Modelling the structure and dynamics of black hole jets. Will Po9er Junior Research Fellow, University College, University of Oxford

Transcription

1 Modelling the structure and dynamics of black hole jets Will Po9er Junior Research Fellow, University College, University of Oxford

2 Talk Structure Why model black hole jet emission? An extended relahvishc fluid jet emission model based on observahons of M87. Constraining the structure and dynamics of jets. How the physical properhes of blazar jets influence their spectra and classificahon. AGN unificahon and the accrehon mode dichotomy. Using radiahve energy losses to constrain the jet magnehsahon and the large-scale magnehc reconnechon rate.

3 Jet simulahons General relahvishc MHD simulahons find jets which start magnehcally dominated and parabolic in the accelerahng region. Once the jets have accelerated and converted most of the magnehc energy into bulk kinehc energy the accelerahon ceases to be efficient (at ~1000 Schwarzschild radii) and the jets become ballishc and conical. McKinney and Blandford 2009

4 ObservaHons of M87 The nearest jet M87 has been observed with radio VLBI and the shape has been found to start parabolic and transihon to conical at 10 5 r s. Asada and Nakamura 2012

5 Jet spectra Jet spectra are characterised by two bumps, well fi9ed by synchrotron and inverse-compton emission of high-energy electrons. This is best seen in blazars AGN jets directed close to the line of sight.

6 Why model Jet emission? There seems to be a reasonable consistency between observahons, simulahons and theory. The informahon we posses on real jets comes from observing the radiahon they emit. It is too computahonally expensive to include a detailed calculahon of non-thermal emission in GRMHD simulahons. We need jet emission models which are able to constrain the jet properhes and predichons from simulahons by comparing to observed spectra. Due to Doppler booshng blazars are the ophmal sources to model since almost all the observed emission is from the jet.

7 Comparison to exishng models ExisHng spherical blob and cylindrical jet emission models are successful at high frequencies but cannot reproduce the observed radio emission produced by the large scale structure of the jet. Bo9cher et al Ghisellini et al. 2009

8 A realishc, extended model for jet emission Transition region. Jet transitions from parabolic to conical. Plasma first comes into equipartition and magnetic acceleration ceases to be efficient. Dominates optically thin synchrotron and SSC emission. Accelerating magnetically dominated parabolic base. Slowly decelerating conical section. Dominates optically thick radio synchrotron emission and external Compton. x 0 x T Po9er and Co9er 2013a L

9 A fluid jet model conservahon of energy We assume jet properhes only depend on the jet length and are homogeneous perpendicular to the jet axis. Since we allow the jet velocity and shape to change as a funchon of distance conservahon of relahvishc energy-momentum takes the form. ρ ρ T µν = µ T µν = 0, T µν = T µν Magnetic + T µν Particles + T µν Losses In order to relate plasma properhes in the rest frame and lab frame we treat the plasma as a relahvishc perfect fluid. ρ 3 0 T µν (x) = µ a T ab ν b = = = 4 3 γ bulk(x) 2 ρ 4 3 γ bulk(x) 2 ρ γ bulk(x) 2 ρ 4 3 γ bulk(x) 2 ρ 0 0 ρ ρ IntegraHng = conservahon of energy over the jet volume and using the µ T µν d 4 V = T µν d 3 S µ = x is the bulk Lorentz factor of the jet divergence theorem we find the conservahon of energy equahon for the jet. ( ) 4 3 γ bulk(x) 2 πr 2 (x)ρ (x) = 0. ρ 3

10 CalculaHng the synchrotron and inverse- Compton emission Divide the jet into hundreds of cylindrical sechons with variable radii and bulk Lorentz factors. Calculate the synchrotron and inverse-compton emission from each sechon as the plasma propagates along the jet with an evolving non-thermal electron populahon. Integrate the synchrotron and pair-produchon opacity to a sechon and sum the emission from all sechons. Take into account radiahve and adiabahc energy losses to the electron populahon, reaccelerahon processes and lepton number conservahon. Include a detailed treatment of all relevant external photon sources: accrehon disc, BLR, dusty torus, NLR, starlight and CMB.

11 External photon fields CMB dominates at large distances Po9er and Co9er 2013a

12 Fihng the model to spectra For the first Hme the model fits to both radio and gamma-ray blazar observahons simultaneously and with unprecedented accuracy Mkn421 J0531 J0531 (archival) Po9er and Co9er 2013b, 2013c and 2015

13 Fihng to all 38 simultaneous mulhwavelength Fermi blazars 10-8 BL Lacertae BL Lacertae (archival) J0035 (quasi-simultaneous) J0035 (archival) J0222 J0222 (archival) J0137 J0137 (archival) J0210 J0210 (archival) J0229 Po9er and Co9er 2013b, 2013c and 2015

14 J0349 J0423 J0423 (archival) J0457 J0457 (archival) J0507 J0507 (archival) J0531 J0531 (archival) J0537 (quasi-simultaneous) J0537 (archival)

15 J0538 J0538 (archival) J0630 (quasi-simultaneous) J0630 (archival) J0730 J0730 (archival) J0855 J0855 (archival) J0921 J0921 (archival) J1015 J1015 (archival)

16 J1057 J1057 (archival) J1159 J1159 (archival) J1221 J1221 (archival) J1229 J1229 (archival) 10-8 J1256 J1256 (archival) J1310 J1310 (archival)

17 J1312 (quasi-simultaneous) J1312 (archival) J1457 J1457 (archival) J1504 J1504 (archival) J1512 J1512 (archival) J1522 J1522 (archival) J1719 J1719 (archival)

