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, I. Vurm, N. Roth, B. W. Grefenstette, V. Savchenko, R. Cartier, J. F. Steiner, G. Terreran, B. Margalit, G. Migliori, D. Milisavljevic, K. D. Alexander, M. Bietenholz, P. K. Blanchard, E. Bozzo, D. Brethauer, I. V. Chilingarian, D. L. Coppejans & 25 others L. Ducci, C. Ferrigno, W. Fong, D. Götz, C. Guidorzi, A. Hajela, K. Hurley, E. Kuulkers, P. Laurent, S. Mereghetti, M. Nicholl, D. Patnaude, P. Ubertini, J. Banovetz, N. Bartel, E. Berger, E. R. Coughlin, T. Eftekhari, D. D. Frederiks, A. V. Kozlova, T. Laskar, D. S. Svinkin, M. R. Drout, A. Macfadyen, K. Paterson

Research output: Contribution to journalArticle

Abstract

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 lesssim 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 ($\dot{M}\sim {10}^{-3}-{10}^{-4}\,{M}_{\odot }{\mathrm{yr}}^{-1}$ 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 lesssim 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.
LanguageEnglish
Pages18
Number of pages32
JournalAstrophysical Journal
Volume872
Issue number1
DOIs
StatusPublished - 6 Feb 2019

Cite this

An Embedded X-Ray Source Shines through the Aspherical AT 2018cow: Revealing the Inner Workings of the Most Luminous Fast-evolving Optical Transients. / Margutti, R.; Metzger, B. D.; Chornock, R.; Vurm, I.; Roth, N.; Grefenstette, B. W.; Savchenko, V.; Cartier, R.; Steiner, J. F.; Terreran, G.; Margalit, B.; Migliori, G.; Milisavljevic, D.; Alexander, K. D.; Bietenholz, M.; Blanchard, P. K.; Bozzo, E.; Brethauer, D.; Chilingarian, I. V.; Coppejans, D. L.; Ducci, L.; Ferrigno, C.; Fong, W.; Götz, D.; Guidorzi, C.; Hajela, A.; Hurley, K.; Kuulkers, E.; Laurent, P.; Mereghetti, S.; Nicholl, M.; Patnaude, D.; Ubertini, P.; Banovetz, J.; Bartel, N.; Berger, E.; Coughlin, E. R.; Eftekhari, T.; Frederiks, D. D.; Kozlova, A. V.; Laskar, T.; Svinkin, D. S.; Drout, M. R.; Macfadyen, A.; Paterson, K.

In: Astrophysical Journal, Vol. 872, No. 1, 06.02.2019, p. 18.

