Central Engines
and Jets oflong GRBPeter Mészáros,Pennsylvania State University
Yukawa Inst. Workshop
Kyoto, Nov. 2013

GRB:

standard paradigm

Bimodal distributionof tγ duration←↓Short(tg< 2 s)→↑Long(tg >2 s)

Classical view of GRB Jet at work
Int. & ext. shocks,
accelerate electronse,B →γ (leptonic);
andaccel. protons too (?)
pγ→ν, γ (hadronic)↙internal shocks↙external shockIdealized Jet & Disk

Numerical Hydro Jet(MacFadyen etal 99,
Zhang et al, 03, ....)DNS merger : →similar central engine

GR-MHD Jets from DNS Merger
Full GR, MHD, disruption, disk → jet

The Astrophysical Journal Letters, 732:L6 (6pp), 2011 May 1

Rezzolla et al’11,et al.
ApJL 762:L18
Rezzolla

Trace out
mag. fieldstructure←of jets,
as well asthat ofdisrupted
←disk

But:
How
Long?
Figure 1. Snapshots at representative times of the evolution of the binary and of the formation of a large-scale ordered magnetic field. Shown with a color-code map isSGRB↓ and/or ↓Kilonova?
Metzger, Berger’12 ApJ 746:48

See talks by
Metzger
Zhang
Beloborodov.....

QUESTION: if DNS accretion disk is MHD“Long” GRB?

Whether BH or MGR: →Hydro jetcollimation
by wind
Bromberg-Levinson ’07,

← ApJ 671:678(early: Levinson-Eichler ’00, PRL 85:236)• External confinement
either by pressure ofenvelope p~z-α• Or confinement byexternal split monopole
wind, ratio χ=Lw/Lj

Hydro jet collimation:
also by envelope pressure
pext ~ z-ηDissipation efficiency

Nalewajko ’12, MN 420:L48

Dissipation rate per u. dist. z

Relativistic Jet hydro confinement
Kohler-Begelman ’12 MN 422:2282• For flat ext.

pressure profilepext~z-η, e.g.
η=7/3, jet recollimates• For steep ext.
profile, e.g.
η=11/3, jetremains open

pext~z-η,pext,0/pj,0=1, Γj,0=50, θ0=1/50

Collateral “benefit” :Cocoon accompanies jet penetration(cocoon: beer foam spill-over analogue)
Earliest work in AGN(observationally motivated),e.g. Scheuer, Rees,
Begelman-Cioffi, etc

Cocoonsin GRB: →Mészáros-Rees, ’01, ApJL, 556:L37,
Ramirez-R et al, ‘02, MN 337:1349
Waxman+PM, ‘03, ApJ 584:390
Matzner ‘03, MN 345:575
Lazzati-Begelman ‘05, ApJ 629:903
Bromberg et al, ’11, ApJ, 740:100
Mizuta-Ioka, arx:1304.0163,..... + others

HYDRO simulation:←Cocoon break-out
Morsony, et al, ’07,
ApJ 665:569

What’s thepoint?
a) cocoon also
constrains jet angleb) cocoon alsoradiates
12

Hydro: cocoon pressure
also → jet confinement

Bromberg et al ’11
ApJ 740:100

Hydro jet-cocoon II
Mizuta & Ioka
arX:1304.0163(see also
Bromberg et al ’11
ApJ 740:100)• Cocoon oblique shocks confine jet to~cylindrical shape• Escaping jet opening angle θj~1/5Γ0,where Γ0 -initial Γ at r0 ; predict max.
θj,max ~12o (larger: 2-component jet? orsome physics is missing)

14

MHD GRB Jets?
Early GRB Poynting jets:
Usov’94. MN 267:1035; Thompson’94, MN270:480; Mészáros-Rees’97 ApJ 482:L29

Important development work:
Lyutikov-Blandford,’03, arXiv:/0312347
M. Lyutikov’11 MN 411:422
Yu. Lyubarsky;’09 ApJ 698:1570’10, ApJ 725, L234
’10, MN 402:353’11, PR E 83:016302

Drenkhahn-Spruit’02, AA 387:714’02, AA 391:1141
Spruit-Daigne-Giannios’01, AA 369:694’07, AA 469:1

J. Granot, Königl, et al’11 MN 411:1323’12 MN 421:244

S. Komissarov, et al’99 MN 308:1069’12 MN 422:326

Russo-Thompson’13, arX:1303.1553,‘13, arX:1303.1554(partial list...)MHD dynamics scaling:similar to Hydro?

