Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userEVLA Observations of the Radio Evolution of SN 2011dh
345
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We report on Expanded Very Large Array (EVLA) observations of the Type IIb supernova 2011dh, performed over the first 100 days of its evolution and spanning 1-40 GHz in frequency. The radio emission is well-described by the self-similar propagation of a spherical shockwave, generated as the supernova ejecta interact with the local circumstellar environment. Modeling this emission with a standard synchrotron self-absorption (SSA) model gives an average expansion velocity of v approx 0.1c, supporting the classification of the progenitor as a compact star (R_* approx 10^11 cm). We find that the circumstellar density is consistent with a {rho} propto r^-2 profile. We determine that the progenitor shed mass at a constant rate of approx 3 times 10^-5 M_odot / yr, assuming a wind velocity of 1000 km / s (values appropriate for a Wolf-Rayet star), or approx 7 times 10^-7 M_odot / yr assuming 20 km / s (appropriate for a yellow supergiant [YSG] star). Both values of the mass-loss rate assume a converted fraction of kinetic to magnetic energy density of {epsilon}_B = 0.1. Although optical imaging shows the presence of a YSG, the rapid optical evolution and fast expansion argue that the progenitor is a more compact star - perhaps a companion to the YSG. Furthermore, the excellent agreement of the radio properties of SN 2011dh with the SSA model implies that any YSG companion is likely in a wide, non-interacting orbit.
rate research
Read More
We present late time, low frequency observations of SN 2011dh made using the Giant Metrewave Radio Telescope (GMRT). Our observations at $325 rm MHz$, $610 rm MHz$ and $1280 rm MHz$ conducted between $93-421 rm days$ after the explosion supplement the millimeter and centimeter wave observations conducted between $4-15 rm days$ after explosion using the Combined Array for Research in Millimeter-wave Astronomy (CARMA) and extensive radio observations ($ 1.0-36.5 rm GHz$) conducted between $16-93 rm days$ after explosion using Jansky Very Large Array (JVLA). We fit a synchrotron self absorption model (SSA) to the $610 rm MHz$ and $1280 rm MHz$ radio light curves. We use it to determine the radius ($R_{rm p}$) and magnetic field ($B_{rm p}$) at $173$ & $323$ days after the explosion. A comparison of the peak radio luminosity $L_{rm op}$, with the product of the peak frequency $ u_{rm p}$ and time to peak $t_{rm p}$ shows that the supernova evolves between the epochs of CARMA, JVLA and GMRT observations. It shows a general slowing down of the expansion speed of the radio emitting region on a timescale of several hundred days during which the shock is propagating through a circumstellar medium set up by a wind with a constant mass loss parameter, $dot M/v_{rm w}$. We derive the mass loss parameter ($A_{star}$) based on $610 rm MHz$ and $1280 rm MHz$ radio light curves, which are found to be consistent with each other within error limits.
We present optical and near-infrared (NIR) photometry and spectroscopy of the Type IIb supernova (SN) 2011dh for the first 100 days. We complement our extensive dataset with SWIFT ultra-violet (UV) and Spitzer mid-infrared (MIR) data to build a UV to MIR bolometric lightcurve using both photometric and spectroscopic data. Hydrodynamical modelling of the SN based on this bolometric lightcurve have been presented in Bersten (2012). We find that the absorption minimum for the hydrogen lines is never seen below ~11000 km/s but approaches this value as the lines get weaker. This suggests that the interface between the helium core and hydrogen rich envelope is located near this velocity in agreement with the Bersten et al. (2012) He4R270 ejecta model. Spectral modelling of the hydrogen lines using this ejecta model supports the conclusion and we find a hydrogen mass of 0.01-0.04 solar masses to be consistent with the observed spectral evolution. We estimate that the photosphere reaches the helium core at 5-7 days whereas the helium lines appear between ~10 and ~15 days, close to the photosphere and then move outward in velocity until ~40 days. This suggests that increasing non-thermal excitation due to decreasing optical depth for the gamma-rays is driving the early evolution of these lines. We also provide and discuss pre- and post-explosion observations of the SN site which shows a reduction by 75 percent in flux at the position of the yellow supergiant coincident with SN 2011dh. The B, V and r band decline rates of 0.0073, 0.0090 and 0.0053 mag/day respectively are consistent with the remaining flux being emitted by the SN. Hence we find that the star was indeed the progenitor of SN 2011dh as previously suggested by Maund et al. (2011) and which is also consistent with the results from the hydrodynamical modelling.
