Jets are found in a variety of astrophysical sources, from young stellar
objects to active galactic nuclei. In all the cases the jet propagates with a
supersonic velocity through the external medium, which can be inhomogeneous,
and inhomogeneities could penetrate into the jet. The interaction of the jet
material with an obstacle produces a bow shock in the jet in which particles
can be accelerated up to relativistic energies and emit high-energy photons. In
this work, we explore the active galactic nuclei scenario, focusing on the
dynamical and radiative consequences of the interaction at different jet
heights. We find that the produced high-energy emission could be detectable by
the current gamma-ray telescopes. In general, the jet-clump interactions are a
possible mechanism to produce (steady or flaring) high-energy emission in many
astrophysical sources in which jets are present.Comment: 4 pages, 2 figures. Accepted for publication in the Proceedings of
  the 275 IAU Symposium: "Jets at all Scales", held in Buenos Aires, September
  13-17, 201

A. T. Araudo

Araudo

G. E. Romero

Raga

V. Bosch-Ramon

English

arXiv

AbstractJets are found in a variety of astrophysical sources. In all the cases the jet propagates with a supersonic velocity through the external medium, which can be inhomogeneous, and inhomogeneities could penetrate into the jet. The interaction of the jet material with an obstacle produces a bow-like shock within the jet in which particles can be accelerated up to relativistic energies and emit high-energy photons. In this work, we explore the active galactic nuclei scenario, focusing on the dynamical and radiative consequences of the interaction at different jet heights. We find that the produced high-energy emission could be detectable by the current γ-ray telescopes. In general, the jet-clump interactions are a possible mechanism to produce (steady or flaring) high-energy emission in many astrophysical sources in which jets are present.</jats:p

Crossref

Proceedings of the International Astronomical Union

Radiation from matter entrainment in astrophysical jets: the AGN case

Jets are found in a variety of astrophysical sources. In all the cases the jet propagates with a supersonic velocity through the external medium, which can be inhomogeneous, and inhomogeneities could penetrate into the jet. The interaction of the jet material with an obstacle produces a bow-like shock within the jet in which particles can be accelerated up to relativistic energies and emit high-energy photons. In this work, we explore the active galactic nuclei scenario, focusing on the dynamical and radiative consequences of the interaction at different jet heights. We find that the produced high-energy emission could be detectable by the current γ-ray telescopes. In general, the jet-clump interactions are a possible mechanism to produce (steady or flaring) high-energy emission in many astrophysical sources in which jets are present.Facultad de Ciencias Astronómicas y Geofísica

Araudo, Anabella Teresa

Bosch Ramon, V.

Romero, Gustavo Esteban

LAReferencia - Red Federada de Repositorios Institucionales de Publicaciones Científicas Latinoamericanas

