Data Challenge II Logo by Stefano Ciprini

Data Challenge 2 This is the beginning of DC2, but getting to the beginning has been the result of a lot of hard work by many people over many months. Work was organised by a steering committee: Jean Ballet, Toby Burnett, Rob Cameron, Valerie Connaughton, Seth Digel, Richard Dubois, Francesco Longo, Julie McEnery, Steve Ritz and Tracy Usher But the actual work has been done by a much larger number of people. Thanks to everyone who helped!

DC2 – What is it? 55 day simulation of the high energy gamma-ray sky Full detector simulation Detailed modeling of astrophysical sources Include updated background model including orbit dependent effects. Goal was to make the DC2 data as realistic as possible Science analysis software and definition of the data products have been made mature

Reconstruction and simulation geometry Updated and checked detector geometry Introduced some “realistic” elements to the detector model: dead strips etc. (we did this before we had a full LAT to get real measurements) Revamped TkrRecon and CalRecon Many new variables added to support background rejection and event classification analysis.

Background Model, Deadtime, orbit model Updated background model including orbit dependent effects Included effect of deadtime (fractional deadtime depends on the event rate after the throttle is applied). Updated orbit and attitude profile including realistic slew rates and yaw flips. Plot of livetime fraction vs geomagnetic latitude (illustrates the effect or orbit dependent trigger rates)

Event Classification and background rejection Several iterations (by several people) of classification tree analyses to identify well-reconstructed gamma-ray events. This converged into an analysis by Bill Atwood, the final result is a small number of high-level variables which can be used as knobs to tune performance for PSF, Energy resolution and background rejection CTBGAM (Energy Resolution) CTBCORE (PSF) CTBBestEnergyProb (Energy resolution)

Analysis Classes The infinite range of possibilities with the “knobs” provided by the classification analysis have been distilled into two analysis classes. Class A: These are a set of cuts that provide good background rejection, angular resolution and energy resolution. All: These are a looser set of cuts which provide additional effective area and may be suitable for analyses where background contamination less important. Use gtselect to create a filtered event file creating events for the analysis class of interest. Select the relevant response functions in the science tools (DC2_A for classA and DC2 for all). The selections made in the data file *must* match the choice of IRF used in the analysis.

Preliminary Catalog Analysis A preliminary catalog analysis has been performed (by Jean Ballet and colleagues) This analysis was run autonomously on the catalog pipeline with minimal human interaction (so not a final polished product – but an excellent demonstration of our current abilities) You can use this as a starting point to identify interesting looking sources to study in greater detail. On Monday there will be an updated version which will have correct test statistic and Significance.

LAT Data Products Root: MeritTuple (event based summary information) pointing_history (spacecraft location and attitude) Recon and Digi trees (detailed low level information) Fits FT1/photon data (event based summary information for events which belong to the “all” analysis class) FT2/pointing data (spacecraft location and attitude) Higher level data (also fits) Livetimecubes – intermediate data product which speeds up exposure calculations. Pulsar Ephemerides Model of the Galactic diffuse emission Preliminary LAT point source catalog

GBM simulations and data Simulated GBM data has been generated for a population of bursts. This includes all the burst data products and also includes a “GCN-like” notice to provide summary GBM information. This allows us to more fully explore the possibilities of GRB studies in the GLAST era.

Data data data data. We generated lots and lots of data. The efficient running of many analysis efforts depended on them being fed promptly with simulated data. The system worked! We ended up generating very much more data than we first estimated in a much shorter time. The system to track data and allow reprocessing worked well (and there was a lot to track) Most of all, there was a human in the loop that made datasets appear seemingly effortlessly. Many, many thanks to Tom Glanzman!

The DC2 Sky DC2 sky in galactic coordinates Plot by Seth Digel

DC2 Sky – Galactic Center region

Contents/features of the data The DC2 data contains: Steady point sources Variable sources Flaring Bursting Periodic Spatially extended sources over several size scales Many of the DC2 sources are located on top of known astrophysical sources (certainly most of the bright ones).

DC2 Goals, requirements and purpose 55 days of LAT data provide a deeper view of the high energy gamma-ray sky than has previously been achieved. Results from previous gamma-ray missions provide, at best, an incomplete guide to the DC2 sky. Part of the challenge of DC2 will be to figure out what was included in the sky model. DC2 data has a fairly realistic level of detail which will support a wide variety of both science and instrument performance studies. Exercise the science tools – but don’t feel restricted to them Improve the documentation and analysis software from user feedback.

Produce LAT point source catalog This will be an update of the catalog produced at the beginning of DC2. See https://confluence.slac.stanford.edu/display/ST/LAT+Source+Catalog+Contents for a description (and discussion) of the contents of the LAT point-source catalog. Requirement: Spectral index and flux (with associated uncertainties), location with 68% and 95% confidence ranges, flux in discrete energy bands. Goal: Variability index, flux history, peak flux, measure of whether a source is extended.

Develop and test source detection algorithms Source detection is a necessary step in producing the LAT point source catalog. Several methods to do this have already been developed (see talks on Thursday), more may be developed during the course of DC2 Requirement: That these algorithms are tested and compared with one another in a systematic way using the DC2 data.

