Contamination WG Telecon #1 (2014-03-31)

• Agenda
  • short (5 minute) summaries from participants about:
    • contamination status of current instruments
      • Steve O. – Chandra ACIS
      • Herman – Chandra ACIS
      • Steve S. – XMM EPIC-MOS and pn
      • Eric – Suzaku XIS
      • Andy – Swift XRT
      • anyone else?
    • plans for future instruments
      • Michael – eROSITA
      • Astro-H?
      • anyone else?
  • discussion about how to structure the 2 x 1.75 hour WG sessions at upcoming IACHEC, which could include:
    • several longer (20 min) presentations for current and future instruments
    • more from Steve S. about combining contamination and response calibration
    • best methods to monitor time, spatial, chemical variations
    • best references for absorption data
    • hands-on cross-calibration? (e.g. real time spectral fitting)
      
       
• Meeting Minutes

Attendees
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E.Miller, S.O'Dell, M.Freyberg, C.Grant, S.Sembay, P.Plucinsky, L.David, T.Gaetz, H.Marshall

Action Items
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• • (A/I) IACHEC presentations
    up to 15 min per talk to allow time for discussion
    scheduled for the first WG session on Monday, May 12, 14:00-15:45:

• • H.Marshall, "Chandra ACIS contamination monitoring"
  • D.Swartz, "Simulations of Chandra ACIS contamination migration"
  • S.Sembay, "Contamination on the EPIC-MOS detectors"
  • E.Miller, "Contamination on the Suzaku XIS"
  • A.Beardmore, "Constraints on contamination on the Swift XRT" 

   scheduled for the second WG session on Tuesday, May 13, 16:15-18:00:

• • (?) V.Burwitz, eROSITA
  • (?) M.Eckart, Astro-H SXS
  • (?) TBD, HXMT
  • general discussion
     
  • (A/I) Herman and Steve S. contact members of Astrosat team about joining and presenting at the WG session
  • (A/I) Eric contact Astro-H team members about same
  • (A/I) Eric contact HXMT team members about same
  • (A/I) Eric contact DIOS team members about same
  • (A/I) Michael contact Vadim about presenting eROSITA contamination plans

Meeting Summary
---------------

Current Mission Status
----------------------

Steve O. presented a summary of the contamination migration modeling he and Doug Swartz have beeen doing for Chandra ACIS. This is a three-pronged effort with MIT (Herman) and SAO working on X-ray absorption measurements, MSFC working on migration models and simulations, and Lockheed responsible for the thermal and geometric modeling. Steve uses a radiative transfer-like method to model the transport of the contaminant, using knowledge of the thermal properties of various components. At this point the transport models do not agree with the observed contamination distribution, but a big question is how the build-up of contaminant affects the thermal properties of the filter. Doug will attend the IACHEC meeting and present a detailed report on this.

Herman presented recent Chandra ACIS results that shows oxygen is building up more rapidly at recent times compared to carbon. Also, from the "Big Dither" observations of Mrk 421, there appears to be a need for nitrogen, and it appears to be thicker at the center of ACIS-S3 than the edge/bottom (opposite what is seen for C and O). The reasons for these effects are not known, although "radiation induced organic fracturing" is a possibility. Herman will present this at the IACHEC meeting.

Steve S. summarized the contamination status of XMM. RGS has had known contamination for a while, inferred as only carbon because no edges are seen and the C-edge is below the passband. EPIC pn has no evidence of contamination, with tight constraints. EPIC MOS1 and MOS2 both have evidence of contamination starting a few years ago, at a level about 20% that of RGS and different on each. The thought is that the contaminant is directly on the detector and not filter(s), and came through the filter wheel through the open position and gaps. The telescope tube itself is suspected as the source of carbon, although questions were raised about how this could happen (high-energy particles? outgassing?). Steve will acquire documentation from ground testing about contamination results and have those for the IACHEC meeting.

Eric summarized the Suzaku XIS contamination, which quickly built up within a few months of launch, reaching a thickness similar to Chandra and leveling off. The amount is different on each chip, apparently thicker at the center due to a temperature gradient, although now the contamination appears to be decreasing and becoming more uniform. He summarized the calibration targets used (E0102, RXJ1856, PKS2155, Perseus, bright Earth limb, Cygnus Loop). The model used is purely phenomenological, with little effort (yet) to understand how the thermal and structural properties of the spacecraft and instrument could be used to model the contamination, except for a 2006 meeting to explore a bake-out. Eric will dig up results from this meeting and present at the IACHEC meeting.

Andy B. was unable to join, but emailed afterwards to say he's been looking at RXJ1856 and doesn't think there is contamination on the Swift XRT, outside of some dandruff dislodged during vibration testing and corrected for. He will present constraints at the IACHEC meeting.

Future Missions
---------------

Michael discussed eROSITA and its plans for multiple contamination shields and mitigation strategies. In particular, the team is currently thinking about: what is the main source of contamination, the large telescope or the camera? how to operate the first weeks for proper outgassing, leave camera open or closed? He will not attend IACHEC, but Vadim will be there and we will force him to present these plans and questions.

Astro-H SXS (micro-calorimeter)
Eric will ask Megan Eckart (GSFC) to join and tell us something about the Astro-H SXS (micro-calorimeter), which has a multi-stage contamination-blocking filter due to the very low instrument temperature.

AstroSat
Herman and Steve S. will ask Astrosat participants to join.

HXMT
?? Eric will contact the HXMT participants and ask them to join.

DIOS
?? ditto

NICER
Bev LaMarr may attend the WG. NICER runs warm compared to other instruments, however it is also in the contamination-rich ISS environment.

Plans for IACHEC
----------------

The presentations at the May IACHEC meeting should include details of what is known about the contamination in each instrument, including the chemical composition, time dependence spatial dependence, and temperature dependence. Secondly, we will try to figure out what common components we all have that could be sources of contamination (e.g. gyros, lubricants). One goal of this WG is to to understand the physics of where this stuff comes from, and collecting all this information in one location is the first step.

• Directions for Connecting

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Meeting information 
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Topic: IACHEC Contamination WG Telecon 
Date: Monday, March 31, 2014 
Time: 9:30 am, Eastern Daylight Time (New York, GMT-04:00) 
Meeting Number: 643 892 836 
Meeting Password: iachec 

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