Radio properties of SS 433

Vistas in Astronomy, Voi.25, pp.79-85, 1 9 8 1 . Printed in Great Britain. All rights reserved.

0083-6656/81/020079-07500.50

per page/O Copyright©f981 Pergamon Press Ltd.

RADIO PROPERTIES OF SS 433 E. R.

Seaquist

David Dunlap Observatory, Toronto, Ontario, Canada

The object SS ~33 is a c o m p a r i t i v e l y intense radio star (L~I032 ergs -I) e x h i b i t i n g v a r i a b l e n o n - t h e r m a l radio e m i s s i o n (Seaquist et al. 1979).

The

c e n t r o i d of the radio e m i s s i o n coincides with the optical p o s i $ i o n to w i t h i n 0~3, w h i c h is w i t h i n t h e

measurement

error (Kaplan et al. 1980).

Fi6~zre 1

shows the radio s p e c t r u m o b t a i n e d w i t h the V L A * and the C u l g o o r a R a d i o h e l i o g r a p h on 1979 J u l y 20 (Seaquist et al. 1980). frequencies

the spectral i n d e x i s ~ - 0 . 6

(~),

law p a r t i c l e energy spectrum w i t h an i n d e x of -2.2. t u r n o v e r or f l a t t e n i n g in the s p e c t r u m a t e 0 . 3 one or m o r e of several mechanisms.

At the h i g h e r

c o r r e s p o n d i n g to a power T h e r e is a d i s t i n c t

GHz~ w h i c h m a y be caused b y

The possible m e c h a n i s m s include the

effects of a low energy cutoff in the r a d i a t i n g p a r t i c l e spectrum~

the

R a z i n Effect~

s y n c h r o t r o n self-absorption~

and f r e e - f r e e a b s o r p t i o n b y

i o n i z e d gas.

An a t t r a c t i v e p o s s i b i l i t y is the last one since there is

abundant evidence from optical e m i s s i o n lines and i n f r a r e d studies that the object is s u r r o u n d e d b y an extensive cloud of ionized gas. This gas m a y result f r o m a stellar wind w i t h a mass loss rate o f ~ 1 0 -5 M@ yr -I or more and a v e l o c i t y of 1 0 0 0 - 2 0 0 0 kms -I (van den Heuvel, 1980).

0strikerp

and P e t t e r s o n

A stellar w i n d could also confine the r e l a t i v i s t i c gas s u f f i c i e n t l y

long to p r o v i d e the steady component of the s y n c h r o t r o n e m i s s i o n (see below). If such a stellar wind has a i/r 2 radial d e n s i t y d e p e n d e n c e then the freefree optical d e p t h w o u l d be u n i t y at 0.3 GHz for a d e p t h c o r r e s p o n d i n g to r~5 x 1015 cm. S y n c h r o t r o n e m i s s i o n from r e l a t i v i s t i c electrons e m b e d d e d in the wind in this r e g i o n w o u l d exhibit a radio s p e c t r u m similar to the one observed. The time d e p e n d e n c e of the radio e m i s s i o n from SS ~33 indicates that t

ro

co°

onoo

c o m p o n e n t w i t h comparable to weeks.

w .

=y

. 0

s t r e n g t h w h i c h is v a r i a b l e on a time scale of days

T h e r e are o c c a s i o n a l cha~ges on a time scale of hours

(Seaquist

et al. 1979). K e n J o h n s t o n has d e s c r i b e d in this c o n f e r e n c e extensive d a t a on variability. T h e r e f o r e l shall not dwell f u r t h e r on the statistics of the v a r i a b i l i t y but r a t h e r look at i n d i v i d u a l i n t e r e s t i n g examples and their

The V L A is a r e s e a r c h f a c i l i t y of the N a t i o n a l Radio A s t r o n o m y ObserVatory,

w h i c h is o p e r a t e d by A s s o c i a t e d U n i v e r s i t i e s Inc. t u n d e r

c o n t r a c t w i t h the N a t i o n a l

Science Foundation. 79

80

E.R. Seaqulst

implication. as part

Figure

of a c o l l a b o r a t i v e

radio v a r i a b i l i t y

10

2 shows

of the p r o f i l e ~ a n

study

(Seaquist

of this object

'''I

I

I

.2

.3

outburst et al.,

in p r e p a r a t i o n )

at 10.9 GHz w i t h

~

I

1 ~ i~

i

i

lllll

I

~

I

i

1.0

2

3

m e a s u r e d b y A.R.

the 46 m e t e r

~

~

I

~ ~ ~ i I

i

i

i

Taylor

of

telescope

[

of

~

7 5 4 3 A

>, --j

t~

t-

C~ x u.

