| 1. |
- Chakraborti, Sayan, et al.
(författare)
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A MISSING-LINK IN THE SUPERNOVA-GRB CONNECTION : THE CASE OF SN 2012ap
- 2015
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 805:2
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Tidskriftsartikel (refereegranskat)abstract
- Gamma-ray bursts (GRBs) are characterized by ultra-relativistic outflows, while supernovae are generally characterized by non-relativistic ejecta. GRB afterglows decelerate rapidly, usually within days, because their low-mass ejecta rapidly sweep up a comparatively larger mass of circumstellar material. However, supernovae with heavy ejecta can be in nearly free expansion for centuries. Supernovae were thought to have non-relativistic outflows except for a few relativistic ones accompanied by GRBs. This clear division was blurred by SN 2009bb, the first supernova with a relativistic outflow without an observed GRB. However, the ejecta from SN 2009bb was baryon loaded and in nearly free expansion for a year, unlike GRBs. We report the first supernova discovered without a GRB but with rapidly decelerating mildly relativistic ejecta, SN 2012ap. We discovered a bright and rapidly evolving radio counterpart driven by the circumstellar interaction of the relativistic ejecta. However, we did not find any coincident GRB with an isotropic fluence of more than one-sixth of the fluence from GRB 980425. This shows for the first time that central engines in SNe Ic, even without an observed GRB, can produce both relativistic and rapidly decelerating outflows like GRBs.
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| 2. |
- Chandra, Poonam, et al.
(författare)
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Type Ib Supernova Master OT J120451.50+265946.6 : Radio-emitting Shock with Inhomogeneities Crossing through a Dense Shell
- 2019
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 877:2
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Tidskriftsartikel (refereegranskat)abstract
- We present radio observations of Type Ib supernova (SN) Master OT J120451.50+265946.6. Our low-frequency Giant Metrewave Radio Telescope (GMRT) data, taken when the SN was in the optically thick phase for observed frequencies, reveal inhomogeneities in the structure of the radio-emitting region. The high-frequency Karl G. Jansky Very Large Array data indicate that the shock is crossing through a dense shell between similar to 47 and similar to 87 days. The data >= 100 days onward are reasonably well fit with the inhomogeneous synchrotron self-absorption model. Our model predicts that the inhomogeneities should smooth out at late times. Low-frequency GMRT observations at late epochs will test this prediction. Our findings suggest the importance of obtaining well-sampled wide-band radio data in order to understand the intricate nature of the radio emission from young supernovae.
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| 3. |
- Nayana, A. J., et al.
(författare)
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Long-term Behavior of a Type IIP Supernova SN 2004dj in the Radio Bands
- 2018
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 863:2
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Tidskriftsartikel (refereegranskat)abstract
- We present radio observations and modeling of one of the nearest and brightest Type IIP supernova SN 2004dj exploded in the galaxy NGC 2403 at a distance of similar to 3.5 Mpc. Our observations span a wide frequency and temporal range of 0.24-43 GHz and similar to 1 day to 12 years since the discovery. We model the radio light curves and spectra with the synchrotron emission. We estimate the mass-loss rate of the progenitor star to be (M)over dot similar to 1 x 10(-6) M-circle dot yr(-1) for a wind speed of 10 km s(-1). We calculate the radio spectral indices using 1.06, 1.40, 5.00, and 8.46 GHz flux density measurements at multiple epochs. We witness steepening in the spectral index values for an extended period predominantly at higher frequencies. We explain this as a signature of electron cooling happening at the supernova shock in the plateau phase of the supernova. We estimate the cooling timescales for inverse Compton cooling and synchrotron cooling and find that inverse Compton cooling is the dominant cooling process.
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