Aquila X-1 observations by the All Sky Monitor on Ariel 5 are presented. Data is compared with that obtained by rocket survey, and by the Uhuru, OSO 7, and OAO 3 satellites. The variability of brightness is discussed as a connection between dwarf novae and long term transient X ray sources

Boldt, E. A.

Holt, S. S.

Kaluzienski, L. J.

Serlemitsos, P. J.

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=19770007017 2020-03-22T12:19:38+00:00Z
, 
1 
i , 
I, 
I 
.. '. 
X-&61-7&-2&0 
PREPRINT . 
RECURRENT X-RAY OUTBURSTS 
, ,/ , " 
FROM AQUILAX-l 
(WAS1-~M-X-712J6) DECURRENT X-BAY OUTEURSTS 
FBOM AQUILA 1-1 (NASA) 12 P He A02/MF AOl 
CSCL 03B 
N77-13960 
------------ --GODDARD SPACE FLIGHT CENTER ., ----, 
aRE~,.8ELT ,MARYLAND 
, i 
I 
1I
l
It
i
1-
RECURRENT X-RAY OUTBURSTS FROM AQUILA X-1
L.J. Kaluzienski, S..S.. Holt, E.A. Boldt, and P.J. Serlemitsos
Laboratory for High Energy Astrophysics
NASA/Goddard Space Flight Center
Greenbelt,, Maryland 20771 U.S.A.
L'
A high degree of variability has been associated with Aquila X-1
(301908+00) since its occasional observation in early rocket surveysl,2,3
k
and its appearance as a variable source of moderate brightness in the Uhuru
4
catalog (S ti 0.07 - 0.2 Scrab) 	 Later observations of the source have been
made from OSO-7 5 during 1971-1973 which suggest the existence of "low"
(&`0.02 
Scrab) and "high" (S -,0.5  ScrabI intensity states, and from
OAO Copernicus, where the source was reported at levels at least an order
of magnitude below the Uhuru range during intermittent exposures over a
two-year period through 1975 May6o This apparent quiescent state was inter
rupted in 1975 June by a sudden flare ? (factor of a 2O increase) to the
level of the Crab nebula. Observations of the declining source by the Sky
Survey Instrument (SSI) on Ariel -5 revealed an ti 10% sinusoidal modulation 
(2-18 keV) at the period P = 1d3+0.04. By August the flux had decayed 	
r
back to the pre-outburst intensity (< .003 S
	 ) as measured by the SS I9,
crab
'	 a
which instrument observed the same low flux from Aql X-1 again in 1976
January.	 In 1976 June, the All-Sky Monitor (ASM) on Ariel -5 detected an
additional outburst of this source1 0, which was confirmed by the SSIi1.
- We report here ASM observations of Aquila X-1 obtained between the launch
of Ariel -5 in 1974 October and 1976, 	 November, and compare them with the
lAlso, Dept. of Physics and Astronomy, University of Maryland
2 1
previously cited additional data available. 	 We suggest that the totality
of these measurements 'imply that Aql X-1 may provide a plausible connection
between dwarf novae and the very bright, long-duration transient X-ray
sources
The proximity of Aql X-1 to the sources Ser X-1 	 (3U1837+04) and
3U1901+033S	 .	 , 	 0.1 S	 respectively) make unambiguous(max	 0	 ^c,rabr 	 crab'
detection of a low Aql X-1 flux (ti 0,2 Scrab) problematic in the ASM
standard resolution mode (see ref. 13 for a complete experiment description).
a
Consequently, occasional fluctuations in detector background and other
systematic	 effects could conceivably result in "accidental" flux measure-
ments (with low probability) as high as 	 ,,0.3 S
	
for this particular source.
crab
The ;data obtained during the 1975 and 1976 flares of Aql X-1 are illustrated^
in Figure 1, and represent the only unambiguous detections of the source
over the	 ti25 months of ASM operation during which the duty cycle for daily
i monitoring of the Aquila-Serpens region was > 75% 	 These plots consist of
ti 1/2 day averages of the 3-6 keV flux (incident photons) with corresponding
+ l6 statistical error bars (estimated 1`a systematic errors are smaller
r than the statistical 	 uncertainties)..
	
