrons and interstellar gas provides a reasonable explanation for the
gamma-ray spectrum.Comment: accepted by ApJ, 34 pages, 6 figure
Polarization and photometric observations of the gamma-ray blazar PG 1553+113
We present the results of an observational photo-polarimetry campaign of the
blazar PG 1553+113 at optical wavelengths. The blazar was recently detected at
very high energies (> 100 GeV) by the H.E.S.S and MAGIC gamma-ray Cherenkov
telescopes.
Our high-temporal resolution data show significant variations in the linear
polarization percentage and position angle at inter-night time-scales, while at
shorter (intra-night) time-scales both parameters varied less significantly, if
at all. Changes in the polarization angle seem to be common in gamma-ray
emitting blazars. Simultaneous differential photometry (through the B and R
bands) shows no significant variability in the total optical flux. We provide B
and R magnitudes, along with a finding chart, for a set of field stars suitable
for differential photometry.Comment: 4 pages, 3 figures. To be published by Astronomy and Astrophysic
Proteomics for early detection of colorectal cancer : recent updates
Funding: This manuscript was not funded.Peer reviewedPostprin
Correlating Fermi gamma-ray sources with ultra-high energy cosmic rays
The origin of ultra-high energy cosmic rays (UHECRs) is one of the enduring
mysteries of high-energy astrophysics. To investigate this, we cross-correlate
the recently released Fermi Large Area Telescope First Source Catalog (1FGL)
with the public sample of UHECRs made available by the Pierre Auger
collaboration. Of the 27 UHECRs in the sample, we find 12 events that arrived
within 3.1 degrees of Fermi sources. However, we find similar or larger number
of matches in 63 out of 100 artificial UHECR samples constructed using
positions randomly drawn from the BATSE 4B catalog of gamma-ray bursts (GRBs)
collected from 1991 until 1996. Based on our analysis, we find no evidence that
UHECRs are associated with Fermi sources. We conclude with some remarks about
the astrophysical origin of cosmic rays.Comment: Revised version that considers a smaller deflection angle for UHECRs
(3.1 degrees) and a declination range for the artificial samples that extends
to decl.= +24.8 in response to the referee comments. 4 pages, 2 figures,
submitted to MNRA
PSRs J0248+6021 and J2240+5832: Young Pulsars in the Northern Galactic Plane. Discovery, Timing, and Gamma-ray observations
Pulsars PSR J0248+6021 (rotation period P=217 ms and spin-down power Edot =
2.13E35 erg/s) and PSR J2240+5832 (P=140 ms, Edot = 2.12E35 erg/s) were
discovered in 1997 with the Nancay radio telescope during a northern Galactic
plane survey, using the Navy-Berkeley Pulsar Processor (NBPP) filter bank. GeV
gamma-ray pulsations from both were discovered using the Fermi Large Area
Telescope. Twelve years of radio and polarization data allow detailed
investigations. The two pulsars resemble each other both in radio and in
gamma-ray data. Both are rare in having a single gamma-ray pulse offset far
from the radio peak. The high dispersion measure for PSR J0248+6021 (DM = 370
pc cm^-3) is most likely due to its being within the dense, giant HII region W5
in the Perseus arm at a distance of 2 kpc, not beyond the edge of the Galaxy as
obtained from models of average electron distributions. Its high transverse
velocity and the low magnetic field along the line-of-sight favor this small
distance. Neither gamma-ray, X-ray, nor optical data yield evidence for a
pulsar wind nebula surrounding PSR J0248+6021. The gamma-ray luminosity for PSR
J0248+6021 is L_ gamma = (1.4 \pm 0.3)\times 10^34 erg/s. For PSR J2240+5832,
we find either L_gamma = (7.9 \pm 5.2) \times 10^34 erg/s if the pulsar is in
the Outer arm, or L_gamma = (2.2 \pm 1.7) \times 10^34 erg/s for the Perseus
arm. These luminosities are consistent with an L_gamma ~ sqrt(Edot) rule.
Comparison of the gamma-ray pulse profiles with model predictions, including
the constraints obtained from radio polarization data, favor emission in the
far magnetosphere. These two pulsars differ mainly in their inclination angles
and acceleration gap widths, which in turn explains the observed differences in
the gamma-ray peak widths.Comment: 13 pages, Accepted to Astronomy & Astrophysic
Solution of an infinite system of differential equations.
We consider an infinite system of differential equations of the second order. Existence and uniqueness questions are discussed in the Hilbert space. We obtain a result which enables the investigation of optimal control and differential game problems described by such a system
Pulsed high energy gamma-rays from thermal populations in the current sheets of pulsar winds
Context. More than one hundred GeV pulsars have been detected up to now by
the LAT telescope on the Fermi gamma-ray observatory, showing peak energies
around a few GeV. Current modelling proposes that the high energy emission
comes from outer magnetospheric gaps, however radiation from the equatorial
current sheet which separates the two magnetic hemispheres outside the light
cylinder has also been investigated. Aims. In this paper we discuss the region
right outside the light cylinder, or "near wind" zone. We investigate the
possibility that synchrotron radiation emitted by thermal populations in the
equatorial current sheet of the pulsar wind in this region can explain the
lightcurves and spectra observed by Fermi/LAT. Methods. We use analytical
estimates as well as detailed numerical computation to calculate the gamma-ray
luminosities, lightcurves and spectra of gamma-ray pulsars. Results. Many of
the characteristics of the gamma-ray pulsars observed by Fermi/LAT can be
reproduced by our model, most notably the position of these objects in the P -
Pdot diagram, and the range of gamma-ray luminosities. A testable result is a
sub-exponential cutoff with an index b = 0.35. We also predict the existence of
a population of pulsars with cutoff energies in the MeV range. These have
systematically lower spindown luminosities than the Fermi/LAT detected pulsars.
Conclusions. It is possible for relativistic populations of electrons and
positrons in the current sheet of a pulsar's wind right outside the light
cylinder to emit synchrotron radiation that peaks in the sub-GeV to GeV regime,
with gamma-ray efficiencies similar to those observed for the Fermi/LAT
pulsars.Comment: 13 pages, submitted to A&
Spectrum and Morphology of the Two Brightest Milagro Sources in the Cygnus Region: MGRO J2019+37 and MGRO J2031+41
The Cygnus region is a very bright and complex portion of the TeV sky, host
to unidentified sources and a diffuse excess with respect to conventional
cosmic-ray propagation models. Two of the brightest TeV sources, MGRO J2019+37
and MGRO J2031+41, are analyzed using Milagro data with a new technique, and
their emission is tested under two different spectral assumptions: a power law
and a power law with an exponential cutoff. The new analysis technique is based
on an energy estimator that uses the fraction of photomultiplier tubes in the
observatory that detect the extensive air shower. The photon spectrum is
measured in the range 1 to 200 TeV using the last 3 years of Milagro data
(2005-2008), with the detector in its final configuration. MGRO J2019+37 is
detected with a significance of 12.3 standard deviations (), and is
better fit by a power law with an exponential cutoff than by a simple power
law, with a probability % (F-test). The best-fitting parameters for the
power law with exponential cutoff model are a normalization at 10 TeV of
, a spectral
index of and a cutoff energy of TeV. MGRO
J2031+41 is detected with a significance of 7.3, with no evidence of a
cutoff. The best-fitting parameters for a power law are a normalization of
and a
spectral index of . The overall flux is subject to an
30% systematic uncertainty. The systematic uncertainty on the power law
indices is 0.1. A comparison with previous results from TeV J2032+4130,
MGRO J2031+41 and MGRO J2019+37 is also presented.Comment: 11 pages, 10 figure
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