Part I

Properties and Origins of Long GRBs

The Origin of Long-Period GRBs

Knicole Colón

High Energy Astrophysics

March 5, 2008

Long-Period GRBs

•Standard total energy > 1051 ergs•Bursts last for t > 2 sec (longest known has t~2000 sec)•Have associated X-ray, optical, and radio afterglows•XRFs are similar to long GRBs but extend to softer, fainter regime (exact connection is still uncertain)

(Aurore Simonnet SSU NASA E/PO)

Long-Period GRBs

•Located near center of SFRs in host galaxies at < z > = 2.3 (from Swift observations)•Hosts are late-type, mostly irregular, dwarf galaxies•Some are found to be associated with luminous core-collapse Type Ic SNe

(Gehrels & Cannizzo 2007)

Swift Observations

•Swift carries 3 instruments:–Burst Alert Telescope (BAT)

–X-Ray Telescope (XRT)

–UV-Optical Telescope (UVOT)

(Data from http://swift.gsfc.nasa.gov/docs/swift/swiftsc.html)

•As of March 4, 2008, 299 GRBs have been detected by Swift

•82 GRBs have both XRT and UVOT detections

•18 also have radio detections

BAT Light Curves

(From http://swift.gsfc.nasa.gov/docs/swift/swiftsc.html)

Long GRB X-Ray Afterglows

(Gehrels 2008)

A Canonical X-Ray Afterglow Light Curve

(Zhang 2007)

Optical Afterglows

(Price et al. 2003)

Radio Afterglows

(Pihlström et al. 2007) (Willingale et al. 2004)

X-ray Optical

Radio

How do these afterglows relate to the origins of long duration GRBs?

What else does the GRB-SNe relation tell us about the progenitors of these GRBs?

Single Stars as Progenitors•Long GRBs associated with core collapse of massive Wolf-Rayet stars•Collapse yields stellar-size BHs or rapidly spinning, highly magnetized neutron stars•Infalling material forms a torus around central compact object•Subsequent accretion of material in the torus fuels gamma-ray jet•Internal shocks within gamma-ray jet and external shocks with residual wind material result in GRBs (or XRFs) and the afterglows

(**Note: the Cannon Ball Model will not be taken into account here**)

Collapsar (or Fireball) Model

(From www.oamp.fr)

Evidence for GRB-SNe Connection•Four direct observations of SNe associated with GRBs•All SNe are confirmed as Type Ic (have no/weak H, He, Si II lines & broad spectral lines)•Rebrightenings detected during late stages of afterglows indicate SN contribution•Most host galaxies have intense SFR

(Della Valle 2008)

GRB050525A

The GRB-SNe Connection

(Nomoto et al. 2007)

GRB-SN/HN

XRF-SN

Non-GRB HN

Normal SN

(Nomoto et al. 2007)

GRB-HNe XRF-SNe Non-SN GRB

Different Progenitors?

Results from Numerical Models

(Nomoto et al. 2007)

GRB-HNe

Non-GRBHNe/SNe

XRF-SN

Normal SN

A Different Single Star Model

(Yoon et al. 2008)

(Massive) Binary Progenitors

•Evolution of massive binaries (initial mass > 20 solar masses) can result in a long GRB

•Primary compact object formed works to tidally spin-up core of secondary star (allowing formation of torus after secondary collapses)

•After the GRB, a binary compact system of NS-NS, NS-BH, or BH-BH can remain

(Davies et al. 2007)

Other Binary ModelsFryer et al. (2007) discussed the following possible progenitors:

•Classic Binary: ejection of H envelope via mass transfer

•Tidal Binary: similar to Davies et al. (2007) model

•Brown Merger: ~equal mass stars merge in second common-envelope phase to form single massive star with ~no H/He

•Explosive Ejection: secondary accretes onto He core of primary, spinning up the core and also producing explosions in the core that eject He shell and H envelope

•He Merger: one star evolves into NS or BH and then merges with companion (He-rich) star

•He case C: similar to above, but merger occurs after He burning

•Cluster: enhanced mergers that require cluster interactions?

