/n/ - 

TWO COMPONENT MODEL FOR X-RAY EMISSION OF RADIO 

SELECTED QSO'S 

T. Isobe and E.D. Feigelson 

The Pennsylvania State University 

Department of Astronomy 

University Park, PA 16802 

K.P. Singh and A. Kembhavi 

Tata Institute of Fundamental Research 

Homi Bhabha Road, Colaba 

Bombay 400 005, India 

ABSTRACT: Using a large database of radio, optical, and 

X-ray luminosities of AGNs with survival analysis, we find 

the X-ray emission of the radio selected QSOs has two 

components. 

the other is related to the radio luminosity. 

One is related to the optical luminosity and 

Although the main emission mechanism of radio selected QSOs 

is thought to be synchrotron emission or a synchrotron self-Compton 

mechanism, we see a relation between the radio luminosity and the X-ray 

luminosit 

(CX = which are definitely non-thermal sources. Owen, Helfand, 

& Spangler (1981) found that the radio luminosity of 10 GHz selected 

radio QSOs is strongly correlated with the X-ray luminosity. Owen & 

Puschell (1982), however, found that the radio luminosity of X-ray 

strong radio selected QSOs is not strongly correlated with the X-ray 

luminosity. Zamorani (1984) proposed an explanation for these results. 

He suggested that the radio selected QSOs have two different X-ray 

emission mechanisms such that 

that is weaker (Ex = Rf-5) than that of BL Lac objects 

a B 

opt + bEradio Ex = aR 

To check this model, we conducted a statistical study with survival 

analysis which treats upper limit problems correctly and removes the 

selection effect due to flux limited observations in luminosity - 

luminosity relations (Feigelson & Nelson 1985; Isobe, Feigelson, & 

Nelson 1986). 

luminosity. Since many radio selected QSOs have extended lobes and jets 

which do not represent present status of the radio activity of the QSOs, 

we carefully selected out the radio cores (Kembhavi, Feigelson 6 Singh 

1986). 

better statistical results compared to previous work. 

We also paid particular attention to the radio 

With 156 radio selected QSOs (61 upper limits), we can get much 

The simplest way to check the model is to make fits to the observed 

data. We fit three models (Fig. 1) : 

1) log(Ex) = 29.0 + 0.48 log(Rr) (solid line), 

{NASA-CB-179923) TWO CCMECNjEl$!I HCDEL FOR N87- 14 2 40 

X-RAY EHISSICN CF RADIC SELECTEE LSO'S 

fpeznsylvanid State utiv.) 3 E; CSCL 03B 

Unclas 

G3/93 43448 
2 I 

I i I I I 1 I 

48- 0 

- 

2) log(Ex) = 19.0 + 0.77 log(Er) [log(E ) > 33.81, r 

log(Ex) = 45.0 [log(ll < 33.83 (broken line), roo63 + b + c (dotted line). r 3) Ex = a Eo 

The value a and B are directly adopted from Zamorani's paper. 

generalized Kendall's T method (Isobe et al. 1986), we fit these lines 

to the data. 

censored (or upper limit) data sets, we compared dispersions of data 

around these models. This computation can be done using the KaplanMeier estimator. The dispersions are 0.65, 0.63, and 0.44, respectively 

for the three models. 

reducing the dispersion of the data. 

Using 

Since there is no reliable goodness-of-fit test for 

Zamorani's model is actually very good in 

To reinforce the result, we also checked partial rank correlations. 

For censored data sets, only relative measures of correlation rather 

than absolute probabilities are obtainable. In Table 1, we show the 

partial rank correlation coefficients for radio selected QSOs, 

optically selected QSOs, X-ray selected AGN, and radio selected BL Lac 

Figure 1: 

GHz radio core luminosity density of the radio selected QSOs. 

circles represent detected points and the bars represent upper limits. 

The dotted line is the straight line model fit, the broken line is the 

two straight line model fit. and the solid line is Zamorani's model. 

The plot of the 0.5-4.5 keV X-ray luminosity against the 5 

The 

X 

- 46 

m - - - ---- 

0 

... U ............ 

- 

42 

44 - 

30 32 34 36 
.. .. 3 

objects. 

selected QSOs and X-ray selected AGNs is related to their optical 

luminosity. 

lation between log(Rr) and logc2,) and this suggests that the X-ray 

emission is due to the non-thermal emission. 

show the highest correlation between log(&,) and log(11,), though the 

relation between log(&) and log(R,) is also strong. 

suggests the two component model. 

As can be seen, the main X-ray emission mechanism of optically 

The radio selected BL Lac objects have the strongest correThe rad50 selected QSOs 

This again 

From these analyses, we conclude that X-ray emission in the radio 

selected QSOs is likely to have two components; one is related to the 

optical luminosity and the other is related to the radio luminosity. 

The X-ray emission related to the optical luminosity may be thermal, 

similar to the optically selected QSOs, and has a flatter spectral 

index (slope c\r 0.5) in Fig. 1. The X-ray emission related to the radio 

luminosity may be non-thermal, similar to the BL Lac objects, and 

appears to have a steeper spectrum (slope % 0.8). 

This work was supported by NASA grant NAG 8-555 and by NSF Award 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 in VLBI and Compact Raze Sources, eds. R. Fanti et 

- 

- 

submitted to Ap.J. Suppl. 

- 

- 250, L55. 

al., (Dordreht: Reidel), p. 85. 

Table 1: Partial rank correlations. The first line shows the relation 

examined and the second line shows the fixed quantity. The results are 

relative and cannot be compared between different samples. 

% &x 'o-'r 

'r IX 

Sample Correlation R -R 

rx 

Fixed Quantity 

Radio Selected QSOs 0.31 0.45 0.13 

Optically Selected QSOs 0.05 0.16 0.08 

X-ray Selected AGNs 0.07 0.64 0.07 

Radio Selected BL Lacs 0.56 0.45 0.34