Gamma-Ray Bursts Recent results Peter Mészáros, Pennsylvania State University Felix Aharonian Fest, Barcelona, 2012
Fermi 2
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Counts/bin Counts/bin 1500 1000 500 0 400 200 GBM NaI 3 + NaI 4 (8 kev-260 kev) 0.0 3.6 7.7 15.8 0 5 10 15 Time since trigger (s) 20 0 20 40 60 80 100 GBM BGO 0 (260 kev-5 MeV) GBM 54.7 Counts/bin 1500 1000 a b c d e GBM Counts/bin 500 400 200 0 5 10 15 Time since trigger (s) 100.8 3000 2000 1000 0 1000 500 Counts/sec Counts/sec GRB 080916c Light-curve E! 0 0 Counts/bin 300 200 100 20 0 20 40 60 80 100 LAT (no selection) LAT Counts/bin 300 200 100 0 5 10 15 Time since trigger (s) 600 400 200 Counts/sec Abdo, A. and Fermi coll., 09, Sci. 323:1688 0 0 Counts/bin Counts/bin 5 0 3 2 1 20 0 20 40 60 80 100 LAT (> 100 MeV) 0 5 10 15 Time since trigger (s) 20 0 20 40 60 80 100 LAT (> 1 GeV) LAT LAT Counts/bin Counts/bin 10 5 1.5 1 0.5 0 5 10 15 Time since trigger (s) 15 10 5 0 6 4 2 Counts/sec Counts/sec Note : GeV photons! lag behind MeV! 0-20 0 20 40 60 80 100 Time since trigger (s) 0 Mészáros
GRB 080916C Spectrum : up to ~10 GeV (obs.) Band (broken power-law) fits, joint GBM/LAT, in all time intervals Soft-to-hard spectral time evolution Long-lived (10 3 s) GeV afterglow No evidence for 2nd spectr. comp. (in some cases) Mészáros
But: in other bursts, Evidence of the extra components (in some cases) GRB 090510 Ackermann, et al. 2010, ApJ, 716, 1178 GRB 090902B Abdo et al. 2009,ApJ, 706L, 138A Joint spectral fit (of binned data) : GBM<40MeV standard LAT data>100mev!constrains main kev-mev component!spectral evolution during prompt phase!additional PL component seen at high and low energies Mészáros
Jets in GRBs int. & ext. shocks Int. & ext. shocks, accelerate electrons e,b!" (leptonic); and accel. protons too (?) p"!#, " (hadronic) internal shocks external shock 8 Mészáros pan05
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: Toma, Wu, Mészáros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hotosphere: prompt, variable MeV broken PL spectr. +#+<$"'(:*.)"56)&$70)!8!966)!::.!966)!8!56)&$70)!:;.!#6<67!6=!$>4!:;.!?0*$! 6=!$>4!:@.!A6>0B07010C!:D3 IS occurs at r!10 15 cm (high ") : Sy=XR, IC(UP)=GeV P'),-%/K%%)$"')A'+'(*.)&(#&'($-'%)#1)$"')&"#$#%&"'(-/)':-%%-#+)*+,)
Photosphere + Internal Shock leptonic model, cont. Generic shape comparablee to Fermi observations!
Hadronic model: 090902B ε!"ε#$%&'()*+, )-. <= 0L <= 0I <= 0K Secondary photons # low en PL # :;<= <> $*+?$Γ;<@==?$A B )A γ ;@?$A C )A γ ;< 56789 C8FG0*6+BH & 0 & 1 0234 & 0 & 1 0DE <=, <= > <= I <= J Secondary photons # µ0234 ε$%&/. Also explain presence of low energy power law spectral component Asano, Inoue, Mészáros, 2010, ApJL 725:L121 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 Mészáros
A hadronic thermal photosphere PL spectrum? p-n collisions below phot. 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% efficiency Sub-photospheric dissipation can give strong photospheric component
p-n coll.$e±$ photosphere %-spectrum & MeV GeV # 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
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 " ~ r 1/3 $ " ~ 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 $to GeV -TeV range Veres & Mészáros, 2012, ApJ 755:12
Phot+ExtSh : Single (Band) PL Veres & Mészáros, 12, ApJ 755:12
Phot+ExtSh : Band + 2nd comp. Veres & Mészáros 12, ApJ 755:12
Magnetic Photosphere (Leptonic) Fit Results Good fits obtained: can reproduce either 1- or 2- component observed spectra with same model In some bursts (e.g. 080916C, where 2nd comp. is absent (or rather, possible evidence for it is <2.5 (), either a single Band or 2-component fit is possible But, best fit parameters are generally not unique; Calculated model parameter error estimates Use GeV-MeV time delay as an additional constraint
090510A magphot P. Veres, BB Zhang & Mészáros, 1210.7811
090510A barphot P. Veres, BB Zhang & Mészáros, 1210.7811
080916C magphot P. Veres, BB Zhang & Mészáros, 1210.7811
080916C barphot P. Veres, BB Zhang & Mészáros, 1210.7811
Or else: Internal Shocks Redux: modified internal shocks currently of two main types: Magnetic dissipation regions, R~ 10 15 cm, allow GeV photons - but hard to calculate quantitatively details of reconnection, acceleration and spectrum, e.g. McKinney- Uzdensky 12, MN 419:573, Zhang & Yan 11, ApJ 726:90 Baryonic internal shocks, protons are 1st order Fermi accelerated, and secondaries are subsequently reaccelerated by 2nd order Fermi ( slow heating ), e.g. Murase et al, 2012, ApJ 746:164 - more susceptible to quantitative analysis, e.g. as follows 26
