Peter Mészáros,Pennsylvania State University
Felix Aharonian Fest, Barcelona, 2012
Gamma-Ray Bursts
Recent results
2
Fermi
3
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Mészáros
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3GBM NaI
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(> 1 GeV)
Abdo, A. and Fermi coll., 09,Sci. 323:1688
GRB 080916c
Light-curveE!
Note :GeV photons!“lag”
behind MeV!
GBM
GBM
LAT
LAT
LAT
Mészáros
GRB 080916C
• “Band” (broken power-law) fits, joint GBM/LAT, in all time intervals
• “Soft-to-hard” spectral time evolution
• Long-lived (103 s) GeV afterglow
• No evidence for 2nd spectr. comp. (in some cases)
Spectrum : up to ~10 GeV (obs.)
Mészáros
Evidence of the “extra components”
Joint spectral fit (of binned data) :GBM100MeV
GRB 090902BAbdo et al. 2009,ApJ, 706L, 138A
GRB 090510Ackermann, et al. 2010, ApJ, 716, 1178
!Constrains main keV-MeV component!Spectral evolution during prompt phase!Additional PL component seen at high and low energies
12
But:
(in some cases)
in other bursts,
Mészáros pan05
Jets in GRBs → int. & ext. shocks
8
↙internal shocks
↙external shock
Int. & ext. shocks,
accelerate electrons
e,B !" (leptonic);
and
accel. protons too (?)
p"!#, " (hadronic)
Theoretical Issues:
• Are single-component spectrum at GeV due to internal or external shocks? - or other, such as photosphere, ..?
• Are photons of purely leptonic or hadronic origin, or mixed?
• Besides delay providing QG upper limits (based on zero intra-source GeV-MeV delay): what are the astrophysical causes of delay?
• Is 2nd component a " zone/rad.mech. than 1st? Do we need at least a two-zone model?
A “leptonic” model:
• Photosphere: prompt, variable MeV broken PL spectr.• IS occurs at r!1015 cm (high ") : Sy=XR, IC(UP)=GeV
Toma, Wu, Mészáros, 2011, MN 415:1663
! !
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Photosphere + Internal Shock leptonic model, cont.
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Mészáros
Hadronic model: 090902B– 5 –
based on a likelihood analysis of the combined GBM and LAT data under the assumption
of a Band function plus an additional power-law (Abdo et al. 2009c).
ε!"ε#$%&'()*+,)-.
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Mészáros
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. + external shock (weak int.sh.)• Photosphere: if dissipative, good rad. efficiency• (Internal shock: if magnetic, may be absent)• External shock: most of GeV and soft afterglow
Mészáros
Evolving Fireball paradigm:
" 2005
!2005
p-n collisions below phot.
• 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% efficiency
• Sub-photospheric dissipation can give strong photospheric component
Beloborodov, ’10, MN 407:1033
A hadronic “thermal” photosphere PL spectrum?
p-n coll.$e±$ photosphere %-spectrum
• The result is a thermal peak at the ~MeV Band peak, plus
• a high energy tail due to the non-thermal e± , whose slope is comparable to that of the observed Fermi bursts with a “single Band” spectrum
• The “second” higher energy component (when observed) must be explained with something else
GeV#
&MeV
A leptonic magnetic photosphere + external shock model
MeV GeV
'Leptonic photosph. spectrum extend to "ph me ~50-100 MeV' Ext. shock upscattering spectrum extend to "es %e,KN me $TeV
Veres & Mészáros ‘12, ApJ 755:12
Magnetic-dominated GRB jets
• Dynamics of expansion " ~ r1/3 $ " ~ const• Dissipative (mag.) scattering photosphere $
results in broken PL MeV spectrum
• No internal shocks expected• Magnetiz. param. ( drops to ~ o(1) at rdecel• External shock present (forward; +reverse?) $both shocks up-scatter photospheric MeV $to GeV -TeV range
Veres & Mészáros, 2012, ApJ 755:12
Phot+ExtSh : Single (Band) PL Veres & Mészáros, ‘12, ApJ 755:12
Phot+ExtSh : Band + 2nd comp.Veres & Mészáros ‘12, ApJ 755:12
Magnetic Photosphere (Leptonic) Fit Results
• Good fits obtained: can reproduce either 1- or 2-component observed spectra with same model
• In some bursts (e.g. 080916C, where 2nd comp. is “absent” (or rather, possible evidence for it is
090510Amagphot
P. Veres, BB Zhang & Mészáros, 1210.7811
090510Abarphot
P. Veres, BB Zhang & Mészáros, 1210.7811
080916C magphot
P. Veres, BB Zhang & Mészáros, 1210.7811
χ2 =113.6/98
080916C barphot
χ2 =129.7/98
P. Veres, BB Zhang & Mészáros, 1210.7811
Or else: Internal Shocks Redux:
modified internal shocks
• Magnetic dissipation regions, R~ 1015 cm, allow GeV
photons - but hard to calculate quantitatively details of
reconnection, acceleration and spectrum, e.g. McKinney-
Uzdensky ‘12, MN 419:573, Zhang & Yan ’11, ApJ 726:90
• Baryonic internal shocks, protons are 1st order Fermi
accelerated, and secondaries are subsequently re-
accelerated by 2nd order Fermi (‘slow heating”), e.g.
