Using a large database of radio, optical, and x ray luminosities of AGNs with survival analysis, it was found that the x ray emission of the radio selected quasars has two components. One is related to the optical luminosity and the other is related to the radio luminosity

Feigelson, E. D.

Isobe, T.

Kembhavi, A.

Singh, K. P.

English

NASA Technical Reports Server

/ n /  - 
TWO COMPONENT MODEL FOR X-RAY EMISSION OF RADIO 
SELECTED QSO'S 
T. I sobe  and E.D. Feigelson 
The Pennsylvania S t a t e  Universi ty  
Department of Astronomy 
Univers i ty  Park, PA 16802 
K.P. Singh and A. Kembhavi 
Tata I n s t i t u t e  of Fundamental Research 
Homi Bhabha Road, Colaba 
Bombay 400 005, I n d i a  
ABSTRACT: Using a l a r g e  database of r ad io ,  o p t i c a l ,  and 
X-ray luminos i t i e s  of AGNs with  s u r v i v a l  a n a l y s i s ,  w e  f i n d  
the  X-ray emission of the  r ad io  s e l e c t e d  QSOs has two 
components. 
the o t h e r  is  r e l a t e d  t o  the r a d i o  luminosity.  
One i s  r e l a t e d  t o  t h e  o p t i c a l  luminos i ty  and 
Although t h e  main emission mechanism of r a d i o  s e l e c t e d  QSOs 
is  thought t o  be synchrotron emission o r  a synchrotron self-Compton 
mechanism, w e  see a r e l a t i o n  between t h e  r a d i o  luminosi ty  and t h e  X-ray 
luminos i t  
(CX = which are d e f i n i t e l y  non-thermal sources. Owen, Helfand, 
& Spangler (1981) found t h a t  t h e  r ad io  luminosi ty  of 10 GHz s e l e c t e d  
r a d i o  QSOs i s  s t rong ly  c o r r e l a t e d  with t h e  X-ray luminosity.  Owen & 
Pusche l l  (1982), however, found t h a t  t h e  r a d i o  luminosi ty  of X-ray 
s t r o n g  rad io  s e l e c t e d  QSOs i s  no t  s t rongly  c o r r e l a t e d  w i t h  t h e  X-ray 
luminosity.  Zamorani (1984) proposed an explana t ion  f o r  t h e s e  r e s u l t s .  
H e  suggested t h a t  t h e  r a d i o  s e l e c t e d  QSOs have two d i f f e r e n t  X-ray 
emission mechanisms such t h a t  
t h a t  is  weaker (Ex = Rf-5) than t h a t  of BL Lac o b j e c t s  
a B 
+ bEradio op t  
Ex = aR 
To check t h i s  model, w e  conducted a statist ical  s tudy wi th  s u r v i v a l  
a n a l y s i s  which treats upper l i m i t  problems c o r r e c t l y  and removes t h e  
s e l e c t i o n  e f f e c t  due t o  f l u x  l i m i t e d  observa t ions  i n  luminos i ty  - 
luminosi ty  r e l a t i o n s  (Feigelson & Nelson 1985; Isobe, Feigelson,  & 
Nelson 1986). 
luminosity.  Since many r ad io  s e l e c t e d  QSOs have extended lobes  and je t s  
which do not r ep resen t  p re sen t  s t a t u s  of t h e  r a d i o  a c t i v i t y  of t h e  QSOs, 
w e  ca re fu l ly  s e l e c t e d  o u t  t h e  r a d i o  cores  (Kembhavi, Fe ige lson  6 Singh 
1986). 
b e t t e r  statist ical  r e s u l t s  compared to  previous work. 
We a l s o  paid  p a r t i c u l a r  a t t e n t i o n  t o  t h e  r a d i o  
With 156 r a d i o  s e l e c t e d  QSOs (61 upper l i m i t s ) ,  we  can g e t  much 
The simplest  way t o  check t h e  model is t o  make f i t s  t o  t h e  observed 
da ta .  W e  f i t  t h r e e  models (Fig. 1) : 
1) log(Ex) = 29.0 + 0.48 log(Rr) ( s o l i d  l i n e ) ,  
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X-RAY EHISSICN CF R A D I C  S E L E C T E E  LSO'S 
f p e z n s y l v a n i d  S t a t e  u t i v . )  3 E; CSCL 03B 
Unclas  
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2 I 
I i I I I 1 I 
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2)  log(Ex) = 19.0 + 0.77 log(Er) [log(E ) > 33.81, r 
log(Ex) = 4 5 . 0  [log(ll < 33.83 (broken l i n e ) ,  r -  
o o 6 3  + b + c (dot ted  l i n e ) .  r 3) Ex = a Eo 
The va lue  a and B are d i r e c t l y  adopted from Zamorani's paper. 
genera l ized  Kendal l ' s  T method (Isobe e t  al. 1986),  we  f i t  t h e s e  l ines 
t o  t h e  data .  
censored (or  upper l i m i t )  da t a  sets,  w e  compared d ispers ions  of  d a t a  
around these  models. This  computation can be  done using t h e  Kaplan- 