2

1.0 .7

.5 .4 .3 .2

.1 l l l l .06 .08 .1

~

.4 .5

.7

4 5

l

[111

7

10

I

I

30 40 50

20

Frequency (GHz)

Fig. i. The radio s p e c t r u m of SS 433 o b s e r v e d on 1980 J u l y 20. T h e d a t a w e r e o b t a i n e d w i t h the V L A and the Culgoora radioheliograph. The arrows a t t a c h e d to the d a t a point at 408 M H z (Spencer, 1979) i n d i c a t e the r a n g e of f l u x d e n s i t y o b s e r v e d d u r i n g the p e r i o d 1979 J u n e to August 12.

the A l g o n q u i n the v e r y time

ar~ent

than about remains when

Radio

indicates 1015

cm.

active. myself,

is high,

observed

of this

the v e r y

of several

the i n i t i a l spectrum

the

indicative spectral

combined

interferometer

sharp rise w i t h i n

days.

size during

spectral

Be

these

i n d e x does

flattening

one d a y and

light

episodes flatten

travel is less

of v a r i a b i l i t y considerably

at c e n t i m e t e r

is shown in F i g u r e s

5-9 w h e n the

from V L A o b s e r v a t i o n s (Green Bank)

usual

of the f l a r i n g r e g i o n

of some o p a c i t y

d u r i n g 1979 O c t o b e r

T h e d a t a were and N R L

that

although

An example

for a flare

Note

a period

T h e radio

non-thermal

the i n t e n s i t y

lengths.

Observatory.

slow d e c a y over

source was b y W.S.

observations

wave3 and 4

especially

Gilmore

and

b y K e n Johnston.

A

Radio Properties of SS 433

similar

flare was o b s e r v e d

through

the

spectra

tron s e l f - a b s o r b e d above

(Seaquist

l a t e r in O c t o b e r

are least component

et al.

squares plus

81

as well.

The

fits of a m o d e l

the o p t i c a l l y

curves d r a w n

containing

thin s t e a d y

a synchro-

component

shown

1980).

0.5'

0.7

0.6

I

h

m

0.5

I ¢_

0.4

m

t o.3

SS

~33

O. 9 GHz

0.2

I

0.1

......I

l

I

DARE. ( J ~ 7 ~ ) Fig. 2. A radio flare at 10.9 GHz in 1979 A u g u s t s h o w i n g a v e r y short rise time. The o b s e r v a t i o n was m a d e b y A.R. T a y l o r w i t h the 46 m e t e r t e l e s c o p e of the A l g o n q u i n Radio Observatory. There

is a s u p e r f i c i a l

van d e r L a a n m o d e l a noteable increases

difference

however.

at a g i v e n f r e q u e n c y

that frequency~ thin regime. optically

The

electrons

into

The o p a c i t y m e c h a n i s m or p o s s i b l y

free-free

a consideration

magnetic

field

signature

the r a d i a t i n g v o l u m e could be

either

by ionized

field.

and the There

t h i c k at

in the o p t i c a l l y

for an i n c r e a s e

as the flare

synchrotron

is

the flux d e n s i t y

of i n j e c t i o n

in the

of progresses.

self-absorption

gas in a s t e l l a r wind.

self-absorption

cm) for ~he size a f

05 1 m i l l i g a u s s .

to the a s s u m e d m a g n e t i c

declines

show cl e a r e v i d e n c e

of s y n c h r o t r o n

sec (~ x 1013

source.

source is o p t i c a l l y

invariably

is a c l e a r

absorption

10 -3 arc

the flare b e h a v i o u r

synchrotron

In the v a n der L a a n model~

SS 433 flares This

expanding

only w h e n the

and the flux d e n s i t y

thin regime.

relativistic

case

similarity between

for an adiabatic

In any

sets a l o w e r limit of

the e m i t t i n g

r e g i o n for a

The c o m p u t e d

size is r a t h e r

If the o p a c i t y

is f r e e - f r e e

insensitive absorption

by

a

82

E.R. Seaquist

I

I

A

I

Oct 5.21

.-t4

m

1.0--

--

k. 0

I.~ 7

OI

_-.1

0.01 ~-I

-I

1.0

I

~.0

I0.0

(GHz)

FREQUENCY" Fig.

3.

Radio

spectra

(displaced

ordinates)

which eccured on 1979 October 5-9. obtained with the Bank. The curves m o d e l f i t to t h e on each spectrum

for

a flare

The data were

V L A a n d t h e N R L i n t e r f e r o m e t e r at G r e e n f i t t e d to t h e d a t a c o r r e s p o n d to a spectra. (see text). The horizontal bar c o r r e s p o n d s to a f l u x d e n s i t y l e v e l o f 1 . 0 Jy.

