The relationship between the hard X-ray and gamma ray emissions during four bursts using the anti-coincidence shields of the High Energy Astronomy Observatory 3 (HEAO 3) Gamma Ray Spectrometer is explored. Recent observations of gamma ray bursts by the Solar Maximum Mission Gamma Ray Spectrometer (GRS) have shown that high energy emission above 1 MeV is a common and energetically important feature (Matz et al. 1985). Time histories of four gamma ray bursts in 3 energy bands ( keV, around 511 keV, and  4 MeV) with 10.24 a resolution show that the  4 MeV flux is only weakly coupled to the spectrum below approximately 600 keV

Jacobson, A. S.

Ling, J. C.

Mahoney, W. A.

Schwartz, R. A.

Wheaton, W. A.

English

NASA Technical Reports Server

OG 1.2-7
51
Gamma-Ray Burst Variability Above 4 MeV
R. A. Schwartz, J. C. Ling, W. A. Mahoney,
Wm. A. Wheaton, and A. S. Jacobson
Jet Propulsion Laboratory, M. S. 169-327
California Institute of Technology
4800 Oak Grove Drive
Pasadena, CA 91109
i. Introduction. We explore the relationship between the hard X-ray and
gamma-ray emissions during four bursts using the anti-coincidence shields
of the High Energy Astronomy Observatory 3 (HEAO 3) Gamma-Ray Spectromet-
er. Recent observations of gamma-ray bursts by the Solar Maximum Mission
Gamma-Ray Spectrometer (GRS) have shown that high energy emission above
1MeV is a common and energetically important feature (Matz et al. 1985).
Time histories of four gamma-ray bursts in 3 energy bands (>i00 keV,
around 511 keV, and >4 MeV) with 10.24 s resolution show that the >4 MeV
flux is only weakly coupled to the spectrum below N 600 keV.
2. Instrumentation. The HEAO 3 detections were made using the Csl anti-
coincidence shield which is a right cylinder in five independent segments
(see Mahoney et al. 1980 for a complete description). The spectrometer
aperture is defined by the disclike collimator shield while the remaining
well is equally divided into four segments. The crystal is 6.62 cm thick
with a roughly isotropic response, and approximately I000 cm2 effective
area (_ 600 cm 2 at 4 MeV) in directions not blocked by the Earth or
spacecraft structure. Events are accumulated for each shield piece in
three energy bands, a lower level discriminator (LLD) above I00 keV every
1.28s, a 150 keY window (WIN) centered at 511 keV every 10.24 s and an
upper level discriminator (ULD) above 4 MeV every 10.24 s. Also, the
logical sum of the LLD and logical sum of the ULD are accumulated in
separate OR'D LLD and ULD rates.
3. Observations. We selected the bursts of 1980 13 FEB, 19 APR, 2 JUN,
and 20 DEC which were four of the most intense bursts detected by HEAO
3. All four bursts were also detected by the Pioneer Venus Orbiter and
the last three were also detected above 5 MeV by the GRS (Share et al.
1982, Share et al. 1981, Nolan et al. 1984). The rates shown in Figure
1 are uncorrected for any instrumental effects. The best HEAO 3 shield
time resolution of 1.28 s is shown by the OR'D LLD rate as well as its
10.24 s average. In the lowest panel for each burst a 10.24 s average
of the LLD rate and the WIN rate are shown for the side shield closest