Generally,No• If baryonic outflow (1-D) → Γ ~ (r/r0) up to Γ ~L/(dM/dt)• If magnetic, reconnection (e.g. “striped wind”), for 1-D conemax

outflow (1-D) → Γ ~ (r/r0)1/3 , up to Γmax ~L/(dM/dt)(Drenkhahn ’72, AA 387:772, Drenkhahn& Spruit, ’72, AA 391:1141)• Why? Can use simple argument• Comoving reconnection time t’ ~ λ’/v’ ~ Γεr /c ~Γ ;• Comoving dynamic time t’ ~r/cΓ ;• Only two indep. timescales: t’ , t’ → determine γ’• Since γ’ must drop, suggest: γ’ ~ t’ /t’ ~ Γ /r ;• energy conservation: γ’.Γ ~const.~Γ /r Γ ~ (r/r0)1/3(PM & Rees ’11, ApJL 733:L1)

r

r

0

d

r

d

r

d

2

3

However: things change if not 1-D (θj ≠ constant)Non-reconnecting Mag. Jet dynamics
Tchekhovskoy et al, 08, MN 388:551(here, θj(r)≠const.)

R=cylindrical, r-radial

Jet external constraint: either stell. pressure ormag. wind pressure from disk

• B (R) ~R , ν=const., when p ~r , where α=2(2-ν) [R=cyl, r-radial]• ν=1, α=2 : wind paraboloidal; ν=0, α=4 : wind split monopole• MHD and Hydro simul. suggest p ~r , with α~2.5 (→ν~0.75; mod. A)
z

ν-2

mag

-α

amb

-α

Lorentz factor along field lines of ≠ footpoint θfp
Tchekhovskoy et al, 08, MN 388:551

ν=0.75 (~ν≤ 1)(α≥2 ; steep press.)

Γ

mod.A

ν=1 (~ν ≥ 1)(α≤2 ; flat press.)

Γ

outer

mod.B

inner

fast sheathslow spine

slow → fast spine
fast→ slow sheath•••

Approx. analytical: 1/Υ2 = 1/Υ12 + 1/Υ22 along field line ;Υ=Γ: from drift velocity vd = E/B(A) Typical behavior (ν≤ 1):

Υ1 ~r1-ν/2 ~ r0.625 , pmag ~r2(ν-2) ;Υ2 ~rν/2 ~ r0.375 , pmag ~r-2(B) Typical behavior (ν≥ 1):

Υ1 ~r1-ν/2 ~ r0.625 , pmag ~r2(ν-2) ;no Υ2Proto-magnetar Central engine?

Metzger et al ’11
MN 413:2031

Proto-magnetar as initial remnant ofcore collapse:
Central Engine
Pulsar Wind

Proto-magnetar model of GRB jet
Metzger et al
11, MN 413:2031

where

Γ~σ0

-CC→magnetar,-rot. →MHD jet-reconnect/dissip→dynamics Γ~r1/3→dissip.photosph+ also shocks

Lyons, O’Brien, Zhang et al, 10, MN 402:705

Magnetareffects:
XR
plateauin l.c.

An MHD jet“reconnection
switch” model
McKinney & Uzdensky ’12
MN, 419:573• Fast rot. collapsar→BH+disk →homopolar field(aligned rotator)• Or, aligned rot. magnetar• Reconnection in principle
not easy (same polarity)

Reconn.
Switch•When density drops low
enough, switch from•slow (Sweet-Parker, i.e.
Spitzer resist.)reconnection to•

fast (Petschek, i.e.
anomalous resist.)reconnection; occurs on
fraction of Alfven
timescale, beyond scatt.
photosphere•

In this regime, not too diff.
from Spruit et al (2001)

GRB“reconnection
switch” mode
McKinney & Uzdensky ’12, MN, 419:573• Tangling →reversing of fieldlines leads:• first (high density), to slow

collisional reconnect/dissipation• higher up (low density), to fast
collisionless reconnection→
prompt emission

Jetstructureand phys.
quantities•

Ideally, if all works
right, get:•••

Lorentz factor•••(id = ideal MHD, no dissip)

Jet angle
Diissip at radiusr~1015 -1016 cm→”prompt emiss.”→Usual afterglow
But spectrum?
Time variability?...

