Gamma-Ray Bursts. Felix Aharonian Fest, Barcelona, Peter Mészáros, Pennsylvania State University. Recent results

Transcription

1 Gamma-Ray Bursts Recent results Peter Mészáros, Pennsylvania State University Felix Aharonian Fest, Barcelona, 2012

2 Fermi 2

3 !"#$%&!"#$%&'&(')*+$,'-'),')(,!"#$%&'&(')*+$,'-'),')(, *,C#-LM2A&#0A:AF'E =>?#JLM2A&#0A:AF'E# *,C#=*+,D#E&22(#0%&0F2< $+N=OCOP>+Q. /0&$!#1$%&'&(',$2345$!"#,$6$7&-89$20-:;$)+$'0&$<=/$>*?. 2J-:;$K)'0$L*8&$-((D8-'&$;*::*KHDM$:*(-:),-')*+,$N7$OK);'$-+%$B8*D+%HN-,&%$*N,&8P-'*8)&,$A!"QRS9$!&L)+)HO9$!&L)+)HR9$?</C! 3

4 Counts/bin Counts/bin GBM NaI 3 + NaI 4 (8 kev-260 kev) Time since trigger (s) GBM BGO 0 (260 kev-5 MeV) GBM 54.7 Counts/bin a b c d e GBM Counts/bin Time since trigger (s) Counts/sec Counts/sec GRB c Light-curve E! 0 0 Counts/bin LAT (no selection) LAT Counts/bin Time since trigger (s) Counts/sec Abdo, A. and Fermi coll., 09, Sci. 323: Counts/bin Counts/bin LAT (> 100 MeV) Time since trigger (s) LAT (> 1 GeV) LAT LAT Counts/bin Counts/bin Time since trigger (s) Counts/sec Counts/sec Note : GeV photons! lag behind MeV! Time since trigger (s) 0 Mészáros

5

6 GRB C 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

7 But: in other bursts, Evidence of the extra components (in some cases) GRB Ackermann, et al. 2010, ApJ, 716, 1178 GRB B 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

8 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

9 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?

10 A leptonic model: Toma, Wu, Mészáros, 2011, MN 415:1663!"#$#%&"'(')*+,)-+$'(+*.)%"#/0)#1)$"')234)5'$ E-('F*..)F*%'!"#$#%&"'(' G+$'(+*.)%"#/0 HI$'(+*.)%"#/0!"#$#%&"'(-/ ( * 678 9<77 B"'$"'()$"'(')-%) %$'..*()'+C'.#&'D ( &" 678 7><7? )/: ( ;<7= )/: Q! %L+/"(#$(#+ (,'/ )/: J"')&"#$#%&"'(-/)':-%%-#+)/*+)+*$K(*..L)&(#C-,')*)"-A")!<(*L)'11-/-'+/L) *+,)$"')$L&-/*.)&"#$#+)'+'(AL)#1)$"')4*+,)%&'/$(K:M)6)7)N'O!"#$%&'()*+!,-.!/0012$(!,-34! J"'),-%%-&*$-#+)F'.#B)$"')&"#$#%&"'(')/#K.,)/*K%')$"')':-%%-#+)$#)F') Photosphere: 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)$"')&"#$#%&"'(-/)':-%%-#+)*+,)

11 Photosphere + Internal Shock leptonic model, cont. Generic shape comparablee to Fermi observations!

12 Hadronic model: B ε!"ε#$%&'()*+, )-. <= 0L <= 0I <= 0K Secondary photons # low en PL # :;<= <> $*+?$Γ;<@==?$A B )A γ ;@?$A C )A γ ;< C8FG0*6+BH & 0 & & 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

13 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

14 Evolving Fireball paradigm: " 2005!2005 Mészáros

15 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

16 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

17 A leptonic magnetic photosphere + external shock model MeV GeV 'Leptonic photosph. spectrum extend to "ph me ~ MeV ' Ext. shock upscattering spectrum extend to "es %e,kn me $TeV Veres & Mészáros 12, ApJ 755:12

18 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

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

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

21 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 C, 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

22 090510A magphot P. Veres, BB Zhang & Mészáros,

23 090510A barphot P. Veres, BB Zhang & Mészáros,

24 080916C magphot P. Veres, BB Zhang & Mészáros,

25 080916C barphot P. Veres, BB Zhang & Mészáros,

26 Or else: Internal Shocks Redux: modified internal shocks currently of two main types: Magnetic dissipation regions, R~ 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

27 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, on, calculate second y photons & second y neutrinos

28 Numerical time dependence of photon & neutrino secondaries 30 :4 30 :< 30 :9 30 :; 30 :30 ε&'ε(!"#)*+,-. +/% " 510/ 50/ 314/ 012./ ε!"#$% 34/ (Asano & PM 12, ApJ 757:115) Generic dissipation region at a radius R~ 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~ , Lp/Le=20, %=600, R~10 16 cm, z=4.5 28

29 Moderate hadronic case Asano & PM 12, ApJ 757:115) Typical GRB params., E"iso~ 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

30 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 > ev Predict substantial nu-gamma delay Asano & PM 12, ApJ 757:115) 6 7?> ()*+,-./& :&' (&3!*.5) &' # 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!"#$%

31 Some observed photon energies and redshifts Eobs(GeV) z 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...

32 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?

33 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

34 !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 " ~ EeV s ) Waxman, Bahcall 97 & 99 PRL Diffuse flux: det. w. km 3 Mészáros, NOW 04

35 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

36 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, c

37 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

38 IC59 model-indep. search Nature 484:351 (2012) UL % CL is similar as for model dep. search Searched 190 "-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

39 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 %~ ) 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

40 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

41 Some model details... p"!' interaction of a Band-" spec. with an E -2 proton spec. p (WB 97) " # 41

42 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

43 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

44 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: ; He, et al 12, ApJ 752:29) 44

45 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

46 #µ from mag.dis.phot. + ext.sh. Gao, Asano, Mészáros 12, JCAP i.p. ( ) 46

47 Compare mag.phot, bar.phot, var., (or %) (tvar=1 ms) Gao et al, arxiv

48 Diffuse nu from MPh, Bph, IS,,=300 & IC3 lim. 48 Gao et al, arxiv

49 Diffuse nu from MPh, Bph, IS,,=1000 & IC3 lim. 49 Gao, Asano, Mészáros 12, JCAP..( )

50 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

51 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.