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

Broadband Observations of the Extraordinary Naked-Eye GRB B 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 Ugarte Postigo, 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/ Formerly titled “GRB B: A Naked-Eye Blast from the Distant Universe”

Discovery of GRB B Swift-BAT discovered extremely bright trigger from GRB B ( keV) Konus-Wind simultaneously detected bright burst (20 keV-15 MeV) T 90 ~ 57 s E peak = 651 ± 15 keV E iso ~ 1.3 × ergs z=0.937 (Vreeswijk et al. GCN 7444)

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

Discovery of GRB B Swift promptly slewed to B, 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

Broadband Observations Facility*EpochBandPeak Flux †† Swift-BAT-120 – – 350 keV 2.3  erg cm -2 s -1 Konus-Wind-2 – – 1160 keV ‡ 2.3  erg cm -2 s -1 Swift-XRT 67 – 2.5  – 10 keV  Pi of the Sky-1380 – 468White5.9 mag TORTORA-20 – 97V5.3 mag Swift-UVOT white, u, v, b, w1, w2, m2  REM51 – 2070R, I, J, H, Ks  Liverpool Telescope 1.8  10 3 – 2.5  10 3 SDSS r,i  Faulkes Telescope North 2.5  10 4 – 2.0  10 5 Bessell R,I, SDSS r,i  VLT435 – 934J, Ks  Gemini N Photometry 3.0  10 5, 4.5  10 5 r, i  HST 1.6  10 6 F606W, F814W  Gemini N Spectroscopy 1.2   Å  HET 2.0  10 4 – 2.1  Å  Westerbork Synthesis Radio Telescope 50.5   GHz  IRAM-Plateau de Bure 6.0   GHz  VLA † 1.98  10 5 – 2.02  GHz 189  Jy Pairitel † 1.27 – 1.77  10 4 J, H, Ks  KAIT † 1.1  10 3 – 1.7  10 4 Clear, B, V, I  Nickel † 7.1  10 3 – 2.4  10 4 B, V, R, I  Gemini S † 8.9  10 4 – 1.7  10 5 g, r, i, z  Spitzer † 2.20  10 4 – 2.24   m  *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

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

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

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

Prompt Emission Mechanism 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)

Exceptional brightness of optical flash suggest ν a 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 ν a, allowing photons to escape Prompt Emission Implications

A 3 rd spectral component would arise from 2 nd -order inverse-Compton scattering If our assumptions are valid, we would expect 3 rd 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 Prompt Emission Predictions

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

Normalized Optical Light Curve α opt,1 ~6.5 α opt,2 ~2.5 α opt,3 ~1.25

X-ray Light Curve α x,1 ~1.45 α x,2 ~2.05 α x,3 ~0.95 α x,4 ~2.70

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

Afterglow Models 1 st X-ray broken power-law (80 s < t < 40 ks) is dominated by forward shock of narrow jet, with t j =2800 s, θ j =0.4°, E γ ~2.1x10 50 ergs 2 nd X-ray broken power-law (t > 40 ks) is dominated by forward shock of wide jet with t j =1 Ms, θ j =8°, E γ ~1.9x10 50 ergs

Afterglow Models 1 st optical segment (t<50 s) is tail of prompt emission 2 nd optical segment (50 s < t < 800 s) consistent with high latitude emission (α=2+β)from reverse shock of the wide jet 3 rd 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

Afterglow Tail of Prompt Emission WJRS WJFS NJFS WJFS

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

Alternative Afterglow Model Complex Density Medium Model

Afterglow Models Complex Density Medium Model t t t

νcνc

ν c ~t n~r -2.5 ν c ~t n~r +4.0

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

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 B, the probability of observing along narrow jet is ~10 -3, corresponding to every years B 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