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Bietenholz M.F.,Hartebeesthoek Radio Observatory | Bietenholz M.F.,York University | Bartel N.,York University | Rupen M.P.,U.S. National Radio Astronomy Observatory
Astrophysical Journal | Year: 2010

We present new Very Long Baseline Interferometry (VLBI) images of supernova (SN) 1986J, taken at 5, 8.4, and 22GHz between t = 22 and 25 yr after the explosion. The shell expands t 0.690.03. We estimate the progenitor's mass-loss rate at (4-10) × 10-5 M ⊙ yr -1 (for v w = 10 km s-1). Two bright spots are seen in the images. The first, in the northeast, is now fading. The second, very near the center of the projected shell and unique to SN 1986J, is still brightening relative to the shell, and now dominates the VLBI images. It is marginally resolved at 22GHz (diameter 0.3 mas; 5 × 1016 cm at 10 Mpc). The integrated VLA spectrum of SN 1986J shows an inversion point and a high-frequency turnover, both progressing downward in frequency and due to the central bright spot. The optically thin spectral index of the central bright spot is indistinguishable from that of the shell. The small proper motion of 1500 1500 km s-1 of the central bright spot is consistent with our previous interpretation of it as being associated with the expected black-hole or neutron-star remnant. Now, an alternate scenario seems also plausible, where the central bright spot, like the northeast one, results when the shock front impacts on a condensation within the circumstellar medium (CSM). The condensation would have to be so dense as to be opaque at cm wavelengths (∼ 103× denser than the average corresponding CSM) and fortuitously close to the center of the projected shell. We include a movie of the evolution of SN 1986J at 5GHz from t = 0 to 25 yr. © 2010. The American Astronomical Society. All rights reserved. Source


Bietenholz M.F.,Hartebeesthoek Radio Observatory | Bietenholz M.F.,York University | Matheson H.,University of Manitoba | Safi-Harb S.,University of Manitoba | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2011

We report on sensitive new 1.4-GHz Very Large Array radio observations of the pulsar wind nebula G21.5-0.9, powered by PSR J1833-1034, and its environs. Our observations were targeted at searching for the radio counterpart of the shell-like structure seen surrounding the pulsar wind nebula in X-rays. Some such radio emission might be expected as the ejecta from the ≲1000yr old supernova expand and interact with the surrounding medium. We find, however, no radio emission from the shell, and can place a conservative 3σ upper limit on its 1-GHz surface brightness of 7 × 10-22Wm-2Hz-1sr-1, comparable to the lowest limits obtained for radio emission from shells around other pulsar wind nebulae. In addition, our wide-field radio image also shows the presence of two extended objects of low surface brightness. We re-examine previous 327-MHz images, on which both the new objects are visible. We identify the first, G21.64-0.84, as a new shell-type supernova remnant, with a diameter of ∼13arcmin and an unusual double-shell structure. The second, G21.45-0.59, ∼1arcmin in diameter, is likely an Hii region. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS. Source


Milisavljevic D.,Harvard - Smithsonian Center for Astrophysics | Margutti R.,Harvard - Smithsonian Center for Astrophysics | Kamble A.,Harvard - Smithsonian Center for Astrophysics | Patnaude D.J.,Harvard - Smithsonian Center for Astrophysics | And 19 more authors.
Astrophysical Journal | Year: 2015

We present optical observations of supernova SN 2014C, which underwent an unprecedented slow metamorphosis from H-poor type Ib to H-rich type IIn over the course of one year. The observed spectroscopic evolution is consistent with the supernova having exploded in a cavity before encountering a massive shell of the progenitor star's stripped hydrogen envelope. Possible origins for the circumstellar shell include a brief Wolf-Rayet fast wind phase that overtook a slower red supergiant wind, eruptive ejection, or confinement of circumstellar material by external influences of neighboring stars. An extended high velocity Hα absorption feature seen in near-maximum light spectra implies that the progenitor star was not completely stripped of hydrogen at the time of core collapse. Archival pre-explosion Subaru Telescope Suprime-Cam and Hubble Space Telescope Wide Field Planetary Camera 2 images of the region obtained in 2009 show a coincident source that is most likely a compact massive star cluster in NGC 7331 that hosted the progenitor system. By comparing the emission properties of the source with stellar population models that incorporate interacting binary stars we estimate the age of the host cluster to be 30-300 Myr, and favor ages closer to 30 Myr in light of relatively strong Hα emission. SN 2014C is the best observed member of a class of core-collapse supernovae that fill the gap between events that interact strongly with dense, nearby environments immediately after explosion and those that never show signs of interaction. Better understanding of the frequency and nature of this intermediate population can contribute valuable information about the poorly understood final stages of stellar evolution. © 2015. The American Astronomical Society. All rights reserved. Source