Murase et al, 2012, ApJ 746:164 - more susceptible to
quantitative analysis, e.g. as follows
26
currently of two main types:
Hadronic int. shock: more detailed
↙ Afterglow FS: X-ray, etc.;RS: Opt. flash
Prompt#' Orig: Waxman & Bahcall ’97 for neutrino prod. in internal shocks
'↙ Asano & PM, 09-12 on, calculate second’y photons &second’y neutrinos
Numerical time dependence of
photon & neutrino secondaries
• 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 & # physics
• $Fermi/LAT param. E"iso~2.1054, Lp/Le=20, %=600, R~1016cm, z=4.5
28ε!"#$%
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012./
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30. 308 304 309 303030:30
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(Asano & PM ’12, ApJ 757:115)
"
“Moderate” hadronic case
29
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“Typical” GRB params., E"iso~5.1050 erg, Lp/Le=10, %=800, R~1014cm
• Predict complying nu-flux, at >1016 eV - may be detectable in future
• Predict larger 2nd photon component than does leptonic model, in all bursts and
starting in the prompt phase - perhaps hard to detect if low photon stats.?
• UHECR flux from escaped neutrons: not sufficient, if Lp/Le=10 - need more work!
Asano & PM ’12, ApJ 757:115)
"
#
n
Fermi/LAT hadronic case
• For very bright, rare bursts (
Some observed photon energies and redshifts
Eobs(GeV) z
13.2 4.357.5 3.575.3 0.7431.3 0.9033.4 1.8219.6 2.102.8 0.8974.3 1.37
• Even z>4 bursts result in Eobs~10 GeV photons
•Some z~1 bursts produce Eobs)30 GeV photons
( 130 GeV in rest frame!)
•⇒ encouraging for low Eth CTs: HAWC, CTA...
What about UHE CR, NU?
• Shocks present in HE non-thermal %-ray sources (or else: magnetic reconnection).
• Electrons are definitely accelerated• %-rays usually attributable to leptonic
mechanisms (synchrotron, inv. Compton)
• But: UHECR must be accelerated somewhere. Likely (?) in same shocks as the e- in one of these HE %-ray sources- but which?
Mészáros pan05
Jets in GRBs → int. & ext. shocks
33
↙internal shocks
↙external shock
Int. & ext. shocks,
accelerate electrons
e,B !" (leptonic);
and if
accel protons too,
p"!# (hadronic)
Mészáros, NOW 04
!s from p! from int. & ext. shocks
• !-res.: E’p E’! ~0.3GeV2 in comoving frame, in lab:
" Ep # 3x106 $2
2 GeV
" E! # 1.5x102 $2
2 TeV
• Internal shock p!MeV "
~100 TeV νs• ( External shock p!UV " ~
0.1-1 EeV νs )• Diffuse flux: det. w. km3Waxman, Bahcall 97 & 99 PRL
Internal shock(prompt)
External shock
( NOTE: internal shock ! old paradigm )
35
currently instrumented
AMANDA
Deep CoreEiffel Tower
324 m
IceTopIceCube
Digital Optical Module (DOM)
5160 DOMs on 86 strings
160 tank ice-Cherenkov surface! air shower array (IceTop) –"! see talk by T. Gaisser
Includes DeepCore infill array! (sensitivity to lower energies)
79 strings deployed to date in 6 construction seasons
(2010)
( 79/86 complete)
36
Alexander Kappes, NUSKY, Trieste, 24.06.2011
c
GRBs with IceCube
• GCN-satellite triggered searches
very low background ! 1 event can be significant !
• Individual modeling of neutrino fluxes(fireball model)
• Measured parameters: ! spectrum, (redshift)
• Average parameters: "jet (316), tvar (10 (1) ms), Liso (1052 (51) erg), !B (0.1), !e (0.1), fe/p (0.1)
15
On-time (blind) Off-timeOff-time
T0prompt
precursor (~100 s)
wide window (several hours)
background
IC59: 98 bursts in northern sky
(Kappes et al, NUSKY, June 2011)
Being tested here : internal shock
prompt #-burst (WB97 simplified)
IC40+59 search for VHE nus
from 190 GRB (105 northern)
• Analyze 190 GRBs
localized w. "-rays
betw, Tstart & Tend
• Use the WB’97 and
Guetta’04 proton
acceleration model in
internal shocks, with
E-2 spectr, &p/&e=10,
and p"!'-res !#µ
• Nu-flux normalized
by obs. "-ray flux, get
F# for 190 (right axis),
and diffuse flux (all)
assuming 677 yr-1
37
Nature 484:351 (2012), the Icecube collab.; Abbasi and 242 others (incl. P.M.)