Jetstructureand phys.
quants., II•

Pair density andscatt. opt. depth
large out tor~1015 -1016 cm• At 10 -10 cm
15

16→fast reconnec→dissip/heat• Fiducial variab.

times are smallenough (butwildly uncertain)
at dissip radius

MHD: also jet + cocoon
Levinson-Begelman ’13 ApJ 764:148(similar results but diff. in details)• Inner cocoon: jet spillover,
outer cocoon: stellar
envelope shoved aside.

• Estimate that instabilities

dissipate magnetization of
inner cocoon (→hydro)• For WR star M=10M⊙,

R✶~R⊙ and ρ✶~z-α with
α<3, jet head becomessemi-relativistic near R✶.

• Jet remains collimatedinside star, and also welloutside it by the cocoon.

Jet Radiationin light of
Swift & Fermi
and other instruments

Paradigm shift• OLD: internal + external shock (weak phot.)• Photosphere: low rad. effic., wrong spectrum• Internal sh.: good for variability, easy to model ; but
poor radiative efficiency• External sh.: was, and is, favored for afterglow model• NEW: phot. + (int.sh? mag.diss?)+ext. shock• Photosphere: if dissipative, → good rad. efficiency• Int. sh: if magnetic, may be absent; but mag. dissip?
• External shock: most of GeV and soft afterglow
MészárosEvolving Fireball paradigm:≤ 2005?

≥2005

mag.diss?

Mészáros

“Cold”(non-dissip.)
photosphere
Mészáros-Rees’ 00 ApJ 530:292
Mészáros-Rees ’11, ApJ 733:L1

1) baryonic: phot.
usually in coastingphase2) magnetic: phot.
usually in accelerating
phase

MészárosMag. vs. baryonic jet dynamics

“Hot” (dissipative) photospheres
Rees-Mészáros 05, ApJ 628:847• If no dissipation,

Temp: T’ ~n’1/3 , n’
~1/r2Γ ~1/r2 →T=Γ T’ ~ r-2/3• Lum: L ~r Γ T’
ph

2

2

4

→ Lph ~ r-2/3• But: if at someradius (e.g. phot.)dissipat. sets in(e.g. shocks,
mag,reconn.,..)• →T ,Lphhigher !

phare

MészárosPhotospheric Dissipation
Mechanisms•• MHD reconnection, accel. → rel. e , γ• Shocks @ photosphere (& below, above) →same• .......
p-n decoupling (⊥, ||) → relativistic e±, γ±Magnetic Photosphere(Leptonic) Fit Results• Good fits obtained: can reproduce either 1- or 2component observed spectra with same model• In some bursts (e.g. 080916C, where 2nd comp. is“absent” (or rather, possible evidence for it is <2.5 σ),either a “single Band” or 2-component fit is possible• Calculated model parameter error estimates• Use GeV-MeV time delay as an additional constraint• But, best fit parameters are generally not unique; andsimilar quality fits for both magn. and baryonic phot.

090510A
magphot

Veres, BB Zhang &Mészáros ’12, ApJ 764:94

090510A
barphot

Veres, BB Zhang &Mészáros ’12, ApJ 764:94

Upshot:
Can obtain similarly good fits to the
MeV - GeV spectrum witheitherbaryonic or magnetic dissipative photospheres
Possible discriminant between them:BB thermal peak energy/flux is ≠ for mag. and bar.
Test of Γ~rμ now in progress;
results suggest μ intermediate betw. 1/3 and 1(Burgess, Veres, et al, 2013 in prep.)Standard internal shocks: have well-known problems; so...

Internal Shocks Redux:
modified internal shocks(address/mitigate/solve these problems)

Modifications currently of two main types:• Magnetic dissipation in int.shock, R~ 1015 cm, allow
GeV photons - but hard to calculate quantitatively details ofreconnection, acceleration and spectrum, e.g. McKinneyUzdensky ‘12, MN 419:573, Zhang & Yan ’11, ApJ 726:90• Hadronic internal shocks, protons are 1st order Fermi
accelerated, and secondaries are subsequently reaccelerated by 2nd order Fermi (‘slow heating”), e.g.
Murase et al, 2012, ApJ 746:164 - more susceptible to40
quantitative analysis

Hadronic int. shock: more efficient● Originally: Waxman& Bahcall ’97 consider
standard int. shock as
leptonic for photons,
hadronic for p,γ→ν

↙ Afterglow

Prompt↓

FS: X-ray, etc.;
RS: Opt. flash

New
Feature:Hadron accel. +photomeson →“dissipation”→inject copious
relativistic sec’y
leptons●↙ Asano & PM,
09-12 on, calculatesecond’y photons &second’y neutrinos
from both original &hadronic sec’y leptons

also: Murase et al, 2012, ApJ 746:164

Questions• Increasing interest in whether the central engine is a
prompt BH - or a magnetar → BH

• If so, what are timescale_mag vs. timescale_BH, and is jet
emission any different in its power & baryon load?

