science requirements verification glast lat project september 15, 2006: pre-shipment review...

Science Requirements Verification

GLAST LAT Project September 15, 2006: Pre-Shipment Review

Presentation 2 of 12

GLAST Large Area TelescopeGLAST Large Area Telescope

Gamma-ray Large Gamma-ray Large Area Space Area Space TelescopeTelescope

GLAST Large Area TelescopeGLAST Large Area Telescope

LAT Pre-Shipment Review

Science Requirements Verification

Steve Ritz, Bill Atwood

2Science Requirements Verification



Science Requirements VerificationScience Requirements Verification

LAT energy range and FOV are vast. Verification consists of a combination of simulations, beam tests, and cosmic ray induced ground-level muon tests.– primary verification is done by analysis, using the simulation (see

following slides)– ground-level muon data provide additional inputs to the

simulation related to instrument characteristics (dead channels, noise, uncovered idiosyncrasies, geometry checks, etc.)

– beam tests provide inputs for tuning the simulation and reconstruction algorithms, and they also sample performance space over the full energy range

For science performance, beam tests can be done with just a few towers together (2 TKR, 3 CAL, 5 ACD tiles).

Full-LAT tests are mainly functional tests.




How the Analysis Pieces Fit TogetherHow the Analysis Pieces Fit Together

Instrument Response

geometry particle transport, interactions

(GEANT4)

sensor response electronics and data system dead channels, impacts noise, etc.

trigger onboard filteronboard science

background fluxes gamma events

Event Reconstruction

Event Classification

Performance

High-level Science Analysis

detailed flux reviewJ. Ormes et al., LAT-TD-08316-01

sky model and benchmark fluxes

muon test data, SVAC runs

FSW algorithms wrapped into SAS; FES+Testbed

beam test; self-consistency checks, basic physics checks

beam test check

planning planning a review a review by the by the SWG in SWG in DecemberDecember

planning planning a review a review by the by the SWG in SWG in DecemberDecember




Aside: some definitionsAside: some definitions

0 1 2 3 4 50

1000

2000Histogram of Data

lower upper

5 0 55

0

5

y

x

68% 95%

Effective area (total geometric acceptance) • (conversion probability) • (all detector and reconstruction efficiencies). Real rate of detecting a signal is (flux) • Aeff

Point Spread Function (PSF) Angular resolution of instrument, after all detector and reconstruction algorithm effects. The 2-dimensional 68% containment is the equivalent of ~1.5 (1-dimensional error) if purely Gaussian response. The non-Gaussian tail is characterized by the 95% containment, which would be 1.6

times the 68% containment for a perfect Gaussian response.




Example (simplified) recipe: AeffExample (simplified) recipe: Aeff

Throw benchmark flux of photons at 6m2 target in which LAT is embedded – “all_gamma” flux, covering all relevant angles and energies

– target area optimized for efficiency while maintaining correct distribution

Pass all events through full simulation, trigger, filter, reconstruction, background rejection, good event selections, etc. (previous slide)

In bins of energy and incident angle (instrument coordinates), calculate Aeff:

(# events passing/#events thrown) * 6m2

Field of view is given by Aeff as a function of incident angle– defined in requirements as integral of Aeff over solid angle

normalized to Aeff at =0.




Performance AnalysisPerformance Analysis

Enormous data sets generated for backgrounds (>5 billion events, sampling orbit variations) and signals (~30 million events).

LAT provides very detailed information about each event.– the performance is as much a function of analysis choices as

hardware performance. Many “knobs” to turn. Analysis choices will be different for different science topic optimization.

– results shown here are for a baseline set of choices that generally represent the most challenging cases.

Great improvements in analyses for energy reconstruction, direction (PSF), and background rejection.




4 Stages of Post Recon Event Analysis4 Stages of Post Recon Event Analysis

Tag – GR_v9r10

Input: Recon

Output: GlastClassier

Energy reconstruction selection– select best energy

method (among 3) PSF- Image control

– select best gamma direction

Background Rejection– (a) divide events into

categories. For each category, a set of selections and classification tree

– (b) global cuts and additional classification tree




Level 1 and Level 2 RequirementsLevel 1 and Level 2 Requirements

14 of 18 Level 2 (SRD) requirements covered in these slides.– two requirements, on time accuracy and deadtime, covered

elsewhere by direct test.

– verification of remaining two requirements on GRB localization onboard and notification time await completion of the onboard science algorithm implementation in FSW.

7 of 7 Level 1 science requirements covered in these slides.




