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Last modified: 25 July 2018


Per-Observation Detections Light Curve Files (lc3.fits)

The light curve files consist of a set of FITS format files, one for each source region of each observation, for each science energy band. Each light curve file records the multi-resolution light curve output by the Gregory-Loredo analysis of the receipt times of the source events within the source region. A background light curve with identical time-binning to the source light curve is derived from an analysis of the events within the background region. The background light curve is recorded in the FITS HDU (CXC Data Model block) immediately following the source light curve HDUs.

Source Region Light Curve

[Thumbnail image: example of source region light curve]

[Version: full-size]

[Print media version: example of source region light curve]

Source Region Light Curve

Gregory-Loredo light curves for the source (blue) and the background (red).

The Gregory-Loredo method is a Bayesian approach to generating lightcurves on some optimal bin/grid, while smoothing the lightcurve and accounting for the effects of spacecraft dither and detector bad pixels that aren't accounted for from standard lightcurves. The smoothing itself is the weighting of the probability of the observed distribution occuring by chance versus the probability of having a constant distribution. How reliable this lightcurve is will be dependent on the Bayesian probabilities calculated. The produced light curve is an estimate of its most probable shape from the source (as opposed to what you just observe with the telescope and instruments).

The per-observation light curve FITS file is named: 〈i〉〈s〉〈obs〉_〈obi〉N〈v〉[_〈c〉]_〈r〉〈b〉_lc3.fits

where 〈i〉 is the instrument designation, 〈s〉 is the data source; 〈obs〉 is the observation identification; 〈obi〉 is the observation interval identification; 〈v〉 is the data product version number; 〈c〉 is the cycle; 〈r〉 is the region ID, formatted as "rnnnn", where nnnn is the 4-digit region number, formatted with leading zeros; and 〈b〉 is the energy band designation. The optional discriminator identified in square brackets is included only for ACIS alternating exposure (interleaved) mode observations.

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