dust scattering x-ray expanding rings around grbs sandro mereghetti andrea tiengo giacomo vianello

Venezia - June 5, 2006 S.Mereghetti - Swift and GRBs Conference 1

Dust scattering X-ray expanding rings

around GRBs

Sandro MereghettiAndrea Tiengo

Giacomo Vianello

INAF – IASF Milano


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, 889Chandra: Tan & Draine 2004, ApJ 606, 296; Xiang et al. 2006, ApJ 628, 769

X-ray dust halos: brief history - 1/3


m] [0.1 a [keV] E

arcmin 10 HALO FO SIZE

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


OBSERVER DUST

X-RAYSOURCE

s

D = x Ds (1-x) Ds

Ds

c

D

x

x S

2

1 DELAY TIME


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)



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)



GRB 031203 EPIC pn

58 ks observation starting at to+ 6 hrs

Two dust layers at D=880 pc and D=1390 pc

EPIC MOS (Vaughan et al 2004)

10’


GRB 050724 (Vaughan et al. 2006)

Swift XRT observation starting at to+ 343 s

Narrow (<22 pc) dust layer at D=139 pc

343-2243 s 6068-8127 s > 10,000 s


GRB 050713A

• Discovered by Swift

• XMM Observation starting at to+23 ks

• 30 ks long but only 9 ks useful due to high background

EPIC pn0.5-2 keV


A new method for detection of faint expanding rings “dynamical images”

(Tiengo & Mereghetti 2006, A&A 449, 203)

GRB 031203

Time since GRB

Ang

ular

dis

tanc

e fr

om G

RB

REBINNING


For each count detected in the X-ray image compute the quantity:

ii

i Dct

2

2

position GRB from distanceangular

GRB thefrom time

i

it

and plot the distribution of the Di values

n(D)

D


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

pc 30240FWHM

counts 1740N

pc 51389D

pc 82FWHM

counts 840N

pc 5870D

2

2702402

2

17141

2101801

1


GRB 050713A

pc 33FWHM

counts 185N

pc 364D

1812

12090

67

-


“dynamical image” for GRB 050724 with Swift XRT data

Time since GRB(dis

tanc

e fr

om G

RB

pos

ition

)2


GRB 0507240.2 – 5 keV

pc 24FWHM

counts 130~N

pc 148D

1913

46

-


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


XMM and Swift GRBs 031203

050724

050713A


Information on the prompt emission

GRBGRBHALO IeII 1

Uncertainties on: - measure of halo intensity IHALO

- knowledge of scat n D

can be estimated from optical absorption:

2

8.1

056.0

15.0

keVV

keVV

EA

EA

Draine & Bond 2004

Predehl & Schmitt 1995


Sazonov et al. 2006, Astronomy Letters 32, 297

GRB 031203The 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


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)


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


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


XMM-EPIC vs. Swift XRT

Swift

XRT

XMM

EPIC

Half Energy Width

@ 1.5 keV

15” 15”

Field of view 23’ 30’

Effective area

@ 1.5 keV

110 cm2 ~2400 cm2 (1300 pn + 1100 2MOS)


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

dust scattering x-ray expanding rings around grbs sandro mereghetti andrea tiengo giacomo vianello

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