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Produced by the NASA Center for Aerospace Information (CASI)
Principal Investigator

Robert P. Lin

GRANT NSG-7592

Lo

r

High Resolution X- and Gamma--ray Spectroscopy

of Cosmic X-ray Sources

FINAL REPORT

February 1, 1979 April 30, 1983

Submitted by

Space Sciences Laboratory

University of California

Berkeley, California 94720

September 1, 1983

Prepared for

NASA Headquarters

Washington, D.C. 20546

(NASA-CR-375368) HIGE RESGLUTION X- AND NB4-18348

GAMMA-.RAY SPECTROSCOPY OF COSN:IC X-RAY

SOURCES ;Final .Report, 3 leb. 1979 - 30 Apr.

9983 (California U.aiv.). 22 p HC A02/M.F A01 Unclas

03B G3/'93 15140
1. Introduction

This grant, NSG-7592, and an accompanying grant (NSG-7527, from NASA's

Solar Physics Division) provided the fureds to develop, fabricate and fly a

balloon-borne Ii- and 7-ray instrument, This instrument has the highest energy

resolution of any instrument flown to date for measurements of solar and

cosmic X-ray and 7-ray emission in the 13 -> 600 keV energy range. The purpose

of the solar measurements was to study electron acceleration and: solar flare

energy release processes. The cosmic observations were to search for cyclotron line features from neutron stars and for low energy 7-ray lines from

nucleosynthesis.

The instrument consists of four 4 can diameter, 1.3 cm thick, planar intrinsic germanium. detectors cooled by liquid nitrogen and sm-rounded by CsI and

Nal anti-coincidence scintillation crystals. A graded z collimator limited the

field of view to 3 0 x 60 and a gondola pointing system provided 0.3° pointing

accuracy.

A tote,' of fo ur flights were made with this instrument. Additional funding

was obtained from NSF for the last three flights, which had primarily solar

objectives. A detailed instrument description is given in section II. The main

scientific results and the data analysis are discussed in section III, with current

work and indications for future work summarized in section IV. A bibliography

of publications resulting from this work is given in Appendix. A. Appendix B consists of abstracts of talks given to the American Astronomical Society on this

work.

A change of principal investigators was made after 1976-79, the first year

of NSG-7592 and NSG-7527, from Professor Kinsey A. Anderson to Dr. Robert P.

Lin.
2

This investigOlon was a collaborative effort involving investigators at the

,Space Sciences Laboratory and Lawrence Berkeley 'Laboratory at U. C., Berkeley; U. C,, San Diego; and Centre d'Etude Spatiale des Rayonnements in

Toulouse, Frat.de. Their names and addre!ises are listed, below:

Dr. Robert P. Lin

Professor Kinsey A. Anderson

Space Sciences Laboratory

University of California

Berkeley, CA 94720

415/6+2-1149

Dr. Richaret Pehl

Lawrence Berkeley Laboratory

University of California

Berkeley, CA 94720

Dr. Michael Pelling

Dr. Janes Matteson

Dr. Lawrence Peterson

Center for Astrophysics and Space Sciences

University of California, San Diego

La Jolla, CA 92093

Dr,, Kevin Hurley

Centre d'Etude Spatiale des Rayonnements

Universite Paul Sabatier

B. P. 4346

31029 Toulouse Cedex, France
11, Instrument ,Description

In 1979 we began development of a high resolution lnstriament For hard Xray spectroscopy. The instrument consists of an array of :Four ti4 em diameter

4 x 1.3 ern thick hyperpure planar germanium detectors, coolest by liquid nitrogen and housed within an aluminum vacuum cryostat (Figure 1), In turn this is

,j surrounded by active anticoincidencc srintillator shields, State of the art clectronles, including cooled FET preamplifiers with pulsed charge feedback, were

'E used to give an in-flight energy resolution of better than i keV FWhM (full width

,j at half maximum) at 50 keV initially, improving to 600 eV on the last flight.

These figures are the best achieved to date for astrophysical instrumentation.

This instrument has been flown, along with a 300 cm NaI/CsI phoswich scintillation hard X-ray detector, on two successful balloon flights from Palestine,

y Texas, one in October, 1479, the second in June, 1980. The scientific targets on

1,E the first flight were the Crab Nebula, the supernova remnant Cas A, and the k

Seyfert galaxy Markaryan 421, The primary target of the second ;light was the

Sun; several solar hard X-ray bursts, including one very intense flare, were

observed. The Crab Nebula was also observed during this flight.

