CASTERA Scintillator-Based

Black Hole Finder Probe

Mark McConnellUniversity of New Hamsphire

The CASTER CastMark McConnell, Jim Ryan, John Macri

University of New Hampshire

Mike Cherry, T. Greg Guzik, Brad Schaefer, J. Greg Stacy, John Wefel

Louisiana State University

R. Marc Kippen, W. Tom VestrandLos Alamos National Laboratory

Bill Paciesas, Rich MillerUniversity of Alabama – Huntsville

Jim CravensSouthwest Research Institute

Black Hole Finder ProbeAll-sky black hole census

Total energy range : 10 – 600 keV

Sensitivity goal ≈0.02 mCrab in 20–100 keV

≈1000x more sensitive than HEAO A-4

1–20x more sensitive than Swift

≈20x more sensitive than BATSE for GRBs

Angular resolution of 3-5 arcmin will be required to avoid source confusion.

CASTER

Proposed as a mission concept for the Black Hole Finder Probe.

Mission concept closely parallels that of EXIST.

Coded aperture imaging (10-600 keV).

Detectors based on new scintillator technologies.

Implications for mission design?

Coded Aperture Survey Telescope for Energetic Radiation

Motivation for CASTER

New scintillator and readout technologies.

New scintillator with high light output :Improved energy resolutionImproved spatial resolution

Traditional technology simplifies implementation.

Potential for low cost detector technology.

Emphasize the importance (uniqueness) of observations at higher energies (up to ≈600 keV).

INTEGRAL Sky Map

Galactic Center Region, 20–60 keV

91 sources, many involve black holes

Bird et al. 2004

Cyg X-1 State Comparison

McConnell et al. 2002

SWIF

T

BHFP

Black Hole Spectra

Observations up to 600 keV explore the range of thermal / non-thermal transitions.

Cyg X-1 spectrum requires non-thermal component.

What other sources exhibit similar behavior?

What is link between galactic black holes and AGN?

Role of pairs in accretion disk spectra?

Annihilation Radiation

Origin of 511 keV diffuse emission (OSSE, SPI).

Contribution of point sources?

Supernovae Ia?

Hypernovae? (Casssé et al. 2004)

Light Dark Matter (LDM)? (Casssé et al. 2004)

GRB Epeak Distribution

GRB spectra – smoothly broken power-law.

Observed break energies up to several hundred keV.

Spectral measurements require data both above and below the break energy.

SWIF

T

BHFP

Detector Requirements

Energy range ≈ 10-600 keV

Good stopping power for energies up to ≈600 keV

Spatial resolution ≈ 1-2 mm in x, y, and z

Availability in large areas and at low cost

Energy resolution

New Scintillator Technology

High Z material (comparable to NaI)

High density (higher than that of NaI)

Higher light output (60% more than NaI)

Significantly improved linearity (E vs. light output)

Significantly better energy resolution (

Energy Resolution

LaBr3 ≈ 2.7% @ 662 keV≈ 3.8% @ 511 keV≈ 6.8% @ 122 keV

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Detector Materials

LaBr3 LaCl3 NaI(Tl) CsI(Na) BGO CZT Ge

Density 5.29 3.86 3.67 4.51 7.13 5.78 5.33

Light Output 63,000 49,000 39,000 39,000 9,000 N/A N/A

∆E/E (FWHM) @ 662 keV

10%

Stopping Power

Thick scintillators are easier to fabricate.

This gives a potential advantage at high energies.

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LaBr3 5mm thick

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CZT 5mm thick

LaBr3 5mm thick

LaBr3 20mm thick

Spatial ResolutionAnger Camera Designs

Performance will depend on several parameters :light output of scintillatorthicknessenergy

Estimated resolution based on increased light output.

Energy Thickness σxy σxyCsI(Tl) (NRL) 60 keV 4 mm 1-2 mm 0.8-1.6 mm

NaI(Tl) (Medical) 141 keV 9.5 mm 1.5 mm 1.2 mmNaI(Tl) (SIGMA) 30 keV – 1 MeV 12.5 mm 2.5-5.0 mm 2.0-4.0 mmNaI(Tl) (GRIP) 662 keV 5 cm 3.0 mm 2.4 mm

New Readout Technologies

wavelength-shifting(WLS) fibers

MCP-PMT (Burle)

Flat-Panel PMT (Hamamatsu)

Depth of Interaction

WLS fiber ribbons can be used to determine depth of interaction (DoI).

Depth measurement comes from light cone projected onto WLS ribbon.

X-Y (and Z?) location and total energy provided by an array of PMT anodes.

Matthews et al. 2003

Availability of Detector Material

Both LaBr3 and LaCl3 still under development

A lot of interest (incl. medical)

Development of LaCl3 leads LaBr3

LaCl3 is available commercially

Largest LaBr3 to date ≈ 2.3 cm3

Cost eventually < $30 / cm33” x 3” LaCl3

(St. Gobain)∆E/E = 4.1%

Challenges

Fabrication (availability) of new scintillator material

Spatial resolution of ≈ 1-mm in x, y and z

On-orbit background of LaX?

Radiation effects on LaX?

Handling of multiple interaction sites?

Ability to do polarimetry?

Implications for Mission Design

Thicker material ==> greater weight, background?

Thicker mask ==> greater weight, background?

Thicker detector/mask ==> restricted FoV?

Separate low-energy and high-energy imagers?

Daily sky coverage?

CASTER Mission Concept Study

Continued Development of LaBr3

Detector Design Studies (various scintillators)

Imager Design Studies

Background Studies (beam tests, MGGPOD)

Sensor Ruggedization

Data Handling

Spacecraft Design

Mission Design

Summary

Coded aperture imaging is an attractive way of doing a hard X-ray survey (10-600 keV).

Alternative detector technologies are worth considering.

The goal of the CASTER study will be to consider some of these alternative technologies and their implications for mission design.