Theory of the Prompt and High Energy Emission of G amma- R ay B ursts sts Peter Mészáros, collabs: Kenji Toma, XueFeng Wu Pennsylvania State University
GRB 080319B A prompt z=0.937 “naked eye” optical GRB Racusin et al, 08 Nature 455:183 γ , opt prompt l.c. appear similar → same emission region, e.g. “internal” shock; but rad. mechanism? Interpret prompt as: i) optical: synchrotron ii) 0.1-1 MeV: IC (SSC) (and) iii) predict 2nd order IC @ ~100 GeV (there are also differing opinions) Mészáros
080319b XR O/UV GRB 080318B Mészáros Hei08
GRB 080319B Afterglow WJ NJ Prompt Mészáros
080319B X-Ray 2-jet fit FS-NJ FS-WJ Mészáros Hei08
080319B optical 2-jet fit RS-WJ FS-WJ Mészáros Hei08
GRB 080916C Spectrum : simple (~) • “Band” fits (joint GBM/LAT) for all the different time intervals • Soft-to-hard, to ”sort-of-soft- peak-but-hard- slope” afterglow • No evidence for 2nd component Mészáros
BUT: GRB 090902B
Plethora of Models • Radiative e ± ext. shock (Ghisellini et al) • Unmag. adiab. ext. shock (Kumar & Barniol) • Critique thereof (Piran & Nakar) • Klein-Nishina IC ext. shock (Wang, He, ..) • Structured adiab. ext. shock (Corsi et al) • Cocoon int. shock upscattering (Toma et al) • Photosp. int. shock upscattering (Toma et al) • Critique phot & magn. outflow (Zhang, Pe’er) • Hadronic models (Razzaque et al, Asano et al)
Radiative ext. shock model Ghisellini et al, 0910.2459 • GeV light curves roughly F E ~ t -1.5 for most LAT obs. • Spectrum roughly F E ~ E -1 , not strongly evolving • Argue it is external shock, with L~ t -10/7 as expected for `radiative’ f’balls Γ ~r -3 ~t -3/7 • To make ‘radiative’, need `enrich‘ ISM with e ± • Argue pair-dominated f’ball obtained from backscatt. of E>0.5 MeV photons by ext. medium, → cascade • External shock (afterglow) delay: explain GeV from MeV delay (MeV prompt is something else (?)) - Problem: r ≳ 10 15 cm needed, where n ± ≲ n p (e.g. ’01, ApJ 554,660)
Adiabatic unmagn. ext. shock Kumar & Barniol Duran, I, II : arXiv.0905.2417, 0910.5726 • Consider late (>4 s) afterglow at >100 MeV • E>E c , E m (sync.) ⇒ spectrum indep. of Γ , n • F E ~ t -1.2±0.2 ⇒ as adiabatic ext. shock • At t< 4s argue KN significant (Y ≲ 1) • Derive ε B , n from argument that ES at t<50 s should not dominate spectrum at <500 keV (which is unspecified ‘prompt’ emiss.) • → ES params. from >0.1 GeV predict XR, O ✓ • → B’ ~ 0.1G → B ext ~10-70 μ G shock comp. ✓
Adiab. Unmagn. ES (cont.) • Smooth match of unspecified prompt and afterglow considered not implausible (‘natural’) • 080916C: XO → ρ ~r -2 wind , 090902B, 090510 → n~1-10 -3 , 10 -1 -10 -5 • PROBLEMS: • Densities rather low • In SNR shocks have indications for B >> B compr. • Adiabaticity reliant on low n (param. fit assumptions)
Adiab. Unmag. (cont), Barniol-Kumar III, 1003.5916 • Confirm previous, expand a bit (but c.f. Piran-Nakar) • Argue B ext ≲ few 10 μ G enough to accel. e - to γ ★ ~10 8 in a few seconds, such that: ν sy ( γ ★ )~10 GeV, provided Rev.Sho. F pk ≤ 1Jy (for 10 GeV), or ≤ 0.1 Jy (for 1 GeV) • For γ ★ ~10 8 (10 GeV Sy photon) → need 4-5 s acc.time, and γ ~10 7 (1 GeV Sy phot) a bit earlier.
