3,220 research outputs found
Observation of TeV Gamma Rays from the Crab Nebula with Milagro Using a New Background Rejection Technique
The recent advances in TeV gamma-ray astronomy are largely the result of the
ability to differentiate between extensive air showers generated by gamma rays
and hadronic cosmic rays. Air Cherenkov telescopes have developed and perfected
the "imaging" technique over the past several decades. However until now no
background rejection method has been successfully used in an air shower array
to detect a source of TeV gamma rays. We report on a method to differentiate
hadronic air showers from electromagnetic air showers in the Milagro gamma ray
observatory, based on the ability to detect the energetic particles in an
extensive air shower. The technique is used to detect TeV emission from the
Crab nebula. The flux from the Crab is estimated to be 2.68(+-0.42stat +-
1.4sys) x10^{-7} (E/1TeV)^{-2.59} m^{-2} s^{-1} TeV^{-1}, where the spectral
index is assumed to be as given by the HEGRA collaboration.Comment: 22 pages, 11 figures, submitted to Astrophysical Journa
An Exploration of Successful Psychosocial Adjustment to Long-Term In-Centre Haemodialysis
Objectives: Haemodialysis extends life for people with end-stage kidney disease (ESKD) worldwide, but it imposes significant psychosocial burdens and there is little evidence about successful adjustment. This study aimed to improve understanding of successful psychosocial adjustment to in-centre haemodialysis (ICHD; dialysis in a hospital or satellite unit).
Methods: Individual semi-structured interviews were conducted with a purposive sample of 18 people with ESKD who had all received in-centre haemodialysis in the UK for at least 90 days in the last two years. An inductive thematic analysis was employed to identify themes from the verbatim interview transcripts.
Results: There were four themes: 1) reaching a state of acceptance, which described the importance of accepting the necessity of dialysis; 2) taking an active role in treatment, which described how being actively involved in treatment gave participants greater feelings of autonomy and control; 3) utilising social support networks, which described the benefits of instrumental and emotional support; and 4) building emotional resilience, which described the importance of optimism and positivity.
Conclusions: The themes demonstrated elements of successful adjustment that could be targeted by interventions to promote psychological flexibility and positive adjustment among people receiving in-centre haemodialysis worldwide
Search for very high energy gamma-rays from WIMP annihilations near the Sun with the Milagro Detector
The neutralino, the lightest stable supersymmetric particle, is a strong
theoretical candidate for the missing astronomical ``dark matter''. A profusion
of such neutralinos can accumulate near the Sun when they lose energy upon
scattering and are gravitationally captured. Pair-annihilations of those
neutralinos may produce very high energy (VHE, above ) gamma-rays.
Milagro is an air shower array which uses the water Cherenkov technique to
detect extensive air showers and is capable of observing VHE gamma-rays from
the direction of the Sun with an angular resolution of . Analysis
of Milagro data with an exposure to the Sun of 1165 hours presents the first
attempt to detect TeV gamma-rays produced by annihilating neutralinos captured
by the Solar system and shows no statistically significant signal. Resulting
limits that can be set on gamma-ray flux due to near-Solar neutralino
annihilations and on neutralino cross-section are presented
TeV Gamma-Ray Sources from a Survey of the Galactic Plane with Milagro
A survey of Galactic gamma-ray sources at a median energy of ~20 TeV has been
performed using the Milagro Gamma Ray Observatory. Eight candidate sources of
TeV emission are detected with pre-trials significance in the
region of Galactic longitude and latitude
. Four of these sources, including the Crab nebula
and the recently published MGRO J2019+37, are observed with significances
after accounting for the trials involved in searching the 3800
square degree region. All four of these sources are also coincident with EGRET
sources. Two of the lower significance sources are coincident with EGRET
sources and one of these sources is Geminga. The other two candidates are in
the Cygnus region of the Galaxy. Several of the sources appear to be spatially
extended. The fluxes of the sources at 20 TeV range from ~25% of the Crab flux
to nearly as bright as the Crab.Comment: Submitted to Ap
Spectropolarimetry of R Coronae Borealis in 1998--2003: Discovery of Transient Polarization at Maximum Brightness
We present an extended optical spectropolarimetry of R CrB from 1998 January
