Transcript ppt

Gamma-Ray Bursts from Magnetar Birth
Brian Metzger
NASA Einstein Fellow
(Princeton University)
In collaboration with
Dimitrios Giannios (Princeton)
Todd Thompson (OSU)
Niccolo Bucciantini (Nordita)
Eliot Quataert (UC Berkeley)
Jon Arons (Berkeley)
Metzger, Giannios, Thompson, Bucciantini & Quataert 2011
Prompt Activity of GRBs (Raleigh, NC 03/05/2011)
Constraints on the Central
Engine
Canonical GRB Lightcurve
• Rapid Variability (down to ms)
-
• Duration - T ~10-100 seconds
• Steep Decay Phase after GRB
• Ultra-Relativistic, Collimated Outflow with
 ~ 100-1000
• Association w Energetic Core Collapse Supernovae
• Late-Time Central Engine Activity (Plateau & Flaring)
BH
versus
NS
from Nakar 07
• Energies - E ~ 1049-52 ergs
“Delayed” Neutrino-Powered
Supernovae (e.g. Bethe & Wilson 1985)
The Fates of Massive Stars (Heger et al. 2003)
Assumes supernova energy ~ 1051 ergs!
(Woosley 93)
(e.g. MacFadyen & Woosley 1999; Aloy et al. 2000; MacFadyen et
al. 2001; Proga & Begelman 2003; Takiwaki et al. 2008; Barkov &
Komissarov 2008; Nagataki et al. 2007; Lindler et al. 2010)
• Energy Accretion / Black Hole Spin
• Duration Stellar Envelope In-Fall
• Hyper-Energetic SNe - Delayed Black Hole Formation
or Accretion Disk Winds
• Late-Time Activity Fall-Back Accretion
Zhang, Woosley & Heger 2004
MacFadyen & Woosley 1999
Collapsar “Failed Supernova” Model
Core Collapse with Magnetic Fields & Rotation
(e.g. LeBlanc & Wilson 1970; Bisnovatyi-Kogan 1971; Akiyama et al. 2003)
Collapsar Requirements:
 Angular Momentum
 Strong, Ordered Magnetic Field
(e.g. Proga & Begelman 2003; McKinney 2006)
ÝIN
M


Neutron Star Mass
ÝOUT
M
Time
Key Insight :
(Thompson, Chang & Quataert 04)
•
Neutrinos Heat Proto-NS Atmosphere (e.g. e + n  p + e-)

Burrows, Hayes, & Fryxell 1995
Neutron Stars are Born Hot,
Cool via -Emission:
~1053 ergs in KH ~ 10-100 s
Drives Thermal Wind Behind SN Shock
Before SN Explosion
(e.g. Qian & Woosley 96)
After SN Explosion
Neutrino-Heated Wind
Evolutionary Wind Models (BDM et al. 2010)
NS Cooling
(Pons+99; Hudepohl+10)
3D Magnetosphere Geometry
(e.g. Bucciantini et al. 2006; Spitkovsky 2006)
Calculate:
Ý(t),
Wind Power EÝ(t), Mass Loss Rate M
 'Magnetization'  (t) ~ EÝ Ý 2  max (t)
Mc
In terms of
Initial Rotation Period P0 , Dipole Field Strength Bdip & Obliquity dip
0
EÝiso


 ~ max
EÝ
B24

 5/3 10/3
2
Ýc
M
L T
Jet Power (Dotted Line)
Max Lorentz Factor (Solid Line)
Example Solution
Jet Collimation via Stellar Confinement
(Bucciantini et al. 2007, 08, 09; cf. Uzdensky & MacFadyen 07; Komissarov &
Barkov 08)
Zooming
Out
 Assume Successful Supernova
(35 M ZAMS Progenitor; Woosley & Heger 06)
 Magnetar with Bdip= 31015G, P0=1 ms
Average jet power and
mass-loading match those
injected by central
Jet vs. Wind Power
Jet Power (Dotted Line)
Jet Breaks Out of Star
Max Lorentz Factor (Solid Line)
Wind becomes relativistic at t ~ 2 seconds;
Jet breaks out of star at tbo ~ R/c ~ 10 seconds
High Energy Emission (GRB) from t ~ 10 to ~100 s as Magnetization
Increases from 0 ~  ~ 30 to ~ 103
Jet Power (Dotted Line)
Jet Breaks Out of Star
Max Lorentz Factor (Solid Line)
GRB
GRB Emission - Still Elusive!
Slide from B. Zhang
Relativistic Outflow ( >> 1)
~ 107 cm
Central Engine
GRB / Flaring
Afterglow
1. What is jet’s composition? (kinetic or magnetic?)
2. Where is dissipation occurring? (photosphere? deceleration radius?)
3. How is radiation generated? (synchrotron, IC, hadronic?)
GRB Emission - Still Elusive!
Slide from B. Zhang
Relativistic Outflow ( >> 1)
Photospheric IC
~ 107 cm
Central Engine
GRB / Flaring
Afterglow
1. What is jet’s composition? (kinetic or magnetic?)
2. Where is dissipation occurring? (photosphere? deceleration radius?)
3. How is radiation generated? (synchrotron, IC, hadronic?)
Prompt Emission from Magnetic Dissipation
(e.g. Spruit et al. 2001; Drenkahn & Spruit 2002; Giannios & Spruit 2006)
e.g. Coroniti 1990
Non-Axisymmetries 
Small-Scale Field Reversals
(e.g. striped wind with RL ~ 107 cm)
 Reconnection at speed vr ~ c
 Bulk Acceleration   r1/3
& Electron Heating
Optically-Thick
Optically-Thin