Two more flights were launched from Brazil in April and November, 1982,

For these flights, a smaller gondola carrying only the germanium detectors

without the 300 cm2 phoswich scintillator, was used. The active galaxy Cen A,

the binary X-ray source GX 1+4, and the Galactic Center were observed in April,

and the. Sun in November. Improvements have been made to the instrument

based on the experience gained from each flight.

Qerman.ium Detectors

The detectors are tat ricated from p type germanium; one face is an n+

diffused lithium positive high voltage contact, while the other face is a p + boron

implant signal contact. They are operated as reverse biased diodes with their
rIPLIER .S

2 SLAT

ATOR

)ETECTO

DTAL AARn

ORIGINAL PAGE ig

OF POOR QUALITY

i

HIGH RESOLUTION X-RAY BALLOON INSTRUMENT

FIGURE la - Schematic of germanium detector system
r

w

FIGURE lb -Instrument Module The high

resolution X-_rav spectrometer and large

area Phoswich detector are co-aligned 'gin

a common elevation gimbal mounting. The

two systems have identical collimation,

3° FWHM in elevation and 6° FWHM in azimuth. Observations are conducted using

"elevation chopping" in which the source

is tracked for one-half of the observing

time and background accumulation is divided equally between a position 5 degrees

above and below the source in elevation.

ORIGINAL, PAGE 19

OF POOR QUALITY

PHOSW4CH DETE

DEWAR , AND COLLIMATO

SPECTROP"ETER

COLLIMATOR

SPEC

PREA

PHOS

cl<<,

CRYOSTAT
volumes fully depleted of free carriers and with a field strength of N 1 kV/em.

The detectors are held in boron nitride cups with pressure-loaded indlum pads

(to maix the electrical nontact), and they are housed in separate aluminum

modules for isolation. These sit within an aluminum vacuum cryostat, and are

cooled to 95°K with liquid nitrogen. The liquid nitrogen coolant is kept at 12

p.s.i. over the ambient pressure by venting the bQ!Ioff gas through a relief valve.

Photons enter through a 0.06" thick x 4.5" diameter beryllium window, and pass

through 4 crn diarnoter holes in the cold plate to enter the detectors through

their boron implant side.

Shields and Collimator

The a, give anticoincidence shield is a modification of a balloon-borne

cosmic X-ray experiment designed, built, .and flown by Space Sciences Laboratory and C. N. S. R. Toulouse [Hurley and Duprat, 1974; Anderson and Mahoney,

1974; Mahoney, 1974]. The active shield has three parts. The phoswich shield is

a central 5 inch diameter x 1/4 inch thick NaI (TI) suintillator optically coupled

to a 5 inch diameter x 2 inch thick CsI (Na) scintillator; a single photomultiplier

tube (PMT) views bu h. The annular shield., a 9 inch outer diameter x 2 1/4 inch

long annulus of Csl (Na) -dewed by 6 PMT's, surrounds the phoswich crystal. In

front of these is the collimator shield with an 6 inch outer diameter and 5 inch

inner diameter x 2 inch thick of CsI (Na;^ viewed by 4 PMT's. All of the shield

lower level discriminators are set to -30 keV. A shield event triggers a 14 μsec

logic signal used for anticoincidence.

Passive shields are used within the cryostat. These are 0.125 inch thick

tantalum shields covered by 0.013 inch of molyb&,,num to prevent tantalum

fluorescent X-rays from reaching the germanium detectors. Indium is used

between the Ta cold plate shield and the detector modules to provide both good

thermal contact and X-ray shielding. Surrounding the cryostat feedthrough

R
ring and directly above the active shields, there is an additional annular shield

of 0.125 inch lead.,

The graded z slat collimator is made from three 10.1 cm long sections,

each consisting of eleven 0.7 mm thick plates, spaced by 1 cm. The plates are

of 0.1 mm Ta, covered on both sides by 0.3 mm tin flashed with copper, The colliniator walls are lined with 2 mrn of lead, Two collimator suctions are stacked

to define a 2.6° FWHM elevation angle field of view (FOV), while a single orthogonal section defines the 5.2 11 FWHM cross-elevation angle FOV, The finite slat

thickness reduces the on-axis transmission to 85%. Above about 300 keV, photons begin 0 leak through the collimator.