Title of your IAU SymposiumProceedings IAU Symposium No. 275, 2011G. E. Romero, R. A. Sunyaev & T. Belloni, eds.c° International Astronomical Union 2011doi:10.1017/S1743921310015802Radiation from matter entrainment inastrophysical jets: the AGN caseA. T. Araudo1,2, V. Bosch-Ramon3 and G. E. Romero1,21 Instituto Argentino de Radioastronomı́a (CCT La Plata, CONICET),C.C.5, 1894 Villa Elisa, Buenos Aires, Argentinaemail: aaraudo@fcaglp.unlp.edu.ar, romero@fcaglp.unlp.edu.ar2Facultad de Ciencias Astronómicas y Geof́ısicas, Universidad Nacional de La Plata,Paseo del Bosque, 1900 La Plata, Argentina3Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2, Irelandemail: valenti@cp.dias.ieAbstract. Jets are found in a variety of astrophysical sources. In all the cases the jet propa-gates with a supersonic velocity through the external medium, which can be inhomogeneous,and inhomogeneities could penetrate into the jet. The interaction of the jet material with anobstacle produces a bow-like shock within the jet in which particles can be accelerated up torelativistic energies and emit high-energy photons. In this work, we explore the active galac-tic nuclei scenario, focusing on the dynamical and radiative consequences of the interaction atdifferent jet heights. We find that the produced high-energy emission could be detectable bythe current γ-ray telescopes. In general, the jet-clump interactions are a possible mechanism toproduce (steady or flaring) high-energy emission in many astrophysical sources in which jets arepresent.Keywords. galaxies: active, radiation mechanisms: nonthermal1. IntroductionJets at different scales are present in astrophysical sources such as protostars, micro-quasars and active galactic nuclei (AGN). The medium that surrounds the jets can beinhomogeneous and clumps from this external medium can interact with the jets.In young stellar objects, the interaction of matter from the external medium withprotostar outflows has been proposed to explain the formation of Herbig-Haro (HH)objects. The dynamical properties of this interaction have been numerically simulatedby Raga et al. (2003), and they conclude that clumps with mass between 10−4 and 0.1times the mass of a giant planet can significantly contribute to the molecular mass ofHH outflows. However, the velocity of HH jets is not relativistic (∼ hundred km s−1),and particle acceleration in the bow shock formed in the jet might be inefficient or thepossible non-thermal emission produced by accelerated particles might be hidden bythermal radiation.In high-mass microquasars, the interaction of clumps from the companion stellar wind(Owocki & Cohen, 2006) with the jets of the compact object (black hole or neutron star)can produce strong bow-like shocks within the jet. Electrons and protons accelerated inthose shocks can radiate significant amount of γ rays in the form of flaring and steadyemission (Araudo et al. 2009). In the case where only few clumps interact with the jet,the produced emission is sporadic and can explain the GeV flares detected from someγ-ray binaries (e.g. Abdo et al. 2009).At extragalactic scales, AGN are composed by an accreting supermassive black hole(SMBH) at the center of the galaxy and relativistic jets. Surrounding the SMBH there is131https://www.cambridge.org/core/terms. https://doi.org/10.1017/S1743921310015802Downloaded from https://www.cambridge.org/core. IP address: 163.10.34.204, on 16 Sep 2019 at 17:54:18, subject to the Cambridge Core terms of use, available at132 A. T. Araudo, V. Bosch-Ramon & G. E. Romeroa population of clouds (Krolik et al. 1981) that move at velocities > 1000 km s−1 formingthe called broad line region (BLR). In the present contribution, we illustrate the mostimportant dynamical and radiative consequences of the interaction of clouds from theBLR with the base of AGN jets. We found that γ rays from jet-cloud interactions shouldbe detectable by present and future instrumentation in nearby low-luminous AGN athigh energy (HE) and very high energy (VHE), and in powerful and nearby quasars onlyat HE because the VHE radiation is absorbed by the dense nuclear photon fields. In thecase of sources exhibiting boosted γ rays (blazars), the isotropic radiation from jet-cloudinteractions will be masked by the jet beamed emission, which will not be the case innon-blazar sources.2. The jet-cloud interactionWe adopt clouds with density nc = 1010 cm−3 , size Rc = 1013 cm, and velocityvc = 109 cm s−1 . The jet Lorentz factor is fixed to Γ = 10, implying a jet velocity vj ≈ c,and the radius/height relation is fixed to Rj = 0.1 z. The jet density nj in the laboratoryreference frame (RF) can be estimated as nj = Lj/((Γ−1)mp c3σj), where σj = πR2j andLj is the kinetic power of the matter-dominated jet.The completely penetration of a cloud into the jet, the ram pressure of the latter shouldnot destroy the former before the cloud has fully entered into the jet. This means thatthe time required by the cloud to penetrate into the jet, tc∼2Rc/vc = 2 × 104 s, shouldbe shorter than the cloud lifetime inside the jet. To estimate this cloud lifetime, we firstcompute the time required by the shock in the cloud to cross it (tcs). The velocity of thisshock is