2.3.3 Long-term stability

It appears that the effective area has not varied significantly since launch. Observations of the sources HZ43, Vega, A2256, and N132D at several epochs yield non-varying count rates (Table 3).

  

Table 3: Quantum Efficiency Monitor

Source	Date of Observation	Count Rate (counts s-1)
A2256	July 1, 1990	0.61 $\pm$ 0.01
	August 3, 1992	0.62 $\pm$ 0.01
HZ43	July 2, 1990	12.3 $\pm$ 0.2
	December 11, 1991	12.0 $\pm$ 0.2
	June 9, 1992	11.91 $\pm$ 0.04
Vega	March 20, 1991	0.10 $\pm$ 0.01
	March 21, 1992	0.11 $\pm$ 0.01
	Sept 18, 1992	0.10 $\pm$ 0.01
	April 15, 1995	0.11 $\pm$ 0.01
N132D	1990 July 3	4.43 $\pm$ 0.09
	1990 July 4	4.50 $\pm$ 0.13
	1991 February 9	4.54 $\pm$ 0.01
	1991 December 11	4.49 $\pm$ 0.09
	1992 June 10	4.40 $\pm$ 0.04
	1992 August 3	4.21 $\pm$ 0.05
	1992 September 17	4.57 $\pm$ 0.05
	1993 April 17	4.46 $\pm$ 0.04
	1994 January 10	4.40 $\pm$ 0.04
	1994 March 10	4.39 $\pm$ 0.06
	1994 June 15	4.56 $\pm$ 0.04
	1994 July 15	4.53 $\pm$ 0.05
	1994 August 15	4.54 $\pm$ 0.06
	1994 September 15	4.49 $\pm$ 0.06
	1995 February 11	4.40 $\pm$ 0.04
	1995 March 11	4.51 $\pm$ 0.04
	1995 October 20	4.54 $\pm$ 0.06
	1995 November 20	4.51 $\pm$ 0.04
	1996 January 20	4.59 $\pm$ 0.05
	1996 February 20	4.34 $\pm$ 0.04
	1996 April 20	4.23 $\pm$ 0.05
	1996 May 20	4.45 $\pm$ 0.07
	1996 June 20	4.10 $\pm$ 0.04
	1996 August 20	4.63 $\pm$ 0.05
	1996 September 20	4.43 $\pm$ 0.05
	1996 December 27	4.36 $\pm$ 0.05
	1997 March 5	4.30 $\pm$ 0.09
	1997 April 5	4.19 $\pm$ 0.04
	1997 October 5	4.23 $\pm$ 0.04
	1998 March 15	4.26 $\pm$ 0.06

Note: The count rate for A2256 is determined from the net emission within a 6' radius.