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GRBs and short X-ray transients observed by MAXI

GRBs and short X-ray transients observed by MAXI. ― a summary of the first year ― Motoko Serino on behalf of the MAXI team. outline. Global characteristics Prompt emissions number of events … more than expected? flux and hardness … are they special?

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GRBs and short X-ray transients observed by MAXI

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  1. GRBs and short X-ray transients observed by MAXI ― a summary of the first year ― Motoko Serino on behalf of the MAXI team

  2. outline • Global characteristics • Prompt emissions • number of events … more than expected? • flux and hardness … are they special? • Afterglow and pre-burst emission search • no detection … is it reasonable? • Individual events • spectral analyses The First Year of MAXI

  3. 16 events in 16 months GRB 091230 GRB 09026B GRB 091012 GRB 091120 GRB 090831 * Swift / Fermi 091201 * Fermi / IPN * INTEGRAL * Fermi 2009 2010 100327 100911 101030 XRF 100315A XRF 100616A XRF 100701A XRF 101117A GRB 100415A GRB 100510A GRB 100823A * Swift MAXI bursts * 5 are simultaneously detected by other satellites The First Year of MAXI

  4. event rate • expected detection rate • actual detection rate 12 / yr ! • why?? • MAXI can detect soft events 400 × 0.02 × 0.4 = 3.2 / yr total number of bursts instantaneous sky coverage of GSC observation efficiency The First Year of MAXI

  5. ( 8-20 keV flux ) ( 2-8 keV flux ) flux and hardness of MAXI bursts • flux2-20 keVaverage • hardness The First Year of MAXI

  6. comparing with HETE’s classification • HETE’s 45 bursts (Sakamoto et al. 2005)Sx /Sg = 2-30 keV / 30-400keV (fluence) • 10 GRBs log(Sx/Sg) -0.5 • 19 XRRs -0.5 < log(Sx/Sg) 0.0 • 16 XRFs 0.0 < log(Sx/Sg) The First Year of MAXI

  7. flux and hardness of MAXI bursts • MAXI bursts and XRF/XRR/GRB classification • XRFs dominate! The First Year of MAXI

  8. afterglow & pre-burst emission • no detection so far • to detect afterglows, GSC should scan <100sec after the trigger • GSC scans a position every 5400sec • probability ~ 0.02 • studying 80 bursts → 1.6 afterglow expected • we should study more bursts! • or better luck?! The First Year of MAXI

  9. individual events • Joint spectral fit • GRB 090926B (MAXI & Fermi) • narrow spectral energy distribution • GRB 100823A (MAXI & Swift) • soft spectral index • see also GRB 090831 by Ohno et al.MAXI / Fermi / Suzaku [P-53] The First Year of MAXI

  10. GRB 090926B • light curve • maxi detected the first 25 seconds of the burst • no significant emission above 350 keV • low flux below 4 keV The First Year of MAXI

  11. Peculiar spectrum of 090926B • spectra • low-energy power index = 0.3 • harder than a limit of the synchrotron shock model limit (-0.67) • Epeak = 90 keV ↓ • narrow spectral energy distribution a: 0.3 b: -2.6 a: 0.3 b: -2.6 The First Year of MAXI

  12. Peculiar spectrum of 090926B The First Year of MAXI

  13. GRB 100823A with Swift • soft power index ~ -2 • may be an upper part of Band function • X-ray flash • good agreement in normalization • within 10% • common to the three bursts The First Year of MAXI

  14. Summary • MAXI GSC detected 16 bursts in 16 months • A study of flux and hardness distribution of MAXI bursts shows that GSC efficiently detect soft bursts (XRRs and XRFs) • We can see good agreement in normalization with other instruments • GRB 090926B has peculiar spectral shape and that may be a emission from photosphere of GRB fireball The First Year of MAXI

  15. 16 events in 16 months GRB 091230 GRB 09026B GRB 091012 GRB 091120 GRB 090831 * Swift / Fermi 091201 * Fermi / IPN * INTEGRAL * Fermi 2009 2010 100327 100911 101030 XRF 100315A XRF 100616A XRF 100701A XRF 101117A GRB 100415A GRB 100510A GRB 100823A * Swift MAXI bursts * 5 are simultaneously detected by other satellites The First Year of MAXI

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