2.0--

~,

--

1.4-65 GHz ~'3

~

/

L5

-

\,

,,"

F

",

{

--

", I

"' 1.0

~,'"

@885GHz

"-,,,

×~

__

-.~.

•-~

,

0.5 -- I"

15.035 GHz

91

"-

....~ .....

--

--~

00 0ci50

I

g0 DATE

I

I

70 80 (197.9 U.'I:,)

I

90

Fig. 4. T h e r a d i o f l u x d e n s i t y vs. t i m e at 1 . 4 6 5 , a n d 1 5 . 0 3 5 G H z f o r t h e f l a r e s h o w n i n F i g u r e 3.

4.885,

Radio Properties of SS 433

s t e l l a r w i n d w i t h i/r 2 d e n s i t y dependence~ declining

o p a c i t y w i t h time m a y i n d i c a t e

relativistic to n o t e

electrons

outward

that if the mass

through

83

as m e n t i o n e d

rapid movement

loss rate and o u t f l o w

particles

near

outward

We n o w turn 5 shows

to h i g h r e s o l u t i o n

the r e s u l t s

maps

earlier

speeds

to e x p l a i n

of d e c l i n e of the opacity. The m e c h a n i s m for t r a n s p o r t i n g t h e r e f o r e be the Jets or b e a m s well k n o w n to be a s s o c i a t e d

Figure

It is i n t e r e s t i n g

speed d i s c u s s e d

105 Fun s -I are r e q u i r e d

then the

of a cloud of

the stellar wind.

(M = 10 -5 M S y r - I , v = i000 k m s -1,~ is applicable, relativistic

earlier,

for these

the rate

the clouds could w i t h this object.

of SS 433 m a d e w i t h the VLA.

of two o b s e r v i n g

runs t one on 1980 Feb.

20

(epoch I) and the other on 1980 M a y 19 (epoch 2) at 4.9 GHz. These o b s e r v a t i o n s were made b y G i l m o r e et al. (1980), B o t h epochs fall w i t h i n I0 Se"

lllll

III0

Io

ER '

•

,,

, ~

MAY

11

/

,U

ER $ / " / " "

,

/

mOs4"~js2"SS' E~ ~:. [~JE #!..... .":, b

,..-

, ~

[

i ./

/

,U

• o4" s," sz"

1ffo¢~.4

2~2 R

A

is' o¢~4

2¢2

1 9BO

Fig. 5. V L A 4°9 GHz radio maps of SS 433 for epochs 1980 Feb. 20 and 1980 H a y 19. Each m a p is shown four times t each s h o w i n g a p o s s i b l e c o n f i g u r a t i o n for the h e l i c a l form of the p r e c e s s i n g jet (see text). Contours for Feb. 20 are 1.5 x ( - i , i t 2 , 4 , 6 , 8 , 1 0 ~ 2 0 , 4 0 , 6 0 , 8 0 , i 0 0 ) mJy. C o n t o u r s for M a y 19 are 1,0 x ( - i , I , 2 , 4 , 6 , 8 , 1 0 , 2 0 , 4 0 , 6 0 p 8 0 ~ i 0 0 ) mJy. The last two maps show the d i s t r i b u t i o n of p o l a r i z e d emission. T h e v e r t i c a l bars to the left o f each p o l a r i z a t i o n m a p give the p o l a r i z e d f l u x scale. The k e y

to the f i g u r e

labels

is:

ER: East R e c e d i n g WR= West R e c e d i n g Cz C l o c k w i s e r o t a t i o n of Jetp seen f r o m West CC: C o u n t e r c l o c k w i s e r o t a t i o n of Jet~ seen from West.

84

E.R. Seaquist

a quiescent

period

for the radio

~ a c h m a p is r e p e a t e d brightness plus

distribution

a clearly

20-3~

several

emission

The

is d e t e c t e d

ations

for

moving

away from

were u s e d

two jets on average that

these

that the epochs

an e x p a n s i o n

(Gi l m o r e

The r e s u l t

activity

in F i g u r e structure

i and 2.

given by Margon ambiguity

comparison

corresponding

is not

inter-

synchrotron

configur-

gas

streams

et al. exists

(1980) for each

is k n o w n n o r w h i c h in F i g u r e

absolutely

of the

5

to the case w h e r e

and the p r e c e s s i o n

the

scale b y

flux b y about

e~t a._~l. 1980)

which

includes

terminated of f i x e d

The polarization polarized,

u~

to i ~

magnetic

field.

