  An alternative scheme is described to estimate the layer 1 LAXPC 20
background for faint sources where the source contribution to the 50-80 keV
count rate is less than 0.25 counts/sec (15 milli-crabs or $6 \times 10^{-11}$
ergs/s/cm$^2$). We consider 12 blank sky observations and based on their 50-80
keV count rate in 100 second time-bins, generate four template spectra which
are then used to estimate the background spectrum and lightcurve for a given
faint source observation. The variance of the estimated background subtracted
spectra for the 12 blank sky observations is taken as the energy dependent
systematic uncertainty which will dominate over the statistical one for
exposures longer than 5 ksecs. The estimated 100 second time bin background
lightcurve in the 4-20 keV band with a 3\% systematic error matches with the
blank sky ones. The 4-20 keV spectrum can be constrained for a source with flux
$\gtrapprox 1$ milli-crab. Fractional r.m.s variability of 10\% can be
determined for a $\sim 5$ milli-crab source lightcurve binned at 100 seconds.
To illustrate the scheme, the lightcurves, and spectra of three different blank
sky observations, three AGN sources (Mrk 0926, Mrk 110, NGC 4593), and LMC X-1
are shown.