Detector Electronics

Each of the four germanium detectors has an independent signal chain,

including a preamplifier, dual shaping amplifiers, pulse stretcher, active baseline restorer, and a 4096 channel pulse height analyzer (PHA). An electronic

block diagram is shown in Figure 2. Each detector is D,C. coupled to a low noise,

charge-sensitive preamplifier whose first stage is a Solitron 310 FET operating

at — 1.5011 K mounted within the detector ,nodule. A key element of the low noise

electronics is the pulsed charge feedback reset system [Landis et al,, 19821

During reset, which occurs -10 times a second, the signal processing electronics are disabled for —200 μsec.

The output from the preamplifier goes into dual shaping amplifiers. The

slow shaper-amplifier-discriminator (-10 Asec shaping tirne) converts the

preamplifier signal into a unipolar pulse, The peak is detected and, converted to

a 12 b ^ PHA word by a run-down Wilkinson-type analog to digital converter for

which a full scale event takes 1 millisecond. The fast shaper-amplifier

discriminator (-400 nsec shaping tune) gives fast pulses for detector-detector

coincidence, pile-tip rejection, tinning, and rate accumulations. This dual
OF, POOR QUALITY

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43 
fast/slow amplitler system, together with the active basoline restorer, allows for

single detector count rates in excess of 20,000 counts/second without spectral

► .` distortion.

The bias voltage for each germanium detector is supplied through one of

i

f four separate high voltage filter boxes, powered in pairs by two separately cones 

mandable (on/off only) high voltage supplies. Each detector also has a 

l separately commendable pulse generator, Approximately every three hours

during an observation, they are turned on for several minutes with a

w20/second pulse rate for electronic calibration.

DIgital. Electronics

Each detector event is encoded into the telemetry stream in a 20 bit word,

12 bits for the PHA, 2 bits for the detector identification, 4 bits for fine timing

to 0.5 millisecond, 1 bit for pair detector coincidence, and I. bit for shield coin- 

cidence. Those Compton events which trigger two detectors set the pair detector coincidence bit. There are two commandable modes for detector shield

anti-coincidence. In one mode, ail detector events are analyzed and encoded

with the shield coincidence bit either set or null, In the "shield veto enable"

mode, the shield logic signal inhibits the PTA's from analyzing any shield coincident events. Polling logic queries each detector's signal rf qdy flip-flop in turn

for the next event to encode into the telemetry. The telemetry system can handle up to 500 total germanium detector events/second,

Scintillator events, fast rate scalars, slow rate scalars, and gondola status

words are also transmitted. The 16 ten bit fast rate scalars, read out every

0.125 sec., accumulate separately each detector's valid event rate both in coincidence (4 rates) and in anti-coincidence (4 rates) with the ac Live shields, the 3

anti-coincidence shields' rates, and the seintillator's rates over 5 energy ranges

22-33, 33-60, 60-120, 120-235, and >235 keV.
The slow rags, each read out every 8.102 senonds. Inuludc cauh ger

innniurn detecLor.'s live time and reset rate. During the time a signal chain is

available, a 128 kHz crystal oscillator advances that detector's live time

counter. The detector resat rates can be replaced by the pair detector coin.

oidenco rates on command. 

For the last two flights this system. was modified to accommodate only the 

germanium detectors, since the phoswich scintillator was not flown.

Burst Memory 

A 850 Kbit burst .memory was installed before the June 1980 flight to store

the total germanium detector event rate and the 3 Lowest energy scintillator

rates. After automatically trigg-oting on an elevated scintillator rate, the

memory stares the-sa four fast rates every 8 milliseconds, until the memory is

half full, then; for 32 msec until filled. This accumulates N 5 minutes of high time

resolution rate data in 65,536 10 bit words. Then on command, the memory is

read out in 65 seconds, replacing the normal germanium detector telemetry, 

Before the 1982 flights this memory was enlarged to 2.6 megabits and

modified to store Ge detector events rather than rates during a burst.

Tracking System.