vcs∼χ−1/2 c, where χ = nc/nj(Γ−1), is derived by ensuring that the jet and thecloud shock ram pressures are equal. This yields a cloud shocking time oftcs∼2Rcvcs' 7×104µRc1013 cm¶ ³ nc1010 cm−3´1/2 ³ z1016 cm´ µ Lj1044 erg s−1¶−1/2s . (2.1)Rayleigh-Taylor (RT) and Kelvin-Helmholtz (KH) instabilities produced in the cloudsurface by the interaction with the jet material will affect the obstacle. The timescale inwhich these instabilities grow up to a scale length ∼Rc is tRT/KH∼tcs . For this reason,we take tcs as the characteristic timescale of our study. Therefore, for a penetration time(tc) at least as long as ∼tcs , the cloud will remain an effective obstacle for the jet flow.Setting tc∼tcs , we obtain the minimum value for the interaction height zint , givingzminint ≈ 2.5 × 1015³ vc109 cm s−1´−1 ³ nc1010 cm−3´−1/2 µ Lj1044 erg s−1¶1/2cm. (2.2)For zint > zminint , the jet crossing time tj∼2Rj/vc results larger than tcs . Once the cloudis inside the jet, a bow shock around the cloud is formed on a time tbs∼Z/vj∼102 s at adistance Z∼0.3Rc cm from the cloud. In this bow shock, particles can be accelerated upto relativistic energies more efficiently than in the cloud shock (because the bow-shockvelocity is vbs À vcs).3. Non-thermal emissionThe non-thermal luminosity of particles accelerated in the bow shock can be estimatedas a fraction ηnt of the bow shock luminosity: Lnt∼ηnt Lbs, where Lbs∼(σc/σj)Lj and σc =πR2c . The accelerator/emitter magnetic field in the bow-shock RF (B) can be determinedby relating UB = ηBUnt, where UB = B2/8π and Unt = Lnt/(σcc) are the magnetic andhttps://www.cambridge.org/core/terms. https://doi.org/10.1017/S1743921310015802Downloaded from https://www.cambridge.org/core. IP address: 163.10.34.204, on 16 Sep 2019 at 17:54:18, subject to the Cambridge Core terms of use, available atRadiation from matter entrainment in astrophysical jets 133Figure 1. Left: acceleration gain, escape, and cooling lepton timescales are plotted. SSC isplotted when the steady state is reached and EC for both the BLR and disc photon fields areshown for the conditions of faint (BLR: 1044 ; disc: 1045 erg s−1 ) and bright sources (BLR: 1046 ;disc: 1047 erg s−1 ). Synchrotron and relativistic bremsstrahlung are also plotted. Right: Upperlimits to the γ-ray luminosity produced by N jc clouds inside the jet as a function of Lj in FR IIsources. Two cases are plotted, one assuming that clouds cross the jet without disruption (greensolid lines), and one in which the clouds are destroyed in a time as short as tcs (green dashedlines). In addition, the sensitivity levels of Fermi in the range 0.1–1 GeV (maroon dotted lines)are plotted for three different distances d = 10, 100, and 1000 Mpc.the non-thermal energy densities, respectively. Fixing ηnt = 0.1 and ηB = 0.01, weobtain Lnt∼4 × 1039(Lj/1044 erg s−1) erg s−1 and B∼10 G. Regarding the accelerationmechanism, we adopt the following prescription for the acceleration rate: Ėacc = 0.1 q B c,where q is the electron charge.We assume that electrons and protons are injected into the bow-shock region followinga power law in energy of index 2.2 and with an exponential cutoff at the maximum energy.The injection luminosity is Lnt. Particles are affected by different losses that balancethe energy gain from acceleration. The escape time downstream from the relativisticbow shock considers advection (tadv∼3Rc/c∼103 s) and diffusion (tdiff = 3Z2/2 rg c)timescales. In the latter expression, rg is the particle gyroradius and the Bohm regimehas been considered. The most important radiative losses that affect the lepton injectionare synchrotron and SSC, determining a maximum energy Emaxe of several TeV, as isshown in Figure 1 (left). In the case of protons, pp cooling is negligible in the bow-shockregion and the maximum energy is constrained by equating the acceleration and diffusiontimescales, given Emaxp ∼5 × 103 (B/10G) TeV. Then, protons with energies > 0.4Emaxpcan reach the cloud by diffusion and radiate there via pp more efficiently than in the jet,since nc À nj(zint).4. Many clouds interacting with the jetsMany of the BLR clouds can be simultaneously inside the jet at different z, eachof them producing non-thermal radiation. Therefore, the total luminosity can be muchlarger than that produced by just one interaction, which is ∼Lnt. The number of cloudswithin the jets, at zminint 6 z 6 Rblr , can be computed from the jet (Vj) and cloud (Vc)volumes, resulting in N jc = 2 f Vj/Vc ∼ 9(Lj/1044 erg s−1)2 , where the factor 2 accountsfor the two jets and f∼10−6 is the filling factor of clouds in the whole BLR. In reality, N jcis correct if one neglects the cloud disruption inside the jet. However, even under cloudfragmentation, strong bow shocks can form around the cloud fragments before these haveaccelerated up to close vj . Then, the real number of interacting clouds inside the jet isdifficult to estimate, but it could be between (tcs/tj)N jc and Njc .https://www.cambridge.org/core/terms. https://doi.org/10.1017/S1743921310015802Downloaded from https://www.cambridge.org/core. IP address: 163.10.34.204, on 16 Sep 2019 at 17:54:18, subject to the Cambridge Core terms of use, available at134 A. T. Araudo, V. Bosch-Ramon & G. E. RomeroThe presence of many clouds inside the jet implies that the total non-thermal lumi-nosity available in the BLR-jet intersection region isLtotnt ∼2Z Rb l rzm inin tdN jcdzLnt(z) dz∼2×1040³ηnt0.1´ µ Rc1013 cm¶−1 µLj1044 erg s−1¶1.7 ergs, (4.1)where dN jc is the number of clouds located in a jet volume dVj = π (0.1z)2 dz. In all thecalculations Lblr has been fixed to 0.1Lj , as approximately found in FR II galaxies, andRblr has been derived from Kaspi et al. (2005).In Fig. 1 (right), we show estimates of the γ-ray luminosity when many clouds interactsimultaneously with the jet. For this, we have followed a simple approach assuming thatmost of the non-thermal luminosity is converted into γ rays. This will be the case aslong as the escape and synchrotron cooling time are longer than the IC cooling time(EC+SSC) at the highest electron energies. In Araudo et al. (2010), we present moredetailed calculations by applying the model presented in this contribution to two char-acteristic sources, Cen A and 3C 273.5. DiscussionWe have studied the interaction of clouds from the BLR with the base of jets in AGNs.For very nearby sources, such as Cen A, the interaction of large clouds (Rc > 1013 cm)with jets may be detectable as a flaring event, although the number of these large cloudsand thereby the duty cycle of the flares are difficult to estimate. Given the weak externalphoton fields in these sources, VHE photons can escape without experiencing significantabsorption. Therefore, jet-cloud interactions in nearby FR I may be detectable in boththe HE and the VHE range as flares with timescales of about one day.In FR II sources, many BLR clouds could interact simultaneously with the jet. Thenumber of clouds depends strongly on the cloud lifetime inside the jet, which could be ofthe order of several tcs . Nevertheless, we note that after cloud fragmentation many bowshocks may still form and efficiently accelerate particles if these fragments move moreslowly than the jet. Since FR II sources are expected to exhibit high accretion rates,radiation above 1 GeV produced in the jet base can be strongly attenuated by the densedisc and the BLR photon fields, although γ rays below 1 GeV should not be affectedsignificantly. Since jet-cloud emission should be rather isotropic, it would be masked byjet beamed emission in blazar sources, although since powerful/nearby FR II jets donot display significant beaming, these objects may produce detectable γ rays throughjet-cloud interactions. As shown in Fig. 1 (right), close and powerful sources could bedetectable by deep enough observations of Fermi.ReferencesAbdo, A. A. et al. 2009, ApJS, 183, 46Araudo, A. T., Bosch-Ramon, V., & Romero, G. E. 2009, A&A, 503, 673Araudo, A. T., Bosch-Ramon, V., & Romero, G. E. 2010, A&A (in press) [arXiv:1007.2199]Begelman, M. C., Blandford, R. D., & Rees, M. J. 1984, Rev. Mod. Phys., 56, 255Kaspi, S., Maoz, D., Netzer, H., Peterson, B. M., Vestergaard, M., & Jannuzi, B. T. 2005, ApJ,629, 61Krolik, J. H., McKee, C. F., & Tarter, C. B. 1981, ApJ, 249, 422Owocki, S. P., & Cohen D. H. 2006, ApJ, 648, 5650Raga, A. C., Velzquez, P. F., de Gouveia dal Pino, E. M., Noriega-Crespo, A., & Mininni,P. 2003, RMxAC, 15, 115https://www.cambridge.org/core/terms. https://doi.org/10.1017/S1743921310015802Downloaded from https://www.cambridge.org/core. IP address: 163.10.34.204, on 16 Sep 2019 at 17:54:18, subject to the Cambridge Core terms of use, available atRadiation from matter entrainment in astrophysical jets 135DiscussionMirabel: Can you apply the same model to the MQSO Cyg X-3 that has a WRayetdonor and LGRBs that usualy have WRayet progenitors?Araudo: We have applied the model to high-mass microquasars (HMMQ), studyingthe interaction between clumps from the wind of the companion star with the jet ofthe compact object (Araudo, Bosch-Ramon & Romero 2009). In this work, we haveconsidered a source with similar parameters to the system Cygnus X-1. Now, we areworking on the application of the model to the HMMQ Cygnus X-3. We have not appliedthe model to gamma-ray bursts.Perucho: Stellar winds shocked by the jet flow could also be an interesting scenario tocheck. Have you considered it?Araudo: We have not considered the interaction between stars and jets in AGNs, but weare going to do this in the near future. A similar scenario has been studied by Bednarek& Protheroe (1997).Drappeau: How do calculate the number of clouds at any given time? i.e. What is thedestruction rate and the entrainment rate of clouds in jets?Araudo: To estimate the number of clouds into the jet, we calculate Nc∼2xfxVj/Vc ,where f∼10−6 is the filling factor of clouds in the broad line region (BLR), Vc is thevolume of the clouds, and Vj is the volume of the jet intesected by the BLR. In thisestimation, we not consider the destruction of clouds into the jet. The previous equationfor Nc takes into account that the entrainment is equal to the escape rate of the jet, andis independent of time.https://www.cambridge.org/core/terms. https://doi.org/10.1017/S1743921310015802Downloaded from https://www.cambridge.org/core. IP address: 163.10.34.204, on 16 Sep 2019 at 17:54:18, subject to the Cambridge Core terms of use, available at

