N. V. Gopalakrishnan

Use of plexiglas sheets coated with wavelength-shifter dyes for detection of atmospheric Cherenkov radiation: A new technique for gamma ray astronomy at energies of ∼ 1013–1014 eV

Abstract A 900 cm2 area plexiglas sheet coated with a thin film of a combination of wavelength shifter dyes is used for detection of atmospheric Cherenkov ultraviolet photons in extensive air showers at Cosmic Ray Laboratory, Ooty in southern India. The response of the coated sheet is compared with an otherwise identical but uncoated plexiglas sheet in showers of different primary energies and at different distances from the axes. It is shown that the coated sheet is an efficient detector of Cherenkov UV photons in showers of energies > 1014 eV. Based on these observations it is suggested that an array of detectors made from plexiglas sheets, coated with wavelength-shifter dyes, with interseparations of about 50 m can be effectively used as a large area detector for studies of cosmic sources of gamma rays of energies > 1013 eV. Using the relative timing technique such an array can provide a large collection area, good angular resolution and wide aperture. The advantages of this new technique, relative to conventional detectors such as large area reflectors for Cherenkov photons and arrays of particle detectors for air showers, are discussed.

SEARCH FOR TACHYONS IN EXTENSIVE AIR SHOWERS

The authors have searched for precursors to air showers using a 0.64 m2 scintillation detector system located under a thick layer of absorber inside a multiplate cloud chamber. They find no evidence for a finite flux of tachyon-like particles in an operating time of 3621 hours compared with the observation of six events in 40 hours with a 2.1 m2 detector as reported by Ashton et al. (1977).

New results from ooty eas array for cosmic sources at PeV energies: CYGNUS X-3, Crab pulsar and Sco X-1

Abstract Ooty group has reported detection of a steady signal from Cyg X-3 based on observations made during 1984–1986 through detection of a directional excess. Further analysis of data has revealed a significant flux enhancement during April 1986, confirming observations reported by the CYGNUS group at Los Alamos and the Baksan group. These results show conclusively that the flux from Cyg X-3 is variable over a time scale of few weeks. We also report here the details of an unusual burst from Cyg X-3, consisting of 5 showers in 13 minutes, on June 19, 1985, which shows the variability of the flux from Cyg X-3 on a much shorter time scale of few minutes. Our analysis of showers arriving from the direction of the Crab pulsar has shown only a small time-averaged excess. But these data, when folded with the Crab pulsar period, show a very significant excess at the expected phase of the optical interpulse. This is the first detection of 33 ms pulsation in the PeV energy flux from the Crab pulsar. The exact alignment of the phase of emission over nearly 20 decades of energy, from meter wavelengths to PeV, makes the Crab pulsar a really unique source to study and understand details of mechanisms for emission and acceleration of particles in compact sources. We also present here a discussion of our observations on another x-ray binary, Sco X-1. Ooty data show a very significant excess in the number of showers from the direction of Sco X-1 during a two month period in 1986, in agreement with observations reported by the Mt. Chacaltaya group. These observations establish this x-ray binary as another important source of PeV energy radiation.