# Presentation: 655582

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** ****30 years and only in the last few years we have began to understand their nature.**

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**Some basic results****.**

**Unsolved problems****.**

**Outline:**

**GRB Parameter Determination**

**Using Multi-wavelength Data**

**How do we determine GRB parameters**.

***Santorini, September 1, 2005***

***Pawan Kumar***

## Evidence for Relativistic outflow

- 030329 was at a redshift of 0.1685; da =589 Mpc.

**Superluminal motion in 030329:**** ****R****t**** ~ 3x10****17****cm at 25d**
**       ******** ****v****t ****=R****t****/t=5c ******** ********≈7 at 25 days**** (Taylor et al. 2004).**

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## What Have We Learned About GRBs?

_**What Have We Learned About GRBs**_**?**

**Energy in relativistic jet is ~ 10****51**** ergs (~SNe energy)**
**& ****the density of the surrounding medium is  ~ 1 cm****-3****.**
**In most cases the CSM density is uniform.**

**GRB ejecta is magnetized**** ****(at least in two cases).**

**The number of e******** per proton in GRB ejecta is not large**.

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## Dynamics

**(4********R****3****/3) n****0 ****(m****p****c****2********2****) = E****iso**

**t****obs****= R/2********2**

*********    ************ ************ ******t******obs******-3/8***

## t ~ -1

- At early time: -1 ≤  **

- At late time: -1 ≥ **

- Area visible to observer = (*R*/)2

- Area visible to observer = **(*R***)2 **** (*R*/)2 (**)2

**** (*R*/)2 *t *-3/4

*t **~ *-1

*t **~ *-1

*t* ~ -2

*t* ~ -2

*R*

*R*

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**Break in afterglow LC occurs when ******** = **********-1********** **

**Substituting ******** = **********-1**** in the dynamics equation:**

******** ****=********o****(n****0****/E****iso,52****)****1/8****(t****jet****/1day)****3/8**

**(4********R****3****/3) n****0 ****(m****p****c****2********2****) = E****iso**

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***We find:***

## Panaitescu & Kumar (2000)

_**Panaitescu & Kumar (2000)**_

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**For a windy CSM n(r) ******** r****-2****    **

**Dynamics:** **r********2**** ******** E****iso**   ****** ****** **t****obs****-1/4**

**This modifies flux scaling.**

**For instance, the flux at ********m****<********< ********c**** is ******** ****t****obs****-(3p-1)/4**

***Whereas for a uniform CSM  f************ ************ t******obs******-(3p-3)/4***

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**(instead of  r****3********2**** ******** E****iso****)**

## Example: Swift burst 050128  (Campana et al. 2005)

_***This implies a uniform CSM for 050128***_**!**

## f  tobs-   

_**Steepening of LC due to a jet for s=0 and s=2 media**_

_**Kumar & Panaitescu 2000**_

**s=2**

**s=0**

****

**f ******** t****obs****-********   **

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****** *********n,  p, ************e****** , ************B****** ***

***Example: ***_***A Recent Swift GRB***_

**The spectral slope between **
**optical & x-ray determines ********c**** **

**The ratio of optical to radio **
**flux upper limit determines ********m**

**From ********c**** & ********m**** we determine**
**n (0.1/cc)  & ********B**** (0.1). **

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##   n,  p, e , B 

******  *********n,  p, ************e****** , ************B****** ***

**by a multi-wavelength LC fitting**
** ****numerically.**

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**(1)**

**(2)**

**(3)**

- 2

- 2

- '

- 2

- )

- cos

- v

- 1

- (

- )

- ,

- (

- 3

- 4

- 1

- d

- f

**

**

**

**

**

- 

- 

- 

- 

*t*

*r*

*d*

*z*

*r*

*L*

**(4)**

_**Light-curve modeling**_
**(Panaitescu & Kumar, 2001)**

**The dynamics is determined by the following equations:**

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**The observed flux is:**

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**We have selected those GRBs which have observations **
**covering x-ray,  optical and radio bands, and thus provide the**
**best constraint on various burst and post-shock gas parameters****.****                                   **

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**We determine energy, jet angle, **

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## Panaitescu & Kumar (2000)

_**Panaitescu & Kumar (2000)**_

## Light curve fit for 8 GRBs

_**Light curve fit for 8 GRBs**_

- _980519, 990123, 990510, 991208, 991216_

- _000301c, 000926 & 010222_

_**Panaitescu & Kumar, 2001**_

## Energy in Relativistic Ejecta, Jet Opening Angle

_**Energy**_ in Relativistic Ejecta, _Jet Opening __**Angle**_

- and  ISM _**Density**_

**(Panaitescu & Kumar, 2002)**

- Berger et al. Claim (Nature, 2004, 430, 648)
- The energy of nearly GRBS -- 980425,  0301203 (z=.105) etc. -- is smaller than classical
- GRBs by a factor ~10. And the energy in the relativisitc component of Sne Ib/Ic is a
- factor 103 smaller.

