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Cosmological Transient Objects Poonam Chandra Royal Military College of Canada Raman Research Institute 14th December 2010 Cosmological Transient Objects Supernovae and Gamma Ray Bursts Supernovae and Gamma Ray Bursts • Supernova energy 1029 more than an atmospheric nuclear bomb explosion. • At the time of explosion, the supernova can shine brighter than the host galaxy consisting of billions of stars. • In one month, a supernova can emit as much energy as Sun would emit in its entire life span of billions of years. • GRBs: biggest source of gamma-rays in universe and 100 times more energetic than supernovae. Outline (Gamma Ray Bursts) • Challenges • How to meet the challenge: multiwaveband modeling • Importance of radio observations • Our radio campaign and some results • Future of gamma ray burst science Gamma Ray Bursts • A big challenge when discovered in 1960s. • Gamma-ray signals for just a fraction of seconds to at most few minutes. • Non-terrestrial origin • BATSE: isotropic Meszaros and Rees 1997 Major breakthrough • BeppoSAX: first detection of X-ray counterpart of GRB 970228. • Optical detection after 20 hours. GRB 970508: a watershed event • • • • X-ray BeppoSAX Optical , z=0.835 => Cosmological Scintillation: fireball model Radio, late time- energetics • GRB 980425/SN1998bw- massive star origin Crisis: GRB 990123 • Assuming isotropy, the g-ray energies spanned three orders of magnitude: 3×1051 to 3×1054 erg • Central engine energy requirements?? The GRB Energy Crisis circa 1999 ApJ 519, L7, 1999 Piran, Science, 08 Feb 2002 Stan Woosley says “I’m a very troubled theorist.” M sun c 2 2 1054 erg Astrophysics at the Extremes, Dec. 1517, 2009, Hebrew University 10 Jet Signatures tjet Flux Density t t -1/3 1/2 t -2 t -1 tj time Harrison et al. 1999 11 The GRB Energy Crisis Resolved Frail et al (2001) That was then… The GRB energy crisis was resolved GRB outflows are highly beamed (θ ~ 1-10 degrees) Geometry measured from jet break signature in light curves Beaming-corrected radiated energies are narrowly distributed around a “standard” value of ~1051 erg • A host of other measurements (X-ray afterglows, broadband modeling, calorimetry) support this energy scale • This energy scale is consistent with models of GRB central engines • • • • 13 This is now… POST-SWIFT 1. The mystery of the missing jets in the Swift era. 2. The emerging population of hyper-energetic events. 3. The established class of sub-energetic gamma-ray bursts. Multiwaveband modeling • Long lived afterglow with powerlaw decays • Spectrum broadly consistent with the synchrotron. • Measure Fm, nm, na, nc and obtain Ek (Kinetic energy), n (density), ee, eb (micro parameters), theta (jet break), p (electron spectral index). Radio Observations • • • • Late time follow up- accurate calorimetry Scintillation- constraint on size VLBI- fireball expansion Density structure- wind-type versus constant Multiwaveband modeling Radio afterglow statistics: 1997-2010 •1/3rd of all GRBs seen as radio afterglows since 1997-2010. •93 out of 244 •46 out of 149 (post Swift) •No strong redshift dependence. •z<2 47/88 • z>2 21/43 Chandra et al. 2011 Radio afterglow statistics: post-Swift •1/3rd of all GRBs seen as radio afterglows since 1997-2010. •93 out of 244 •46 out of 149 (post Swift) •No strong redshift dependence. •z<2 47/88 • z>2 21/43 Chandra et al. 2011 Radio spectral luminosity at 8.5 GHz (erg/s/Hz) Canonical radio afterglow light curve 1e+32 1e+31 1e+30 1e+29 980425 030329 060218 070125 090423 1e+28 1e+27 1e+26 0.1 1 10 Days since bursts 100 1000 GRB 070125 (Chandra et al. 2008) • One of the brightest Swift burst with isotropic energy of 1.1x1054 erg. • Followed extensively in X-ray, optical, mm and radio bands. • In radio bands, observed for more than a year. GRB 070125: Scintillation (Chandra et al. 2008) Jet break in GRB 070125 Chandra et al. 2008 • Chromatic jet break… • Optical band, day 3 • X-ray band, day 10 • Explanation— – Inverse-Compton Mechanism Inverse-Compton in X-rays Inverse Compton Scattering • Possible explanation for the delay in jet breaks or chromatic jet breaks in various GRBs. • Does not affect radio and optical bands but dominates in X-ray bands. • More effective in high-density environments. Radio data is crucial. GRB 070125: Highlights (Chandra et al. 2008) • Diffractive scintillation- constrain the fireball size • Chromatic jet break- Inverse Compton • Collimated g-energy 2.5x1052 erg. • Kinetic energy 1.7x1051 erg. GRB 090423 • Highest redshift GRB at z=8.2 • Highest redshift object of any kind known in our Universe. • Must have exploded just 630 million years after the Big Bang. GRB 090423 • • • • • • X-ray observtions: 73 s after detection Optical observations: 109 s after detection No optical transient. Detection in J band onwards. Photo-z=8.06+/-0.25 Spectral-z=8.23+/-0.08 Radio observations of GRB 090423 (Chandra et al. 2010) Detections VLA: 8.5 GHz on Apr 25-Jun 27. – 74 +/- 22 uJy at Δt~8 d – 2-hr integrations every 2 days – Data sets averaged (in UV plane) to improve detection sensitivity – Undetectable after Δt~65 d PdBI: 95 GHz on Apr 23-24 – Castro-Tirado et al. report a secure source detection of 200 uJy (no error bar given) Non-Detections WSRT: 4.9 GHz on May 22-23 CARMA: 95 GHz on Apr. 25 IRAM 30-m: 250 GHz on Apr 25 29 Multiwaveband modeling: (Chandra et al. 2010) Broadband modeling • High energy burst exploded in constant density medium. • No jet break occurred until day 50. 31 Reverse shock emission in GRB 090423 • Reverse shock emission at day 9 (time dilated) • After 1+z correction, reverse shock on day 1 • Seen is 250 GHz data also at around 10 hours (1+z corrected). • Implications for high Lorentz factor Previous high redshift GRB 050904 z=6.26 Afterglow Properties – – GRB 050904 (z=6.26). Both are hyper-energetic (>1051 erg) but they exploded in very different environments. (in situ n=600 cm-3 for GRB 050904) – Large energy predicted for Pop III. Not unique. – Low, constant density predicted for Pop III. Not unique. – No predictions for θj, εB, εe & p – Reverse shock detection in both GRBs Radio spectral luminosity at 8.5 GHz (erg/s/Hz) Canonical radio afterglow light curve 1e+32 1e+31 1e+30 1e+29 980425 030329 060218 070125 090423 1e+28 1e+27 1e+26 0.1 1 10 Days since bursts 100 1000 Reverse shock in radio GRBs Chandra et al. 2010b • Swift had expected to find many RS • At most, 1:25 optical AG have RS • Favored explanation – – – Ejecta are magnetized (i.e. σ>1). Do not need to be fully Poynting-flux dominated Suppresses RS emission Kulkarni et al. (1999) • Does not explain why prompt radio emission is seen more frequently. • About 1:4 radio AG may be RS • Possible Explanation: The RS spectral peak is shifted out of the optical band to lower frequencies 36 A seismic shift in radio afterglow studies • • • • The VLA got a makeover! More bandwidth, better receivers, frequency coverage 20-fold increase in sensitivity Capabilities started in 2010 • GRBs at higher frequencies where ISS is reduced • Measure polarization and rotation measures • Absorption lines possible (CO; see Inoue et al. 2007) Future of GRB Physics • Expanded Very Large Array (EVLA) • 20 times more sensitive than the VLA. Future: The EVLA- accurate calorimetry EVLA, 3-s, z=8.5 1 hr EVLA, 3-s, z=2.5 1 hr Future: Atacama Large Millimeter Array (ALMA) Accurate determination of kinetic energy Future: ALMA Debate between wind versus ISM solved Future: ALMA Reverse Shock at high redshifts mm emission from RS is bright, redshiftindependent (no extinction or scintillation) (Inoue et al. 2007). ALMA will be ideal. Conclusions • Multiwaveband modeling required to understand the GRB afterglow Physics. • New class of hyperenergetic GRBs such as GRB 070125. • Star formation taking place even at 630 million years after the big bang. • New explanation for the delay in jet breaks in Swift bursts • Radio and mm is crucial as they are unique in estimating the accurate energy, density and type of medium. • Future lies with the EVLA and the ALMA. Supernovae • Chandra, Dwarkadas, et at. 2009, ApJ 699, 388 – X-rays from the explosion site: 15 years of light curves of SN 1993J. • Nymark, Chandra, Fransson 2009, A &A 494, 179 – Modeling the X-ray emission of SN 1993J. • Patat, Chandra, et al. 2007, Science 317, 924 – Detection of circumstellar material in a normal Type Ia supernova. • Chandra, Ray, et al. 2005, ApJ 629, 933 – Chandra’s tryst with SN 1995N. • Chandra, Ray, Bhatnagar 2004, ApJ 612, 974 – The late time radio emission from SN 1993J at meter wavelengths. • Chandra, Ray, Bhatnagar 2004, ApJL 604, 97 – Synchrotron aging and radio spectrum of SN 1993J. Collaborators for GRB work • • • • • • • Dale Frail Shri Kulkarni Brad Cenko Derek Fox Edo Berger Fiona Harrison Mansi Kasliwal THANKS