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MODEL PSF EFFECTS OF PILE-UP. Jonathan Gimeno Boal, UCM. Tutor: Martin Stuhlinger. Tutor: Martin Stuhlinger. Index:. Aim of the project. Selection of the observations. Selection of point sources. Determination of the counts per second. Determination of pile-up. Next steps. - PowerPoint PPT Presentation
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Jonathan Gimeno Boal, UCM
MODEL PSF EFFECTS OF PILE-UP
Jonathan Gimeno Boal, UCM
Tutor: Martin StuhlingerTutor: Martin Stuhlinger
Jonathan Gimeno Boal, UCM
Index:
• Selection of the observations.
• Determination of the counts per second.
• Selection of point sources.
• Determination of pile-up.
• Aim of the project.
• Next steps.
Jonathan Gimeno Boal, UCM
Aim of the project:
- Pile-up: Arrival of two or more photons within the readout time of the detectors.
- For very bright sources there is a considerable amount of pile-up.
- The centre of the PSF (Point Spread Function) gets distorted:
Loss of counts at the centre of the PSF.Clean PSF.
Jonathan Gimeno Boal, UCM
Aim of the project:
Finally a 3D model of the PSF will be created:
Jonathan Gimeno Boal, UCM
What is pile-up?
Pattern pile-up: Two or more photons arriving next to each other in the same readout time.
Photon pile-up: One single photon causes multiple pixel activation
SAS task Epatplot output.
Consequences:
• Less counts at the PSF centre.
• Shifts the spectrum towards higher energies.
Jonathan Gimeno Boal, UCM
Selection of observations:
● Distinguish point sources:
• Observation Modes
• Filters
Jonathan Gimeno Boal, UCM
Selection of point sources:
In order to automatically determine if an observation is of an extended source or a point source the counts per second of two annuli around the source were calculated and then the ratio of these two count-rates.
Point source: ratio =counts outer
counts innerExtended source: >X%=[5% , 15%]
Jonathan Gimeno Boal, UCM
Determination of counts per second:
Once the number of events registered by the detectors and the exposure time is known, the count rate is determined.
Jonathan Gimeno Boal, UCM
Source coordinates determination:
Annuli extraction needs PSF centre, position of the source in the detector.
First Attempt:
Header sky coordinates
Detector coordinates
SAS task esky2det
Jonathan Gimeno Boal, UCM
Chosen Solution:
Find the centre of mass using IDL software
Work on the Generated Image
( , )
( , )ij
ij
I x y x dxdy I ix
II x y dxdy
( , )
( , )ij
ij
I x y y dxdy I jy
II x y dxdy
Jonathan Gimeno Boal, UCM
Similar ratio as in the extended source case:
Avoid the identification of extended sources as strong pile-up observations
Strong pile-up case
Chosen Solution:
Extended source
singles
doublesratio:
inner annulusouter annulus
Jonathan Gimeno Boal, UCM
Ratio between the single events and double events in energy band of 1keV to 1.8keV. (TBD)
singles
doubles~=2
Determination of pile-up:
Pile-up singles
doubles
Clean PSF:
Jonathan Gimeno Boal, UCM
Investigating in using vertical and horizontal bipixels: (S. Molendi & S. Sembay, 2003 “Assessing the EPIC spectral calibration in the hard band with a 3C 273 observation”)
Determination of pile-up:
Clean PSF: Probability true horizontal bipix. < True vertical bipix.
Pile-up: Probability horizontal bipix.from 2 piled up photons = Vertical bipix.
from 2 piled up photons
To assess pile-up calculate:vertical bipix.
pattern 0On the source and inside an annulus, then calculate the ratio of both results.
Repeat with horizontal bipix. and compare with vertical
Equal ratios: pile-up free.
Different ratios: Pile-up case.
Jonathan Gimeno Boal, UCM
Sum up observations with clean PSF:• Superposition.• Normalize.
Next steps:
Summing up observations in different pile-ups and comparison with clean
PSF:
MOS camera examples.
Jonathan Gimeno Boal, UCM
Questions?
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