**Berger et al. (2004) find the energy in the highly relativisitic **
**outflow for 2 bursts to be ~ 5x10****49**** ergs, but the total energy**
**to be ~ 10****51**** ergs.**

## Slide 17

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**several  bursts is believed to**
**come from shock heated ejecta**
**predicted by Sari & Piran, 1999.**

_**Determining GRB-ejecta compostion**_

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**The composition/property of the ejecta can be deter-**
**mined from the radiation it emits when heated by the**
**reverse shock at early times. **

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## The early afterglow combined with later afterglow – 

_**ROTSE 1999**_** (GRB990123)**

**The early afterglow combined with later afterglow – **
**which originates in the forward shock in the ISM**** –  **
**provides a handle on GRB ejecta composition****†****.**

**†****The jecta property could undergone substantial changes by the time it is**
**  ****heated by the RS e.g., B could have  decayed, baryons entrained, leptons **
**  ****generated or decayed etc.. **

## Optical Data for 021211

**•** **Reverse shock flux = Forward shock flux at 10.8 min**

**•** **R-band flux at 90s (RS) --- 7.2 mJy (14.1 mag)**

**•** **R-band Forward shock flux at 10.8 min --- 0.2 mJy**

**• ****The peak flux (FS) at 10.8 min > 0.2 mJy**

**• ****The peak frequency at 10.8 min < 4.3x10****14 ****Hz**

**• ****The deceleration time ~ 3 s.**

******if ****= 37 t****-3/2 ****/A********   ****kev**

**F****pf **** = 0.2 A****f****  mJy  (s=0)**

**F****pf **** = 5.4 A****f ****t****-1/2 ****  mJy  (s=2)**

## • The peak flux from forward shock at deceleration 

**•**** ****The peak flux from forward shock at deceleration**** **

**•**** ****Peak flux from reverse shock**

**•**** ****The observed flux from reverse shock (extrapolated to t****d****) ~ 1Jy (9 mag)**

** ****0.2 ********d**** mJy**** **

** ****3 ********d****    mJy**

**•**** ****And the peak frequency is: 7 ********d****-2  ****kev;  if ********B   ****in RS same as FS)**

**These together imply that ********B ,RS ****>>**** ********B ,FS**

**(Zhang et al. 2003 find similar result for 990123) **

******B ,RS  ****=**** ********B ,FS**

**(GRB 021211)**

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**emissions for 990123 & 021211 shows that****:**
**       ****the magnetic field in the ejecta is much larger **
**      ****than in the FS by a factor of ~10 – 10****2**** ****(Kumar &**
**      ****Panaitescu, 2003;  Zhang et al. 2003).**

**These results suggest that some GRBs produce **
**magnetized outflow****. **

**Blandford & Lyutikov, Spruit, Drenkhahn... have a series of**
**interesting papers investigating GRB energy carried outward**
**by poynting outflow and its implications.**

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_**Magnetized Outflow**_**?**

**Moreover, for poynting outflow the ********-ray emission could arise**
**from the decay of magnetic field and we should therefore look**
**for differences in the radiation property during the burst and**
**the afterglow phases.**

**The total magnetic energy in the shock heated **
**Ejecta is a good fraction of GRB energy.**

## Summary of Results

**     ****of a massive star**** (****at least in several cases!****)****.**

_**Summary of Results**_

-  **4. ****Mean Kinetic energy in relativistic ejecta = 7x10****50****erg**
**     ****(this is similar to supernova KE release);**** ****the energy dispersion is small – a factor 3**** – ****but there might be some outliers.**
**     ****. **

_**Note:**_  This is an animation slide. You need to click on the mouse several times to display all the texts.

**3. ****The afterglow radiation over a very wide range of**
**    ****EM spectrum, and time interval, is in quantitative**
**     ****agreement with the external relativisitc shock model****.**

**2. The outflow from the explosion is highly collimated**
**    ****(jet angle of  2 ****–**** 10 degrees), and has high Lorentz **
**    ****factor (~100).**

## Unsolved Problems

**    ****perhaps in 1 or 2 cases****). And very low density found**
**    ****in several cases is puzzling.**

**5. ****The mechanism for ********-ray generation is poorly known.**

**3.** **The nature of the central engine is not understood****. **

_**Unsolved Problems**_

**2.** **Is the energy from the explosion carried outward**
**    ****by magnetic field, e****±****, or baryonic material?**

**1. What are Short duration GRBs?**

## Future Missions

**30 Mev – 30 Gev & 10 – 40 kev **
**is expected to launch in 2005****. **

**ICECUBE, ANTARES, NESTER will explore **
**Neutrino emission from GRBs:  10 Gev – 10****5****Tev**.

_**AMANDA:**_ at the south pole has an effective area of 10^4 m^2, and its sensitivity is about 3-orders
-       of magnitude below the expected neutrino flux from GRBs (neutrino energy between 100 Tev
- And 10^7 Tev).   Kilometer-cube size detectors are needed to detect neutrinos from GRBs.
_**ICECUBE:**_ is a one-cube-kilometer neutrino observatory being built in the clear deep ice on the
- South Pole.
_**ANTARES:**_  detectors in sea water,  Mediterrarian sea, the expected size is several-cubic-kilometer.
_**NESTER:**_ is also a sea based detector.

