The Einstein Observatory imaging proportional counter was used to search for X-ray emission from nine nearby historical novae. Six of the novae were detected with estimated X-ray intensities between .1 to 4 keV of 10 to the -13th power to 10 to the -11th power ergs/sq cm-s, comparable to the intensities of previously detected cataclysmic variables. The X-ray intensity of one of the novae, V603 Aql, varies over times of several hundred seconds. The data suggest a correlation between the decay rate of the historical outburst and the current X-ray luminosity. Alternatively, the X-ray luminosity may be related to the inclination of the binary system

Becker, R. H.

Marshall, F. E.

English

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'	 (NASA-Tri--82014) AN X^-RAY SURVEY 0V NINE
N81-12961
HISTO41CAL NOVAE (NASA) 13 p HC A02/%F A01	 cf
CSCL 03A
Unclas
G3/90 39805
^i
Technical Memorandum 82014,E
0
_r
An X-Ray	 °^ 	  Survey o f
Nine Historical Novae
CID
R.H. Becker and F.E. Marshall
o
c,
SEPTEMBER 1980
	
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15^s^^ 	 .R3ational Aeronautics aid
	 ^'^4	 B!9Space Administration
^ DECGoddard Space Flight Center
	
1980
 o	 ,.,
Greenbelt, Maryland 20771
	
	 RECEIVED	 N
°^°. NASA STI FACIU1tY.
r	 CUs ACCESS
aAN X-RAY BOOZY OF NINE IIISTORTCAL NOVA%
	
11,11. -Be,	 I and F.E. Marshall
	
3 	
c
Laboratory for High UdrS'y^ Aet;rophysics
NASA/Goddard 'Space 1{l.ight Center
Graoi'tbal.t, Maryland 20771
ABSTRACT
^	 er
The Einstein Observatory imaging proportionxal, Counter has been used to
search for X-ray emiseion from nine nearby -. histx^rical, novae. Six of the novae
have been detected with es timated -ray intensities between ,I - G keV- of
10-13 .. 1' 11 ergs /cnt^^-o, ctauapat"table to the iwtens:lties of previously detected
cataclysmic variables. The X-ray Intensity of one of the aovtae, V603 Aq1,, 	 tom.
I` varies over timee of several hundred seconds. The data suggest a correlation
j	 between the decay rate of the hi.st orIcal outburst aa(f the currentk X-ray 	 ^
luminosity.Alternatively, the x-ray luminositymay be related to the
intl. nation of the binary system.	
^I
f4	 ,
ti IA so Dept. ftysics & Astr000my, 'Urti.v• -4„ Maryland}t	 r V `,
y	 ,
a
F^	 2
1, INTRODUCTION
Classical novae are a subset of cataclysmic binary systems whose defin ing
charact4ris ties are based on their aruptiya behavior (for review gala
Paylie-Capoochkin 1957, 0alloghar and Starrfield 1970). Detailed studies of 
I
classical nova binary systema l
 both before and after outburst, allow they are
qualitatively similar to other eataclysmic binary systams such as dwarf
novae• It is now accepted that these phenomena are the result of mass
transfer from a 14te-type companion onto a white dwarf through an accretion
di	 X-ray emission Is expected front the release of gravitational QOQSY
from iliatart%l falling otit ,Ahe surface 	ray emissiqjn has of the whit  dwarf. X
been detected previously from several dwarf novae, tiava-like objects, and one
classical nova (Cordova ) Mason and Nelson 1980 and'references therein) * In
light of soma of these obseryations as well as the "
 
prodiction. of X-ray
emiss-io-n from classical novae <-Iylenda 1977), -a survey 
or 
--nearby- classical
D
novae was undertaken.
11 THE EXPERIMENT AND THE l RVE Y
Thd observations were made with the imaging pron^, tion4l counter ^(IPC) onP
Q,ie Mnstain Observatory. A detailed description of the IPC call be found `in
G14tcoai et al. (1979). To sum4arize, the IPC produces an X-ray image of
a - I sq., deg. field with - 1 are min angtilar resolution. The image is sorted
into 8" pixels, After determining the intensity of the note.-X-ray background
for a given observation, localized variations above this background are
analyzed for statistical significance and spatial distribution Each event
detected by the IPC undergoes a pulse height analysis so that in principle t:he
energy spectrum oof each detected sourc%,,qn,^-b-.--,,estituated. In addition, each
X-ray event is time tagged so that variability of the X-ray intensity cd^ ii be
studied,.
For the purr.9sa of this survey, nine, nearby classical novae were selected
f rout 
the 
catalog compiled in Payne-Paposelikin (1957). Thqse are listed in
3Table I along with the data of cacti abservAtioirt and tho estimated distance to
cacti system. Thli,$ survey is not complete and than 	 objects do not
make up as homogeneous close of novae.,, Since there:
	 boon very little
^Y
Information Available on the *-ray behavior of classical novae, the primary
pUrpOG0 Of OGG(% Observations Was to provide some indications Cor future lines
of research,
	
