# Presentation: 154984

## Unusual Behavior in Radio Supernovae

- Poonam Chandra

- Jansky Fellow, National Radio Astronomy Observatory
- Astronomy Department , University of Virginia

## SN 1993J

- Unusually well understood

## SN 1993J: Why so special???

-  Exploded just 3 Mpc away, extremely bright
-  First clear case of transition between supernova Type IIP to Ib.
-  Was detected in X-rays and Radio bands just 5 days after the explosion.
-  Maund et al (2004) detected unambiguously the signature of the massive binary companion in HST observations, 10 years after the explosion.
-  Excellent VLBI measurements, Radio emitting zone  resolved.

## Still lot more to learn from SN 1993J

## ?

- Radio emission in a supernova arises due to synchrotron emission, which arises by the
_**ACCELERATION  OF ELECTRONS**_
-  in  presence of an
_**ENHANCED MAGNETIC FIELD**_.

**?**
**?**

## Radio data: 

- We found synchrotron cooling break in combined  GMRT and VLA  _**(0.2 GHz to 44 GHz)**_ near simultaneous observations on day 3200.

## On Day 3200...... GMRT+VLA spectrum

- Synchrotron cooling break at **4 GHz**

- Chandra, P. et al. 2004

## Is synchrotron cooling break real?

- Unsettled Issue!!!

## Observations of SN 1993J on Day 3770

| Date of observation | Frequency GHz | Flux density mJy |
| --- | --- | --- |
| June 17, 03 | 0.239 | 58.2 ± 11.0 |
| June 17, 03 | 0.619 | 33.4± 4.3 |
| June 13, 03 | 1.280 | 20.2± 2.1 |
| June 26, 03 | 4.885 | 8.35 ± 0.42 |
| June 26, 03 | 14.940 | 0.98 ± 0.32 |
| June 26, 03 | 22.485 | 0.82 ± 0.27 |

- But on day 3770..............

- GMRT

- VLA

## 1.5 years later.............  ~Day 3750

## We predicted the evolution of break frequency with roughly 1.2 GHz per year. Our shift in the synchrotron cooling frequency is consistent with this calculation.

- (PC, Ray, Bhatnagar, 2004)

## F=

******1****=**** ********2****=**** ********3**

******1****<**** ********2****<**** ********3**

## On Day 3200...... GMRT+VLA spectrum

- Chandra, P. et al. 2004

## 1.5 years later.............  ~Day 3750

## Synchrotron Aging in SN 1993J

** **Synchrotron losses
-  Adiabatic expansion
-  Diffusive Fermi acceleration

**Energy losses due to adiabatic expansion**

- Ejecta velocity
- Size of the SN

## Energy gain due to diffusive Fermi acceleration 

- Upstream velocity
- Downstream velocity
- Spatial diffusion coefficient of the test particles across ambient magnetic field
- Particle velocity

**Energy gain due to diffusive Fermi acceleration**** **

## For

- and

**Break frequency**** **

- .
- .

- (Fransson & Bjornsson, 1998, ApJ, 509, 861)

## B=330 mG

**B=330 mG**

- On day 3770
**B=280 mG**

- Magnetic Field follows 1/t decline trend

## ISM magnetic field is few microGauss. Shock wave will compress magnetic field at most by a factor of 4, still few 10s of microGauss. Hence magnetic field inside the forward shock is highly enhanced, most probably due to instabilities

- ISM magnetic field is few microGauss. Shock wave will compress magnetic field at most by a factor of 4, still few 10s of microGauss. Hence** magnetic field inside the forward shock is highly enhanced**, most probably due to instabilities

- Equipartition magnetic field is 10 times smaller than actual B, hence magnetic energy density is 4 order of magnitude higher than relativistic energy density

## Acceleration diffusion constant 

- .

- Acceleration diffusion constant

- Ball & Kirk 1992

## For SN 1987A 

- For SN 1987A

- cm2 sec-1

- cm2 sec-1

- Scaled value of diffusion coefficient for 1993J

- (Ball & Kirk, 1992, ApJL)

## R=2.65 x 1017 cm

- on day 3200
- R=2.65 x 1017 cm
- On day 3770
- R=3.8 x 1017 cm

- break(3200)=4 GHz
- break(3770)=4 GHz

## Diffusion acceleration coefficient

- =(5.3 +/- 3.0) x 1024 cm2 s-1

## First time direct measurement of

- ENHANCED MAGNETIC FIELD
- and
- ACCELERATION DIFFUSION COEFFICIENT
- responsible for **radio emission**
- by observing the synchrotron cooling break and its evolution with time

- Result:

## Radio Emission in a Supernova

- Radio emission in a supernova arises due to synchrotron emission, which arises by the
_**ACCELERATION  OF ELECTRONS**_
-  in  presence of an
_**ENHANCED MAGNETIC FIELD**_.

## Chris Stockdale: Marquette Univ. Alak Ray: TIFR, Mumbai, India 

- Kurt Weiler: NRL, Washington
- Chris Stockdale: Marquette Univ. Alak Ray: TIFR, Mumbai, India
- Roger Chevalier: Univ Virginia
- Juan Uson: NRAO, Charlottesville

## Thanks