Radiation from matter entrainment in astrophysical jets: The AGN case

El Servicio de Difusión de la Creación Intelectual

Title of your IAU Symposium
Proceedings IAU Symposium No. 275, 2011
G. E. Romero, R. A. Sunyaev & T. Belloni, eds.
c° International Astronomical Union 2011
doi:10.1017/S1743921310015802
Radiation from matter entrainment in
astrophysical jets: the AGN case
A. T. Araudo1,2, V. Bosch-Ramon3 and G. E. Romero1,2
1 Instituto Argentino de Radioastronomı´a (CCT La Plata, CONICET),
C.C.5, 1894 Villa Elisa, Buenos Aires, Argentina
email: aaraudo@fcaglp.unlp.edu.ar, romero@fcaglp.unlp.edu.ar
2Facultad de Ciencias Astrono´micas y Geof´ısicas, Universidad Nacional de La Plata,
Paseo del Bosque, 1900 La Plata, Argentina
3Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2, Ireland
email: valenti@cp.dias.ie
Abstract. Jets are found in a variety of astrophysical sources. In all the cases the jet propa-
gates with a supersonic velocity through the external medium, which can be inhomogeneous,
and inhomogeneities could penetrate into the jet. The interaction of the jet material with an
obstacle produces a bow-like shock within the jet in which particles can be accelerated up to
relativistic energies and emit high-energy photons. In this work, we explore the active galac-
tic nuclei scenario, focusing on the dynamical and radiative consequences of the interaction at
different jet heights. We find that the produced high-energy emission could be detectable by
the current γ-ray telescopes. In general, the jet-clump interactions are a possible mechanism to
produce (steady or flaring) high-energy emission in many astrophysical sources in which jets are
present.
Keywords. galaxies: active, radiation mechanisms: nonthermal
1. Introduction
Jets at different scales are present in astrophysical sources such as protostars, micro-
quasars and active galactic nuclei (AGN). The medium that surrounds the jets can be
inhomogeneous and clumps from this external medium can interact with the jets.
In young stellar objects, the interaction of matter from the external medium with
protostar outflows has been proposed to explain the formation of Herbig-Haro (HH)
objects. The dynamical properties of this interaction have been numerically simulated
by Raga et al. (2003), and they conclude that clumps with mass between 10−4 and 0.1
times the mass of a giant planet can significantly contribute to the molecular mass of
HH outflows. However, the velocity of HH jets is not relativistic (∼ hundred km s−1),
and particle acceleration in the bow shock formed in the jet might be inefficient or the
possible non-thermal emission produced by accelerated particles might be hidden by
thermal radiation.
In high-mass microquasars, the interaction of clumps from the companion stellar wind
(Owocki & Cohen, 2006) with the jets of the compact object (black hole or neutron star)
can produce strong bow-like shocks within the jet. Electrons and protons accelerated in
those shocks can radiate significant amount of γ rays in the form of flaring and steady
emission (Araudo et al. 2009). In the case where only few clumps interact with the jet,
the produced emission is sporadic and can explain the GeV flares detected from some
γ-ray binaries (e.g. Abdo et al. 2009).
At extragalactic scales, AGN are composed by an accreting supermassive black hole
(SMBH) at the center of the galaxy and relativistic jets. Surrounding the SMBH there is
131
https://www.cambridge.org/core/terms. https://doi.org/10.1017/S1743921310015802
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132 A. T. Araudo, V. Bosch-Ramon & G. E. Romero
a population of clouds (Krolik et al. 1981) that move at velocities > 1000 km s−1 forming
the called broad line region (BLR). In the present contribution, we illustrate the most
important dynamical and radiative consequences of the interaction of clouds from the
BLR with the base of AGN jets. We found that γ rays from jet-cloud interactions should
be detectable by present and future instrumentation in nearby low-luminous AGN at
high energy (HE) and very high energy (VHE), and in powerful and nearby quasars only
at HE because the VHE radiation is absorbed by the dense nuclear photon fields. In the
case of sources exhibiting boosted γ rays (blazars), the isotropic radiation from jet-cloud
interactions will be masked by the jet beamed emission, which will not be the case in
non-blazar sources.
2. The jet-cloud interaction
We adopt clouds with density nc = 1010 cm−3 , size Rc = 1013 cm, and velocity
vc = 109 cm s−1 . The jet Lorentz factor is fixed to Γ = 10, implying a jet velocity vj ≈ c,
and the radius/height relation is fixed to Rj = 0.1 z. The jet density nj in the laboratory
reference frame (RF) can be estimated as nj = Lj/((Γ−1)mp c3σj), where σj = πR2j and
Lj is the kinetic power of the matter-dominated jet.
The completely penetration of a cloud into the jet, the ram pressure of the latter should
not destroy the former before the cloud has fully entered into the jet. This means that
the time required by the cloud to penetrate into the jet, tc∼2Rc/vc = 2× 104 s, should
be shorter than the cloud lifetime inside the jet. To estimate this cloud lifetime, we first
compute the time required by the shock in the cloud to cross it (tcs). The velocity of this
shock is vcs∼χ−1/2 c, where χ = nc/nj(Γ−1), is derived by ensuring that the jet and the
cloud shock ram pressures are equal. This yields a cloud shocking time of
tcs∼2Rc
vcs
' 7×104
µ
Rc
1013 cm
¶ ³ nc
1010 cm−3
´1/2 ³ z
1016 cm
´µ Lj
1044 erg s−1
¶−1/2
s . (2.1)
Rayleigh-Taylor (RT) and Kelvin-Helmholtz (KH) instabilities produced in the cloud
surface by the interaction with the jet material will affect the obstacle. The timescale in
which these instabilities grow up to a scale length ∼Rc is tRT/KH∼tcs . For this reason,
we take tcs as the characteristic timescale of our study. Therefore, for a penetration time
(tc) at least as long as ∼tcs , the cloud will remain an effective obstacle for the jet flow.
Setting tc∼tcs , we obtain the minimum value for the interaction height zint , giving
zminint ≈ 2.5× 1015
³ vc
109 cm s−1
´−1 ³ nc
1010 cm−3
´−1/2 µ Lj
1044 erg s−1
¶1/2
cm. (2.2)
For zint > zminint , the jet crossing time tj∼2Rj/vc results larger than tcs . Once the cloud
is inside the jet, a bow shock around the cloud is formed on a time tbs∼Z/vj∼102 s at a
distance Z∼0.3Rc cm from the cloud. In this bow shock, particles can be accelerated up
to relativistic energies more efficiently than in the cloud shock (because the bow-shock
velocity is vbs À vcs).
3. Non-thermal emission
The non-thermal luminosity of particles accelerated in the bow shock can be estimated
as a fraction ηnt of the bow shock luminosity: Lnt∼ηnt Lbs, where Lbs∼(σc/σj)Lj and σc =
πR2c . The accelerator/emitter magnetic field in the bow-shock RF (B) can be determined
by relating UB = ηBUnt, where UB = B2/8π and Unt = Lnt/(σcc) are the magnetic and
https://www.cambridge.org/core/terms. https://doi.org/10.1017/S1743921310015802
Downloaded from https://www.cambridge.org/core. IP address: 163.10.34.204, on 16 Sep 2019 at 17:54:18, subject to the Cambridge Core terms of use, available at
Radiation from matter entrainment in astrophysical jets 133
Figure 1. Left: acceleration gain, escape, and cooling lepton timescales are plotted. SSC is
plotted when the steady state is reached and EC for both the BLR and disc photon fields are
shown for the conditions of faint (BLR: 1044 ; disc: 1045 erg s−1 ) and bright sources (BLR: 1046 ;
disc: 1047 erg s−1 ). Synchrotron and relativistic bremsstrahlung are also plotted. Right: Upper
limits to the γ-ray luminosity produced by N jc clouds inside the jet as a function of Lj in FR II
sources. Two cases are plotted, one assuming that clouds cross the jet without disruption (green