Hadronic int. shock: more detailed ' Orig: Waxman & Bahcall 97 for neutrino prod. in internal shocks Prompt# Afterglow FS: X-ray, etc.; RS: Opt. flash ' Asano & PM, 09-12 on, calculate second y photons & second y neutrinos
Numerical time dependence of photon & neutrino secondaries 30 :4 30 :< 30 :9 30 :; 30 :30 ε&'ε(!"#)*+,-. +/% " 510/ 50/ 314/ 012./ 30. 30 8 30 4 30 9 30 30 ε!"#$% 34/ 678125 (Asano & PM 12, ApJ 757:115) Generic dissipation region at a radius R~10 14-10 16 cm (could be Int.Sh. or mag. diss. region, etc.) Numerical Monte Carlo one-zone rad. transfer model with all EM & # physics $Fermi/LAT param. E"iso~2.10 54, Lp/Le=20, %=600, R~10 16 cm, z=4.5 28
Moderate hadronic case Asano & PM 12, ApJ 757:115) Typical GRB params., E"iso~5.10 50 erg, Lp/Le=10, %=800, R~10 14 cm ε&'ε(!"#)*+,-. % BC >F " 9:;)678, <=3>:?@A BC >G /0)#12!3#45678, # n BC >BC BC. BC D BC E BC F BC BC BC B. ε!"#$% Predict complying nu-flux, at >10 16 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! 29
Fermi/LAT hadronic case For very bright, rare bursts (<10% of all cases) Get 2nd GeV "- comp. & its delay Predict complying #-flux, but on rare LAT bursts and at > 10 16 ev Predict substantial nu-gamma delay Asano & PM 12, ApJ 757:115) 6 7?> ()*+,-./&012-34 967:&' (&3!*.5)167 68 &' # BC >H ε&'ε(!"#)*+,-. % 9:;)678, /0)#12!3#45678, 7?8 7?= " %&' 9;7:&' BC >E BC >G " <=3>:?@A 7?< 7 < = 8 > 67 6< 6= 68 6> <7 << <= <8 <> ;7!"#$ BC >F 30 BC. BC D BC E BC F BC BC BC B. ε!"#$%
Some observed photon energies and redshifts Eobs(GeV) z 13.2 4.35 7.5 3.57 5.3 0.74 31.3 0.90 33.4 1.82 19.6 2.10 2.8 0.897 4.3 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?
Jets in GRBs int. & ext. shocks Int. & ext. shocks, accelerate electrons e,b!" (leptonic); and if accel protons too, p"!# (hadronic) internal shocks external shock 33 Mészáros pan05
!s from p! from int. & ext. shocks ( NOTE: internal shock! old paradigm ) Internal shock (prompt) External shock!-res.: E p E! ~0.3GeV 2 in comoving frame, in lab: " E p # 3x10 6 $ 2 2 GeV " E! # 1.5x10 2 $ 2 2 TeV Internal shock p! MeV " ~100 TeV s ( External shock p! UV " ~ 0.1-1 EeV s ) Waxman, Bahcall 97 & 99 PRL Diffuse flux: det. w. km 3 Mészáros, NOW 04
IceCube (2010) 5160 DOMs on 86 strings IceTop currently instrumented 160 tank ice-cherenkov surface! air shower array (IceTop) "! see talk by T. Gaisser Includes DeepCore infill array! (sensitivity to lower energies) AMANDA 79 strings deployed to date in 6 construction seasons ( 79/86 complete) 324 m Digital Optical Module (DOM) Deep Core 35 Eiffel Tower
GRBs with IceCube (Kappes et al, NUSKY, June 2011) GCN-satellite triggered searches Being tested here : internal shock prompt #-burst (WB97 simplified) Off-time On-time (blind) Off-time T0 very low background! 1 event can be significant! prompt precursor (~100 s) background wide window (several hours) Individual modeling of neutrino fluxes (fireball model) Measured parameters:! spectrum, (redshift) Average parameters: "jet (316), tvar (10 (1) ms), Liso (10 52 (51) erg),!b (0.1),!e (0.1), fe/p (0.1) IC59: 98 bursts in northern sky Alexander Kappes, NUSKY, Trieste, 24.06.2011 15 36 c
IC40+59 search for VHE nus from 190 GRB (105 northern) 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 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
IC59 model-indep. search Nature 484:351 (2012) UL % CL is similar as for model dep. 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
IC59 2-year conclusions (190 GRBs) Nature 484:351 (2012) 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
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... p"!' interaction of a Band-" spec. with an E -2 proton spec. p (WB 97) " # 41
However... (Li, Zh 12, PRD 85:027301) 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 <E),cool; Also for E<Eb, have f) "E, because of decr. # of photons Net result: model #µ flux overestimated by factor ~5 In addition, ignored multipion, Kaon decay, etc. 42
Graphically... 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) 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 mfp 43
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! (" Hümmer et al, 11, PRL 108:231101) (see also Li, 12, PRD 85:027301 ; He, et al 12, ApJ 752:29) 44
Note also that... 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
#µ from mag.dis.phot. + ext.sh. Gao, Asano, Mészáros 12, JCAP i.p. (1210.1186) 46
Compare mag.phot, bar.phot, int.shock @ var., (or %) (tvar=1 ms) Gao et al, arxiv 1210.1186 47
Diffuse nu from MPh, Bph, IS,,=300 & IC3 lim. 48 Gao 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.