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Very High Energy Transient Extragalactic Sources: GRBs

Very High Energy Transient Extragalactic Sources: GRBs. David A. Williams Santa Cruz Institute for Particle Physics University of California, Santa Cruz. October 20, 2005. Two Classes of Bursts. Short, Hard Bursts 19 sr -1 yr -1 Prompt emission too short to catch with slewed response

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Very High Energy Transient Extragalactic Sources: GRBs

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  1. Very High Energy Transient Extragalactic Sources: GRBs David A. Williams Santa Cruz Institute for Particle Physics University of California, Santa Cruz October 20, 2005

  2. Two Classes of Bursts • Short, Hard Bursts • 19 sr-1 yr-1 • Prompt emission too short to catch with slewed response • May be “nearby” • z = 0.16, 0.225?, 0.258 • Delayed X-ray flare from 050724 ~200 seconds later • Long, Soft Bursts • 38 sr-1 yr-1 • 14% longer than 100 s • 28% longer than 63 s • z ~ 1, but wide range • z = 0.0085 to 6.3 • Several types of delayed emission Milagro/HAWC 2 sr yr annually VERITAS 3 x 10-4 sr yr annually "Towards the Future" Workshop — DAW

  3. Redshift Distribution Redshifts established for 32 bursts (as of 2004) 1.3 < z < 2.5 difficult– spectra lack suitable lines These are all long duration (>2 s) bursts Klose, http://www.mpe.mpg.de/~jcg/grbrsh.html "Towards the Future" Workshop — DAW

  4. High-Energy g-Rays GRB 940217 18 GeV! EGRET data BATSE data Hurley et al., Nature 372, 652 (1994) Ulysses data "Towards the Future" Workshop — DAW

  5. High-Energy g-Rays II • EGRET saw >100 MeV emission from three other bursts • dN/dE ~ E-1.95 up to 10 GeV • Limited exposure so such emission may be typical • Longer duration, hard component in GRB 941017 (Gonzalez et al 2003) and 980923 (Gonzalez 2004) "Towards the Future" Workshop — DAW

  6. VHE g-Rays from GRB 970417a? Astrophysical Journal583, 824 (2003) Astrophysical Journal Letters533, L119 (2000) • Evidence for TeV emission from GRB 970417a seen by Milagrito • Probability of background fluctuation 1.5 x 10-3 (3s) • More luminosity at TeV energies than MeV • (Lack of) EBL absorption implies GRB must be close, so total energy released is not unusually large • z~0.1, then Eg < 700 GeV, so L < 5 x 1051 ergs • z~0.03, then Eg < 10 TeV, so L < 1 x 1049 ergs "Towards the Future" Workshop — DAW

  7. VHE g-Rays from GRB? • Amenomori et al. 1996 (Tibet AS- • 6 excess at ~10 TeV in stacked analysis of 57 BATSE GRB • Padilla et al. 1998 (HEGRA) • 2.7 excess above 20 TeV from GRB 920925c • Atkins et al. 2005; Saz Parkinson 2005 (Milagro) • Limits >100 GeV from 33 GRB during 2000–2003 • Connaughton et al. 1997 (Whipple) • Limits >250 GeV from follow-up observations of 9 BATSE bursts • Horan 2005 (Whipple) • Limits >400 GeV from follow-up observations of 10 GRB 2002–2004 • Jarvis et al. 2005 (STACEE) • No detection in follow-up observations of 8 GRB 2002–2005 • Bastieri et al. 2005 (MAGIC) • Upper limit starting 40 s after onset, overlapping T90 for 30 s, of GRB 050713a "Towards the Future" Workshop — DAW

  8. The Fireball Model Central engine injects 1051 ergs over 1 second Expanding g,e+,e- plasma at 1010 K Variability can produce multiple thin shells 107 cm Zhang & Meszaros, Intl. J. Mod. Phys. A. 19, 2385 (2004) "Towards the Future" Workshop — DAW

  9. The Fireball Model Baryons are accelerated by radiation pressure until they share a common bulk Lorentz factor G~300 with the plasma Fireball coasts 1013 cm 1000 s / 5 ms Zhang & Meszaros, Intl. J. Mod. Phys. A. 19, 2385 (2004) "Towards the Future" Workshop — DAW

  10. The Fireball Model 5 x 1014 cm 104 s / 0.05 s Typical radius at which shells with different G overtake each other, creating “internal” shocks Zhang & Meszaros, Intl. J. Mod. Phys. A. 19, 2385 (2004) "Towards the Future" Workshop — DAW

  11. The Fireball Model 3 x 1016 cm 105 s / 5 s Deceleration radius – the fireball is decelerated by the ambient medium “External” shock propagates into the ambient medium “Reverse” shock propagates into fireball shell Zhang & Meszaros, Intl. J. Mod. Phys. A. 19, 2385 (2004) "Towards the Future" Workshop — DAW

  12. External Shock Model Predictions c c For burst at z ~ 1, dL ~ 1028 cm, log10[F] = 47.4 corresponds to Crab flux (c)at log10[] = 25.4 (100 GeV) Dermer & Chiang, AIP Conf. Proc. 515, 225 (2000) "Towards the Future" Workshop — DAW

  13. Internal Shocks–The Bad News Emission is at smaller radius Fireball is denser— Typically opaque above 10–100 GeV Razzaque, Meszaros & Zhang, Astrophys. J. 613, 1072 (2004) "Towards the Future" Workshop — DAW

  14. Reprocessing by EBL–Better News 50 s c c 104 s 102 s 106 s Flux for burst at z = 1 Includes EBL absorption a la Malkan & Stecker 2001 for z = 1 BIG = 10-20 G BIG = 10-17 G Razzaque, Meszaros & Zhang, Astrophys. J. 613, 1072 (2004) "Towards the Future" Workshop — DAW

  15. Afterglow Emission c c c T0 1 m • Fluxes for burst at z = 1 • (But no EBL absorption) • Different values of • Density of surrounding medium • Magnetic field • Fraction of energy in e± 1 h 1 d 1 mo Zhang & Meszaros, Astrophys. J. 559, 110 (2001) "Towards the Future" Workshop — DAW

  16. Modeling GRB 941017 c • Color curves are IC from afterglow (external shock) electrons in scenarios with different • Total energy • Density of surrounding medium • Bulk Lorentz factor • Magnetic field • constrained to fit the EGRET data • Black curve is model based on rapid variability in prompt emission Spectrum between 100 and 200 s after start of burst Pe’er & Waxman, Astrophys. J. Lett. 603, L1 (2004) "Towards the Future" Workshop — DAW

  17. Summary • Solid evidence for prompt and afterglow emission from EGRET up to 10 GeV • No firm VHE signal from a burst yet • Low threshold desirable • Elude EBL absorption in transit • Elude self-absorption in source • Prompt emission • Potentially quit strong (many Crab) once below absorption cutoffs • Can determine burst parameters, e.g.B from intrinsic cutoff • Short bursts can only be caught with large (~sr) field of view • Tail of longer bursts can be caught with slewed responses of ≤1 minute • Afterglow emission • Can be quit strong (~Crab or more) initially. How long is it interesting to follow? • Can be as valuable for determining burst properties, e.g. GRB 941017 • Accessible to slewed instruments "Towards the Future" Workshop — DAW

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