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Recent Progress in Theoretical Understanding of GRBs from Fermi LAT and GBM Results

Deciphering the Ancient Universe with GRBs Kyoto, Japan 19-23 April 2010. Recent Progress in Theoretical Understanding of GRBs from Fermi LAT and GBM Results. Chuck Dermer Naval Research Laboratory Washington, DC USA charles.dermer@nrl.navy.mil On behalf of the Fermi Collaboration

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Recent Progress in Theoretical Understanding of GRBs from Fermi LAT and GBM Results

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  1. Deciphering the Ancient Universe with GRBs Kyoto, Japan 19-23 April 2010 Recent Progress in Theoretical Understanding of GRBs from Fermi LAT and GBM Results Chuck Dermer Naval Research Laboratory Washington, DC USA charles.dermer@nrl.navy.mil On behalf of the Fermi Collaboration Including research with Soeb Razzaque and Justin Finke Outline 1. Motivation: GRBs as sources of UHECRs 2. Brief Review of Fermi results (talk by M. Ohno) 3. Gmin 4. Leptonic Models: synchrotron/SSC model 5. Hadronic Model: proton synchrotron model 6. Are GRBs UHECR sources?: Evidence from Fermi 7. EBL Dermer Deciphering the Ancient Universe with GRBs, Kyoto, Japan 22 April 2010

  2. GRBs and UHECR Sources Local UHECR emissivity requirements knee ankle (Waxman 1995, Vietri 1995) Sources of (>1018 eV) UHECRs need to have a local luminosity density (emissivity) of 1044 erg/Mpc3-yr Dermer Deciphering the Ancient Universe with GRBs, Kyoto, Japan 22 April 2010

  3. GRB Rate Densities and Energies • Long-duration GRB rate density: ~ 1 Gpc-3 yr-1 universe-1 •  E × 0.1 (SFR factor)× 10-9 Mpc-3 yr-1  1044 erg Mpc-3 yr-1  E  1054 erg (apparent isotropic energy release in UHECRs) • Beaming factor increases rate density with correspondingly smaller absolute energy release, so argument is unchanged • Requires ~10 -- 100 × more energy in UHECRs than measured in g rays Low Luminosity (sub-energetic) GRBs also have sufficient emissivity to power UHECRs (Guetta et al. 2005) Murase, Ioka, Nagataki, & Nakamura 2006, 2008; Murase and Takami 2009 Dermer Deciphering the Ancient Universe with GRBs, Kyoto, Japan 22 April 2010

  4. Baryon Loading fb = 1 Ftot = 310-4 erg cm-2 G = 100 Wick, CD, and Atoyan 2004 UHECRs from Long-Duration GRBs • Inject -2.2 spectrum of UHECR protons to E > 1020 eV • Injection rate density determined by star formation rate of GRBs corrected, e.g., for metallicity • GZK cutoff from photopion interactions with cosmic microwave radiation photons • Ankle formed by photo-pair processes (Berezinskii, et al.) Requires large baryon load ~ 50 Requires strong photohadronic production Requires G <~ 200 Makes cascade spectrum (talk by Asano) Hopkins & Beacom 2006 Dermer Deciphering the Ancient Universe with GRBs, Kyoto, Japan 22 April 2010

  5. Summary of Fermi Results 8 – 10000 keV Fluences of Fermi GRBs through 2009

  6. Apparent Isotropic Energies of Swift and Fermi LAT GRBs 090328A 090510A 090902B 090926A 080916C 090323A LAT GRBs (blue) have large apparent isotropic energy releases Bright Swift bursts (in gray) (in terms of apparent isotropic energy release): determine absolute energy release from beaming breaks Do Fermi LAT GRBs have larger absolute energies or preferentially smaller jet opening angles? Cenko et al. (2010)

  7. Fluence-Fluence Diagram Abdo, et al. 2010, ApJ, 712, 558 Fluence/fluence diagram for EGRET GRBs. Look for different classes of GRBs on the basis of fluence ratios (Le & Dermer 2009) Short GRBs appear to have systematically larger high-energy LAT/GBM fluence ratios (Better to use a sample with redshift) Why do short GRBs have larger LAT/GBM fluence ratios than long GRBs?