We report on third epoch VLBI observations of the radio-bright supernova SN 2011dh located in the nearby (7.8 Mpc) galaxy M51. The observations took place at $t=453$ d after the explosion and at a frequency of 8.4 GHz. We obtained a fairly well resolved image of the shell of SN 2011dh, making it one of only six recent supernovae for which resolved images of the ejecta are available. SN 2011dh has a relatively clear shell morphology, being almost circular in outline, although there may be some asymmetry in brightness around the ridge. By fitting a spherical shell model directly to the visibility measurements we determine the angular radius of SN 2011dhs radio emission to be $636 pm 29$ $mu$as. At a distance of 7.8 Mpc, this angular radius corresponds to a linear radius of $(7.4 pm 0.3) times 10^{16}$ cm and an average expansion velocity since the explosion of $19000^{+2800}_{-2400}$ kms$^{-1}$. We combine our VLBI measurements of SN 2011dhs radius with values determined from the radio spectral energy distribution under the assumption of a synchrotron-self-absorbed spectrum, and find all the radii are consistent with a power-law evolution, with $R sim t^{0.97pm0.01}$, implying almost free expansion over the period $t=4$ d to 453 d.
We present radio light curves and spectra of the classical nova V1723 Aql obtained with the Expanded Very Large Array (EVLA). This is the first paper to showcase results from the EVLA Nova Project, which comprises a team of observers and theorists utilizing the greatly enhanced sensitivity and frequency coverage of EVLA radio observations, along with observations at other wavelengths, to reach a deeper understanding of the energetics, morphology, and temporal characteristics of nova explosions. Our observations of V1723 Aql span 1-37 GHz in frequency, and we report on data from 14-175 days following the time of the nova explosion. The broad frequency coverage and frequent monitoring show that the radio behavior of V1723 Aql does not follow the classic Hubble-flow model of homologous spherically expanding thermal ejecta. The spectra are always at least partially optically thin, and the flux rises on faster timescales than can be reproduced with linear expansion. Therefore, any description of the underlying physical processes must go beyond this simple picture. The unusual spectral properties and light curve evolution might be explained by multiple emitting regions or shocked material. Indeed, X-ray observations from Swift reveal that shocks are likely present.
We present the results of observations of the radio emission from Supernova 2001gd in NGC 5033 from 2002 February 8 through 2006 September 25. The data were obtained using the Very Large Array at wavelengths of 1.3 cm (22.4 GHz), 2 cm (14.9 GHz), 3.6 cm (8.4 GHz), 6 cm (4.9 GHz), and 20 cm (1.5 GHz), with one upper limit at 90 cm (0.3 GHz). In addition, one detection has been provided by the Giant Metrewave Radio Telescope at 21 cm (1.4 GHz). SN 2001gd was discovered in the optical well past maximum light, so that it was not possible to obtain many of the early radio turn-on measurements which are important for estimating the local circumstellar medium (CSM) properties. Only at 20 cm were turn-on data available. However, our analysis and fitting of the radio light curves, and the assumption that the Type IIb SN 2001gd resembles the much better studied Type IIb SN 1993J, enables us to describe the radio evolution as being very regular through day ~550 and consistent with a nonthermal-emitting model with a thermal absorbing CSM. The presence of synchrotron-self absorption (SSA) at early times is implied by the data, but determination of the exact relationship between the SSA component from the emitting region and the free-free absorption component from the CSM is not possible as there are insufficient early measurements to distinguish between models. After day ~550, the radio emission exhibits a dramatically steeper decline rate which, assuming similarity to SN 1993J, can be described as an exponential decrease with an e-folding time of 500 days. We interpret this abrupt change in the radio flux density decline rate as implying a transition of the shock front into a more tenuous region of circumstellar material. A similar change in radio evolution has been seen earlier in other SNe such as SN 1988Z, SN 1980K, and SN 1993J.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
