111 research outputs found
Constraining the Ratio in TeV Cosmic Rays with Observations of the Moon Shadow by HAWC
An indirect measurement of the antiproton flux in cosmic rays is possible as
the particles undergo deflection by the geomagnetic field. This effect can be
measured by studying the deficit in the flux, or shadow, created by the Moon as
it absorbs cosmic rays that are headed towards the Earth. The shadow is
displaced from the actual position of the Moon due to geomagnetic deflection,
which is a function of the energy and charge of the cosmic rays. The
displacement provides a natural tool for momentum/charge discrimination that
can be used to study the composition of cosmic rays. Using 33 months of data
comprising more than 80 billion cosmic rays measured by the High Altitude Water
Cherenkov (HAWC) observatory, we have analyzed the Moon shadow to search for
TeV antiprotons in cosmic rays. We present our first upper limits on the
fraction, which in the absence of any direct measurements, provide
the tightest available constraints of on the antiproton fraction for
energies between 1 and 10 TeV.Comment: 10 pages, 5 figures. Accepted by Physical Review
Very high energy particle acceleration powered by the jets of the microquasar SS 433
SS 433 is a binary system containing a supergiant star that is overflowing
its Roche lobe with matter accreting onto a compact object (either a black hole
or neutron star). Two jets of ionized matter with a bulk velocity of
extend from the binary, perpendicular to the line of sight, and
terminate inside W50, a supernova remnant that is being distorted by the jets.
SS 433 differs from other microquasars in that the accretion is believed to be
super-Eddington, and the luminosity of the system is erg
s. The lobes of W50 in which the jets terminate, about 40 pc from the
central source, are expected to accelerate charged particles, and indeed radio
and X-ray emission consistent with electron synchrotron emission in a magnetic
field have been observed. At higher energies (>100 GeV), the particle fluxes of
rays from X-ray hotspots around SS 433 have been reported as flux
upper limits. In this energy regime, it has been unclear whether the emission
is dominated by electrons that are interacting with photons from the cosmic
microwave background through inverse-Compton scattering or by protons
interacting with the ambient gas. Here we report TeV -ray observations
of the SS 433/W50 system where the lobes are spatially resolved. The TeV
emission is localized to structures in the lobes, far from the center of the
system where the jets are formed. We have measured photon energies of at least
25 TeV, and these are certainly not Doppler boosted, because of the viewing
geometry. We conclude that the emission from radio to TeV energies is
consistent with a single population of electrons with energies extending to at
least hundreds of TeV in a magnetic field of ~micro-Gauss.Comment: Preprint version of Nature paper. Contacts: S. BenZvi, B. Dingus, K.
Fang, C.D. Rho , H. Zhang, H. Zho
All-particle cosmic ray energy spectrum measured by the HAWC experiment from 10 to 500 TeV
We report on the measurement of the all-particle cosmic ray energy spectrum
with the High Altitude Water Cherenkov (HAWC) Observatory in the energy range
10 to 500 TeV. HAWC is a ground based air-shower array deployed on the slopes
of Volcan Sierra Negra in the state of Puebla, Mexico, and is sensitive to
gamma rays and cosmic rays at TeV energies. The data used in this work were
taken from 234 days between June 2016 to February 2017. The primary cosmic-ray
energy is determined with a maximum likelihood approach using the particle
density as a function of distance to the shower core. Introducing quality cuts
to isolate events with shower cores landing on the array, the reconstructed
energy distribution is unfolded iteratively. The measured all-particle spectrum
is consistent with a broken power law with an index of prior to
a break at ) TeV, followed by an index of . The
spectrum also respresents a single measurement that spans the energy range
between direct detection and ground based experiments. As a verification of the
detector response, the energy scale and angular resolution are validated by
observation of the cosmic ray Moon shadow's dependence on energy.Comment: 16 pages, 11 figures, 4 tables, submission to Physical Review
Search for very-high-energy emission from Gamma-ray Bursts using the first 18 months of data from the HAWC Gamma-ray Observatory
The High Altitude Water Cherenkov (HAWC) Gamma-ray Observatory is an
extensive air shower detector operating in central Mexico, which has recently
completed its first two years of full operations. If for a burst like GRB
130427A at a redshift of 0.34 and a high-energy component following a power law
with index -1.66, the high-energy component is extended to higher energies with
no cut-off other than from extragalactic background light attenuation, HAWC
would observe gamma rays with a peak energy of 300 GeV. This paper
reports the results of HAWC observations of 64 gamma-ray bursts (GRBs) detected
by and , including three GRBs that were also
detected by the Large Area Telescope (-LAT). An ON/OFF analysis
method is employed, searching on the time scale given by the observed light
curve at keV-MeV energies and also on extended time scales. For all GRBs and
time scales, no statistically significant excess of counts is found and upper
limits on the number of gamma rays and the gamma-ray flux are calculated. GRB
170206A, the third brightest short GRB detected by the Gamma-ray Burst Monitor
on board the satellite (-GBM) and also
detected by the LAT, occurred very close to zenith. The LAT measurements can
neither exclude the presence of a synchrotron self-Compton (SSC) component nor
constrain its spectrum. Instead, the HAWC upper limits constrain the expected
cut-off in an additional high-energy component to be less than
for reasonable assumptions about the energetics and redshift of the burst.Comment: 19 pages, 6 figures, published in Ap
Wall roughness induces asymptotic ultimate turbulence
Turbulence is omnipresent in Nature and technology, governing the transport
of heat, mass, and momentum on multiple scales. For real-world applications of
wall-bounded turbulence, the underlying surfaces are virtually always rough;
yet characterizing and understanding the effects of wall roughness for
turbulence remains a challenge, especially for rotating and thermally driven
turbulence. By combining extensive experiments and numerical simulations, here,
taking as example the paradigmatic Taylor-Couette system (the closed flow
between two independently rotating coaxial cylinders), we show how wall
roughness greatly enhances the overall transport properties and the
corresponding scaling exponents. If only one of the walls is rough, we reveal
that the bulk velocity is slaved to the rough side, due to the much stronger
coupling to that wall by the detaching flow structures. If both walls are
rough, the viscosity dependence is thoroughly eliminated in the boundary layers
and we thus achieve asymptotic ultimate turbulence, i.e. the upper limit of
transport, whose existence had been predicted by Robert Kraichnan in 1962
(Phys. Fluids {\bf 5}, 1374 (1962)) and in which the scalings laws can be
extrapolated to arbitrarily large Reynolds numbers
VAMOS: a Pathfinder for the HAWC Gamma-Ray Observatory
VAMOS was a prototype detector built in 2011 at an altitude of 4100m a.s.l.
