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HETE-2 Observation of the extremely soft X-ray flashes, XRF010213 and XRF020903

HETE-2 Observation of the extremely soft X-ray flashes, XRF010213 and XRF020903. T. Sakamoto , D.Q. Lamb, C. Graziani, N. Kawai, M. Suzuki, Y. Nakagawa, Y. Shirasaki, T. Tamagawa, K. Torii, A. Yoshida, M. Matsuoka, E. E. Fenimore, M. Galassi, T. Q. Donaghy,

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HETE-2 Observation of the extremely soft X-ray flashes, XRF010213 and XRF020903

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  1. HETE-2 Observation of the extremely soft X-ray flashes, XRF010213 and XRF020903 T. Sakamoto, D.Q. Lamb, C. Graziani, N. Kawai, M. Suzuki, Y. Nakagawa, Y. Shirasaki, T. Tamagawa, K. Torii, A. Yoshida, M. Matsuoka, E. E. Fenimore, M. Galassi, T. Q. Donaghy, J-L. Atteia, C. Barraud, M. Boer, J-P. Dezalay, J-F. Olive, G. Ricker, J. Doty, R. Vanderspek, G. B. Crew, J. Villasenor, N. Butler, J. G. Jernigan, K. Hurley, S. E. Woosley and HETE-2 science team

  2. X-ray flashes (XRF) and X-ray-rich GRBs 2 1 a 0 -1 1 10 100 1000 E0 (keV) WFC (BeppoSAX) + BATSE (CGRO) GINGA 1000 100 Ep (keV) 10 Peak Flux P1024 (ph cm-2 s-1) (Kippen et al. 2002) (Strohmayer et al. 1998) HETE can do better !! S 2-30 keV / S 30-400 keV > 1.0 (XRF)

  3. XRF010213 • Burst time : 13 February 2001 12:35:35 UT • (4 months after the launch) • Burst location: (R.A., Dec.) = (10h31m26s, 5o30’30’’) (J2000) with a 95% error radius of 30’ Burst Properties ・Duration: 20.9 s (T90 WXM 2-25 keV band) ・X-ray / g -rayfluence ratio: S (2-30 keV) / S (30-400 keV) = 13.5 ・Total fluence (2 - 30 keV) : (6.3 ±0.6) x 10-7 erg cm-2 ・Peak flux 　　　 ・No afterglow was found. (Boer et al., Hudec et al., Henden et al., Berger et al. and Zhu et al.)

  4. XRF010213 • Burst time : 13 February 2001 12:35:35 UT • (4 months after the launch) • Burst location: (R.A., Dec.) = (10h31m26s, 5o30’30’’) (J2000) with a 95% error radius of 30’ Burst Properties ・Duration: 20.9 s (T90 WXM 2-25 keV band) ・X-ray / g -rayfluence ratio: S (2-30 keV) / S (30-400 keV) = 13.5 ・Total fluence (2 - 30 keV) : (6.3 ±0.6) x 10-7 erg cm-2 ・Peak flux 　　　 ・No afterglow was found. (Boer et al., Hudec et al., Henden et al., Berger et al. and Zhu et al.)

  5. Spectrum of XRF010213

  6. Photon index : -1.9 ±0.7 c2 (dof) : 13.92 (18) Power-law model WXM FREGATE Spectrum of XRF010213

  7. Region 2 (Band function) a = -1.0 (fixed) b = -2.6 (-0.6/+0.3) Ep (keV) = 4.9 (-0.8/+1.0) c2 (dof) = 37.77 (39) (PL: c2 (dof) = 49.65 (40)) Spectrum of XRF010213

  8. Region 3 (Band function) a = -1.0 (fixed) b < -3.4 Ep (keV) = 2.6 (-0.3/+0.2) c2 (dof) = 38.84 (34) (PL: c2 (dof) = 75.39 (35)) Spectrum of XRF010213

  9. Region all (Band) a = -1.0 (fix) b = -3.0 (-0.5/+0.3) Ep = 3.5 (keV) (-0.5/+0.3) c2 (dof) = 41.10 (43) (PL: c2 (dof) = 66.08 (44)) Spectrum of XRF010213

  10. (5 – 10 keV) (2 – 5 keV) Hardness ratio softening 2 - 5 keV WXM 5 -10 keV WXM

  11. XRF020903 Trigger time: 10:05:37.96 on 2002 September 3 Burst properties: ・Duration (2-10 keV): 4.9 s (T50),9.8 s(T90) ・X-ray / g –ray fluence ratio: S(2-30 keV) / S(30-400 keV) > 3.4 ・Peak flux (1s, 2-10 keV): (2.2 ±0.8) ph cm-2 s-1 ・Total fluence (2-10 keV): (5.9 ±1.4) x 10-8 erg cm-2 Afterglow candidate: ・Optical transient(Palomar 200-inch, Soderberg et al.) ・Redshiftof underlying galaxyz = 0.25±0.01 (Soderberg et al., Chornock & Filippenko) ・Radio sourceat OT position (VLA, Berger et al.) ・Host galaxy is anirregular galaxy(HST, Levan et al.)