The upper limits obtained ( 0,1
et cm 2sec l ) immediately prior to the 1975.flare are consistent with the 7
SAS-3 observations 7 , and no positive detections of the source above
z,
ti 0,2 cm 2sec^^ were made during the preceding 7 1/2 months. 	 A similar
search of the ASM data over the period between the flares yielded no
unambiguous source sightings through 1976 April, with a possible detection
` at \.D.3 cm 2sec- 1	(for ti l day) two weeks prior to the 1976 outburst.
We note finally l=aat the apparently differing peak flux levels of the i
r
r-3
flares are actually consistent with a single limiting value (S 	 S	 ),
max	 crab
as degradation in the effective 3-6 keV detector efficiency of.-. 10% between
the two flare observations can not be excluded.
As a 1.3-day modulation has been reported
8 from the 1975 SST
flare'data `(obtained during the time interval 	 in Figure la labelled	 -
"equator")	 we have investigated both the 1975 and 1976 ASM data for periods
in the range 0.3-3 days.	 The technique employed consisted of separately
folding the data over the range of trial periods and noting deviations
in the X 2-period distribution to the hypothesis of source constancy.	 The
r most prom ,vent peak in the 1,975 ASM data is, indeed, consistent with the
SSI result.	 As,the two experiments have mutually exclusive fields-of -view,
' the ASM result at a level of 3% + 1% is an independent measure of the
same effect, but cannot be claimed to be an independent detection owing
to its marginal statistical 	 significance.	 Assuming its reality, we can
refine the period estimation to 1.28 ± 0.02 days. No such modulation is
evident at this period in the 1976 data, however, with statistical errorsi
comparable to those in 1975.
A summary of the totality of the 1.971-76 data is displayed in
Figure 2, from which there is a clear indication that the'OSO-7 data are
consistent with flaring episodes similar to those in 1975-76. As there
is no exact period which can be fit to the four flares for which there is
observational evidence, we have derived a mean flare interval of 435 days
s	 with an rms scatter of Nl0%, and have indicated a possible history of
€	
s
identical flares which satisfy all of the observations.
z
t
is	
'
-4_
Y
f` The irregularity of the proposed flare cycle has several obvious
implications for source models. 	 In particular, Jones et al. 	 have recently
recurrent flares from 3U1630-47 similar to those discussed here, «..•,
h
reported
but which exhibit a regular period of P = 615+5 days. 	 Those authors
f have suggested that the 3U1630-47 flare cycle may represent the orbital
period of an eccentric	 binary system (as has also been suggested for
F
15,16
several transient sources 	 ),	 but the observed scatter in the presumed
t
Aquila X-1 flare period is inconsistent with the relatively precise timing
expected from binary phase-related variations in the accretion flow.
The same consideration lessens the likelihood of an association of the
r 'esent behavior with a Mira Variable-type binary as proposed for the
transients 3U1543-47 17
 and A1118-61 1 8, or with a Her X-1 -like precession-
19,20
governed modulation
	 (as opposed to actual flares).
We suggest that the observations are most easily interpreted in
terms of an "X-ray dwarf nova" binary of the type .proposed by Avni,	 r
Fabian, and Pringle2 1
	for the transient source A0620-00, as the observed
X-ray phenomenology is not unlike that of the optical light curves of
Fdwarf novae (and some recurrent novae).
	 Using the empirical period-
^A amplitude relation for U Gem stars and recurrent novae of Payne-Gaposchkin 22
 ,_
the inferred luminosity ratio L
	 - /L	 ' u
 500 (assuming that most of the
max	 min )
x'
i
radiation emerges in X-rays) yields an expectation value for the interval t
between flaring episodes of N465 days.
	 The excellent agreement between the
predicted and observed mean flare cycles should not be taken literally,
s
as the uncertainty in L 	 /L	 implies a correspondingly wide dispersion
max	 min
3in the expectation flare interval. Recognizing further that X -ray dwarf
novae may deviat^ significantly from period-amplitude relations describing
their optical analogues 2l,23 , we can conclude only that the observed flare
Y
interval	 is not inconsistent with that which might be expected from such
i a source.	 The close similarity of the two ASM flare 'light curves is another
model constraint, as it suggests detailed reproduceability.
	
