The relativistic beaming model has been successfully used to explain many of the observational properties of active galactic nuclei. In this model the total emission is formed by two components, one beamed, one unbeamed. However, the exact contribution from each component in unresolved sources is still not clear. In the radio band, the core and extended emissions are clearly separated. We adopt the method proposed by Kembhavi to separate the two contributions in the X-ray emissions in a sample of 19 gamma-ray loud blazars. It is clearly shown that the beamed emission dominates the X-ray flux and the unbeamed X-ray emission is correlated with the extended radio emission of the considered objects. We also find that the ratio of the beamed to the unbeamed X-ray luminosity is correlated with the X-ray spectral index, an effect that should be a consequence of the underlying X-ray emission mechanism.Fil: Fan, Jun Hui.  Guangzhou University. Center for Astrophysics; ChinaFil: Romero, Gustavo Esteban. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; ArgentinaFil: Wang, Yong Xiang. College of Science and Trade; ChinaFil: Zhang, Jiang Shui.  Guangzhou University. Center for Astrophysics; Chin

Fan, Jun Hui

Romero, Gustavo Esteban

Wang, Yong Xiang

Zhang, Jiang Shui

Chinese Journal of Astronomy and Astrophysics

English

CONICET Digital

Chin. J. Astron. Astrophys. Vol. 5 (2005), No. 5, 457–462(http:/ www.chjaa.org)Chinese Journal ofAstronomy andAstrophysicsSeparation of Diﬀerent Contributions to the Total X-rayLuminosity in Gamma-ray Loud BlazarsJun-Hui Fan1,2, Gustavo E. Romero3, Yong-Xiang Wang4 and Jiang-Shui Zhang11 Center for Astrophysics, Guangzhou University, Guangzhou 510400; fjh@gzhu.edu.cn2 National Astronomical Observatories, Chinese Academy of Sciences, Beijing 1000123 Instituto Argentino de Radioastronomı´a, C.C.5, (1894) Villa Elisa, Bs. As., Argentina4 College of Science and Trade, Guangzhou University, Guangzhou 511442Received 2005 January 6; accepted 2005 June 6Abstract The relativistic beaming model has been successfully used to explainmany of the observational properties of active galactic nuclei. In this model thetotal emission is formed by two components, one beamed, one unbeamed. However,the exact contribution from each component in unresolved sources is still not clear.In the radio band, the core and extended emissions are clearly separated. We adoptthe method proposed by Kembhavi to separate the two contributions in the X-rayemissions in a sample of 19 gamma-ray loud blazars. It is clearly shown that thebeamed emission dominates the X-ray ﬂux and the unbeamed X-ray emission iscorrelated with the extended radio emission of the considered objects. We also ﬁndthat the ratio of the beamed to the unbeamed X-ray luminosity is correlated withthe X-ray spectral index, an eﬀect that should be a consequence of the underlyingX-ray emission mechanism.Key words: galaxies: active-galaxies – jets – X-rays: galaxies1 INTRODUCTIONUrry & Shafer (1984) proposed that the total emission from AGNs can be separated intotwo components, namely a beamed and an unbeamed component. Then, the observed totalluminosity, Ltot, is the sum of the unbeamed, Lunb, and beamed, Lb, emissions, i.e., Ltot =Lunb + Lb.In the radio region, the two contributions can be separated by VLBI observations, and theratio of the beamed to unbeamed (or extended, Lext) luminosities deﬁnes the core-dominanceparameter R = LbLunb (orLbLext). In the X-ray band, the observed emission should also be separableinto two parts as was assumed by Brown & Murphy (1987), but the lack of angular resolutionin the observations of most sources renders a clear separation not easy. However, some methodshave been recently proposed to achieve an adequate separation of the diﬀerent contributions.In the context of the radio beaming model it was assumed that the ratio of the beamed radioemission, in the transverse direction, to the extended radio emission is a constant (Orr & Brown458 J. H. Fan, G. E. Romero, Y. X. Wang et al.1982). Browne & Murphy (1987) applied this idea to the X-ray luminosity and assumed that thetransverse beamed X-ray luminosity (Lx, b(90 deg)) is also proportional to the extended radioemission (Lr, unb), i.e., Lx, b(90 