Pulsars (1) There are many simulated pulsars in the DC2 data. We provide an ephemeris for most of the “radio-loud” pulsars. These ephemerides are mostly (but not always) valid during the DC2 time period, i.e. in some cases the ephemeris can be only considered as a guide. Requirement: Determine the gamma-ray lightcurves for at least 6 pulsars which have an exact ephemeris. This can be done using the science tools (gtbary, gtpphase) Requirement: Determine timing properties of pulsars and produce gamma-ray lightcurves for at least one pulsar with an approximate ephemeris. This can be done using the science tools (gtbary, gtpsearch) Goal: Determine lightcurves for more of the fainter pulsars in the DC2 data. Goal: Phase resolved spectra for bright (EGRET) pulsars.

Pulsars (2) Not all of the pulsars will be included in the ephemerides. Goal: blind periodicity searches on candidate DC2 pulsars Goal: Pulsar population studies: the ratio of radio-loud to radio-quiet pulsars is sensitive to the emission mechanism for producing the gamma-rays. It will be possible to study this in the DC2 data by comparing the number of pulsars with ephemerides to those without.

Extended sources Several source types may produce objects which can be resolved by the LAT as extended sources: SNRs, Galaxy Clusters, Dark matter… Goal: To identify extended sources in the DC2 data (there are some…) Goal: Perform spatially resolved spectroscopy.

Variable sources Many sources in the DC2 sky are variable. Requirement: Produce lightcurves for at least 20 bright sources (from the data release plan, these are the sources we will release high level data from in year 1) Goal: look at lightcurves for many more sources There are several variable sources in the DC2 sky which are not AGN or GRB. Some of these may have very distinct variability properties. Goal: To find and study variable sources that might not be blazars (i.e. the AGN folk do not get to have all the fun)

Spectral Studies Sources in the DC2 data may have spectra that are more complicated than simple power-laws. This opens up many analysis possibilities: Goal: Study spectra of pulsars to determine the shape of spectral cutoffs Goal: EBL attenuation studies (redshift dependent cutoffs) Goal: Search for spectral signatures of dark matter

Gamma-ray bursts (1) Gamma-ray bursts are included in the DC2 sky. This includes both LAT and GBM data. There are also “GCN-like” notices which provide summary information about the GBM flux and location (including statistical uncertainties). Requirement: Perform joint spectral fits of at least one burst using both LAT and GBM data. (gtbin, rspgen, xspec) Requirement: Temporal studies/comparison of at least one GRB Requirement: Produce preliminary GRB catalog, this should include GBM + LAT properties (goal: include LAT upper limits for GRB with no LAT detection).

Gamma-Ray Bursts (2) Goal: Search for LAT only GRB Goal: Search for additional high energy components and/or afterglows Goal: Compare the LAT and GRB locations and quoted statistical uncertainties to study the systematic GBM localisation uncertainty.

Other sources Requirement: Identify at least one source that is not a pulsar, AGN or GRB (there are some that can be unambiguously identified from the gamma-ray data) This could be done based on location Or location combined with variability properties Or by a discovery of periodic emission

Diffuse sources There are two major components of diffuse emission, extragalactic and galactic. Studies of these are likely to be quite sensitive to the presence of residual background. Goal: Study flux, spectra and spatial distribution of the galactic diffuse and compare with the diffuse model provided for source analysis. Goal: Study flux and spectral properties of the extragalactic background. This will include a study of the effect of residual background, contribution from galactic diffuse and resolving the point sources.

Quicklook and transient release tasks During the first year of LAT operations we will be releasing data to the public on 20 selected sources. The DC2 data can be used to explore how this will work and what information is useful. Requirement: define the format of the summary data that will be released for these objects (i.e. what variables etc) and pull the analysis results into this format. Goal: Search for and produce time resolved summary data for any source that exceeds 2x10-6 photons/cm^2/sec

General Studies Localisation Stability/accuracy of the likelihood analysis Alignment calibration Identify warts (data not perfect) Studies of background level with orbit position Study effect of different event cuts (driven by a specific science topic: diffuse – low background, GRB – high Aeff etc) Don’t limit yourself to these suggestions, there are many other analysis possibilities.

The Next Phase of DC2 Expect many things to change during DC2 – this is the beginning, not the end. We expect that throughout DC2 there will be: Updated releases of the software – we have already identified and fixed a few bugs. Updated documentation – based on user feedback Updated/improved IRFs – either because someone has come up with a better set of analysis cuts, or to improve the implementation into IRFs for the cuts we currently use Possible reprocessing, if someone comes up with an improved analysis that add (or changes) variables in the data.

Where to from Here? At this meeting We will describe the details of how the data were made and the analyses developed (Wednesday, Thursday morning) Detailed tutorials on how to perform science analyses on the data (Thursday, Friday morning) Discuss how the DC2 analysis will be coordinated across the large number of DC2 participants (Friday). DC2 closeout (May 16-18, 2006 at GSFC) Describe in detail how the astrophysical sources in the sky were defined (this involves detailed contributions from many people) Contributions and discussions of the analyses that were performed during DC2