in the state of Puebla, Mexico. The aim of VAMOS was to finalize the design,
construction techniques and data acquisition system of the HAWC observatory.
HAWC is an air-shower array currently under construction at the same site of
VAMOS with the purpose to study the TeV sky. The VAMOS setup included six water
Cherenkov detectors and two different data acquisition systems. It was in
operation between October 2011 and May 2012 with an average live time of 30%.
Besides the scientific verification purposes, the eight months of data were
used to obtain the results presented in this paper: the detector response to
the Forbush decrease of March 2012, and the analysis of possible emission, at
energies above 30 GeV, for long gamma-ray bursts GRB111016B and GRB120328B.Comment: Accepted for pubblication in Astroparticle Physics Journal (20 pages,
10 figures). Corresponding authors: A.Marinelli and D.Zaboro
First HAWC Observations of the Sun Constrain Steady TeV Gamma-Ray Emission
Steady gamma-ray emission up to at least 200 GeV has been detected from the
solar disk in the Fermi-LAT data, with the brightest, hardest emission
occurring during solar minimum. The likely cause is hadronic cosmic rays
undergoing collisions in the Sun's atmosphere after being redirected from
ingoing to outgoing in magnetic fields, though the exact mechanism is not
understood. An important new test of the gamma-ray production mechanism will
follow from observations at higher energies. Only the High Altitude Water
Cherenkov (HAWC) Observatory has the required sensitivity to effectively probe
the Sun in the TeV range. Using three years of HAWC data from November 2014 to
December 2017, just prior to the solar minimum, we search for 1--100 TeV gamma
rays from the solar disk. No evidence of a signal is observed, and we set
strong upper limits on the flux at a few TeV cm
s at 1 TeV. Our limit, which is the most constraining result on TeV
gamma rays from the Sun, is of the theoretical maximum flux (based
on a model where all incoming cosmic rays produce outgoing photons), which in
turn is comparable to the Fermi-LAT data near 100 GeV. The prospects for a
first TeV detection of the Sun by HAWC are especially high during solar
minimum, which began in early 2018.Comment: 14 pages, 6 figures. See also companion paper 1808.05624. Accepted
for publication in Physical Review
Constraints on Spin-Dependent Dark Matter Scattering with Long-Lived Mediators from TeV Observations of the Sun with HAWC
We analyze the Sun as a source for the indirect detection of dark matter
through a search for gamma rays from the solar disk. Capture of dark matter by
elastic interactions with the solar nuclei followed by annihilation to
long-lived mediators can produce a detectable gamma-ray flux. We search three
years of data from the High Altitude Water Cherenkov Observatory and find no
statistically significant detection of TeV gamma-ray emission from the Sun.
Using this, we constrain the spin-dependent elastic scattering cross section of
dark matter with protons for dark matter masses above 1 TeV, assuming an
unstable mediator with a favorable lifetime. The results complement constraints
obtained from Fermi-LAT observations of the Sun and together cover WIMP masses
between 4 GeV and GeV. The cross section constraints for mediator decays
to gamma rays can be as strong as cm, which is more than
four orders of magnitude stronger than current direct-detection experiments for
1 TeV dark matter mass. The cross-section constraints at higher masses are even
better, nearly 7 orders of magnitude better than the current direct-detection
constraints for 100 TeV dark matter mass. This demonstration of sensitivity
encourages detailed development of theoretical models in light of these
powerful new constraints.Comment: 11 pages, 4 figures. See also companion paper 1808.05620. Accepted
for publication in Physical Review
Rab11 and Actin Cytoskeleton Participate in Giardia lamblia Encystation, Guiding the Specific Vesicles to the Cyst Wall
The encystation process is crucial for survival and transmission of Giardia lamblia to new hosts. During this process, vesicular trafficking and the cytoskeleton play important roles. In eukaryotic cells, intracellular transport is regulated by proteins, including Rab-GTPases and SNAREs, which regulate vesicle formation along with recognition of and binding to the target membrane. Cytoskeletal structures are also involved in these processes. In this study, we demonstrate the participation of Rab11 in the transport of encystation-specific vesicles (ESVs). Additionally, we demonstrate that disruption of actin microfilaments affects ESVs transport. The modification of actin dynamics was also correlated with a reduction in rab11 and cwp1 expression. Furthermore, down-regulation of rab11 mRNA by a specific hammerhead ribozyme caused nonspecific localization of CWP1. We thus provide new information about the molecular machinery that regulates Giardia lamblia encystation. Given our findings, Rab11 and actin may be useful targets to block Giardia encystation
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