to 2003 September. The polarization was almost constant in the phase of maximum
brightness, being consistent with past observations. We detected, however,
temporal changes of polarization ( %) in 2001 March and August, which
were the first detection of large polarization variability in R CrB near
maximum brightness. The amplitude and the position angle of the `transient
polarization' were almost constant with wavelength in both two events. There
was a difference by about 20 degrees in the position angle between the two
events. Each event could be explained by light scattering due to short-lived
dust puff occasionally ejected off the line of sight. The flatness of the
polarization against the wavelength suggests that the scatterer is a mixture of
dust grains having various sizes. The rapid growth and fading of the transient
polarization favors the phenomenological model of dust formation near the
stellar photosphere (e.g., within two stellar radii) proposed for the time
evolution of brightness and chromospheric emission lines during deeply
declining periods, although the fading timescale can hardly be explained by a
simple dispersal of expanding dust puff with a velocity of km s
. Higher expansion velocity or some mechanism to destroy the dust grains
should be needed.Comment: 22 pages, 10 figures, accepted for publication in A
Evidence for TeV Emission from GRB 970417a
Milagrito, a detector sensitive to very high energy gamma rays, monitored the
northern sky from February 1997 through May 1998. With a large field of view
and a high duty cycle, this instrument was well suited to perform a search for
TeV gamma-ray bursts (GRBs). We report on a search made for TeV counterparts to
GRBs observed by BATSE. BATSE detected 54 GRBs within the field of view of
Milagrito during this period. An excess of events coincident in time and space
with one of these bursts, GRB 970417a, was observed by Milagrito. The excess
has a chance probability of of being a fluctuation of the
background. The probability for observing an excess at least this large from
any of the 54 bursts is . No significant correlations were
detected from the other bursts.Comment: 10 pages, 3 figure
Detection of 6 November 1997 ground level event by Milagrito
Solar Energetic Particles (SEPs) with energies exceeding 10 GeV associated with the 6 November 1997 solar flare/CME (coronal mass ejection) have been detected with Milagrito, a prototype of the Milagro Gamma Ray Observatory. While SEP acceleration beyond 1 GeV is well established, few data exist for protons or ions beyond 10 GeV. The Milagro observatory, a ground based water Cherenkov detector designed for observing very high energy gamma ray sources, can also be used to study the Sun. Milagrito, which operated for approximately one year in 1997/98, was sensitive to solar proton and neutron fluxes above ∼4 GeV. In its scaler mode, Milagrito registered a rate increase coincident with the 6 November 1997 ground level event observed by Climax and other neutron monitors. A preliminary analysis suggests the presence of \u3e10 GeV particles
First results of a study of TeV emission from GRBs in Milagrito
Milagrito, a detector sensitive to γ-rays at TeV energies, monitored the northern sky during the period February 1997 through May 1998. With a large field of view and high duty cycle, this instrument was used to perform a search for TeV counterparts to γ-ray bursts. Within the Milagrito field of view 54 γ-ray bursts at keV energies were observed by the Burst And Transient Satellite Experiment (BATSE) aboard the Compton Gamma-Ray Observatory. This paper describes the results of a preliminary analysis to search for TeV emission correlated with BATSE detected bursts. Milagrito detected an excess of events coincident both spatially and temporally with GRB 970417a, with chance probability 2.8×10−5 within the BATSE error radius. No other significant correlations were detected. Since 54 bursts were examined the chance probability of observing an excess with this significance in any of these bursts is 1.5×10−3. The statistical aspects and physical implications of this result are discussed
The high-energy gamma-ray fluence and energy spectrum of GRB 970417a from observations with Milagrito
Evidence of TeV emission from GRB970417a has been previously reported using
data from the Milagrito detector. Constraints on the TeV fluence and the energy
spectrum are now derived using additional data from a scaler system that
recorded the rate of signals from the Milagrito photomultipliers. This analysis
shows that if emission from GRB970417a has been observed, it must contain
photons with energies above 650 GeV. Some consequences of this observation are
discussed.Comment: Submitted to the Astrophysical Journa
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