Masnori Ohno (ISAS/JAXA)

Long/Short GRBs are different ?

There are two GRB classes, Long/Short GRBs in T90 distribution Different origin ? Hardness ratio; short/hard, long/soft (Kouvelioutou et al. 1993) Spectral properties (Paciesas et al. 2003, Ghirlanda et al. 2004, Ohno et al. yesterday’s talk.. etc) How about z distribution ? <z>~1 from Swift result GRB080913 (z=6.7 T90,src~1s), Short ? Long ? Low statistics

Paciesas et al. 2001α Epeak Ghirlanda et al. 2004

Epeak-Eiso/Liso correlation Epeak-Liso as the redshift indicator for long GRBs (Yonetoku et al. 2004)

Short GRBs do not satisyf Epeak-Eiso due to much lower energy (Amati 2006, 2008, Ohno et al. 2007 …etc)How about Epeak-Liso for short GRBs ??

Total energy (Eiso)Short (WAM)

LongLong (Amati 2006)Long (WAM sample)

Ep-Eiso relation forRedshift-”unknown”Short GRBs by the WAM

Epeak-Eiso/Liso correlation for short GRBs

Both z and Epeak informationz from Swift, but Swift can not determine Epeak

Wide-band and good statistics is needed for short GRB Epeak

Joint analysis between Swift/BAT and Suzaku Wide-band All-sky Monitoris very useful to test these correlations for short GRBs

cross section top view

Yamaoka et al. 09

Suzaku HXD-WAM

Suzaku/HXD is surrounded by thick (4cm), large (40cm) 20 high-z BGO crystals for active shielding.

Wide-band All-sky Monitor(Suzaku/WAM)Energy band: 50—5000 keVEffective area: 400cm2@1MeV

Suzaku Wide-band All-sky Monitor

Powerful tool forshort GRB spectrum

WAM Short GRB correlations (1) sample

GRB051221AZ=0.545T90=0.22

GRB060801Z=1.13T90=0.44

GRB061006Z=0.44T90=0.42

GRB061210Z=0.41T90=0.05

GRB070714BZ=0.92T90=2.56

GRB071227Z=0.383T90=0.8

1sec

※T90:50-5000 keV

Swift leads redshift measurement even for short GRBsWAM provides Epeak for 6 redshift-measured short GRBs !

WAM Short GRB correlations (2) spectral analysisEpeak is obtained from WAM/BAT joint spectral analysisCutoff PL model is best fit for all sampleLpeak from WAM light curve (16ms time scale)

GRB051221AZ=0.545T90=0.22

GRB060801Z=1.13T90=0.44

GRB061006Z=0.44T90=0.42

GRB061210Z=0.41T90=0.05

GRB070714BZ=0.92T90=2.56

GRB071227Z=0.383T90=0.8

BAT

WAM

WAM short GRB correlations (3) Epeak-Eiso correlation

Ghirlanda et al. (arXiv 0902.0983)-Long-Short

Eiso (1052 erg)10-5 10-4 10-3 0.01 0.1 1 10 100 1000

WAM short GRBs

Short GRBs do not satisfy Amati relationdue to its much lower total energySimilar result to Ghirlanda et al. 2009

WAM short GRB correlations (4)Epeak-Liso correlation

WAM Short GRBs

Lpeak(1sec) (1052 erg)10-5 10-4 10-3 0.01 0.1 1 10 100 1000

Almost data seem to be consistent within dispersion of Ghirlanda et al result.Tend to be harder than long GRBs ?GRB 071227 is clear outlier. different correlation ? systematics ?It is difficult to conclude that short GRBs follow the Epeak-Liso relation, need more sample !

GRB071227

SummaryWe performed correlation analysis such as Epeak-Eiso and Epeak-Liso relation for short GRBs using BAT/WAM sample.

(1) Short GRBs do not satisfy Epeak-Eiso relation

(2) Roughly consistent with Epeak-Liso relation, however…. - large dispersion - tend to locate at harder Epeak regime - outlier ? (GRB071227) different correlation ? It is difficult to conclude that we can use the Epeak-Liso relation

as the redshift indicator for short GRBs.Need more samples !