1. The Present and Future of GRB Cosmography Andrew S. Friedman (Harvard-CfA) & Joshua S. Bloom (Harvard-CfA / UC Berkeley) www.cosmicbooms.net

2. Outline Motivations: What is GRB Cosmography? Brief History Current Work Future Prospects

3. Motivations GRBs – brightest explosions in universe Detectable out to high z (>5, ~10-20?) Gamma-rays penetrate dust Any evolution likely to be orthogonal to that of Type Ia SNe Swift satellite in space! Years before SNAP (2010?, z max ~ 1.7) A GRB standard candle could serve as an independent probe of the geometry & expansion history of the universe, complementary to SNe Ia

4. But wait, high z is Ω M -dominated – boring! Only low z regime is good for Ω Λ, w, right? And very few low-z GRBs (now), including peculiar bursts 980425, 031203, (+future) However, survey in full range 0 < z < 2 is crucial to pin down dark energy systematics (Linder & Huterer 2003) GRBs already comparable in number to SNe Ia in 1<z<2, (z max ~ 1.7 now, SNAP) Ultimately, independent techniques are always a good thing in science Motivations

5. Empirical standard candle ultimately derives from microphysics (e.g. SNe Ia, Chandra. Limit) Scatter about standard candle can help quantify burst diversity (e.g. peculiar Ia’s) Empirical corrections to scatter (e.g. MLCS, stretch – Ia’s), can yield new physical insight Large deviations from the standard candle (outliers) may indicate different physical mechanisms for making GRBs – i.e. different progenitor systems (e.g. Type II SNe) Turning the game around - Pick a cosmology - GRB standard candles can tell you about the progenitors of GRBs Motivations

6. GRB Cosmography? It must be indep. of redshift (z), i.e. roughly constant from burst to burst It can depend on properties of both the prompt emission and the afterglow, although the latter are more observationally expensive Let’s review the search in the set of GRBs with known z (now ~40 events) What function of observables might serve as a useful GRB standard candle? Purely empirical approach.

7. History E iso distribution – spans several orders of mag. – E iso is a bad standard candle Data from Friedman & Bloom 2004 (astro-ph/0408413), ApJ/subm Fluence in observed bandpass Cosmological k-correction Luminosity Distance (theory) Hubble constant /70 kms -1 Mpc -1 Redshift

8. But GRBs are beamed. E γ distribution is much narrower than E iso (Frail et. al 2001, Piran et. al 2001, Bloom et. al 2003), but not sufficient for cosmology (Bloom et. al 2003) History 15 GRBs (f b ), 17 GRBs (z) Frail et. al 2001 24 GRBs (f b ), 28 GRBs (z) Bloom et. al 2003

9. Updated comparison of E iso and E γ dist. History Data from Friedman & Bloom 2004 (astro-ph/0408413), ApJ/subm 33 GRBs (f b ), 39 GRBs (z)

10. E γ is getting worse as a standard candle with new data: e.g. 030329, 031203, XRF 020903,… Bloom et. al 2003 Frail et. al 2001 Ghirlanda et. al 2004 History Friedman & Bloom 2004 1 2 3 4

11. Beaming inferred from steepening of afterglow light curve Stanek et. al 1999 History

12. This prescription of Egamma is model dependent! Top hat jet. Eg meaningful, modulo external density (usually unconstrained), gamma-ray efficiency, kcor bandpass, and jet model History