  8. (long) GRB 090902B (short) GRB 090510 8 - 260 keV 8 – 14.3 keV 14.3 – 260 keV 260 keV – 5 MeV 260 keV – 5 MeV all LAT events LAT (all events) >100 MeV > 100 MeV > 1 GeV > 1 GeV 0 -0.5 20 0 0.5 40 1 1.5 60 2 80 2.5 3 t(s) t(s) Delayed Onset and Extended GeV Radiation of Fermi LAT GRBs Abdo, A. A., et al. 2009, ApJ, 706, L138 Ackermann et al., ApJ, submitted

  9. GRB 090902B: A Hard Component in Long GRB GRB 090902B • Best fit spectrum to interval b (T0+4.6 s to T0 + 9.6 s) is a Band function + power-law component • Narrow MeV component • Delayed appearance of a component at low (<~20 keV) and high (> 10 MeV) Dermer Deciphering the Ancient Universe with GRBs, Kyoto, Japan 22 April 2010

  10. GRB 090510: A Short Hard GRB with an extra component Clear detection of an extra component inconsistent with the Band function. Dermer Deciphering the Ancient Universe with GRBs, Kyoto, Japan 22 April 2010

  11. Long-lived Emission with power-law temporal decays t-1.5 t-1.380.07 GRB 090510 GRB 090902B t-1.20.2 De Pasquale, M., et al. 2010, ApJ, 709, L146 GRB 080916C

  12. Minimum Bulk Lorentz Factor: Simple Estimate Gmin fe = nFn spectrum at energy mec2e z = 0.9030.003, dL = 1.80×1028 cm, tv = 0.01 t-2 s Time bin b: 3.4 GeV Gmin = 950 (total), 720 (PL) Time bin c: 30.5 GeV Gmin = 1370 (total), 1060 (PL) GRB 090510 a b c c d Dermer Deciphering the Ancient Universe with GRBs, Kyoto, Japan 22 April 2010

  13. Gmin for Fermi LAT GRBs Greiner et al., A&A (2009) GRB 080916C GRB 080916C INTEGRAL-SPI at 50 ms resolution; Variability as short as 100 ms  Gmin  900, GRB 080916C 1000, GRB 090902B 1200, GRB 090510

  14. GRB 090926A ARR to GRB 090926A • Spectral cutoff at  500 MeV • If interpreted as due to gg opacity cutoff, then G 200-700 SED of GRB 090926A Target photon energy density  G-5 Search for neutrino emission from high-GBM fluence, low LAT-fluence GRBs ~0.1 s spike in LAT and GBM emission See poster 095 by Uehara Dermer Deciphering the Ancient Universe with GRBs, Kyoto, Japan 22 April 2010

  15. Leptonic Models: Synchrotron/SSC model Given synchrotron spectrum and tv (defining size scale of emission region), SSC component depends only on G and B′ Cascade to make hard component Model for time interval b: B′ = 1 kG (near equipartition), B′ = 1 MG, G = 500, 1000 Problems: 1. Line-of-death 2. Time to make synchrotron cascade • If large B, then need to invoke separate origin for hard component • Extension of hard component to energies below synchrotron peak GRB 090510 Dermer Deciphering the Ancient Universe with GRBs, Kyoto, Japan 22 April 2010

  16. Afterglow Synchrotron Model Identifying peak of LAT flux (0.2 s after main GBM emission) with tdec G0 n-1/8 For uniform external medium, n >nc, nm Adiabatic blast wave: Radiative blast wave: LAT radiation due to nonthermal synchrotron emission from decelerating blast wave (Kumar and Barniol Duran 2009, Ghirlanda et al. 2009, Ghisellini et al. …) Razzaque (2010) Problems (talk by Mészáros): 1. Closure relation 2. Highest energy photon 3. Condition for highly radiative blast wave 3. Variability (?) Dermer Deciphering the Ancient Universe with GRBs, Kyoto, Japan 22 April 2010

  17. Hadronic Model: Proton Synchrotron Instantaneous energy flux F (erg cm-2 s-1); variability time tv, redshift z Implies a jet magnetic field ee is baryon loading-parameter (particle vs. leptonic g-ray energy density) eB gives relative energy content in magnetic field vs. total G > Gmin 103G3 from gg opacity arguments Dermer Deciphering the Ancient Universe with GRBs, Kyoto, Japan 22 April 2010

  18. Synchrotron Radiation from UHE Protons Accumulation and cooling of protons makes delayed proton synchrotron g radiation ggprocesses induce second-generation electron synchrotron spectrum Energetics difficulties (requires ~100 – 1000 more energy in magnetic field and protons than observed in g rays) see also Zhang & Mészáros (2001) Wang, Li, Dai, Mészáros (2009) Only plausible for 1. small jet opening angle 2. G ~< Gmin • nFn • (erg cm-2 s-1) Razzaque, Dermer, Finke (2010) Dermer Deciphering the Ancient Universe with GRBs, Kyoto, Japan 22 April 2010

