Computerized polar plots by a cathode ray tube/grid overlay method

Overlay is aligned with four calibration dots so it is not affected by CRT drift or changes in vertical or horizontal gain when producing Nyquist /frequency-response phase/amplitude/ plots. Method produces over 50 plots per hour

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

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 $2.8 \times 10^{-5}$ of being a fluctuation of the background. The probability for observing an excess at least this large from any of the 54 bursts is $1.5 \times 10^{-3}$. No significant correlations were detected from the other bursts.Comment: 10 pages, 3 figure

Milagro: A TeV observatory for gamma-ray bursts

Observation of prompt TeV γ-rays from GRBs requires a new type of detector to overcome the low duty factor and small field of view of current TeV observatories. Milagro is such a new type of very high energy (\u3e a few 100 GeV) gamma-ray observatory, which has a large field of view of \u3e1 steradian and 24 hours/day operation. Milagrito, a prototype for Milagro, was operated from February 1997 to May 1998. During the summer of 1998, Milagrito was dismantled and Milagro was built. Both detectors use a 80 m×60 m×8 m pond of water in which a 3 m×3 m grid of photomultiplier tubes detects the Cherenkov light produced in the water by the relativistic particles in extensive air showers. Milagrito was smaller and had only one layer of photomultipliers, but allowed the technique to be tested. Milagrito observations of the Moon’s shadow and Mrk 501 are consistent with the Monte Carlo prediction of the telescope’s parameters, such as effective area and angular resolution. Milagro will have improved flux sensitivity over Milagrito due to larger effective area, better angular resolution and cosmic-ray background rejection

Milagro: A TeV gamma-ray monitor of the Northern Hemisphere Sky

A new type of very high energy (\u3e a few 100 GeV) gamma-ray observatory, Milagro, has been built with a large field of view of \u3e1 steradian and nearly 24 hours/day operation. Milagrito, a prototype for Milagro, was operated from February 1997 to May 1998. During the summer of 1998, Milagrito was dismantled and Milagro was built. Both detectors use a 80 m×60 m×8 mpond of water in which a 3 m×3 m grid of photomultiplier tubes detects the Cherenkov light produced in the water by the relativistic particles in extensive air showers. Milagrito was smaller and had only one layer of photomultipliers, but allowed the technique to be tested. Milagrito observations of the Moon’s shadow and Mrk 501 are consistent with the Monte Carlo prediction of the telescopes parameters, such as effective area and angular resolution. Milagro is larger and consists of two layers of photomultiplier tubes. The bottom layer detects penetrating particles that are used to reject the background of cosmic-ray initiated showers

Results from the Milagrito experiment

The Milagro water Cherenkov detector near Los Alamos, New Mexico is the first air shower detector capable of continuously monitoring the sky at energies between 500 GeV and 20 TeV. Preliminary results of the Milagro experiment are presented. A predecessor of the Milagro detector, Milagrito, was operational from February 1997 to May 1998. Milagrito consisted of 228 8″ photomultiplier tubes (PMTs) arranged in a grid with a 2.8 meter spacing and submerged in 1–2 meters of water. During its operation, Milagrito collected in excess of 9 billion events with a median energy of about 3 TeV. The detector’s sensitivity extends below 1 TeV for showers from near zenith. The results of an all sky search for the Milagrito data for both transient and DC sources will be presented, including the Crab Nebula and active galaxies Markarian 501 and 421, which are known sources of TeV gamma-rays. Also presented will be a study of the TeV emission from gamma ray bursts (GRBs) in Milagrito’s field of view detected by the BATSE experiment on the Compton Gamma-Ray Observatory

The Milagro gamma-ray observatory

The Milagro water Cherenkov detector began full operation in January 2000. This detector is capable of monitoring the Northern sky at energies above 500 GeV for sources of equivalent strength to the Crab Nebula over one year of integration. We report on the current performance and sensitivity of Milagro

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 $m^2$ 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

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