Numerical Simulations of FRI jets Manel Perucho Pla Max-Planck-Institut für Radioastronomie and J.M. Martí (Universitat de València)

Introduction: Laing & Bridle 2002a,b Assumptions Axisymmetric, time-stationary, relativistic jet Symmetric jet/counterjet system Parameterized distributions of velocity, magnetic field and synchrotron emissivity. Comparison with VLA total intensity and polarization data allows to fix parameterizations. Dynamical model based on conservation laws. External gas density and pressure distributions are taken from Hardcastle et al. (2002) Pressure equilibrium with the external medium assumed in the outermost studied region. Results: Jet axial structure: inner, flaring and outer regions Spine velocity decreases (from 0.9 to 0.25 c) due to entrainment in the flaring region Transversal structure: spine + shear layer Jet dynamics: The jet is overpressured at the inlet: expansion and acceleration. Recollimation occurs when the jet becomes underpressured (wrt ambient). Entrainment: peak in the entrainment rate at the recollimation site (stellar mass loss?); outwards the jet is slowly entrained and decelerated.

Evolution of FRI jets: setup Perucho & Martí 2007, MNRAS Jet injected according to Laing & Bridle (2002a,b) model at 500 pc from the core r m = 7.8 kpc Axisymmetric simulation of a purely leptonic jet with L j ~ erg/s. Physical domain: 18 kpc x 6 kpc [Resolution: 8 cells/R j (axial) x 16 cells/R j (radial)] ambient medium conditions from Hardcastle et al. 2002

Evolution of FRI jets: picture at years Perucho & Martí 2007, MNRAS Last snapshot (T = yrs ~ 10 % lifetime of 3C31) beam cavity/cocoon shocked ambient bow shock shocked ambient

Evolution of FRI jets: dynamics Perucho & Martí 2007, MNRAS Extended B&C model:  ~  0.1,  ~  1 Cocoon evolution: t  1.3 t 1t 1 ~ constant for negligible pollution with ambient particles (N c b ~ N c a ), and assuming self-similar transversal expansion N c b N c a PsPs TcTc RsRs vbsvbs PcPc cc

Evolution of FRI jets: dynamics in the beam Perucho & Martí 2007, MNRAS As in Laing & Bridle’s model, the evolution is governed by adiabatic expansion of the jet, recollimation, oscillations around pressure equilibrium, mass entrainment and deceleration. However, in the simulation there are more shocks and all the entrainment is due to a destabilization of the jet as a result of those shocks. recollimation shock and jet expansion jet disruption and mass load jet deceleration L&B model adiabatic expansion pressuredensityMach number Simulation

Evolution of FRI jets: some thoughts Perucho & Martí 2007, MNRAS jet disruption and mass load jet deceleration Comparison with L&B Simulations confirm the FRI paradigm qualitatively, but jet flare occurs in a series of shocks the presence of the cocoon is crucial: the jet is not interacting directly with the ambient, but with the cocoon. comparison wth L&B model is difficult as the jet has not reached a steady state Strong vs mild shock Hardcastle et al found X-ray emission from the flaring region of the northern jet, where the jet decollimates and shows brighter radio emission. this is the region which we identify with the post-recollimation shock region, where particles could gain enough energy to emit in the X-ray this fact favors the presence of a strong shock, as seen in the simulation The simulated jet is very young if compared to 3C31, but how does it compare to younger FRI jets like CenA or NGC3801?

Comparison with young FRI’s Perucho & Martí 2007, MNRAS jet disruption and mass load jet deceleration Mach number of the bow shock by the end of the simulation M ~ 2.5, consistent with X-ray observations by Kraft et al (Cen A) and Croston et al (NGC3081): M ~ for the bow shock of those sources with ages ~ 10 6 yrs (NGC3801). Pressure, number density and Temperature in the shocked ambient gas (shell) and the ambient medium of the galactic gas are comparable too. The high temperature in the shell compared to observations could be due to: Initial jet power of the simulated jet is erg/s (cf erg/s in NGC 3801, Croston et al. 2007). Lack of thermal cooling in the simulation. The ambient medium in 3C 31 is modelled as hotter (  10 7 K) and denser (  10 4 m -3 ) than those in NGC3801 or Cen A (  10 6 K,  10 3 m -3 ). X-ray observing energies in those sources are low for these temperatures.

Thermal emission from young FRI’s jet disruption and mass load jet deceleration t  10 6 yrs (LS  3 kpc) T sh  10 9 K  100 keV n e,sh  6 x cm -3 V sh  cm 3 t  yrs (LS  16 kpc) T sh  10 9 K  100 keV n e,sh  6 x cm -3 V sh  cm 3 3C31 – NGC3801: D L  50 Mpc νS V  erg cm -2 s -1 3C31 – NGC3801: D L  50 Mpc νS V  erg cm -2 s -1 CenA: D L  3 Mpc νS V  erg cm -2 s -1 CenA: D L  3 Mpc νS V  erg cm -2 s -1 Kraft et al Cen A (t  ?) νS V  erg cm -2 s -1 L X  erg s -1 ( keV) Croston et al NGC3801 (t  2 x 10 6 yrs) νS V  6 – 7 x erg cm -2 s -1 L X  erg s -1 (0.4-2 keV) Our pre/post-diction is that young (t<10 7 yrs) FRI sources present bow-shocks in general and these should be observable in X-rays to gamma-rays, depending on the jet power. The evolution of the luminosity with time is as predicted by Kino et al. (2007):  t -1 L (100 keV)  erg s -1 L (100 keV)  erg s -1 Siemiginowska et al. (2008) have found X-ray luminosities ( keV) in GPS sources within erg/s. Suggested to be related to the accretion power. A significant fraction of this flux could come from thermal emission if the sources are very young (t ≤ 10 3 yrs), depending also on their power (FRI’s or FRII’s).

Long term simulations (up to 100 kpc). –Supercomputation. RATPENAT: a 3D RHD code parallelised for the use of supercomputers. The parallelisation of the numerical grid has been performed in the direction of propagation of the flow. –Physics. Relativistic EoS. Mass load from stars. Bremsstrahlung cooling....(couple of years)... Magnetic fields. FRI jets: next steps RATPENAT