1. Venezia - June 5, 2006S.Mereghetti - Swift and GRBs Conference1 Dust scattering X-ray expanding rings around GRBs Sandro Mereghetti Andrea Tiengo Giacomo Vianello INAF – IASF Milano

2. Venezia - June 5, 2006S.Mereghetti - Swift and GRBs Conference2 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 Observatory Rolf 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, 889 Chandra: Tan & Draine 2004, ApJ 606, 296; Xiang et al. 2006, ApJ 628, 769 X-ray dust halos: brief history - 1/3

3. Venezia - June 5, 2006S.Mereghetti - Swift and GRBs Conference3 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

4. Venezia - June 5, 2006S.Mereghetti - Swift and GRBs Conference4 OBSERVERDUST X-RAY SOURCE  ss D = x D s (1-x) D s DsDs

5. Venezia - June 5, 2006S.Mereghetti - Swift and GRBs Conference5 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) X-ray dust halos: brief history - 2/3

6. Venezia - June 5, 2006S.Mereghetti - Swift and GRBs Conference6 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) X-ray dust halos: brief history - 3/3

7. Venezia - June 5, 2006S.Mereghetti - Swift and GRBs Conference7 GRB 031203 EPIC pn 58 ks observation starting at t o + 6 hrs Two dust layers at D=880 pc and D=1390 pc EPIC MOS (Vaughan et al 2004) 10’

8. Venezia - June 5, 2006S.Mereghetti - Swift and GRBs Conference8 GRB 050724 (Vaughan et al. 2006 ) Swift XRT observation starting at t o + 343 s Narrow (<22 pc) dust layer at D=139 pc 343-2243 s 6068-8127 s > 10,000 s

9. Venezia - June 5, 2006S.Mereghetti - Swift and GRBs Conference9 GRB 050713A Discovered by Swift XMM Observation starting at t o +23 ks 30 ks long but only 9 ks useful due to high background EPIC pn 0.5-2 keV

10. Venezia - June 5, 2006S.Mereghetti - Swift and GRBs Conference10 A new method for detection of faint expanding rings  “dynamical images” (Tiengo & Mereghetti 2006, A&A 449, 203) GRB 031203 Time since GRB Angular distance from GRB REBINNING

11. Venezia - June 5, 2006S.Mereghetti - Swift and GRBs Conference11 For each count detected in the X-ray image compute the quantity: and plot the distribution of the D i values n(D) D

12. Venezia - June 5, 2006S.Mereghetti - Swift and GRBs Conference12 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 GRB 031203

13. Venezia - June 5, 2006S.Mereghetti - Swift and GRBs Conference13 GRB 050713A

14. Venezia - June 5, 2006S.Mereghetti - Swift and GRBs Conference14 “dynamical image” for GRB 050724 with Swift XRT data Time since GRB (distance from GRB position) 2

15. Venezia - June 5, 2006S.Mereghetti - Swift and GRBs Conference15 GRB 050724 0.2 – 5 keV

16. Venezia - June 5, 2006S.Mereghetti - Swift and GRBs Conference16 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

17. Venezia - June 5, 2006S.Mereghetti - Swift and GRBs Conference17 XMM and Swift GRBs 031203 050724 050713A

18. Venezia - June 5, 2006S.Mereghetti - Swift and GRBs Conference18 Information on the prompt emission Uncertainties on: - measure of halo intensity I HALO - knowledge of  scat  n D  can be estimated from optical absorption: Draine & Bond 2004  Predehl & Schmitt 1995 

19. Venezia - June 5, 2006S.Mereghetti - Swift and GRBs Conference19 Sazonov et al. 2006, Astronomy Letters 32, 297 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

20. Venezia - June 5, 2006S.Mereghetti - Swift and GRBs Conference20 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)

21. Venezia - June 5, 2006S.Mereghetti - Swift and GRBs Conference21

22. Venezia - June 5, 2006S.Mereghetti - Swift and GRBs Conference22 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/cm 2 (15-350 keV) Optical and radio afterglows Off-center of elliptical galaxy at z=0.258

23. Venezia - June 5, 2006S.Mereghetti - Swift and GRBs Conference23 GRB 031203 Discovered by INTEGRAL FRED profile - 40 s long Fluence 2x10 -6 erg/cm 2 (20-200 keV) Photon index ~1.63 z = 0.106 E iso ~ (0.6-1.4)x10 50 erg

24. Venezia - June 5, 2006S.Mereghetti - Swift and GRBs Conference24 XMM-EPIC vs. Swift XRT Swift XRT XMM EPIC Half Energy Width @ 1.5 keV 15” Field of view23’30’ Effective area @ 1.5 keV 110 cm 2 ~2400 cm 2 (1300 pn + 1100 2MOS)

25. Venezia - June 5, 2006S.Mereghetti - Swift and GRBs Conference25 Search in all Swift bursts 125 GRBs Ring around GRB 050724 clearly visible No other rings detected GRB 031203 N H = 6 10 21 cm -2 GRB 050713A N H =1.1 10 21 cm -2 GRB 050724 N H =1.5 10 21 cm -2