Probing the High Redshift Universe with GRBsJon Oiler10/5/2007Overview•Background•Detecting GRBs at VHR•Probing SF with GRB afterglow•Finding SN at VHR•Measuring the redshifts of VHR GRBs•Tracing Metallicity•Probing Large-Scale Structure•Determining Epoch of Reionization•ConclusionConstants•Constants used are from WMAP1 results:•Total matter density ΩM = 0.3•Dark energy density ΩΛ = 0.7•Hubble constant H0 = 65 km s-1 Mpc-1Useful Acronyms•GRB: Gamma-ray burst•VHR: Very high redshift•SFR: Star formation rate•SNe: Supernova explosion•BATSE: Burst and Transient Source Experiment on Compton Gamma Ray Observatory•HETE - 2: High Energy Transient Explorer•BeppoSAX: Italian-Dutch X-ray satellite•Gamma-ray bursts (GRBs) are the most luminous events seen in the Universe– Bursts last from milliseconds to minutes– Followed by an afterglow at longer wavelengths•Likely caused by shocked gas encountering magnetic fields and give off synchrotron radiationBackground•GRB found with BeppoSAX (1997)–Afterglow contains X-ray, Optical, Radio components•Light of GRB host galaxy is detected and is very blue (1998)–Implies GRBs may be associated with SF Galaxies•GRB might contain an SN component (1999)–GRBs associated with core-collapse SNDetecting GRBs at VHRsDetecting GRBs at VHRsPeak photon number luminosityPeak photon number fluxComoving distance to the GRBDetecting GRBs at VHRsDetecting GRBs at VHRsDetecting GRBs at VHRs•Factors decreasing spectral energy flux:1. Distance away2. Redshift•Factor increasing spectral energy flux:1. Time dilation–Space between GRB and observer decreases and amount of energy released over an hour is received in less time•Effects cancel  little or no decrease in fluxDetecting GRBs at VHRsDetecting GRBs at VHRsDetecting GRBs at VHRs•Implications of light curve:–Detecting VHR GRBs require deep near-infrared observations•HETE-2 and Swift can do this–Deep optical observations needed to constrain the redshift•Looking for optical dropoutProbing Star Formation• Collapsar model predicted GRBs caused by core-collapse SN–≥40 M_solar as a main sequence star–Must be rapidly rotating to develop jets–Low Z so that jets can strip off H-envelope and reach surfaceProbing Star Formation•Recall that in 1999, a SN component was detected in GRB afterglow–Suggests that GRBs are related to the deaths of massive stars–If GRBs related to collapse of massive stars then GRB rate proportional to SFR–Should occur out to z ~ 10-20  Probe VHR star formationProbing Star FormationProbing Star FormationFinding SN at VHR•GRBs are likely caused by core-collapse SN–Therefore we should be able detect SN component if we know what to look for and when to look for itFinding SN at VHRFinding SN at VHRMeasuring GRB Redshifts•There 2 ways to measure the GRB redshift1. Taking spectrum of afterglow at early times•Lower-limit for measured redshift2. Taking spectrum of host galaxy•Not always easy to match host galaxy with GRB •Both get harder to do at larger redshiftsMeasuring GRB RedshiftsMeasuring GRB Redshifts•A possible third method:–Imagine a GRB at z = 10•Because of high redshift, the afterglow spectrum will be detectable in K-band•We will not detect signature in J-band due to drop-out from Lyα forest absorption–Therefore a ‘dark’ J-band switching on to ‘bright’ K-band is a signature of the GRB and can provide a good measure of the redshiftTracing Metallicity•Comparing GRBs to Quasi-stellar objects:–QSOs probe low Z of Halos and IGM–GRBs probe higher Z of disks and SF regionsTracing Metallicity•Two other metallicity studies:–Determine contribution from different SNe by looking at relative abundances of metals–Determine whether [Fe/H] is a good chronometer at high redshift•Probing metallicity at high redshifts requires extreme instrument sensitivity which is not doable any time soonProbing Large-Scale Structure•GRBs are useful because they are detectable at VHRs–But we would need a lot of recorded burst locations•At such high redshifts there is not much large scale structuring yet (over-under densities much more modest at high z)Probing Reionization•Looking for signs of Gunn-Peterson Trough (GPT) in GRB spectra–GPT is the transition zone between where neutral H absorbs high flux of radiation and becomes ionized H–Location in redshift may point to mechanism of reionizationProbing Reionization•Totani et al. paper put limit on reionization at z > 6 with GRB 05094 (2006)Conclusion•Background Findings:–GRB afterglow can be seen in x-ray, optical and radio–GRBs associated with SF–GRBs associated with core-collapse SNeConclusion1. Detectability at VHR  have been detected out to z ~ 6.4 with Swift3. Probing SF at VHR  can tell us where star forming regions are located and how active5. Finding SN at VHR  has been confirmed at lower redshift and should work for high redshiftConclusion4. Measuring redshifts of GRB  looking for cut-off frequency method used to determine redshift of most distant GRB ever identified5. Tracing metallicity  likely would take highly sensitive equipment and therefore not feasible6. Tracing large-scale structure  need lots of recorded GRBs and not much out there to probe at high redshiftsConclusion7. Probing Reionization  seems to be a great method; have already changed constraints on reionization to