to the burst direction. The relative shield rates indicate that all
four bursts were located in the forward 2_ steradians facilitating
comparisons between the bursts.
In Table 1 we give three numbers for each 10.24 s interval indicated
at the top of Figure I. The LLD rate is the sum of 10.24 s averages of
the above background burst LLD rate in the collimator shield and the two
side shields which subtend the direct burst flux. In the next column we
show the ratio of this summed LLD rate to a similarly formed WIN rate.
The next column gives the approximate variance of this ratio. The error
1 
a ma-Ray urst ariability bove 4 eV 
. . chwartz, . . ing, . . ahoney, 
m. . heaton, and . . Jacobson 
Jet ropulsion aboratory, . S. 169-327 
alifornia stitute f echnology 
00 ak rove rive 
asadena,  91109 
 . -7 
1. I troduction. e explore t e relati nship bet een t e hard -ray and 
ga ma-ray e issions during four ursts sing t e a ti-coincidence s ields 
f t e igh nergy stronomy bservatory 3 ( E  3) a ma-Ray pectromet-
r. ecent bservations f a ma-ray ursts  t  olar axi um ission 
Gamma-Ray Spectrometer (GRS) have shown that high energy e ission above 
1 MeV is a co on and nergetically i portant f ture ( atz t l. 85). 
i e istories f r ma-ray ursts i   ergy ds ( 1 0 , 
around 511 ke , and >4 eV) ith 10.24 s resolution sho  t at t e >4 e  
fl  i  nly eakly upled t  t  s ectr m l  ~ 0 . 
. str mentation. he O  etections ere ade si g  sI ti-
incidence ield hich   t li der  i  i ependent ents 
(see ahoney et al. 1980 for a co plete description). The spectrometer 
aperture is defined by the disclike colli ator shield hile the re aining 
ell is e ually i i ed i t  f ur seg ents. he r stal is 6.62 e  t ic  
ith a r ghly is tropic r s onse, a  proximately 1 0 c 2 ffective 
r a ~6  c 2 t  eV) i  ir ctions t l cked  t  arth r 
spacecraft str cture. vents are accumulated for each s ield piece i  
three energy bands, a lower level discri inator (LLD) above 100 keV every 
1.28s, a 150 keV indow ( I ) centered at 511 ke  every 10.24 s and an 
upper level discriminator (ULD) above 4 MeV every 10.24 s. Also, the 
l gical su  of the LL  and l gical su  of t e L  are accumulated i  
separate ORID LLD and ULD rates. 
. bservations. e l cted t  ursts f 80  ,  R,  , 
a d   hich ere f r f t  ost i t se ursts t cted   
3. ll four bursts ere also detected by the ioneer enus rbiter and 
t  l st t r e ere ls  tected a ve  e   t  S ( are t l. 
1982, Share et al. 1981, Nolan et al. 1984). The rates shown in Figure 
1 are uncorrected for any instru ental effects. he best HEAO 3 s ield 
ti e lution f .    n  t  I  O t   ell   
10.24 s average. In the lo est panel f r each burst a 10.24 s average 
f   t    I  t  r  n r   i ld sest 
  rst irection. he l ti e ield t s icate t ll 
f ur ursts ere l cated i  t e for ard 2n steradians f cilitating 
co parisons bet een the bursts. 
In Table 1 we give three nu bers for each 10.24 s interval indicated 
at the top of Figure 1. The LLD rate is the su  of 10.24 s averages of 
the above background burst LLO rate in the colli ator shield and the two 
e i lds hich t nd  i ct rst .   xt n  
 t  ti  f t i  ed O t  t   i ilarly f r ed I  t . 
