High sensitivity and high time resolution solar observations at 90 GHz (lambda = 3.3 mm) have identified a unique impulsive burst on May 21, 1984 with emission that was more intense at this frequency than at lower frequencies. The first major time structure of the burst was over 10 times more intense at 90 GHz than at 30 GHz, 7 GHz, or 2.8 GHz.Only 6 seconds later, the 30 GHz impulsive structures started to be observed but still with lower intensity than at 90 GHz. Hard X-ray time structures at energies above 25 keV were almost identical to the 90 GHZ structures (to better than one second). All 90 GHz major time structures consisted of trains of multiple subsecond pulses with rise times as short as 0.03 sec and amplitudes large compared to the mean flux. When detectable, the 30 GHz subsecond pulses had smaller relative amplitude and were in phase with the corresponding 90 GHz pulses

Correia, E.

Costa, J. E. R.

Dennis, B. R.

Kaufmann, P.

Vaz, A. M. Z.

English

NASA Technical Reports Server

General Disclaimer 
One or more of the Following Statements may affect this Document 
 
 This document has been reproduced from the best copy furnished by the 
organizational source. It is being released in the interest of making available as 
much information as possible. 
 
 This document may contain data, which exceeds the sheet parameters. It was 
furnished in this condition by the organizational source and is the best copy 
available. 
 
 This document may contain tone-on-tone or color graphs, charts and/or pictures, 
which have been reproduced in black and white. 
 
 This document is paginated as submitted by the original source. 
 
 Portions of this document are not fully legible due to the historical nature of some 
of the material. However, it is the best reproduction available from the original 
submission. 
 
 
 
 
 
 
 
Produced by the NASA Center for Aerospace Information (CASI) 
https://ntrs.nasa.gov/search.jsp?R=19840027193 2020-03-20T21:45:21+00:00Z
I ,
a.
	
j
k,
	
E
RECEIVED BY
r
i
t
.a
41
w
'
r^
^
I
b
,t
i{	 }
m
d
i
fi
`E
i
r	 I
(NASA-TM-87369) A NEW CLASS GF SOLAR BURST
	 N84-35264
WITH .MM-WAVE EMISSION BUT CNLY AT THE
HIGHEST FREQUENCY (90 Gfi2) (NASA)
	
