GRB 030328: the burst beforethe Burst Elisabetta Maiorano IASF/INAF, Sezione di Bologna &Dip. Astronomia, Universit di Bologna

CollaboratorsEvert RolNicola Masetti Eliana PalazziElena PianPaul VreeswijkJavier GorosabelAntonio de Ugarte Postigo

On behalf of the GRACE collaboration

HEADLINES

GRB030328: overview

Prompt event

Optical photometry

Optical spectroscopy

Optical polarimetry

Broadband spectrum

Discussion

Conclusions

GRB030328Trigger: 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

ObservationsBVRI 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 imageThe Optical Transient is clearly detected

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

R = 21.17 0.04NEField size: 2x2 arcmin(2.2m+WFI @ ESO)

BVRI light curvesI/10RBx100Vx10(Maiorano et al. in preparation)

VLT+FORS1 SpectrumSpectrum 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) %

= (170 7) degrees

5 different cycles of polarizationmeasurements were obtained, the percentage of linearpolarization P and the polarization angle 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 = 1.25 0.54. Co-added C1+C2+C3+C4 image of the host galaxy obtained with 2.2m + BUSCA @ 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 = 1.25 0.54.

X-ray afterglow analysis (Butler et al.)0.5-5 keV spectrum is well fitted using an absorbed powerlaw with photon index = 2.0 0.2 NH = NH (Gal) = 1021 cm-2No X-ray emission linesThe X-ray afterglow decreases in brightness following a powerlawwith index x = 1.5 0.1 (ACIS-S @ CXO)

R-band light curve analysisabc = 1.070.05 = 1.50.11 = 0.80.12 = 1.60.2tb = 0.70.1 daysabc

Broadband spectrum (tsed = 0.78 d)opt = 0.5 0.1

x = 1.0 0.2

c = 1.7 x 10 16 Hz

x-opt= 0.84 0.01

Closure Relations (1)(x=opt)x = 1.5 1.1

1.5 opt Break

No break x = opt = 3(p1)/4 = 1.2 ism = (1-3p)/4 = 1.7 wind

1 = 3(p-1)/4 = 1.22 = p = 2.61 = 3(p-1)/4+1/2 = 1.7 2 = 3(p-1)/4+1 = 2.2=p/2 =(p-1)/2

c > x p=2.6spherejetc < o p=1.6 = (p+6)/4 = 1.9 < 1sphere

jet ismwind1 = 0.82 = 1.6

Closure Relations (2)(xopt)x = 1 = 3(p-1)/4 = 0.75 = (3p-1)/4 = 1.25

1 = 3(p-1)/4 = 0.75 2 = 3(p-1)/4+3/4 = 1.5 1 = 3(p-1)/4+1/2 = 1.252 = 3(p-1)/4+1 = 1.75x=p/2spherejeto < c < x p = 2 opt = 0.5x = 1.5 c = 1.7 x 10 16 Hzopt = (p-1)/2 = 0.5o < c < xEiso~1.8x1053 erg jet=4.3E= 5x1050 ergismwindismwind

SummaryOptical 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