1. Dermer Deciphering the Ancient Universe with GRBs, Kyoto, Japan 22 April 2010 1 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 Deciphering the Ancient Universe with GRBs Kyoto, Japan 19-23 April 2010 Outline 1. Motivation: GRBs as sources of UHECRs 2. Brief Review of Fermi results (talk by M. Ohno) 3.  min 4. Leptonic Models: synchrotron/SSC model 5. Hadronic Model: proton synchrotron model 6. Are GRBs UHECR sources?: Evidence from Fermi 7. EBL

2. Dermer Deciphering the Ancient Universe with GRBs, Kyoto, Japan 22 April 2010 2 GRBs and UHECR Sources knee ankle (Waxman 1995, Vietri 1995) Sources of (>10 18 eV) UHECRs need to have a local luminosity density (emissivity) of  10 44 erg/Mpc 3 -yr Local UHECR emissivity requirements

3. 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  10 44 erg Mpc -3 yr -1   E   10 54 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  rays Low Luminosity (sub-energetic) GRBs also have sufficient emissivity to power UHECRs Murase, Ioka, Nagataki, & Nakamura 2006, 2008; Murase and Takami 2009 (Guetta et al. 2005)

4. Dermer Deciphering the Ancient Universe with GRBs, Kyoto, Japan 22 April 2010 4 Wick, CD, and Atoyan 2004 UHECRs from Long-Duration GRBs  Inject  2.2 spectrum of UHECR protons to E > 10 20 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.) Hopkins & Beacom 2006 Requires large baryon load ~ 50 Requires strong photohadronic production Requires  <~ 200 Makes cascade spectrum (talk by Asano) Baryon Loading f b = 1  tot = 3  10 -4 erg cm -2  = 100

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

6. Apparent Isotropic Energies of Swift and Fermi LAT GRBs 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? 080916C090510A 090323A 090902B090926A090328A Cenko et al. (2010)

7. Fluence-Fluence Diagram 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) Abdo, et al. 2010, ApJ, 712, 558 Why do short GRBs have larger LAT/GBM fluence ratios than long GRBs?

8. Delayed Onset and Extended GeV Radiation of Fermi LAT GRBs (long) GRB 090902B t(s) 0 20406080 8 – 14.3 keV 14.3 – 260 keV 260 keV – 5 MeV LAT (all events) > 100 MeV > 1 GeV (short) GRB 090510 t(s) 00.511.5232.5-0.5 > 1 GeV all LAT events >100 MeV 260 keV – 5 MeV 8 - 260 keV Abdo, A. A., et al. 2009, ApJ, 706, L138 Ackermann et al., ApJ, submitted

9. Dermer Deciphering the Ancient Universe with GRBs, Kyoto, Japan 22 April 2010 9 GRB 090902B: A Hard Component in Long GRB Best fit spectrum to interval b (T 0 +4.6 s to T 0 + 9.6 s) is a Band function + power-law component Narrow MeV component Delayed appearance of a component at low ( 10 MeV) GRB 090902B

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

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

12. Dermer Deciphering the Ancient Universe with GRBs, Kyoto, Japan 22 April 2010 12  min z = 0.903  0.003, d L = 1.80×10 28 cm, t v = 0.01 t -2 s f  = F spectrum at energy m e c 2  Time bin c: 30.5 GeV  min = 1370 (total), 1060 (PL) a b c c d Time bin b: 3.4 GeV  min = 950 (total), 720 (PL) GRB 090510 Minimum Bulk Lorentz Factor: Simple Estimate

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

14. Dermer Deciphering the Ancient Universe with GRBs, Kyoto, Japan 22 April 2010 14 GRB 090926A  Spectral cutoff at  500 MeV  If interpreted as due to  opacity cutoff, then  200-700 Target photon energy density   -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 ARR to GRB 090926A SED of GRB 090926A

15. Dermer Deciphering the Ancient Universe with GRBs, Kyoto, Japan 22 April 2010 15 Leptonic Models: Synchrotron/SSC model Given synchrotron spectrum and t v (defining size scale of emission region), SSC component depends only on  and B′ Cascade to make hard component Model for time interval b: B′ = 1 kG (near equipartition), B′ = 1 MG,  = 500, 1000 Problems: 1.Line-of-death 2.Time to make synchrotron cascade 3. If large B, then need to invoke separate origin for hard component 4. Extension of hard component to energies below synchrotron peak GRB 090510

16. Dermer Deciphering the Ancient Universe with GRBs, Kyoto, Japan 22 April 2010 16 Afterglow Synchrotron Model LAT radiation due to nonthermal synchrotron emission from decelerating blast wave (Kumar and Barniol Duran 2009, Ghirlanda et al. 2009, Ghisellini et al. …) Identifying peak of LAT flux (  0.2 s after main GBM emission) with t dec   0 n -1/8 For uniform external medium,  > c, m Adiabatic blast wave: Radiative blast wave: Problems (talk by Mészáros): 1. Closure relation 2. Highest energy photon 3. Condition for highly radiative blast wave 3. Variability (?) Razzaque (2010)

17. Dermer Deciphering the Ancient Universe with GRBs, Kyoto, Japan 22 April 2010 17 Hadronic Model: Proton Synchrotron Instantaneous energy flux  (erg cm -2 s -1 ); variability time t v, redshift z Implies a jet magnetic field  e is baryon loading-parameter (particle vs. leptonic  -ray energy density)  B gives relative energy content in magnetic field vs. total  >  min  10 3  3 from  opacity arguments

18. 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  radiation  processes induce second-generation electron synchrotron spectrum Energetics difficulties (requires ~100 – 1000 more energy in magnetic field and protons than observed in  rays) see also Zhang & Mészáros (2001) Wang, Li, Dai, Mészáros (2009) Only plausible for 1. small jet opening angle  ~<  min  F  (erg cm -2 s -1 ) Razzaque, Dermer, Finke (2010)

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

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

21. Dermer Deciphering the Ancient Universe with GRBs, Kyoto, Japan 22 April 2010 21 L-  diagram  Sources with jet Lorentz factor  must have jet power L exceeding heavy solid and dot-dashed curves to accelerate protons and Fe respectively, to E = 10 20 eV.  Upper limits to L and  defined by competition between synchrotron losses and acceleration time (dashed lines), and synchrotron losses and available time (dotted lines).  Variability times t v = 10 4 s and 1 ms, and  = 10 and 10 3, are used for UHECR proton acceleration in blazars and GRBs, respectively.  LLGRBs? (Dermer & Razzaque 2010)

22. Dermer Deciphering the Ancient Universe with GRBs, Kyoto, Japan 22 April 2010 22 How Realistic is the L-  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

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

24. Dermer Deciphering the Ancient Universe with GRBs, Kyoto, Japan 22 April 2010 24 Requirements on IGM Field from GRB Space Density for a Long-Duration GRB Origin of UHECRs  Long GRB rate  f b Gpc -3 yr -1 at the redshift z  1–2  10 × smaller at  100d 100 Mpc due to the star formation rate factor f b > 200 larger due to a beaming factor  60E 60 EeV UHECR deflected by an angle in IGM field with mean strength B nG nG coherence length of 1 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 (assuming anisotropy of arrival directions of UHECRs)

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

26. 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-  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)   -ray observations of blazars and GRBs rule out Stecker et al. (1996, 2007) EBL