GRB 080319B: A Naked-Eye Blast from the Distant Universe

1. GRB 080319B: A Naked-Eye Blast from the Distant Universe Judy Racusin Penn State University 2008 Nanjing GRB Workshop, Nanjing, China, June 23-27

2. Broadband Observations of the Extraordinary Naked-Eye GRB 080319B J. L. Racusin, S.V. Karpov, M. Sokolowski, J. Granot, X. F. Wu, V. Pal'shin, S. Covino, A.J. van der Horst, S. R. Oates, P. Schady, R. J. Smith, J. Cummings, R.L.C. Starling, L. W. Piotrowski, B. Zhang, P.A. Evans, S. T. Holland, K. Malek, M. T. Page, L. Vetere, R. Margutti, C. Guidorzi, A. P. Kamble, P.A. Curran, A. Beardmore, C. Kouveliotou, L. Mankiewicz, A. Melandri, P.T. O'Brien, K.L. Page, T. Piran, N. R. Tanvir, G. Wrochna, R.L. Aptekar, S. Barthelmy, C. Bartolini, G. M. Beskin, S. Bondar, M. Bremer, S. Campana, A. Castro-Tirado, A. Cucchiara, M. Cwiok, P. D'Avanzo, V. D'Elia, M. Della Valle, A. de UgartePostigo, W. Dominik, A. Falcone, F. Fiore, D. B. Fox, D. D. Frederiks, A. S. Fruchter, D. Fugazza, M. A. Garrett, N. Gehrels, S. Golenetskii, A. Gomboc, J. Gorosabel, G. Greco, A. Guarnieri, S. Immler, M. Jelinek, G. Kasprowicz, V. La Parola, A. J. Levan, V. Mangano, E.P. Mazets, E. Molinari, A. Moretti, K. Nawrocki, P.P. Oleynik, J. P. Osborne, C. Pagani, S. B. Pandey, Z. Paragi, M. Perri, A. Piccioni, E. Ramirez-Ruiz, P. W. A. Roming, I. A. Steele, R. G. Strom, V. Testa, G. Tosti, M.V. Ulanov, K. Wiersema, R. A. M. J. Wijers, J. M. Winters, A. F. Zarnecki, F. Zerbi, P. Mészáros, G. Chincarini, D. N. Burrows Submitted to Nature on May 11, 2008, astro-ph/0805.1557 Formerly titled “GRB 080319B: A Naked-Eye Blast from the Distant Universe”

3. Discovery of GRB 080319B • Swift-BAT discovered extremely bright trigger from GRB 080319B (15-350 keV) • Konus-Wind simultaneously detected bright burst (20 keV-15 MeV) • T90 ~ 57 s • Epeak = 651 ± 15 keV • Eiso~ 1.3 × 1054 ergs • z=0.937 (Vreeswijk et al. GCN 7444)

4. Discovery of GRB 080319B • Serendipitously ~10° away from GRB 080319A (discovered by Swift 30 minutes earlier) • Wide-field ground optical telescopes “Pi of the Sky” and TORTORA had 080319B in FOV starting before BAT trigger • Optical Flash peaked at a V magnitude of ~5.3 “Pi of the Sky” Movie http://grb.fuw.edu.pl/pi/

5. Discovery of GRB 080319B • Swift promptly slewed to 080319B, with XRT & UVOT observations beginning at ~60 s • Observations followed by REM, Liverpool, Faulkes-N, Gemini-N/S, Pairitel, Nickel, Kait, Raptor, Super-LOTIS, PROMPT, Lulin, Mercator, VLT, HET, IRAM, WSRT, VLA, HST, Spitzer, Chandra • Probably the best broadband GRB observations ever obtained

6. Broadband Observations *Time since BAT trigger in seconds †Observations obtained from external sources (Bloom et al. 2008, GCN circulars 7506, 7509) ‡KW light curve measured in 20 – 1160 keV range, peak flux measured in 20 keV – 7 MeV ††Peak fluxes listed only if a peak was actually observed