deg) = A Lr, unb, with A =constant. The beamed luminosityfor an inclination angle ψ between the beam direction and the line of sight is Lx, b(ψ) =gx(β, ψ)Lx, b(90 deg), where gx(β, ψ) is the X-ray beaming factor, given bygx(β, ψ) =12[(1 − β cosψ)−(2+αx) + (1 + β cosψ)−(2+αx)]. (1)In this expression, β is the relativistic bulk velocity in units of c and αx is the spectral indexof the beamed X-ray emission. Here, β cosψ can be obtained for each source from the followingrelationRradio = R90 deg12[(1− β cosψ)−2 + (1 + β cosψ)−2], (2)which is valid for ﬂat-spectrum radio AGNs. Rradio =Lr, bLr, ext is a core-dominance ratio andR90 deg was found to be 0.024 by Orr & Browne (1982) from numerical ﬁts of their sample. Theratio of the beamed to unbeamed X-ray luminosity isRx =Lx, bLx, unb= Rtxgx(β, ψ), Rtx =Lx, b(90 deg)Lx, b. (3)Here, Rtx is assumed to be a constant.In 1987, Browne and Murphy proposed a model, in which they assumed that the X-rayemission is proportional to the extended radio emission and the correlation between the X-rayand extended radio emissions is from the observed X-ray luminosity and radio luminosity(seeKembhavi & Narlikar 1999). Later on, Kembhavi (1993) proposed a beaming model that usesthe formalism suggested by Browne and Murphy but with a diﬀerent scheme for separatingthe X-ray luminosity into beamed and isotropic parts. Kembhavi (1993) chose a subset of 34quasars with Lr, bLr, unb > 10 from Browne and Murphy’s sample, and found a signiﬁcant correlationbetween logLx and logLr, b. Because the ﬁt is dominated by beamed emission, the logLx −logLr, b relation suggests that there may also be a relation between the beamed X-ray and radiocomponents. Since the launch of Gamma Ray Observatory (GRO) in the early 1990s, manyactive galactic nuclei (AGNs) have been detected at the E >100 MeV band with the EGRETinstrument (Hartman et al. 1999). Gamma-ray emission is one of the most interesting topics inAGN research, but the exact nature of the emission mechanism is still an open problem. Rapidvariability observed in some sources and γ − γ opacity arguments suggest that the gamma-rayemission is highly beamed. In the present paper, we will apply Kembhavi’s proposal to a sampleof 19 gamma-ray loud blazars with Lr, bLr, unb > 10 in order to establish the beaming level of X-rayemission for these sources.2 SAMPLEFrom the available literature, we selected a sample of γ-ray loud blazars with Lr, bLr, unb > 10. Therelevant information (along with the results described in the next section) is listed in Table 1.In this table column 1 gives the object name; column 2, the redshift (z); column 3, the coreluminosity at 5GHz in units of W Hz−1; column 4, the extended luminosity at 5GHz in unitsof W Hz−1; column 5, the references for the radio data; column 6, the X-ray luminosity at 1 keVin units of W Hz−1; column 7, the corresponding references for the X-ray data; column 8, theX-ray spectral index; and ﬁnally column 9, the ratio of the beamed to the unbeamed X-rayluminosities Rx =Lx, bLx, unb.Separation of Diﬀerent Contributions to the Total X-ray Luminosity 459Table 1 A Sample of 19 γ-ray Loud BlazarsName z Lr, ba Lr, unba Ref Ltotxa Ref αx Rx(1) (2) (3) (4) (5) (6) (7) (8) (9)0234+285 1.207 28.20 26.20 BM 21.050 C97 0.67 499.530235+164 0.940 27.61 26.41 Mu 21.971 C97 1.57 1029.740336–019 0.852 28.00 26.50 BM 20.710 C97 0.67 116.100420–014 0.915 28.20 25.80 BM 21.430 C97 0.67 1669.840537–441 0.894 28.20 25.90 BM 21.810 C97 1.16 12454.350735+178 0.424 27.18 25.37 Mu 20.474 C97 1.25 3120.110804+499 1.430 27.84 26.24 Mu 21.474 C97 0.56 99.800851+202 0.306 26.81 24.03 K92 20.768 C97 1.45 552049.891127–145 1.187 28.50 26.80 BM 21.610 C97 0.67 218.231222+216 0.435 26.48 25.48 H92 20.538 C97 0.67 22.721253–055 0.538 28.10 27.00 BM 21.400 C97 0.83 54.771510–089 0.361 27.30 25.80 BM 20.750 C97 0.90 288.871611+343 1.401 28.40 27.00 BM 21.680 C97 0.76 110.661633+382 1.814 28.60 26.70 BM 22.120 C97 0.53 213.191730–130 0.908 28.30 26.50 BM 21.580 C97 0.67 262.381739+522 1.375 27.90 26.20 BM 21.450 C97 0.67 218.232032+107 0.601 27.11 26.02 AU 20.216 C97 1.43 440.272230+114 1.037 28.30 26.90 BM 21.390 C97 0.67 78.492251+158 0.559 28.60 27.40 BM 21.410 C97 0.62 34.48Refs. to Table 1:a: in units of W Hz−1; AU: Antonucci & Ulvestad (1985); BM: Browne & Murphy (1987); C97: Comastriet al. (1997); Mu: Murphy et al. (1993); K92: Kollgaard et al. (1992); H92: Hooimeyer et al. (1992).3 RESULTSFollowing Kembhavi’s proposal, for the relevant data listed in Table 1, we can obtain a linearregression correlationlogLx = (0.64± 0.14) logLr, b + 3.49.The total X-ray luminosity should be formed by two components. We assume that the linearcorrelation holds for all gamma-ray loud blazars, and can be expressed aslogLx = 0.64 logLr, b + log k,where k is a constant. In this sense, the total X-ray luminosity is given byLtotx = Lx, b + Lx, unb = Lx, b(1 +1Rtxgx(β, ψ))= kL0.64r, b(1 +1Rtxgx(β, ψ)), (4)where Lx,unb = Lx,b/Rtxgx(β, φ).The two constants, log k = 3.48, and Rtx =Lx, b(90 deg)Lx, u= 5.9 × 10−3 are determinedby minimizing Σ[log(Lx/Ltotx )]2 for the objects in our sample as Browne & Murphy (1987)and Kembhavi (1993) did. The ratio of the two components in X-ray band, Rx, which can beobtained from relations (1) and (3), is listed in column 9 of Table 1.460 J. H. Fan, G. E. Romero, Y. X. Wang et al.4 DISCUSSIONBlazars are characterized by large and violent ﬂux variations, high and variable polarization,predominantly non-thermal emission over almost the entire electromagnetic spectrum and rel-ativistic electrons tangled with magnetic ﬁeld in a relativistic jet nearly pointing towards us.The blazar phenomenon can be described with a jet plus a supermassive black hole surroundedwith an accretion disk (see Urry & Padovani 1995; Wang 2003). The EGRET on Gamma-RayObservatory (GRO) has detected about 120 possible blazars (Yang & Fan 2005). Many authorshave investigated the gamma-ray emission mechanism. They showed that both the synchrotronself-Compton (SSC) and the external inverse Compton (EIC) processes are good possibilitiesto explain the gamma-ray emission, but it is not determined yet which one is the case in mostgamma-ray sources. If the beamed and the unbeamed emission in X-rays follow those in radiobands, then it will favor the SSC model since the gamma-ray emission is strongly beamed. Inthe present paper, we chose the gamma-ray loud blazars as our sample in order to separate thebeamed and the unbeamed X-ray emissions from the observed data.According to the standard model, the emission of blazars at diﬀerent wavebands should befrom two components, something that was used by several authors to explain the observationalproperties of blazars. Based on the model, Fan (2003) proposed a method to calculate theintrinsic ratio of the luminosity in the jet to the unbeamed luminosity in the co-moving frame,and found that the average ratio in BL Lacertae objects is greater than that in ﬂat spectrumradio quasars. Diﬀerent average ratios probably give rise to diﬀerent observed emission linestrengths in BL Lacertae objects, which show no emission lines or very weak emission lines andin ﬂat spectrum radio quasars that show very strong emission lines. When we considered theeﬀect of the ratio f in the polarization-core-dominance parameter plot, the BLs and FSRQssatisfy a similar correlation, which suggests that the polarization nature is quite similar inBLs and FSRQs (Fan et al. 2004). At the X-ray band, the emission should also be formed bytwo components, but they are hard to separate. Kembhavi (1993) found a tight correlationbetween radio core-luminosity and the X-ray luminosity, giving a key to separate the X-raydiﬀerent types of emission. It is then possible to discuss the relationship between X-ray andradio emission of the core and the extended regions.Fig. 1 Plot of unbeamed X-ray luminosity(W Hz−1) against unbeamed radio luminos-ity (W Hz−1). The solid line represents thebest ﬁtting result.Fig. 2 Plot of ratio RX against X-ray spec-tral index αX . The solid line represents thebet ﬁtting result.Separation of Diﬀerent Contributions to the Total X-ray Luminosity 461Fig. 3 Histogram of ratio RX.In Kemhavi’s work, Rxt was found to be 1.3× 10−2, which is twice our value of 5.9× 10−3.The diﬀerence is not large which is understandable since our and his samples are both of radioloud sources. Our Rxt gives the ratio Rx as listed in column 9 of Table 1, from which one canobtain the extended (unbeamed) X-ray emission, logLx, unb = logLtotx − logRx. The extended(unbeamed) X-ray luminosity is found to be correlated with the extended radio luminosityas shown in Figure 1, logLx, unb = (1.39 ± 0.18) logLr, unb − (17.92 ± 4.6) with a correlationcoeﬃcient r = 0.787 and a chance probability p = 4.22×10−7. This correlation may come fromthe fact that logLx, unb and logLr, unb are both closely associated with the redshift. This canbe tested if we use Padovani’s method (Padovani 1992, see also Fan et al. 1996) to deal withthe relevant data. If rij is the correlation coeﬃcient between xi and xj , in the case of threevariables the correlation between two of them, excluding the eﬀect of the third one, isr12,3 =r12 − r13r23√(1− r213)(1− r223).When the relevant data listed in Table 1 are used to the above formulae, one can ﬁnd thatlogLx, unb and logLr, unb are still correlated with a chance probability of p < 10−4. So, the coreX-ray and radio emissions are correlated and the extended ones are also correlated. It perhapsfavors the SSC model for the gamma-ray emission.In the X-ray region, the spectral index is found to change from one source to the next.Worrall & Marshall (1984) found that BLs show steeper X-ray spectral index than ﬂat spectrumradio sources. Later, Comastri et al. (1997) conﬁrmed that result. It is possibly caused by theemission mechanism of the X-rays. In BL Lacertae objects, the X-ray emission is probably fromthe synchrotron tail and shows a steeper spectrum, whereas in ﬂat spectrum radio quasarsthe X-ray emission is thought to originate from inverse Compton scattering and even, to someextent, from thermal processes in the innermost region, so it shows a ﬂatter spectrum. If thisis true, one can expect that the X-rays in BL Lacertae objects are mainly from the jet, hencedisplaying a high ratio RX , while for ﬂat spectrum radio quasars, the X-rays would be from boththe jet and the accretion disk (see Grandi & Palumbo 2004), giving a lower ratio Rx. Therefore,a correlation between Rx and αx can be expected. This is shown in Figure 2, using the data ofTable 1. The solid line represents the best ﬁt result, logRx = (2.04± 0.55)αx+0.83± 0.51 witha correlation coeﬃcient r = 0.443 and a chance probability p = 2 × 10−3. Although the pointsare somehow scattered, there seems to be a real trend for steeper X-ray spectra to correspondto higher Rx ratio, as expected. In ﬂat spectrum radio quasars, if the X-ray emission consists of462 J. H. Fan, G. E. Romero, Y. X. Wang et al.an inverse Compton contribution plus other emissions of diﬀerent origin, then it is more diﬃcultto expect that these objects could present inverse Compton TeV emission. In contrast, in BLLacertae objects, the synchrotron emission reaches the X-ray range, then one can expect thatthe inverse Compton emission can reach the TeV domain. Observations indicate that the TeVgamma-ray blazars are all BL Lacertae objects being consistent with these expectations.From Table 1, one can ﬁnd that the average ratio Rx of the sources considered in the presentpaper satisﬁes logRx = 2.60± 1.01. The corresponding histogram for Rx is shown in Figure 3.For core-dominated blazars, the X-ray emission is dominated by jets. Therefore, it is possibleto ignore the extended contribution in X-ray studies of these objects.We have separated the beamed and unbeamed contributions to the total X-ray emissionfor a sample of 19 γ-ray loud blazars. We have found that 1) The ratio of the beamed to theunbeamed luminosity is log〈Rx〉 = 2.60±1.01; 2) The unbeamed X-ray and radio emissions arecorrelated; and 3) The luminosity ratio is correlated with the X-ray spectral index.Acknowledgements The authors thank the referee for his constructive suggestions andcomments. This work was supported by the National 973 project (NKBRSF G19990754),the National Science Fund for Distinguished Young Scholars (10125313), and the Fund forTop Scholars of Guangdong Province (Q02114). J. H. Fan also thanks the support from theGuangzhou Education Committee. The GER research on high energy astrophysics is mainlysupported by the Argentine agencies CONICET and ANPCT (PICT No. 03-13291).ReferencesAntonucci R. R. J., Ulvestad J. S., 1985, ApJ, 294, 158Browne I. W. A., Murphy D. W., 1987, MNRAS, 226, 601Comastri A. et al., 