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THE EPIC SIMULATOR AND PILE-UP MODELLING
Prashin Jethwa EPIC BOC 2012 7/3/2012


OUTLINE

Introduction to the EPIC simulator · What is it? · How does it work? · Validation Pile-up modelling · Flux losses · Spectral distortions Pile-up mitigation · Correcting spectral distortions

The EPIC simulator & Pile Up Modelling | Prashin Jethwa | EPIC BOC 2012 | Pag. 2


THE EPIC SIMULATOR: what is it?

New tool developed in IDL by Richard Saxton, Pedro Rodriguez, Prashin Jethwa Realistically simulate EPIC observations What does it do? · Input: 1) 2) 3) 4) 5) in s tru m e n t number of counts per frame number of frames in observation s p e c tra l m o d e l c a l i b r a t i o n fi l e s

· Simulate · Output:

(details on next slide...) 1) event list 2) spectral files (PI vs. counts) and ARFs

The EPIC simulator & Pile Up Modelling | Prashin Jethwa | EPIC BOC 2012 | Pag. 3


THE EPIC SIMULATOR: how does it work?

For a given (counts / frame), generate Poisson distributed photon numbers / frame For a given spectral model and ARF, assign energy to each photon For a photon of given energy, assign: 1) position (PSF) 2) PI channel (RMF) 3) pattern (pattern fraction calibration)

The EPIC simulator & Pile Up Modelling | Prashin Jethwa | EPIC BOC 2012 | Pag. 4


THE EPIC SIMULATOR: un-piled-up spectrum

Simulated input spectrum = 2 power-law Residuals ~ 2keV ... consequence of ARF/RMF interpolation differences between XSPEC and simulator?

The EPIC simulator & Pile Up Modelling | Prashin Jethwa | EPIC BOC 2012 | Pag. 5


THE EPIC SIMULATOR: how does it work?

For a given (counts / frame) , generate Poisson distributed photon numbers / frame For a given spectrum and ARF, assign energy to each photon For a photon of given energy, assign 1) position (PSF) 2) PI channel (RMF) 3) position (pattern fraction calibration)

Combine events within a single frame and identify resultant events · Sum energies · Merge patterns · Remove bad patterns Produce output spectrum and ARF for a given event pattern and extraction region

The EPIC simulator & Pile Up Modelling | Prashin Jethwa | EPIC BOC 2012 | Pag. 6


THE EPIC SIMULATOR: piled up spectra

Spectra are fit with pattern-appropriate ARF Black: Input = 1.997 Flux = 3.5e-11 Red: Output singles+doubles = 1.985 Flux = 1.9e-11 Green: Output singles = 1.992 Flux = 1.7e-11
The EPIC simulator & Pile Up Modelling | Prashin Jethwa | EPIC BOC 2012 | Pag. 7


THE EPIC SIMULATOR: piled-up Gaussian

Input: Gaussian at 2keV Output: Gaussians at 2keV, 4keV, 6keV, 8keV, 10keV...

The EPIC simulator & Pile Up Modelling | Prashin Jethwa | EPIC BOC 2012 | Pag. 8


THE EPIC SIMULATOR: piled-up images

Core suppression as a consequence of pile-up. Left: 1 count / frame, Centre: 100 counts / frame, Right: 1000 counts / frame

Uses ell-beta PSF Extract spatial information · images · spectra from different extraction regions

The EPIC simulator & Pile Up Modelling | Prashin Jethwa | EPIC BOC 2012 | Pag. 9


THE EPIC SIMULATOR: validation

Self-consistent: for low count rates the output spectrum = input spectrum Comparison against theoretical work (J. Ballet 1999)

The EPIC simulator & Pile Up Modelling | Prashin Jethwa | EPIC BOC 2012 | Pag. 10


PILE-UP MODELLING: flux loss in PN full frame

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PILE-UP MODELLING: flux loss in PN small window

The EPIC simulator & Pile Up Modelling | Prashin Jethwa | EPIC BOC 2012 | Pag. 12


PILE-UP MODELLING: flux loss

The EPIC simulator & Pile Up Modelling | Prashin Jethwa | EPIC BOC 2012 | Pag. 13


PILE-UP MODELLING: flux measurement with excised core

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PILE-UP MODELLING: spectral distortions

The EPIC simulator & Pile Up Modelling | Prashin Jethwa | EPIC BOC 2012 | Pag. 15


PILE-UP MITIGATION
Provides a control to test any pile-up correction method Can also be used in a new pile-up correction procedure (Andy Pollock):
­ Piled-up spectrum = FUNCTION ( Original spectrum , pile-up parameters ) ­ Use the simulator to generate a grid of pile-up parameters
­ Instrument dependent ­ Count rate dependent ­ Weakly spectrum dependent?

­ Incorporate these into XSPEC pile-up model

Other correction procedures under consideration: · J. Ballet 1999, 2000, 2003
­ based on his theoretical pile up equations ­ alter response matrix to consider pile-up in fitting process

· Idea proposed by Norbert Schartel
­ based on nuclear physics ­ as described in Radiation Detection and Measurement, G.F. Knoll
The EPIC simulator & Pile Up Modelling | Prashin Jethwa | EPIC BOC 2012 | Pag. 16