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

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

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 10 -3.5 Z solar Can be found only via stellar deaths

6. Tanvir et al. 2009

8. 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).

9. Last Chandra measurement

14. Signatures of Population III star: Low metalicity and the absence of dust extinction NIR spectroscopy Time is the enemy Spectra taken 1-3.5 days later. AG has faded +5 mag Need satellite with NIR imaging and spectroscopy capabilities  JANUS

15. 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.

17. Afterglow properties not sufficient enough to suggest different kind of Progenitor for GRB 090423. More high-z GRBs required to make a more coherent picture.

18. High z GRBs are rare – Theory. 5 (Loeb & Bromm 2006) – Only 3 GRBs with redshift > 6 GRB 090423 (z=8.2) GRB 080913 (z=6.7) GRB 050904 (z=6.3) NOW GRB 090429B (z=9.4 photometric) astroph-1105.4915 18

19. 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

20. 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).

21. 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 090423 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.