SONG and mini-SONG Observations

of GRB Pulsed EmissionJon Hakkila

Presented at the 4th SONG Workshop

September 17, 2011

Collaborators: Rob Preece, Tom Loredo, Carlo Graziani, Robert Wolpert, Bruce Grossan, Jim Neff, Jason Jackiewicz, Frank Hill, Travis Metcalfe, Alex Greene.

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

General Gamma-Ray Burst Properties

25-50 keV25-50 keV, , 50-100 keV50-100 keV, , 100-300 keV100-300 keV, , 300 keV-1 300 keV-1

MeVMeV

Spectra

Epk

Light Curves

Synchrotron shock model (e.g. Rees & Meszaros, ApJL, 1994, 430, 94) or jitter radiation (Medvedev 2000, ApJ 540, 704.

GRB Progenitors

Short LongHypernova Central Engine Model of

Long GRBs

Merging Compact Objects Central Engine Model of Short GRBs

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)?

• GRB complexity results from overlapping pulses. • Long and Short GRBs appear to be inherently different.• Relativistic cosmology alters GRB observed properties:

Energy shift: distant GRBs have their fluxes shifted to lower observed energies than similar nearby ones.

Inverse square law: distant GRBs appear fainter than similar nearby ones 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.

• 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.

GRBs can be deconvolved into pulses exhibiting• Inherent time asymmetries (longer decay than rise rates),• Hard-to-soft spectral evolution, and • Longer durations at lower energies.

Black - summed 4-channel emissionGreen - high energy channel emissionRed - low energy channel emission

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):

Pulse-fitting example: GRB 950325a (BATSE

3480)25 keV - 1 MeV

1 2

3

100 keV - 300 keV

50 keV - 100 keV

25 keV - 50 keV

300 keV - 1 MeV

Pulse 1

Pulse 2

Pulse 3

lag

0.01 s ± 0.01

0.11s ± 0.05

0.85 s ± 0.15

duration 1.00 s ± 0.08 3.06 s ± 0.10 9.45 s ± 0.52

peak flux (256 ms)

19.47 c/s ± 0.21 6.35 c/s ± 0.14 1.35 c/s ± 0.03

100 keV - 300 keV

50 keV - 100 keV

25 keV - 50 keV

Pulse-fitting example: GRB 910930 (BATSE

0840)

Pulse 1

Pulse 2

Pulse 3

Pulse 4

lag

0.00 s ± 0. 0.02 s ± 0. 0.00 s ± 0. 0.06 s ± 0.

duration 4.84 s ± 12.54 1.97 s ± 0.47 2.22 s ± 6.29 1.6 s ± 0.35

peak flux (256 ms)

1.260 c/s ± 927. 0.818 c/s ± 0.05 0.492 c/s ± 12.15 0.647 c/s ± 0.1

25 keV - 1 MeV

1 2 3 4

300 keV - 1 MeV

100 keV - 300 keV

50 keV - 100 keV

25 keV - 50 keV

25 keV - 1 MeV

1 2

Pulse-fitting example: GRB 930123 (BATSE

2600)

Pulse 1

Pulse 2

lag

6.71 s ± 0.31

0.70s ± 0.30

duration 45.8 s ± 4.6 6.4 s ± 0.3

peak flux (256 ms)

0.39 c/s ± 0.01 0.80 c/s ± 0.02

The GRB pulse lag and pulse duration vs. pulse luminosity

relations

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

-5 -4 -3 -2 -1 0 1 2

log(pulse peak lag)

log(pulse duration)

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.

Peak luminosity (L) vs. duration (w) and lag (l0) for BATSE GRBs.

Some low-z BATSE Some low-z BATSE burstsbursts

BATSE 0332; z ≈ 0.9

BATSE 0563; z ≈ 0.8

BATSE 1406; z ≈ 0.8

BATSE 0111; z ≈ 0.9

BATSE 0214; z ≈ 4.3

BATSE 0237; z ≈ 5.3

BATSE 0803; z ≈ 4.6

BATSE 0594; z ≈ 5.4

Some high-z BATSE Some high-z BATSE burstsbursts

Correlated pulse properties can be used to estimate GRB redshifts (Hakkila, Fragile, & Giblin, 2009, AIP Conf. 1133, 479) .

Related Pulse Property Correlations

1338 pulses in 610 BATSE GRBs: (Hakkila and Preece, 2010 ApJ (in press))

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

-2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5

log(pulse duration)

log(pulse fluence)

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

pulse asymmetry

log(pulse duration)

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

-2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5

log(pulse duration)

log(pulse hardness)

-2.5

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

-2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5

log(pulse duration)

log(pulse peak flux)

Long (upper) and Short (lower) GRB Pulse CorrelationsLong (upper) and Short (lower) GRB Pulse Correlations

Uncorrelated probability

Lag

p256

Hardness Asymmetry Fluence

Duration

<0.01% <0.01%

<0.01% <0.01%

<0.01% 6.8%

<0.01% 76%

<0.01% 11%

Lag --- <0.01% 54%

<0.01% 25%

<0.01% 22%

<0.01% 50%

p256 --- --- <0.01% <0.01%

0.03% 54%

<0.01% <0.01%

Hardness --- --- --- <0.01% 93%

3.1% <0.01%

Asymmetry --- --- --- --- <0.01% 43%

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)).

Pulse Observations from HETE-2 and Swift

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).

X-ray flares intensities decrease and pulse durations increase with time after the trigger (Margutti et al. 2010, MNRAS, 406, 2149).

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).

Short GRB Pulses

1

10

100

1000

10000

1 10 100 1000log[duration(ms)]

log[intensity(c/s)]

EEnon-EE

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.).

Correlative properties are bulk measurements of hard-to-

soft pulse evolution

Epeak pulse decay (Peng et al. 2009, ApJ 698, 417)

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

• 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).

Implications of Correlated GRB Pulse Properties:

Optical flares accompany prompt emission…

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How can SONG and mini-SONG help us better

understand GRB pulse physics?

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Optical flares appear to be low-energy counterparts of x-ray flares.

…and are also seen in the afterglow.

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?