OSO-I data analysis for comparison of solar X-rays and microwave radiatio

White, W. A.

English

NASA Technical Reports Server

gI
f , : jP - t ,
J
SOLAR X-RAYS: A COMPARISON WITH MICROWAVE
RADIATION
W. A. WHITE
Analysisof data fromtheOSO-1 satelliteshowsthat solarX-raysshortwardof 10Angstroms
exhibit a violent dynamicbehaviorwhich howevercontainswithin counterpartsof the some-
what less dramticbehaviorof the solarmicrowaveflux. Specifically,the solar X-ray flux con-
tains: (1) a slowly-varyingcomponent,(2) "gradual rise and fall" bursts, and (3) impulsive
bursts. The OSO-1datashowsthe firsttwo to be relatedto their microwavecounterparts,and
the empericalrelationsare given in this paner. Observationsat 10 Angstromsof the third
component(impulsivebullsts)could not be associateddirectly with microwaveobservations
owing to the ext]_medisparityin _ensitivitirsof the two methodsof observationof this phe-
nomenon. However,observatiol_sby Frost (reportedat this Symposium)of solar X-rays in
the 20 Key--100 Key regiondo s,ow a directcounterpartof the microwaveimpulsiveburst.
!. INTRODUCTION The conversion efficiency as a function of
With the launching of the OSO-1 on March 7, wavelength is shown in Fig. 1.
1962, it became possible for the first time to point 1.0 _
instruments at the sun accurately and continu- ,,_
ously for entire daylight portions of a satellite
orbit; for the 550-Km orbit of OSO-1 the_ ob-
serving time intervals were the order of one hour /I/I /XEUON ___ \
each, separated by darkness intervals of about
two-thirds of an hour. The observing periods
were long enough to disclose some interesting / I/ C0NV_S!_ WlN00W \
dynamic eflects which would be difficult to study 0.1 / V EFFICIENCYTRaNSmiSSION1
otherwise. /2. SENSORCHARACTERISTICS
OSO-1 provided coverage of the solar X-ray _ -THEORETICAL x
radiation near a wavelength of 10 Angstroms by _ XEXPERIMENTAL
means of an ion chamber whose characteristics are /
given in Table 1. %BLZ1 0.01 1 n I I , J
0.1 0.3 1.0 3 10
WindowMaterial......................... Beryllium
WindowThickness........................ 9.005 inch A INANGSTROMS
jtal WindowArea(Twochambersin 3.38 cmt Fzoua_ 1.--OSO-1 ion chamberconversionefficiencyas
parallel) functionof wavelength.
AbsorbingGas........................... Xenon
Gas Pressure............................. 780mm Amplified ion-chamber current was sampled for 2
Ion ChamberDept at NormalIncidence..... 2.19 cm seconds every 20 seconds by the telemetry.IonPairspererg......................... 2.8 (10)_°
The full-scah sensitivity of such a broad-band
sensor is, of course, dependent upon the shape of
*Published aa Ooddad ,Space RicAt Ccnt_ Docum_t X- 810-84-41,
February 1964. the input spectrum. It has been shown _ that
319
1966028656-342
https://ntrs.nasa.gov/search.jsp?R=19660028664 2020-03-11T17:49:54+00:00Z
320 PITBLICATIONSOF GSFC, 1964: I. SPACE SCIENCES
for non-flare periods it is reasonable to a_sume a 36
spectral shape consistent with a 2.8(10)6°K Plasma _32 ! .! It _f! _I_
composed of ionized hydrogen and helium in the _ 2e i _:
ratio of their solar abundances. Over the fie- ,_ .
p _,2_
quently used band limits of 2-8/_, the full-scale _ 20 i. _ __1 ,
sensitiv:oy is then 3.6(10) -4 ergs cm-2 sec -1. ,_ E 16
3. COMPONENTSOF THE SOLAR X-RAY FLUX _ 12 ,Changes in the solar X-ray flux as observed by 6 ! i . MEASUREDOHOSO.I
+ PREDICTEDFROM2600-McFLUX
OSO-1 occurred over a broad range of time scales; 4 .... PREDICTEDFROMCaPLAGEDATA1962
from fractions of a second to many weeks. In 6 12 16 24 361 5 I1 17 23 291 5 11 IT
particular, counterparts to the microwa', e slowly- MARCH APRIL MAY
varying component and to the microwave "grad- FIGURE2.--Slowly-varying component of solar x-ray flux
ual rise and fall" burst are clearly seen.
The markedly dynamic character of the solar It is fruitful to look in more detail at the rela-
X-ray flux as contrasted with the 2800-Mc radia- tionship between the calcium plages and the X-ray
