Abstract We present a population of 19 radio-luminous supernovae (SNe) with emission reaching L ν ∼ 10 26 –10 29 erg s −1 Hz −1 in the first epoch of the Very Large Array Sky Survey (VLASS) at 2–4 GHz. Our sample includes one long gamma-ray burst, SN 2017iuk/GRB 171205A, and 18 core-collapse SNe detected at ≈1–60 yr after explosion. No thermonuclear explosion shows evidence for bright radio emission, and hydrogen-poor progenitors dominate the subsample of core-collapse events with spectroscopic classification at the time of explosion (79%). We interpret these findings in the context of the expected radio emission from the forward shock interaction with the circumstellar medium (CSM). We conclude that these observations require a departure from the single wind–like density profile (i.e., ρ CSM ∝ r −2 ) that is expected around massive stars and/or from a spherical Newtonian shock. Viable alternatives include the shock interaction with a detached, dense shell of CSM formed by a large effective progenitor mass-loss rate, M ̇ ∼ 10 − 4 – 10 − 1 M ⊙ yr −1 (for an assumed wind velocity of 1000 km s −1 ); emission from an off-axis relativistic jet entering our line of sight; ormore »
A flat-spectrum flare in S4 0444+63 revealed by a new implementation of multiwavelength single-dish observations
Relativistic amplification boosts the contribution of the jet base to the total emission in blazars, thus making single-dish observations useful and practical to characterize their physical state, particularly during episodes of enhanced multiwavelength activity. Following the detection of a new gamma-ray source by Fermi-LAT in 2017 July, we observed S4 0444+63 in order to secure its identification as a gamma-ray blazar. We conducted observations with the Medicina and Noto radio telescopes at 5, 8, and 24 GHz for a total of 12 epochs between 2017 August 1 and 2018 September 22. We carried out the observations with on-the-fly cross-scans and reduced the data with our newly developed Cross-scan Analysis Pipeline, which we present here in detail for the first time. We found the source to be in an elevated state of emission at radio wavelength, compared to historical values, which lasted for several months. The maximum luminosity was reached on 2018 May 16 at 24 GHz, with $L_{24}=(1.7\pm 0.3)\times 10^{27}\ \mathrm{W\, Hz}^{-1}$; the spectral index was found to evolve from slightly rising to slightly steep. Besides the new observations, which have proved to be an effective and efficient tool to secure the identification of the source, additional single dish and very long more »
- Publication Date:
- NSF-PAR ID:
- 10131401
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 492
- Issue:
- 2
- Page Range or eLocation-ID:
- p. 2807-2817
- ISSN:
- 0035-8711
- Publisher:
- Oxford University Press
- Sponsoring Org:
- National Science Foundation
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