solid lines), and one in which the clouds are destroyed in a time as short as tcs (green dashed
lines). In addition, the sensitivity levels of Fermi in the range 0.1–1 GeV (maroon dotted lines)
are plotted for three different distances d = 10, 100, and 1000 Mpc.
the non-thermal energy densities, respectively. Fixing ηnt = 0.1 and ηB = 0.01, we
obtain Lnt∼4 × 1039(Lj/1044 erg s−1) erg s−1 and B∼10 G. Regarding the acceleration
mechanism, we adopt the following prescription for the acceleration rate: E˙acc = 0.1 q B c,
where q is the electron charge.
We assume that electrons and protons are injected into the bow-shock region following
a power law in energy of index 2.2 and with an exponential cutoff at the maximum energy.
The injection luminosity is Lnt. Particles are affected by different losses that balance
the energy gain from acceleration. The escape time downstream from the relativistic
bow shock considers advection (tadv∼3Rc/c∼103 s) and diffusion (tdiff = 3Z2/2 rg c)
timescales. In the latter expression, rg is the particle gyroradius and the Bohm regime
has been considered. The most important radiative losses that affect the lepton injection
are synchrotron and SSC, determining a maximum energy Emaxe of several TeV, as is
shown in Figure 1 (left). In the case of protons, pp cooling is negligible in the bow-shock
region and the maximum energy is constrained by equating the acceleration and diffusion
timescales, given Emaxp ∼5 × 103 (B/10G) TeV. Then, protons with energies > 0.4Emaxp
can reach the cloud by diffusion and radiate there via pp more efficiently than in the jet,
since nc À nj(zint).
4. Many clouds interacting with the jets
Many of the BLR clouds can be simultaneously inside the jet at different z, each
of them producing non-thermal radiation. Therefore, the total luminosity can be much
larger than that produced by just one interaction, which is ∼Lnt. The number of clouds
within the jets, at zminint 6 z 6 Rblr , can be computed from the jet (Vj) and cloud (Vc)
volumes, resulting in N jc = 2 f Vj/Vc ∼ 9(Lj/1044 erg s−1)2 , where the factor 2 accounts
for the two jets and f∼10−6 is the filling factor of clouds in the whole BLR. In reality, N jc
is correct if one neglects the cloud disruption inside the jet. However, even under cloud
fragmentation, strong bow shocks can form around the cloud fragments before these have
accelerated up to close vj . Then, the real number of interacting clouds inside the jet is
difficult to estimate, but it could be between (tcs/tj)N jc and N
j
c .
https://www.cambridge.org/core/terms. https://doi.org/10.1017/S1743921310015802
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134 A. T. Araudo, V. Bosch-Ramon & G. E. Romero
The presence of many clouds inside the jet implies that the total non-thermal lumi-
nosity available in the BLR-jet intersection region is
Ltotnt ∼2
Z Rb l r
zm inin t
dN jc
dz
Lnt(z) dz∼2×1040
³ηnt
0.1
´µ Rc
1013 cm
¶−1 µ
Lj
1044 erg s−1
¶1.7 erg
s
, (4.1)
where dN jc is the number of clouds located in a jet volume dVj = π (0.1z)
2 dz. In all the
calculations Lblr has been fixed to 0.1Lj , as approximately found in FR II galaxies, and
Rblr has been derived from Kaspi et al. (2005).
In Fig. 1 (right), we show estimates of the γ-ray luminosity when many clouds interact
simultaneously with the jet. For this, we have followed a simple approach assuming that
most of the non-thermal luminosity is converted into γ rays. This will be the case as
long as the escape and synchrotron cooling time are longer than the IC cooling time
(EC+SSC) at the highest electron energies. In Araudo et al. (2010), we present more
detailed calculations by applying the model presented in this contribution to two char-
acteristic sources, Cen A and 3C 273.
5. Discussion
We have studied the interaction of clouds from the BLR with the base of jets in AGNs.
For very nearby sources, such as Cen A, the interaction of large clouds (Rc > 1013 cm)
with jets may be detectable as a flaring event, although the number of these large clouds
and thereby the duty cycle of the flares are difficult to estimate. Given the weak external
photon fields in these sources, VHE photons can escape without experiencing significant
absorption. Therefore, jet-cloud interactions in nearby FR I may be detectable in both
the HE and the VHE range as flares with timescales of about one day.
In FR II sources, many BLR clouds could interact simultaneously with the jet. The
number of clouds depends strongly on the cloud lifetime inside the jet, which could be of
the order of several tcs . Nevertheless, we note that after cloud fragmentation many bow
shocks may still form and efficiently accelerate particles if these fragments move more
slowly than the jet. Since FR II sources are expected to exhibit high accretion rates,
radiation above 1 GeV produced in the jet base can be strongly attenuated by the dense
disc and the BLR photon fields, although γ rays below 1 GeV should not be affected
significantly. Since jet-cloud emission should be rather isotropic, it would be masked by
jet beamed emission in blazar sources, although since powerful/nearby FR II jets do
not display significant beaming, these objects may produce detectable γ rays through
jet-cloud interactions. As shown in Fig. 1 (right), close and powerful sources could be
detectable by deep enough observations of Fermi.
References
Abdo, A. A. et al. 2009, ApJS, 183, 46
Araudo, A. T., Bosch-Ramon, V., & Romero, G. E. 2009, A&A, 503, 673
Araudo, A. T., Bosch-Ramon, V., & Romero, G. E. 2010, A&A (in press) [arXiv:1007.2199]
Begelman, M. C., Blandford, R. D., & Rees, M. J. 1984, Rev. Mod. Phys., 56, 255
Kaspi, S., Maoz, D., Netzer, H., Peterson, B. M., Vestergaard, M., & Jannuzi, B. T. 2005, ApJ,
629, 61
Krolik, J. H., McKee, C. F., & Tarter, C. B. 1981, ApJ, 249, 422
Owocki, S. P., & Cohen D. H. 2006, ApJ, 648, 5650
Raga, A. C., Velzquez, P. F., de Gouveia dal Pino, E. M., Noriega-Crespo, A., & Mininni,
P. 2003, RMxAC, 15, 115
https://www.cambridge.org/core/terms. https://doi.org/10.1017/S1743921310015802
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Radiation from matter entrainment in astrophysical jets 135
Discussion
Mirabel: Can you apply the same model to the MQSO Cyg X-3 that has a WRayet
donor and LGRBs that usualy have WRayet progenitors?
Araudo: We have applied the model to high-mass microquasars (HMMQ), studying
the interaction between clumps from the wind of the companion star with the jet of
the compact object (Araudo, Bosch-Ramon & Romero 2009). In this work, we have
considered a source with similar parameters to the system Cygnus X-1. Now, we are
working on the application of the model to the HMMQ Cygnus X-3. We have not applied
the model to gamma-ray bursts.
Perucho: Stellar winds shocked by the jet flow could also be an interesting scenario to
check. Have you considered it?
Araudo: We have not considered the interaction between stars and jets in AGNs, but we
are going to do this in the near future. A similar scenario has been studied by Bednarek
& Protheroe (1997).
Drappeau: How do calculate the number of clouds at any given time? i.e. What is the
destruction rate and the entrainment rate of clouds in jets?
Araudo: To estimate the number of clouds into the jet, we calculate Nc∼2xfxVj/Vc ,
where f∼10−6 is the filling factor of clouds in the broad line region (BLR), Vc is the
volume of the clouds, and Vj is the volume of the jet intesected by the BLR. In this
estimation, we not consider the destruction of clouds into the jet. The previous equation
for Nc takes into account that the entrainment is equal to the escape rate of the jet, and
is independent of time.
https://www.cambridge.org/core/terms. https://doi.org/10.1017/S1743921310015802
Downloaded from https://www.cambridge.org/core. IP address: 163.10.34.204, on 16 Sep 2019 at 17:54:18, subject to the Cambridge Core terms of use, available at