(not looked at in detail yet…)

(Fryer et al. 2007)

Conclusions•The most likely progenitor of long-period GRBs is…not determined!

•Problems exist with every model!

•Many factors to consider makes solving this rather difficult (metallicity, initial mass, mass-loss rate, rotational velocity, angular momentum, host galaxies, properties of afterglows, etc.)

•There is no unified model for GRBs yet…

(and who knows if there will ever be one)

References

Davies, M. B., Levan, A. J., Larsson, J., King, A. R., & Fruchter, A. S. 2007, in AIP Conf. Proc. 906, Gamma-Ray Bursts: Prospects for GLAST, ed. M. Axelsson, & F. Ryde, 69

Della Valle, M. 2008, in AIP Conf. Proc. 966, Relativistic Astrophysics – 4th Italian-Sino Workshop, ed. C. L. Bianco, & S.-S. Xue, 31

Fryer, C. L., et al. 2007, PASP, 119, 1211

Gehrels, N. 2008, in AIP Conf. Proc. 968, Astrophysics of Compact Objects, International Conference on Astrophysics of Compact Objects, ed. Y.-F. Yuan, X.-D. Li, & D. Lai, 3

Gehrels, N., & Cannizzo, J. K. 2007, in AIP Conf. Proc. 937, Supernova 1987A: 20 Years After, ed. S. Immler, K. Weiler, & R. McCray, 451

Kaneko, Y., et al. 2007, ApJ, 654, 385

Lapi, A., Kawakatu, N., Bosnjak, Z., Celotti, A., Bressan, A., Granato, G. L., & Danese, L. 2008, MNRAS, in press (astro-ph/0802.0787)

Nomoto, K., Tominaga, N., Tanaka, M., Maeda, K., Suzuki, T., Deng, J. S., & Mazzali, P. A. 2007, Il Nuovo Cimento, in press (astro-ph/0702472)

Pihlström, Y. M., Taylor, G. B., Granot, J., & Doeleman, S. 2007, ApJ, 664, 411

Price, P. A., et al. 2003, Nature, 423, 844

Willingale, R., Osborne, J. P., O’Brien, P. T., Ward, M. J., Levan, A., & Page., K. L. 2004, MNRAS, 349, 31

Yoon, S.-C., Langer, N., Cantiello, M., Woosley, S. E., & Glatzmaier, G. A. 2008, in IAU Symp. 250, Massive Stars as Cosmic Engines, ed. F. Bresolin, P. A. Crowther, & J. Puls, in press (astro-ph/0801.4362)

Zhang, B. 2007, CJAA, 7, 1

Part II

Optical Afterglows of Long GRBs

Optical Afterglows of Long GRBs & The Naked-Eye GRB 080319B

Knicole ColónHigh Energy Astrophysics

April 30, 2008

Image Credit: NASA, ESA, N. Tanvir (University of Leicester), and A. Fruchter

A Brief Review of Long GRBs•Total E > 1051 ergs

•Duration > 2 sec (longest known has t~2000 s)

•Have associated X-ray, optical, and radio afterglows

•Located near center of SFRs in mostly late-type, irregular, dwarf galaxies

•Single Star Progenitors: Collapsar/Fireball Model

•Definite associations with luminous core-collapse Type Ic SNe

•Massive Binary Progenitors: Several Models!

