Elisabetta Maiorano IASF/INAF, Sezione di Bologna

&Dip. Astronomia, Università di

Bologna

GRB 030328: the burst before

the Burst

Collaborators

• Evert Rol• Nicola Masetti • Eliana Palazzi• Elena Pian• Paul Vreeswijk• Javier Gorosabel• Antonio de Ugarte Postigo

On behalf of the GRACE collaboration

HEADLINESHEADLINES

•GRB030328: overview

•Prompt event

•Optical photometry

•Optical spectroscopy

•Optical polarimetry

•Broadband spectrum

•Discussion

•Conclusions

GRB030328•Trigger: March 28.473 UT 2003 (by HETE-2)

•Coordinates (J2000): RA = 12h 10m 51s.00 DEC = -09° 21’ 05’’.00 error circle = 52’’

•Optical Transient: obs ~ 1 hr after the GRB, R ~ 18 (Peterson & Price 2003)

•X-ray Transient: obs ~ 15 hr after the GRB (exp=94 ks), Chandra (Butler et al. 2003)

•Redshift: z = 1.52 (Martini et al. 2003; Rol et al. 2003)

•Host galaxy: obs ~ 1 yr after the GRB, R ~ 24.4 (Gorosabel et al. 2005)

Prompt event

Prompt event light curve

•Duration (30-400 keV): ~ 100 s (T90)

•Total Fluence (30-400 keV): 3 x 10-5 ergs cm-2

• Peak Flux (30-400 keV): 7.3 x 10-7 ergs cm-2 s-1

(Villasenor et al. 2003; Butler et al. 2005)

(7-40 keV)

(7-80 keV)

(30-400 keV)

Hete-2

Observations

•BVRI Photometry (2.2m+WFI @ ESO)

•Spectroscopy (VLT+FORS1 @ ESO)

•Polarimetry (VLT+FORS1 @ ESO)

•X-ray Observations (ACIS-S @ CXO)

•Host galaxy Observations (2.2m+BUSCA @ CAHA)

WFI R-band image

The Optical Transient is clearly detected

Mid exp time = 29.272 UT(0.79 d after the trigger)

R = 21.17 ± 0.04

N

E

Field size: 2x2 arcmin(2.2m+WFI @ ESO)

BVRI light curves

I/10

R

Bx100

Vx10

(Maiorano et al. in preparation)

VLT+FORS1 Spectrum

Spectrum acquired 0.59 days after the GRB and corrected for the Galactic extinction E(B-V) = 0.047Significant lines explained assuming two systems at redshiftsz = 1.5223 ± 0.0006 (GRB redshift) and z = 1.295

Polarimetry

P = (2.4 ± 0.6) %

θ = (170 ± 7) degrees

5 different cycles of polarizationmeasurements were obtained, the percentage of linearpolarization P and the polarization angle θ do not vary across the 5 cycles.

We thus summed the images on each angle to increase the S/N.

t start = 0.13 dt end = 0.34 dV = 21.25 ± 0.10

(VLT+FORS1 @ ESO)

Host galaxy analysis(Gorosabel et al.)

The restframe Spectral Energy Distribution of the host galaxy.The best-fit is obtained using a Starburst galaxy (green template).The red dashed line shows the fit obtained using a powerlaw with index β = 1.25 ± 0.54.

Co-added C1+C2+C3+C4 image of the host galaxy obtained with 2.2m + BUSCA @ Calar Alto Telescope

X-ray afterglow analysis (Butler et al.)

0.5-5 keV spectrum is well fitted using an absorbed powerlaw with photon index Γ = 2.0 ± 0.2 NH = NH (Gal) = 1021 cm-2

No X-ray emission lines

The X-ray afterglow decreases in brightness following a powerlawwith index αx = 1.5 ± 0.1

(ACIS-S @ CXO)

R-band light curve analysis

a b

c

α = 1.07±0.05

α = 1.5±0.1

α1 = 0.8±0.1α2 = 1.6±0.2tb = 0.7±0.1 days

a

b

c

Broadband spectrum (tsed = 0.78 d)

βopt = 0.5 ± 0.1

βx = 1.0 ± 0.2

νc = 1.7 x 10 16 Hz

βx-opt= 0.84 ± 0.01

Closure Relations (1)(βx=βopt)

αx = 1.5 1.1

1.5 αopt Break

No break

βx = βopt

α = 3(p1)/4 = 1.2 ismα = (1-3p)/4 = 1.7 wind

α1 = 3(p-1)/4 = 1.2α2 = p = 2.6α1 = 3(p-1)/4+1/2 = 1.7 α2 = 3(p-1)/4+1 = 2.2

β=p/2

β=(p-1)/2

νc > νx p=2.6

sphere

jet

νc < νo p=1.6 α = (p+6)/4 = 1.9 α < 1

sphere

jet

ism

wind

α1 = 0.8α2 = 1.6

Closure Relations (2)(βx≠βopt)

βx = 1

α = 3(p-1)/4 = 0.75 α = (3p-1)/4 = 1.25

α1 = 3(p-1)/4 = 0.75 α2 = 3(p-1)/4+3/4 = 1.5 α1 = 3(p-1)/4+1/2 = 1.25α2 = 3(p-1)/4+1 = 1.75

βx=p/2

sphere

jet

νo < νc < νx

p = 2

βopt = 0.5 αx = 1.5

νc = 1.7 x 10 16 Hz

βopt = (p-1)/2 = 0.5νo < νc < νx

Eiso~1.8x1053 erg

Θjet=4°.3

Eγ= 5x1050 erg

ism

wind

ismwind

Summary•Optical and X-ray afterglow well detected

•Redshift: z = 1.522

•Polarization: P ~ 2.4%

•Host galaxy: Starburst

•Preferred regimes in fireball scenario: (1) isotropic expansion within a wind-shaped medium, p ~ 2.6 (2) jet collimated expansion within a homogeneous medium, p ~ 2

•…more data (if any) are welcome