_**GLAST:**_ anticipated launch is 2007. It will cover
- Energy range of 10 Kev to 300 Gev. GALST/LAT
- Will have a field of view of 2.5 stradians, and 50 times
- The sensitivity of CGRO/EGRET at 100 Mev and better
- At higher energies; the limiting flux is 10^{-9} photons/cm^2/s.
- It should be able to locate sources to better than 5 arc-min.

_**INTEGRAL:**_ International Gamma-ray Astrophysics Laboratory
- an ESA mission was launched on October 17, 2002 using a Soviet
- proton launcher in a 72 hr orbit. It has instruments covering
- 15 kev to 10 Mev; the mission cost 330M Euros. It will have a
- sensitivity of 10^{-6} photons/cm^2/s in 10-100 kev range for
- an integration time of 10^6 s, & 10^{-7} photons at 10 Mev.
- The imaging instrument has a resolution of 12 arc-minutes.

_**AGILE:**_ is an Italian mission which will have an energy range
- of 30Mev to 50Gev & 10-40 kev with 2 steradian field of
- view. AGILE is a small mission (weighing 80 kg!) which will
- be placed in an equatorial orbit at about 550 km height. The
- X-ray camera (10-40 kev) should have an angular resolution
- Of about 5 arc-min, and the gamma-ray telescope 35 arc-min.
- Sensitivity at 100Mev is expected to be 6x10^{-9} photons/cm^2/s
- for 10^6s integration time, and 4x10^{-11} at 1Gev, and the timing
- accuracy is 25-micro-sec. The spectral resolution in gamma-rays
- is expected to be about 1 i.e. dE/E~1.

_**Future Missions**_

**EGRET energy range was 30Mev to 10Gev**.

**GLAST, due for launch in 2007,**
**will cover 10 Kev – 300 Gev, and**
**detect > 200 GRBs yr****-1****.**

**Gravitational waves from GRBs**?

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## Slide 26

## Slide 27

## Slide 28

## Polarization

_**Granot & Konigl**_** (ApJL, 2003, 594, L83)**
**suggest an ordered magnetic field (part of**
**total B) to explain polarization observations.  **

**Structured jet model**

- Polarization measurement potentially are powerful tool to study jets. However, the we
- have had only limited success in this thus far.
- Observations don’t fit the simplest possible model; and we need either structured jets or
- some ordered magnetic field to fit the polarization data.

## Superluminal motion in GRB 030329 

_**Superluminal motion in GRB 030329 **_
_**(Taylor et al., 2004, 609, L1)**_

-  ≈ 50

_**Solid line**_**:** Spherical outflow in a uniform ISM; E52/n0 =1

_**Dashed line**_: jet model with tj =10 days & E52/n0 =20.

- VLBI observations
- Were carried out
- Between 8.4 and 15.3 GHz.

## GRB light-curves

- _[GRB light-curves](slide3.xml)_

- Fishman & Meegan, 1995 (Ann. Rev. A&A)

- The CGRO was launched in 1991 and removed from orbit on June 4, 2000. It detected a total of 2704 GRBs during the 9 year
-  period. The energy range for COMTEL was 1-30 Mev; EGRET energy range was 20 Mev to 30 Gev. And the  BATSE had

- detectors covering energy range of 25-50 kev, 50-100 kev and 100-300 kev.

## • Duration:   ~ 3s

**•** **Duration:**   ~ **3s**

**•** **Peak of the spectrum (********f********)****:**  **47 kev**

**•** **Flux at the peak:**  ~ **4 mJy**

**•** **Low energy spectral slope (f********):** **0.24 ******** 0.12**

**(Crew et al. 2003)**

## Jet dynamics 

## The Internal-External Fireball Model

_**The Internal-External Fireball Model**_

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

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**context of the collapsar model. **

_**Very Low density and constant **__***n***__** medium**_

**GRBs 990123 & 021211 seem to have gone off in a**
**Low density medium: n******** 10****-2**** cm****-3****.**** A number of **
**different lines of arguments support this conclusion.**

**For instance, at higher densities the RS cooling-******** falls**
**below the optical band shortly after the deceleration**
**time, and the RS emission would have decayed much**
**more rapidly than observed.**

**The density in the CMB appears to be uniform.**

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