Jets are found in a variety of astrophysical sources. In all the cases the jet propagates with a supersonic velocity through the external medium, which can be inhomogeneous, and inhomogeneities could penetrate into the jet. The interaction of the jet material with an obstacle produces a bow-like shock within the jet in which particles can be accelerated up to relativistic energies and emit high-energy photons. In this work, we explore the active galactic nuclei scenario, focusing on the dynamical and radiative consequences of the interaction at different jet heights. We find that the produced high-energy emission could be detectable by the current γ-ray telescopes. In general, the jet-clump interactions are a possible mechanism to produce (steady or flaring) high-energy emission in many astrophysical sources in which jets are present.Fil: Araudo, Anabella Teresa. 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: Bosch Ramon, Valentí. Dublin Institute for Advanced Studies; IrlandaFil: 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; Argentina275th Symposium of the International Astronomical Union: Jets at all ScalesArgentinaInternational Astronomical Unio

Bosch Ramon, Valentí

CONICET Digital

Title of your IAU SymposiumProceedings IAU Symposium No. 275, 2011G. E. Romero, R. A. Sunyaev & T. Belloni, eds.c© International Astronomical Union 2011doi:10.1017/S1743921310015802Radiation from matter entrainment inastrophysical jets: the AGN caseA. T. Araudo1,2, V. Bosch-Ramon3 and G. E. Romero1,21 Instituto Argentino de Radioastronomı́a (CCT La Plata, CONICET),C.C.5, 1894 Villa Elisa, Buenos Aires, Argentinaemail: aaraudo@fcaglp.unlp.edu.ar, romero@fcaglp.unlp.edu.ar2Facultad de Ciencias Astronómicas y Geof́ısicas, Universidad Nacional de La Plata,Paseo del Bosque, 1900 La Plata, Argentina3Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2, Irelandemail: valenti@cp.dias.ieAbstract. Jets are found in a variety of astrophysical sources. In all the cases the jet propa-gates with a supersonic velocity through the external medium, which can be inhomogeneous,and inhomogeneities could penetrate into the jet. The interaction of the jet material with anobstacle produces a bow-like shock within the jet in which particles can be accelerated up torelativistic energies and emit high-energy photons. In this work, we explore the active galac-tic nuclei scenario, focusing on the dynamical and radiative consequences of the interaction atdifferent jet heights. We find that the produced high-energy emission could be detectable bythe current γ-ray telescopes. In general, the jet-clump interactions are a possible mechanism toproduce (steady or flaring) high-energy emission in many astrophysical sources in which jets arepresent.Keywords. galaxies: active, radiation mechanisms: nonthermal1. IntroductionJets at different scales are present in astrophysical sources such as protostars, micro-quasars and active galactic nuclei (AGN). The medium that surrounds the jets can beinhomogeneous and clumps from this external medium can interact with the jets.In young stellar objects, the interaction of matter from the external medium withprotostar outflows has been proposed to explain the formation of Herbig-Haro (HH)objects. The dynamical properties of this interaction have been numerically simulatedby Raga et al. (2003), and they conclude that clumps with mass between 10−4 and 0.1times the mass of a giant planet can significantly contribute to the molecular mass ofHH outflows. However, the velocity of HH jets is not relativistic (∼ hundred km s−1),and particle acceleration in the bow shock formed in the jet might be inefficient or thepossible non-thermal emission produced by accelerated particles might be hidden bythermal radiation.In high-mass microquasars, the interaction of clumps from the companion stellar wind(Owocki & Cohen, 2006) with the jets of the compact object (black hole or neutron star)can produce strong bow-like shocks within the jet. Electrons and protons accelerated inthose shocks can radiate significant amount of γ rays in the form of flaring and steadyemission (Araudo et al. 2009). In the case where only few clumps interact with the jet,the produced emission is sporadic and can explain the GeV flares detected from someγ-ray binaries (e.g. Abdo et al. 2009).At extragalactic scales, AGN are composed by an accreting supermassive black hole(SMBH) at the center of the galaxy and relativistic jets. Surrounding the SMBH there is131132 A. T. Araudo, V. Bosch-Ramon & G. E. Romeroa population of clouds (Krolik et al. 1981) that move at velocities > 1000 km s−1 formingthe called broad line region (BLR). In the present contribution, we illustrate the mostimportant dynamical and radiative consequences of the interaction of clouds from theBLR with the base of AGN jets. We found that γ rays from jet-cloud interactions shouldbe detectable by present and future instrumentation in nearby low-luminous AGN athigh energy (HE) and very high energy (VHE), and in powerful and nearby quasars onlyat HE because the VHE radiation is absorbed by the dense nuclear photon fields. In thecase of sources exhibiting boosted γ rays (blazars), the isotropic radiation from jet-cloudinteractions will be masked by the jet beamed emission, which will not be the case innon-blazar sources.2. The jet-cloud interactionWe adopt clouds with density nc = 1010 cm−3 , size Rc = 1013 cm, and velocityvc = 109 cm s−1 . The jet Lorentz factor is fixed to Γ = 10, implying a jet velocity vj ≈ c,and the radius/height relation is fixed to Rj = 0.1 z. The jet density nj in the laboratoryreference frame (RF) can be estimated as nj = Lj/((Γ−1)mp c3σj), where σj = πR2j andLj is the kinetic power of the matter-dominated jet.The completely penetration of a cloud into the jet, the ram pressure of the latter shouldnot destroy the former before the cloud has fully entered into the jet. This means thatthe time required by the cloud to penetrate into the jet, tc∼2Rc/vc = 2 × 104 s, shouldbe shorter than the cloud lifetime inside the jet. To estimate this cloud lifetime, we firstcompute the time required by the shock in the cloud to cross it (tcs). The velocity of thisshock is vcs∼χ−1/2 c, where χ = nc/nj(Γ−1), is derived by ensuring that the jet and thecloud shock ram pressures are equal. This yields a cloud shocking time oftcs∼2Rcvcs 7×104(Rc1013 cm) ( nc1010 cm−3)1/2 ( z1016 cm) ( Lj1044 erg s−1)−1/2s . (2.1)Rayleigh-Taylor (RT) and Kelvin-Helmholtz (KH) instabilities produced in the cloudsurface by the interaction with the jet material will affect the obstacle. The timescale inwhich these instabilities grow up to a scale length ∼Rc is tRT/KH∼tcs . For this reason,we take tcs as the characteristic timescale of our study. Therefore, for a penetration time(tc) at least as long as ∼tcs , the cloud will remain an effective obstacle for the jet flow.Setting tc∼tcs , we obtain the minimum value for the interaction height zint , givingzminint ≈ 2.5 × 1015( vc109 cm s−1)−1 ( nc1010 cm−3)−1/2 ( Lj1044 erg s−1)1/2cm. (2.2)For zint > zminint , the jet crossing time tj∼2Rj/vc results larger than tcs . Once the cloudis inside the jet, a bow shock around the cloud is formed on a time tbs∼Z/vj∼102 s at adistance Z∼0.3Rc cm from the cloud. In this bow shock, particles can be accelerated upto relativistic energies more efficiently than in the cloud shock (because the bow-shockvelocity is vbs  vcs).3. Non-thermal emissionThe non-thermal luminosity of particles accelerated in the bow shock can be estimatedas a fraction ηnt of the bow shock luminosity: Lnt∼ηnt Lbs, where Lbs∼(σc/σj)Lj and σc =πR2c . The accelerator/emitter magnetic field in the bow-shock RF (B) can be determinedby relating UB = ηBUnt, where UB = B2/8π and Unt = Lnt/(σcc) are the magnetic andRadiation from matter entrainment in astrophysical jets 133Figure 1. Left: acceleration gain, escape, and cooling lepton timescales are plotted. SSC