# Presentation: 116028

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

**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**

## HEADLINES 

**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  =   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 (30-400 keV):**** **
** ****~ 100 s (T****90****)**
**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) = 0.047**
**Significant lines explained assuming two systems at redshifts**
**z = 1.5223 ****± ****0.0006 ****(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 = 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**

## 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.)

**0.5-5 keV spectrum is well fitted using an absorbed  powerlaw with photon index**** **
**Γ**** = 2.0 ****± 0.2**** **
**N****H**** = ****N****H ****(Gal) = 10****21**** 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**** **

**(ACIS-S @ 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 (tsed = 0.78 d)

**β****opt ****= 0.5 ****± 0.1**
**β****x ****= 1.0 ****± 0.2 **
**ν****c ****= 1.7 x 10 ****16**** Hz**
**β****x-opt****= 0.84 ****± 0.01**

## Closure Relations (1)(βx=βopt)

**α****x**** = 1.5  **

**1.1**
**1.5 **

**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)(βx≠βopt)

**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 ****= 0.5**

**α****x ****= 1.5**

** **

**ν****c ****= 1.7 x 10 ****16**** Hz**

**β****opt ****= (p-1)/2 = 0.5**

**ν****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 = 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**