• baryonic vs. magnetic jets: how to distinguish them?
• Prompt emission: hadronic or leptonic?
• Are photospheres needed? Magn. or baryon. phot?
• Are modified internal shocks competitive? Magnetized or
hadronic internal shocks?

• Reconnection or Fermi acceler’n? Pairs: important?
• Combined Swift + Fermi obs. crucial for above

Some Theoretical Issues:• Are “single Band” spectra at GeV due tointernal or external shocks? - or magnetic
dissipation? or a photosphere, ..?

• Is 2nd component always present at some level?
Is it a ≠ zone/rad.mech. than 1st? Do weneed two-zone models?

• Are photons leptonic, hadronic, or mixed?
• What are astrophysical causes of GeV-MeV
delay? (aside from posible QG effects)

Numerical dissip. photospheres- 2 scenarios: slow dissip. and shock dissip.
- Incl. synchro+ Compton, pair form+annih

τ=1

Left: synch peak, middle: thermal peak
Right: Comptonized spectrum + annih. peak

Pe’er et al 06 ApJ 642:995

τ=100

Slow dissipation: thin lines, shock dissipation: thick lines
Solid lines: high εB=0.3, dot-dashed lines: low εB=10-6
MészárosHadronic GRB Fireballs:
p,n decouple → VHE

ν, γ• Radiation pressure acts on e-, with p+coming along (charge neutrality)• The n scatter inelastically with p+• The p,n initially expand together, while
tpn <texp (p,n inelastic)• When tpn ~texp → p,n decouple• At same time, vrel ≥ 0.5cp,n becomes inelastic → π+→

• Decoupling important when Γ≥400,
resulting in Γp >Γn• ⇒ dissipation• Decay → ν, of Eν ≥30-40 GeV
Bahcall & Mészáros 2000

• And ALSO:

γ-rays !

46

Decoupling of p-n
also possible transversallyA hadronic “thermal” photosphere PL spectrum?

p-n collisions in sub-photosphere
Beloborodov, ’10, MN 407:1033• Long history: Derishev-Kocharovsky 89, Bahcall-Meszaros 00, Rossi et al 04, etc• Either p-n decoupling or internal colls. → relative p-n streaming, inelastic colls.
• Highly effective dissipation (involves baryons directly)- can get >50% effic’y• Sub-photospheric dissipation can give strong photospheric component

p-n coll.→e±→ photosphere γ-spectrum• The result is a thermal

peak at the ~MeV Bandpeak, plus↑
MeV

• a high energy tail due
GeV↓to the non-thermal e± ,whose slope iscomparable to that of
the observed Fermi
bursts with a “single
Band” spectrum• The “second” higher

energy component(when observed) must
be explained withsomething else

Beloborodov, ’10, MN 407:1033

pn sub-photosphere w. mag.fields
Wurm et al, ’11 ApJ 738:77

Mag. fields =>synchr, get apartial 2ndcomponent,to ~<10 GeV

Photosphere + Internal Shockleptonic model, cont.
!"#$%&$'%()*+,-"./(0#"(-1+(1231(&$"4#'(5#$%(,$)+

612)(023."+(%#+)('#-(-$7+(2'-#($,,#.'-(-1+()+,#'%$"4(+/2))2#'(&4(Generic
shape comparable to Fermi observations ✔
-1+(+8+9(*$2")(,"+$-+%(&4(-1+(12319+'+"34($&)#"*-2#'(:$'%(-1+(,$),$%+(*"#,+));<(=12,1(,#.5%(/$7+(-1+(>?<()4',1"#-"#'<($'%(

a hadronic model: 090902B–5–

based on a likelihood analysis of the combined GBM and LAT data under the assumptionof a Band function plus an additional power-law (Abdo et al. 2009c).

ε!"ε#$%&'()*+,)-.

:;<=<>$*+?$Γ;<@==?$AB)Aγ;@?$AC)Aγ;<

<=0L

<=0I

Secondaryphotons ↓low enPL ↓Secondaryphotons ↓56789

C8FG0*6+BH

<=

0K

<=,

<=>

<=I

Assume phot. makes
Band function &shock or mag. dissip.
at r~1015 -1016 cm
accelerates p+, e±Also explain
presence of
low energy
power law
spectralcomponent&0&10234&0&10DE

µ0234

<=J

ε$%&/.

