Acceleration and Collimation of Relativistic Magnetized Jets

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1 Acceleration and Collimation of Relativistic Magnetized Jets Alexander (Sasha) Tchekhovskoy with Ramesh Narayan and Jonathan McKinney Harvard University

2 Chandra X-ray Observatory Magnificent Galaxy Jets M87 galaxy (radio, 20 cm) Centaurus A galaxy (radio/optical/x-ray) X-ray: NASA/CXC/CfA/R.Kraft et al; Radio: NSF/VLA/Univ.Hertfordshire/M.Hardcastle; Optical: ESO/WFI/M.Rejkuba et al light years 4000 light years 10 8 solar mass black hole (radio, 7 mm) 10 9 solar mass black hole 1 light year 1000 black hole radii NRAO/AUI and F. Owen Walker et al. 2008

3 Superluminal Motion in Jets: Different Masses, Similar Speeds Chandra XRC Chandra XRC Active Galaxy M87 with M BH = 3 x 10 9 M : X-ray Binary GRS with M BH = 15 M : 16 March 1994 John Biretta, Space Telescope Science Institute 27 March April April April 1994 NRAO/AUI Relativistic jet from a supermassive BH 1.9c Relativistic jet from a stellar-mass BH

4 Different masses, similar jets Mirabel & Rodriguez, 2002, Sky and Telescope Active Galactic Nuclei (e.g., M87, M BH =3 x 10 9 M ) Black Hole X-ray Binaries (e.g., GRS , M BH =15 M ) Gamma-Ray Bursts (e.g., GRBYYMMDD, M BH 3 M )

5 How do magnetic jets work? p = B 2 Á=(8¼) Field toroidallydominated B Á À B z field line t=0 t=t 1 t=t 2

6 How do magnetic jets work? p = B 2 Á=(8¼) Field toroidallydominated B Á À B z field line t=0 t=t 1 t=t 2

7 How do magnetic jets work? p = B 2 Á=(8¼) µ ¾= m ² m /½c 2 field line t=0 t=t 1 t=t 2

8 AGN and GRB Jets AGN: 10 µ 1 GRB: 100 ¾= m ² m /½c 2 Simulations of magnetized confined jets: µ 1 Confined (Komissarov et al., MNRAS, 2009) Is there any hope for magnetized GRB jets? Confined µ = 2 IGM Wall star Wall µ = 2 r * Central black hole Central black hole

9 AGN and GRB Jets AGN: 10 µ 1 GRB: 100 ¾= m ² m /½c 2 Simulations of magnetized confined jets: µ 1 Confined (Komissarov et al., MNRAS, 2009) GRB jets are DEconfined: (Tchekhovskoy, Narayan, McKinney, New Astronomy, 2010) Deconfined µ = 2 µ = 20 IGM Wall star Wall r * Central black hole Central black hole

10 Why is µ 1 in confined jets? Communication is essential GRB: 100 ¾= m ² m /½c 2 jet axis A B

11 Why is µ 1 in confined jets? Communication is essential Jet boundary B needs to keep announcing its trajectory to the rest of the jet GRB: 100 ¾= m ² m /½c 2 jet axis A B

12 Why is µ 1 in confined jets? Communication is essential Jet boundary B needs to keep announcing its trajectory to the rest of the jet to avoid collisions GRB: 100 ¾= m ² m /½c 2 jet axis A B

13 Why is µ 1 in confined jets? jet axis» Communication is essential Jet boundary B needs to keep announcing its trajectory to the rest of the jet to avoid collisions GRB: 100 ¾= m ² m /½c 2 All signals travel inside Mach cone»: ¼ ( mp m =½)» s 1=2 = ¾1=2 B

14 Why is µ 1 in confined jets? jet axis µ» Communication is essential Jet boundary B needs to keep announcing its trajectory to the rest of the jet to avoid collisions GRB: 100 ¾= m ² m /½c 2 All signals travel inside Mach cone»: ¼ ( mp m =½)» s 1=2 = ¾1=2 For communication across jet need µ», so µ ¾ 1/2 / B Robust conclusion: µ ¾ 1/2 1

15 5r GRB Jets are Deconfined 0 1 log 2 3 Confined Deconfined GRB: 100 r = 100 µ = 0.02 µ = 2 star = 500 µ = 0.04 µ = 20 0:2r 0:2r BH BH