tion should be emphasized; for instance, on only flux. For example, is the brightness of a plage in
3 occasions out of 70 days (7 March through 15 Ca emission a measure of its brightness in X-rays?
May, 1962) was the X-ray flux "quiet") i.e., free "so. we might expect a relationship somewhat as
from bursts) for an interval of as much as 8 hours, lollows:
The brightness of a plage in Ca K emission is
3.1 Slowly-Varying Component expressed by an Intensity Number assigned by
Solar rotation markedly affects the X-ray flux. the McMath-Hulburt Observatory apparently on
In fact, if one defines the non-burst X-ray flux the basis of a subjective estimate of relative densi-
background as the minimum flux reached in a 6- ties on a patrol photograph; as such, it is likely to
hour interval and evaluates this for a succession c: be approximately logarithmic.
such intervals, one finds that for the spring of 1962 The other routinely reported parameter charae-
the 0SO-1 data empirically fits the relation terizing a Ca plage is its area. Since we are deal-
ing at X-ray wavelengths with a volume source,
(I)2-8A _--_-kl ((I)--(I)0)?.800Mc erg cm-2 sec -t (1) an assumption has to be made regarding the de-
pendence of the X-ray source volume upon the
That is, the daily mean non-burst X-ray flux is area of the plage. It is found from the 0SO-1
proportional to the difference between the daily data that it is much better to assume that the
mean of the 2800-Mc flux and a value of 2800-Me thickness of the X-ray source is proportional to
flux which is presumably a "quiet sun" asymptote the mean plage diameter, than to assume a con-
for the appropriate phase of the solar cycle. _ stant thickness. The volume of the i th plage is
Note that any such quiet sun asymptote in the then given by
X-ray flux is zero, at least to the sensitivity and (dV)_ ¢X (A_)s/s
a_uracy of this empirical fit. Apparently a truly where A_ is the reported area.
quiet sun, stripped of plage, would be dark in The hypothesis that the X-ray flux arises from i-
X-rays while still emitting an appreciable 2800- such a plage-associated volume sources with '
Me flux. Fig. 2 shows the measured mean non- X-ray brightness proportional to Ca K brightness
burst X-ray flux and the index values calculated can be written as
from Eqn. (1) with K_=1.4(10) -b, (¢),00 _ in
units of lO-_Wm-2(c/s)-t, and (_o)_00M,ffi73 such ¢_-8a _K._ _(A_)S/2(b)l_ erg cm -2 see -1 (2)
units, where A_ is the volume af the i th plage in thou°
I White, W. A., "Sohr Xoraye' Slow Variatlona and Tra_ient Events" sandths, I is the McMath Ca K intensity number,
--COSPAR IV, Warsaw, June1963. NASAGSFCDocument and k_ and b are constants to be empiricallyx-e14-ea-loa.
, A.S.Co_i_gton,d_. A.Hard,r.ADtroph_.Jolt._S*(_0) _S_. determined from the OSO-1 data.
1966028656-343
gSOLAR PHYSICS 321
The best fit to date is plotted in Fig. 2, for 3_,
plages of area > 1 thousandth, for
.*°%.
" • X-RAYBURST0S0-1
__ 28 "'. .ARC.o,w.:,
k_=0.134 (10) -5, 1 _ "'.
j and for _ •
..
"....
Plage data reported by the McMath-Hulburt _ 20 "......
Observatory and published in the CRPL Bulletin
' was used, with times of rising and setting of the "...........".
X-ray sources calculated from plage Central _2Meridian Passage minus and plus 7.8 days respec ...... "
tiveo. This corresponds to an assumed source -011_ 01s0 01is 0_0_--_0s 0fi0,r
• height extending to some 21,000 Km above the FmVRE3.--X-ray burst OSO-1 March8, 1962
photosphere.
Two types of gross discrepancy can be seen
between the X-ray flux and the hypothetical in- was in all cases accompanied by an off-scale X-ray
dices derived from plage and 2800-Mc data. The burst; larger bursts at 2800-Mc were of course
_ first type, exemplified by the periods March 12- also off-scale in X-rays, but again times of onset
14, April 10-14, and May 1-2, show too low a and recovery were found to agree with the corre-