1997, ApJ, 480, 534Fan J. H., 2003, ApJ, 585, L23Fan J. H., Wang Y. J., Yang J. H., Su C. Y., 2004, ChJAA, 4, 533Grandi P., Palumbo G. G. C., 2004, Sci, 306, 998Kembhavi A., 1993, MNRAS, 264, 683Kollgaard R. I. Wardle J. F. C., Roberts D. H. et al., 1992, AJ, 104, 1687Murphy D. W., Browne I. W. A., Perley R. A, 1993, MNRAS, 264, 298Hooimeyer J. R. A., Schilizzi R. T., Miley G. K. et al., 1992, A&A, 261, 25Orr M. J. L., Brown I. W. A., 1982, MNRAS, 200, 1067Urry C. M., Shafer R. A., 1984, ApJ, 280, 569Urry C. M., Padovani P., 1995, PASP, 107, 803Valtaoja E., Lahteenmaki A., Terasranta H., Lainela, M., 1999, ApJS, 120, 95Vermeulen R. C., Cohen M. H., 1994, ApJ, 430, 467Veron-Cetty M.-P., Veron P., 1998, ESO Scientiﬁc Report, No. 18Wang J.-M., 2003, AJ, 125, 2859Wills B. J., Wills D., Breger M., Antonucci R. R. J., Barvainis R., 1992, ApJ, 398, 454Wills B. J., Browne I. W. A., 1986, ApJ, 302, 56Worrall D. M., Marshall F. E., 1984, ApJ, 276, 434Yang J. H., Fan J. H., 2005, ChJAA, 5(3), 229Zensus J. A., Pearson T. J., 1988, IAU Symp. 129, 7

Separation of Different Contributions to the Total X-ray Luminosity in Gamma-ray Loud Blazars

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Chin. J. Astron. Astrophys. Vol. 5 (2005), No. 5, 457–462(http:/ www.chjaa.org)Chinese Journal ofAstronomy andAstrophysicsSeparation of Different Contributions to the Total X-rayLuminosity in Gamma-ray Loud BlazarsJun-Hui Fan1,2, Gustavo E. Romero3, Yong-Xiang Wang4 and Jiang-Shui Zhang11 Center for Astrophysics, Guangzhou University, Guangzhou 510400; fjh@gzhu.edu.cn2 National Astronomical Observatories, Chinese Academy of Sciences, Beijing 1000123 Instituto Argentino de Radioastronomı́a, C.C.5, (1894) Villa Elisa, Bs. As., Argentina4 College of Science and Trade, Guangzhou University, Guangzhou 511442Received 2005 January 6; accepted 2005 June 6Abstract The relativistic beaming model has been successfully used to explainmany of the observational properties of active galactic nuclei. In this model thetotal emission is formed by two components, one beamed, one unbeamed. However,the exact contribution from each component in unresolved sources is still not clear.In the radio band, the core and extended emissions are clearly separated. We adoptthe method proposed by Kembhavi to separate the two contributions in the X-rayemissions in a sample of 19 gamma-ray loud blazars. It is clearly shown that thebeamed emission dominates the X-ray flux and the unbeamed X-ray emission iscorrelated with the extended radio emission of the considered objects. We also findthat the ratio of the beamed to the unbeamed X-ray luminosity is correlated withthe X-ray spectral index, an effect that should be a consequence of the underlyingX-ray emission mechanism.Key words: galaxies: active-galaxies – jets – X-rays: galaxies1 INTRODUCTIONUrry & Shafer (1984) proposed that the total emission from AGNs can be separated intotwo components, namely a beamed and an unbeamed component. Then, the observed totalluminosity, Ltot, is the sum of the unbeamed, Lunb, and beamed, Lb, emissions, i.e., Ltot =Lunb + Lb.In the radio region, the two contributions can be separated by VLBI observations, and theratio of the beamed to unbeamed (or extended, Lext) luminosities defines the core-dominanceparameterR = LbLunb (orLbLext). In the X-ray band, the observed emission should also be separableinto two parts as was assumed by Brown & Murphy (1987), but the lack of angular resolutionin the observations of most sources renders a clear separation not easy. However, some methodshave been recently proposed to achieve an adequate separation of the different contributions.In the context of the radio beaming model it was assumed that the ratio of the beamed radioemission, in the transverse direction, to the extended radio emission is a constant (Orr & Brown458 J. H. Fan, G. E. Romero, Y. X. Wang et al.1982). Browne & Murphy (1987) applied this idea to the X-ray luminosity and assumed that thetransverse beamed X-ray luminosity (Lx, b(90 deg)) is also proportional to the extended radioemission (Lr, unb), i.e., Lx, b(90 deg) = A Lr, unb, with A =constant. The beamed luminosityfor an inclination angle ψ between the beam direction and the line of sight is Lx, b(ψ) =gx(β, ψ)Lx, b(90 