isplotted when the steady state is reached and EC for both the BLR and disc photon fields areshown for the conditions of faint (BLR: 1044 ; disc: 1045 erg s−1 ) and bright sources (BLR: 1046 ;disc: 1047 erg s−1 ). Synchrotron and relativistic bremsstrahlung are also plotted. Right: Upperlimits to the γ-ray luminosity produced by N jc clouds inside the jet as a function of Lj in FR IIsources. Two cases are plotted, one assuming that clouds cross the jet without disruption (greensolid lines), and one in which the clouds are destroyed in a time as short as tcs (green dashedlines). In addition, the sensitivity levels of Fermi in the range 0.1–1 GeV (maroon dotted lines)are plotted for three different distances d = 10, 100, and 1000 Mpc.the non-thermal energy densities, respectively. Fixing ηnt = 0.1 and ηB = 0.01, weobtain Lnt∼4 × 1039(Lj/1044 erg s−1) erg s−1 and B∼10 G. Regarding the accelerationmechanism, we adopt the following prescription for the acceleration rate: Ėacc = 0.1 q B c,where q is the electron charge.We assume that electrons and protons are injected into the bow-shock region followinga power law in energy of index 2.2 and with an exponential cutoff at the maximum energy.The injection luminosity is Lnt. Particles are affected by different losses that balancethe energy gain from acceleration. The escape time downstream from the relativisticbow shock considers advection (tadv∼3Rc/c∼103 s) and diffusion (tdiff = 3Z2/2 rg c)timescales. In the latter expression, rg is the particle gyroradius and the Bohm regimehas been considered. The most important radiative losses that affect the lepton injectionare synchrotron and SSC, determining a maximum energy Emaxe of several TeV, as isshown in Figure 1 (left). In the case of protons, pp cooling is negligible in the bow-shockregion and the maximum energy is constrained by equating the acceleration and diffusiontimescales, given Emaxp ∼5 × 103 (B/10G) TeV. Then, protons with energies > 0.4Emaxpcan reach the cloud by diffusion and radiate there via pp more efficiently than in the jet,since nc  nj(zint).4. Many clouds interacting with the jetsMany of the BLR clouds can be simultaneously inside the jet at different z, eachof them producing non-thermal radiation. Therefore, the total luminosity can be muchlarger than that produced by just one interaction, which is ∼Lnt. The number of cloudswithin the jets, at zminint  z  Rblr , can be computed from the jet (Vj) and cloud (Vc)volumes, resulting in N jc = 2 f Vj/Vc ∼ 9(Lj/1044 erg s−1)2 , where the factor 2 accountsfor the two jets and f∼10−6 is the filling factor of clouds in the whole BLR. In reality, N jcis correct if one neglects the cloud disruption inside the jet. However, even under cloudfragmentation, strong bow shocks can form around the cloud fragments before these haveaccelerated up to close vj . Then, the real number of interacting clouds inside the jet isdifficult to estimate, but it could be between (tcs/tj)N jc and Njc .134 A. T. Araudo, V. Bosch-Ramon & G. E. RomeroThe presence of many clouds inside the jet implies that the total non-thermal lumi-nosity available in the BLR-jet intersection region isLtotnt ∼2∫ Rb l rzm inin tdN jcdzLnt(z) dz∼2×1040(ηnt0.1) ( Rc1013 cm)−1 (Lj1044 erg s−1)1.7 ergs, (4.1)where dN jc is the number of clouds located in a jet volume dVj = π (0.1z)2 dz. In all thecalculations Lblr has been fixed to 0.1Lj , as approximately found in FR II galaxies, andRblr has been derived from Kaspi et al. (2005).In Fig. 1 (right), we show estimates of the γ-ray luminosity when many clouds interactsimultaneously with the jet. For this, we have followed a simple approach assuming thatmost of the non-thermal luminosity is converted into γ rays. This will be the case aslong as the escape and synchrotron cooling time are longer than the IC cooling time(EC+SSC) at the highest electron energies. In Araudo et al. (2010), we present moredetailed calculations by applying the model presented in this contribution to two char-acteristic sources, Cen A and 3C 273.5. DiscussionWe have studied the interaction of clouds from the BLR with the base of jets in AGNs.For very nearby sources, such as Cen A, the interaction of large clouds (Rc > 1013 cm)with jets may be detectable as a flaring event, although the number of these large cloudsand thereby the duty cycle of the flares are difficult to estimate. Given the weak externalphoton fields in these sources, VHE photons can escape without experiencing significantabsorption. Therefore, jet-cloud interactions in nearby FR I may be detectable in boththe HE and the VHE range as flares with timescales of about one day.In FR II sources, many BLR clouds could interact simultaneously with the jet. Thenumber of clouds depends strongly on the cloud lifetime inside the jet, which could be ofthe order of several tcs . Nevertheless, we note that after cloud fragmentation many bowshocks may still form and efficiently accelerate particles if these fragments move moreslowly than the jet. Since FR II sources are expected to exhibit high accretion rates,radiation above 1 GeV produced in the jet base can be strongly attenuated by the densedisc and the BLR photon fields, although γ rays below 1 GeV should not be affectedsignificantly. Since jet-cloud emission should be rather isotropic, it would be masked byjet beamed emission in blazar sources, although since powerful/nearby FR II jets donot display significant beaming, these objects may produce detectable γ rays throughjet-cloud interactions. As shown in Fig. 1 (right), close and powerful sources could bedetectable by deep enough observations of Fermi.ReferencesAbdo, A. A. et al. 2009, ApJS, 183, 46Araudo, A. T., Bosch-Ramon, V., & Romero, G. E. 2009, A&A, 503, 673Araudo, A. T., Bosch-Ramon, V., & Romero, G. E. 2010, A&A (in press) [arXiv:1007.2199]Begelman, M. C., Blandford, R. D., & Rees, M. J. 1984, Rev. Mod. Phys., 56, 255Kaspi, S., Maoz, D., Netzer, H., Peterson, B. M., Vestergaard, M., & Jannuzi, B. T. 2005, ApJ,629, 61Krolik, J. H., McKee, C. F., & Tarter, C. B. 1981, ApJ, 249, 422Owocki, S. P., & Cohen D. H. 2006, ApJ, 648, 5650Raga, A. C., Velzquez, P. F., de Gouveia dal Pino, E. M., Noriega-Crespo, A., & Mininni,P. 2003, RMxAC, 15, 115Radiation from matter entrainment in astrophysical jets 135DiscussionMirabel: Can you apply the same model to the MQSO Cyg X-3 that has a WRayetdonor and LGRBs that usualy have WRayet progenitors?Araudo: We have applied the model to high-mass microquasars (HMMQ), studyingthe interaction between clumps from the wind of the companion star with the jet ofthe compact object (Araudo, Bosch-Ramon & Romero 2009). In this work, we haveconsidered a source with similar parameters to the system Cygnus X-1. Now, we areworking on the application of the model to the HMMQ Cygnus X-3. We have not appliedthe model to gamma-ray bursts.Perucho: Stellar winds shocked by the jet flow could also be an interesting scenario tocheck. Have you considered it?Araudo: We have not considered the interaction between stars and jets in AGNs, but weare going to do this in the near future. A similar scenario has been studied by Bednarek& Protheroe (1997).Drappeau: How do calculate the number of clouds at any given time? i.e. What is thedestruction rate and the entrainment rate of clouds in jets?Araudo: To estimate the number of clouds into the jet, we calculate Nc∼2xfxVj/Vc ,where f∼10−6 is the filling factor of clouds in the broad line region (BLR), Vc is thevolume of the clouds, and Vj is the volume of the jet intesected by the BLR. In thisestimation, we not consider the destruction of clouds into the jet. The previous equationfor Nc takes into account that the entrainment is equal to the escape rate of the jet, andis independent of time.

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Radiation from matter entrainment in astrophysical jets: the AGN case

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