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Timing analysis of unusual GRB 090709A observed by Suzaku Wide-band All-sky Monitor

Timing analysis of unusual GRB 090709A observed by Suzaku Wide-band All-sky Monitor. Wataru.Iwakiri (Saitama university).

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Timing analysis of unusual GRB 090709A observed by Suzaku Wide-band All-sky Monitor

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  1. Timing analysis of unusual GRB 090709A observed by Suzaku Wide-band All-sky Monitor Wataru.Iwakiri (Saitama university) Tuneyoshi Kamae (SLAC/KIPAC), Masanori Ohno (ISAS), Yukikatsu Terada, Makoto.S.Tashiro (Saitama Univ.), Yujin.E.Nakagawa (RIKEN), Atsumasa.Yoshida, Kazutaka Yamaoka (Aoyama gakuin Univ.) , Kazuo Makishima (RIKEN & Univ. of Tokyo) and Suzaku-WAM team

  2. GRB090709A BAT(10 – 350 keV) Sec High- amplitude periodicity (about 8 sec) ●T0: 07:38:34 (UT)●T90: 89 sec ●Fluence (15-150 keV): 2.57(±0.03) x10-5 erg/cm2 ●The 8 sec periodicity reported by Markwardt et al (GCN 9645). We will perform the statistical significance of the periodicity.

  3. The Light curves WAM TRN data 1 s resolution WAM: BGO scintillator (70 – 5000 keV) WAM BST data 128 ms resolution Konus data 128 ms resolution Konus: NaI scintillator (50 – 220 keV) BAT data 128 ms resolution BAT: CdZnTe semiconductor (15 – 350 keV)

  4. The Light curves WAM TRN data 1 s resolution ・Only using the BAT data, the periodicity is less than 3 sigma. (A.De Luca et al.2010; Cenko et al 2010) ・These light curves contain of GRB signal and instrumental white noise (Poisson noise). ・ The GRB signal is common in the 3 detectors, but instrumental noise is individual. WAM BST data 128 ms resolution Konus data 128 ms resolution ・To improve the signal-to-noise ratio, we sum up the 3 data. Problem: The time resolution and data length is different. BAT data 128 ms resolution 4

  5. Emulate the WAM light curve ・For 1 sec bin WAM-TRN data, we re-distributed photon into 8 sec times bin according to Poisson statistics and covers whole duration with WAM-BST data. TRN data (1 s time resolution) BST data exist only 64 s. Sec

  6. Emulate the WAM light curve ・For 1 sec bin WAM-TRN data, we re-distributed photon into 8 sec times bin according to Poisson statistics and covers whole duration with WAM-BST data. Emulate data (128 ms time resolution) BST data exist only 64 s. Sec

  7. Emulate the Konus light curve ・Konus covers only 100 sec data, we extended the light curve with a Poisson noise with the average of bgd level. Sec

  8. Emulate the Konus light curve ・Konus covers only 100 sec data, we extended the light curve with a Poisson noise with the average of bgd level. Sec

  9. Sum up the 3 data WAMv.sBAT Cross correlation 0.9 WAM(70 – 5000 keV) BAT(15 – 350 keV) Konus(50 – 220 keV) 0 Sec 0.9 WAMv.sKonus 0 0.9 BATv.sKonus ・ The cross correlation functions show that good coincidence of these data. 0

  10. Sum up the 3 data WAMv.sBAT Cross correlation 0.9 WAM(50 – 5000 keV) BAT(15 – 300 keV) Konus(10 – 770 keV) Summed up the 3 data 0 Sec 0.9 WAMv.sKonus 0 0.9 BATv.sKonus ・ The cross correlation functions show that good coincidence of these data. 0

  11. The Power spectrum of GRB 090709A 8 sec

  12. What is a Color noise ? a noise : ∝f-α Light curve Power spectrum White noise Alpha=0 Pink noise Alpha=1 Red noise Alpha=2

  13. Color noise index of GRBs Suzuki et al. 2002 The distribution of the color noise index alpha for 297 BATSE burst.

  14. The Power spectrum of GRB 090709A White noise Color noise

  15. Estimation of white noise bgd light curve Power spectrum The white noise level is derived the bgd power spectrum from – 100 s to –20 s before trigger.

  16. Estimation of the color noise index Suzuki et al. 2002 Power-law index: 1.9

  17. Comparison the simulation and observation Green: average of 1000 times simulated data Magenta: 99.85 % level of deviation Red: 99.9% level Null hypothesis probability is about 0.1 % Green:deviation of 1000 times simulated data Blue:deviation of observed data Power Period [sec]

  18. Discussion • A period of 8 sec is comparable to typical time scale of soft gamma-ray repeater in our galaxy. • However, we see no evidence of periodic oscillation in the afterglow (A.De Luca et al 2010) but see features we often see from GRB afterglows. • (See Nakagawa et al. Poster 064 in this conference; A.De Luca et al 2010; Cenko et al 2010) . • The origin of the periodicity is a GRB inner engine ??

  19. Summary • GRB090709A detected by WAM, BAT, and Konus. • We summed up 3 detector’s data to obtain good signal-to-noise ratio data by emulation of the light curve. • Comparison the 1000 times color noise simulation and observed power spectrum density, we detected the 8 sec periodic signal with the null hypothesis probability of 0.1 %.

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