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

3. 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).

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

6. 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

8. Tanvir et al. 2009 Detected by Swift-BAT on 23 rd April 2009. At T 0 +73s : X-ray begins. Detection At T 0 +109s: Optical begins. No detection At T 0 +20min: UKIRT begins. Detection in K band.

10. Last Chandra measurement

14. Negligible host extinction (Av<0.08, Tanvir et al. 2009) High energy burst with E/4  ~2.5 x 10 52 erg. (X-ray around 10 hrs, Freedman and Waxman 2001) Quasi-spherical outflow In a constant-density medium IR  cooling  X-ray  electron energy index p=2.46

16. 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

17. Signatures of Pop III progenitor: Hyper-energetic explosion Low magnetic field 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.

18. Signatures of Pop III progenitor: Hyper-energetic explosion Low magnetic field 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. BUT not Unique!

19. Signatures of Pop III progenitor: Hyper-energetic explosion Low magnetic field 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.

20. Signatures of Pop III progenitor: Hyper-energetic explosion Low magnetic field 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. BUT not Unique!

21. Signatures of Pop III progenitor: Hyper-energetic explosion Low magnetic field 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.

22. Signatures of Pop III progenitor: Hyper-energetic explosion Low magnetic field 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. BUT not Unique!

23. Signatures of Pop III progenitor: Hyper-energetic explosion Low magnetic field 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.

24. Signatures of Pop III progenitor: Hyper-energetic explosion Low magnetic field 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. ?

25. Signatures of Pop III progenitor: Hyper-energetic explosion Low magnetic field 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. ? ?

26. 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.

27. 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) 27

28. Reverse shock emission from GRB 090423 and implications for future observations Reverse shock seen in GRB 050904 (z=6.26) too RS seen in PdBI data too on day 1.87

29. mm emission from RS if observed few hours after the burst is bright, redshift-independent as effects of time-dilation compensates for frequency-redshift. (no extinction or scintillation). ALMA will be ideal with 75 uJy/4 min sensitivity. 29 Inoue, Omukai, Ciardi (2007) Reverse shock emission from high-z GRBs and implications for future observations

30. 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

31. Radio emission discovered from the highest known redshift object in the Universe. 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 are coming (soon). They will be important tools for both detecting and studying the first generations of stars in the early universe.

32. Radio emission discovered from the highest known redshift object in the Universe. 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 are coming (soon). They will be important tools for both detecting and studying the first generations of stars in the early universe.

33. Radio emission discovered from the highest known redshift object in the Universe. 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 are coming (soon). They will be important tools for both detecting and studying the first generations of stars in the early universe.

34. Radio emission discovered from the highest known redshift object in the Universe. 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 are coming (soon). They will be important tools for both detecting and studying the first generations of stars in the early universe.

35. Radio emission discovered from the highest known redshift object in the Universe. 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 are coming (soon). They will be important tools for both detecting and studying the first generations of stars in the early universe.

36. GRB 050904 at z=6.26 Both high energy bursts. Density environment: Density for GRB 050904 ~ 600 cm -3 (Frail et al. 2006) Density for GRB 090423 ~ 1 cm -3 Geometry of the outflow: GRB 050904, jet break on day 2.6 (Frail et al. 2006) GRB 090423, no jet break until day 50, Quasi- spherical

37. Signatures of Pop III progenitor (Heger et al. 2003): Hyper-energetic explosion Low magnetic field 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.

38. GRB 050904 was a jet-like outflow and exploded in high density region, so most likely progenitor was a normal Pop II star. WHAT ABOUT PROGENITOR OF GRB 090423?

39. Radio Observations Late time follow up- accurate calorimetry Scintillation- constraint on size VLBI- fireball expansion Density structure- wind-type versus constant

40. Object NameRedshift Milky Wayz=0.0 Virgo Clusterz=0.004 Quasar 3C273z=0.158 “Era of Galaxy formation”z=1-2 Most distant quasarz=6.43 Most distant galaxyz=6.96 GRB 090423z=8.2 First Stars appearz=20-30 Cosmic Microwave Background (CMB) z=1089 Big Bangz->∞ 40