The most distant Cosmological Explosion Poonam Chandra Royal

The most distant Cosmological Explosion Poonam Chandra Royal Military College of Canada COLLABORATORS: Dale Frail, Derek Fox, Shri Kulkarni, Fiona Harrisson, Edo Berger, Douglas Bock, Brad Cenko and Mansi Kasliwal CASCA 2011 1 st June, 2011

Gamma Ray Bursts • Detectable at high redshift because of their extreme luminosities. Ionized f(HI) ~ 0 Neutral f(HI) ~ 1 Reionized f(HI) ~ 1 e-5

Gamma Ray Bursts • Excellent probe of IGM and ISM at high-z

Gamma Ray Bursts • Indicative of massive star formation

First stars in the high-z universe Barkana and Loeb (2007) • Initially formed from dark matter mini-halos at z=20 -30 before galaxies • Pop III: M~100 Msun L~105 Lsun T~105 K, Lifetime~2 -3 Myrs • Dominant mode of star formation below 10 -3. 5 Zsolar • Can be found only via stellar deaths

GRB 090423: z=8. 26 Tanvir et al. 2009 Radio Observations of GRB 090423 – CARMA observations, 95 GHz on day 1, 450+/-180 u. Jy – VLA observations starting day 1 until day 65 – First VLA detection on day 7. – Pd. BI, day 1 in 90 GHz. Detection 200 u. Jy.

Detectable in radio due to negative-k correction

Multiwaveband modeling • Long lived afterglow with powerlaw decays • Spectrum broadly consistent with the synchrotron. • Measure Fm, na, nc and obtain Ek (Kinetic energy), n (density), ee, eb (micro parameters), theta (jet break), p (electron spectral index).

Multiwaveband modeling of GRB 090423 (Chandra et al. 2010) Last Chandra measurement

Semianalytic constraints: GEOMETRY OF THE OUTFLOW

Semianalytic constraints: IMMEDIATE ENVIRONS

Semianalytic constraints: ELECTRON ENERGY INDEX

Multiwaveband modeling Yost et al. 2004 using

Discussion on Progenitor star • 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

Discussion on Progenitor star of GRB 090423 (z=8. 26) 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.

Comparison of afterglow properties

Discussion on Progenitor star of GRB 090423 (z=8. 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.

Observational Challenge • High z GRBs are rare – Theory. <10% Swift GRBs at z>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 090429 B (z=9. 4 photometric) astroph-1105. 4915 18

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=8. 5, EVLA 3σ, Δt=1 hr z=2. 5, EVLA 3σ, Δt=1 hr

ALMA Multiwaveband modeling • Long lived afterglow with powerlaw decays • Spectrum broadly consistent with the synchrotron. • Measure Fm, na, nc and obtain Ek (Kinetic energy), n (density), ee, eb (micro parameters), theta (jet break), p (electron spectral index).

CONCLUSIONS • 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 quasispherical (θj>12 o), hyper-energetic (1052 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.