Meier est imator .  The d ispers ions  a r e  0 . 6 5 ,  0 . 6 3 ,  and 0 . 4 4 ,  r e s p e c t i v e l y  
f o r  t h e  t h r e e  models. 
reducing the  d i spe r s ion  of t h e  data.  
Using 
Since the re  is no r e l i a b l e  goodness-of-fit test f o r  
Zamorani's model is a c t u a l l y  very good i n  
To r e i n f o r c e  t h e  r e s u l t ,  we  a l s o  checked p a r t i a l  rank c o r r e l a t i o n s .  
For censored d a t a  sets, only r e l a t i v e  measures of c o r r e l a t i o n  r a t h e r  
than  abso lu te  p r o b a b i l i t i e s  are obtainable.  In Table 1, w e  show t h e  
p a r t i a l  rank c o r r e l a t i o n  c o e f f i c i e n t s  f o r  r a d i o  se l ec t ed  QSOs, 
o p t i c a l l y  s e l e c t e d  QSOs, X-ray se lec ted  AGN, and r ad io  s e l e c t e d  BL Lac 
Figure  1: 
GHz r a d i o  co re  luminosi ty  dens i ty  of t h e  r ad io  s e l e c t e d  QSOs. 
circles represent  de tec ted  po in t s  and t h e  b a r s  represent  upper l i m i t s .  
The do t t ed  l i n e  is the  s t r a i g h t  l i n e  model f i t ,  t he  broken l ine  i s  the  
two s t r a i g h t  l i n e  model f i t .  and t h e  s o l i d  l i n e  i s  Zamorani's model. 
The p l o t  of t h e  0.5-4.5 keV X-ray luminosi ty  a g a i n s t  t he  5 
The 
X - 46 
m - - - ---- 
0 
... U ............ 
-
44  
42 30 32 34 36 
. .  . .  3 
objec ts .  
s e l ec t ed  QSOs and X-ray se l ec t ed  AGNs is r e l a t e d  t o  t h e i r  o p t i c a l  
luminosity.  
l a t i o n  between log(Rr) and logc2,) and this sugges ts  that t h e  X-ray 
emission i s  due to  the  non-thermal emission. 
show the highest  c o r r e l a t i o n  between log(&,) and log(11,), though t h e  
r e l a t i o n  between log(&) and log(R,) is a l s o  s t rong.  
suggests  t he  two component model. 
A s  can be seen, t h e  main X-ray emission mechanism of o p t i c a l l y  
The r a d i o  se l ec t ed  BL Lac o b j e c t s  have the  s t r o n g e s t  corre-  
The rad50 s e l e c t e d  QSOs 
T h i s  a g a i n  
From these  ana lyses ,  w e  conclude t h a t  X-ray emission i n  t h e  r a d i o  
se l ec t ed  QSOs is  l i k e l y  t o  have two components; one i s  r e l a t e d  t o  t h e  
o p t i c a l  luminosi ty  and the  o the r  is r e l a t e d  t o  the  rad io  luminosity.  
The X-ray emission r e l a t e d  t o  the  o p t i c a l  luminosi ty  may be thermal,  
similar t o  t h e  o p t i c a l l y  se l ec t ed  QSOs, and has a f l a t t e r  s p e c t r a l  
index (s lope c\r 0.5) i n  Fig. 1. The X-ray emission r e l a t e d  t o  t h e  r a d i o  
luminosi ty  may be non-thermal, similar t o  t h e  BL Lac objec ts ,  and 
appears t o  have a s t eepe r  spectrum (slope % 0.8). 
This  work w a s  supported by NASA grant  NAG 8 -555  and by NSF A w a r d  AST 83-51447 .  
References 
Feigelson,  E.D. &.Nelson, P.1. '1985, Ap. J., 293, 192. 
Isobe, T., Feigelson,  E.D., & Nelson, P.I. 1986, Ap.J., 306, 490. 
Isobe,  T., Feigelson,  E.D., Singh, K.P., & Kembhavi, A. 1986, 
Kembhavi, A., Feigelson, E.D., & Singh, K . P .  1986, M.N.R.A.S., 220, 51. 
Owen, F.N., Helfand, D.J . ,  & Spangler, S.R. 19.81, Ap.J. (Letters), 
Owen, F.N. & .Puschell, J.J. 1982, A.J . ,  87, 595. 
Zamorani, G. 1984 i n  VLBI and Compact Raze Sources, eds. R. F a n t i  e t  
-
-
submitted t o  Ap.J. Suppl. 
-
- 250, L55. 
al., (Dordreht: Reide l ) ,  p. 85. 
Table  1: Part ia l  rank cor re la t ions .  The f i r s t  l i n e  shows the  r e l a t i o n  
examined and t h e  second l i n e  shows the  f i x e d  quant i ty .  The r e s u l t s  are 
relative and cannot be compared between d i f f e r e n t  samples. 
% &x 'o-'r 
'r I X  
Sample Corre la t ion  R -R r x  
Fixed Quantity 
Radio Se lec ted  QSOs 0.31 0.45 0.13 
Op t i ca l ly  Se lec ted  QSOs 0.05 0.16 0.08 
X-ray Se lec ted  AGNs 0.07 0.64 0.07 
Radio Se lec ted  BL Lacs 0.56 0.45 0.34 


Two component model for X-ray emission of radio selected QSO's

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