Elisabetta Maiorano IASF/INAF, Sezione di Bologna & Dip. Astronomia, Università di Bologna GRB : 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

HEADLINES GRB030328: overview Prompt event Optical photometry Optical spectroscopy Optical polarimetry Broadband spectrum Discussion Conclusions

GRB Trigger: March UT 2003 (by HETE-2) Coordinates (J2000): RA = 12 h 10 m 51 s.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 ( keV): ~ 100 s (T 90 ) Total Fluence ( keV): 3 x ergs cm -2 Peak Flux ( keV): 7.3 x ergs cm -2 s -1 (Villasenor et al. 2003; Butler et al. 2005) (7-40 keV) (7-80 keV) ( keV) Hete-2

Observations BVRI Photometry ESO) Spectroscopy ESO) Polarimetry ESO) X-ray Observations CXO) Host galaxy Observations CAHA)

WFI R-band image The Optical Transient is clearly detected Mid exp time = UT (0.79 d after the trigger) R = ± 0.04 N E Field size: 2x2 arcmin 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) = Significant lines explained assuming two systems at redshifts z = ± (GRB redshift) and z = 1.295

Polarimetry P = (2.4 ± 0.6) % θ = (170 ± 7) degrees 5 different cycles of polarization measurements were obtained, the percentage of linear polarization 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 d t end = 0.34 d V = ± 0.10 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 ± Co-added C1+C2+C3+C4 image of the host galaxy obtained with 2.2m + Calar Alto Telescope

Host galaxy analysis (Gorosabel et al.) The restframe Spectral Energy Distribution of the host galaxy from the UV band (left panel) to the Optical and Infrared bands (right panel). The best fit is obtained using a Starburst galaxy of age 15 Myr (green template). The red dashed line in the left panel indicates the fit obtained using a powerlaw with index β = 1.25 ± 0.54.

X-ray afterglow analysis (Butler et al.) keV spectrum is well fitted using an absorbed powerlaw with photon index Γ = 2.0 ± 0.2 N H = N H (Gal) = cm -2 No X-ray emission lines The X-ray afterglow decreases in brightness following a powerlaw with index α x = 1.5 ± 0.1 CXO)

R-band light curve analysis a b c α = 1.07±0.05 α = 1.5±0.1 α 1 = 0.8±0.1 α 2 = 1.6±0.2 t b = 0.7±0.1 days a b c

Broadband spectrum (t sed = 0.78 d) β opt = 0.5 ± 0.1 β x = 1.0 ± 0.2 ν c = 1.7 x Hz β x-opt = 0.84 ± 0.01

Closure Relations (1) (β x =β opt ) α x = α opt Break No break β x = β opt α = 3(p1)/4 = 1.2 ism α = (1-3p)/4 = 1.7 wind α 1 = 3(p-1)/4 = 1.2 α 2 = p = 2.6 α 1 = 3(p-1)/4+1/2 = 1.7 α 2 = 3(p-1)/4+1 = 2.2 β=p/2 β=(p-1)/2 ν c > ν x p=2.6 sphere jet ν c < ν o p=1.6 α = (p+6)/4 = 1.9 α < 1 sphere jet ism wind α 1 = 0.8 α 2 = 1.6

Closure Relations (2) (β x ≠β opt ) β x = 1 α = 3(p-1)/4 = 0.75 α = (3p-1)/4 = 1.25 α 1 = 3(p-1)/4 = 0.75 α 2 = 3(p-1)/4+3/4 = 1.5 α 1 = 3(p-1)/4+1/2 = 1.25 α 2 = 3(p-1)/4+1 = 1.75 β x =p/2 sphere jet ν o < ν c < ν x p = 2 β opt = 0.5α x = 1.5 ν c = 1.7 x Hz β opt = (p-1)/2 = 0.5ν o < ν c < ν x E iso ~1.8x10 53 erg Θ jet =4°.3 E γ = 5x10 50 erg ism wind ism wind

Summary Optical and X-ray afterglow well detected Redshift: z = 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