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Identification of the host galaxy of Swift short GRBs by the Chandra sub- arcsecond position

Identification of the host galaxy of Swift short GRBs by the Chandra sub- arcsecond position. T. Sakamoto, N. Gehrels , E. Troja , J. Norris, S. Barthelmy , J. Racusin , N. Kawai, A. Fruchter. Mystery solved for short GRBs?. 70% of short GRBs has afterglow

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Identification of the host galaxy of Swift short GRBs by the Chandra sub- arcsecond position

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  1. Identification of the host galaxy of Swift short GRBs by the Chandra sub-arcsecond position T. Sakamoto, N. Gehrels, E. Troja, J. Norris, S. Barthelmy, J. Racusin, N. Kawai, A. Fruchter

  2. Mystery solved for short GRBs? • 70% of short GRBs has afterglow • Host galaxy: star forming and non-star forming (e.g. long GRBs: always star forming galaxy) We though we found a distinct difference in short GRB redshifts onearly 2005…. 050509B (z=0.226), 050709 (z=0.1606) and 050724 (z=0.257) However Redshift of short GRBs: z = 0.1 - 2 (everywhere)

  3. Mystery solved for short GRBs? Problem 1: None of the redshifts of short GRBs has been directly measured from the afterglow. Redshifts from the “associated” host galaxy. GRB 090417B (long GRB) Relatively large Swift/XRT error circle (2-10”) might cause a false ID for the host galaxy Need sub-arcsecposition for the secure ID of the host galaxy

  4. Mystery solved for short GRBs? Problem 2: Different population in short GRBs? Short GRBs with or without the extended emission (E.E.) No E.E. No lag With E.E. No lag

  5. Mystery solved for short GRBs? X-ray afterglow of short GRBs: Short lived X-ray afterglow (45%) Long lived X-ray afterglow (55%) Precise position of short GRBs: 1. secure redshift 2. could distinguish among different populations

  6. Table of Swift short GRBs

  7. Chandra ToO for a Swift short GRB Swift short GRBs: Optical AG: 35%, X-ray AG: 73% Two unsuccessful previous Chandra ToO for Swift short GRBs: long delay (>4 days after the trigger) Trigger criteria: 1. Swift short GRBs localized by Swift/XRT BAT: duration and spectral lag (TDRSS and/or BAT event data) XRT: arcsec position from TDRSS event data (U of Leicester) 2. No confirmation of an optical afterglow within 5 hours after a GRB trigger (Chandra response time within 1-3 days after T0) Event rates which meet our ToO criteria: 5 (2005), 6 (2006), 5 (2007), 5 (2008) and 3 (2009) Chandra can detect XA: T0< 3.5 days (SL) and T0+23 days (LL)

  8. Summary • Chandra ToO opportunity for a Swift short GRB in Cycle 13 (Nov/Dec 2011-Nov/Dec 2012) to obtain subarcsec position of XA • Trigger criteria 1) Swift short GRBs localized by Swift/XRT and 2) no OA confirmation T0<5 hours • Chandra response time 1-3 days after the trigger (faster judgment, therefore faster than previous Swift short GRBs ToO program) • Announce our ToO to the public (our ToO program is an asset for a whole GRB community) • Publish the result to the public ASAP

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