A search of data from the High Energy X-Ray and Low Energy Gamma Ray Experiment on HEAO-1 uncovered 14 gamma ray bursts. Nine of these events are reported for the first tiome. Except for the faintest events, all of the bursts detected by this experiment have been measured above an MeV, thereby confirming the hard spectral character of gamma ray burst spectra reported by SMM. Results give a burst rate of at least 105 per year above 6 times 10 to the minus 7th power ergs, which is consistent with previous measurements of burst frequency

Hueter, G. J.

Matteson, J. L.

English

NASA Technical Reports Server

I OG I. I- 1
HEAO-I OBSERVATIONS OF GAMMA RAY BURSTS
Geoffrey J. Hueter and James L. Matteson
Center for Astrophysics and Space Sciences
University of California, San Diego, La Jolla, CA 92093 U.S.A.
ABSTACT
A search of data from the High Energy X-Ray and Low
Energy Gamma Ray Experiment on HEAO-I uncovered 14 gamma ray
bursts. Nine of these events are reported for the first time.
Except for the faintest events, all of the bursts detected by
this experiment have been measured above an MeV, thereby
confirming the hard spectral character of gamma ray burst
spectra reported by SMM. Our results give a burst rate of at
least ].05 per year above 6x10-7 ergs, which is consistent with
previous measurements of burst frequency.
1. Instrumentation
The HEAO-I mission lasted from August, 1977, to February, 1979. The
UCSD/MIT High Energy X-Ray and Low Energy Gamma Ray Experiment consisted I of
three sets of shielded NaI/CsI phoswich detectors with differing fields of view
and effective energy ranges (Table I ).
Table I. HEAO A4 Detectors
Number and Area Field of Energy Spectral
Name (cm 2 ) View Range Integration
( °FWHM) (Xev)
1 High Energy 120 43 0.1-6.1 i0.24 seconds
Detector (HED) 512 channels
4 Medium Energy 42 16 0.03-2. 5.12 seconds
Detector (MED) 512 channels
2 Low Energy 103 1.7x20 0.01-.2 0.64 seconds
Detector (LED) 64 channels
In order to provide temporal information on timescales shorter than the nominal
integration times listed in Table I, the counts from the five higher energy
detectors (HED and MED's) were summed and read out every 0.32 seconds. We
searched for bursts in these data using an algorithm which triggered" on
significant 0.32 second excesses.
2. Observations
Table II lists the bursts discovered in a search of the entire 18 month
mission. As indicated in the table, four of the bursts were detected by other
spacecraft, two of which, GH771020 and GB771110, have already been discussed by
Knight et ak 2 The March 25, 1978 event, which showed an absorption feature at 55
keV in its spectrum, has been discussed by Hueter et al.3 4.
The time given for a burst is the Universal Time at which the burst
reached its maximum intensity. Durations are the total time that the event was
1 OG 1.1-1 
EAO-1 BSERVATIONS F A MA Y RSTS 
eoffrey J. ueter and .James L. atteson 
center f r strophysics a d pace ciences 
niversity of alifornia, San iego, a Jolla, CA 92093 .S.A. 
BSTACT 
 arch f ata fr  t e igh nergy -Ray nd ow 
ne.rgy a ma ay xperiment on EAO-l ncovered 4 ga ma r y 
ur ts. ine f t ese vents re r ported f r t e irst ti e. 
xcept f r t e f intest events, ll f t e ursts etected by 
t is xperiment ave een easured a ove a  eV, t ereby 
confirming the hard s ectral character of ga ma ray burst 
ectra r ported y S M. ur r sults ive a urst r te f t 
l ast 10  er ear ove xlO - 7 rgs, hich i  on istent ith 
revious easurements f urst fr uency. 
. strumentation 
he EAO-l i sion sted fr  ugust, ' '7,  ebruary, '79. he 
CSD/MlT igh nergy -Ray a d o  nergy a ma ay xperiment onsisted l f 
r e ts f ielded aI/csl hoswich etectors ith i fering i lds f iew 
and ffective e ergy ranges ( able I). 
able . EAO 4 etectors 
umber and rea ield f nergy s ectral 
a e ( 2 ) iew ange tegration 
( °F HM) (Mev) 
1 igh Energy 120 43 .1-6.1 10.24 seconds 
etector ( D) 2 a nels 
4 edium nergy  16 . 3-2. . 2 seconds 
etector ( ED) 12 a nels 
  nergy 3 . x20 .01-.2 . 4 s conds 
etector (LED) 64 channels 
In order to provide te poral information on ti escales shorter than the nominal 
