...
- the name precision is guided by the source localization precision rather than by source separation to allow comparison with other catalogues.
- given the IAU guidelines and the brightest LAT sources localization down to a fraction of an arcminute, the only possible naming scheme in R.A and Dec is 1GL JHHMMSS.s-DDMMSS. IAU does not want decimals before the arcsecond and time second levels, nor decimal degrees in R.A. and Dec (no 1GL JDDD.ddd-DDD.ddd) even though it is much easier for your brain to grasp and memorize.
- Practice from INTEGRAL and HESS sources tells that 1GL JHHMMSS.s-DDMMSS names are extremely difficult to memorize and use efficiently. One gets lost only after a few sources, especially if they are closeby. For instance, try to memorize NGC4151 = J121032.6+392420 for a few days!
- One can use decimal degrees in Galactic coordinates, which would lead to 1GL GLLL.lll-BB.bbb and your brain will round the number up to help your memory. The COS-B catalogue was in Galactic coordinates. Yet, quasars (that will dominate the LAT catalogue) are usually in R.A. and Dec. So, what do we choose ?
- We can use 1GL, 1GLA, or 1LAT acronyms as long as it is longer or equal to 3 letters.
16. Galactic coordinates (25 July 2007)
Isabelle asks if we should include Galactic coordinates in the catalog. Sounds reasonable, right?
To compare source positions and lock different frames in ds9 to compare counterpart positions, we need Galactic coordinates as well as R.A. and Dec !
17. Technical issues in generating the catalog (25 July 2007)
These are from Isabelle:
...
Comments from Jürgen:
- do we really need so many digits? Comparing to HESS (which uses HESS JHHMM+DD.d) we could also use 1GL JHHMM+DD.D. Although GLAST can localise more precisely than this precision it would not be able to distinguish two sources at this precision. So the names should be unique and also easy to remember. Another advantage: since the names would not include too many digits there is a fair chance that the names will not change from one catalogue to another (this was somewhat enoying for the EGRET catalogues). So a source detected in the 1GL would keep (probably) its name throughout all succeeding catalogues.
- concerning galactic versus RA/Dec: personnally I also think in galactic coordinates, but so many catalogues relevant for GLAST (radio, X-rays, gamma-rays) are in RA/Dec so that I would prefer also using RA/Dec for GLAST (otherwise one would also have to convert from one system into the other to compare sources ...)
16. Galactic coordinates (25 July 2007)
Isabelle asks if we should include Galactic coordinates in the catalog. Sounds reasonable, right?
To compare source positions and lock different frames in ds9 to compare counterpart positions, we need Galactic coordinates as well as R.A. and Dec !
Comments from Jürgen:
- I agree completely, we should also have galactic coordinates!
Comments from Jean: Yes, and galactic coordinates have always been included in the test catalogs that we have produced.
17. Technical issues in generating the catalog (25 July 2007)
These are from Isabelle:
- are we able to give ellipses for the 1st release?
- are we able to deliver a 30-100 MeV flux for all sources?
- we cannot fill the flux monthly history for sources that are just significant over one year. So we need to define what TS threshold allows to measure monthly lightcurves above 100 MeV. The vast majority of the sources, being too faint, won't have lightcurves.
Questions from Jürgen:
- Should the catalogue format be always the same over the succeeding catalogue versions? If we have no error ellipses in the first edition but in later ones, should we make evolve the catalogue format?
- As we discussed during the past LAT meeting we should take provision for more than a single counterpart association (to use the new term
. For how many should we take provision? For each counterpart association we would have a counterpart name and a counterpart probability.
Comments from Jean:
- I see no reason why we should not deliver a 30-100 MeV flux for all sources (unless we think we do not master the IRF well enough), as well as a monthly flux history. A faint but very soft source can have a significant flux below 100 MeV, and faint sources can also be variable enough that they will show up in a few time bins. The real issue here is to decide how to handle upper limits.
18. Catalogue entry names (26 July 2007)
I (Jürgen) would like to reiterate the point 14: we should have more standard column names. By standard I mean names similar to those found in other catalogues. The coordinates would be RAJ2000, DECJ2000, GLON and GLAT, uncertainties would be preceeded by "e_..." etc.
19. Prefactor missing (20 November 2007)
I jusr recognised that the prefactor of the powerlaw fit was missing in the above catalogue format description. Jean's DC2 & SC2 catalogues had this prefactor but no error on it. I stronly recommend to officially add 'Prefactor' and 'e_Prefactor' to the catalogue (and to rename error quantities as suggested above using the standard 'e_<quantity>' scheme implemented by CDS.