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Dust scattering X-ray expanding rings around GRBs Sandro Mereghetti Andrea Tiengo Giacomo Vianello

Dust scattering X-ray expanding rings around GRBs Sandro Mereghetti Andrea Tiengo Giacomo Vianello INAF – IASF Milano. X-ray dust halos: brief history - 1/3.

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Dust scattering X-ray expanding rings around GRBs Sandro Mereghetti Andrea Tiengo Giacomo Vianello

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  1. Dust scattering X-ray expanding rings around GRBs Sandro Mereghetti Andrea Tiengo Giacomo Vianello INAF – IASF Milano S.Mereghetti - Swift and GRBs Conference

  2. X-ray dust halos: brief history - 1/3 1965: Overbeck points out that celestial point X-ray sources should be surrounded by diffuse emission due to dust scattering (Overbeck 1965, ApJ 141, 864) 1970  1980: it is recognized that this can be an important tool to obtain information on size, spatial distribution and composition of interstellar dust (e.g., Hayakawa 1970, Progr. Theor. Phys.43, 1224) 1983: first detections with Einstein ObservatoryRolf 1983 Nature 302, 46 (PSPC, GX 339-4 ) Catura 1983 ApJ 275, 645 (HRI, several GX sources) 1985  now: Many works on galactic sources with all imaging X-ray telescopes Einstein Observatory: Mauche & Gorenstein 1986, ApJ 302, 371 ROSAT: Predehl & Schmitt 1995, A&A 293, 889Chandra: Tan & Draine 2004, ApJ 606, 296; Xiang et al. 2006, ApJ 628, 769 S.Mereghetti - Swift and GRBs Conference

  3. For dust grains of radius a : • Halo profile is energy-dependent • and is determined by: • grain properties: • composition (e.g. silicates / carbonaceus) • size distribution • dust distribution along line of sight S.Mereghetti - Swift and GRBs Conference

  4. s  D = x Ds (1-x) Ds X-RAY SOURCE OBSERVER DUST Ds S.Mereghetti - Swift and GRBs Conference

  5. X-ray dust halos: brief history - 2/3 1973: Trumper & Schonfelder propose to use dust scattering halos to derive distance of variable sources (Trumper & Schonfelder 1973, A&A 25, 445) 1980: an X-ray ring observed around the dwarf nova SU UMa, but interpreted as ejected material (Cordova & Mason 1980, Nature 287, 25). Later Norwell et al. show that it was a dust scattering expanding ring. (Norwell et al. 1983, Nat. 303, 49) 1994: application to GRB distance problem(Klose 1994, ApJ 423, L23; A&A 289, L1) S.Mereghetti - Swift and GRBs Conference

  6. X-ray dust halos: brief history - 3/3 2003: expanding rings detected with XMM around GRB 031203 (Vaughan et al. 2004, ApJ 603, L3) 2004: Draine & Bond proposal to use variable AGNs behind galaxies to measure their distance – e.g. 10 Ms with Chandra could give M31 distance with 1% precision(Draine & Bond 2004, ApJ 617, 987) 2005: expanding rings found for: GRB 050713A with XMM (Tiengo & Mereghetti 2006, A&A 449, 203) GRB 050724 with Swift (Vaughan et al. 2006, ApJ 639, 323) S.Mereghetti - Swift and GRBs Conference

  7. GRB 031203 EPIC MOS (Vaughan et al 2004) 10’ EPIC pn 58 ks observation starting at to+ 6 hrs Two dust layers at D=880 pc and D=1390 pc S.Mereghetti - Swift and GRBs Conference

  8. 343-2243 s 6068-8127 s > 10,000 s GRB 050724(Vaughan et al. 2006) Swift XRT observation starting at to+ 343 s Narrow (<22 pc) dust layer at D=139 pc S.Mereghetti - Swift and GRBs Conference

  9. EPIC pn 0.5-2 keV GRB 050713A • Discovered by Swift • XMM Observation starting at to+23 ks • 30 ks long but only 9 ks useful due to high background S.Mereghetti - Swift and GRBs Conference

  10. GRB 031203 REBINNING Angular distance from GRB Time since GRB A new method for detection of faint expanding rings  “dynamical images”(Tiengo & Mereghetti 2006, A&A 449, 203) S.Mereghetti - Swift and GRBs Conference

  11. n(D) and plot the distribution of the Divalues D For each count detected in the X-ray image compute the quantity: S.Mereghetti - Swift and GRBs Conference

  12. GRB 031203 By fitting the peaks with Lorentzians one gets number of counts in the rings and distance of the dust layer Can be done in different energy bins to extract halo spectrum S.Mereghetti - Swift and GRBs Conference

  13. GRB 050713A S.Mereghetti - Swift and GRBs Conference

  14. (distance from GRB position)2 Time since GRB “dynamical image” for GRB 050724 with Swift XRT data S.Mereghetti - Swift and GRBs Conference

  15. GRB 050724 0.2 – 5 keV S.Mereghetti - Swift and GRBs Conference

  16. We applied this method to all GRBs observed with XMM-Newton and Swift • XMM: 15 GRBs with follow-up observations starting at t ~ 20-60 ks and lasting few tens of ks • No other dust rings detected, besides 031203 and 050713A • Swift: follow-up data for ~125 GRBs, with different quality/sensitivity S.Mereghetti - Swift and GRBs Conference

  17. XMM and Swift GRBs 031203 050713A 050724 S.Mereghetti - Swift and GRBs Conference

  18. t can be estimated from optical absorption: Draine & Bond 2004  Predehl & Schmitt 1995  Information on the prompt emission Uncertainties on: - measure of halo intensity IHALO - knowledge of t = sscatnD S.Mereghetti - Swift and GRBs Conference

  19. GRB 031203 The estimate of the X-ray “prompt” emission is subject to a large uncertainty … but even the most conservative value is above the extrapolation of the high energy INTEGRAL spectrum Sazonov et al. 2006, Astronomy Letters 32, 297 S.Mereghetti - Swift and GRBs Conference

  20. Conclusions • Expanding dust rings detected in 3 GRBs (out of ~140) • “Dynamical images” and distribution of “D” values offer a sensitive detection method • In principle halos can provide information on prompt emission, not directly observed (e.g. GRB 031203) • Very powerful to study dust properties and distribution when both direct and scattered radiation are detected ( extremely accurate distance measurements for dust layers) S.Mereghetti - Swift and GRBs Conference

  21. S.Mereghetti - Swift and GRBs Conference

  22. GRB 050724 • Discovered by Swift • Short (0.25 s) hard spike (ph.index ~1.7) followed by low flux tail (>200 s) with softer spectrum (ph.index ~ 2.5) • Fluence 6.3x10-7 erg/cm2 (15-350 keV) • Optical and radio afterglows • Off-center of elliptical galaxy at z=0.258 S.Mereghetti - Swift and GRBs Conference

  23. GRB 031203 • Discovered by INTEGRAL • FRED profile - 40 s long • Fluence 2x10-6 erg/cm2 (20-200 keV) • Photon index ~1.63 • z = 0.106 • Eiso ~ (0.6-1.4)x1050 erg S.Mereghetti - Swift and GRBs Conference

  24. XMM-EPIC vs. Swift XRT S.Mereghetti - Swift and GRBs Conference

  25. Search in all Swift bursts • 125 GRBs • Ring around GRB 050724 clearly visible • No other rings detected GRB 031203 NH = 6 1021 cm-2 GRB 050713A NH =1.1 1021 cm-2 GRB 050724 NH=1.5 1021 cm-2 S.Mereghetti - Swift and GRBs Conference

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