deg), where gx(β, ψ) is the X-ray beaming factor, given bygx(β, ψ) =12[(1 − β cosψ)−(2+αx) + (1 + β cosψ)−(2+αx)]. (1)In this expression, β is the relativistic bulk velocity in units of c and αx is the spectral indexof the beamed X-ray emission. Here, β cosψ can be obtained for each source from the followingrelationRradio = R90 deg12[(1 − β cosψ)−2 + (1 + β cosψ)−2], (2)which is valid for flat-spectrum radio AGNs. Rradio =Lr, bLr, ext is a core-dominance ratio andR90 deg was found to be 0.024 by Orr & Browne (1982) from numerical fits of their sample. Theratio of the beamed to unbeamed X-ray luminosity isRx =Lx, bLx, unb= Rtxgx(β, ψ), Rtx =Lx, b(90 deg)Lx, b. (3)Here, Rtx is assumed to be a constant.In 1987, Browne and Murphy proposed a model, in which they assumed that the X-rayemission is proportional to the extended radio emission and the correlation between the X-rayand extended radio emissions is from the observed X-ray luminosity and radio luminosity(seeKembhavi & Narlikar 1999). Later on, Kembhavi (1993) proposed a beaming model that usesthe formalism suggested by Browne and Murphy but with a different scheme for separatingthe X-ray luminosity into beamed and isotropic parts. Kembhavi (1993) chose a subset of 34quasars with Lr, bLr, unb > 10 from Browne and Murphy’s sample, and found a significant correlationbetween logLx and logLr, b. Because the fit is dominated by beamed emission, the logLx −logLr, b relation suggests that there may also be a relation between the beamed X-ray and radiocomponents. Since the launch of Gamma Ray Observatory (GRO) in the early 1990s, manyactive galactic nuclei (AGNs) have been detected at the E >100 MeV band with the EGRETinstrument (Hartman et al. 1999). Gamma-ray emission is one of the most interesting topics inAGN research, but the exact nature of the emission mechanism is still an open problem. Rapidvariability observed in some sources and γ − γ opacity arguments suggest that the gamma-rayemission is highly beamed. In the present paper, we will apply Kembhavi’s proposal to a sampleof 19 gamma-ray loud blazars with Lr, bLr, unb > 10 in order to establish the beaming level of X-rayemission for these sources.2 SAMPLEFrom the available literature, we selected a sample of γ-ray loud blazars with Lr, bLr, unb > 10. Therelevant information (along with the results described in the next section) is listed in Table 1.In this table column 1 gives the object name; column 2, the redshift (z); column 3, the coreluminosity at 5GHz in units of W Hz−1; column 4, the extended luminosity at 5GHz in unitsof W Hz−1; column 5, the references for the radio data; column 6, the X-ray luminosity at 1 keVin units of W Hz−1; column 7, the corresponding references for the X-ray data; column 8, theX-ray spectral index; and finally column 9, the ratio of the beamed to the unbeamed X-rayluminosities Rx =Lx, bLx, unb.Separation of Different Contributions to the Total X-ray Luminosity 459Table 1 A Sample of 19 γ-ray Loud BlazarsName z Lr, ba Lr, unba Ref Ltotxa Ref αx Rx(1) (2) (3) (4) (5) (6) (7) (8) (9)0234+285 1.207 28.20 26.20 BM 21.050 C97 0.67 499.530235+164 0.940 27.61 26.41 Mu 21.971 C97 1.57 1029.740336–019 0.852 28.00 26.50 BM 20.710 C97 0.67 116.100420–014 0.915 28.20 25.80 BM 21.430 C97 0.67 1669.840537–441 0.894 28.20 25.90 BM 21.810 C97 1.16 12454.350735+178 0.424 27.18 25.37 Mu 20.474 C97 1.25 3120.110804+499 1.430 27.84 26.24 Mu 21.474 C97 0.56 99.800851+202 0.306 26.81 24.03 K92 20.768 C97 1.45 552049.891127–145 1.187 28.50 26.80 BM 21.610 C97 0.67 218.231222+216 0.435 26.48 25.48 H92 20.538 C97 0.67 22.721253–055 0.538 28.10 27.00 BM 21.400 C97 0.83 54.771510–089 0.361 27.30 25.80 BM 20.750 C97 0.90 288.871611+343 1.401 28.40 27.00 BM 21.680 C97 0.76 110.661633+382 1.814 28.60 26.70 BM 22.120 C97 0.53 213.191730–130 0.908 28.30 26.50 BM 21.580 C97 0.67 262.381739+522 1.375 27.90 26.20 BM 21.450 C97 0.67 218.232032+107 0.601 27.11 26.02 AU 20.216 C97 1.43 440.272230+114 1.037 28.30 26.90 BM 21.390 C97 0.67 78.492251+158 0.559 28.60 27.40 BM 21.410 C97 0.62 34.48Refs. to Table 1:a: in units of W Hz−1; AU: Antonucci & Ulvestad (1985); BM: Browne & Murphy (1987); C97: Comastriet al. (1997); Mu: Murphy et al. (1993); K92: Kollgaard et al. (1992); H92: Hooimeyer et al. (1992).3 RESULTSFollowing Kembhavi’s proposal, for the relevant data listed in Table 1, we can obtain a linearregression correlationlogLx = (0.64 ± 0.14) logLr, b + 3.49.The total X-ray luminosity should be formed by two components. We assume that the linearcorrelation holds for all gamma-ray loud blazars, and can be expressed aslogLx = 0.64 logLr, b + log k,where k is a constant. In this sense, the total X-ray luminosity is given byLtotx = Lx, b + Lx, unb = Lx, b(1 +1Rtxgx(β, ψ))= kL0.64r, b(1 +1Rtxgx(β, ψ)), (4)where Lx,unb = Lx,b/Rtxgx(β, φ).The two constants, log k = 3.48, and Rtx =Lx, b(90 deg)Lx, u= 5.9 × 10−3 are determinedby minimizing Σ[log(Lx/Ltotx )]2 for the objects in our sample as Browne & Murphy (1987)and Kembhavi (1993) did. The ratio of the two components in X-ray band, Rx, which can beobtained from relations (1) and (3), is listed in column 9 of Table 1.460 J. H. Fan, G. E. Romero, Y. X. Wang et al.4 DISCUSSIONBlazars are characterized by large and violent flux variations, high and variable polarization,predominantly non-thermal emission over almost the entire electromagnetic spectrum and rel-ativistic electrons tangled with magnetic field in a relativistic jet nearly pointing towards us.The blazar phenomenon can be described with a jet plus a supermassive black hole surroundedwith an accretion disk (see Urry & Padovani 1995; Wang 2003). The EGRET on Gamma-RayObservatory (GRO) has detected about 120 possible blazars (Yang & Fan 2005). Many authorshave investigated the gamma-ray emission mechanism. They showed that both the synchrotronself-Compton (SSC) and the external inverse Compton (EIC) processes are good possibilitiesto explain the gamma-ray emission, but it is not determined yet which one is the case in mostgamma-ray sources. If the beamed and the unbeamed emission in X-rays follow those in radiobands, then it will favor the SSC model since the gamma-ray emission is strongly beamed. Inthe present paper, we chose the gamma-ray loud blazars as our sample in order to separate thebeamed and the unbeamed X-ray emissions from the observed data.According to the standard model, the emission of blazars at different wavebands should befrom two components, something that was used by several authors to explain the observationalproperties of blazars. Based on the model, Fan (2003) proposed a method to calculate theintrinsic ratio of the luminosity in the jet to the unbeamed luminosity in the co-moving frame,and found that the average ratio in BL Lacertae objects is greater than that in flat spectrumradio quasars. Different average ratios probably give rise to different observed emission linestrengths in BL Lacertae objects, which show no emission lines or very weak emission lines andin flat spectrum radio quasars that show very strong emission lines. When we considered theeffect of the ratio f in the polarization-core-dominance parameter plot, the BLs and FSRQssatisfy a similar correlation, which suggests that the polarization nature is quite similar inBLs and FSRQs (Fan et al. 2004). At the X-ray band, the emission should also be formed bytwo components, but they are hard to separate. Kembhavi (1993) found a tight correlationbetween radio core-luminosity and the X-ray luminosity, giving a key to separate the X-raydifferent types of emission. It is then possible to discuss the relationship between X-ray andradio emission of the core and the extended regions.Fig. 1 Plot of unbeamed X-ray luminosity(W Hz−1) against unbeamed radio luminos-ity (W Hz−1). The solid line represents thebest fitting result.Fig. 2 Plot of ratio RX against X-ray spec-tral index αX . The solid line represents thebet fitting result.Separation of Different Contributions to the Total X-ray Luminosity 461Fig. 3 Histogram of ratio RX.In Kemhavi’s work, Rxt was found to be 1.3× 10−2, which is twice our value of 5.9× 10−3.The difference is not large which is understandable since our and his samples are both of radioloud sources. Our Rxt gives the ratio Rx as listed in column 9 of Table 1, from which one canobtain the extended (unbeamed) X-ray emission, logLx, unb = logLtotx − logRx. The extended(unbeamed) X-ray luminosity is found to be correlated with the extended radio luminosityas shown