14 p
HC A02/MF A01	 CSCL 03B	 Unclas
G3/92 23169
M	 SECRETARIA DE PLANEJAMENTO DA PRESIDENCIA DA REPUBLICA
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTIFICO E TECNOL6GICO
NAM ST1 IFACIL
CAA rf
	 —
L
.rsS
FACILMY
n SA - MS n AlAA
^ ;
nr^ 1NSTITUTO
	 OI	 PESQUISAS
	 ESPACIAIS y
6.
9	 ')
r	 I
i
r
t
i
^ t
i
Qi) i^
u
c
1.	 Publication NO 2.	 Version 3.	 Date 5.	 Distribution
INPE -3241-PRE/587 August 1984 D Internal ® External
q Restricted4. Origin	 Program
DAS—DRA	 RADIO
6.	 Key words - selected by the author(s)
Solar mm-wave bursts; mm-wave(onZy) bursts; mm-wave and hard X-ray burs ts
7.	 U.D.C.:	 523.745
8. Title	 INPE-3241-PRE1587 10.	 No of pages: 13
A NEW CLASS OF SOLAR BURST WITH. MM-WAVE EMISSION
11 .	 Last page: 12
BUT ONLY AT THE HIGHEST FREQUENCy (90 GHz)
12.	 Revised by
9. Authorship
P. Kau fbtann Pierre Kaufmann
E. Correia 13.	 Authorized byJ. E. R. Costa
A. M. Zodi Vaz
B.R. Dennis*
Nelson
	 e Jesus Parada
Responsible author
Director GeneraZ
14. Mstract/Notes - The first high sensitivity and high time resolution
solar observations at 90 GHz (a = 3.3 mm). have identified a unique impulsive
burst on 21 May 1984 with emission that was more intense at this frequency
than at Zower frequencies.	 The first major time structure of the burst was
over 10 times more intense at 90 GHz than at 30 GHz,
	 7 GHz or 2.8 GHz.	 OnZy
6 seconds Zater, the 30 GHz impuZsive structures started to be observed but
stiZZ with Zower intensity than at 90 GHz.
	 Hard X-ray time structures at
energies above 25 keV were almost identicaZ to the 90 GHz structures-to
better than one second.
	 All 90 GHz major time structures consisted of trains
of muZtiple subsecond puZses with rise times as short as 0.03 s and ampZitu-
des Zarge compared to the mean fLux.	 When detectabZf;, the 30 GHz subsecond
puZses had smaZZer reZative amplitude and were in pr'tase with the
corresponding 90 GHz puZses.'
*NASA/GSFC-LASP
15. Remarks - Submitted to Nature. Supported partially by FINEP.
f
d
F
r
^y
a
i
t
^,	 r
0
W
^r
r
o
A'NEW.CLASS OF SOLAR BURST WITH MM-WAVE EMISSION BUT ONLY AT THE HIGHESTi
FREQUENCY ( 90 Gliz )
P. Kaufmann*, E. Correia*, J.E.R. Costa*, A.M. Zodi Vaz* and B.R. Dennis'
*INPE: Instituto de Pesquisas Espaciais, C.P. 515, 12.200 - Sao Jose dos
Campos, S.P., Brazil
'f-NASA, Goddard Space Flight Center, Laboratory for Astronomy and Solar
Physics, Greenbelt, MD 20771, U.S.A.
The first high sensitivity and high time resolution solar observations at
90 GHz (a = 3.3 mm) have identified a unique impulsive burst on 21 May 1984
with emission that was more intense at this frequency than at lower frequencies.
The first major time structure . of the burst was over 10 times more intense at
90 GHz than at 30 GHz, 7 GHz or 2.8 GHz. Only 6 seconds later, the 30 GHz
impulsive structures started to be observed but still with lower intensity
than at 90 GHz. Hard X-ray time structures at energies above 25 keV were
almost identical to the 90 GHz structures to better than one second. All 90
GEIz major time structures consisted of trains of multiple subsecond pulses
with rise times as short as 0.03 s and amplitudes large compared to the mean
flux. When detectable, the 30 GHz subsecond pulses had smaller relative amplitude
and were in phase with the corresponding 90 GHz pulses.
r
F
1
rt	 y
r
i
i
The past knowledge of solar burst emission at shorter mm-wavelengths is
based on low sensitivity data with relatively poor time resolution (Refs. 1-7). 	 1
Y
9
r`
4a
One of the main results of these previous observations is that certain cm-mm
bursts display turnover frequencies higher than 30 GFIz (i.e.
	 X < 10 mm).
	 One
mx
very large burst exhibited a spectral "flattening" in the range 30-71 GHz4,5^
which was also found for a few other events 7 .	 Another peculiar event has shown
emission at 90 GHz (1 = 3.3 mm) and no emission reported bb patrol in the microwave
range 8 .	 More recently, 80 GHz (a = 3.75 mm) and 92.5 GHz (X = 3.2 mm) solar
a
measurements were started in Japan  and Switzerland 30 , respectively, with
	 10 s.f.u.
0
sensitivity (1 s.f.u. = 10 -Z2 W M-2  Hz-1 ) and 0.3 s time resolution.
The observations presented here were made with the Itapetinga 13.7m, radome-
enclosed antenna, used for the first time at 90 GHz (a = 3.3 mm) for solar measurements
in May 1984. The antenna aperture of U ciency at that frequency is nearly 25 percent at
the zenith and decreases with elevation angle. For solar elevation angles of 60 to 10
degrees, the corresponding sensitivity in the antenna main beam ranged from 0.07 to
0.25 s.f.u. with a time constant of 1 ms. This represents an improvement of more
than two orders of magnitude in sensitivity and in time resolution over all previous
observations at this frequency.
Simultaneous observations were made at 30 Giiz by the same antenna with a
sensitivity of 0.03 s.f.u. and a time constant of 1 ms. Active regions were
tracked at the position of their maximum intensity in one of the antenna beams
(usually the 90 GHz beam), and the flux scales were established by assuming
that the burst sources were coincident in space with the active region maximum
position. Therefore, as a result of the lack of knowledge of the source location,
the flux scales are uncertain but the error should not exceed 50% in the most
-2
4
f$
N
if	 h
E
'	 t
1	
,
I
i
`f
i
i
i
}
ci
P.
.	 i
i
i
t
t
t
any
a
r
0
I'
extreme case. The antenna halt power beam size at 90 GHz was of about 80 aresec at
about 60 degrees of elevation, at the time the burst was observed, and of about
3 arcmin at 30 GHz. The two beams axis separation was of 3 arcmin. The tracking
accuracy was better than 2 aresec r,m.s. Other details of the observational setup
at Itapetinga are published elsewhere 11. Observations were also made at 7 GHz by a
patrol radio telescope using a 1.5 m antenna with a sensitivity of 3 s.f.u. and a
time constant of 20 ms.
Simultaneous observations were also made with the Hard X-ray Burst Spectrometer
(HXRBS) on the Solar Maximum Mission (SMM) satellite 12 . A 15 channel counting
rate spectrum covering the energy range from 24 to 400 keV was obtained with
this instrument every 128 ms throughout the flare.
The 90 GHz impulsive burst that occurred on 21 May 1984 at 1326 UT presented
the unique characteristic of emission at the shortest mm-wavelengths only. It
cannot be included in any known class of solar radio bursts. Figure 1 shows
the impulsive event at 90 GHz, 30 GHz, and 7 GHz and in two hard X-ray energy
ranges, 24-108 keV and 108-219 keV. The mm-wave emission spectrum suggests a
turnover frequency as high as or higher than 90 GHz. The negligible rise at 7
GHz of 4 s.f.u. was confirmed by data obtained at 2.8 GHz showing a < 3 s.f.u.
increase at the same timel3,
The first major impulsive component was observed at 90 GHz nearly 6 seconds
before the first impulsive structure at 30 GHz. Assuming the flux scales are
correct, the first structure, labelled A in Figure 1, reached about 70 s.f.u.
at 90 GHz and 6 s.f.u. at 30 GHz. , The second major structure (B in Figure 1)
reached 56's.f.u. at 90 GHz and 23 s.f.u. at 30 GHz, and the third structure
(C) reached 24 s.f.u.- at 90 GHz and 14 s.f.u. at 30 GHz. The power law spectral
index a in the relation S a fa where S is the .flux density and f is the
frequency is estimated from the 30 and 90 GHz fluxes to be 2.2 for the structure
A, 0.8 for B and 0.5 for C.
-3-
r3
a	 i
a
The hard X-ray time profiles in Figure 1 show a striking similarity to thep^u,90 GHz time profile. Features coincide to within the 128 ms time resolution of
the hard X-ray observations. It is interesting to compare the relative amplitudes,
a	 o
of structures A and B at different X-ray energies and mm-wave frequencies. For
the 24-108 keV X-rays and the 30 GHz emission, structure B is more intense than 	 i
structure A, whereas for the 108-219 keV X-rays and the 90 GHz emission,
structure A is more intense than structure B. This suggests that the 90 GHz
i
emission comes primarily from the higher energy electrons or at least from
ka	
electrons with a harder spectrum: The power law spectral index y in the relation
	