Fig. 1.— Model spectrum for parameters listed at the top as thick red curve compared withobservations of GRB 090902B, for which the gray shaded area represents the 1-σ confidence
region of the best-fit, unfolded spectrum for the joint Fermi GBM and LAT data. The best-

Asano, Inoue,Mészáros, 2010,
ApJL 725:L121
MészárosMHD / Poynting jets?

ICMART model(“Internal Collision Magnetic Reconnection Transient”)
B. Zhang & H.Yan ’11, ApJ, 726:90•• Magn. reconn. in intern. shock (aided by turbulence)• Accel e : direct (recon.) or stochast. turb. →rad: SY• Need reconn. over λ ≤10 cm lengths , envisage

Int. coll. w. 1≲σ≲100, where σ=B’2/4πρ’c2 (MHD)
-

par

4

blobs w. same directions spiral but staggered,have↓↑ regions of Bperp →turb. resist. →reconn.
(early colls. distort B, at large r much distort., recon)ICMART
model
B. Zhang & H. Yan’11, ApJ, 726:90

Non-magnetic leptonic“first response” models to Fermi,
concentrating mainly on GeV• Kumar & Barniol-Duran 2010: adiabatic
external shock synchrotron (low B)• Ghisellini et al 2010: radiative (pair-enriched)external shock synchrotron• Wang et al, He et al & Corsi et al, 2010-11:
external shock synchrotron + IC

A leptonic magnetic photosphere+ external shock model

MeV

GeV

●Leptonic photosph. spectrum extend to Γph me ~50-100 MeV● Ext. shock upscattering spectrum extend to Γes γe,KN me →TeV
Veres & Mészáros ‘12, ApJ 755:12

Magnetized GRB jet radiation•• Dissipative (magn. or baryon.) scattering

Dynamics of expansion Γ ~ r1/3 → Γ ~ const
photosphere → broken PL MeV spectrum• No internal shocks expected• Magnetiz. param. σ drops to ~ o(1) at r
• External shock present (forward; +reverse?)
decel→both shocks up-scatter photospheric MeV→to GeV -TeV range
Veres & Mészáros, 2012, ApJ 755:12

Phot+ExtSh : Band + 2nd comp.
Veres & Mészáros ‘12, ApJ 755:12

Phot+ExtSh : Single (Band) PL
Veres & Mészáros, ‘12, ApJ 755:12

Numerical time dependence ofphoton & neutrino secondaries(Asano & PM ’12, ApJ 757:115)εε





γ

















• Generic dissipation
region at a radius
R~1014-1016 cm (could
be Int.Sh. or mag. diss.
region, etc.)• Numerical Monte
Carlo one-zone rad.
transfer model with all
EM & ν physics
• ←Fermi/LAT param.
Eγiso~2.1054, Lp/Le=20,
Γ=600, R~1016cm,

 ε
z=4.560

Fermi/LAT hadronic case
• For very bright, rare bursts (<10% of all cases)• Get 2nd GeV γ- comp. & its delay• Predict complying ν-flux, but on rare LAT bursts and at > 1016 eV• Predict substantial nu-gamma delay
Asano & PM ’12, ApJ 757:115)

εε




ν
















γ

γ





               










61






ε

To pair or not to pair (e±)?
• Pair-loaded fireballs proposed 10+ years ago• For high LMeV, pair cascade almost inevitable• With advent of Fermi GeV detections, newinterest in such models (e.g. Ghisellini etal, 10, MN403:926)• → Beloborodov ( arX:1307.2663) addresses various
features of early GeV emission (+opt)

62

Outlook• Prospects for multi-waveband astrophysics of GRB are

encouraging - have enough bursts w. good photons statistics!

• New discovery space: high-redshift → cosmology impact• Major theoretical issues: 1) baryonic vs. magnetic jets: how to

distinguish them? 2) Prompt emission: hadronic or leptonic?
3) Are photospheres needed? Magn. or baryon. photospheres?
4) Are modified internal shocks competitive? Magnetized or
hadronic internal shocks? 5) Reconnection or Fermi acceler’n?
6) MeV-GeV delay: astrophysical cause? 7) Pairs: important?

• Combined Swift + Fermi obs. are crucial for above questions• TeV spectra→new constraints on hadronic vs. leptonic models• Would constrain particle acceleration / shock parameters,
emission region compactness (dimension, mag.field), etc.