he next colu n gives the approximate variance of t is rati . he err r 
https://ntrs.nasa.gov/search.jsp?R=19850025604 2020-03-20T17:55:33+00:00Z
OG 1.2-7
52
is almost entirely due to large non-Poisson fluctuations in the background
(also discussed in Wheaton et al 1982). A smaller ratio crudely indicates
a harder spectrum below ~ 600 keV. The LLD/ULD ratio using the OR'D rates
is a measure of the gamma-ray hardness followed by the percent error in
the ULD rate.
4. Results. Both the LLD/WIN ratio in Table 1 and the bottom panel of
Figure 1 show that the LLD and WIN rates track each other closely through-
out any given burst. Also, for each burst the interval with the high-
est LLD rate has a hard LLD/WIN ratio. This effect is particularly
pronounced for 20 DEC during interval 2 and for 2 JUN during interval 3
(low LLD and soft LLD/WIN). The only significant exception is interval
i for 2 JUN which is harder than interval 2 which has a higher LLD rate.
However, the 1.28 s time history shows an intense spike during the
first 10.24 s interval. Comparing bursts, three of the bursts have
LLD/WlN ratios clustered from ~ 7-8.5 but the 2 JUN burst is clearly the
softest overall below N 600 keV and its interval 3 is the softest
interval overall.
At first glance the LLD/ULD ratio seems much more variable, however
we mast assess the importance of the poorer signal-to-noise ratio in the
ULD. Examining the burst of 13 FEB in Figure 1 and Table i, there is a
large ULD spike in interval 1 and a LLD/ULD ratio of 70. Interval 2 is
as impulsive in the 1.28 s LLD rate as interval I, but with a little more
than half the LLD and WIN intensity. But, the ULD rate does not show any
significant increase over background. Summing the OR'D ULD and OR'D LLD
rates over all of the 13 intervals (except interval 4 for 13 FEB) obtains
an overall LLD/ULD ratio of 135. We use that ratio to compute a reduced
chi-squared statistic from
1 (ULD i - LLD i (EULD/ZLLD))2.
X_2 = l-_Z
_i 2
is the ULD variance for each interval with a LLD rate. Thus, X_I
7.5. Using a similar _echnique over the 13 FEB burst we obtain an average
LLD/ULD of 122 and X_ = 8.8. The large value of the reduced chi-
square statistic clearly shows a large variability in the gamma-ray to
hard X-ray ratio within a burst and from burst to burst. Note that the
19 APR burst is the hardest burst overall in the MeV range.
The spectral hardness in the below 600 keV range is not directly re-
lated to the burst intensity above 4 MeV. The 19 APR burst has the hard-
est LLD/ULD ratio of 43 and a median LLD/WIN ratio of 8.4. In contrast
interval 2 of 20 DEC has the hardest LLD/WIN ratio of 6.8 but its LLD/ULD
ratio is 220 ± 50 which is the softest interval having a significant
ULD flux.
5. Conclusions. Over the 10.24 s intervals used here, the highest rates
over 4 MeV occur during the highest rates above 100 keV. However,
throughout a given burst the > 4 MeV flux is not a constant fraction of
the >I00 keV flux. Also, spectral hardness below 600 keV is not a reliable
indicator of gamma-ray hardnesS. Finally, the below 600 keV hardness cor-
relates with the >i00 keV intensity, although hardness within a burst
changes less than from burst to burst.
O  1. 2  
 
