LAT OBSERVATIONS OF GRBS AND THE VERY BRIGHT AND NEARBY GRB130427A - - PowerPoint PPT Presentation
LAT OBSERVATIONS OF GRBS AND THE VERY BRIGHT AND NEARBY GRB130427A Thomas Tam ( NTHU ) Qingwen Tang, Xiangyu W ang ( NJU ) , Shu - Jin Hou ( PMO ) Ruo - Y u Liu ( NJU, MPIK ) Xue - Feng Wu ( PMO ) , Yi - Zhong Fan ( PMO ) ApJL ( 2013 ) 771, L13
Thomas Tam (NTHU) Qingwen Tang, Xiangyu W ang (NJU), Shu-Jin Hou (PMO) Ruo-Y u Liu (NJU, MPIK) Xue-Feng Wu (PMO), Yi-Zhong Fan (PMO)
ApJL (2013) 771, L13
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Gamma-ray Bursts (GRBs) LAT Observations of GRBs Intense and Nearby GRB 130427A Revealing an Extra Hard Component
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Intense bursts of gamma-rays Duration: ~10ms - hundreds of seconds happen at a random position on the sky never repeat
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Discovery of optical & X-ray afterglows in 1997 Cosmological origin van Paradijs et al. (1997)
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Piran (2004)
gamma-rays X-ray, optical, radio afterglow
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GRB 941017 GRB 940217
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from N. Omodei as of 2011-01-20
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from N. Omodei as of 2011-01-20 however, LAT does not see GeV emission from most GRBs (see, e.g., Ackermann et al., 2012)
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from Nicola Omodei
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Delayed onset of high-energy emission (prompt phase) extra spectral components (prompt phase) extended GeV emission
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Delayed onset of LAT emission compared to GBM emission
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Delayed onset of LAT emission compared to GBM emission
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GRB 090902B
Abdo et al. (2009) GRB 090510 Ackermann, et al. 2010
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Swenson et al. (2010) Abdo et al. (2010)
GRB 090926A
GRB 090510
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Ackermann et al., arXiv:1303.2908
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from Nicola Omodei
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Ackermann et al., arXiv:1303.2908
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LAT detection: TS=32
within 3-sigma
Abdo et al. (2011)
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W eighted background
Power-law fit
deviates from PL at 96.77%
Tam et al. (2012)
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T90 ~ 138s Fluence~2x 10-3 erg cm-2, putting it as the GRB with the highest fluence in GBM and Konus-Wind mission lives Also highest fluence in LAT energy range, and the most luminous GRB at z<0.5 Twelve >10 GeV photons were detected in the first 700s after the burst onset a 95 GeV photon arrived at T0 + 243s, corresponding to an intrinsic photon energy 128 GeV at z=0.34, breaking the records
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Fan, et al., arXiv:1305.1261 Tam et al. (2013)
GRB 130427A is peculiar, that it emits many high-energy gamma-rays during the afterglow period
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Fan, et al., arXiv:1305.1261 Tam et al. (2013)
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GRB 130427A does not look so much different in numbers
Ackermann et al., arXiv:1303.2908
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Two spectral components are found to co-evolve Tam et al. (2013)
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Two spectral components are found to co-evolve Tam et al. (2013)
Significance of broken power law
Power law index doesn’t change!
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Synchrotron emission (e.g., Kumar & Barniol 2009, Ghisellini et al. 2010) but there exists a maximum synchrotron energy, it is hard to explain the >10 GeV photons
Fan, Tam, Zhang, et al. (2013)
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Synchrotron emission (e.g., Kumar & Barniol 2009, Ghisellini et al. 2010) but there exists a maximum synchrotron energy, it is hard to explain the >10 GeV photons Inverse-Compton emission, long suspected, provides a natural explanation for the extra hard component at >10 GeV energies (Fan et al. 2013, Liu et al. 2013)
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Liu, W ang & Wu, arXiv: 1306.5207
synchrotron
inverse Compton
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z=0.145 (GRB 130427A has z=0.34) Fluence ~ 6x 10-6 erg cm-2, 3.6x 1050 erg, a relatively low luminosity GRB 5 photons detected by the LAT closest LAT GRB
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First detection of an extra-hard spectral component a GeV energies during the afterglow LAT GRBs are rare, but each individual burst is interesting Fermi/LAT GRBs are diverse! Still significant progress can be done 5 years after the launch
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