High Energy Emissions from Gamma-ray Bursts (GRBs) Soeb Razzaque Penn State University TeV 06
Download ReportTranscript High Energy Emissions from Gamma-ray Bursts (GRBs) Soeb Razzaque Penn State University TeV 06
High Energy Emissions from Gamma-ray Bursts (GRBs) Soeb Razzaque Penn State University TeV 06 1 Gamma Ray Burst Most violent explosion in the Universe! Bright flash of rays outshining the entire universe for seconds • Total energy output in -rays ~1049-1051 erg • Peak photon energy ~0.1-1 MeV Credit: Tyce DeYoung • Non-thermal -ray spectrum • Isotropic distribution • Rate ~1000/year • Extra-galactic (redshift~1-2) TeV 06 2 GRB Prompt Emission Highly variable -ray emission (down to milliseconds) Compact source Long bursts Short bursts Time (s) Bi-modal distribution of burst duration Different origins TeV 06 3 GRB Afterglow Late time (hours-days) emission of X-ray, UV, optical light Feb 28 TeV 06 GRB 970228 Mar2 • Identify host galaxy redshift 4 X Core collapse ISM UV O Afterglow • Isotropic-equivalent total energy outflow GRB Lo 1050 - 1052 erg/s • Initial fireball radius 1 Accretion disk Ro 10 -10 cm 6 Relativistic jetted outflow 7 • Initial temperature To 1 10 MeV TeV 06 Binary mergers 5 Gamma-ray Spectrum • Time-averaged spectrum fitted by broken power-laws (Band fit) dN / dE E Non-thermal E ,b • Origin: Internal shocks e-synchrotron radiation (low energy) Inverse Compton scattering (high energy) • Theoretical model: Observation: Break energy ~0.1-1 MeV E 1, 2 E =2 for strong shock dN Ee p e - shock acceleration dEe • Fast cooling: dN E ( p 2) / 2 ; E E , pk Synch/IC spectrum dE shock accelerated e - population lose energy completely (e to ) within dynamic time TeV 06 ~0.1 model parameter E e Ek 6 Afterglow Spectrum e -synchrotron cooling time longer than dynamic time Ambient medium Reverse | Forward shocks Break frequency decreases in time at rate depending on constant (ISM) or wind (density r -2 ) ambient medium Sari, Piran & Narayan ’98 TeV 06 7 TeV -ray Detection Status ► Milagrito: GRB 970417a Milagro Tentative 3 detection Unknown redshift (less than 100 Mpc?) Atkins et al. ‘00 ► Tibet Array Tibet Array: 50-60 GRB stacked in time coincidence with MeV 6 significance Amenomori et al. ‘96 ► GRAND: GRB 971110 Reported significance 2.7 Poirier et al. ’03 ► MAGIC: GRB050713a GRAND Array MAGIC Flux upper limits Albert et al. ‘06 TeV 06 8 GeV -ray Detection Hurley et al. ‘94 GRB 970217 GRB 941017 t<14 s t <47 s t < 80 s t < 113 s t < 211 s TeV 06 Gonzalez et al. ‘03 • • • • Handful of GRB detection at ~GeV by EGRET Hard spectra and delayed emission More energy in HE component? Need more data! Future detector 9 High Energy -rays from GRBs ► Electromagnetic process: Inverse Compton (IC) Maximum electron energy ~100 TeV Maximum -ray energy ~TeV Inefficient in the Klein-Nishina limit ► Hadronic Process: Photomeson 0 decay Maximum proton energy ~1020 eV Maximum -ray energy ~EeV In general inefficient: opacity~1 (long) <1 (short) ► ► ► Single or multi (internal-external shocks) zone(s) emission? High energy -rays may attenuate at the source -rays with energy >100 GeV are attenuated in background radiation fields (IR/CMB) TeV 06 10 Which Model? One zone model for MeV and HE Time delay by slower p cascade and secondary radiation Early Afterglow: >100 MeV IC e-sync Boettcher & Dermer ‘98 Internal shock MeV -rays External shock high energy Insignificant proton contribution TeV 06 tdec p-sync Zhang & Meszaros ’01 Granot & Guetta ‘03 ~2 11 -ray Opacity of the Universe e >100 GeV -rays from GRBs suffer attenuation