•No other conclusions…(Gehrels & Cannizzo 2007)

Optical Afterglows•Synchrotron emission resulting from a relativistic expanding jet colliding with ambient medium

•Continuous transfer of energy to swept-up medium and shock front physics (reverse/forward) yield power-law decaying curves

•Two components:–counterpart emission tracks prompt gamma-rays

–afterglow emission starts during prompt phase or shortly after and dims progressively for hours to days

•Light curves contaminated by host galaxy light, SN bumps

(Della Valle 2008)

GRB050525A

“Early” Afterglows

(Panaitescu & Vestrand 2008)

•At early times (30-104 s after trigger), behavior is different in different bursts

•Angular structure of relativistic outflow and variations in observer location may account for diversity manifested by early light curves

“Late” Afterglows

Late time behavior includes:

1. Jet Breaks (sudden increase of the fading rate due to jet geometry, typically few days after initial GRB)

(Dai et al. 2008)

3. SN bumps

2. Flares

Overall Afterglow Behavior

•Narrow/Clustered bimodal distribution of optical afterglow luminosity

–Intrinsic?

–60% of bursts are absorbed by large amount (> 1.5 mag) of gray dust?

–Clear separation between luminous and sub-luminous families

(Nardini et al. 2008)

Knowing all of this about optical afterglows… where does GRB 080319B fit in?

The Naked-Eye GRB 080319B•GRB duration ~ 60 sec

•Gamma-Ray E ~ 1054 erg

•V ~ 5.6 mag (Mpeak ~ -38.0)

•z = 0.937 (relatively nearby)

•At 10 kpc, would peak at V ~ -28.5

•Highest-fluence event & isotropic-equivalent energy release ever recorded

Image Credit: NASA/Swift/Stefan Immler, et al.

Swift’s XRT & UVOT Images

Animation Credit: Pi of the Sky

(Bloom

et al. 2008)

Brightest Optical Afterglow Ever!

•Fast-rising afterglow

•“Early” afterglow decays extremely rapidly (drops from 5th to 21st mag in < 1 day)

•2 short-timescale flares

•Smooth AG overall (note that many GRBs show significant jaggedness)

(Bloom et al. 2008)

•“Late” time afterglow

•No jet break seen– Occurred extremely early (within first 100 sec)?

– Early rapid decay reverse-shock dominated, & jet break hidden in transition region around 103 sec?

•Second scenario: brought on by extreme level of collimation

•Rather unremarkable at late times

•Similar to 3 other “ultra-luminous” GRBs

(Bloom et al. 2008)

Fits “Cannon Ball” Model…?•Ordinary GRB produced by jet of highly relativistic plasmoids (CBs) ejected in core-collapse SN•Viewed very near axis of CB-emission•Generated by “typical” GRB SNe, SN1998bw? Or most-luminous one detected, SN2006gy?

(Dado et al. 2008)

Results (?)

•Bloom et al. (2008) conclude the extreme brightness is related to macroscopic parameters of central engine (primarily collimation angle… maybe also Mejecta, initial Lorentz factor, circumburst medium?) rather than extrema in shock parameters

•Similarly, Dado et al. (2008) claim “cannon ball” model fits… (but this model is not as widely accepted by GRB community – “fire ball” model dominates)

•Also claim AG properties fit those of other AG/GRBs associated with “typical” SN (remains to be seen…)

•Final Fun Fact: disregarding absorption, this GRB would be observable even if placed at the epoch of reionization!

References

Bloom, J.S., et al. 2008, astro-ph/0803.3215Dado, S., Dar, A., & De Rujula, A. 2008, astro-ph/0804.0621

Dai, X., et al. 2007, astro-ph/0712.2239

Della Valle, M. 2008, in AIP Conf. Proc. 966, Relativistic Astrophysics – 4 th Italian-Sino Workshop, ed. C. L. Bianco, & S.-S. Xue, 31

Gehrels, N., & Cannizzo, J. K. 2007, in AIP Conf. Proc. 937, Supernova 1987A: 20 Years After, ed. S. Immler, K. Weiler, & R. McCray, 451

Nardini, M., Ghisellini, G., & Ghirlanda, G. 2008, MNRAS, 386, L87

Panaitescu, A., & Vestrand, W. T. 2008, submitted to MNRAS, astro-ph/0803.1872Uemura, M., et al. 2003, astro-ph/0306396