Status report on Light Simulator
Claudia Cecchi
Francesca Marcucci
Monica Pepe
Software meeting Udine
January 30-31 2003
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)
Next step: generation of a database with photon’s information
available on the web.
The code (C++) is working under windows and under Linux
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
galactic background
sources
exposure
convolution
Output: FITS-images of sky-map view and sources
Convolution with PSF, SA and ED
Background and Sources
In each pixel P0:
Bkg-differential flux C (P0) (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.
D(E) = 0-60°
E(θ,E)
· I0 •E
–a
dθ
For Bkg:
a = 2.1
I0 =C (P0) • W
W =dl · db · cos(b)
Generation of a photon list
N g = DE D(E)
Each g randomly distributed in the map with:
 random energy Etrue[Emin, Emax] according to D(E)
 inclination angle θ distributed according to E(θ, Etrue)
Emeas obtained using the function ED(Etrue , Emeas )
 angular distance, ρ, from origin point P0  (l0, b0) consistent with PSF( ,
Etrue )
final position of each photon is P1  (l1, b1) obtained considering
that the total angular distance from P0 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% X0 – 12 layers), back (25%
X0 – 4 layers).
Faint sources, model from Stecker and Salomon ’96; flux (E> 100 MeV)
between 10-10 and 10-7 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 DT where DT is the minimun interval of
time with Nph different from zero
 DT 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  timephoton = 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)
PSF
PSF front/back vs PSF total
E=300 MeV Theta=60deg
Old PSF
0,3
0,25
0,2
0,15
0,1
0,05
0
New PSF
1
6 11 16 21 26 31 36 41 46 51 56 61
angular dist. [-70,70]deg
Lat (deg)
Exposure 827 orbits
Long (deg)
2.2e+10
2.4e+10
2.6e+10
2.8e+10
Emeas
GeV
0,09
0,26
0,16
Etrue
GeV
0,11
0,19
0,15
SC y
km
-3570
-3230
-3230
EndDate
s
60
90
120
SCposX
Km
6920
6910
6890
SCposY
Km
200
400
600
SCposZ
Km
109
218
326
LatRaZ
deg
1,33
1,43
1,53
LatDecZ
deg
-29,4
-28,6
-27,7
LatRaX
deg
12,2
12,5
12,7
LatDecX
deg
-35,9
-36,8
-37,7
RaZ
deg
0,11
0,22
0,33
DecZ
deg
0,9
1,8
2,7
SCmode
Tlive
s
27
27
27
ins SAA
SClon
deg
-108
-100
-107
SClat
deg
0,91
1,81
2,72
SCalt
km
550
550
550
SunRA
deg
4,9
4,9
4,9
SunDEC
deg
-0,4
-0,4
-0,4
ED(Etrue)
GeV
0,1
0,08
0,09
DecMeasphoton time
deg
s
-28,6
54,4
-26,6
112
-29,9
117
SC x
km
5630
5880
5880
StartDate
s
30
60
90
time
s
90
150
150
SC z
km
-1890
-1710
-1710
Theta
deg
26
14
16,1
RAtrue
deg
275
275
275
DecTrue
deg
-27,7
-27,7
-27,7
RAmeas
deg
279
273
274
DeadTime
Zenith angle
Earth Azimut angle
s
deg
deg
0
62
75,1
0
65,6
77,8
0
65,6
77,8
B
gauss
3750
3820
3820
L Lat
Earth radii
146
142
142
GeoMag
Long Geomag
deg
deg
1,48
5,24
1,48
5,24
1,48
5,24
1
1
1
0
0
0
MoonRA MoonDEC
deg
deg
4,45
-0,41
4,45
-0,41
4,45
-0,41
Previous version
All sky + sources 0.1-30 GeV
827 orbits bg with PSF
Bkg + sources
sources
New version
All sky + sources 0.1-30 GeV
827 orbits bg with PSF
Bkg + sources
sources
Previous version
3C279-60 sky + sources 0.1-30GeV
Bg with PSF 827 orbits
sources
Lat (deg)
Lat (deg)
Bkg + sources
Long (deg)
Long (deg)
New version ANGLE- PSF total
3C279-60 sky + sources 0.1-30GeV
Bg with PSF (no Front-Back) 827 orbits
Bkg + sources
sources
New version
3C279-60 sky + sources 0.1-30GeV
Bg with PSF 827 orbits
sources
Lat (deg)
Lat (deg)
Lat (deg)
Lat (deg)
Bkg + sources
Long (deg)
0
20
40
60
Long (deg)
0
10
20
30
40
50
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
3EG J0010+7309
3EG J0038-0949
3EG J0118+0248
3EG J0130-1758
3EG J0159-3603
3EG J0204+1458
3EG J0210-5055
3EG J0215+1123
3EG J0222+4253
3EG J0229+6151
AR
DEC
Long.
Lat.
Spectral index
2.56 73.17 119.92 10.54
9.74 -9.82 112.69 -72.44
19.6 2.81 136.23 -59.36
22.7 -17.97 169.71 -77.11
29.84 -36.06 248.89 -73.04
31.11 14.97 147.95 -44.32
32.58 -50.93 276.1 -61.89
34 11.38 153.75 -46.37
35.7 42.9 140.22 -16.89
37.32 61.86 134.2 1.15
1.8464610E+00
2.7042760E+00
2.6336160E+00
2.5050740E+00
2.8922490E+00
2.2321450E+00
1.9899620E+00
2.0280930E+00
2.0100220E+00
2.2863630E+00
Standard energy Flux @st.energy
4.8522080E+02
1.5626760E+02
1.7153680E+02
1.9170150E+02
1.2666270E+02
2.6488440E+02
2.8397580E+02
6.0997420E+02
4.1280090E+02
2.3071570E+02
1.6500180E-10
5.3436390E-10
2.3813020E-10
3.2784570E-10
8.0606110E-10
1.3811020E-10
8.8435840E-10
8.8540930E-12
9.5417540E-11
5.4674250E-10
The orbit
Elliptic orbit defined by the following parameters:
·
·
·
·
·
where
·
·
·
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
we start to calculate the orbit)
i inclination of the orbit with respect to the terrestrial equator
(28.5°)
W(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.
Diffuse extra galactic background
Differential flux of photons from diffuse extra galactic
background described (Skreekumer, 1997) as:
dN
 7.3 ·10 -6 · 0.4512.1 · E -2.1
dE
(photons · cm -2· s
-1
[1]
· GeV -1· sr -2)
Total contribution of the extra galactic background obtained by
the integration of (1) between Emin and Emax
taken into account only if |b| > 15°.
The gamma ray 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 0.001 to 104 GeV
EGRET map measured between 0.1 and 30 GeV
Sources
First approximation: sources point-like
located at an infinite distance
Intensity of photons:
I ( E ) I 0  E
a
(photons  cm -2  s -1  GeV
-1
)
Sources information: localization, a and I0 from Third Egret
Catalogue.
Exposure
Observation time not fixed:
E(θ, E) = Sr0 E0 (θ, E) · ε
E0 (θ, E) = SA(θ, E) • t
ε = 90%
Observation time fixed:
E(θ, E) = SA(θ, E)  t  cos θ
r0
r
q
Zenith