6,347 research outputs found
Constraints on the cosmic ray diffusion coefficient in the W28 region from gamma-ray observations
GeV and TeV gamma rays have been detected from the supernova remnant W28 and
its surroundings. Such emission correlates quite well with the position of
dense and massive molecular clouds and thus it is often interpreted as the
result of hadronic cosmic ray interactions in the dense gas. Constraints on the
cosmic ray diffusion coefficient in the region can be obtained, under the
assumption that the cosmic rays responsible for the gamma ray emission have
been accelerated in the past at the supernova remnant shock, and subsequently
escaped in the surrounding medium. In this scenario, gamma ray observations can
be explained only if the diffusion coefficient in the region surrounding the
supernova remnant is significantly suppressed with respect to the average
galactic one.Comment: To appear in the proceedings of "Journ\'ees de la SF2A 2010"
Marseille 21-24 June 2010, 4 pages, 4 figure
HESS J1641-463, a very hard spectrum TeV gamma-ray source in the Galactic plane
HESS J1641-463 is a unique source discovered by the High Energy Stereoscopic
System (H.E.S.S.) telescope array in the multi-TeV domain. The source had been
previously hidden in the extended tail of emission from the bright nearby
source HESS J1640-465. However, the analysis of the very-high-energy (VHE) data
from the region at energies above 4 TeV revealed this new source at a
significance level of 8.5. HESS J1641-463 showed a moderate flux level
F(E > 1 TeV) = (3.64 +/- 0.44_stat +/- 0.73_sys) 10^-13 cm^-2s^-1,
corresponding to 1.8% of the Crab Nebula flux above the same energy, and a hard
spectrum with a photon index Gamma = 2.07 +/- 0.1_stat +/- 0.20_sys. The light
curve was investigated for evidence of variability, but none was found on both
short (28-min observation) and long (yearly) timescales. HESS J1641-463 is
positionally coincident with the radio supernova remnant (SNR) G338.5+0.1.
There is no clear X-ray counterpart of the SNR, although Chandra and XMM-Newton
data reveal some weak emission that may be associated. If the emission from
HESS J1641-463 is produced by cosmic ray protons colliding with the ambient
gas, then the proton spectrum extends up to 0.1 PeV (99% confidence level) and
likely to higher energies, > 0.27 PeV (90% confidence level). If this is the
case, then HESS J1641-463 may be a member of a larger source population
contributing to the Galactic cosmic-ray flux around the knee.Comment: In Proceedings of the 34th International Cosmic Ray Conference
(ICRC2015), The Hague, The Netherland
Acceleration of cosmic rays and gamma-ray emission from supernova remnants in the Galaxy
Galactic cosmic rays are believed to be accelerated at supernova remnant
shocks. Though very popular and robust, this conjecture still needs a
conclusive proof. The strongest support to this idea is probably the fact that
supernova remnants are observed in gamma-rays, which are indeed expected as the
result of the hadronic interactions between the cosmic rays accelerated at the
shock and the ambient gas. However, also leptonic processes can, in most cases,
explain the observed gamma-ray emission. This implies that the detections in
gamma rays do not necessarily mean that supernova remnants accelerate cosmic
ray protons. To overcome this degeneracy, the multi-wavelength emission (from
radio to gamma rays) from individual supernova remnants has been studied and in
a few cases it has been possible to ascribe the gamma-ray emission to one of
the two processes (hadronic or leptonic). Here we adopt a different approach
and, instead of a case-by-case study we aim for a population study and we
compute the number of supernova remnants which are expected to be seen in TeV
gamma rays above a given flux under the assumption that these objects indeed
are the sources of cosmic rays. The predictions found here match well with
current observational results, thus providing a novel consistency check for the
supernova remnant paradigm for the origin of galactic cosmic rays. Moreover,
hints are presented for the fact that particle spectra significantly steeper
than E^-2 are produced at supernova remnants. Finally, we expect that several
of the supernova remnants detected by H.E.S.S. in the survey of the galactic
plane should exhibit a gamma-ray emission dominated by hadronic processes (i.e.
