Recent Progress on Improving the RXTE Proportional Counter Array Instrumental Background

Dave Smith & Keith Jahoda (GSFC)
Rossi 2000 Meeting

22 March 2000

What's New? And What's Next?

• Background models are available for all gain epochs and source brightnesses

• Characteristics of the PCA residual background and the next generation models

• Latest background models are available from http://heasarc.gsfc.nasa.gov/docs/xte/pca_news.html#quick_table

• Details of these models, and their performance can be found by visiting http://asd.gsfc.nasa.gov/~keith/pca/dasmith/pca_bkgd.html

Systematic Error in 3pcu (1 mCrab ~7 cts/s/3pcu; 2-10 keV)

Energy band	cts/s	cts/s/chan	% bkgd rate
2-10 keV	0.15	7.5E-3	1.5%
10-20 keV	0.03	1.3E-3	0.5%
20-50 keV	0.10	2.2E-3	0.6%

The residual background can be described as follows

• Daily variation in the 30-70 keV band
  
  The observed rate (sky plus internal background), model predicted rate, and the observed-model rate are shown for the 4-day background observation (Figure 1). The observed-model rate (lower points) was fitted by a sine wave to emphasize the daily period.

• Long term trend in the background subtracted light curves
  
  The observed-model rate for the 2-6 (Figure 2) and 20-30 keV (Figure 3) bands are shown. The SAA dosage, as measured by the particle monitor on board HEXTE, is shown for the same period (Figure 4). The long term trend in the the SAA dosage is present in the background subtracted light curves.

Next generation models

• Model component based on either VLE rate or Cut-off Rigidity (COR)
  
  The dependence of the VLE rate on the COR is shown for the non-SAA orbits (Figure 5). Following Hayashida et al. (1989), the data were fitted by a power-law model: VLE = K x COR^-1.1. The dependence of the 30-70 keV background subtracted count rate on the COR (Figure 6) and VLE rate (Figure 7) are shown for the non-SAA orbits. There is a clear correlation between the VLE rate and observed-model rate. A similar result is evident in data accumulated from the SAA orbits.

• Subtract the long term trend from the data

 

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