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GRB 030328 : the burst before the Burst

GRB 030328 : the burst before the Burst. Elisabetta Maiorano IASF/INAF, Sezione di Bologna & Dip. Astronomia, Università di Bologna. Collaborators. Evert Rol Nicola Masetti Eliana Palazzi Elena Pian Paul Vreeswijk Javier Gorosabel Antonio de Ugarte Postigo

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GRB 030328 : the burst before the Burst

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

  2. Collaborators • Evert Rol • Nicola Masetti • Eliana Palazzi • Elena Pian • Paul Vreeswijk • Javier Gorosabel • Antonio de Ugarte Postigo On behalf of the GRACE collaboration

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

  4. 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)

  5. Prompt event Hete-2 (7-40 keV) • 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) (7-80 keV) (30-400 keV)

  6. 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)

  7. WFI R-band image N The Optical Transient is clearly detected Mid exp time = 29.272 UT (0.79 d after the trigger) R = 21.17 ± 0.04 E (2.2m+WFI @ ESO) Field size: 2x2 arcmin

  8. BVRI light curves Bx100 Vx10 R I/10 (Maiorano et al. in preparation)

  9. VLT+FORS1 Spectrum Spectrum acquired 0.59 days after the GRB and corrected for the Galactic extinctionE(B-V) = 0.047 Significant lines explained assuming two systems at redshifts z = 1.5223 ± 0.0006 (GRB redshift)and z = 1.295

  10. Polarimetry t start = 0.13 d t end = 0.34 d V = 21.25 ± 0.10 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. (VLT+FORS1 @ ESO)

  11. 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

  12. 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 powerlaw with indexαx = 1.5 ± 0.1 (ACIS-S @ CXO)

  13. R-band light curve analysis a b α = 1.07±0.05 a α = 1.5±0.1 b α1 = 0.8±0.1 α2 = 1.6±0.2 tb = 0.7±0.1 days c c

  14. 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

  15. Closure Relations (1)(βx=βopt) βx = βopt 1.1 1.5 α1 = 0.8 α2 = 1.6 αx = 1.5 αopt Break No break β=p/2 sphere jet α = (p+6)/4 = 1.9 α < 1 νc< νo p=1.6 α = 3(p1)/4 = 1.2 ism α = (1-3p)/4 = 1.7 wind α1 = 3(p-1)/4 = 1.2 α2 = p = 2.6 α1 = 3(p-1)/4+1/2 = 1.7 α2 = 3(p-1)/4+1 = 2.2 sphere β=(p-1)/2 νc> νx p=2.6 ism jet wind

  16. Closure Relations (2)(βx≠βopt) βx = 1 βopt = 0.5 αx = 1.5 νo < νc< νx νc = 1.7 x 10 16 Hz βx=p/2 p = 2 νo < νc< νx βopt = (p-1)/2 = 0.5 ism 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 = 1.25 α2 = 3(p-1)/4+1 = 1.75 sphere wind Eiso~1.8x1053 erg ism Θjet=4°.3 jet wind Eγ= 5x1050 erg

  17. 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

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