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Characteristics of the HRC Background

Michael Juda

Outline of Talk

  1. HRC Background Reduction Measures
  2. Background Components
  3. Temporal Behavior
  4. HRC-I Spatial Distribution
  5. HRC-S Spatial Distribution
  6. Future Directions

For more details see "Characteristics of the On-Orbit Background of the Chandra X-ray Observatory High Resolution Camera", 2002, SPIE Proc. 4851

HRC Background Reduction Measures

HRC MCPs made from ``low-noise'' glass

The HRC detector housing is surround on five sides by plastic scintillator for use as an active anti-coincidence shield.

For each MCP event, telemetry contains info on the shape of the charge distribution from the MCP as well as state of on-board hardware checks. Particle event signature is different from x-ray event. (see poster by C. Wilton)

HRC telemetry also contains scalars to report rates: MCP triggers (Total rate), triggers that pass on-board validity checks (Valid rate), and antico-shield rate.

Background Components

CXO particle detector (EPHIN) measures the local radiation envirnoment.

four energy channels in the range 0.25-10 MeV
four energy channels in the range 5.0-53 MeV
Integral channel
electrons with E > 8.7 MeV, protons and nuclei with E > 53 MeV/nucleon

Temporal Behavior

Variation in the background observed since mission start.

Flaring on time scales of seconds to hours observed on top of a quiescent level.

Reasons for variability:


HRC-I MCP trigger rate correlates with the EPHIN high-energy particle flux (ignoring X-rays and the flaring component)
hrci_total_v_int_flux.gif hrci_valid_v_total.gif

Flaring Background

HRC-I Spatial Distribution

Reasons for spatial variation

Non-Sky-Viewing Background
hrci_nil_bkg.gif hrci_nil_bkg_filt.gif
Raw Filtered

Combined AR Lac Fields Background
hrci_arlac_bkg.gif hrci_arlac_bkg_filt.gif
Raw Filtered

Coincidence shield flagged Events

HRC-S Spatial Distribution

Reasons for spatial variation

HRC-S is operated in several different modes depending on the type of observation. Modes select different areas of the detector.

HRC-S Spectroscopy Mode (Default)

HRC-S Spectroscopy Mode (Default) - Filtered

HRC-S ``Timing'' Mode
hrcs_timing_img_color.gif hrcs_timing_filt_img_color.gif
Raw Filtered

HRC-S Edge-Blank Center vs ``Timing'' Mode

Future Directions

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On 22 Nov 2002, 11:55.


2002 : background : CfA : Chandra : CXC : HRC : HRC background : HRC-I : HRC-S : Juda
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Last modified: Fri Nov 22 12:43:48 EST 2002

Dr. Michael Juda
Harvard-Smithsonian Center for Astrophysics
60 Garden Street, Mail Stop 70
Cambridge, MA 02138, USA
Ph.: (617) 495-7062
Fax: (617) 495-7356
E-mail: mjuda (at) cfa.harvard.edu