X-ray and radio prompt emission from a hypernova SN 2002ap

Here we report on combined X-ray and radio observations of SN 2002ap with XMM-Newton ToO observation and GMRT observations aided with VLA published results. In deriving the X-ray flux of SN 2002ap we account for the contribution of a nearby source, found to be present in the pre-SN explosion images obtained with Chandra observatory. We also derive upper limits on mass loss rate from X-ray and radio data. We suggest that the prompt X-ray emission is non-thermal in nature and its is due to the repeated compton boosting of optical photons. We also compare SN's early radiospheric properties with two other SNe at the same epoch.Comment: 4 pages, 5 figures. Uses espcrc2.sty. To appear in proceedings of symposium on X-ray astronomy "The Restless High-Energy Universe", May 2003, Amsterdam, The Netherlands, eds. E.P.J. van den Heuvel, J.J.M. in 't Zand, and R.A.M.J. Wijer

The late time radio emission from SN 1993J at meter wavelengths

We present the investigations of SN 1993J using low frequency observations with the Giant Meterwave Radio Telescope. We analyze the light curves of SN 1993J at 1420, 610, 325 and 243 MHz during $7.5-10$ years since explosion.The supernova has become optically thin early on in the 1420 MHz and 610 MHz bands while it has only recently entered the optically thin phase in the 325 MHz band. The radio light curve in the 235 MHz band is more or less flat. This indicates that the supernova is undergoing a transition from an optically thick to optically thin limit in this frequency band. In addition, we analyze the SN radio spectra at five epochs on day 3000, 3200, 3266, 3460 and 3730 since explosion. Day 3200 spectrum shows a synchrotron cooling break. SN 1993J is the only young supernova for which the magnetic field and the size of the radio emitting region are determined through unrelated methods. Thus the mechanism that controls the evolution of the radio spectra can be identified. We suggest that at all epochs, the synchrotron self absorption mechanism is primarily responsible for the turn-over in the spectra. Light curve models based on free free absorption in homogeneous or inhomogeneous media at high frequencies overpredict the flux densities at low frequencies. The discrepancy is increasingly larger at lower and lower frequencies. We suggest that an extra opacity, sensitively dependent on frequency, is likely to account for the difference at lower frequencies. The evolution of the magnetic field (determined from synchrotron self absorption turn-over) is roughly consistent with $B \propto t^{-1}$. Radio spectral index in the optically thin part evolves from $\alpha \sim 0.8-1.0$ at few tens of days to $\sim 0.6$ in about 10 years.Comment: 37 pages, 9 figures in LaTex; scheduled for ApJ 10 September 2004, v612 issue; send comments to: [email protected]

Synchrotron aging and the radio spectrum of SN 1993J

We combine the GMRT low frequency radio observations of SN 1993J with the VLA high frequency radio data to get a near simultaneous spectrum around day 3200 since explosion. The low frequency measurements of the supernova determine the turnover frequency and flux scale of the composite spectrum and help reveal a steepening in the spectral index, $\Delta \alpha \sim 0.6$, in the optically thin part of the spectrum. This is the first observational evidence of a break in the radio spectrum of a young supernova. We associate this break with the phenomenon of synchrotron aging of radiating electrons. From the break in the spectrum we calculate the magnetic field in the shocked region independent of the equipartition assumption between energy density of relativistic particles and magnetic energy density. We determine the ratio of these two energy densities and find that this ratio is in the range: $8\times 10^{-6}-5\times 10^{-4}$. We also predict the nature of the evolution of the synchrotron break frequency with time, with competing effects due to diffusive Fermi acceleration and adiabatic expansion of the radiative electron plasma.Comment: 12 pages, 2 figures. Accepted for publication in ApJ

Analytical and numerical investigation of escape rate for a noise driven bath

We consider a system-reservoir model where the reservoir is modulated by an external noise. Both the internal noise of the reservoir and the external noise are stationary, Gaussian and are characterized by arbitrary decaying correlation functions. Based on a relation between the dissipation of the system and the response function of the reservoir driven by external noise we numerically examine the model using a full bistable potential to show that one can recover the turn-over features of the usual Kramers' dynamics when the external noise modulates the reservoir rather than the system directly. We derive the generalized Kramers' rate for this nonequilibrium open system. The theoretical results are verified by numerical simulation.Comment: Revtex, 25 pages, 5 figures. To appear in Phys. Rev.

Environment-induced dynamical chaos

We examine the interplay of nonlinearity of a dynamical system and thermal fluctuation of its environment in the ``physical limit'' of small damping and slow diffusion in a semiclassical context and show that the trajectories of c-number variables exhibit dynamical chaos due to the thermal fluctuations of the bath.Comment: Revtex, 4 pages and 4 figure

Fluctuation-dissipation relationship in chaotic dynamics

We consider a general N-degree-of-freedom dissipative system which admits of chaotic behaviour. Based on a Fokker-Planck description associated with the dynamics we establish that the drift and the diffusion coefficients can be related through a set of stochastic parameters which characterize the steady state of the dynamical system in a way similar to fluctuation-dissipation relation in non-equilibrium statistical mechanics. The proposed relationship is verified by numerical experiments on a driven double well system.Comment: Revtex, 23 pages, 2 figure

The noise properties of stochastic processes and entropy production

Based on a Fokker-Planck description of external Ornstein-Uhlenbeck noise and cross-correlated noise processes driving a dynamical system we examine the interplay of the properties of noise processes and the dissipative characteristic of the dynamical system in the steady state entropy production and flux. Our analysis is illustrated with appropriate examples.Comment: RevTex, 1 figure, To appear in Phys. Rev.

Chandra's tryst with SN 1995N

We present the spectroscopic and imaging analysis of a type IIn supernova SN 1995N observed with the Chandra X-ray observatory on 2004 March 27. We compare the spectrum obtained from our Chandra observation with that of the previous observation with ASCA in 1998. We find the presence of Neon lines in the Chandra spectrum that were not reported in the ASCA observation. We see no evidence of Iron in both epochs. The observed absorption column depth indicates an extra component over and above the galactic absorption component and is possibly due to a cool dense shell between the reverse-shock and the contact discontinuity in the ejecta. The ASCA and the ROSAT observations suggested a non-linear behavior of the X-ray light curve. However, with the higher spatial resolution and sensitivity of Chandra, we separate out many nearby sources in the supernova field-of-view that had additionally contributed to the supernova flux due to the large Point Spread Function of the ASCA. Taking out the contribution of those nearby sources, we find that the light curves are consistent with a linear decline profile. We consider the light curve in the high energy band separately. We discuss our results in the context of models of nucleosynthesis and the interaction of the shock waves with the circumstellar medium in core collapse supernovae.Comment: 35 pages, 12 figures, accepted for publication in Astrophysical Journa