This char-
:i acteristic of the source behavior can be reconciled with accretion dwarf
nova models invoking relatively continuous mass transfer to an accretion
disk which is eventually "dumped" by an instability 24 or, alternatively,
23
quasi-periodic unstable Roche-lobe overflow of the red star 	 In the
former model, the similarity of the flares results from the comparable
m
_	 3
amounts of material accumulated between episodes, while in the latter a
H
Alhigh regularity of the magnitude of Roche-lobe spills and/or a feedback
loop (regulated first by self-excited transfer and later by Eddington-
limited flow) may be implied.	 Finally, we note that the non- flaring
	 3
source behavior observed by Uh uru25 may be analogous to the "standstills"
w
observed in several dwarf novae including Z Cam24 (S	 ti 0.3 -
standstill
0.5 S	 E
max'
The similarity, of the Aql X-1 flares reported here to the more
p'	 transient X-ray sources has been pointed out byextreme e isodes of the
several observersg 2b .	 The abrupt (ti l week) rise by tit orders of magnitude 	 l
and subsequent gradual nova-like decay (e-folding time ti 1 month) back to
the pre-flare level are reminiscent of the characteristic transient source
light curves, apparently differing only in the degree of brightening
(L	 /L	 for transients is, by definition, 	 103 } and the absence of a
minmax
:' clear precursor peak.	 This behavior is, on the other hand, qualitatively 	 '
L.A
6_
f
27
a
different from the recurrent flares of Cyg X-1 	 or the extended "highs"
(sometimes lasting for hundreds of days) exhibited by sources such as
Cen X-3.	 In the context of a transient source association for Aql X-1,
T
F 6we note that the relatively soft flare X-ray spectrum
	
suggests a generic
relation to the class of "long-duration" transients 12 (e.g., A0620-00,
A1524-62, and A1742-28), as opposed to the harder-spectral, shorter-lived
transients exemplified by A1118-61 and A0535+26.
	
The identification of
k the transient A0620-00 with a recurrent nova 28 and there-semblance of the
r
r long-term behavior of Aql X-1 to both the transient X -ray sources and -
f dwarf novae suggests that at least some members of the former group may
arise from systems similar to the latter, but with the blue-dwarf binary
component replaced by a neutron star or black hole.
The authors are indebted to R. Rothschild for bringing the avail-
3
E ability of the OSO-7 observations to our attention.	 L.J.K. acknowledges
f
support from the University of Maryland.
u
r
t
v
a
j
4
c ;
REFERENCES	
Y
1. _ Friedman, H., Byram, E.T., and Chubb, T.A., Science, T56, 374 (1967).
If
2. Seward, F., An Illustrated Catalog of Cosmic X-Ray Sources, LLL Report
UCID-15622 (1970).
fr
3. Price, R.E., Seward, F.D., and Swift, C.D., Astrophys. J., 176, 611 (1972).
4. Giacconi, R., Murray, S., Gursky, H., Kellogg, E., Schreier, E.,
a Matilsky, T., Koch D., and Tananbaum, H., Astrophys. J. Suppl., No. 237,
27, 37 (1974).
5,	 Markert, T.H., Ph. D. Thesis (1974).
6. Davidsen, A., Sanford, P., Davison, P., and Mason, K., I.A.U. Circ.,
No. 2793 (1975).
y 7. Buff. J., I.A.U. Circ., No. 2788 (1975).^ 
8. Watson, M.G.,._Mon. Not. R. astr. Soc., 176, 19P (1976).
9. Villa, G., Page, C.G., Turner, M.J.L., Cooke, B.A., Ricketts,'M.J., and
Pounds, K.A., Mon. Not. R. astr. Soc., 176 (in the press).
10. Kaluzienski, L.J., Holt, S.S., Esfandiari, M., Boldt, E.A., and
Serlemitsos, P.J., I.A.U. Circ., No. 2965 (1976).
11. Watson, M.G., Private communication _(1976), 	 1
12. Kaluzienski, L.J., Holt, S.S., Boldt., E.A. and Serlemitsos, P.J.,
Astrophys. J. (in the press).
13. : Holt, S.S., Astrophys. Space Sci., 42, 123 (1976).
14. Jones, C. Forman, W., Tananbaum, H., and Turner, M.J.L., Center for
Astrophys. Preprint, No. 589 (1976).
1^5. Pacni, F. and Shapiro, S-.L., Nature, 255, 618 (19.74).
?lft
IlVQ pAGE B
	