The gondola uses an alt-azimuth pointing system ,referenced to gravitational vertical and the local magnetic field direction. The balloon payload

rotates beneath a field aligned magnetometer table to the target azimuth computed on the ground and sent up periodically by command. Concurrently, the

thermally insulated instrument cage housing the germanium instrument and

coaligned phoswich scintillator is rotated to the computed elevation angle. The

pointing system automatically tracks a source in between ground commands,

which are sent every 15 to 30 minutes.

1
A similar pointing systera was used In the lightweight gondola for the 1082

flights.
111. ScIont;l a Results

A total of four balloon flights were made with this Instrument, the first two

from Palestine, Texas, the last two from Uburaba and Cachoeira Paulista in Brazil. Data were obtained in all four flights from this Instruniunt.

In the first sight on October 17-18, 1979, the Crab nebula (5 hrs), Cas A (3.5

hrs) and Mk 421 (5 'ms) were observed. Ling et al. had reported an apparent

cyclotron line feature from the Crab at 73 keV. We found no line emission at 73

keV (1 keV farther) with a 3 a upper limit of 1 x 10-'3 ph / cm2 sec. From the

observation of the recent supernova remnant Cas A we obtained a 3 a upper

limit of 1 x 10"3 ph / =2 see for the combined 75,4 and 67.9 keV lines from the 

decay of Ti44 an isotope with 48 year half life predicted to be produced in

nucleosynthesis.

The T-cond flight on 27 June 1980 concentrated on the Sun (3 hrs). A large

rare observed at 1614 UT in which a new component of solar hard X-ray was

discovered. This component was emission from a closely isothermal, very hot,

-35 x 100 °K plasma. The spectrum is so steep that it is unmeasurable by scintillation detectors [Lin et al„ 1981].

A second major discovery of this flight was that of solar hard X-ray

microflares, hard X-ray bursts from the Sun too small to be associated with a

flare or subflare. These occur at the rate of almost one per flve minutes above

a threshhold of w7 x 10-3 ph / cm2 sec keV at 20 keV. The germanium detectors

provided accurate energy spectra for the larger of these microflares. These

showed that these bursts had power law, i.e., non-thermal, rather than thermal

spectral shapes (see attached preprint, Appendix A).

This flight also showed that the Sun was no(-, a source of 73 keV flue emission. A 3Q tipper limit of 1:.5x10 -3 ph / cm2 sec observations, because of their

instrument's wide fleld of view, was inconsistent with either the Crab or the Sun
OF POOR QUALITY

as the source of Lhe 73 koV line.

Finally, an add4lonal 2.5 hours' observation of the Crab again gave a negative result for the '1'2 keV line 3 a upper limit of 1 x 10° s pli / cm2 see, The Crab

data from the First two flights were later re-analyzed to look for a transient 73

keV line occurring only during the pulsed emission from the Crab pulsar. Such

line emission was reported by Mrickman et al. [1982]. No evidence for such a

transient at 73 keV wsspresent in these 

1! or the third and fourth flights a lightweight gondola was used with sixtaller

(11 million ou ft) balloons to facilitate launches from Brazil. Thus only the germanium detectors were flown. Becaus r, of unfavorable winds at dawn in Uberaba, the third flight was launched in the evening of April 19, 1962. One or the

two-detector high voltage power supplies failed upon balloon ascent, leaving two

germanium detectors (25 cmz ) operating, As expected, the background in Brazil was about ,half of that in Texas. The cosmic sources observed were Cen .A (3

hrs), GX 1+4 (5 hours), and the Galactic, Center region (1 hr). Due to telemetry

interference from. a Brazilian TV station (radiating outside its assigned band)

the data analy.p ;.s has been slow and complex. No results are yet available.

The final flight was launched in the morning of November 24, 1982, from

Cachoeira Paulista in Brazil, following several drenching rainstorms, The elevation drive jammed, so that only 40 minutes of solar data were obtained in the

six hour fight. No large flare hard X-ray bursts were observed, but detailed

data analysis has yet to be done.
IV. Current and Puture Work

Mr. Richard, Schwartz, a graduate student, is currently finishing his thesis

on the results from this balloon instrument. The major part of his thesis deals

with the large flare of 27 June 1060, both 411: new hot isothermal component

and the non-thermal electron acceleration. Ile has found that there may be as

many as three distinct electron acceleration phases in this flare. The data also

provide, for the first time, hard X-ray spectra accurate enough to show that the

> 30 keV emission can not be due to a single very high temperature Uiermal

plasma,

The analysis of the solar hard X-ray m1croflares is just beginning. Comparisons with SMM and ground based data are needed to determine the origin

and morphology of these tiny events, Further measurements are clearly

needed to see whether these hard X-ray .rricroflares generally accompany most,

if not all, transient energy releases by the Sun.

