If we assume an incident X-ray energy spectrum of a power law form:
I(E) = 
(photons/s/cm
/keV), we can estimate hard X-ray flux at
20 keV (A) and photon index (G) by the following command:
IDL> p = hxt_powerlaw(index,data,1,bkgd,time=time)
which provides us with time profiles of A (p(0,*)) and G (p(1,*)) with the
highest temporal resolution (e.g. 0.5 s in high-bit rate). The number `1' in
the above command specifies the lower band of a pair of two adjacent energy
bands from which A and G are calculated; you can specify `0' (M1/L),
`1' (M2/M1), or `2' (H/M2). The variable bkgd is the BGD data obtained in
section 3.6.1. For example, a time profile of photon index is displayed as
follows:
IDL> utplot,time,p(0,*),index(0)
Values of p for each major frame are obtained by adding an option /sf to
the arguments of HXT_POWERLAW:
IDL> p = hxt_powerlaw(index,data,1,bkgd,/sf,time=time)
which is useful when the flare is not very intense and you need to accumulate
HXT data to increase count statistics.