Jet Break-Out
EÝjet
Metzger et al. 2010
Time-Averaged Light Curve
Hot Electrons 
IC Scattering (-rays)
and Synchrotron (optical)
Spectral Snapshots
E FE (1050 erg s-1)
Optically-Thick

Optically-Thin
Jet Break-Out
EÝjet
Metzger et al. 2010
Time-Averaged Light Curve
IC Tail
Synch
t ~ 15 s
E (keV)
t ~ 30 s
Parameter Study
3 1014 G < Bdip< 3 1016 G, 1 ms < P0 < 5 ms,  = 0, /2
GRB Energy (ergs)
solid = oblique,
dotted = aligned
Average Magnetization
Ave Magnetization avg
avg  L1-1.5
Ave Wind Power (erg s-1)
avg-L
Correlation
Prediction:
More Luminous / Energetic
GRBs  Higher 
Ave Magnetization avg
avg-L
Correlation
avg  L1-1.5
Prediction:
More Luminous / Energetic
GRBs  Higher 
Assuming Magnetic Dissipation Model
Agreement with
Epeak  Eiso0.4
(Amati+02)
and Epeak  Liso0.5
(Yonetoku+04)
Correlations
Ave Peak Energy Epeak
Ave Wind Power (erg s-1)
Epeak Liso0.11 00.2 0.33
Epeak Liso0.5
Peak Isotropic Jet Luminosity (erg s-1)
End of the GRB = Neutrino
Transparency
Ultra High-
Outflow 
- Full Acceleration to
~  Difficult
(e.g. Tchekovskoy et al. 2009)
- Reconnection Slow
- Internal Shocks Weak
(e.g. Kennel & Coroniti 1984)
TGRB ~ T thin ~ 10 - 100 s
End of the GRB = Neutrino
Transparency
Ultra High-
Outflow 
- Full Acceleration to
~  Difficult
(e.g. Tchekovskoy et al. 2009)
- Reconnection Slow
- Internal Shocks Weak
(e.g. Kennel & Coroniti 1984)
TGRB ~ T thin ~ 10 - 100 s
Steep Decline
Phase
GRB
Late-Time
(Force-Free)
Spin-Down
SD
GRB
Willingale et al. 2007
X-ray Afterglow
`Plateau’
Time after trigger (s)
Late-Time
(Force-Free)
Spin-Down
SD
e.g. Zhang & Meszaros 2001; Troja et al.
2007; Yu et al. 2009; Lyons et al. 2010
The Diversity of Magnetar Birth
Classical GRB
Bdip (G)
E~1050-52 ergs,
jet < 1,  ~ 102-103
Thermal-Rich GRB (XRF?)
E~1050 ergs, jet ~ 1,  < 10
P0 (ms)
Buried Jet
Recap - Constraints on the Central
Engine
GRB Duration ~ 10 - 100 seconds & Steep Decay Phase
- Time until NS is transparent to neutrinos
 Energies - EGRB ~ 1050-52 ergs
- Rotational energy lost in ~10-100 s (rad. efficiency ~30-50%)
 Ultra-Relativistic Outflow with  ~ 100-1000
- Mass loading set by physics of neutrino heating (not fine-tuned).
 Jet Collimation
- Exploding star confines and redirects magnetar wind into jet
 Association with Energetic Core Collapse Supernovae
- Erot~ESN~1052 ergs - MHD-powered SN associated w magnetar birth.
 Late-Time Central Engine Activity
- Residual rotational (plateau) or magnetic energy (flares)?
Predictions and Constraints
• Max Energy - EGRB, Max ~ few 1052 ergs
- So far consistent with observations (but a few Fermi
bursts are pushing this limit.)
- Precise measurements of EGRB hindered by
uncertainties
in application of beaming correction.
• Supernova should always accompany GRB
- So far consistent with observations.
•  increases monotonically during GRB and positively
correlate with EGRB
- Testing will requires translating jet properties (e.g.
power and magnetization) into gamma-ray light curves
and spectra.
Summary
• Long duration GRBs originate from the deaths of massive
stars, but whether the central engine is a BH or NS remains
unsettled.
• Almost all central engine models require rapid rotation and
strong magnetic fields. Assessing BH vs. NS dichotomy must
self-consistently address the effects of these ingredients on
core collapse.
• The power and mass-loading of the jet in the magnetar model
can be calculated with some confidence, allowing the
construction of a `first principles’ GRB model.
• The magnetar model provides quantitative explanations for
the energies, Lorentz factors, durations, and collimation of
GRBs; the association with hypernova; and, potentially, the
steep decay and late-time X-ray activity.
• Magnetic dissipation is favored over internal shocks and the
emission mechanism because it predicts a roughly constant