SONG and mini-SONG Observations of GRB Pulsed Emission

1. SONG and mini-SONG Observationsof GRB Pulsed Emission Presented at the 4th SONG Workshop September 17, 2011 Jon Hakkila Collaborators: Rob Preece, Tom Loredo, Carlo Graziani, Robert Wolpert, Bruce Grossan, Jim Neff, Jason Jackiewicz, Frank Hill, Travis Metcalfe, Alex Greene.

2. Gamma-ray bursts are the most energetic explosions in the Universe.

3. Synchrotron shock model (e.g. Rees & Meszaros, ApJL, 1994, 430, 94) or jitter radiation (Medvedev 2000, ApJ 540, 704. General Gamma-Ray Burst Properties Light Curves Spectra  Epk  25-50 keV, 50-100 keV, 100-300 keV, 300 keV-1 MeV

4. Hypernova Central Engine Model of Long GRBs Merging Compact Objects Central Engine Model of Short GRBs GRB Progenitors Short Long

5. Many GRB bulk properties (e.g. lag, Epeak, variability) correlate with luminosity. How can the intrinsic effects leading to these correlations be separated from other effects (e.g. class differences and selection biases)? • Inverse square law: distant GRBs appear fainter than similar nearby ones • GRB complexity results from overlapping pulses. • Long and Short GRBs appear to be inherently different. • Relativistic cosmology alters GRB observed properties: • Time dilation: distant GRBs have longer durations and temporal structures than similar nearby ones. • Energy shift: distant GRBs have their fluxes shifted to lower observed energies than similar nearby ones. • Energy shift: distant GRBs have their fluxes shifted to lower observed energies than similar nearby ones.

6. Black - summed 4-channel emission Green - high energy channel emission Red - low energy channel emission GRBs can be deconvolved into pulses exhibiting Observable Pulse Properties - obtained using semi-automated 4-parameter pulse model (Norris et al. 2005 ApJ, 627, 324; Hakkila et al. 2008 ApJ 677, L81): • Inherent time asymmetries (longer decay than rise rates), • Hard-to-soft spectral evolution, and • Longer durations at lower energies. • Pulse peak flux (p256) - peak flux of summed multichannel data (black) measured on 256 ms timescale. • Pulse duration - time span when flux is e-3 of pulse peak flux. • Pulse peak lag- time span between channel 3 peak (100-300 keV; green) and channel 1 peak (25-50 keV; red). • Fluence - time-integrated flux. • Hardness - ratio of channel 3 fluence to channel 1 fluence. • Asymmetry - pulse shape measure; 0 is symmetric and 1 is asymmetric.

7. 300 keV - 1 MeV 100 keV - 300 keV 25 keV - 1 MeV 50 keV - 100 keV 3 2 1 25 keV - 50 keV Pulse-fitting example: GRB 950325a (BATSE 3480)

8. 300 keV - 1 MeV 100 keV - 300 keV 50 keV - 100 keV 1 2 3 4 25 keV - 1 MeV 25 keV - 50 keV Pulse-fitting example: GRB 910930 (BATSE 0840)

9. 100 keV - 300 keV 50 keV - 100 keV 1 2 25 keV - 1 MeV 25 keV - 50 keV Pulse-fitting example: GRB 930123 (BATSE 2600)

10. Peak luminosity (L) vs. duration (w) and lag (l0) for BATSE GRBs. The GRB pulse lag and pulse duration vs. pulse luminosity relations The GRB lag vs. luminosity relation (Norris, Marani, & Bonnell 2000, ApJ 534, 248) is actually a pulse lag vs. pulse luminosity relation (Hakkila et al. 2008, ApJ 677, L81). Pulse duration also correlates with pulse lag, so pulse duration also indicates luminosity.