References

Landis, D. A., Goulding, F, S., and Pehl, R. H„ 1971, LURE Trans, Nuct ,Sci, NS-113, No. 1, Part 1, 115.

Lin, R. P., Schwartz, R, A„ Pelling, R. M„ and Hurley, K, C., 1961, . Ap. J. 251, L109.

Ling, J. C,, Mahoney, W. A„ Willett, J, D„ and Jacobson, A. S„ 1979, Ap. J 231., 896,

Strickman, 11. S., Kurfess, J, D„ and Johnson, W. N., 1982, Ap, J. 255, L23-27.
Bibliography of Publication s Supported Wholly or in Part by NSG-7592

Bai, T., ki. S. Hudson, R. M. Palling, R. P. Lin, R. A. Schwartz and T. T. von

Rosenvinge, First-order Fermi acceleration in solar flares as a mechanism for

the second-step acceleration of prompt protons and relativistic electrons,

Astrophys. J., 267, 433, 1983.

Lin, R. P., Solar flare energetics, in Gamma Ray Transients and Related Astrophysical Phenomena, ATP Conference Proc. No. 77, ed. by R. E. Lingenfelter et 

a1. 0 p. 419, American Institute of Physics, New York 1982.

Lin, R. P., R. A. Schwartz, R. M. Pelling and K. C. Hurley, A new component of

hard X-rays in solar flares, Astrophys. J. Lett,, 251, 109, 1981.

Lin, R. P., R. A. Schwartz S. R. Kane, R. It. Pelling and K. C. Hurley, Solar

hard X-ray microflares, submitted to Astro h s. J.Lett., 1983.

Schwartz, R. A., High resolution of hard X-ray spectra of solar and cosmic

sources, Ph.D. Dissertation, Department of Physics, UC Berkeley, in preparation,

1983.

w..^ +^h.. rw .^^.Ip•.+4u^^•.. .w ^... ...n ^.o.a.. .... .tY i.lfl•w-
APPENDIX B

Abstracts of Talks Presented to the American Astronomical Society

.,

., .. +mow 
ORIGINAL PAQ9 14

OF POOR QUALITY

92.09.09 High Resulutton Observntlon of She Crab Nob

61C

-

ula, R. SUTZ And R. .^ LUN, U, Calif. BerKeley_,_ SSL;

R. PELLINC, U. Calif. San • 0i, vu ; and K. HURLEY, C.E,S.R.,

Toulouse. France - Ot fligot from Palestine,

Texas ca October 17-18, 1979, wa observed the Crab Nebula, cam A. and Markaryan 421 with an x-ray spectrometer

consisting o f an actively shielded array of four liquid

0.trogen coded planar germanium detectore with a total

area of W cmz . The speetrnl revolution was t. 1 keV

$WHM over the instrument's energy range of 30 - 200 keV.

We Rind no evidence for Line emission from the Crab over

this range. In particular for the line feature at 770

t 1 keV with intensity 3.8 a 10

-3

 photons/cm = sec (4o)

previously reported by Lln; at d1., (1979); we obtain a

3d upper limit of 2 n 10-1 photannlcm2 der.. With their

best fit line width of 3.2 keV 1t1HM this feature, if

present, should have been observed it 4.7a significance

in our data.

June, 1980

University of Maryland 

- ^wiaa
®RIQINAL ME 10

OF POOR QUALITY

PT aer limits t o the 68 and 78 ke V T144

line emission from t t"sup e e rnova remnant Ca ste,

R. A, Schwartz, R. 

P^i44

Lin, YCQ, R. M. Pelling, m..

