aglc - ACIS Grating Light Curve


2010.08.10 version 1.5.0 - bug fixes: Fixed a bug in aglc_phased() which caused a discontinuity in the phase curve, do to an error in the exposure grid relative to the counts grid.

NOTE: 2010.08.04 version 1.4.0 - bug fixes: thanks to Manfred Hanke; there were errors in the calculations of rates and exposures for multiple CCD light-curves when there were frame-drops. This occurs for very bright sources. Version 1.4.0 contains fixes in aglc(). Similar changes will be forthcoming for phased curves, with aglc_phased().

aglc is a suite of slang functions for generating light curves binned in time or phase from ACIS and grating (HETG or LETG) data. The functions are specific to ACIS because they use the EXPNO column as an implicit time coordinate, and also to determine the exposure. (Also see ACIS exposure time keywords and Event Quick Reference for more information regarding event files and event times.)

NOTE THAT since aglc uses EXPNO and not the event times, no changes to event times will be recognized (such as barycentric correction). This is up to the user to implement on the output products.

Curves may be binned from arbitrary selections of grating types, orders, source, or background regions. Multiple chips and their exposures are properly computed. While CC-mode data can also be binned, these programs do not provide precise timing accuracy, in which the staggered start and stop times of each CCD are important (order of seconds to tens of seconds).

The functions are scripts written in ISIS/S-Lang scripts.

Quick Start

% load the file (assuming is in the current directory or path)

  isis> require("aglc");

%  read event files (grating events, and exposure reference)

 isis> s = aglc_read_events( "obs_evt2.fits", "obs_stat1.fits" ) ;

%  Bin Ne X 12A (11.9-12.2A) and O VIII 19A (18.9-19.2A) regions into
%  4000s bins  for HEG and MEG, for orders -3 to +3 (except 0).

 isis> c = aglc(s, 4000, [11.9, 18.9], [12.2, 19.2], ["H","M"], [-3,-2,-1,1,2,3] );

%  Bin a broader, short-wavelength region (1.7-7A) into finer bins:

 isis> cs = aglc(s, 500, 1.7, 7.0, ["H","M"], [-3,-2,-1,1,2,3] );

% plot the light curves:

 isis> hplot( cs.time_min, cs.time_max, cs.count_rate, blue );
 isis> ohplot( c.time_min,  c.time_max,  c.count_rate,  red );

% Define the ephemeris, JD of zero phase and period in days:

 isis> ephem = [ 2452506.4328, 0.27831149 ] ;

% Make a phased light curve from phase 0.0 to 1.0 in bins of 0.02, for
% wavelength range 1.7-25, HEG plus MEG orders -1 and +1:

 isis> p = aglc_phased( s, [0.0, 1.0, 0.02], ephem, 1.7, 25, ["H","M"], [-1,1] );

% plot the phase curve:

 isis> hplot( p.phase_min, p.phase_max, p.count_rate );

% save the curves:

 isis> aglc_write_curve( "LC_lines.fits", s.fevt_1a, c, "O VIII + Ne X, H+M 1-3" ) ;
 isis> aglc_write_curve( "LC_shortw.fits", s.fevt_1a, cs, "1.7-7.0A" ) ;
 isis> aglc_write_curve( "LC_phased.fits", s.fevt_1a, p, "1.7-25.0A, HM/-1,1" ) ;
See the Examples section for more details, including hardness ratio curves and flare filtering.

This page was last updated Aug 10, 2010 by David P. Huenemoerder. To comment on it or the material presented here, send email to
Valid HTML 4.01! Made with JED. Viewable With Any Browser.