i tegration ti es li ted i  able I, t e unts fr  t e fi e igher ergy 
etectors D d ED 's) ere Sli med d d ut ery . 2 conds. e 
arched r ursts  ese ata sing  l orithm hich gered'  
i n ficant . 2 cond ces es. 
. bservations 
able  ts e ursts iscov red   arch f e tire  onth 
ission. s dicated  e le, ur f e ursts ere etected  ther 
acecraft, t o f hich, B771 20 d B77 110, ve lready een i cussed y 
night t l. 2 he arch , 78 ent, hich wed  sorption ature t  
e  i  it  s ectrum, as een i cussed y ueter et al. 3 . 
he e i en r  urst   niversal. Time t hich  rst 
reached it  aximum i tensity. urations r  t  t tal ti e t at t  ent as 
https://ntrs.nasa.gov/search.jsp?R=19850025590 2020-03-20T17:55:17+00:00Z
2 0GI.1-I
seen above background. For the March 25, 1978 event and the bursts which have
been observed by other spacecraft thefluences are well known. _ The remaining
bursts have not been completely analyzed with regard to spectral shape, and
aperture modulation, so that only approximate fluences can be given. These
values, given in parentheses, may vary by a factor of three or more. The peak
flux of a burst is the maximum rate in a 0.32 second interval and is subject to
the same uncertainties as the fluence.
Table II. Bursts Detected by HEAO A4
Date Time T d Peak flux Fluence
(UT ) (ergs/cm 2-s ) (ergs/cm 2 )
August 16, 1977 II:23:26 30 (ixlO -6) (8xlO -6 )
October 20 7:54:55 39 2x10 -5 2xi0-4
November I0 17:12:45 3 6x10 -s 7xlO-5
March 25, 1978 6:29:03 90 1.2x10 -6 1.5xi0-5
March 30 I0:40:38 21 >5x10 -7 >3x10 -6
April 17 7:32:30 9 (3xlO -5 ) (ixlO -s )
May 18 23:53:32 30 (2x10 -7 ) (ixlO-6)
May 21 21:53:46 4 2x10 -5 5xlO -5
June 30 3:14:32 7 (2xlO -7 ) (6xlO -7 )
July 6 13:13:51 5 (6xlO -7) (ixlO -6)
July 24 9:11:04 1 >5xlO -8 >ixl0 -7
July 31 20:32:47 2 >5X10 -8 >iXl0 -7
November 19 9:26:56 13 9x10 -5 3.2xi0-4
December 27 21:28:12 4 (6x10 -7 ) (4x10 -6 )
3. Discussion
Data from the SMM Gamma Ray Spectrometer have demonstrated that >MeV
emission is a common feature of gamma ray bursts 5 . In our observations we find
measurable >MeV emission in 9 of the 14 bursts. During two of the remaining five
bursts the High Energy Detector was inactive, while the other three are
sufficiently faint that we would not expect to detect the higher energy
photons. In addition, by examining the instrument telemetry, we can reconstruct
the >MeV time profiles down to 1.28 seconds. These profiles show no significant "
lag behind the lower energy emission. In fact the spectra of these bursts are
generally hardest at the beginning of the bursts and in the August 16, 1977
burst (Figure 2) the _MeV rate increases in the 1.28 second interval before the
rest of the emission appears. More study is needed, however, to determine to
what extent burst hardness correlates with burst intensity, since the initial
stages of most bursts are also the most intense.
If we consider only the seven bursts for which it is certain that the
burst fell within the field of view of at least the HED, then the net
observation time of .57 years in the search combined with the 12% coverage of
the sky by the HED gives a burst rate of 105 yr -I greater than 6xlO -? ergs/cm 2,
which agrees with the uncorrected rate obtained by Mazets eta#. 7 for the KONUS
experiment. This is not surprising, since the triggering criteria used here is
similar to that used by KONUS. This burst rate is most certainly a lower limit
on the true rate because the 0.32 second burst trigger is inefficient for
bursts which vary in intensity on timescales much longer than the trigger time.
 OG 1.1-1 
n ove ckground. r t  arch S, 78 ent d t e ursts hich ve 
been observed by other spacecraft the fluences are ell known. 5 The re aining 
bursts have not been completely analyzed ith regard t  spectral shapP. and 
aperture odulation, so that only approximate fluences can be given. These 
values, given in parentheses, ay vary by a factor of three or ore. The peak 
flux of a burst is the maximum rate in a 0.32 second interval and is subject to 
. e e ncerta nt ies   nce. 
able II. ursts etected  AO 4 