(A) Model dependent search
Model
0.27
Data is factor 0.27 below model F# at 90% CL
IC59 model-indep. search• Searched 190 GRB
@ "-trigger ± 't window up to 1 day, also using ( spectra & params
• Two candidate events seen at low signif., probably due to (other) CRs
• $ Results shown are for E-2 spectra as function of 't
• Right axis is data
deficit below F# model
38
Nature 484:351 (2012)
UL % CL is similar as for model dep. search
IC59 2-year conclusions (190 GRBs)
• The fireball (more accurately: internal shock) model overpredicts the TeV-PeV nu-flux by a factor 3.7 ,(asuming Lp/Le=10, '-res only, Lorentz %~300-600)
• In the same model, the 95% CL nu-flux allowed by the data falls below 2-3" of what expected if GRBs contribute most of GZK UHECR flux.
• In these models, either Lp/Le must be substantially below factor 3-10 assumed here, or the production efficiency of neutrinos is lower than was assumed.
39
Nature 484:351 (2012)
Conclusion on the conclusions:
• These are conservatively stated conclusions
• The first time VHE nus have put a significant constraint on a well-calculable astrophysical UHECR-UHENU model, at 90-95% CL
• This is very valuable
• Icecube is doing exciting astrophysics
• A significant first step towards GZK physics
40
Some model details ....
41
p"!' interaction of a Band-" spec. with an E-2 proton spec.
(WB 97)
"
p
#
However ...
• IC22-59 analysis used a simplified version of WB97 , which
results in overestimated model nu-fluxes
• Assumed F#IC /Fp = (1/8) f),b , where 1/8 because 1/2 p"
lead to )+ and each #µ carries 1/4 E), and f),b=f) (E=Eb)
• But f) (E) = f),b is OK only for Eb < E
Graphically....
• fC: energy of all photons approx. by break energy
• f* : 0.7 (rounding error in one eq.)
• f+ : 2/3(negelected width of '-res.)
• Cs : correct en. loss of second’s & E-dep of proton mfp43
Even using the (old paradigm) int. shock
model, the simplifications have an effect
• IC-FC: IceCube Fball. Calc.
• RFC: “Revised” Fball.Calc. #
• NFC: Numerical Fball.Calc.
(Hümmer et al ’11, PRL 108:231101)
In summary .... • Even when using old paradigm of internal shock, but more detailed physics (incl. multi-pion and Kaon production, ( cool’g. break for ), µ, and numerical as opposed to analytical calcul.)
• ⇒ F! predictions below IC40+59 !
44
(" Hümmer et al,
’11, PRL 108:231101)
(see also
Li, ’12, PRD 85:027301 ;
He, et al ’12, ApJ 752:29)
• Internal shock model use is expedient: best documented so
far, and easy to calculate # reason why its use is widespread
• But ... int. shocks known (past 10 years) to have difficulties
for gamma-ray phenomenology (efficiency, spectrum, etc)
• And, acceleration rate of protons vs. electrons is unknown;
are protons injected into accel. process at = or ( rate as
electrons? Only energy restriction on model is Lp/Le " 10.
• Alternatives to internal shock: being investigated - but so far,
are less easy to calculate. Progress, however, is being made.
• Even if GRB are not GZK sources, model indep. searches
leave possibility of lower, observable nu-fluxes from GRB
45
Note also that.....
#µ from mag.dis.phot. + ext.sh.
46
Gao, Asano, Mészáros ’12, JCAP i.p. (1210.1186)
Compare mag.phot, bar.phot, int.shock @ var. , (or %)
47
(tvar=1 ms)
Gao et al, arXiv 1210.1186
Diffuse nu from MPh, Bph, IS, ,=300 & IC3 lim.
48Gao et al, arXiv 1210.1186
Diffuse nu from MPh, Bph, IS, ,=1000 & IC3 lim.
49
Gao, Asano, Mészáros ’12, JCAP ..(1210.1186)
Models and IC3 next steps:
• Need 3-5 years data accumulation to test the current (Fermi & Swift "-ray tested) models
• Will have to redo the IC3 statistical model fit evaluation of upper limits for these newer (non-WB) models, whose neutrino spectra and model parameters are different
50
Outlook
• Observational prospects for ground-based multi-GeV astrophysics of GRB are encouraging - there are enough bursts that show photons there!
• If GRB spectra reaching TeV are detected, this would provide new constraints on hadronic vs. leptonic GRB models - but much further theoretical work is needed to specify models
• Of course, GeV-TeV neutrino observations could clinch this issue - further address GRB-GZK UHECR contrib.
• Will be able to constrain particle acceleration / shock parameters, compactness of emission region (dimension, mag.field,.), etc.