is almost entirely due to large non-Poisson fluctuations in the background 
(also discussed in heaton et al 1982). A s aller ratio crudely indicates 
a harder spectrum below ~ 600 keY. The LLD/ULD ratio using the aRID rates 
is a easure of the ga a-ray hardness follo ed by the percent error in 
  . 
4. Results. Both the LLD/WIN ratio in Table 1 and the bottom panel of 
Figure 1 show that the LLD and WIN rates track each other closely through-
out any given burst. Also, for each burst the interval with the high-
est LLD rate has a hard LLD/WIN ratio. This effect is particularly 
pronounced for 20 DEC during interval 2 and for 2 JUN during interval 3 
(low LLD and soft LLD/ IN). The only significant exception is interval 
1 for 2 JUN which is harder than interval 2 which has a higher LLD rate. 
However, the 1. 28 s time history shows an intense spike during the 
first 10.24 s interval. Co paring bursts, three of the bursts have 
LLD/WIN ratios clustered from~ 7-8.5 but the 2 JUN burst is clearly the 
ftest erall l   Y   t rval   th  ftest 
t rval erall. 
t first glance the LLD/ULD ratio see s uch ore variable, ho ever 
e ust ssess t e i portance f t e orer si al-to-noise r ti  i  t e 
ULD. Examining the burst of 13 FEB in Figure 1 and Table 1, there is a 
lar e L  s i e i  i terval 1 and a / LD r ti  of 70. I terval 2 is 
as i pulsive i  the 1.28 s LL  rate as i terval 1, but ith a littl  ore 
than half theLLD and WIN intensity. But, the ULD rate does not show any 
si nificant increase over background. Su ming the a I  ULD and RI  LLD 
rates over all of the 13 intervals (except interval 4 for 13 FEB) obtains 
an verall LLD/ LD rati  of 135. e use t at rati  to co pute a reduced 
i-squared t tistic  
2 1 (ULD  - LLDi (~ULD/~LLD»2. X12=i2~ 
2 O"i is the ULD variance for each interval with a LLD rate. Thus, X12 
7.5. Using a si ilar zechnique over the 13 FEB burst we obtain an average 
LLD/ULD of 122 and X4 = 8.8. The large value of the reduced chi-
square statistic clearly shows a large variability in the gamma-ray to 
hard -ray ratio ithin a burst and fro  burst to burst. ote that the 
19 APR burst is the hardest burst overall in the eV range. 
The spectral hardness in the below 600 keY range is not directly re-
l ted t  t e urst i tensity ove  eV. he 9 PR urst as t e ard-
st LLD/ULD tio f 3 and  edian LD/ IN ratio f .4. I  ontrast 
interval 2 of 20 DEC has the hardest LLD/WIN ratio of 6.8 but its LLD/ULD 
ratio is 220 ± SO which is the softest interval having a significant 
ULD fl x. 
5. Conclusions. Over the 10.24 s intervals used here, the highest rates 
over 4 MeV occur during the highest rates above 100 keY. However, 
t roughout a given urst t e > 4 MeV fl x i  not a constant fraction of 
t e >1 0 keY fl x. lso, spectral hardness below 6 0 keY i  not a reliable 
indicator of ga ma-ray hardness. inally, the below 600 keY hardness cor-
relates with the >1 0 keY intensity, alt ough hardness ithin a urst 
changes le s t an fr  burst t  burst. 
OG 1.2-7
S8
6. Acknowledgements. R. A. Schwartz is supported under a National
Research Council Resident Research Associateship. This research was
performed at the Jet Propulsion Laboratory, California Institute of
Technology, under contract with the Natlonal Aeronautics and Space
Administration.
REFERENCES
Mahoney, W. A., et al, 1980, Nucl. Instr. and Meth., 178, 363.
Matz, S. M., et al. 1985, Ap. J. (Letters), 288, L 37.
Nolan, P. L., et al. 1984, in High Energy Transients in Astrophysics,
ed. S. E. Woosley (New York: American Institute of Physics), p. 399.
Share et al. 1981, Proc. 17th Int. Cosmic Ray Conf. (Late Vol.).
Share, G. H., et al. 1982, in Gamma Ray Transients and Related Astro-
physical Phenomena, ed. R. E. Lingenfelter, H. S. Hudson, and D. M.
Worrall (New York: American Institute of Physics), p. 45.
Wheaton, Wm. A., et al. 1982, in Gamma Ra_ Transients and Related
Astrophysical Phenomena, ed. R. E. Lingenfelter, H. S. Hudson, and
D.M. Worrall (New York: American Institute of Physics), p. 55.
TABLE I
Net Burst Rates
Burst Interval LLD (LLD/WIN) _ (LLD/ULD) _ (ULD)
13 FEB 1 21500 7.7 .I 70 10%
2 11200 7.6 .i >200 -
3 7000 8.0 .2 160 70%
.....
5 10900 8.1 .i 190 45%
6 9600 8.4 .I 110 30%
Average i0000 7.7 123 13%
19 APR I 3900 8.4 .i 43 14%
2 1500 8.4 .2 70 60%
Average 2700 8.4 50 20%
02 JUN 1 4200 10.4 .I - -
2 12200 II.i .05 Ii0 11%
3 1700 14.7 .4 - -
Average 6000 11.2 172 20%
20 DEC i 3400 7.8 .i 170 50%
2 12700 6.8 .05 220 19%
3 3400 8.2 .I - -
Average 6500 7.2 253 24%
Table I. LLD and LLD/WIN are computed using the summed rates of three
shield pieces. LLD/ULD is obtained from the OR'D rates.
  