11. BATSE 0111; z ≈ 0.9 BATSE 0332; z ≈ 0.9 Some low-z BATSE bursts BATSE 0563; z ≈ 0.8 BATSE 1406; z ≈ 0.8 Correlated pulse properties can be used to estimate GRB redshifts (Hakkila, Fragile, & Giblin, 2009, AIP Conf. 1133, 479) . BATSE 0214; z ≈ 4.3 BATSE 0237; z ≈ 5.3 BATSE 0594; z ≈ 5.4 BATSE 0803; z ≈ 4.6 Some high-z BATSE bursts

12. Related Pulse Property Correlations 1338 pulses in 610 BATSE GRBs: (Hakkila and Preece, 2010 ApJ (in press))

13. Long (upper) and Short (lower) GRB Pulse Correlations GRB pulse property correlations: short duration pulses have shorter lags, are brighter, are harder, and are more time symmetric than long duration pulses (Hakkila and Preece, ApJ 2011 (in press)).

14. Pulse Observations from HETE-2 and Swift X-ray flares intensities decrease and pulse durations increase with time after the trigger (Margutti et al. 2010, MNRAS, 406, 2149). Pulse lag and pulse duration vs. pulse luminosity relations are found in HETE-2 (Arimoto et al. 2010, PASJ, 62, 487) and Swift x-ray flares (Chincarini et al. (MNRAS, 2010, 406, 2113).

15. Short Swift GRBs (Norris, Gehrels, and Scargle 2011, ApJ 735, 23) extend the peak flux vs. duration relation to ms timescales. > Short and Long burst observable pulse properties appear to indicate a single distribution. GRB pulses have similar correlated properties independent of GRB class (and potentially of progenitor, environment, etc.). How can peak flux correlations be reconciled with differing luminosities of Short and Long GRBs? (Margutti 2010, private communication). > Short and Long GRB pulses might represent two parallel luminosity distributions, or might represent a single distribution offset by an unknown parameter (e.g. beaming angle).

16. Correlative properties are bulk measurements of hard-to-soft pulse evolution Pulses start near-simultaneously at all energies (Hakkila and Nemiroff 2009, ApJ 705, 372), then have spectra which evolve from high- to low-energy dominant Epeak pulse decay (Peng et al. 2009, ApJ 698, 417)

17. Implications of Correlated GRB Pulse Properties: • Pulse physics appears ubiquitous and is easily replicated across a variety of GRB environments. Properties of individual pulses within Long and Short GRBs may not be appropriate classification tools whereas pulse distributions within a GRB may be. • Theoretical pulse model needs not have many free parameters. • Standard model: Kinematic energy injection into a medium via relativistic shocks; the medium cools. Standard spectral model is preferentially a synchrotron spectrum (e.g. Rees & Meszaros, ApJL, 1994, 430, 94) or a thermal plus power law spectrum (e.g. Goodman 1986, ApJ 308, L47; Daigne & Mochkovitch 2002, MNRAS 336, 1271). • Correlative pulse relations are not a direct and simple consequence of the standard synchrotron shock model, which has no time-dependent component (Boci, Hafizi, & Mochkovitch 2010, A&A, 519, 76). • Electromagnetic jitter radiation appears to produce reasonable spectra coupled with short intensity tracking time histories that do not have correlated pulse properties (e.g. Medvedev, Pothapragada, & Reynolds 2009, ApJL, 702 L91). • Curvature in a relativistic outflow can explain some late, but few early evolving pulse correlations (e.g. Qin et al., Phys. Rev. D, 2006).

18. How can SONG and mini-SONG help us better understand GRB pulse physics? Optical flares accompany prompt emission…

19. …and are also seen in the afterglow. Optical flares appear to be low-energy counterparts of x-ray flares.

20. Optical pulses appear to belong to the same phenomenon as prompt and afterglow pulses. Optical pulse observations can be made: • as part of a scheduled SONG observation. • with offline SONG telescopes. • with mini-SONG telescopes. • with SONG and/or mini-SONG telescopes in conjunction with ancillary telescopes (e.g. UVI). Questions needing to be addressed: • How closely does prompt optical emission track high energy emission? • Are prompt optical pulses low-energy components of prompt pulses, or are they simultaneous but separate low-energy pulses? • Are late optical pulses a low-energy extension of x-ray flares? • How are prompt and late optical pulses related? • What constraints do pulse energetics and timing place on GRB models?