Definition of the Contents of the LAT Source Catalog
The current draft definition of the contents of the source catalog is in the draft of the Science Data Products Interface Control Document, available in Word and (in a document prepared for the review of the plans for the science tools in 2002) in {HTML| http://www-glast.slac.stanford.edu/sciencetools/reviews/sept02/report/html/review_091601.htm#_Toc19942911
].
The draft is in need of updating in several respects. Some of the issues were discussed during a splinter session
of the LAT collaboration meeting in September 2004. This presentation also includes the high-level requirements for producing the catalog.
This confluence page presents a summary of the issues and some suggested resolutions. Broadly speaking the issues are related either to what should be included in the catalog or how best to represent the included items in FITS. The issues and proposed resolutions, or any other aspect of the definition of the contents are open for discussion.
Issues (numbered)
1. Source_Name
(Ballet) I do not believe it is appropriate to define TLMIN/MAX for a string column (or is it ?). In any case, most likely we will number the versions of our catalog as everybody does, so that will be 1GL, 2GL, ... Are those registered at the IAU already ?
2. Conf_68_Region and Conf_95_Region
(Ballet) I think we had better split those fields into individual scalar columns. This is much easier to use in searches with standard tools.
3. Spectral_Index
(Ballet) We should add an uncertainty (1 sigma) to it.
4. Energy bands
(Ballet) I suggest we add the source count rates or fluxes (plus uncertainty) in several broad energy bands. This can be very useful when looking for unusual spectra (very different from a power law). I imagine the way to get that would be to run likelihood after event selection on energy in each energy band, then converting the prefactor value to a flux in that band for the spectral index of the source. Running likelihood directly on the image accumulated in that band would be another option, but this unfortunately requires an assumption on the spectral index as well (to build the PSF).
A simple choice of bands would be logarithmically spaced, with boundaries at log(EMeV) = 1.5, 2, 2.5, 3, 3.5 and maximum.
5. Flux_History
(Ballet) Did anybody study what was the best energy interval (in particular the lower boundary) to look for variability? Is 100 MeV indeed the best trade-off between number of source photons and number of background photons plus contamination by other sources ?
6. Hist_Start/End
(Ballet) If I understood correctly the ideas developed in the September 2002 review of how to obtain a light curve, this will be done by running likelihood in each time bin (fixing the diffuse emission and the spectral indices). That document implied that this would be done in smaller time bins for brighter sources.
It would be much more homogeneous to do that in the same time intervals for all sources. It would ensure that the likelihood results for closeby sources would be obtained consistently, and would also be easier to use for systematic studies.
I would like to propose that we do that in large time intervals (like one month) for all sources. So the time interval (not the number of bins) would be fixed. In addition, we could add specific files (one per source) for bright sources where much more detailed information can be obtained (including spectral variability for example, or going beyond 100 bins).
7. Flags
(Ballet) 1 Byte (8 binary flags) is not much. Let's use I (2 Bytes) instead. This is a negligible size increase anyway.