53 
6. cknowledgements. . . chwartz is s ported under a ational 
esearch ouncil esident esearch ssociateship. his research as 
erf r ed t t  t r pulsion aboratory, alifornia I stitute f 
Technology, under contract ith the ational eronautics and Space 
dministration. 
FERENCES 
ahoney, . ., et al. 1980, ucl. Instr. and eth., 178,363. 
Matz, S. M., et al. 1985, Ap. J. (Letters), 288, L 37. 
Nolan, P. L., et al. 1984, in High Energy Transients in Astrophysics, 
ed. S. E. oosley ( e  ork: merican Institute of Physics), p. 399. 
Share et al. 1981, Proc. 17th Int. Cosmic Ray Conf. (Late Vol.). 
Share, G. ., et al. 1982, in Gamma Ray Transients and Related stro-
physical Phenomena, ed. R. E. Lingenfelter, H. S. Hudson, and D. M. 
orrall ( e  ork: merican Institute of Physics), p. 45. 
heaton, Wm. ., et al. 1982, in Gamma ~ Transients and elated 
strophysical Phenomena, ed. R. E. Lingenfelter, H. S. Hudson, and 
. M. orrall ( e  ork: merican I stitute f hysics), . 55. 
BLE  
et urst ates 
urst I terval LLD (LL 7wIN) (J (LL 7uLD) (j ( L ) 
   00 .  1   
 00 .  1 00 
 0 .     
4 
 00 .  .1 0  
 00 .  1   
verage 1 000 .    
 PR 1 00 .  1   
 00 .     
verage 00 .    
   0 .  1 
 200 11.1 .  11   
 00 .   
verage 00 .    
 EC 1 00 .  1   
 700 .  .    
 00 .  1 
verage 6500 .  253  
able 1.  and D/ IN re co puted using the su ed rates f t ree 
s ield ieces. LLD/ULD is obtained from the ORID rates. 
r--
I
o
HEAO 3 Burst Time Histories
l_lzl :11213,
37000 260(30 _ ; -- 30000 [_ b I I tr I / 254)00 t ,I I ! 2; .3 i I
........... _ I_ ........ J ! _ 20 D_CREDMLB:R1980 1
....... L JItY..........J
25O00 14O00 15000 _ 10.24 SAVG 13000
2620 590 10.24S AVG 570 _- 10.24S AVG
. i i _ __o 2460 I 770
i II
55OO 250 17co 12o 26o0 19o
7:28:36 7:2e:16 7:2e:SS 7:30:36 1:f9:CI7 1:19:47 1:20:27 1:2_:07 73:_9:_0 _3:_9:50 13:20:30 13:2_:_0 _e:3o:o2 _:30:42 _e:_:_ _e:32:e2
UNIVERSALTiME
Figure i. Selected rates of four bursts detected by the anti-coincidence shield.
LLD events > 100 keV, WINDOW events within 75 keV of 511 keV, and ULD events > 4 MeV.
r--. 
I 
N 
o 
o 
z 
~ 
8 
3300() 
29000 
25000 
21000 
2700 fL-~+--~+-~+~-+~---j~-I 
2460 
2380 
OR'O UlO 
10.24SAVG 
9500 Il-~-I--~+~+~-+~~i----I 650 
8~~ 
4500 '-~L-~..L~-'-~--L~~~--" 150 
7:28:30 7:29:16 7:29:56 7:30:36 
HEAO 3 Burst Time Histories 
26000 ,--~~_:~1,-:,-,,-2 "---,--~-,--~--,-~-, 
2200/) 
18000 
14000 
10000 
19APRIl1980 
OR'O LlD 
1.28SAVG 
10.24SAVG 
610 i-~+-----'-+-~-+~-+~---j-'----'1 
59<J , 
510 
550 
530 
QR'O ULO 
10.24SAVG 
:: !-~~-+~~i-~+--~+-~+~--1 280 
2500 ~j ~ 
LlD r:: 
2100 16<) 
1700 120 
1300 t:"=:L=---,---':'::=5==~=-J 80 
t:19:07 1:19:47 1:20:27 1:21:07 
1.28SAVG 
10.24SAVG 
10000 
I IZJUNE ~98() ] 
OR'O LLD ~ 
~ j 
-"'""'""'~~~ 
89Qr-~+-~+-~-+-~-t~---j--I 
13:19:50 13:20:30 13;21:10 
UNIVERSAL TIME 
OR'O UlD 
570 ~ 10.24SAVG 
5J n 
" ' I 
I ' 530 ~~-u I~ . ; 
510 ~ LJlLr--
6100 , 
5100 ~ 
4100 ~ j 
::] 
SHIELD 1 
10.24SAVG 
LLD 
1050 
1100 E=====:L~-'---':::::L'~==~ 50 
18:30:02 18:30:42 18.31:22 18:3f:02 
Figure 1. Selected rates of four bursts detected by the anti-coincidence shield. 
LLD events> 100 keV, WINDOW events within 75 keV of 511 keV, and ULD events> 4 MeV. 


Gamma-ray burst variability above 4 MeV

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