u	
U	 =;^
	 1	
`ch	 p7 -obj '^ P ^^1.14 ' ,^^baorvod for 1-3 x 103 sec without regard to binary
phase. In light or the nntura of cataclysillie variabloso All these data 8110014
be considered #a sti psliots of what may"^bo highly variable behavior.
OURVATION
The avora8ad X-r ►y properties for each of 
the 
nine novae, iQ. the X-ray
ii
position If detected and the meftauved counting rate or 20 upper limit Are
o
given, In Table I , Six of the nine objects, bava been positively dotectedo bottl
on the basis of positional coincidence with the optical noy>'and a
statistically signifleatiL counting rate. Upper limits for that remaining three
sources havq-, been, calculated by summing the counts tit the optical novae
popitiont
o All of the detected sources have boon examined, for time variability and
spatial extent, althouah only two objects, GK Per and V603 Aqlo provided
enough pboto"a for 111eaOingr4l analysis ' "k he Light curve for V603 tvql 
is 
shown
In Figure 1. The tiova"V603 A91 appears to have experienced a stiort-lived
flare lastiag - 200 s during whi qb, the X-ray intensity doubled. The Iiitonsity
of GK Per remained constant tbroughout its observation. All the X-ray Images
were consistent with that of a point sourcg'
The time-nvera^ 4 spectra for each source was also examinad, All the
spectra were relatively hard, The calculated hardness ratio (counts above
0.55 koV to counts below 0.55) ranged from 2.2	 s9 for RR Pic to >23 for
Olt por t siIIiIIAr to values dotermiaed try Cordova at al. (1980) for other
	
jt	 cataclysmic variables is general and CK Per specifically, A spo^kzr I form
j
9
4
must be Adopted in order to convert 1pC eta into an X-raay.
 inta nalty. Since
the data are consistent with at hard therrmal, component as obaerved In other
cataclysmic variables (Swank 1979, /.ordova and ttieglar 1979) we will assadm a
nominal 10 kaV thermalbromastrahl,ung spectrums with Nlt a 1 :e 10 20 ollr2 t
 
as was
done by Cordova at al.. (1980) in. her study of tataclysrmi:c variables. As
Cordova pointed out'' the derived X-raf^ -^ ntaiasities are, a ^alattvalyl4negnslti.vo
to these assumptions. The intensities are given i,►a Table
 I.
s
„	 3
IV. U18CUSS1gN
	 I
Rith a sample of 11 old novae (includes observations of UQ Her and V533
Her roam Cordova at al. (1980)) it is feasible to attampt to correlate L x
 with
other observable s. Cordovaa pt -Al . (1'180) has Suggested that the lack of X-ray
omission from AQ Her may be at goometrie effect from the high 4nelinaatipaa of
the binary system. Indeed, tw^'Othar'old nova systems, x,Amr and itit,_ Pic— atia
high im linaatioa systems (1461ker 1953, Vogt 1,975) sand they too are sat hest
weak X—ray amitturs while the low i.ncl anti.on system V603 Aq1 (Draft 1964) is
1
One of the rrlost lunai.nous. (Howev t# we ;note that recen t observations by
lloggess at Al. 1980 indicate V603 Aql may actually be An eclipsing systam.)
Additional determinaatiaos of i are needed to strengthen this possible
correlation betwoen h and inclination, Lambert at al. (1980) has suggested
that i of as nova system is strongly correlated with bhe mature of , the UV
	 t
ii
speotra of cataclysmic variables in general and old novae In particular,
supporting the likelihood that ,geometric effec s could be vory iloportont. }
Cardovo et al. (1980) noted than the only two old nova which pulse
optically, DQ Her (Valker 1986) and V533 Her (l?aatterson 1979), both lack X-ray
a`.
	