i
I « 8 Y where I is the X-ray flux and a is the photon energy was estimated to
be 3.2 for structure A, 3.8 for B, and 4 . 5 for C. Nearly 1 minute after
structure C, a sudden increase in Y to about 5.8 corresponding to a secondary
rise in the hard X-ray flux was accompanied by weak fluctuations observed at 7
5	 •
GHz and 2.8 GHz 13. This was apparently the begining of a conventional microwave
burst with a peak frequency at 8-15 GHz and a peak flux of 40 s.f.u. at 8.8 GHz
i
occurring at 13:31 UT 14 , some four minutes after the initial hard X-ray and 90
GHz spikes. A minor peak in the > 24 keV X-ray flux also occurred at this time
but with a HXRBS counting rate of only 300 counts s -1 compared to 1630 counts s-1
at the time of the earlier, more impulsive spikes. 	 I
^	 I
The high time resolution achieved in the 90 and 30 GHz observations allowed	 ► f
the detection of even faster intensity variations than are evident in Figure 1.
All the major impulsive structures appeared as trains of several very fast
^H
peaks when plotted on an expanded. time scale. Figure 2 shows an expanded plot
of structure A at 90 GHz and in 24 - 219 keV X-rays. Rapid variations are clearly
s'	 detected in the 90 GHz intensity with at least 13 resolved peaks in just over
-4- ,
two seconds.
	 The e-folding rise time of the initial peak is
	 0.03 s.	 The
g
detection of similar rapid variations in hard X-rays was precluded in this
q case by the 128 ms time resolution of the observations.
	 However, other events
have been detected by HXRBS with a time resolution of 10 ms showing equally
` rapid fluctuations in the hard X-ray flux 15 .	 In the present case, we can
see from Figure 2 that the initial rise of structure A in hard X-rays is
simultaneous with the rise of the 90 Gtiz profile to within the 128 ms resolution
e of the X-ray observations.	 The overall X-ray and 90 GHz time profiles appear
slightly different, however.
In order to show these rapid mm-wave fluctuations more clearly, the p
gradually varying component of the 90 and 30 GHz flux has been removed in the
plots shown in-Figure 3 by subtracting a running mean. 	 Plots for the three
' major structures A, B and C are shown together with a similar plot for a 4 s
ti
interval prior to the burst. 	 Note that the system noise amplitude is negligible
compared to the pulse sizes.
It is clear from Figure 3 that the rapid fluctuations in structure A are evident
only at 90 GHz.	 The pulse repetition rate is - 5 Hz but a Fourier analysis16
shows that there is significant power at frequencies extending from 1 to 8 Hz.
The relative amplitudes of the pulses range from 30 to 50% of the mean flux.
Such pulses are barely noticeable at 30 GHz, however, and they have much smaller x
amplitude.	 The situation for structure B is somewhat different with pulse
f	 ^
c trains evident at both 90 and 30 GHz.	 The five pulses observed in approximately
one second starting at 13 h 26m 43s UT are essentially in phase at the two
frequencies but the relative amplitudes are still much larger at 90 GHz (60%)
R
than at 30 GHz 0%).	 Structure C in Figure.3 also shows a train of pulses but,
with lower relative amplitude at both frequencies. yj
The pulse trains at 30 GHz with relative amplitudes of < 1% are comparable
to the ultra fast structuresobserved for other bursts at 22 and 44 GlIzI7 ► 18.
Similar subsecond pulses have been detected in hard X-rays in coincidence with
microwave pulse at these same frequencies 19
 but the relative amplitudes of
the hard X-ray pulses were 30 - 40%, comparable to the amplitudes of the 90 GHz
pulses reported here.
The apparent brightness temperature of the burst source at mm-waves can be
estimated if some assumptions are made for the velocity scales involved at the pulses
acceleration site. If we assume the speed of light as a limit, the scale sizes for
the 30 ms,rise times becowes L < 9 x 10 8
 cm (or apparent size 0
s
 < 13 arcsec). If
we assume Alfv-en speeds (10 8
 cm s -1 ), we obtain L <•5 x 10 6
 cm (or 0
s
 < 0.04 arcsec).
The apparent brightness temperature TB  is related to the excess antenna noise
temperature TA by the well known relationship TB Z TA ('A /a S )
2
where 0A
 is the
antenna beamwidth. For structure A pulses we obtained antenna temperatures of 2500K
at 90 GHz and 1400K at 30 GHz. With 0 = 80 at 90 GHz
	 eA	 rcsec a	 z an A = 3 arcmin at
30 GHz, we obtain comparable apparent brightness temperatures at both frequencies of
about 105K (speed of light) and 10 10K (Alfven speed), respectively.
The class of solar burst emitting at the shortest mm-wavelengths brings
important constraints to existing models for explaining the geometry and
mechanisms of particle accelerations in the impulsive phase. Further investigations
at > 90 GHz are required in order to determine the turnover frequency of this
new spectral component of burst emission.
0
►
-6-
u	
r
We acknowledge the help received in Itapetinga observations from R.C. Schaal.,
J.L. Homor and R.H. Trevisan. The assistance of Shelby Kennard in the analysis of the
HXRBS data is also acknowledged. INPE operates CRAAM and the Itapetinga Radio
Observatory, This research received partial support from the Brazilian research
a
agency PINEP,
h
4
Yt	 e
a
i A
	
