357 research outputs found
Calibration of the Milagro Cosmic Ray Telescope
The Milagro detector is an air shower array which uses the water Cherenkov
technique and is capable of continuously monitoring the sky at energies near 1
TeV. The detector consists of 20000 metric tons of pure water instrumented with
723 photo-multiplier tubes (PMTs). The PMTs are arranged in a two-layer
structure on a lattice of 3 m spacing covering 5000 area. The direction
of the shower is determined from the relative timing of the PMT signals,
necessitating a common time reference and amplitude slewing corrections to
improve the time resolution. The calibration system to provide these consists
of a pulsed laser driving 30 diffusing light sources deployed in the pond to
allow cross-calibration of the PMTs. The system is capable of calibrating times
and the pulse-heights from the PMTs using the time-over-threshold technique.
The absolute energy scale is provided using single muons passing through the
detector. The description of the calibration system of the Milagro detector and
its prototype Milagrito will be presented.Comment: 4 pages, submitted to the XXVI International Cosmic Ray Conferenc
Search for Short Duration Bursts of TeV Gamma Rays with the Milagrito Telescope
The Milagrito water Cherenkov telescope operated for over a year. The most
probable gamma-ray energy was ~1 TeV and the trigger rate was as high as 400
Hz. We have developed an efficient technique for searching the entire sky for
short duration bursts of TeV photons. Such bursts may result from "traditional"
gamma-ray bursts that were not in the field-of-view of any other instruments,
the evaporation of primordial black holes, or some as yet undiscovered
phenomenon. We have begun to search the Milagrito data set for bursts of
duration 10 seconds. Here we will present the technique and the expected
results. Final results will be presented at the conference.Comment: submitted to XXVI International Cosmic Ray Conference, Salt Lake Cit
Instrumented Water Tanks can Improve Air Shower Detector Sensitivity
Previous works have shown that water Cherenkov detectors have superior
sensitivity to those of scintillation counters as applied to detecting
extensive air showers (EAS). This is in large part due to their much higher
sensitivity to EAS photons which are more than five times more numerous than
EAS electrons. Large area water Cherenkov detectors can be constructed
relatively cheaply and operated reliably. A sparse detector array has been
designed which uses these types of detectors to substantially increase the area
over which the Milagro Gamma Ray Observatory collects EAS information.
Improvements to the Milagro detector's performance characteristics and
sensitivity derived from this array and preliminary results from a prototype
array currently installed near the Milagro detector will be presented.Comment: 4 pages, submitted to XXVI International Cosmic Ray Conference, Salt
Lake Cit
Study of the Shadows of the Moon and the Sun with VHE Cosmic Rays
Milagrito, a prototype for the Milagro detector, operated for 15 months in
1997-8 and collected 8.9 billion events. It was the first extensive air shower
(EAS) array sensitive to showers intiated by primaries with energy below 1 TeV.
The shadows of the sun and moon observed with cosmic rays can be used to study
systematic pointing shifts and measure the angular resolution of EAS arrays.
Below a few TeV, the paths of cosmic rays coming toward the earth are bent by
the helio- and geo-magnetic fields. This is expected to distort and displace
the shadows of the sun and the moon. The moon shadow, offset from the nominal
(undeflected) position, has been observed with high statistical significance in
Milagrito. This can be used to establish energy calibrations, as well as to
search for the anti-matter content of the VHE cosmic ray flux. The shadow of
the sun has also been observed with high significance.Comment: 4 pages, submitted to XXVI International Cosmic Ray Conference, Salt
Lake Cit
Milagrito Detection of TeV Emission from Mrk 501
The Milagro water Cherenkov detector near Los Alamos, New Mexico, has been
operated as a sky monitor at energies of a few TeV between February 1997 and
April 1998. Serving as a test run for the full Milagro detector, Milagrito has
taken data during the strong and long-lasting 1997 flare of Mrk 501. We present
results from the analysis of Mrk 501 and compare the excess and background
rates with expectations from the detector simulations.Comment: 4 pages, submitted to XXVI International Cosmic Ray Conference, Salt
Lake Cit
Search for a TeV Component of GRBs using the Milagrito Detector
Observing gamma ray bursts (GRBs) in the TeV energy range can be extremely
valuable in providing insight to GRB radiation mechanisms and in constraining
source distances. The Milagrito detector was an air shower array which used the
water Cherenkov technique to search for TeV sources. Data from this detector
was analyzed to look for a TeV component of GRBs coincident with low energy
-rays detected by the BATSE instrument on the Compton Gamma Ray Observatory. A
sample of 54 BATSE GRBs which were in the field of view of the Milagrito
detector during its lifetime (February 1997 to May 1998) was used.Comment: 4 pages, submitted to XXVI International Cosmic Ray Conference, Salt
Lake Cit
Detection of 6 November 1997 Ground Level Event by Milagrito
Solar Energetic Particles from the 6 November 1997 solar flare/CME(coronal
mass ejection) with energies exceeding 10 GeV have been detected by Milagrito,
a prototype of the Milagro Gamma Ray Observatory. While particle acceleration
beyond 1 GeV at the Sun 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 ~5- 10 GeV. Milagrito
operated in a scaler mode, which was primarily sensitive to muons, low energy
photons, and electrons, and the detector operated in a mode sensitive to
showers and high zenith angle muons. 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 >10 GeV particles.Comment: 4 pages, submitted to XXVI International Cosmic Ray Conference, Salt
Lake Cit
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