	 emission. Assuming that the pulsations are iudieaative, of high magnetic
fields it is possible that I -ray amissioai^ 1s tieing suppressed in favor 01
P
	
	 cyclotron radiation (Lamb and Masters 1980). l:£ so, then L way be an
indicator of the white dwarf maagnoti.e field.
We have !f'oaand an additional: paaramatq,' , the Speed Glass of the ,,rove
i... . -. ,, u. ,.. e<,d.'•t.:,..,.,. :..I.....)t.µ-.uwiru,..,,., -a. tieuaA",,...	 -.-
rfi
outburst, which appears to correlate-, with Lx. iai' Figure 2, we have plotted
tile state of decay of tlae nova outburst Va. Lx for tho tea old novas, for 1r11 ch
this is known. We find that the tour most luminous old novae were all "fast,"
nova*:, while those old novae with the severeat upper limits ware all "slow"	 }
novae. if this apparent correlation is true, then. Lx is dale first observable
quantity in post-outburst novae which "predicts" (after the fact) the speed of
the nova outburst.
t)uatlitaati a,^ Iy * the optical light curves of till novae are similar.
Qteantitatively, the light eurvcs allow s i.gaifieant di.ffereaaces in title rate of
decrease following maximum, Le., thn speed of the outburst. Calculations
biased Ott hydrodynamic models for, novae indicate that the speed or- the voutburst
dnnnndn can both _HiA CM(I Abundanna in the*- white dwArf (Riark&a	 An
xruran 1974) and the mass of the white dwarf envelope (Tsaam And palulkuaar
1975). In tiles first case, Sparks et al.. found that hightr ONO abundances
resulted in faster novae outbursts, Timm and Faulkner found that lower
envelope mass at the time Of tie outburst also led to faster outbursts. More
recently, Shwm Frialni,k, and Shavi.v caaa:riod out calculations varying both
ONO abundances and envelope arises, and 041110 to the sa lie conic, usio a for ONO
abundances near solar and envelope masses from 10-6 -to ^ 10'"3 solall
masses. These results have shown how the speed of the uovax tdeponds On the;
condition of the envelope at th
y"- 
tune of the Outburst«
The correlation between Lx And outburst speed therefore relates the
envelope at outburst to the X-ray emission between oattbursts. Pringle and
F	 Salvon1 je (1979) have shown that for a given white dwarf 'lass and radius, L x is	 t
" approximately proportional to ,tile raeu'retion rate 'until the aactretion rate is
so large that th!p system becomes optically think. for X-rays. 'thus for a rcaula';^
of novae,to should be correlated with the accretion, rate. If In this context
we note that "A,14am (1977) allowed that higher accretion rotes onto the white
dwarf lead to tv Higher envelope temperature and hence to a "premature"
"	 ^
..	 '
^	 `	 ,
`	 .
thermonuclear runaway and therefore a lower envelope mass at the moment of
outbuesti, Similarly $ Starrfield and Sparks (1979) have compared the interval
between outbursts to the diffusion time of heavy elements in the white dwarf
envelope and concluded that high accretion rates will lead to higher CNO
abundances at the time of outbursts. Irt effect^, higher accretion rates result
in the conditions hypothe'),4;e
	
^o resuit ,in fast novae.
In, summary, this X-ray survey of old novae sugg4'sts several lines of
inquiry, There4s some support for correlations between Lx and both the
inclination of the binary system and the speed class of the nova outburst.
Currently ) the inclination of most old nova systems is unknown and further
optical observations could help q9rifirm- or, do" dia ca-LrAlo-tion afth
inclinatioix. Secondly, the X-ray survey should be extended to additional old
novae, again witli the Alm to confirm or deny either of the suggested 0
correlations. A correlation between Lx and novae speed class would be
supporti	 of models for novae outbursts ,, which relate accretion rates with the
IV
lie wish to,thank Jean Swank and Ron Taam for useful discussions. We
thank F.R. Hartiden for discussions concerning IPC analysis software. Special
thanks go to Dr. Joseph Ashbrook , for providing tile unpublished light curve for
REFERENCES
3
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iFIGURE CAPTIONS
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Figure 1	 X-ray light curve for classical - novaeV693 Aql from
a
I
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rigure 2 - Current X-ray luminosity vs, historical rate of decline for
classical novae.,, Values for declina rates come from 0hyne-Geposchkin ( 1957)
except for V533 Her and CK Vul hich were Calculated booed on light curves
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An X-ray survey of nine historical novae

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