16 Understand This Analytically After jets lose ambient pressure support, they switch from the fully confined solution to the fully unconfined solution. GRB: 100 ¾= m ² m /½c 2 Numerical deconfined jet µ = 2 Analytic fully confined jet (AT+ 2008) µ = 20 = 500 µ = 0.04 µ = 20 Analytic fully unconfined jet (AT+ 2009) Stellar surface Alexander (Sasha) Tchekhovskoy 16

17 Understand This Analytically After jets lose ambient pressure support, they switch from the fully confined solution to the fully unconfined solution. increases by 5x and µ by 2x. So, µ rises from 2 to 20 (AT+ 2010) GRB: 100 ¾= m ² m /½c 2 Numerical deconfined jet µ = 2 { Analytic fully confined jet (AT+ 2008) µ = 20 = 500 µ = 0.04 µ = 20 Analytic fully unconfined jet (AT+ 2009) Stellar surface Alexander (Sasha) Tchekhovskoy 17

18 Understand This Analytically After jets lose ambient pressure support, they switch from the fully confined solution to the fully unconfined solution. increases by 5x and µ by 2x. So, µ rises from 2 to 20 (AT+ 2010) GRB: 100 ¾= m ² m /½c 2 Numerical deconfined jet µ = 2 { Analytic fully confined jet (AT+ 2008) µ = 20 = 500 µ = 0.04 µ = 20 ¾ = 1 Analytic fully unconfined jet (AT+ 2009) Stellar surface ¾ = Alexander (Sasha) Tchekhovskoy 18

19 Understand This Analytically After jets lose ambient pressure support, they switch from the fully confined solution to the fully unconfined solution. increases by 5x and µ by 2x. So, µ rises from 2 to 20 (AT+ 2010) GRB: 100 ¾= m ² m /½c 2 Numerical deconfined jet µ = 2 { Analytic fully confined jet (AT+ 2008) µ = 20 x ¾ 1/2 (AT+ 2010) = 500 µ = 0.04 µ = 20 ¾ = 1 Analytic fully unconfined jet (AT+ 2009) Stellar surface ¾ = Alexander (Sasha) Tchekhovskoy 19

20 Acceleration and Collimation Relation between jet acceleration and collimation µ' C¾ 1=2 confined, C 1 deconfined, C 20 What do observations tell us? (AT+ 2010) GRB: 100 ¾= m ² m /½c 2 µ AGN: µ 1, no indication of deconfinement GRB: µ 10 30, jets must be deconfined Some GRBs: µ 100 ¾ 20 1 If many more GRBs show µ 100, this will challenge standard GRB emission models that require B A 90 Panaitescu & Kumar 2002 Cenko+ '10

21 GRB Jets: Jets: Required Ingredients Both propagation inside and outside the star required 1) Fully confined jets are too slow for their opening angles: µ 1 2) Fully deconfined jets have too large opening angles: µ 1 Bottom line: need 1) confinement to collimate the jet initially and 2) deconfinement to accelerate the jet AGN Jets: Either confined or deconfined jet scenarios allowed

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23 Jet Structure Summary 5r 0 1 log 2 3 Fully unconfined jet: µ ' 20¾ 1=2 (AT+ 2010) 3r Fully confined jet, large distance. Centrifugal force limits jet velocity (AT+ 2008): ¼ µ 3Rc R 1=2 r star Fully confined jet, small distance. Linear increase: ¼ R (Michel 1969) 0:2r BH 0:2r

24 Understand this analytically Centrifugal force slows jet down (approximate) F m = rp m = ² m R F m = F c ² m R = ² m 2 R c R c field line F c = ² m 2 R c = µ Rc R 1=2 R

25 Jet cross-section The further the jet propagates, the more uniform it becomes Jet is surrounded by vacuum (p = 0)

26 Magnetic nozzle for field lines Hydro: de Laval nozzle: flow opens up after sonic surface pressure drops p accelerates flow: MHD: reduction in field line density as the rest of field lines bunch up at the jet axis. F = rp p 1 > p 2 v < c s F = rp Bunch up v = c s v > c s > p 1 p 2 (Begelman & Li 1994, Komissarov 2009, AT+ 2009)

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