ES Sy shock model critique Piran-Nakar, 1003.5919 • Late photons (E >10 GeV, t > 100 s) cannot arise from ES Synchrotron (from general accel + sy constraints) → must be ≠ process • few mJy IR flux from RS → quench GeV emiss. (by IC), unless B is amplified in shock • If no amplification → need B ext ≥ 100 μ G (adiabatic; (unless n ext very low, n<10 -6 ) - or B higher for radiative • If ES Sy model is true, → no late >10 GeV phot (t>100 s), and → no simult.. < mJy IR flux should be observed -- Other recent ES Sy critique: Zhuo Li, 1004.0791, argue need 5n 05/8 mG <B u <10 2 n 03/8 mG → upstr. preamplification
KN adiabatic ES model (see poster) Wang, He et al, 0911.4189 • KN effects influence IC emission through Y parameter • Calc. Y( γ L ), where ν L (γ L )= 0.1GeV; also calc. Y(γ c ), Y(γ m ) • At t ≲ 10 s, Y( γ L ) ≲ 1 (SSC in KN) → 0.1 GeV is SY (and strong) • but Y(γ c ,γ m ) >> 1 → this SSC is NOT in KN → X, O are low • Y( γ L ) incr. in time (KN gets weaker) → SY GeV gets weaker → Light curve steeper than simple t -1.2 adiab. decay • Early steep LAT decay (SY modif. by SSC w. decr. KN), followed by flatter decay (SY w/o SSC) • Argue Kumar’s late X not steep enough & early LAT too flat , while KN can make LC in LAT & X steeper, as seen
ES shock model: 090510 Corsi, Guetta, Piro, arXiv:0911.4453 • ES: fit LAT, X, O, Γ n ~10 4 , E iso,n ~4x10 53 , ε e ~3x10 -3 , p~2.3, n~10 -6 , θ j,n ~0.12 o • IS: fit GBM, BAT, Γ w~300, E iso,w ~1.7x10 53 , ε e ~3x10 -3 , p~2.7, θ j,w ~0.64 o Or, another IS + ES model: De Pasquale et al ’09, next slide
IS-ES shock model: 090510 De Pasquale + Fermi/Swift team, 2010, ApJ 709:146 • Early LAT and XRT could be due to IS and O rise could be due to onset of simple FS • Or, FS may produce full spectrum from O thru GeV, but temporal behavior → structured jet
A Cocoon + IS Upscattering model of GRB lags, for GRB 080916C Toma, Wu & Mészáros, ApJ 09, 707:1404 cocoon Int. Shock • Assume jet emits synchrotron in optical, and 1st ord SSC is in MeV • Cocoon emits soft XR, jet upscatters this to ~0.3 GeV; time lag ~3s Mészáros
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Photon time lags • photon arrival time in different energy bands • GeV band: delayed 2-3 s, due to geometry (source photons come from high latitude cocoon) Mészáros
Cocoon + jet IS Pulse b • L 55= 1.1, Γ 3 =0.93, 1st SSC Δ t j =2.3 s, 2nd SSC γ m =400, γ c =390, τ T =3.5x10 -4, , ε B =10-5, ups-coc ε e =0.4 coc Data: courtesy of Fermi GBM/LAT coll. Mészáros
Photosphere + IS model Toma, Wu, Mészáros, arX:1002.2634 !"#$#%&"'(')*+,)-+$'(+*.)%"#/0)#1)$"')234)5'$ HI$'(+*.)%"#/0 G+$'(+*.)%"#/0 !"#$#%&"'(' E-('F*..)F*%' !"#$#%&"'(-/ Q! ( * 678 9<77 )/: %L+/"(#$(#+ ( &" 678 7><7? )/: @,'&'+,-+A)#+) ( - 678 7;<7= )/: B"'$"'()$"'(')-%) %$'..*()'+C'.#&'D ( ,'/ 678 79 )/: • Photosphere: prompt, variable MeV J"')&"#$#%&"'(-/)':-%%-#+)/*+)+*$K(*..L)&(#C-,')*)"-A") γ <(*L)'11-/-' • IS occur at r ≳ 10 15 cm (high Γ ) : Sy=XR, IC(UP)=GeV
Phot-IS model, cont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
Phot-IS model, cont. !"#$%&$'%()*+,-"./(0#"(-1+(1231(&$"4#'(5#$%(,$)+ 612)(023."+(%#+)('#-(-$7+(2'-#($,,#.'-(-1+()+,#'%$"4(+/2))2#'(&4( -1+(+8+9(*$2")(,"+$-+%(&4(-1+(12319+'+"34($&)#"*-2#'(:$'%(-1+( ,$),$%+(*"#,+));<(=12,1(,#.5%(/$7+(-1+(>?<()4',1"#-"#'<($'%( @@A(+/2))2#'($**+$"($)($(&"#$%(,#/*#'+'-B(6#(%+"2C+($(/#"+(
Phot-IS model, cont. !"#$%&'(#%$)"#)*'&'+,%,&$)-"&).($%(#/%0)1&(23%)45),+($$("# 6"7)1'&8"#)9"'.)&,2("#) :*3"%"$*3,&(/)."+(#'#%; A A: Phot., UP B merged (080916C) 6"7) γ <&'8),--(/(,#/8)&,2("#) :$8#/3&"%&"#<==!)."+(#'#%; B: Phot.. UP distinct (090902B) 53"%"$*3,&(/)F)45)."+(#'#% >).($%(#/%0)1&(23%)45),+($$("#).",$)#"%)#,,.)')$%&"#2)-(#,)%?#(#2)"-)%3,) *38$(/'9)*'&'+,%,&$0)1?%)%3,)'**&"*&('%,)*'&'+,%,&)&'#2,$)'&,)9(+(%,.0) 73(/3)($)/"#$($%,#%)7(%3)%3,)-'/%)%3'%)#"%)'99)%3,)6>@)ABC$)3'D,)').($%(#/%) ! ! 3(23<,#,&28)/"+*"#,#%E
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