COLLABORATORS: Dale Frail, Derek Fox, Shri Kulkarni, Fiona Harrisson, Edo Berger, Douglas Bock, Brad Cenko and Mansi Kasliwal

Ionized f(HI) ~ 0 Neutral f(HI) ~ 1 Reionized f(HI) ~ 1e-5

Barkana and Loeb (2007) Initially formed from dark matter mini-halos at z=20-30 before galaxies Pop III: M~100 M sun L~10 5 L sun T~10 5 K, Lifetime~2-3 Myrs Dominant mode of star formation below Z solar Can be found only via stellar deaths

Tanvir et al. 2009

Long lived afterglow with powerlaw decays Spectrum broadly consistent with the synchrotron. Measure F m, m, a, c and obtain E k (Kinetic energy), n (density),  e,  b (micro parameters), theta (jet break), p (electron spectral index).

Last Chandra measurement

Signatures of Population III star: Low metalicity and the absence of dust extinction NIR spectroscopy Time is the enemy Spectra taken days later. AG has faded +5 mag Need satellite with NIR imaging and spectroscopy capabilities  JANUS

Signatures of Pop III progenitor: Hyper-energetic explosion Low density HII region – Strong radiation pressure from Pop III star – creates low density (1 cm -3 ) constant density region (10 pc) Low metallicity No published predictions on other afterglow parameters.

Afterglow properties not sufficient enough to suggest different kind of Progenitor for GRB More high-z GRBs required to make a more coherent picture.

High z GRBs are rare – Theory. 5 (Loeb & Bromm 2006) – Only 3 GRBs with redshift > 6 GRB (z=8.2) GRB (z=6.7) GRB (z=6.3) NOW GRB B (z=9.4 photometric) astroph

A seismic shift in radio afterglow studies with EVLA With EVLA and 20-fold increase in sensitivity, better constraints on geometry, energy and density. No assumptions of geometry required at high redshifts. z=2.5, EVLA 3σ, Δt=1 hr z=8.5, EVLA 3σ, Δt=1 hr

Long lived afterglow with powerlaw decays Spectrum broadly consistent with the synchrotron. Measure F m, m, a, c and obtain E k (Kinetic energy), n (density),  e,  b (micro parameters), theta (jet break), p (electron spectral index).

Radio emission discovered from the highest known redshift object in the Universe. Star formation taking place at 630 million years age. The best-fit broad-band afterglow model is a quasi- spherical (θ j >12 o ), hyper-energetic (10 52 erg) explosion in a constant, low density (n=1 cm -3 ) medium. The high energy and afterglow properties of GRB are not sufficiently different from GRBs at moderate redshift to suggest a different type of progenitor model (e.g. Pop III). EVLA and ALMA will be important tools for both detecting and studying the first generations of stars in the early universe.