value for the plage-derived index. Each of these sponding times for the accompa,lying X-ray burst.
periods saw the birth at one or more small plages It is important to note that the relationship be-
:_ upon the disc which were not included in the index tween burst flux at 2800-Mc and at 2-8 A is dif-
computation of Fig. 2. The second type of dis- ferent from the relationship between the slowly-
" crepancy is seen during the period May 3-7 for varying component at 2800-Mc and at 2-8 A.
which the index derived from the 2800-Mc flux is As has been shown (Eqn. 1), a change in 2800-Mc
low. This period included a large plage (McMath slowly-varying component of 1 flux unit is accom-
6412) which was reported to be declining in Ca K panied by a change in 2-8 A flux of about 1.4
: intensity; this plage contained a single sunspot (10) -_ crg cm-2 sec -_" whereas a burst type change
which was seen to die on the disc. at 2800-Mc of 1 flux unit is accompanied by a
: 3.2 Gradual Rise and Fall Bursts change in 2-8 A flux of at least 30.(10) -_ erg cm -_
see-t. This increase in the X-ray/microwave
•_ Superimposed upon the X-rz:." -!owly-varying ratio of more taan 20 times is suggestive of a dif-
component and occurring so frequently as to make ferent physical process being responsible for the
difficult the finding of intervals comple*ely free two phenomena.
from their effects, are X-ray bursts analogous to Several apparent associations of certain X-ray
the "graduaI rise and fall" bursts seen ;n solar bursts into groups displaying a definite pattern
microwave radiation. A complete statistical were observed; Fig. 4 shows such grouping. Simi-
analysis of the X-ray bursts observed by OSO-1 lar groupings are present in the data for the first
has not yet been made, but typical on-scale bursts week in April 1962; in fac_, the one-particular
" (see Fig. 3) have rise times of 2 to 4 minutes and March group shown in Fig. 4 appears to have an
fall times of 10-20 minutes. However, many exact April counterpart 27.1 days later with
bursts carry the experiment output offscale; for identical time-separations between events and
these, the duration of the event can be as long as with identical peak excursmns above mean back-
6 hours. A comparison of the X-ray data with ground level. In addition to these two groups,
2800-Mc records (kindly made available by A.E. two others each having 4 members and one other
Covington) taken at Ottawa shows that all 2800- having 3 members were found. For all five
Me gradual bursts had a time-coincident counter- groups, the envelope joining the peaks of the
par* in the X-ray data. A peak amplitude on bursts within a group is a straight line of slope
only 1 or 2 units of 10-_ W m-_ see -t at 2800-Mc +_1.51(10) -_ erg cm -_ see -_ for wavelengths be-
1966028656-344
322 PUBLICATIONS OF GSFC, 1964: I. SPACE SCIENCES
2a tween 2 and 8A; three groups displayed positive
_\.. slopes, two groups negative.
\
\
\ 3.3 Impulsive Bursts
|_ \\\ Several instances of very fast bursts (entire
"-_'BI' t _ If\\ _12t/ _ \\\ duration le_s than 2 minutes) were seen by Frost
\\ (reported at this Symposium) from an OSO-1
sensor responsive to photons of energy greater
_ e}- - \_- than 20 Key. For every one of these instances
_i4__ _ -., t:'/_ I--_ the lower-energy ion-chamber channel was off-
ffi ! scale prior to and during the time interval of the
1200[_ m'000o'0006'00 ' ' , , , , impulsive burst. It is indeed unfortunate that
_2oo_ moooeoo12oo!_ oaoo we are thus unable to obtain an X-ray/microwavewc, ? MARC.0 UARC.9
umwt_Ju.Tat[lu2 ratio for an impulsive burst to compare with the
values obtained for gradual bursts and for theFz(]traE 4.---Solar x-rays (2-8A) showing grouping of x-ray
bursts, slowly-varying component.
1966028656-345


Solar X-rays - A comparsion with microwave radiation

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server