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 13年7月9⽇旦星期⼆亍
Contents Gamma - ray Bursts ( GRBs ) LAT Observations of GRBs Intense and Nearby GRB 130427A Revealing an Extra Hard Component 13年7月9⽇旦星期⼆亍
What are GRBs? Intense bursts of gamma - rays Duration: ~10ms - hundreds of seconds happen at a random position on the sky never repeat 13年7月9⽇旦星期⼆亍
Optical/X-ray afterglows Discovery of optical & X - ray afterglows in 1997 Cosmological origin van Paradijs et al. ( 1997 ) 13年7月9⽇旦星期⼆亍
The Fireball Model gamma - rays X - ray, optical, radio afterglow Piran ( 2004 ) 13年7月9⽇旦星期⼆亍
EGRET observations of GRBs GRB 940217 GRB 941017 13年7月9⽇旦星期⼆亍
“Band” function 13年7月9⽇旦星期⼆亍
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Fermi era 13年7月9⽇旦星期⼆亍
What does Fermi see? as of 2011 - 01 - 20 from N. Omodei 13年7月9⽇旦星期⼆亍
What does Fermi see? as of 2011 - 01 - 20 however, LAT does not see GeV emission from most GRBs ( see, e.g., Ackermann et al., 2012 ) from N. Omodei 13年7月9⽇旦星期⼆亍
from Nicola Omodei 13年7月9⽇旦星期⼆亍
LAT observations of GRBs Delayed onset of high - energy emission ( prompt phase ) extra spectral components ( prompt phase ) extended GeV emission 13年7月9⽇旦星期⼆亍
GRB 080916C Delayed onset of LAT emission compared to GBM emission 13年7月9⽇旦星期⼆亍
GRB 080916C Delayed onset of LAT emission compared to GBM emission 13年7月9⽇旦星期⼆亍
GRB 090217 - single component case 13年7月9⽇旦星期⼆亍
Second component during prompt phase GRB 090510 GRB 090902B Ackermann, et al. 2010 Abdo et al. ( 2009 ) 13年7月9⽇旦星期⼆亍
Power-law decay index GRB 090926A GRB 090510 Swenson et al. ( 2010 ) Abdo et al. ( 2010 ) 13年7月9⽇旦星期⼆亍
Catalog light curves Ackermann et al., arXiv:1303.2908 13年7月9⽇旦星期⼆亍
The Big four from Nicola Omodei 13年7月9⽇旦星期⼆亍
Light curve properties Ackermann et al., arXiv:1303.2908 13年7月9⽇旦星期⼆亍
GRB 100728A: LAT detection during X-ray flares within 3 - sigma Abdo et al. ( 2011 ) LAT detection: TS=32 13年7月9⽇旦星期⼆亍
GRB 110625A: LAT detection without X-ray flares Power - law fit W eighted background deviates from PL at 96.77 % Tam et al. ( 2012 ) 13年7月9⽇旦星期⼆亍
GRB 130427A T 90 ~ 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 T 0 + 243s, corresponding to an intrinsic photon energy 128 GeV at z=0.34, breaking the records 13年7月9⽇旦星期⼆亍
10-100 GeV photons GRB 130427A is peculiar, that it emits many high - energy gamma - rays during the afterglow period Fan, et al., arXiv:1305.1261 Tam et al. ( 2013 ) 13年7月9⽇旦星期⼆亍
Light curves Fan, et al., arXiv:1305.1261 Tam et al. ( 2013 ) 13年7月9⽇旦星期⼆亍
Light curve properties GRB 130427A does not look so much di ff erent in numbers Ackermann et al., arXiv:1303.2908 13年7月9⽇旦星期⼆亍
Look deeper.. Two spectral components are found to co - evolve Tam et al. ( 2013 ) 13年7月9⽇旦星期⼆亍
Look deeper.. Two spectral components are found to co - evolve Significance of broken power law over power law Power law index doesn’t change! Tam et al. ( 2013 ) 13年7月9⽇旦星期⼆亍
extended emission mechanism 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 ) 13年7月9⽇旦星期⼆亍
extended emission mechanism 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 ) 13年7月9⽇旦星期⼆亍
Are we seeing two mechanisms? synchrotron inverse Compton Liu, W ang & Wu, arXiv: 1306.5207 13年7月9⽇旦星期⼆亍
GRB 130702A z=0.145 ( GRB 130427A has z=0.34 ) Fluence ~ 6x 10 - 6 erg cm - 2 , 3.6x 10 50 erg, a relatively low luminosity GRB 5 photons detected by the LAT closest LAT GRB 13年7月9⽇旦星期⼆亍
Summary 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 13年7月9⽇旦星期⼆亍
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