v
t
}
a	 l+'
v
,
if
b^'r r
-7-
)w
^	 ll
r References
o
1. Coates,	 R.J.,	 Proc. National Electronics Conf 	 1--12 (1957).
y 2. Coates,	 R.J.,	 Proc.	 IRE,	 ra,	 122-126 (1958).
N 3. Croom,	 D.L. and Powell, R.J., Nature, 221,	 945 (1969).
+ 4. Croom,	 D.L.,	 Solar Phys.,	 15,	 414-423 (1970).
5. Cogdell,	 J.R.,	 Solar Phys.,	 22,	 147-149 (1972).
6,'Feix, G.,	 J. Geophys ► 	 Res.,	 75,	 211-218 (1970).
. y	 7. Shimabukuro, F.I., Solar Phys.,	 15, 424-432	 (1970).
8• Shimabukuro, F.I.,	 Solar Phys., 23,	 169-177	 (1972).
y« 9. Nakajima• ,7 !i. ,	 Sekiguchi,	 H.,	 Sawa,	 M.,	 Kai,	 K.,	 Kawas.,ima,	 S.,	 Kosugi,	 T.,
` Shibuya,	 N., Shinohara, N. and Shiomi, Y.,	 Publ. Astron. Soc. Japan,
submitted	 (1984).
10. Magun, A., private communication (1984).
11. Kaufmann,	 P.,	 Strauss, F.M.,	 Schaal,	 R.E. and Laporte, C.,	 Solar Phys.,
78,	 389
	