neutral pion decay). The fraction of the detected remnants for which the
leptonic emission dominates over the hadronic one depends on the assumed values
of the physical parameters and can be as high as roughly a half.Comment: 14 pages, 4 figures, 4 tables, submitted to MNRA
The diffuse neutrino flux from the inner Galaxy: constraints from very high energy gamma-ray observations
Recently, the MILAGRO collaboration reported on the detection of a diffuse
multi-TeV emission from a region of the Galactic disk close to the inner
Galaxy. The emission is in excess of what is predicted by conventional models
for cosmic ray propagation, which are tuned to reproduce the spectrum of cosmic
rays observed locally. By assuming that the excess detected by MILAGRO is of
hadronic origin and that it is representative for the whole inner Galactic
region, we estimate the expected diffuse flux of neutrinos from a region of the
Galactic disk with coordinates . Our estimate has
to be considered as the maximal expected neutrino flux compatible with all the
available gamma ray data, since any leptonic contribution to the observed
gamma-ray emission would lower the neutrino flux. The diffuse flux of
neutrinos, if close to the maximum allowed level, may be detected by a
km--scale detector located in the northern hemisphere. A detection would
unambiguously reveal the hadronic origin of the diffuse gamma-ray emission.Comment: submitted to Astroparticle Physic
Love That Dirty Water : A Preliminary Investigation of Microbial Diversity in On-Street Hot Dog Water
Standard microbiological methods were utilized to assess the microbial diversity and abundance in the hot dog water found in mobile food carts. Since we could not directly assay the water, we devised a method of washing hot dogs with sterile water to indirectly assess the presence of microorganisms both growing in the water and on the hot dogs. Plating on LB-agar and LB-agar supplemented with antibiotics was used to isolate microbes from hot dog water from randomly selected vendors in twenty-six Manhattan neighborhoods and the Bronx. In addition, five major hot dog brands were similarly tested as store-bought controls. As expected, on-street hot dog water contained culturable microbes, ranging from 0 to more than 1.25 x 105 Colony Forming Units (CFU’s) per hot dog (X = 8,000 CFU’s/hot dog). Control hot dogs had considerably fewer culturable microorganisms (from 0 to to 2.5 x 103 CFU’s per hot (X = 1,100 CFU’s/hot dog). We have also discovered antibiotic resistant bacteria at 5 of our 26 sites (20%), including Ampicillin, Chloramphenicol, Kanamycin and Tetracycline resistance. In addition, our data suggests a possible correlation between CFU’s and serving temperature of hot dogs. Those served at temperatures of 145 F or greater had a mean of 33.9 CFU’s/hot dog, whereas those below 145 F had a mean of 9,897 CFU’s/hot dog. PCR-based amplification using the 16S locus for DNA barcoding was utilized to identify isolated colonies. We identified 22 different microbial species in on-street hot dogs, and 10 different species in store-bought (control) hot dogs. In summary, the hot dog water microbiome is complex and shows greater diversity than that associated with control hot dogs
Constraining the Origin of Local Positrons with HAWC TeV Gamma-Ray Observations of Two Nearby Pulsar Wind Nebulae
The HAWC Gamma-Ray Observatory has reported the discovery of TeV gamma-ray
emission extending several degrees around the positions of Geminga and B0656+14
pulsars. Assuming these gamma rays are produced by inverse Compton scattering
off low-energy photons in electron halos around the pulsars, we determine the
diffusion of electrons and positrons in the local interstellar medium. We will
present the morphological and spectral studies of these two VHE gamma-ray
sources and the derived positron spectrum at Earth.Comment: Presented at the 35th International Cosmic Ray Conference (ICRC2017),
Bexco, Busan, Korea. See arXiv:1708.02572 for all HAWC contribution
Quantum Simulation of Dissipative Processes without Reservoir Engineering
We present a quantum algorithm to simulate general finite dimensional
Lindblad master equations without the requirement of engineering the
system-environment interactions. The proposed method is able to simulate both
Markovian and non-Markovian quantum dynamics. It consists in the quantum
computation of the dissipative corrections to the unitary evolution of the
system of interest, via the reconstruction of the response functions associated
with the Lindblad operators. Our approach is equally applicable to dynamics
generated by effectively non-Hermitian Hamiltonians. We confirm the quality of
our method providing specific error bounds that quantify itss accuracy.Comment: 7 pages + Supplemental Material (6 pages
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