An Embedded X-Ray Source Shines through the Aspherical AT 2018cow: Revealing the Inner Workings of the Most Luminous Fast-evolving Optical Transientsстатья

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[1] An embedded x-ray source shines through the aspherical at 2018cow: Revealing the inner workings of the most luminous fast-evolving optical transients / R. Margutti, B. D. Metzger, R. Chornock et al. // Astrophysical Journal. — 2019. — Vol. 872, no. 1. — P. 18. We present the first extensive radio to γ-ray observations of a fast-rising blue optical transient, AT 2018cow, over its first ̃100 days. AT 2018cow rose over a few days to a peak luminosity L pk ̃ 4 × 1044 erg s-1, exceeding that of superluminous supernovae (SNe), before declining as L ∝ t -2. Initial spectra at δt ≲ 15 days were mostly featureless and indicated large expansion velocities v ̃ 0.1c and temperatures reaching T ̃ 3 × 104 K. Later spectra revealed a persistent optically thick photosphere and the emergence of H and He emission features with v ̃ 4000 km s-1 with no evidence for ejecta cooling. Our broadband monitoring revealed a hard X-ray spectral component at E ≥ 10 keV, in addition to luminous and highly variable soft X-rays, with properties unprecedented among astronomical transients. An abrupt change in the X-ray decay rate and variability appears to accompany the change in optical spectral properties. AT 2018cow showed bright radio emission consistent with the interaction of a blast wave with v sh ̃ 0.1c with a dense environment (.{M}̃ {10}-3-{10}-4 {M}☉ {yr}}-1 for v w = 1000 km s-1). While these properties exclude 56Ni-powered transients, our multiwavelength analysis instead indicates that AT 2018cow harbored a “central engine,” either a compact object (magnetar or black hole) or an embedded internal shock produced by interaction with a compact, dense circumstellar medium. The engine released ̃1050-1051.5 erg over ̃103-105 s and resides within low-mass fast-moving material with equatorial-polar density asymmetry (M ej,fast ≲ 0.3 M ☉). Successful SNe from low-mass H-rich stars (like electron-capture SNe) or failed explosions from blue supergiants satisfy these constraints. Intermediate-mass black holes are disfavored by the large environmental density probed by the radio observations. [ DOI ]

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