Kondagunta Umamaheswaram Sivaprasad

Extensive air shower experiment at Kolar Gold Fields

Abstract An experiment to determine the nature of primary cosmic rays of energy > 1014 eV by studying high energy (> 220 GeV) muons and their correlations with other parameters of extensive air showers generated by them, was carried out at Kolar Gold Fields, India (atmospheric depth of 920 g cm−2). An accurate estimate of shower parameters in showers as small as 104 particles was achieved by means of a closely packed array of large area detectors and by employing special methods of analysis. In this paper, the details of the array, the data recording system, the procedure of data analysis and error estimates are described.

First simultaneous detection of PeV energy burst from Crab

We report the first ever simultaneous burst of PeV energy radiation from a potential source. We recorded 35 showers against an expected background of 17.8, with the KGF air shower array, from Crab during 13:15-1600 UT 23 February 1989, the day on which the Baksan group reported a burst. The EASTOP group also reported excess on the same day. Our data show that the muon content of source showers is same as that in background showers. All three observations show correlation with the Crab pulsar period. These results suggest that either gamma ray interactions are similar to hadron interactions at PeV energies, or the primaries are neutrinos interacting with a large cross section predicted by some composite models or a hitherto unknown strongly interacting neutral particle with mass{lt}40 MeV c{sup {minus}2} is responsible for the events.

Search for UHE counter-parts of Gamma Ray Bursts

Several Gamma Ray Bursts detected in the keV energy range by the Burst and Transient Source Experiment (BATSE) have been observed by the Energetic Gamma Ray Experiment Telescope (EGRET) in the MeV/GeV energy range. The energy spectra of γ-rays in some of the bursts continues from keV to GeV without a break or any evidence for a high energy cut-off. If the same slope continues up to the PeV range the expected γ-ray flux falls within the sensitivity of the Extensive Air Shower array operating at the Kolar Gold Fields, India. In view of the enormous astrophysical implications of the results, we have conducted a systematic search for PeV γ-rays from the locations of about 39 high fluence GRB’s detected during April 1991 and March 1993. The results of a search from 8 highest fluence GRB’s are presented here.

Data acquisition and monitoring system for the UHE gamma ray experiment at Kolar Gold Fields

Abstract A computerised on-line data acquisition system has been implemented to acquire data and monitor all the detectors in an extensive air shower experiment at Kolar Gold Fields, India, designed to search for point sources of Ultra High Energy gamma rays. It is based on the LSI-11 microcomputer, which has a powerful instruction set and a daisy chained vectored interrupt facility. Two personal computers are linked with LSI-11 through a 16-bit communication bus, to transfer data for a quick analysis. While the system performs this function in the background, it can be interrupted, at different priority levels, by several foreground functions, such as event data acquisition, detector monitoring, etc. The hardware and software features of the data acquisition system are described in detail.

UHE gamma ray observations with the KGF air shower array

Results on search for point sources based on the data collected from October 1984 to January 1987 from the EAS array at KGF are presented. The array has a pointing accuracy of better than 1.5° to look at point sources. We present upper limit on the long term flux of gamma rays from Cygnus-X3 and report possible episodic emission from Cyg X-3 and Her X-1 during 1985.