K. Alatalo - Extensions to the Standard Model1 Extensions to the Standard Afterglow Model Katey Alatalo October 10 th, 2005

K. Alatalo - Extensions to the Standard Model2 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 C –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 –E. Nakar, T. Piran, & J. Granot Gravitational Microlensing by the Galactic Halo –B. Paczyński

K. Alatalo - Extensions to the Standard Model3 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 Model4 Why do we need the extension?

K. Alatalo - Extensions to the Standard Model5 A “Regular” Afterglow Light Curve Light curve decays in the standard way  t  is satisfied. Steepening/changes in the decay occurs due to a break frequency (or a jet break) passing through the observed band ( c or m ) A [Yost et al., 2005]

K. Alatalo - Extensions to the Standard Model6 Light Curves Gone Wild Some light curves are not “standard” C GRB000301C GRB030329

K. Alatalo - Extensions to the Standard Model7 The Competing Models

K. Alatalo - Extensions to the Standard Model8 The Standard (no extensions yet) Dependences of important parameters of the shock

K. Alatalo - Extensions to the Standard Model9 Varying Density n changes over radius (thus, time) F becomes: Plug in equation for mass ( m < < c ): Assume  m changes very slowly with time Solution for c < : *note: this includes ISM and Wind models.

K. Alatalo - Extensions to the Standard Model10 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 Model11 Varying Energy (ISM Case)(Wind Case) E changes with time while n stays constant. These equations must be solved numerically

K. Alatalo - Extensions to the Standard Model12 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 progenitor shock shock (stronger) massive shell ejected reverse shock

K. Alatalo - Extensions to the Standard Model13 Varying Energy: two possibilities Initial Energy Inhomogeneities The “Patchy Shell” scenario: only material within an angle of  -1 can “talk” to each other, meaning inhomogeneities are only smoothed to  -1 scale. Numerical simulations [Kumar & Granot, 2002] show that the jet conserves its initial inhomogeneities for a very long time. When  -1 ~  n, the fluctuations begin to appear –The number of fluctuations we can see is N fl ~(  n ) -1 –The amplitude of the fluctuations is   piece of jet we can see whole jet

K. Alatalo - Extensions to the Standard Model14 Off-axis Viewing Observer is not looking directly into the jet symmetry axis At a certain time,  -1 will have spread to  obs When this happens, a single bump appears in the light curve

K. Alatalo - Extensions to the Standard Model15 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

K. Alatalo - Extensions to the Standard Model16 Gravitational Lensing Einstein was the first to think about it where R 0 is the radius of stuff that gets lensed (the extension of gravity’s ability to bend light)

K. Alatalo - Extensions to the Standard Model17 Mirolensing and GRBs GRBs are significantly “limb-brightened” (recall B. Metzger’s talk) Angular size of jet ~  as, which is the same as the Einstein radius of a solar mass lens jet

K. Alatalo - Extensions to the Standard Model18 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 Model19 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 Model20 GRB Discovered only ~500s after the GRB 3 bumps: –~4000s –7×10 4 s –3×10 5 s Models: –density variations –“patchy shell” model –refreshed shocks –passage of m plus a reverse shock*

K. Alatalo - Extensions to the Standard Model21 GRB C Bump appeared in light curve ~2 days after the GRB 2 proposed models: –standard GRB model > c ISM density profile reasonable fit –Microlensing much better fit s not constrained GRB000301C

K. Alatalo - Extensions to the Standard Model22 GRB Light curve contained undulations beginning ~1day after the burst Models –2 jets? –single broken power law? note: this is also SN2003dh GRB030329

K. Alatalo - Extensions to the Standard Model23 What next? Recently, a new “kink” to the standard afterglow model has been reported: underluminosity at early times : ROTSE reported a very shallow initial decay Nothing in the standard model can predict this Courtesy of GRBlog

K. Alatalo - Extensions to the Standard Model24 The End Special thanks to Dr. Sarah Yost and Prof. Josh Bloom for their helpful advice on supplemental papers to read.