in IR & CMB background Coppi & Aharonian ‘97 High energy -ray attenuation from GRBs may probe astrophysical model(s) TeV 06 Baring ‘99 12 HE Photon Opacity in GRBs Optical depth Internal shock radius TeV 06 Razzaque, Meszaros & Zhang ‘04 13 GRB Prompt and Delayed Spectra Re-processed high energy -ray GRB bkg e ; e bkg e HE L ,iso 1052 erg/s 2.5 z 1 800 10-17 G IG B-field 10-20 G t 1 s E , pk 1 MeV E , ssa 10 keV Razzaque, Meszaros & Zhang ‘04 TeV 06 14 Diffuse <TeV -rays from GRBs GRB 0.44 Gpc-3 yr -1 316; t 1 s; tGRB 20 s TeV 06 Casanova, Dingus & Zhang ‘06 15 >TeV -ray from UHE Cosmic-ray >1 TeV -ray fluence 1051 erg GRB energy at 100 Mpc Shock-acceleration in GRB ≥1020 eV cosmic-rays Cascades on IR/CMB background radiation pCR bkg pe / p 0 / n e e TeV ; synchrotron Delayed emission ~day Patchy IGM (80% voids w. B10-15 G, 20% w. B~10-11 G) TeV Fluence ~2% of energy in GZK protons Waxman & Coppi ’96 Dermer ’02 Armengaud, Sigl & Miniati ‘06 TeV 06 16 GRB Fireball Evolution n, f p , f ~ 300 ~1 Coulomb e p Baryon loading Compton e n nuclear p n Initial fireball n p e n p e e pn e e 0 n, f p , f rel 1 Inelastic p-n scattering np Initial fireball TeV 06 coasting fireball Derishev, Kocharovsky & Kocharovsky ‘99 n e p n-p decouples17 n-p Decoupling in Short GRB o nn' / n'p Lkin 1050 erg/s R0 106 cm n-p Decoupling Radius Rnp~RTh TeV 06 Razzaque & Meszaros ‘06 18 n-p Decoupling Gamma-rays • Only photons produced at photosphere may escape un-attenuated • 0 decay photon energy E Probability ' 70 cm p, f 10 GeV (LGRB) MeV~ 60 GeV (SGRB) ' P 0 np ( RTh ) Rnp / RTh 0.4 Bahcall & Meszaros ‘00 Razzaque & Meszaros ‘06 • Flux from an SGRB at z=0.1 N , 0 P 0 Lˆ 4 DL2 p , f m p c 2 2 106 cm-2s-1 • GLAST : Too small effective area • MILAGRO TeV 06 Aeff 5105 cm2 Energy below threshold? 19 Short GRB Model Flux Predictions Model parameters Lkin 10Liso ; =316 ; o nn' / n'p 10 GRB Distance (z) L_iso (erg/s) Duration (s) E (GeV) Flux (/cm2/s) 040924 050509b 051103 051221 0.859 0.225 0.001(?) 0.547 1.48E52 8.6E48 2.6E47 1.7E51 0.6 0.128 0.17 1.4 22 59 36 22 9.7E-6 2.3E-7 8.6E-4 2.3E-6 Data credits: Pablo Saz Parkinson Predictions • These are still below detection • Need bigger detectors with lower threshold TeV 06 20 GeV Gamma-rays from Short GRB o nn' / n'p E ,b 2.82To ( R / Ro ) p , f b e 0 e IC scattering Ri 22p, f c(t / ms) TeV 06 E ,c mec 2 p , f Razzaque & Meszaros ‘06 21 Late X-ray Flares in GRB Various models: GRB • • • • • X-ray flare Underlying afterglow light curve Burrows et al. ’05, Zhang et al. ‘05 Refreshed shocks IC from reverse shock External density bumps Multiple component jet Late central engine activity Main constraints: sharp rise and decline t -0.8 GeV-TeV rays: IC scattering of x-ray photons by external forward shocked electron Wang, Li & Meszaros ‘06 TeV 06 22 HE from Old GRB Remnants HESS J1301-631 Age: 1.5×104 yr ; Distance: 12 kpc 0 decay model ≤10’ TeV 06 10’≤≤25’ 25’≤≤1o Atoyan, Buckley & Krawczynski ‘06 23 HE from Old GRB Remnants GRB jet: p +n neutron decay: n e - e - CMB e - HETeV TeV 06 W49B Ioka, Kobayashi & Meszaros ‘04 24 Conclusion ► ► ► ► GRBs are the brightest MeV -ray transient sources in the universe GeV and TeV (tentative) -rays have been observed from a few bursts Both Leptonic and Hadronic models may account for GeV data Need more data! Short GRBs may produce ~100 GeV -rays Less luminous than long GRBs but much nearer Less attenuation in background radiation ► ► TeV detection in current detectors requires luminous and nearby GRBs Need more GeV-TeV data need bigger detector! TeV 06 25