Flasher calibration of the T1 and T2 CANGAROO telescopes and TeV gamma ray observation of Markarian 421 and EXO 055625-3838.6 BL Lacertae blazars.

Abstract

Calibration tests were made on the T1 and T2 telescopes of the CANGAROO collaboration in 2001 to 2003, using a custom-made LED light flasher apparatus to test the two (T1 and T2) telescope responses to a fixed amplitude light signal. The flasher apparatus was set up (a kilometre distance from the telescopes), to trigger the telescopes with a 10 nanosecond or 20 nanosecond pulse width flash, running at a rate of 1 kilohertz. Measurement of the light intensity of the flasher was achieved by using a custom-made PIN diode monitor coupled to the flasher output. After data analysis, it was found that the principal flasher signal amplitude variation (from month to month) as measured by a telescope, was due to errors in the encoders upon slewing and parking the telescope. This effect was found and measured by taking the two dimensional cross-correlation of the flasher pixel images (acquired in the camera of the two telescopes), taken monthly. Measurement of the T1 telescope energy threshold was attempted, using cosmic ray showers at the zenith, on two separate occasions. Finally, 2313.9 on-source minutes of data on the HBL Lac. blazar, Markarian 421 data was acquired by T1 in 2001 to 2003, and 1013 on-source minutes of data on the BL Lac. blazar EXO 055625-3838.6 were acquired in 2002 and 2003, by T1. From alpha plot distributions (where alpha ≤ 40°), it was found that the TeV gamma ray signal significance for Markarian 421 was 2.8 σ (in 2001-03); 3.3 σ (in 2001) and 0.4 σ (upper limit in 2002-03). Furthermore, from (alpha < 20°) to maximize signal over noise, the significance for Markarian 421 was found to be 3.5 σ (2001-03); 3.5 σ (in 2001) and 1.2 σ (upper limit in 2002-03). The TeV gamma ray signal significance (where alpha ≤ 20°), was 2.2 σ for EXO 055625-3838.6 over 2002-03.