22 nd February 2007 Poonam Chandra Unusual Behavior in Radio Supernovae Poonam Chandra Jansky Fellow, National Radio Astronomy Observatory Astronomy Department, University of Virginia

22 nd February 2007 Poonam Chandra SN 1993J Unusually well understood

22 nd February 2007 Poonam Chandra 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.

22 nd February 2007 Poonam Chandra Still lot more to learn from SN 1993J My talk is based on the new surprises, it is offering to us

22 nd February 2007 Poonam Chandra 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 ENHANCED MAGNETIC FIELD. ????

22 nd February 2007 Poonam Chandra Radio data: We found synchrotron cooling break in combined GMRT and VLA (0.2 GHz to 44 GHz) near simultaneous observations on day 3200.

22 nd February 2007 Poonam Chandra On Day 3200…… GMRT+VLA spectrum GMRT VLA Synchrotron cooling break at 4 GHz Chandra, P. et al. 2004

22 nd February 2007 Poonam Chandra Is synchrotron cooling break real? Unsettled Issue!!!

22 nd February 2007 Poonam Chandra Observations of SN 1993J on Day 3770 Date of observation Frequency GHzFlux density mJy June 17, ± 11.0 June 17, ± 4.3 June 13, ± 2.1 June 26, ± 0.42 June 26, ± 0.32 June 26, ± 0.27 But on day 3770………….. GMRT VLA

22 nd February 2007 Poonam Chandra 1.5 years later…………. ~Day 3750 Synchrotron cooling break at ~ 5.5 GHz GMRT VLA

22 nd February 2007 Poonam Chandra 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)

22 nd February 2007 Poonam Chandra F =  Frequency Flux Density 1= 2= 31= 2= 3 11 22 33 1< 2< 31< 2< 3 22 3 3 11

22 nd February 2007 Poonam Chandra On Day 3200…… GMRT+VLA spectrum GMRT VLA Chandra, P. et al. 2004

22 nd February 2007 Poonam Chandra 1.5 years later…………. ~Day 3750 GMRT VLA

22 nd February 2007 Poonam Chandra Synchrotron Aging in SN 1993J Synchrotron losses Adiabatic expansion Diffusive Fermi acceleration Energy losses due to adiabatic expansion Ejecta velocity Size of the SN

22 nd February 2007 Poonam Chandra Upstream velocity Downstream velocity Spatial diffusion coefficient of the test particles across ambient magnetic field Particle velocity Energy gain due to diffusive Fermi acceleration

22 nd February 2007 Poonam Chandra Forand Break frequency (Fransson & Bjornsson, 1998, ApJ, 509, 861)

22 nd February 2007 Poonam Chandra On day 3200 B=330 mG On day 3770 B=280 mG Magnetic Field follows 1/t decline trend

22 nd February 2007 Poonam Chandra 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

22 nd February 2007 Poonam Chandra Acceleration diffusion constant Ball & Kirk 1992

22 nd February 2007 Poonam Chandra For SN 1987A cm 2 sec -1 Scaled value of diffusion coefficient for 1993J (Ball & Kirk, 1992, ApJL)

22 nd February 2007 Poonam Chandra From VLBI (Bartel, 2002, ApJ), on day 3200 R=2.65 x cm On day 3770 R=3.8 x cm break (3200)=4 GHz break (3770)=5.5 GHz

22 nd February 2007 Poonam Chandra Diffusion acceleration coefficient  =(5.3 +/- 3.0) x cm 2 s -1

22 nd February 2007 Poonam Chandra 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:

22 nd February 2007 Poonam Chandra 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 ENHANCED MAGNETIC FIELD. Take it with caution!!!! We need at least 4-5 simultaneous datasets showing the synchrotron cooling break to feel more confident!!!

22 nd February 2007 Poonam Chandra Thanks to: Kurt Weiler: NRL, Washington Chris Stockdale: Marquette Univ. Alak Ray: TIFR, Mumbai, India Roger Chevalier: Univ Virginia Juan Uson: NRAO, Charlottesville

22 nd February 2007 Poonam Chandra Thanks