LPS7 - Gamma Energy RangeLPS7 - Gamma Energy Range

Requirement:– The LAT shall measure gamma rays in the range of 20 MeV to

greater than 300 GeV. Verification:

– flows directly into LPS143, LPS144, LPS145 (see following) Compliance Statement: LAT Complies




LPS143 - Effective Area at 20 MeVLPS143 - Effective Area at 20 MeV

Requirement: The instrument shall have an Effective Area of greater than 300 cm2 at 20 MeV.

Test/Analysis Summary: The all_gamma simulation (v9r6) is used to calculate the effective area at downlink, after onboard trigger and onboard filter selections.

Result: At normal incidence (cos()<-0.99) at 20 MeV, the effective area is 1600 cm2 (1400 cm2 with reconstructed track requirement). Additional selections, specific to particular science topics, will trade effective area against other performance parameters (background fraction, PSF, energy resolution).

Compliance Statement: LAT Complies

20 MeV 1 GeV 10 GeV 100 GeV




LPS144 - Effective Area at 100 MeVLPS144 - Effective Area at 100 MeV

Requirement: The instrument shall have an Effective Area of greater than 3000 cm2 at 100 MeV.

Test/Analysis Summary: The all_gamma simulation is used to calculate the effective area after all selections.

Result: At normal incidence at 100 MeV, the effective area is 3,700 cm2, for the current standard background rejection selections. Different selections, specific to particular science topics, will trade effective area against other performance parameters (background fraction, PSF, energy resolution).





LPS145 - Effective Area at 300 GeVLPS145 - Effective Area at 300 GeV

Requirement: The instrument shall have an Effective Area of greater than 6400 cm2 at 300 GeV.


Result: At normal incidence at 300 GeV, the effective area is 7,000 cm2, for the current standard background rejection selections. Different selections, specific to particular science topics, will trade effective area against other performance parameters (background fraction, PSF, energy resolution).

Compliance Statement: LAT Complies– further work underway on

optimization at the highest energies

log(E)

(smoothed)




LPS15 - Peak Effective AreaLPS15 - Peak Effective Area

Requirement: The peak effective area of the LAT shall be greater than 8000 cm2.


Result: At normal incidence, the peak effective area is 9,000 cm2, for the current standard background rejection selections. Different selections, specific to particular science topics, will trade effective area against other performance parameters (background fraction, PSF, energy resolution).

Compliance Statement: LAT Complies (smoothed)

log(E)




LPS32 - Field of ViewLPS32 - Field of View

Requirement: The field of view shall be greater than 2 sr. Test/Analysis Summary: The all_gamma simulation is used to

calculate the effective area after all selections. Result: In the energy range corresponding to that of the peak

effective area, the FOV is 2.2 sr. Different selections, specific to particular science topics, will trade effective area and FOV against other performance parameters (background fraction, PSF, energy resolution).

Compliance Statement: – LAT Complies

log(E)




LPS18, LPS150 - Effective Area KnowledgeLPS18, LPS150 - Effective Area Knowledge

Requirement: The effective area shall be known to within 50% (1-sigma) in the energy range 20 MeV to 100 MeV (LPS18). The effective area shall be known to within 25% (1-sigma) in the energy range 100 MeV - 300 GeV (LPS150).

Test/Analysis Summary:– Sources of uncertainty, estimates

• geometry, active area of silicon detectors <2%• material, probability of conversion <1%• ACD material conversions <1%• reconstruction inefficiencies <2%• energy calibration impacts < 8% (<1% for E>1 GeV)

– Checks for consistency, and monitoring, will be done on orbit. Result: <14% uncertainty, added linearly ( < ~7% E>1 GeV) Compliance Statement: LAT Complies [Note this is a requirement that is internal to LAT. It is not a

mission-level science requirement.]




LPS10 - Energy Resolution 20-100 MeVLPS10 - Energy Resolution 20-100 MeV

Requirement: The energy resolution of normal incidence gamma rays shall be better than or equal to 50% in the energy range of 20-100 MeV, equivalent Gaussian 1sigma.

Test/Analysis Summary: The all_gamma simulation is used to calculate the energy response after all selections.

Result: see following slide

Compliance Statement: LAT Complies.




LPS146 - Energy Resolution 100 MeV - 10 GeVLPS146 - Energy Resolution 100 MeV - 10 GeV

Requirement: The energy resolution of normal incidence gamma rays shall be better than or equal to 10% in the energy range of 100 MeV - 10 GeV, equivalent Gaussian 1sigma.