in Figure 1, logLx, unb = (1.39 ± 0.18) logLr, unb − (17.92 ± 4.6) with a correlationcoefficient r = 0.787 and a chance probability p = 4.22×10−7. This correlation may come fromthe fact that logLx, unb and logLr, unb are both closely associated with the redshift. This canbe tested if we use Padovani’s method (Padovani 1992, see also Fan et al. 1996) to deal withthe relevant data. If rij is the correlation coefficient between xi and xj , in the case of threevariables the correlation between two of them, excluding the effect of the third one, isr12,3 =r12 − r13r23√(1 − r213)(1 − r223).When the relevant data listed in Table 1 are used to the above formulae, one can find thatlogLx, unb and logLr, unb are still correlated with a chance probability of p < 10−4. So, the coreX-ray and radio emissions are correlated and the extended ones are also correlated. It perhapsfavors the SSC model for the gamma-ray emission.In the X-ray region, the spectral index is found to change from one source to the next.Worrall & Marshall (1984) found that BLs show steeper X-ray spectral index than flat spectrumradio sources. Later, Comastri et al. (1997) confirmed that result. It is possibly caused by theemission mechanism of the X-rays. In BL Lacertae objects, the X-ray emission is probably fromthe synchrotron tail and shows a steeper spectrum, whereas in flat spectrum radio quasarsthe X-ray emission is thought to originate from inverse Compton scattering and even, to someextent, from thermal processes in the innermost region, so it shows a flatter spectrum. If thisis true, one can expect that the X-rays in BL Lacertae objects are mainly from the jet, hencedisplaying a high ratio RX , while for flat spectrum radio quasars, the X-rays would be from boththe jet and the accretion disk (see Grandi & Palumbo 2004), giving a lower ratio Rx. Therefore,a correlation between Rx and αx can be expected. This is shown in Figure 2, using the data ofTable 1. The solid line represents the best fit result, logRx = (2.04± 0.55)αx +0.83± 0.51 witha correlation coefficient r = 0.443 and a chance probability p = 2 × 10−3. Although the pointsare somehow scattered, there seems to be a real trend for steeper X-ray spectra to correspondto higher Rx ratio, as expected. In flat spectrum radio quasars, if the X-ray emission consists of462 J. H. Fan, G. E. Romero, Y. X. Wang et al.an inverse Compton contribution plus other emissions of different origin, then it is more difficultto expect that these objects could present inverse Compton TeV emission. In contrast, in BLLacertae objects, the synchrotron emission reaches the X-ray range, then one can expect thatthe inverse Compton emission can reach the TeV domain. Observations indicate that the TeVgamma-ray blazars are all BL Lacertae objects being consistent with these expectations.From Table 1, one can find that the average ratio Rx of the sources considered in the presentpaper satisfies logRx = 2.60 ± 1.01. The corresponding histogram for Rx is shown in Figure 3.For core-dominated blazars, the X-ray emission is dominated by jets. Therefore, it is possibleto ignore the extended contribution in X-ray studies of these objects.We have separated the beamed and unbeamed contributions to the total X-ray emissionfor a sample of 19 γ-ray loud blazars. We have found that 1) The ratio of the beamed to theunbeamed luminosity is log〈Rx〉 = 2.60±1.01; 2) The unbeamed X-ray and radio emissions arecorrelated; and 3) The luminosity ratio is correlated with the X-ray spectral index.Acknowledgements The authors thank the referee for his constructive suggestions andcomments. This work was supported by the National 973 project (NKBRSF G19990754),the National Science Fund for Distinguished Young Scholars (10125313), and the Fund forTop Scholars of Guangdong Province (Q02114). J. H. Fan also thanks the support from theGuangzhou Education Committee. The GER research on high energy astrophysics is mainlysupported by the Argentine agencies CONICET and ANPCT (PICT No. 03-13291).ReferencesAntonucci R. R. J., Ulvestad J. 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Separation of Different Contributions to the Total X-ray Luminosity in Gamma-ray Loud Blazars

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