(1982).	 .
12. Orwig,	 L.E.,	 Frost,	 K.J. and Dennis,	 B.R.,	 Solar Phys.,	 65,	 25 (1980).
w ,.	 13. Hertzberg Institute of Astrophysics, Solar Activity report for May 1984,
NRC, Ottawa, Canada (1984).	 x
14. Sagamore Hill Radio Observatory, U.S. Air Force.
15. Kiplinger, A.L.,	 Dennis,	 B.R.,	 Emslie, A.G.,	 Frost,	 K.J.,	 and Orwig,	 L.E.,
Ap.J. Letters,	 265,	 L99 (1983).
16, Brenner, N., in Astrophysics, 	 Part C: Radio Observations (Methods of
Experimental Physics)	 (Ed.	 by M.L. Meeks), Academic Press, 	 New York,	 S
vol	 12,	 p.	 284	 (1976).
17. Kaufmann,	 P., Strauss, F.M., Opher, R. and Laporte, C., Astron. Astrophys.,
s 87, 58 (1980).
18. Kaufmann,	 P.,	 Correia, E.,	 Costa,	 J.E.R.,	 Dennis, B.R.,	 Hurford, G.J. and
Brown, J.C.,	 Solar Phys.,	 in press	 (1984).
19. Takakura, T.,	 Kaufmann,	 P., Costa, J.E.R.,	 Degaonkar,	 S.S., Ohki,	 K. and
f` Nitta,	 N.,	 Nature, 302,	 317 (1983).
-8 -
t
:Z*.)
ad
a
xi
M
0
FIGUR.B CAPTIONS
Figure 1. The solar burst on 1984 May 21 at 13 h 26m
 UT as observed by HXRBS
in X-rays at 24 - 108 keV and 108 - 219 keV, and in mm/cm waves
at 90, 30 and 7 GHz. The s.f.u, scale is subject to an uncertainty
of a factor of < 2. Major structures in the time profiles labelled
A, B, and C are discussed in the text and are plotted on expanded
time scales in Figures 2 and 3.
Figure 2. 4s expansion of the 24 - 440 keV X-ray and 90 G1Iz intensities in
structure A of the burst Chown in Figure 1. The vertical bars on
4ae X-ray plot indicate i 1 a uncertainties in the measured rate
based on the square-root of the observed number of counts in each
interval. The horizontal bars indicate the 128ms time intervals
over which the counting rates, corrected for instrumental dead time,
were determined. The time constant used for the 90 GHz plot was 1Oms
,
and the system noise was comparable to the thickness of the line.
Figure 3. Major burst structures at 90 and 30 GIIz, labelled A, 8, and C in
Figure 1, plotted on an expanded time scale with a running mean
subtracted from the measured fluxes. The flux variations in a 4s
interval are plotted for each structure at the two fvequencies
with a similar plot at the top of the figure showing the system
noise in a 4s interval one minute before the start of the burst.
The vertical scale for the 90 GHz plots is the same for all four
intervals and is given to the left of the curves for structure A.
Similarly, the common scale for the 30 GHz plots is given to the
left of the curves for structure B.
F
g
•	 i
ti
p
2,000 ,..----------,----------------, 
I 
, ~ 
~" 
~ 
" 
1,500 
k l' 
t 
" ~~ ~. 1,000 
~ /-
i 
y"t • 
, 
• ! t 
~ , 
i:' f~ . 
, I 
" ,. . 
", 
500' 
° 
. 
70 S.F.~. ~ 
90GHz 
30GHz 
7GHz 
. 1· 
~ 4 S.F.U. 
13:26:10 :20 :30 :40 
U.T. 
. Figure 1 
:50 13:27:00 :10 
, , 
n 
, 
o
 I
 