Result: See following slide





Off Axis: cos() > -.7

On Axis: cos() < -.95

Default "Best"

Default "Best"

Energy ResolutionEnergy Resolution

log(E) log(E)

log(E)log(E)




LPS147 - Energy Resolution 10 GeV - 300 GeVLPS147 - Energy Resolution 10 GeV - 300 GeV

Requirement: The energy resolution of normal incidence gamma rays shall be better than or equal to 20% in the energy range of 10 GeV - 300 GeV, equivalent Gaussian 1sigma.


Result: See previous slide





LPS12 - Off-axis Energy ResolutionLPS12 - Off-axis Energy Resolution

Requirement: The energy resolution of tracked gamma rays of greater than 60 degrees incidence shall be better than 6% in the energy range 10 to 300 GeV, with an effective area > 10% that of normal incidence.


Result: see previous slide





CAL3-6, 21, 22, 26, 29 CAL3-6, 21, 22, 26, 29

These requirements are flowed down from higher-level requirements to level 3 CAL requirements, and they are verified automatically by the verification of the preceding requirements:– CAL3-6 CAL shall support LAT Calorimetry in the energy range 20

MeV to 300 GeV, verified along with LAT-LPS7.

– CAL3-21 (Energy resolution 20-100 MeV) verified along with LAT-LPS10. A separate analysis will also be done using photons that don’t convert in the TKR.

– CAL3-22 (energy resolution 100 MeV - 10 GeV) verified along with LAT-LPS146.

– CAL3-26 (energy resolution 10 GeV - 300 GeV) verified along with LAT-LPS147.

– CAL3-29 (off-axis energy resolution >10 GeV) verified along with LAT-LPS12.




CAL3-56CAL3-56

Requirement: Each layer of the calorimeter shall position the centroid of a Minimum Ionizing charged particle energy deposition to less than 3.0 cm (1-sigma) in all three dimensions for particle incident angles of <45 degrees.

Test/analysis Summary: use ground muon data collected during LAT testing.

Result: all layers <<3.0 cm – (typically <1cm)

Compliance Statement:

LAT Complies

(SVAC B30 runs 135005404 to 14)




CAL3-59CAL3-59

Requirement: The single particle angular resolution at 68% containment for the CAL shall be better than 15 degrees * cos2()for cosmic muons traversing all 8 layers.

Test/analysis Summary: use ground muon data collected during LAT testing (SVAC B30 runs 135005404 to 14).

Result: (see following slide)





CAL3-59CAL3-59




CAL3-37CAL3-37

Requirement: The calorimeter shall be capable of energy calibration in orbit using energy depositions from the array of cosmic ray particles.


Species (Z) Abundance Relative to H

Enormal (MeV)*

He (2) 14% 45

C (6) 0.38% 400

N (7) 0. 096% 550

O (8) 0.35% 720

Ne (10) 0.062% 1120

Mg (12) 0.073% 1610

Si (14) 0.054% 2200

Fe (26) 0.041% 7600

* Does not include quenching effects

Range 5- Emin (MeV)

Emax (MeV)

MeV/ADC

LEX8 2 100 0.03

LEX1 2 1000 0.27

HEX8 60 8000 2.2

HEX1 60 70000 19

Fluxes and energy depositions Calorimeter scales to be calibrated

Estimates of collection times for 1000 good events per log: 1-2 weeks

Detailed simulation studies underway to prepare the on-orbit data analysis.




LPS21, LPS151 - SPAR at 100 MeVLPS21, LPS151 - SPAR at 100 MeV

Requirement: The single photon angular resolution (SPAR) at 68% containment for 100 MeV photons at normal incidence shall be better than 3.5 degrees for the photons converting in the front of the TKR (LPS21) and better than 6 degrees for photons converting in the back of the TKR (LPS151).


Result: see following slides.





LPS22, LPS152 - SPAR at >10 GeVLPS22, LPS152 - SPAR at >10 GeV

Requirement: The single photon angular resolution (SPAR) at 68% containment for >10 GeV photons at normal incidence shall be better than 0.15 degrees for the photons converting in the front of the TKR (LPS22) and better than 0.3 degrees for photons converting in the back of the TKR (LPS151).







LPS26 - SPAR at 95% ContainmentLPS26 - SPAR at 95% Containment

Requirement: The on-axis SPAR at 95% containment shall be better than 3 times the on-axis SPAR at 68% containment.