Soderberg A.M.,Harvard - Smithsonian Center for Astrophysics | Brunthaler A.,Max Planck Institute for Radio Astronomy | Nakar E.,Tel Aviv University | Chevalier R.A.,University of Virginia | And 2 more authors.
Astrophysical Journal | Year: 2010

We present extensive radio and X-ray observations of the nearby Type Ic SN 2007gr in NGC 1058 obtained with the Very Large Array (VLA) and the Chandra X-ray Observatory and spanning 5 to 150 days after explosion. Through our detailed modeling of these data, we estimate the properties of the blast wave and the circumstellar environment. We find evidence for a freely expanding and non-relativistic explosion with an average blast wave velocity, v̄ ≈ 0.2c, and a total internal energy for the radio emitting material of E ≈ 2 ×1046 erg assuming equipartition of energy between electrons and magnetic fields (εe = εB = 0.1). The temporal and spectral evolution of the radio emission points to a stellar wind-blown environment shaped by a steady progenitor mass loss rate of Ṁ ≈ 6×10-7M⊙ yr-1 (wind velocity, v w = 103 km s-1). These parameters are fully consistent with those inferred for other SNe Ibc and are in line with the expectations for an ordinary, homologous SN explosion. Our results are at odds with those of Paragi et al. who recently reported evidence for a relativistic blast wave in SN 2007gr based on their claim that the radio emission was resolved away in a low signal-to-noise Very Long Baseline Interferometry (VLBI) observation. Here we show that the exotic physical scenarios required to explain the claimed relativistic velocity-extreme departures from equipartition and/or a highly collimated outflow-are excluded by our detailed VLA radio observations. Moreover, we present an independent analysis of the VLBI data and propose that a modest lossof phase coherence provides a more natural explanation for the apparent flux density loss which is evident on both short and long baselines. We conclude that SN 2007gr is an ordinary Type Ibc supernova. © 2010. The American Astronomical Society. Source


Kamble A.,Harvard - Smithsonian Center for Astrophysics | Margutti R.,Harvard - Smithsonian Center for Astrophysics | Soderberg A.M.,Harvard - Smithsonian Center for Astrophysics | Chakraborti S.,Harvard - Smithsonian Center for Astrophysics | And 7 more authors.
Astrophysical Journal | Year: 2016

We present radio and X-ray observations of the nearby SN IIb 2013df in NGC 4414 from 10 to 250 days after the explosion. The radio emission showed a peculiar steep-to-shallow spectral evolution. We present a model in which inverse Compton cooling of synchrotron emitting electrons can account for the observed spectral and light curve evolution. A significant mass-loss rate, - M 8 10 M 5 yr-1 for a wind velocity of 10 km s-1, is estimated from the detailed modeling of radio and X-ray emission, which are primarily due to synchrotron and bremsstrahlung, respectively. We show that SN 2013df is similar to SN 1993J in various ways. The shock wave speed of SN 2013df was found to be average among the radio supernovae; vsh c ∼ 0.07. We did not find any significant deviation from smooth decline in the light curve of SN 2013df. One of the main results of our self-consistent multiband modeling is the significant deviation from energy equipartition between magnetic fields and relativistic electrons behind the shock. We estimate∈e = 200∈ B. In general for SNe IIb, we find that the presence of bright optical cooling envelope emission is linked with freefree radio absorption and bright thermal X-ray emission. This finding suggests that more extended progenitors, similar to that of SN 2013df, suffer from substantial mass loss in the years before the supernova. © 2016. The American Astronomical Society. All rights reserved. Source

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