  19. Efficiency of Hadronic (Proton Synchrotron and Photopion) Models Proton-synchrotron energy requirements (Wang et al. 2009; Razzaque et al. 2009) Photopion efficiency (Waxman & Bahcall 1997; Murase & Nagataki 2006) Large G-factors unfavorable for ~PeV neutrino/neutral beam production Problem: Large amounts, ~100 x amount of energy radiated at MeV energies, required Dermer Deciphering the Ancient Universe with GRBs, Kyoto, Japan 22 April 2010

  20. Are GRBs Sources of UHECRs? Evidence from Fermi Particle Acceleration to Ultra-High Energies by GRBs by Fermi processes Proper frame (´) energy density of relativistic wind with apparent luminosity L R Maximum particle energy G Lorentz contraction: Dermer Deciphering the Ancient Universe with GRBs, Kyoto, Japan 22 April 2010

  21. L-G diagram • Sources with jet Lorentz factor G must have jet power L exceeding heavy solid and dot-dashed curves to accelerate protons and Fe respectively, to E = 1020 eV. • Upper limits to L and G defined by competition between synchrotron losses and acceleration time (dashed lines), and synchrotron losses and available time (dotted lines). • Variability times tv = 104 s and 1 ms, and G = 10 and 103, are used for UHECR proton acceleration in blazars and GRBs, respectively. • LLGRBs? (Dermer & Razzaque 2010) Dermer Deciphering the Ancient Universe with GRBs, Kyoto, Japan 22 April 2010

  22. How Realistic is the L-G Diagram? Treat Colliding Shells Four Asymptotic Regimes Conditions for Acceleration to highest energies Most favorable conditions for acceleration: RRS/RFS and NRS/RFS Short times between shell ejecta Large Lorentz factor contrast Dermer Deciphering the Ancient Universe with GRBs, Kyoto, Japan 22 April 2010

  23. Cumulative Emissivity of g-Ray Galaxies from Fermi Data • Need Adequate Emissivity and Sources within GZK radius • Need Adequate Power (rejects star-forming galaxies) • Fermi data favors ion acceleration by BL Lacs/FR1 radio galaxies • GRB origin requires nG IGM; proton and ion escape difficult • 1LAC AGNs • FSRQs • BL Lac • Misaligned Radio Galaxies • Starburst (and Star-forming) Dermer Deciphering the Ancient Universe with GRBs, Kyoto, Japan 22 April 2010

  24. Requirements on IGM Field from GRB Space Densityfor a Long-Duration GRB Origin of UHECRs (assuming anisotropy of arrival directions of UHECRs) • Long GRB rate  fb Gpc-3 yr-1 at the redshift z  1–2 • 10 × smaller at 100d100 Mpc due to the star formation rate factor • fb > 200 larger due to a beaming factor • 60E60 EeV UHECR deflected by an angle • in IGM field with mean strength BnGnG coherence length of l1 Mpc • Number of GRB sources within 100 Mpc with jets pointing within 4 of our line-of-sight is • Strong field to spread the arrrival time due to small space density • Weak field to account for correlation Dermer Deciphering the Ancient Universe with GRBs, Kyoto, Japan 22 April 2010

  25. Constraints on EBL Models For Stecker et al. (remark by Kusenko; g rays from UHECRs in IGM) Dermer Deciphering the Ancient Universe with GRBs, Kyoto, Japan 22 April 2010

  26. Summary • Occurrence of delayed onset (and extended emission) can be explained in both leptonic and hadronic models, but energy requirements much greater for the latter • No “smoking gun” hadronic emission signature observed from photopion processes, as expected if GRBs accelerate UHECRs • Fermi results give minimum values of apparent jet luminosity and bulk outflow Lorentz factor which, in Fermi acceleration scenarios, imply maximum accelerated particle energies • L-G diagram and cumulative emissivity constrain allowed sites of UHECRs • Fermi results consistent with UHECR ions accelerated from FR1 and BL Lac objects; UHECRs could still be accelerated by GRBs depending on rate density and intergalactic magnetic field within GZK radius (escape problem from impulsive source remains) • g-ray observations of blazars and GRBs rule out Stecker et al. (1996, 2007) EBL Dermer Deciphering the Ancient Universe with GRBs, Kyoto, Japan 22 April 2010

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