  12. OT WXM SXC XRF020903 Trigger time: 10:05:37.96 on 2002 September 3 Burst properties: ・Duration (2-10 keV): 4.9 s (T50),9.8 s(T90) ・ X-ray / g –ray fluence ratio: S(2-30 keV) / S(30-400 keV) > 3.4 ・Peak flux (1s, 2-10 keV): (2.2 ±0.8) ph cm-2 s-1 ・Total fluence (2-10 keV): (5.9 ±1.4) x 10-8 erg cm-2 Afterglow candidate: ・Optical transient(Palomar 200-inch, Soderberg et al.) ・Redshiftof underlying galaxyz = 0.25±0.01 (Soderberg et al., Chornock & Filippenko) ・Radio sourceat OT position (VLA, Berger et al.) ・Host galaxy is anirregular galaxy(HST, Levan et al.)

  13. XRF020903 Trigger time: 10:05:37.96 on 2002 September 3 Burst properties: ・Duration (2-10 keV): 4.9 s (T50),9.8 s(T90) ・ X-ray / g –ray fluence ratio: S(2-30 keV) / S(30-400 keV) > 3.4 ・Peak flux (1s, 2-10 keV): (2.2 ±0.8) ph cm-2 s-1 ・Total fluence (2-10 keV): (5.9 ±1.4) x 10-8 erg cm-2 Afterglow candidate: ・Optical transient(Palomar 200-inch, Soderberg et al.) ・Redshiftof underlying galaxyz = 0.25±0.01 (Soderberg et al., Chornock & Filippenko) ・Radio sourceat OT position (VLA, Berger et al.) ・Host galaxy is anirregular galaxy(HST, Levan et al.)

  14. Time average spectrum (Power-law model) Photon index:-2.8 (-0.6/+0.5) c2 (dof) : 45.21 (54) Spectrum of XRF020903

  15. 2.7 keV 68% 95% 99.7% Constrain Ep of XRF020903 WXM spectrum ・power-law model with photon indexa = –2.8 (a < -2 at 99.3% confidence level) Ep lies near or below 2 keV(WXM lower energy boundary) Constrained Band function ・parameterized Ep and b (high-energy index) ・Only the high-energy part of the Band function is allowed to produce a pure power-law spectrum. (Details about this model are in appendix of Sakamoto et al.) Ep of XRF020903using the constrained Band function 1.1 keV < Ep < 3.6 keV, 68% Ep < 4.1 keV, 95% Ep < 5.0 keV, 99.7%

  16. Constrain Ep of XRF020903 WXM spectrum ・power-law model with photon indexa = –2.8 (a < -2 at 99.3% confidence level) Ep lies near or below 2 keV(WXM lower energy boundary) Constrained Band function ・parameterized Ep and b (high-energy index) ・Only the high-energy part of the Band function is allowed to produce a pure power-law spectrum. (Details about this model are in appendix of Sakamoto et al.) Ep of XRF020903using the constrained Band function 1.1 keV < Ep < 3.6 keV, 68% Ep < 4.1 keV, 95% Ep < 5.0 keV, 99.7%

  17. Spectral evolution 1st peak 2nd peak • 1st peak • a1 = -2.7 (-0.6/+0.5) • c2 (dof) = 75.1 (62) • 2nd peak • a2 = -4.2 (-3.7/+1.1) • c2 (dof) = 71.1 (62) • a1=a2=a • a = -2.9 (-0.8/+0.4) • c2 (dof) = 152.2 (125) • Dc2 = 6.0 (1 dof) spectral softening 98.6% confidence level

  18. S30-400 keV and S7-30 keV correlation S 7-30 = 3 x 10-3 S 30-4000.643 (Barraud et al. 2003) XRF010213 XRF020903

  19. 2-400 keV Flux and Peak energy correlation XRF010213 XRF020903

  20. Summary XRF010213 XRF020903 Duration (sec.) 20.9 9.8 Sx / Sg 13.5 >3.4 Ep (keV) 3.6 2.7 (<5.0, 99.7% limit) Softening yes yes (Ep: 4.9 g 2.6 keV) • S 30-400keV and S 7-30keV correlation • F 2-400keV and Ep correlation XRFs, X-ray-rich GRBs, and GRBs form a continuum and are a single phenomenon.

  21. XRF010213 (region all, Band) a = -1.0 (fix) b = -3.0 (-0.5/+0.3) Ep = 3.5 (-0.5/+0.3) c2 (DOF) = 41.10 (43)

  22. Photon index: -1.3 (fixed) Ep (keV) : 5.3 ± 1.1 c2(DOF) : 42.69 (40) Cutoff power-law F(E) = k Eaexp (-E(2+a)/Ep) Spectrum of XRF010213

  23. Photon index: -1.0 (fixed) Ep (keV) : 2.6 ± 0.2 c2 (DOF) : 39.73 (35) Cutoff power-law Spectrum of XRF010213

  24. Photon index: -1.1 ± 0.8 Ep (keV) : 3.6 (-1.5/+0.6) c2(DOF) : 51.23 (43) Cutoff power-law Spectrum of XRF010213

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