Publications

1999
Atkins R, Benbow W, Berley D, Chen M-L, Coyne DG, Delay RS, Dingus BL, Dorfan DE, Ellsworth RW, Evans D, et al. An All-Sky Search for Steady VHE Gamma-Ray Sources . [Internet]. 1999;4 :133. Publisher's VersionAbstract

The Milagrito water Cherenkov detector in the Jemez Mountains near Los Alamos, New Mexico took data from February 1997 to April 1998. Milagrito served as a prototype for the larger Milagro detector, which has just begun operations. Milagrito was the first large-aperture gamma-ray detector with sensitivity to gamma rays below 1 TeV. We report here on a search for steady emission from point sources over most of the northern sky using data from Milagrito.

9906369.pdf
Arndt M, Bennett K, Connors A, McConnell M, Rank G, Ryan JM, Schoenfelder V, Sulciman R, Young CA. Gamma Ray Measurements of the 1991 November 15 Solar Flare. International Cosmic Ray Conference. 1999;6 :256–256.
Atkins R, Benbow W, Berley D, Chen M-L, Coyne DG, Delay RS, Dingus BL, Dorfan DE, Ellsworth RW, Evans D, et al. Milagrito Detection of TeV Emission from Mrk 501 . 26th International Cosmic Ray Conference [Internet]. 1999;3 :330-332. Publisher's VersionAbstract

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.

9906384.pdf
McConnell M. A Polarimeter for Studying Hard X-Rays from Solar Flares. International Cosmic Ray Conference. 1999;6 :21–21.
Ryan JM, Castaneda CM, Holslin D, Macri JR, McConnel ML, Romero JL, Wunderer CB. A scintillating plastic fiber tracking detector for neutron and proton imaging and spectroscopy. NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT [Internet]. 1999;422 :49–53. Publisher's Version
Atkins R, Benbow W, Berley D, Chen M-L, Coyne DG, Delay RS, Dingus BL, Dorfan DE, Ellsworth RW, Evans D, et al. Search for a TeV Component of GRBs using the Milagrito Detector . 26th International Cosmic Ray Conference [Internet]. 1999;4 :12-15. Publisher's VersionAbstract

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.

9906385.pdf
Atkins R, Benbow W, Berley D, Chen M-L, Coyne DG, Delay RS, Dingus BL, Dorfan DE, Ellsworth RW, Evans D, et al. Search for Short Duration Bursts of TeV Gamma Rays with the Milagrito Telescope . 26th International Cosmic Ray Conference [Internet]. 1999;4 :16-19. Publisher's VersionAbstract

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.

Mayer M, Hamel LA, Tousignant O, Macri JR, Ryan JM, McConnell ML, Jordanov VT, Butler JF, Lingren CL. Signal formation in a CdZnTe imaging detector with coplanar pixel and control electrodes. NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT [Internet]. 1999;422 :190–194. Publisher's Version
Atkins R, Benbow W, Berley D, Chen M-L, Coyne DG, Delay RS, Dingus BL, Dorfan DE, Ellsworth RW, Evans D, et al. Status of the Milagro Gamma Ray Observatory . 26th International Cosmic Ray Conference [Internet]. 1999;2 :369-372. Publisher's VersionAbstract

The Milagro Gamma Ray Observatory is the world's first large-area water Cherenkov detector capable of continuously monitoring the sky at TeV energies. Located in northern New Mexico, Milagro will perform an all sky survey of the Northern Hemisphere at energies between  250 GeV and 50 TeV. With a high duty cycle, large detector area ( 5000 square meters), and a wide field-of-view ( 1 sr), Milagro is uniquely capable of searching for transient and DC sources of high-energy gamma-ray emission. Milagro has been operating since February, 1999. The current status of the Milagro Observatory and initial results will be discussed.

Atkins R, Benbow W, Berley D, Chen M-L, Coyne DG, Delay RS, Dingus BL, Dorfan DE, Ellsworth RW, Evans D, et al. Study of the Shadows of the Moon and the Sun with VHE Cosmic Rays . 26th International Cosmic Ray Conference [Internet]. 1999;7 :218-221. Publisher's VersionAbstract

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.

Atkins R, Benbow W, Berley D, Chen M-L, Coyne DG, Delay RS, Dingus BL, Dorfan DE, Ellsworth RW, Evans D, et al. Calibration of the Milagro Cosmic Ray Telescope . 26th International Cosmic Ray Conference [Internet]. 1999;5 :308-311. Publisher's VersionAbstract

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.

McConnell ML. CGRO Guest Investigator Program: Cycle 7. NASA STI/Recon Technical Report N. 1999;99.
McConnell ML. COMPTEL Studies of Gamma-Ray Bursts at MeV Energies. NASA STI/Recon Technical Report N. 1999.
Atkins R, Benbow W, Berley D, Chen M-L, Coyne DG, Delay RS, Dingus BL, Dorfan DE, Ellsworth RW, Evans D, et al. Detection of 6 November 1997 Ground Level Event by Milagrito . 26th International Cosmic Ray Conference [Internet]. 1999;6 :378-381. Publisher's VersionAbstract

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.

McConnell ML, Macri JR, McClish M, Ryan J, Forrest DJ, Vestrand WT. Development of a hard X-ray polarimeter for astrophysics. IEEE TRANSACTIONS ON NUCLEAR SCIENCE [Internet]. 1999;46 :890–896. Publisher's Version
Atkins R, Benbow W, Berley D, Chen M-L, Coyne DG, Delay RS, Dingus BL, Dorfan DE, Ellsworth RW, Evans D, et al. Instrumented Water Tanks can Improve Air Shower Detector Sensitivity . 26th Internnational Cosmic Ray Conference [Internet]. 1999;5 :316-319. Publisher's VersionAbstract

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.

McConnell M. The MeV Gamma-Ray Spectrum of Cygnus X-1. International Cosmic Ray Conference. 1999;4 :119–119.
Briggs MS, Band DL, Kippen RM, Preece RD, Kouveliotou C, van Paradijs J, Share GH, Murphy RJ, Matz SM, Connors A, et al. Observations of GRB 990123 by the Compton Gamma Ray Observatory. ASTROPHYSICAL JOURNAL [Internet]. 1999;524 :82–91. Publisher's Version
Atkins R, Benbow W, Berley D, Chen ML, Coyne DG, Delay RS, Dingus BL, Dorfan DE, Ellsworth RW, Espinoza C, et al. TeV observations of Markarian 501 with the Milagrito water Cerenkov detector. ASTROPHYSICAL JOURNAL [Internet]. 1999;525 :L25–L28. Publisher's Version
McConnell ML. Broad-Band Gamma-Ray Spectra of Cygnus X-1. NASA STI/Recon Technical Report N. 1999.

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