I 
I S.
F.
U.
 
5
0
-
>- l-
40
 
(f
) z w
 
30
 
0 
20
 
I 
X ::>
 
-
1
 
.
 
1 
10
 
LL
 
\ 
0 
13
:2
6:
30
 
~
I
:
~
m
~
 
.
,
 
I 
I 
+1
 
90
G
H
z 
1\ 
e 
•
 
/\1 
\ I
 V
\/ 
'
J 
\1\
 f
\ 
/ 
v
 
'\ 
U
.t.
 
F
ig
ur
e 
2 
0
0
 
'T
1:
;:o
 
-
o
i5
 
0
-
0
2 
::
u
t?
! 
.
o
~
 
C
~
 
»
~
 
e
m
 
~~
 
:3
4 
I': ~~ I~ ~" 1 ~ H~ ~~ ,,) ~ E , i\i 
50
40
30
LZ
Lo
20
N
10
0
3
cn	 2
N
0
90 GHz
wq
30 GHz	
NOISE PREVIOUS TO BURST
	
:L C-'
1325:00	 :01	 -02	 :03	 UT
I.
II	
ORIGINAL PAQ' 10
OF POOR QUALHY
90 GHz
^' I vI
STRUCTURE A
f.
30 GHz
	1326:31
	
:32
	
:33	 :34 UT
90 GHz..
	 ^' l
STRUCTURE B
j	 ^^	 z	 .;
30 GHz
	1326:38
	
:39
	
-40	 :41 UT
90 GHz
30 CiHz	
STRUCTURE C
1326:43	 :44	 :45	 :46 UT
FIG. 3


A new class of solar burst with MM-wave emission but only at the highest frequency (90 GHz)

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server