Results from theBalloon-borne Hard X-ray Spectrometer

Ken Kobayashi1, S. Tsuneta2, T. Tamura2, K. Kumagai2,Y. Katsukawa1, M. Kubo1, Y. Sakamoto1, N. Kohara1,T. Yamagami3, Y. Saito3, K. Mori4
1: University of Tokyo
2: National Astronomical Observatory of Japan (NAOJ)
3: Institute for Space and Astronautical Science (ISAS)
4: ClearPulse Co.

Introduction
High resolution hard X-ray spectra in the 20-100 keV region
provides quantitative information on particle acceleration and>20MK plasma.

Lin et al. observed M6 flare with high-resolution Ge detector in1980; no successful follow-up until RHESSI.

Recent advances in CdTe detectors make high-resolution
hard X-ray spectroscopy simpler.

Goal is to make independent observation of high-resolution (<3 keV FWHM) solar flare spectra.



Two flights conducted:• August 2001 flight partially successful, no flares.
• May 2002 flight successful, M1.1 flare observed.

Instrument Overview
Detector type:

CdTe, 1cm2 x 16
Passively cooled

Resolution:< 3 keV @ 60 keV (goal)(2.6 keV actual)

Energy range:

20-130 keVSpatial resolution:(none)

Pointing:azimuth only, ± 5° accuracy



Field of view:

Collimated to 10x60 degrees



Total gondola weight:80 kg

Flight altitude:41 km

Flight duration:

1 day (morning→evening)

Instrument Overview

Detectors

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10x10x0.5mm CdTe detectors, fabricated by AcroRad(formerly Japan Energy)
In/Pt Schottky electrodes
Bias voltage = 200V
Operating temperature: < 0 ℃ (for 3 keV resolution)
Passive shielding only (2mm lead)Detector Enclosure
collimator (W + Sn + Cu)
CFRP windowdetectorsrear shield (Pb)side shield (Pb)
preamp boards

290mm

270V battery
pressurised enclosure
feedthroughs•••

Detector enclosure pressurised at 1 atm
Enclosure contains detectors, preamp boards, battery (200 V bias),
Pb shield
14cm diameter CFRP/RohacellTM window provided by Mitsubishi
Heavy Industries, weight = 0.1 g/cm2

Thermal Design••••

Detector temperature of 0℃ achieved with passive cooling only.
High emissivity Ag/Teflon tape on detector enclosure surface.
Shielded from sunlight and ground IR while maximising view of sky.
Detector system insulated from gondola.

Electronics•••

16 separate spectra, 128 channels each (1 keV / channel).
Pulses integrated into spectra by onboard electronics→ constant load on microprocessor and telemetry.
All spectra read every 0.54 seconds.

Detector Performance
Am-241•••

Cd-109Co-57

Calibration tests done using Am-241, Cd-109 and Co-57 sources.
Resolution: FWHM = 2.6 keV @ 60 keV.
Line at 85 keV is secondary emission from Pb shield.

Quantum Efficiency••

QE measured using calibrated sources
Fit to 0.45mm thick CdTe ＋ 0.08 g/cm2 carbon

Flights••

2001/8/29 First flight:– 45 min. observation.
– No flare seen.
2002/5/24 Second flight:– 8 hours of observation.
– Successful flareobservation.

Altitude & Temperature Profiles••

Temperature of exposed frame varies between -10°C and +10°C
Detector temperature maintained below –15°C throughout level flightTotal light curve
flare!

EIT image offlare loops•••

Noise during ascent caused by transponder and sirens.
Background stable during level flight.
Class M1.1 flare seen at 6:41 UT.

Background••Pb line from shields seen at 75 and 85 keV.
Gain and resolution of Pb line stable.

Flare Light Curve••

4 minutes of X-ray emission observed.
Emission is primarily in low energy (< 35 keV), high energy X-ray
flux is very small for this size flare.

Raw Spectra••

Solid line: background (200 minute period before flare).
Data points: flare flux.

Spectrum Analysis•

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（ error bar ＝ １ σ ）Result of spectral fit topurely thermal spectra
Solid lines show fit at fixedtemperatures; dashed line
is best fit
Best fit values:– Ｔ＝４７ＭＫ– ＥＭ＝ 1.9e46 cm-3
Thermal spectra agrees
with data; no non-thermalemission detectedLight Curves•••

Top: Nobeyama solar microwave polarimeter data (flux at 2, 4, 9 and17 GHz). Note good correlation between balloon data and 4GHz flux.
Middle: GOES soft X-ray flux
Bottom: Balloon dataRHESSI Spectrum

Best fit: T=47MK thermal

Analysis Results (preliminary)•••Spectrum consistent with single-temperature thermal emission
with T=47 MK.
Microwave (4GHz) shows corresponding emission at 4GHz.
Possible interpretations:•Hard X-ray emission dominated by 47MK thermal emission,
nonthermal component only visible in microwave.
•Superhot component absent; “47MK thermal emission” isactually multiple nonthermal components.

Summary••••

2.6 keV resolution (at 60keV) achieved using 1cm2 CdTedetectors.
-20 °C detector temperature achieved by passive cooling.
Successful observation of a class M1.1 solar flare.
First successful scientific observation using CdTe detectors.