Research output: Contribution to journalArticle

Margutti, R, Metzger, BD, Chornock, R, Vurm, I, Roth, N, Grefenstette, BW, Savchenko, V, Cartier, R, Steiner, JF, Terreran, G, Margalit, B, Migliori, G, Milisavljevic, D, Alexander, KD, Bietenholz, M, Blanchard, PK, Bozzo, E, Brethauer, D, Chilingarian, IV, Coppejans, DL, Ducci, L, Ferrigno, C, Fong, W, Götz, D, Guidorzi, C, Hajela, A, Hurley, K, Kuulkers, E, Laurent, P, Mereghetti, S, Nicholl, M, Patnaude, D, Ubertini, P, Banovetz, J, Bartel, N, Berger, E, Coughlin, ER, Eftekhari, T, Frederiks, DD, Kozlova, AV, Laskar, T, Svinkin, DS, Drout, MR, Macfadyen, A & Paterson, K 2019, 'An Embedded X-Ray Source Shines through the Aspherical AT 2018cow: Revealing the Inner Workings of the Most Luminous Fast-evolving Optical Transients', Astrophysical Journal, vol. 872, no. 1, pp. 18. https://doi.org/10.3847/1538-4357/aafa01
Margutti, R. ; Metzger, B. D. ; Chornock, R. ; Vurm, I. ; Roth, N. ; Grefenstette, B. W. ; Savchenko, V. ; Cartier, R. ; Steiner, J. F. ; Terreran, G. ; Margalit, B. ; Migliori, G. ; Milisavljevic, D. ; Alexander, K. D. ; Bietenholz, M. ; Blanchard, P. K. ; Bozzo, E. ; Brethauer, D. ; Chilingarian, I. V. ; Coppejans, D. L. ; Ducci, L. ; Ferrigno, C. ; Fong, W. ; Götz, D. ; Guidorzi, C. ; Hajela, A. ; Hurley, K. ; Kuulkers, E. ; Laurent, P. ; Mereghetti, S. ; Nicholl, M. ; Patnaude, D. ; Ubertini, P. ; Banovetz, J. ; Bartel, N. ; Berger, E. ; Coughlin, E. R. ; Eftekhari, T. ; Frederiks, D. D. ; Kozlova, A. V. ; Laskar, T. ; Svinkin, D. S. ; Drout, M. R. ; Macfadyen, A. ; Paterson, K. / An Embedded X-Ray Source Shines through the Aspherical AT 2018cow: Revealing the Inner Workings of the Most Luminous Fast-evolving Optical Transients. In: Astrophysical Journal. 2019 ; Vol. 872, No. 1. pp. 18.
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title = "An Embedded X-Ray Source Shines through the Aspherical AT 2018cow: Revealing the Inner Workings of the Most Luminous Fast-evolving Optical Transients",
abstract = "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 lesssim 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 ($\dot{M}\sim {10}^{-3}-{10}^{-4}\,{M}_{\odot }{\mathrm{yr}}^{-1}$ 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 lesssim 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.",
author = "R. Margutti and Metzger, {B. D.} and R. Chornock and I. Vurm and N. Roth and Grefenstette, {B. W.} and V. Savchenko and R. Cartier and Steiner, {J. F.} and G. Terreran and B. Margalit and G. Migliori and D. Milisavljevic and Alexander, {K. D.} and M. Bietenholz and Blanchard, {P. K.} and E. Bozzo and D. Brethauer and Chilingarian, {I. V.} and Coppejans, {D. L.} and L. Ducci and C. Ferrigno and W. Fong and D. G{\"o}tz and C. Guidorzi and A. Hajela and K. Hurley and E. Kuulkers and P. Laurent and S. Mereghetti and M. Nicholl and D. Patnaude and P. Ubertini and J. Banovetz and N. Bartel and E. Berger and Coughlin, {E. R.} and T. Eftekhari and Frederiks, {D. D.} and Kozlova, {A. V.} and T. Laskar and Svinkin, {D. S.} and Drout, {M. R.} and A. Macfadyen and K. Paterson",
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TY - JOUR

T1 - An Embedded X-Ray Source Shines through the Aspherical AT 2018cow: Revealing the Inner Workings of the Most Luminous Fast-evolving Optical Transients

AU - Margutti, R.

AU - Metzger, B. D.

AU - Chornock, R.

AU - Vurm, I.

AU - Roth, N.

AU - Grefenstette, B. W.

AU - Savchenko, V.

AU - Cartier, R.

AU - Steiner, J. F.

AU - Terreran, G.

AU - Margalit, B.

AU - Migliori, G.

AU - Milisavljevic, D.

AU - Alexander, K. D.

AU - Bietenholz, M.

AU - Blanchard, P. K.

AU - Bozzo, E.

AU - Brethauer, D.

AU - Chilingarian, I. V.

AU - Coppejans, D. L.

AU - Ducci, L.

AU - Ferrigno, C.

AU - Fong, W.

AU - Götz, D.

AU - Guidorzi, C.

AU - Hajela, A.

AU - Hurley, K.

AU - Kuulkers, E.

AU - Laurent, P.

AU - Mereghetti, S.

AU - Nicholl, M.

AU - Patnaude, D.

AU - Ubertini, P.

AU - Banovetz, J.

AU - Bartel, N.

AU - Berger, E.

AU - Coughlin, E. R.

AU - Eftekhari, T.

AU - Frederiks, D. D.

AU - Kozlova, A. V.

AU - Laskar, T.

AU - Svinkin, D. S.

AU - Drout, M. R.

AU - Macfadyen, A.

AU - Paterson, K.

PY - 2019/2/6

Y1 - 2019/2/6

N2 - 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 lesssim 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 ($\dot{M}\sim {10}^{-3}-{10}^{-4}\,{M}_{\odot }{\mathrm{yr}}^{-1}$ 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 lesssim 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.

AB - 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 lesssim 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 ($\dot{M}\sim {10}^{-3}-{10}^{-4}\,{M}_{\odot }{\mathrm{yr}}^{-1}$ 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 lesssim 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.

U2 - 10.3847/1538-4357/aafa01

DO - 10.3847/1538-4357/aafa01

M3 - Article

VL - 872

SP - 18

JO - Astrophysical Journal

T2 - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 1

ER -