pattern,

the

is c o u n t e r c l o c k w i s e

convincing, verify

but

is at

the h e l i c a l

This

end if this

information

maps

The

about

Faraday rotation In summary,

1979.

at the b o t t o m There

field

There

t u r n o v e r b o t h in the q u i e s c e n t

synthesis

maps

the lobes

on the SNR WSO.

an u n r e s o l v e d

core

a moderately

Definite be r e l a t e d

changes

a

will

by

clearly

radio

source w i t h a for a low component.

a "jet"

VLA

aligned with

occur in the jet on a time

to the f l a r i n g

o f 5 . 5 kpo was u s e d i n t h e s e c o m p u t a t i o n s .

give

as yet no u n a m b i g u o u s

evidence

plus

ordered

the h e l i x

depolarized

vectors

and the f l a r i n g (®40~2)

suggests

5 s h o w that the jet is

but

non-thermal

frequency

*A d i s t a n c e

also

of flare

represents

w o u l d be ~ a r t i a l l y

is d e f i n i t e

an e x p a n d i n g

the jet.

therefore

alignment,

is available. SS 433 is a v a r i a b l e

which may

which

of F i g u r e

exists

of f l a r i n g

the p r o d u c t

is that the field follows

is so the signal

i n d e x n e a r ~ = -0.6.

of m o n t h s

through

analysis

~a~

analysis

aligTunent of the p o l a r i z a t i o n

the m a g u e t i c

show

suggests

The

shown)

data indicate

w i t h the periods

analysis

(not

and a d e c r e a s e

A detailed

and f l u x is p r e s e n t

gas o u t w a r d

or more.

data

significantly

of two,

w h i c h is p r o b a b l y

in D e c e m b e r size

a factor

of 1.4.

a comparison

(1980).

visibility

expended

fit to the v i s i b i l i t y

a factor

One p o s s i b i l i t y

smearing.

jet has

about

( w i t h v ~ 0.3 o) is p r e s e n t

a component

spectral

5 and the a s s o c i a t e d within

Simple m o d e l s

s t e a d y f l o w of r e l a t i v i s t i c

scale

in o t h e r

the star.

f u r t h e r maps m a y c o l l e c t i v e l y

the d a t a of J o h n s t o n

component

beam

fit,

same as that of the found

for twin p r o c e s s i n g

The

~0~2)

jet c o n t a i n s

one of four p o s s i b l e

A four-fold

to the w e s t

in the a n g u l a r

in the i n t e g r a t e d

that

cm from

core

This

Therefore,

the sense of the p r e c e s s i o n

the west.

B o t h the maps

from

1017

one.

The

in the jets.

indicate between

curves*.

to that 1980).

expected

is the r e c e d i n g

that

I05°~5 °.

et al.

The parameters

(c) is the b e s t

suggestive

pattern

pattern

axis r e c e d e s

as seen from

Walker

to at least

the star.

to c o m p u t e

precession

(cf.

six months.

below.

of an u n r e s o l v e d

of the jet is the

for each e p o c h shows

epo c h b e c a u s e n e i t h e r

indicates

alignment

out

the h e l i c a l

indicated

a l o n g p.a.

SNR WS0 and s i m i l a r

observations

E a c h of the maps

least

jet e x t e n d e d

on the a s s o c i a t e d

ferometric

lasted for about

for r e a s o n s

at each e p o c h c o n s i s t s

resolved

of the flux.

lobes

source which

times

activity.

85

Radio Properties of SS 433

REFER/~NCES Gilmore,W.S., Seaquist E.R., Stocks J.S. and Crane P.C. Johnston,K. 1980 : private communication. Kaplan G.H., Kallarkal V.V.,Harrington

(1980),

AoJ.

8.,.,~, 64.

Margon B.,Grandi

S.A. and Downes R.A.

(1980):

R.S., Johnston K.J. (1980):

submitted

Seaquist E.R., Garrison R.F., Gregory P.C.,Taylor

A.R.

in preparation

and Spencer J.H.,

to Ap.J. and Crane P.C.

(1979),

A.J. 84, 1037. Seaquist E.R.,Gilmore W.S., Nelson G.J., Payten W.J. and Slee 0.B. (1980): Ap.J.Letters, in the press. Seaquist E.R.,Gilmore W.S.,Seward F.S.,and Grindlay J. (1980): submitted to Na Spencer R.e. 1979

Nature 282, 483.

Van den Heuvel E.P.J., Walker R.C. et al.,

0striker J.P.,and Petterson J.A.

1980, in press.

(1980):A and A,81, LT.