Generating the Sky Model for DC2

For DC1, we could get away with a sky model that was closely based onEGRET observations. The DC2 sky will take much more work.

- AGN variability - Pulsar periodicity- Lots more sources (need reasonable logN/logS distributions for each source class).- Extending GRBs to lower energy (for GBM simulations)- More care in source locations (implications for EGRET unids)- More source classes.

How we proceeded

Start with the major source classes: AGN, GRB, pulsars, ‘unid’ sources, including SNR, and Galactic Diffuse. The idea is to test that the mechanics of producing the source model/ distribution works. The details can be refined later.

AGN/Pulsars: Produce a population of sources with realistic source properties(variability, periodicity etc). Produce simulated data using obsSim. Produce one month of data and test lightcurves.

Galactic diffuse: Produce at least one updated map of Galactic diffuse gamma-ray emission (the map used to produce the simulations does not need to be preciselythe same as the one used for the analysis). Verified that the map can be used for GLAST simulations with obsSim.

GRB: Produced a few (2-3) bursts with LAT and GBM data products.

Details of these source classes will be described in later talks.

Organisation/people

Small groups containing people with technical skills to implement the sources andastrophysics knowledge to guide what goes in. Important to keep the groupssmall, for efficiency and to maximise the number of “users” of DC2.

Pulsars: David Smith, Toby Burnett, Massimiliano Razzano, Alice Harding

AGN: Jim Chiang, Toby Burnett, Julie McEnery

Galactic Diffuse: Seth Digel (coordinator)

GRB: Valerie Connaughton (coordinator)

SNR and unids: Diego Torres, Johann Cohen-Tanugi, Seth Digel.

For SNR/unidentified sources

The name may be a bit of a misnomer: This is a catch-all for other source classes, especially those that might be detectable by the LAT but not by EGRET

‘SNR’ sources would be extended, at least some of them, and have fluxes and positions appropriate for some candidates (and consistent with some EGRET unidentified sources that are not already pretending to be pulsars in the DC2 data set)

Other extended sources would be local group galaxies like the LMC and SMC, some small high-latitude molecular clouds [ask me why they won’t be in the diffuse model] and blobs of dark matter if we go that far

Point sources may include (at the sensitivity of the LAT for DC2 time scales) likely clusters of galaxies, starburst galaxies, plerions, OB associations and microquasars

Yes, it is possible to go overboard in defining components of the sky model. The level of care with which this should be done depends on the analysis goals for DC2.

Attenuation on Background Radiation Fields. High energy gamma-ray photons from extragalactic sources will be attenuated by pair production with low energy photons on intergalacticspace. The magitude of this effect depends on the distance of the sourceand on the spectrum and flux of background radiation fields.

Currently implemented by Jim Chiang in the SpectralTransient source class (i.e. used for AGN simulations).

Originally provided a choice of four attenuation models provided by Liz Hays/Julie McEnery. There is a small snag:

- two of the models are valid only above 100 GeV- and the other two are valid for z<0.3

(i.e. neither are suitable for LAT simulations) Luis Reyes is adding two models appropriate for the LAT energy range. One (Salamon and Stecker) has been added and tested, the other will be completed soon.

Ideally the same attenuation should be applied to all extragalactic sources,AGN, GRB, Galaxy clusters etc.

Summary

● We are in good shape. Most of the technical details/software needed to produce the required source properties in DC2 have been developed and tested.

● Lots of work lies ahead in producing the final sky model. We need to create populations of each source class and pull everything together in a consistent way.