7. Broadband Observations Optical light curve is normalized to UVOT v-band X-ray and γ-ray arbitrarily scaled

8. Prompt Emission See Beskin talk for details of TORTORA and γ-ray correlations

9. Prompt Emission

10. Prompt Emission • Temporal coincidence and shape of prompt optical and γ-rays emission indicates that they stem from same physical region • Optical flux ~4 orders of magnitude above extrapolation of γ-rays • Therefore, optical and γ-rays must come from different emission components

11. Prompt EmissionMechanism • Problems • Usual interpretation of optical flash as arising from reverse shock cannot explain initial steep rise or constant optical pulse widths • Usual interpretation of soft γ-rays as synchrotron emission cannot explain bright optical flash • Solution • Optical: Synchrotron • γ-rays: Synchrotron Self-Compton See also Kumar & Panaitescu (2008)

12. Prompt EmissionImplications • Exceptional brightness of optical flash suggest νa was not far above optical band at time of peak flux • Implies very large Γ, which causes the internal shocks occur at an unusually large radius • Leads to a low νa, allowing photons to escape

13. Prompt EmissionPredictions • A 3rd spectral component would arise from 2nd-order inverse-Compton scattering • If our assumptions are valid, we would expect 3rd component to peak at a few 10’s of GeV • In which case it would have been easily detectable by GLAST • If mechanism is common, perhaps GLAST will detect this emission from some future GRBs

14. Afterglow Optical light curve is normalized to UVOT v-band X-ray and γ-ray arbitrarily scaled

15. Normalized Optical Light Curve αopt,1~6.5 αopt,2~2.5 αopt,3~1.25

16. X-ray Light Curve αx,1~1.45 αx,2~2.05 αx,3~0.95 αx,4~2.70

17. Afterglow ModelsTwo-Component Jet Additional theoretical details will be presented in next talk by X. F. Wu

18. Afterglow Models • 1st X-ray broken power-law (80 s < t < 40 ks) is dominated by forward shock of narrow jet, with tj=2800 s, θj=0.4°, Eγ~2.1x1050 ergs • 2nd X-ray broken power-law (t > 40 ks) is dominated by forward shock of wide jet with tj=1 Ms, θj=8°, Eγ~1.9x1050 ergs

19. Afterglow Models • 1st optical segment (t<50 s) is tail of prompt emission • 2nd optical segment (50 s < t < 800 s) consistent with high latitude emission (α=2+β)from reverse shock of the wide jet • 3rd optical segment (t > 800 s) is due to the forward shock of wide jet • Closure relations require Wind environment, p>2, requires 3 spectral components

20. Afterglow NJFS Tail of Prompt Emission WJRS WJFS WJFS

21. Afterglow Modeling • Temporal behavior relatively straightforward • What about spectral behavior? Sari, Piran, Narayan (1998)

25. Alternative Afterglow Model Complex Density Medium Model

28. Afterglow ModelsComplex Density Medium Model t t t

29. νc

30. νc~t+1.08 n~r-2.5 νc~t-1.00 n~r+4.0

31. Complex Density Medium Model • Relatively straightforward single component spectral model with moving cooling frequency • Temporal decays cannot be explained in context of closure relations even with non-standard environments • Perhaps whole light curve is post-jet break, but still hard to reconcile • More detailed modeling required to possibly make this model work

32. Conclusions • To get this bright optical flash, need high γ-ray isotropic energy, wind environment, very high initial Γ • Reverse shock was at least mildly relativistic, but outflow must have been moderately magnetized when crossing RS or optical emission would have been suppressed • Best afterglow model is two-component jet, which leads to interpretation of wind environment and is consistent with properties of prompt emission • If all GRBs were structured like 080319B, the probability of observing along narrow jet is ~10-3, corresponding to every 3-10 years • 080319B had special (but not unreasonable) set of parameters, and also had special observational conditions • Consequently challenges standard models, and will surely be studied for years to come