18 J1751 J1751 (archival) J1849 J1849 (archival) J2000 J2000 (archival) J2143 J2143 (archival) 10-8 J2158 J2158 (archival) 10-8 J2254 J2254 (archival)

19 J2327 J2327 (archival) J2345 J2345 (archival) J J (archival) J J (archival) 10-8 Mkn421 Mkn

20 Constraining the radius of the transihon region OpHcally thick OpHcally thin break Po9er and Co9er 2013b

21 An approximately linear relahon between jet power and transihon region radius! Jet radius at transition (pc) FSRQ BL Lac 3C 273 Mkn 421 HSP BL Lacs Unidentified Jet power (W) Po9er and Co9er 2015

22 Jet power vs. bulk Lorentz factor Length of accelerating region x T (pc) FSRQ BL Lac 3C 273 Mkn 421 HSP BL Lacs Unidentified Maximum bulk Lorentz factor Po9er and Co9er 2015

23 Evidence for an accrehon mode dichotomy Assuming a fiducial mass MBH=5x10 8 M Sun for all FSRQs and BL Lacs (Shaw et al. 2013). The distance in r s at which the jet comes into equiparhhon is much larger in FSRQs than BL Lacs. The Eddington accrehon rate is much lower in BL Lacs than FSRQs FSRQs BL Lacs 10 8 FSRQs BL Lacs Frequency 6 4 Frequency Jet power/l Edd P+C 2015 x T /r s

24 Evidence for AGN unificahon Similar Eddington distribuhon to AGN observahons of radiahvely inefficient Low ExcitaHon Radio Galaxies (FRIs) and radiahvely efficient High ExcitaHon Radio Galaxies (FRIIs) FSRQs BL Lacs Frequency Jet power/l Edd Mingo et al P+C 2015

25 How important are radiahve energy losses? The synchrotron lifehme of a relahvishc electron at the jet base is very short compared to the travel Hme. We know that high energy non-thermal leptons exist throughout the jet from their radio and ophcal emission. A large frachon of the inihal jet power must remain in the jet to large distances from the energy requirements of radio lobes. We assume a power-law electron energy distribuhon with an exponenhal cutoff, a parabolic accelerahng jet base as observed in M87 and typical jet properhes from blazars. For a given jet shape, accelerahon profile and electron distribuhon we can calculate the magnehsahon (or equiparhhon frachon) that is required in the jet base such that radiahve energy losses are not devastahng.

26 Powerful jets must be highly magnehsed! We demand that at least 5% of the total inihal energy in the plasma remains in the plasma to large distances and is not radiated away by synchrotron and synchrotron self-compton (i.e. f loss >0.05). For typical jet parameters with a fixed magnehsahon we constrain high power jets (>0.1L Edd ) to be strongly magnehcally dominated U B /U e± >10 4, independently of black hole mass. for E 4 max = 10 m e c 2 Po9er 2016 in press

27 In-situ parhcle accelerahon and magnehc reconnechon It has long been known that in-situ parhcle accelerahon is required to maintain a populahon of non-thermal electrons against radiahve energy losses. Since the jet base is magnehcally dominated, with no clear evidence for repeated shocks, the conversion of magnehc energy into accelerahng non-thermal electrons via magnehc reconnechon seems the most plausible scenario e.g. Sironi & Spitkovsky We derive a set of relahvishc fluid equahons which conserve energy-momentum and lepton number whilst including bulk accelerahon, magnehc reconnechon, and synchrotron and inverse-compton energy losses. Ee z E z ln z ± bulk = 2E γ e± B = 2E e± lnγ z bulk E + z rec E z rec E z We solve these equahons numerically to calculate the evoluhon of the jet magnehsahon and radiahve energy losses for different models of the magnehc reconnechon rate, mohvated by PIC simulahons. rad E E 2 e± = πr ΔzU e± = πr Δ 2 B zu B

28 Is reconnechon viable? If the jet does not to radiate away more than 95% of its total energy we can calculate the allowed large-scale rate of magnehc reconnechon along jets. High power jets cannot come into equiparhhon at a distance smaller than ~10 4 r s due to large radiahve energy losses close to the jet base. The amount of energy injected by reconnechon should be distributed close to evenly per unit logarithmic distance along the jet. Reconnecti on power A rec z d U B ' Po9er 2016 in press

29 Conclusions Blazar spectra are fi9ed with unprecedented precision by a realishc fluid jet model with a parabolic accelerahng base transihoning to a conical jet at equiparhhon based on M87. The radius of the jet at equiparhhon appears to scale linearly with jet power. The jet speed increases with the length of the accelerahng base. We find evidence for a bimodal accrehon rate and correspondence between BL Lacs and FRIs and FSRQs and FRIIs. Using radiahve energy losses we can constrain the magnehsahon at the base of jets, independently of black hole mass. Powerful jets must be very highly magnehsed in the parabolic accelerahng region to avoid devastahng energy losses. We can understand and constrain the large-scale magnehc reconnechon rate by considering radiahve energy losses. It is necessary for accurate simulahons of powerful jets to include a self-consistent treatment of non-thermal radiahve energy losses.

30 Summary R T /x T Jet Power 10-3 /0.1pc 5x10 36 W (~5x10-4 L EDD ) x T R T BL Lacs - Small radius transition region with large magnetic field strength leading to high peak synchrotron frequency. Gamma rays dominated by SSC emitted within transition region. 0.1/10pc BL Lacs: γ ~6 20 5x10 38 W (~0.05L EDD ) R T Jet Power Max. bulk Lorentz factor R T 1/4 FSRQs: γ ~ /200pc W (~1L EDD ) R T FSRQs - Large radius transition region with small magnetic field strength leading to low peak synchrotron frequency. Gamma rays dominated by scattering CMB photons at large distances. x T