The MOS Background (and XMM-ESAS)?

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The MOS Background(and XMM-ESAS)?

• K.D. Kuntz
• The Henry A. Rowland Dept of PA
• Johns Hopkins University
• And occasionally GSFC
• With PN additions from
• S.L.Snowden
• GSFC

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Overview

• Review of the Goddard/ESAS method
• Update on instrument/detector evolution
• (a purely phenomenological approach)?
• Future updates automation
• A few notes about the PN from SLS

3
Method Review Philosophy

• Emission from the Galactic ISM fills the FOV
• Sufficiently faint that it must be summed over
  large regions in order to produce a good spectrum
• The same is true of extended extragalactic
  emission (e.g. galaxies clusters)?
• Background subtraction method must provide good
  statistics over large regions of the FOV
• And still be sensitive to the small-scale
  spatial/temporal variations in the detector

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Method Review

• The corner pixels are a measure of the particle
  background

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Method Review

• The corner pixels are a measure of the quiescent
  particle background (QPB) for a given observation
• There are not enough counts in the corner pixels
  of a single observation for a robust
  characterization of the backgroundso
• Measure the rate and hardness ratio for your
  observation and then
• Augment with corner spectra from other obsids
  that have the same rate and hardness ratio

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Method Review
Rate 0.3-10.0 keV Hardness 2.5-5.0/0.4-0.8
keV
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Method Review

• The corner pixels are a measure of the quiescent
  particle background (QPB) for a given observation
• There are not enough counts in the corner pixels
  of a single observation for a robust
  characterization of the backgroundso
• Measure the rate and hardness ratio for your
  observation and then
• Augment with corner spectra from other obsids
  that have the same rate and hardness ratio

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Method Review
From a collection of all corner pixel spectra,
extract those with similar ratees and hardnesses
with an accumulated exposure time of at least X
seconds, where X106s
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Method Review

• The corner pixels are a measure of the quiescent
  particle background (QPB) for a given observation
• There are not enough counts in the corner pixels
  of a single observation for a robust
  characterization of the backgroundso
• Measure the rate and hardness ratio for your
  observation and then
• Augment with corner spectra from other obsids
  that have the same rate and hardness ratio

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Method Review

• The corner pixel spectrum is not representative
  of the QPB spectrum within the FOV
• The filter-wheel-closed (FWC) data do not reflect
  the obsid-to-obsid variation
• Assume that overall changes in spectral shape
  seen in the corner pixel data are reflected in
  the FWC data
• FOV FWCobserved corner/FWC corner

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Method Review

• Method seems to work reasonably well
• yielding good repeatability

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Method Review

• Must maintain up-to-date
• Databases of corner pixel spectra
• Databases of FWC images
• (in particular we need to make sure we continue
  to accumulate new FWC data)?
• Eternal vigilance for instrumental changes
• Ensure that method remains valid

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Current QPB Update

• Using all obsids public before September 2008
• Removed all time intervals with Soft Proton (SP)
  flare contamination
• Removed all obsids with clean time lt 5 ks

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Current QPB Update

• Evolution of rate upward since Rev 725
• Evolution of hardness slightly downward

Epoch 0
Epoch 1
Epoch 2
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Current QPB Update

• Compare spectra with 3ltHRlt4 for three epochs
• Results consistent for MOS1-2,3,6,7
  MOS2-2,3,4,6,7
• Minor differences for Elt0.3 keV

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Anomalous States

• Some chips have intermittent states where the QPB
  spectrum is very different
• Usually characterized by high Rs and low HRs

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Current QPB Update

• Chips with anomalous states show strong evolution
  in Rate-Hardness diagram

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Current QPB Update

• Chips with anomalous states show strong evolution
  in Rate-Hardness diagram

What happens to the spectra?
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Current QPB Update
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Current QPB Update
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Current QPB Update
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Current QPB Update

• MOS 2-5
• Currently in anomalous state for the bulk of time
• Spectral shape stable but very strong
• MOS 1-5
• Incidence of anomalous states currently low
• Spectral shape unstable
• MOS 1-4
• Currently in anomalous state for 50 of time
• Spectral shape unstable
• Data from chips in anomalous states should
  probably be discarded for low surface brightness
  studies
• Spectral shapes in non-anomalous times stable
• Will need to re-write descriptions for anomalous
  states

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Future QPB Updates

• Past Construction
• Filtered out periods with strong SP flares
  (espfilt)?
• Hand selection of obsids for inclusion
• Current Construction (not yet released)?
• Filtered out periods with strong SP flares
• Selection of obsids
• Histogram Center lt 4
• Histogram Width lt 0.175
• Cleaned exposure time gt 5 ks
• Roughly reproduces by-hand process

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Future QPB Updates

• Future construction
• Must use automatic selection of obsids
• Use parameters describing good obsids?
• Rethink this process

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Future QPB Updates

• Soft Proton Flares do not affect corner data
• So SP filtering is pointless and a waste of time

FOV
Corner
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Future QPB Updates

• There is contamination of the corner data by
  Particle Background Excesses (PBEs?)?
• Usually when S/C entering or exiting particle
  belts
• Can be filtered using same routines, diff. params

Corner
Corner
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Future QPB Updates

• Filtering the corner data
• Increases available corner data by 1.3-1.5
• Fully automatic selection criteria
• Currently being test-implemented at JHU/GSFC

Corner
Corner
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Current FWC Update

• MOS FWC campaign to determine whether the FWC
  images/spectra are temporally variable
• Compare FWC data for 1130ltrev w/ revgt1130
• Construct images of (post-1130/pre-1130) -1

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Current FWC Update
MOS1
All
5-14
2.5-5
1-2
0.4-0.8
1S
2S
4S
4H
5S
5H
6S
7S
3S
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Current FWC Update

• Variation within expected range if w/o temporal
  var.
• Negative tail may be due to the increase of bad
  pixels

MOS1
MOS2
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Current FWC Update

• MOS FWC campaign to determine whether the FWC
  images/spectra are temporally variable
• Compare FEC for 1130ltrev w/ revgt1130
• Construct (post-1130/pre-1130) -1 images
• No significant signs of temporal variability
• Compare spectra
• No significant signs of temporal variability
• Continued monitoring necessary
• Every nth calclosed slew to be converted to closed

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Future FWC Updates

• Difficult to make automatic
• Must inspect each observation of each chip to
  determine whether chip in standard or anomalous
  state
• Anomalous state definitions are evolving with
  time, so dependent on up-to-date inspection of
  corner data.
• Given rate at which FWC data accumulates, human
  interaction no big deal

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PN in ESAS

• PN software nearly complete
• Needs testing on additional data sets
• Possible over-estimation of background
• Data probably not useful
• below 0.4 keV or above 7.2 keV

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Progress on ESAS for the PN model particle
background. Radial profile spectral fit of Abell
1795 using 10 annuli and a RASS
spectrum. ???1.5 for 7829 DOF
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PN in ESAS

• PN software nearly complete
• Needs testing on additional data sets
• Possible over-estimation of background
• Data probably not useful
• below 0.4 keV or above 7.2 keV
• PN QPB (FWC?) databases constructed
• QPB shows little temporal variation
• PN flare vignetting images constructed

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FINE