$Id: lcv.html,v 1.1 2019/09/05 09:27:11 wwwadmin Exp $

NeSDaC

lcv, lightcurve

NAME

lcv, create lightcurve for each source listed in an irs output file.

SYNOPSIS

lcv
lcv -p [options] irs lcv
lcv -q

The program can be started with no arguments at all, in which case the parameter values are taken from the parameterfile.
Alternatively, values can be passed via the commandline, the required items as command arguments, the optional ones as valued switches.

The last form (-q) creates the parameterfile in $PFILES.

The table lists all the parameters used by lcv, the second column lists the paramater key names used in the parameterfile, the first column gives the corresponding switch letter.

lcv parameters
switch key value IO description
resfile string i irs file, iros data file.
lcvfile string o lcv, lightcurve for every source in the inputfile.
b tbin real i time bin size in seconds (default is 100.0).
a islfile int i file with a list of additional skylocations for which a lightcurve is to be produced, entries in catalog format.
t t_filtr range i select events within one of the time intervals, the time interval must be specified in modified julian days (MJD).
T t_ftrsec range i as -t, however the interval time(s) is in seconds from the start time of the first input(event) file.
(if both -t and -T are present, the -T switch is ignored.
I insfile string i overrides the IDF name in expfile.

p, L, i StageII global switches

lcv parameters
switch	key	value	IO	description
	resfile	string	i	irs file, iros data file.
	lcvfile	string	o	lcv, lightcurve for every source in the inputfile.
b	tbin	real	i	time bin size in seconds (default is 100.0).
a	islfile	int	i	file with a list of additional skylocations for which a lightcurve is to be produced, entries in catalog format.
t	t_filtr	range	i	select events within one of the time intervals, the time interval must be specified in modified julian days (MJD).
T	t_ftrsec	range	i	as -t, however the interval time(s) is in seconds from the start time of the first input(event) file. (if both -t and -T are present, the -T switch is ignored.
I	insfile	string	i	overrides the IDF name in expfile.

p, L, i	StageII global switches

DESCRIPTION

Given the solution of iros, where the positions of, presumably all, n sources in the field of view were determined, we can write the following expression for the expected value for teh detector data (iros):

the least-squares solution of which is

^-1

Lcv computes the matrix (S^T S)^-1 once in its initialisation phase, and then evaluates S^Td for each timebin. The processing of each detected event in this timewindow requires only n (number of source positions) additions.
v = S^Td, is an n element vector, an event occuring at d[m], just adds S_i[m] to v_i.
At the end of the timebin the flux vector f is computed.

LIMITATIONS

Lcv will produce lightcurves for the given iros solutions only, ie. only in the energy bands found in the inputfile.
A previous version of lcv used a different method to produce lightcurves and resolved all energy channels. This method is afflicted with an unacceptable crosstalk between sources in the field of view. We try to find a solution for the problems, for the time being the present implementation, though not providing full energy resolution, is the best we can offer.

The computation of the least-squares solution via the so-called normal equations is certainly not the numerically most stable one, there are better solutions, eg. orthogonalization methods (Gram-Schmidt). These require, here the original system has 680² equations!, much more core memory and a lot more cpu time.

EXAMPLE

We have an reduced skyimage w817w1.res, the result of an iros run. The command (assuming valid environment variables are set)

lcv -p2 w817w1 w817w1

produces the following output

===============================================================================
 lcv[99.99]                                Fri Jul  4 11:53:21 1997  page    1
   ------------------------------------------------------------
[1]           source data
 +        ra      dec     na         x       y
 +      85.272  29.069 178.754 ->    0.00    0.00 (      pointing)
 +     -------------------------------------------------------
 +      83.616  22.077         ->   86.58   17.11 (    X0531+219 ) 
 +      85.272  29.069         ->    0.00    0.00 (  :background:) 
[1]lcv: computing the normal equations, chnls 2-10 ........
[1]evt_open: "/ruurq2/817/WOP817_0001w1prn1.fits"[SCI_NM], 1 of 2.
 +          time  50318.48730 - 50318.53446 (MJD)  [  4074.54 sec.]
[1]evt_open: "/ruurq2/817/WOP817_0001w1pdt1.fits"[LIFETIME], 1 of 2.
 +          time  50318.48751 - 50318.53458 (MJD)  [  4067.00 sec.]
[1] ..... reading the eventfile(s)
[1]evt_open: "/ruurq2/817/WOP817_0003w1prn1.fits"[SCI_NM], 2 of 2.
 +          time  50318.54530 - 50318.56055 (MJD)  [  1318.09 sec.]
[1]evt_open: "/ruurq2/817/WOP817_0003w1pdt1.fits"[LIFETIME], 2 of 2.
 +          time  50318.54529 - 50318.56062 (MJD)  [  1325.00 sec.]
[W]lcv_roundup: bin[63]+  6350.00sec. short bin, width= 28.706 sec.
[1]lcv: computing the normal equations, chnls 11-18 ........
[1]evt_open: "/ruurq2/817/WOP817_0001w1prn1.fits"[SCI_NM], 1 of 2.
 +          time  50318.48730 - 50318.53446 (MJD)  [  4074.54 sec.]
[1]evt_open: "/ruurq2/817/WOP817_0001w1pdt1.fits"[LIFETIME], 1 of 2.
 +          time  50318.48751 - 50318.53458 (MJD)  [  4067.00 sec.]
[1] ..... reading the eventfile(s)
[1]evt_open: "/ruurq2/817/WOP817_0003w1prn1.fits"[SCI_NM], 2 of 2.
 +          time  50318.54530 - 50318.56055 (MJD)  [  1318.09 sec.]
[1]evt_open: "/ruurq2/817/WOP817_0003w1pdt1.fits"[LIFETIME], 2 of 2.
 +          time  50318.54529 - 50318.56062 (MJD)  [  1325.00 sec.]
[W]lcv_roundup: bin[63]+  6350.00sec. short bin, width= 28.706 sec.

and produces a file w817w1.lcv. The ftool fstruct run on w817w1.lcv produces

  No. Type     EXTNAME      BITPIX Dimensions(columns)      PCOUNT  GCOUNT
 
   0  PRIMARY                 32     0                           0    1
   1  BINTABLE lightcrv_2_10   8     36(8) 64                    0    1
   2  BINTABLE lightcrv_11_1   8     36(8) 64                    0    1

The input file two energy bands, channels 2 to 10 (incl.) and 11 to 18.
Lcv thus creates two binary table extensions, named lightcrv_2_10 and lightcrv_11_18 (the lightcrv_11_1 is an fstruct limitation). The time bin size used was 100 seconds (default value), the table has 64 rows.
Each binary table extension contains the columns:

dlc columns
name	type	description
time	1D	timetag for bin center, in modified julian day (MJD)
ltf	1E	detector life time fraction.
eon	1E	earth occultation status for FOV center, not yet implemented.
nevents	1E	total number of events used.
X0531+219	1E	flux assigned to this source, cts/sec.cm².
error	1E	error in above flux, not assigned in this version, set to 0.
the source name - error column pair is repeated for every source.
:background:	1E	flux assigned to the background, cts/sec.cm², for the full field of view.
error	1E	error in above flux, not assigned in this version, set to 0.