# Presentation: 115238

## Catching a SN in the act of exploding:XRF060218 one year later

- Sergio Campana
- Osservatorio astronomico di Brera

## The discovery

- (UVOT)

**An unusually long burst, with T****90**** = ****2032****±****97**** ****s**
**Soft spectrum, with E****peak****~5 keV, hence classified as an X-Ray Flash **
**Low E****iso**** of ~ 6.2 ****±0.3**** x 10****49**** erg (1-10000 keV)**
***z***** = 0.03345 ± 0.0006 (145 Mpc, Mirabal et al. 2006); second nearest GRB**

## The evolution

- BB flux

- Afterglow
- -1.25±0.05

**UV-optical**

**X-ray**

- UV bump

- SN

** ****Mandatory soft component kT********0.17 keV (no emission lines)**
** ****At the end of the prompt phase, BB is the dominant component**
** ****Total BB energy few 10****49**** erg**

## XRF060218/SN2006aj

**XRF060218/SN2006aj**

** ****Lack of H and He lines **
**2006aj = SN-Ic**
** ****M****V**** (host) = -16**
** ****Host has brightness **
**similar to SMC**
** ****Z/Z******** ~ 0.05 (Wiersema **
**et al. 2007)**

- Masetti et al. 2006
- Mirabal et al. 2006
- Modjaz et al. 2006
- Mazzali et al. 2006
- Pian et al. 2006
- Ferrero et al. 2006
- Soderberg et al. 2006
- and more...

## Early SN (type II) observations

**Early SN (type II) observations**

- SN 1987A

## Catching a SN in the act of exploding: the record holder XRF 060218

**1993J**

**1987A**

**BAT observed the XRF when it was already started. Observing a SN within 1 hr from its collapse (much better than for SN1987A)**

**Notes:**
SN type II have longer break out times

## The shock break out

**The shock break out**

- BB power of GRB

- radiation density constant

- thermal temperature

**characteristic radius**
**of emitting region**

** ****BUT**** lack of hydrogen and helium lines implies a more compact star: larger radius explained by *****massive stellar wind***** **
** ****Assuming linear expansion, estimate star radius of (4 ****± 1) x 10****11**** cm**

**Progenitor was a Wolf-Rayet star**

## The model

**The shock becomes visible when it reaches the radius where the wind becomes optically thin: this is the *****shock breakout***

- jet

- stellar wind

## Details (prompt)

_** **__**Radius**_**: (E****BB****/aT)****1/3**** ****** **5x10****12**** cm (********1)**
_** **__**Mass**_**: 4****π****r****2****/****κ**** ******** 10****-6**** M****o**** (κ=0.17 g cm****-2**** is the Thomson opacity)**
_** **__**Density**_**: 1/κr=10****-12**** g cm****-3**
_** **__**Velocity**_**: ****β=v/c ******** 0.84 (very similar to SN1998bw****)**
_** **__**Timescale**_**: R/c ******** 200 s but we observe ******** 1000 s => **_**anisotropy explosion**_** either the explosion or the wind profile (as also testified by linear polarization observations; Gorosabel et al. 2007)**
**(Lack of breaks in the X-ray light curve would imply a lower limit to the opening angle at late times of ****θ********55°)****  **

- Wang, Waxman & Meszaros 2007

## Details (afterglow)

- Waxman, Meszaros & Campana 2007

** **_**Mass loss**_**: for a v=10****3**** km s****-1**** we have 10****-4**** M****o**** yr****-1****                           ****	**
**Interaction of the ejected relativistic shell with the progenitor’s wind**
** ****Emission by synchrotron (X-ray spectrum ν****f****ν ********ν****0****) ****and by IC (steeper spectrum)**
** ****Model well matches X-ray observation terms of source flux, decay index and spectral change for an input kinetic energy of a few 10****49**** erg, consistent with the total black body energy (change between synchrotron and IC emission occurring around 10****4**** s as observed)**

- UVOT

## Details (UV bump)

** ****Envelope is heated by the SN shock and then it cools. Taking total SN kinetic energy of E****K****=10****51**** erg (Mazzali et al. 2006) we can predict at 10****5**** s a photospheric radius of 3x10****14**** cm and a temperature of 2.2 eV, as observed**

- Blackbody peak centred in UVOT band at 120 ks:
- kTBB = 3.7+1.9-0.9 eV
- RBB = 3.29+0.94-0.93 x 1014 cm

- Waxman, Meszaros & Campana 2007

## Conclusions

** ****At least some (cf. 060614) GRBs highlight the onset of bright SN Ic explosions **
**(start observations, also spectroscopic, as soon as possible!)**
** ****XRF060218 allowed us to observe SN2006aj  <1 hr from its explosion**
** ****We observed in X-rays a shock break out from a compressed (anisotropic) wind 10****-6**** M****o**** shell, at a radius much larger than the progenitor star**
** ****Classical X-ray afterglow from stellar wind - GRB interaction and UV bump due to energization of the stellar envelope by the SN have been observed as well**

## Don’t think too much when skiing

**Don’t think too much when skiing**

## No shock break out papers (I)

_**Ghisellini et al.**_**: optical-UV data do not match X-ray extrapolation and X-ray and optical expansion velocities are different**
**X-rays come from a close wind shell (10****-6**** M****o****); **
**Optical-UV photons come from the energization of the stellar envelope by the SN**
**The two component do not necessarily match when computing a spectral energy distribution**

## No shock break out papers (II)

_**Li**_**: temperature and luminosity of the black body component are consistent with observations only if the W-R radius is 100 R****o**
**This is the radius we predict since the shock break out radius is the one corresponding to ********=1 in the stellar wind**

## No shock break out papers (III)

_**Fan & Piran (and also Soderberg et al.)**_**: modelling radio observations rule out a massive wind **
**Radio data alone cannot constrain the explosion parameters. It is true that in our model the radio component is largely underestimated and we cannot explain it, but the radio component represents only a negligible fraction of the total energy**

- Soderberg et al. 2006

## SN2006aj in the context

- Pian et al. 2006

## .

**.**

- Red Supergiant
- R~4x1013 cm

**Supernovae Core-collapse (II, Ib, Ic)**

- Blue Supergiant
- R~4x1012 cm

- Wolf-Rayet Star
- R~4x1011 cm

## E(B-V) estimate

**The expanding stellar remnant**

**32 ks**

- Rayleigh-Jeans tail of blackbody

- dip in UV is due to host galaxy extinction with E(B-V)~0.20±0.03, assuming SMC reddening law