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Short GRBs and their Progenitors (in the era of pre-Gravitational Waves)

Short GRBs and their Progenitors (in the era of pre-Gravitational Waves). Wen-fai Fong Harvard University Advisor: Edo Berger. GRB 070809 ACS/F606W. LIGO Open Data Workshop, Livingston, LA 10.27.2011. Outline. 1. Introduction to GRBs and our program

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Short GRBs and their Progenitors (in the era of pre-Gravitational Waves)

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  1. Short GRBs and their Progenitors(in the era of pre-Gravitational Waves) Wen-fai Fong Harvard University Advisor: Edo Berger GRB 070809 ACS/F606W LIGO Open Data Workshop, Livingston, LA 10.27.2011

  2. Outline 1. Introduction to GRBs and our program 2. Hubble Space Telescope (HST) host galaxy study 3. “Host-less” population  best evidence for mergers to date

  3. X-ray Optical NIR Radio Physics of GRBs: The big picture and open questions External forward shock Progenitor Internal shocks Central engine Interesting questions: Nature of central engine? How energy dissipated? Structure of outflow? Nature of the progenitor??? Prompt γ-ray emission LONG GRBs ONLY: Θj ~ 1-10⁰ Afterglow EK Adapted from Gehrels et al. 2007

  4. Two classes of GRBs originate from different progenitors Kouveliotou et al. 1993, Nakar 2007 Long GRBs have a supernova association, short GRBs do not How can we know more about the progenitors at present? Host galaxy and environmental studies.

  5. The multi-wavelengthTarget-of-Opportunity afterglow chase Swift discovers a burst… Essential post-docs! Ashley Zauderer Ryan Chornock Magellan (Chile) Chandra Swift satellite EVLA (New Mexico) …and we chase after the afterglow (and eventually host)! Gemini-North (HI) and South (Chile)

  6. What can we learn from host galaxy studies? LONG GRBs Median offset at ~1 re Wainwright, Berger & Penprase 2007 • Exclusive association with highly SF galaxies • Offsets consistent with massive stars Bloom et al. 2002

  7. HST host galaxy study Fong, Berger & Fox 2010 Morphologies, offsets, host light distribution 8 short GRBs with host galaxies and HSTdata

  8. What offsets can we expect?

  9. Short GRB (with hosts) offsets compared to models and long GRBs Fong et al. 2010 • Short GRBs have significantly larger offsets than long GRBs • Physical offsets consistent with NS-NS merger progenitor (lower limit) Long GRBs from Bloom et al. 2002

  10. Short GRBs arise from all types of environments… Early type Star- forming GRB101219A Gemini-South GRB070809 ACS/F606W GRB 100206A Gemini-South GRB100625A Gemini-South ? “Host-less”

  11. Short GRBs without a home:six “hostless” bursts Stratta et al. 2007; Fong et al. 2010; Berger 2010 GRB 061201 GRB 070809 HST/ACS/F606W 1. large offsets? 2. high redshift faint hosts?

  12. How far out are potential hosts? host-less w/hosts P(<δR ) If these systems are highly kicked,offsets~10’’ δR (arcsec) What is the probability of chance coincidence? (What is the likelihood of finding an unrelated galaxy?) Extension of Berger 2010

  13. Short GRBs offsets consistent with NS-NS mergers Fong et al. 2010, Berger 2010 Models from Bloom et al. 1999; Fryer et al. 1999; Belczynski et al. 2006 globular clusters Best agreement with NS-NS models!

  14. Using results to constrain progenitor model predictions Consistent with NS-NS, partial contribution from other populations?

  15. Swift-GW-ground-based synergy • Localize to: • 1-4 arcmin within 15 seconds (gamma-ray) • 2-3 arcsec within an hour (X-ray) • Sub-arcsec within several hours (opt/NIR) !!! Target-of-opportunity programs

  16. Summary • Short GRBs with hosts: • Older stellar populations • Larger physical offsets (than long GRBs) • Larger masses, sizes, metallicities and luminosities • Include short GRBs without hosts: • If highly kicked, provide best evidence for NS-NS/NS-BH merger origin to date

  17. Recommended Reading HST host galaxy study: Fong, W., Berger, E., & Fox, D. ApJ, 708: 9, 2010. Host-less bursts: Berger, E. ApJ, 722: 1946, 2010. EM counterparts of mergers: Metzger, B. & Berger, E. arXiv:1108.6056

  18. Extra 1: Stellar population ages Leibler & Berger 2010 τshort,SF~ 0.3 Gyr τshort,E~ 3 Gyr τlong~ 60 Myr -Short GRB hosts (including star-forming) have older ages than long GRB hosts. -Timescale for mergers

  19. Extra 2: Short GRB redshift distribution z = 0.410 z = 0.438 z = 0.827 z = 0.257 z = 0.160 z = 0.915 GRB 050724 GRB 050709 z ~ 0.1  400 Mpc z ~ 0.2  900 Mpc Berger et al. 2005; Fox et al. 2005; Berger et al. 2007; Berger 2009; Fong et al. 2011; Berger 2010

  20. Extra 3: Short GRB stats: BATSE, Fermi & Swift BATSE (1991-2000) Long:short 3:1 Swift (since 2004) Long:short 10:1 ~60 short bursts (a few arcmin) (10 per year) 70 short bursts per year! No afterglows. ~40 X-ray afterglows (a few arcsec) 8 w/ hosts, some coincident Few confirmed redshifts 21 optical afterglows (sub-arcsecond) Fermi/LAT (arcmin to degrees) 15 w/ coincident hosts 10 w/ confirmed redshifts 6 “host-less” (highly kicked?) 1 short GRB optical afterglows Several short GRB detections

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