Thin Radiator PSF Thick Radiator PSF

Off Axis: cos() > -.7

On Axis: cos() < -.95

log(E)

log(E)

log(E)

log(E)= requirement, compare w/ blue line




LPS29 - Off-axis SPARLPS29 - Off-axis SPAR

Requirement: The off-axis SPAR at 55 degrees shall be better than 1.7 times the on-axis SPAR at 68% containment.







PSF off axisPSF off axis

Thin (Front) Thick (Back)

100 MeV

1 GeV

10 GeV 100 GeV 300 GeV

100 MeV

1 GeV

10 GeV 100 GeV 300 GeV

55˚ 55˚




LPS35 - Point Source Location DeterminationLPS35 - Point Source Location Determination

Requirement: The source location determination shall be less than or equal to 0.5 arcmin for a source flux of 1 x 10-7 ph cm-2 s-1 (E > 100 MeV) or greater. Assumes high galactic latitude source with spectral index -2 (1/E2) above a flat background and no cutoff up to 10 GeV. Does not include spacecraft systematics. 1 radius. 1-year survey.

Test/Analysis Summary: The instrument response functions (IRFs) derived from the full event reconstruction analysis are used to calculate the localizations.

Result: location determination <0.4 arcmin (to be updated)





LPS38 - Point Source SensitivityLPS38 - Point Source Sensitivity

Requirement: The point source sensitivity (E > 100 MeV) shall be <6x10-9 cm-2 s-1. Sensitivity at high galactic latitudes after a 1-year survey for a 5 sigma detection.

Test/Analysis Summary: The instrument response functions (IRFs) derived from the full event reconstruction analysis are used to calculate the localizations.

Result: point source sensitivity is <4x10-9 cm-2s-1. See following slide.




Presentation 2 of 12C&A at Stockholm 29 Aug 06 T. Burnett

Point source sensitivity: Point source sensitivity: Check TS for 4x10Check TS for 4x10-9-9 cm cm-2 -2 ss-1-1, one year livetime, one year livetime

E-2 power law Standard EGRET extragalactic background Combined 0-66 deg in one bin, scanning mode Ignore effects of dispersion

ClassCTBCORE

range

TS

front back

#1 0.1-0.5 1.90 0.27

#2 0.5-0.7 4.42 1.40

#3 0.7-0.85 7.30 3.65

#4 0.85-1 6.86 4.14

(Sum) 20.48 9.46

2-4 combined 0.5-1 19.10 8.94

DC2 classA 21.0 10.0

‘5” requirement: (TS) > 25

Total for LAT is 28.0




LPS44 - Background Rejection CapabilityLPS44 - Background Rejection Capability

Requirement: LAT shall have a background rejection capability such that the contamination of the observed high latitude diffuse flux (assumed to be 1.5x10-5 cm-2 s-1 sr-1) in any decade of energy ( > 100 MeV) is less than 10%, assuming a photon spectral index of -2.1 with no spectral cut-off.

Test/Analysis Summary: The background simulation and the extragalactic diffuse gamma-ray flux simulation are used to calculate the residual rates after all trigger, filter, reconstruction, and event selections.

Result: see following slide.

Compliance Statement: LAT Complies directly for E>3 GeV. For the energy band 100 MeV < E < 3 GeV, using the standard event selections, the residual background contamination fraction is >10%. For this energy range, the residual contamination energy spectrum will be subtracted from the measured diffuse energy spectrum. A systematic error due to the background subtraction of <10% will bring the LAT into compliance. An analysis will be presented at the science performance review, with final verification on orbit.




Background ContaminationBackground Contamination

log(E)

Resulting spectra Background fraction by decade of energy (no

subtraction)

signal

bkgdmin

req

result of updated background model




SummarySummary

LAT meets or beats Science Requirements– instrument data idiosyncrasies and relevant real-world behavior

(e.g., bad channels) uncovered during testing incorporated into the simulation.

– beam test results will be used to update the simulation.

– further analysis to be performed on background rejection and effective area knowledge requirements. Updates to come on point source localization and on-orbit CAL calibration analyses.

– these are analysis tasks that are decoupled from instrument shipment schedule.

Verification of two science requirements pending completion of FSW burst algorithm implementation.

Review by the GLAST Science Working Group of performance against all three requirements tables (GBM, LAT, Observatory) in the Science Requirements Document (SRD) later this year.

science requirements verification glast lat project september 15, 2006: pre-shipment review...

Documents

lat tests

science performance

lat td

beam tests

primary verification

reconstruction algorithms

gamma flux

previous slide