# Presentation: 115235

## GRB Afterglow in the Swift Era

**Pawan Kumar**

**Santorini, September 1, 2005**

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- _[Rapidly decaying early ](slide14.xml)__[lightcurve ](slide14.xml)__[in the x-ray band](slide14.xml)_

- _[Slowly decaying ](slide15.xml)__[lightcurve ](slide15.xml)__[in the x-ray and optical bands](slide15.xml)_

- _[Sudden increase in flux (flare) during the “afterglow”](slide16.xml)_

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**Afterglow from short duration GRB**

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**The central engine**** **
**Internal-external fireball model**

_**Piran et al. 1993; Rees & Meszaros 1994; Paczynski & Xu 1994**_

**The first three observations are useful for exploring:**

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**The steep decline (t****-3****) unlikely to be due to FS emission:  **

**this steep decline never seen after jet break for any GRB.**

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**It could be produced by the same source that gave rise**
** ****to the gamma-ray burst emission.**

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**We will consider two mechanisms...**

##      Rapid decay of x-ray LC: Off-Axis Emission?

**(Kumar & Panaitescu 2000)**

**

- 

*t *=*R* -2/2

*t **~ *-1

*t *=*R* **2/2

*t* ~ -2-**

***f*********** ******** *****t *****-2-********

*** ************p***** ******** *****t *****-1**

*R*

- _[GRB050219a](slide17.xml)_
**       ****XRT: *****f*********** ******** *****t *****-3.1**** *********** *****-1.1****  **
**	****(****consistent with *****t*****-2-**********)**
**      **** ****BAT****: *****f*********** ******** *********** *****0.75****  –  **
**	*****problem for off-axis model*****?**
**            ****at 10s**** – ***********p*****= 75 kev**** ******** **
**	****at 100s****  ***********p*****= 7.5 kev**** **

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**Expected decline:**** f******** ******** t****-2.7**

** ********p**** ******** t****-2**

**at 10s****:  ********p****= 75 kev**** **
**                     ******** ****at 100s:****  ********p****= 0.75 kev**

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**(consistent with observations)**

******c****ic  ****needs to be > 1Mev.**

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**(Campana et al., Chincarini et al.,  Nousek et al., **
**Vaughan et al., Zhang et al...) **

**It is the transition phase to the Blandford-McKee **
**Self-similar solution.**

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**f******** ******** t****3**** ********10****  **

**A slightly weaker decline of****  ******** ****with time -- before the onset**
**of self-similar solution can give rise to a shallow LC decay.**

**Such a behavior is natural to expect when the ejecta has a**
**finite range of ********.**

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**(Kumar et al. 2005)**

- sync or IC*** *********

***e*, *B*, , ***i*

**Search 4-parameter space to match GRB**
**spectral slope, **********-ray energy & duration.**
**Decide if the solutions are consistent with**
**internal shocks, or external reverse**
**Shock or...**

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## GRB 050219a: Generation of γ-rays

_**GRB 050219a: Generation of **__**γ**__**-rays**_

## Slide 10

## Slide 11

## Slide 12

## GRB 050126

_**GRB 050126**_

_**GRB 050219A**_

## Tagliaferri et al., Nature – 2005

_**GRB 050125**_

_**GRB 050125**_

- _[Tagliaferri et al., Nature –](slide2.xml)__[ ](slide2.xml)__[2005](slide2.xml)_

**t**** ****-1**

**t**** ****-2.52**

**t**** ****-3.15**

**t**** ****-0.82**

## GRB 050315: X-ray Lightcurve – Vaughan et al. 2005

- _[GRB 050315: X-ray ](slide2.xml)__[Lightcurve ](slide2.xml)__[– Vaughan et al. 2005](slide2.xml)_

**t**** ****-5.2**

**t**** ****-0.4**

**t**** ****-0.7**

****** ****-1.9********0.9**

****** ****-0.73********0.11**

## X-ray Flares

- _[X-ray Flares](slide2.xml)_

**Burrows et al. 2005**

## Nousek et al.  2005

- _[Nousek ](slide6.xml)__[et al.](slide6.xml)__[  ](slide6.xml)__[2005](slide6.xml)_

## GRb 050315: BAT lightcurve – Vaughan et al. 2005

_**GRb 050315: BAT lightcurve – Vaughan et al. 2005**_