Status report on Light Simulator Claudia Cecchi Francesca Marcucci Monica Pepe Software meeting Udine January

Why the light simulator… Fast simulation of the sky map seen by GLAST to be used starting point for statistical analysis. Generation of a photon list, with photons distributed randomly, according to PSF, AS and ED distributions (determination of the true and measured energy, the incidence angle, the true and the measured position and the arrival time of the photons) The code (C++) is working under windows and under Linux Next step: generation of a database with photon’s information available on the web.

Input: map of the galactic background (Egret or Galprop) Third Egret Catalogue with sources photon energy range (0.1 – 100 GeV) region of the sky (-90° - 90°, -180° - 180°) orbit or fix time Simulation: extragalactic background Output: FITS-images of sky-map view and sources galactic background sources exposure convolution

Bkg-differential flux C (P 0 ) ( g cm -2 t -1 W -1 ) = S all contributions map of the sky in small regions of 0.5° x 0.5° without detector effects convolution of our result with the SA, PSF and ED. Convolution with PSF, SA and ED Background and Sources For Bkg: a = 2.1 I 0 =C (P 0 )   =dl · db · cos(b) In each pixel P 0 : D(E) =  0-60° E (θ,E) · I 0E – a dθ

Generation of a photon list N g =  D E D(E) Each g randomly distributed in the map with:  random energy E true  [E min, E max ] according to D(E)  inclination angle θ distributed according to E (θ, E true )  E meas obtained using the function ED(E true, E meas )  angular distance, ρ, from origin point P 0  (l 0, b 0 ) consistent with PSF( , E true ) final position of each photon is P 1  (l 1, b 1 ) obtained considering that the total angular distance from P 0 is 

New w.r.t. the previous version Calculation of Sun/Moon positions and angle with respect to SC Mcllwain’s parameters calculation with GEOPAK New Exposure improved SC latitude and longitude calculation New PSF from S. Digel and J. Norris, depending on the incidence angle and on conversion point in the detector, front (2.5% X 0 – 12 layers), back (25% X 0 – 4 layers). Faint sources, model from Stecker and Salomon ’96; flux (E> 100 MeV) between and photons  cm -2  s -1. Arrival photon’s time : the number of generated photons follows a Poissonian distribution Spacecraft and orbit parameters Output: two tables Photon parameters FITS-images of sky-map view and sources

Photon Time Arrival photon’s time : the number of generated photons follows a Poissonian distribution   Time interval from zero to  T where  T is the minimun interval of time with N ph different from zero   T divided into n steps  t of 100  s (GLAST dead time)  For each step calculate the probability P that a photons is in  t if P < Rate   t  time photon = n   t

PSF comparison  OLD PSF (S. Ritz) is assumed to be a single gaussian, does not depend on the incidence angle and is averaged over converter thickness  NEW PSF (S.Digel & J.Norris) is the sum of two gaussians,  1 (95%)  2 (68%), depends on the incidence angle and on the conversion point (Front or Back) Old PSF New PSF

Exposure 827 orbits 2.2e+102.4e+102.6e+102.8e+10 Long (deg) Lat (deg)

All sky + sources GeV 827 orbits bg with PSF Bkg + sources sources Previous version

All sky + sources GeV 827 orbits bg with PSF Bkg + sources sources New version

Bkg + sources sources Long (deg) Lat (deg) Long (deg) 3C sky + sources GeV Bg with PSF 827 orbits Previous version

New version ANGLE- PSF total 3C sky + sources GeV Bg with PSF (no Front-Back) 827 orbits Bkg + sources sources

Bkg + sources sources Long (deg) Lat (deg) Long (deg) 3C sky + sources GeV Bg with PSF 827 orbits New version Lat (deg) 3010

3C279 region seen by EGRET x 2.0 E05

CONCLUSIONS and PERSPECTIVES  Last version is not running under Linux, problems with GEOPAK, under investigation  Simulation of 1 year of GLAST data tacking  generation of a photon’s DB (under Linux)  First version of a note has been sent to S. Digel, new version with modifications ready for next week  Implementation of an algorithm to retrieve photon information from pixel index (Gino)  Implementation of the simulator in Gaudi as a standalone package (in collaboration with Toby)  Possibility of studying the PSF from Gleam to be used in the simulator (discussion)

255 sources from the Third Egret Catalogue Source name AR DEC Long. Lat. Spectral index Standard energy

Elliptic orbit defined by the following parameters: · a semi-major axis of the ellipse (distance of the orbit from the Earth  550 Km) · e eccentricity (is set to zero, because we assume a circular orbit) · P epoch (time of transit to the perigee) · T period ( 5739 s ) · anomaly (the angle between the perigee and the point from where we start to calculate the orbit) · i inclination of the orbit with respect to the terrestrial equator (28.5°) ·  (t) the orientation of the semi-major axis of the ellipse · R rocking (35°). Simulated with a geometrical approach by steps of 30  (  2°) assuming that within each step the parameters are constant. Output  total exposure calculated as the sum over all the steps. The orbit

Differential flux of photons from diffuse extra galactic background described (Skreekumer, 1997) as: [1] (photons · cm -2 · s -1 · GeV -1 · sr -2 ) Total contribution of the extra galactic background obtained by the integration of (1) between E min and E max taken into account only if |b| > 15°. Diffuse extra galactic background

Galprop simulates the gamma ray background taking into account:  neutral pion decay;  bremsstrahlung;  inverse Compton scattering. Galprop produces FITS file containing 24 images in the energy range from to 10 4 GeV The gamma ray galactic background EGRET map measured between 0.1 and 30 GeV

First approximation: sources point-like located at an infinite distance Intensity of photons: (photons  cm -2  s -1  GeV -1 ) Sources information: localization,  and I 0 from Third Egret Catalogue. Sources

Observation time fixed: E (θ, E) = SA(θ, E)  t  cos θ Exposure q r0r0 r Observation time not fixed: E (θ, E) = S r0 E 0 (θ, E) · ε E 0 (θ, E) = SA(θ, E) t ε = 90% Zenith