Date Time Td Peak flux Fluence 
( UT) (er s/cm 2-s) (er s/cm2 ) 
ugust 16, 1977 11:23:26 30 ( 1x10- 6 ) ( xI0- 6 ) 
october  : 4: 5  10 5 X10- 4 
ovember 1  :12:45  XI0 5 10- 5 
arch 5, 78 :29:03  . 2x10 6 . 5x10- 5 
arch  10:40:38  5xl0- 7 3xlO- 6 
pril 17 7:32:30 9 (3X10- 6 ) (lxl - 5) 
Kay 18 23:53:32 30 (2x10- 7 ) (lx10- 6 ) 
ay  1:53:46  10- 5 l 5 
ne  : 4:32  ( X10- 7 ) ( xlO- 7 ) 
July 6 13:13:51 5 (6x10- 7 ) (lxl0- 6 ) 
uly 4 : 1:04  5Xl0 8 lx10 7 
uly  0:32:47  5XIO- 8 lxlO- 7 
ovember  : 6:56  xl0 5 . 2x10- 4 
ecember  1:28:12  (6X10- 7 ) (4xlO- 6 ) 
. iscussion 
ata  e  a ma ay s ectrometer ave emonstrated at eV 
ission i   mon ature f a ma y ur ts 6 . I  ur bservations e i d 
easurable > eV e ission i  9 f t e 14 ursts. uring t o f t e re aining fi e 
ur ts e igh nergy etector as active, hile t e ther r e re 
s fficiently faint t at e ould not expect t  etect t e igher energy 
hotons. I  a dition, by examining t e i strument telemetry, e can reconstruct 
the > eV ti e profiles do n to 1.28 seconds. These profiles show no significant 
lag behind the lo er energy e ission. In fact the spectra f these ursts are 
enerally ardest t t e egin ing f t e ur ts and i  t e ugust 6, 9 7 
urst igu.re ) t e > eV te i creases i  e .28 econd terval efore t e 
st f t e ission pears. ore t dy i  eded, ow ver, t  etermine t  
hat xtent urst ardness orrelates ith urst i tensity, Since t e i itial 
tages f ost ur ts re lso t e ost tense. 
f e onsider nly e ven ur ts r hich t  ertain at t e 
urst e l ithin t e fi ld f iew f t ast e ED, t en t e et 
bservation ti e f . 7 ears i  t e earch ombined ith t e  coverage f 
t e sky by t e ED ives a urst rate f 105 r- 1 reater t an xlO- 7 ergs/cm2 , 
hich grees ith e ncorrected rate btained y azets et a/. 7 for t e ONUS 
experiment. his is not surprising, since t e tri gering riteria sed ere is 
i ilar t  at sed by ONUS. his urst rate is ost ertainly  l wer li it 
on t e true rate ecause t e .32 second urst tri ger i  i efficient f r 
bursts hich vary in intensity on ti escales uch longer than the trigger ti e. 
HED (1-6 MeV) 
Figure 1. GB770816 detector rates.  The dashed l ine  indicates the >MeV 
rates infered from telemetry. The >MeV emission peaks before the burst 
appears in  the 0.32 second rates. 
!-A 
200 
100 
- 
W O R D  ( .03-6 MeV) 
a 
HED ( .I-I. MeV) 
I 
. 
L 1 
3 
nC::l.1-1 
I I 
I I 6 :, 
I 
I 
I 
I  (1.-  e ) 
I 
I I 
I I 
I I 
r-' 
., 
I I 3 I 
I 
I 
2 
I 
I 
I 
I I I 
1 L-!
2  HED ( .1-1 eV) 
100 
60 MED's ( .03-2 MeV) 
u 
~ 50 
...... 
~ 40 
8 
280 SWORD (.03-6 MeV) 
240 
200 
160 
1.20 
80 
4:0 
1.1:23;00 11:2.4:00 
Figure 1.. GB77081.6 detector rates. The dashed line indicates the >MeV 
rates infered from te1emetry. The >MeV emis ion peaks before the burst 
ap ears in the 0.32 second rates. 
Subsequent searches of the data with longer integration times should yield more 
low luminosity, slow rising bursts. Other effects which must be considered in 
future searches before a sensible size-frequency distribution can be 
constructed are the decrease in effective sky coverage for faint bursts and the 
variations in the instrument background. (For a more detailed discussion of 
these effects , see Higdon and Lingenfeltern elsewhere in these Proceedings. ) 
5. Acknowledgements 
This work was supported by the National Aeronautics and Space 
Administration under contracts NAS 8-27974 and NAS 8-36081. 
Ftef erences 
J.L. Matteson, Proc. A.I.A.A., 78-35. 
F .K. Knight, et a/,, Astrophys. Sp. Sci. 35, 21 (1981 ). 
G . J. Hueter and D .E . Gruber, Accreting Neutron Stars (MPI , 1982 ), p. 213. 
G. J. Hueter ei at., 18th ICRC Papers (Bangalore ) 1, 54 ( 1983 ) . 
W.A. Baity et el., High Energy Transients in Astrophysics (AIP, 1984), p. 434. 
S .M. Matz et a/., Ap. J .  (Letters) 288, L37 ( 1985 ). 
E . P. Mazets et el.. Sov. Astron. Letters 5, 318 ( 1980). 
J . C . Higdon and R. E . Lingenfelter , these proceedings. 
4 OG 1.1-1 
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HEAO-1 observations of gamma ray bursts

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