The decay of , produced during explosive

nucleosynthasis, results in the emission of two low

energy gamma ray lines of nearly equal strength at

73.4 keV and 0.9 keV. Using an array of four planar

germanium detectors with a total area of 50 cm 2 and

< 1 keV resolution, we observed the supernova remnant

has A for four hours on Oct. 17-18, 1979, on a balloon

flight from Palestine, Texas. For a line width < .1 KeV

we obtain a 3o upper limit of 1 X 10 -3 ph/cm2 sec for

each line.

January, 1981

Albuquerque, New Mexico
R.P. L- in, - Schwartz, . UC - BERKELEY -, M, Pelli q UCSD.. G. Hurford, CALTECH

In a balloon 7_fl_iT g`ht on June 27, 1980 we observed an

intense solar flare x-ray burst at N 1613-20 U.T.

with a 5 0 cm2 array of four planar germanium detectors

and a separate ,, 300 cm2 phoswich scintillation

detector. These provided the best hard x-ray flare

observations ever obtained in terms of energy resolution

N6 I keV), time resolution (-. 8 ms) and sensitivity.

We have discovered a new hard x-raycomponent occurring

during the decay of the burst which is characterized

by a very steep spectrum, dJ - E-11.2 between 20 and 40

d 

keV with a significant excess above that energy, This

component is too energetic to be an extension of the

soft 10-20 X 106 O K thermal spectrum. During the

burst maximum the energy spectrum is observed to be

very accurately power law between 20 and > 200 keV,

thus ruling out single or a few temperature thermal

models. Finally the 10 GHz microwave intensity observed

at Owens Valley on a 50 ms time scale appears to be

related to the integral of the hard x-ray intensity,

indicating that it is not produced by gyrosynchrotron

emission but perhaps by bremsstrahlung from a very hot

plasma produced by the energy loss of the hard x-ray

electrons.

January, 1983. (Solar Physics Division)

Taos, New Mexico
OF POOR QUALITY

A search for line emission from the sun in

the 20-200 keV en,ergy . range. R. Schwartz, R. P. Lin,

2v3, 11. 14. Felling, W181).

Ling et al. have reported a line at 73.3 kjV with

intensity of 3.3 X 10` 3 ph/cm2 sec (ba) and a MIM width

< 2.5 keV from the Crab Nebula. However, both the Sun

and the Crab Nebula were in their field of view. The

observed temporal variation of the line feature fits

equally well to the transit of the Sun or of the Crab

Nebula. On two separate flights of our high resolution

( 1 keV) four germanium detector array we observed the

Crab without the Sun in our field of view. No line emission at. 73.3 keV was detected 'to a 3a upper limit of

1 X 10^ 3 ( cm2 sec ) -1 . Ling et al. suggests lead flourescence as a possible source for the line emission.

We have also searched for line emission from the

Sun. 0ur3 observation sets a 3a upper limit of

1.2 X 10^ ph/cm2 sec for narrow line emission at 73.3

keV. Also we will present the results of a search for

quiet time continuum emission from the Sun.

References

1. Ling * J. C., Ap. J., 234, 753, 1979•

January, 1981 (Solar Physics Division)

Taos, New Mexico
Very High Spectral and Tem p oral Resolution

Observation of a Solar bard X-raX Burst, R. Schwartz,

R. P. Lin, UC BERKELEY, M. Pelling, UC SAN DIEGO, K.

Hurley, CESR TOULOUSE

During a balloon flight on June 27, 1980 we observed an

intense solar Aare X-ray burst using a 50 cm 2 array of

four planar germanium detectors and a separate 300 cm2

phoswich scintillation detector. Using the narrow energy resolution of the germanium detector (ti 1 keV.from

15-200 keV) and the 128 cosec. saintillator rate: channels, we have made a detailed analysis of the hard X-ray

flux during the impulsive phase (1614-1617:30 UT). The

flare consists of a series of Elementary Flare Bursts

(EFB), each with a FWHM of 3-13 seconds at around 100

keV. These bursts become broader at lower energies

cohere the burst profiles merge into a smoother time profile. The EFB time profiles do not become narrower at

enemies above 100 keV, Also, there is a delay seen at f

the highest energies which is due to a second step acceleration mechanism. Additionally, 50-100,keV electrons are present throughout the decay phase (1618-1614

UT) and show both impulsive and gradual behavior.

June, 1983 (Solar Physics Division)

Pasadena, California