Extensions to the Standard Afterglow Model

1. Extensions to the Standard Afterglow Model Katey Alatalo October 10th, 2005 K. Alatalo - Extensions to the Standard Model

2. Papers Used • Microlensing of Gamma-Ray Bursts by Stars and Machos • E. Baltz & L. Hui • Microlensing and the Surface Brightness Profile of the Afterglow Image of Gamma-Ray Burst 000301C • B.S. Gaudi, J. Granot, & A. Loeb • Modeling Fluctuations in Gamma-Ray Burst Afterglow Light Curves • E. Nakar & T. Piran • Variability in GRB afterglows ad GRB 021004 • E. Nakar, T. Piran, & J. Granot • Gravitational Microlensing by the Galactic Halo • B. Paczyński K. Alatalo - Extensions to the Standard Model

3. Introduction • Why do we need the extension? • What are our options? • External density fluctuations • Energy re-injection • Off-axis viewing • Microlensing • What else? K. Alatalo - Extensions to the Standard Model

4. Why do we need the extension? K. Alatalo - Extensions to the Standard Model

5. A “Regular” Afterglow Light Curve • Light curve decays in the standard way • nbta is satisfied. • Steepening/changes in the decay occurs due to a break frequency (or a jet break) passing through the observed band (ncor nm) 050502A [Yost et al., 2005] K. Alatalo - Extensions to the Standard Model

6. GRB000301C GRB030329 Light Curves Gone Wild • Some light curves are not “standard” • 021004 • 000301C • 030329 K. Alatalo - Extensions to the Standard Model

7. The Competing Models K. Alatalo - Extensions to the Standard Model

8. The Standard (no extensions yet) • Dependences of important parameters of the shock K. Alatalo - Extensions to the Standard Model

9. n changes over radius (thus, time) Fn becomes: Plug in equation for mass (nm<n<nc): Assume dm changes very slowly with time Solution for nc<n: *note: this includes ISM and Wind models. Varying Density K. Alatalo - Extensions to the Standard Model

10. Varying Density: effects • Nakar & Piran show what would happen to a light curve if the shock crashed into an overdense ISM region with a Gaussian distribution in R. • The numerical simulations of changing energies and densities only stands for slowly varying profiles K. Alatalo - Extensions to the Standard Model

11. (ISM Case) (Wind Case) Varying Energy • E changes with time while n stays constant. • These equations must be solved numerically K. Alatalo - Extensions to the Standard Model

12. Varying Energy: two possibilities Refreshed Shocks • Produced by massive and slow shells ejected late in GRB • When the progenitor spews out slower more massive shells, it gives the shock more energy • This energy “refreshes” the forward shock and produces a reverse shock shock progenitor shock (stronger) progenitor reverse shock massive shell ejected K. Alatalo - Extensions to the Standard Model

13. piece of jet we can see whole jet Varying Energy: two possibilities Initial Energy Inhomogeneities • The “Patchy Shell” scenario: only material within an angle of G-1 can “talk” to each other, meaning inhomogeneities are only smoothed to G-1 scale. • Numerical simulations [Kumar & Granot, 2002] show that the jet conserves its initial inhomogeneities for a very long time. • When G-1~qn, the fluctuations begin to appear • The number of fluctuations we can see is Nfl~(Gqn)-1 • The amplitude of the fluctuations is  G K. Alatalo - Extensions to the Standard Model

14. Off-axis Viewing • Observer is not looking directly into the jet symmetry axis • At a certain time, G-1 will have spread to qobs • When this happens, a single bump appears in the light curve K. Alatalo - Extensions to the Standard Model

15. Microlensing: what it is • A gravitational object (star) passes through the jet • The source object (in this case, the jet) becomes brighter as the gravitational object passes Microlensing Simulation http://cfa-www.harvard.edu/~sgaudi/Movies/centroid_s0.gif K. Alatalo - Extensions to the Standard Model

16. Gravitational Lensing • Einstein was the first to think about it • where R0 is the radius of stuff that gets lensed (the extension of gravity’s ability to bend light) K. Alatalo - Extensions to the Standard Model

17. Mirolensing and GRBs • GRBs are significantly “limb-brightened” (recall B. Metzger’s talk) • Angular size of jet ~ mas, which is the same as the Einstein radius of a solar mass lens jet K. Alatalo - Extensions to the Standard Model

18. Microlensing and GRBs (cont…) • The magnitude and fluctuation in the light curve due to a microlensing event depend strongly on the surface brightness profile (SBP) K. Alatalo - Extensions to the Standard Model

19. Microlensing and GRBs (cont…) • Model (a.k.a. make an equation fit) the flux • This equation is then used to fit the GRB light curve and determine if it was lensed. K. Alatalo - Extensions to the Standard Model

20. GRB 021004 • Discovered only ~500s after the GRB • 3 bumps: • ~4000s • 7×104s • 3×105s • Models: • density variations • “patchy shell” model • refreshed shocks • passage of nm plus a reverse shock* K. Alatalo - Extensions to the Standard Model

21. GRB000301C GRB 000301C • Bump appeared in light curve ~2 days after the GRB • 2 proposed models: • standard GRB model • n > nc • ISM density profile • reasonable fit • Microlensing • much better fit • s not constrained K. Alatalo - Extensions to the Standard Model

22. GRB030329 GRB 030329 • Light curve contained undulations beginning ~1day after the burst • Models • 2 jets? • single broken power law? • note: this is also SN2003dh K. Alatalo - Extensions to the Standard Model

23. What next? • Recently, a new “kink” to the standard afterglow model has been reported: underluminosity at early times • 050801: ROTSE reported a very shallow initial decay • Nothing in the standard model can predict this 050801 Courtesy of GRBlog K. Alatalo - Extensions to the Standard Model

24. The End • Special thanks to Dr. Sarah Yost and Prof. Josh Bloom for their helpful advice on supplemental papers to read. K. Alatalo - Extensions to the Standard Model