^
16. Clark, D.H., and Parkinson, J.H., Nature, 258, 408 (1975). 	 j
17. Li, F.K., Sprott, G.F., and Clark, G.W., Astrophys. J	 203, 187 (1976).
18. Fabian, A.C., Pringle, J.E., and Rees, M., Nature, 255, 618 (1975).
19. Roberts, W.J., Astrophys. J., 187, 575 (1974).
20. Petterson, J.A., Astrophys. J Lett., 201, L61 (1975).
21. Avni,	 Y.,	 Fabian, A.C., and Pringle,	 J.E., Mon.	 Not.	 R.	 astr..	 Soc.,
175,	 297	 (1976).
22. Payne-Gaposchkin, C., The Galactic Novae (North-Holland Publishing
Company, Amsterdam, 1957).
i
23. Bath,	 G.T.,	 Evans, W.D.,	 Papaloizou,'J., and Pringle, J.E.,. Mon.	 Not.
R.	 astr.	 Soc.,	 169, 447	 (1974).
24.
3
Osaki, Y.,	 Publ. Astron.	 Soc. Japan, 26, 429 (1974).
25. Jones, C., Private communication (1976).
26.s Kaluzienski,	 L.J., Holt,	 S.S.,	 Boldt,	 E.A.,	 and Serlemitsos,	 P.J., 3
} _
Symposium on X-Ray Binaries, NASA SP-389, 311 	 (1976). 
27, Ho y t, S.S.,	 Kaluzienski,	 L.J.,,Boldt,	 E.A., and Serlemitsos,	 P.J.,
Nature, '261,	 213	 (1976).
28.
I
Eachus,	 L.J., Wright, E.L., and Liller, W., Astrophys. J.
	 Lett.,
2039	 L17	 (1976).
x
F
s+
FIGURE CAPTIONS
' Figure 1
	
ASM chronologies of the 1975 (a) and 1976 (b) flares
of Aquila X-1.	 The points are ti 1/2-day averages, and }
the error bars are +la (statistical error only). 	 The x
I shaded areas labelled "equator" are times when Aquila X-1 4
z` was close to the equatorial plane of the Ariel-5
satellite; during these times the source wasinaccessible
to the ASM, but observable by the SSI.
Figure 2	 Summary of Aquila X-1 observations over the period y
y. 1971-1976.	 The OSO-7 data is taken from Markert5
and has been approximately converted to ASM units via
normalization with respect to the Crab nebula. 	 Error
bars in all data have been conservatively estimated to
include possible systematic and normalization errors.
C Intermittent Copernicus6	measurements duri n g	 -1975g 1973
r	
^ a
l< (not displayed) are at the level ti .01-.02, and do not
preclude a 1974 outburst as hypothesized.
t
r
-_A
r 
". 
',L,,' , 
It) 
• 
-
I I 
I: 
• I 
• 
I • 
'. 
e 
I 
, . 
e 
I 
t , 
• 
• 
., 
., 
• 
. '
-t 
e. , 
t=!=o====Jt ' 
· " • i • l... . 
r , I ' ... t .1 
- iii' e1.. 
t I 
b • 
o 
• 
-
... 
It) 
o 
• 
. I.Qt• z_UlO SN010Hd 1\8~ -9~~£ 
o g 
, . 
.e 
-
u. 
o 
.~ 
o 
i· 
I , 
-
• , 
I 
I 
, 
, . 
• , , 
I 
•• 
• I 
• 
• 
, 
• • • 
'i= I 
:J4 
J I 
• t=, I I 
I • , 
, 
• I 
• 
~J • • . i 
• 
, 
I 
• I 
. " . ~
, =- • J r I 
I. .! I 
• < • I 0 
I I 
•• • 
I • ..1,. 
\. . 
I~
I i 
. , . 
I,. I • , 
I' .-. I 
, I i • 
• 
I 
, I, • 
I I • 
• 
, 
I 
• i I 
I 
I • .' " 
.\ .... 
1_318 a'-WO SNO!OHd 1.8"-9-£ 
o 
'0) 
I~ 
-
5a z 
::J 
-M---' 
~:',O 
~ ,-
',-
I 
, 
I- :::J!r-
0:::: 
:E ~:o 
~'I,'n en 
:::J 0 « 
~ • I 
I- X • 
1 • 
I-
,..... 
l-
! [ 
I l-
, 
1 
It) 
. 
-
• 
I 1 
-
.' t: 
I • I 
.---.---1 .... ---~ 
. 1--------- ,-
r-.-
I-
r= -. -.= L· .J.::--==-~ -=--F , 
-+ 
. 
0 
__.-==-r---=-__=_ __=_ __=_ --=-__ --=-=--=- - --
-
-
-----=- " ._ ===: -== __ -I-x-+-X-i --
.. ·-----I-X~- -
I 
., 
i 
--=-=--=" ____ - I-X-i - - - 1-,,"",-
-----------
~ 
" I 
o It) 
. . 
-
o 
z 
« 
J 
<.D 
r-
z 
« 
J 
-
It) 
r-
z 
« 
J 
-
v 
r-, 
, 
z 
« 
J 
-
-
C\J 
r-
z 
« 
J 
-
-I'-
Z 
-


Recurrent X-ray outbursts from Aquila X-1

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server