Swift spectra of AT2018cow

A white dwarf tidal disruption event?

N. Paul M. Kuin, Kinwah Wu, Samantha Oates, Amy Lien, Sam Emery, Jamie A. Kennea, Massimiliano De Pasquale, Qin Han, Peter J. Brown, Aaron Tohuvavohu, Alice Breeveld, David Nelson Burrows, S. Bradley Cenko, Sergio Campana, Andrew Levan, Craig Markwardt, Julian P. Osborne, Mat J. Page, Kim L. Page, Boris Sbarufatti & 2 others Michael Hiram Siegel, Eleonora Troja

Research output: Contribution to journalArticle

7 Citations (Scopus)

Abstract

The bright transient AT2018cow has been unlike any other known type of transient. Its high brightness, rapid rise and decay, and initially nearly featureless spectrum are unprecedented and difficult to explain using models for similar burst sources. We present evidence for faint γ-ray emission continuing for at least 8 d, and featureless spectra in the ultraviolet bands - both unusual for eruptive sources. The X-ray variability of the source has a burst-like character. The UV-optical spectrum does not show any CNO line but is well described by a blackbody. We demonstrate that a model invoking the tidal disruption of a 0.1-0.4M helium white dwarf (WD) by a 105-106M black hole located in the outskirts of galaxy Z 137-068 could provide an explanation for most of the characteristics shown in the multiwavelength observations. A blackbody-like emission is emitted from an opaque photosphere, formed by the debris of the WD disruption. Broad features showing up in the optical/infrared spectra in the early stage are probably velocity broadened lines produced in a transient high-velocity outward moving cocoon. The asymmetric optical/infrared lines that appeared at a later stage are emission from an atmospheric layer when it detached from thermal equilibrium with the photosphere, which undergoes more rapid cooling. The photosphere shrinks when its temperature drops, and the subsequent infall of the atmosphere produced asymmetric line profiles. Additionally, a non-thermal jet might be present, emitting X-rays in the 10-150 keV band.

Original languageEnglish (US)
Pages (from-to)2505-2521
Number of pages17
JournalMonthly Notices of the Royal Astronomical Society
Volume487
Issue number2
DOIs
StatePublished - Jan 1 2019

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photosphere
optical spectrum
bursts
debris
cocoon
rays
brightness
x rays
infrared spectra
helium
galaxies
cooling
atmospheres
decay
profiles
atmosphere
temperature

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Kuin, N. Paul M. ; Wu, Kinwah ; Oates, Samantha ; Lien, Amy ; Emery, Sam ; Kennea, Jamie A. ; De Pasquale, Massimiliano ; Han, Qin ; Brown, Peter J. ; Tohuvavohu, Aaron ; Breeveld, Alice ; Burrows, David Nelson ; Cenko, S. Bradley ; Campana, Sergio ; Levan, Andrew ; Markwardt, Craig ; Osborne, Julian P. ; Page, Mat J. ; Page, Kim L. ; Sbarufatti, Boris ; Siegel, Michael Hiram ; Troja, Eleonora. / Swift spectra of AT2018cow : A white dwarf tidal disruption event?. In: Monthly Notices of the Royal Astronomical Society. 2019 ; Vol. 487, No. 2. pp. 2505-2521.
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title = "Swift spectra of AT2018cow: A white dwarf tidal disruption event?",
abstract = "The bright transient AT2018cow has been unlike any other known type of transient. Its high brightness, rapid rise and decay, and initially nearly featureless spectrum are unprecedented and difficult to explain using models for similar burst sources. We present evidence for faint γ-ray emission continuing for at least 8 d, and featureless spectra in the ultraviolet bands - both unusual for eruptive sources. The X-ray variability of the source has a burst-like character. The UV-optical spectrum does not show any CNO line but is well described by a blackbody. We demonstrate that a model invoking the tidal disruption of a 0.1-0.4M⊙ helium white dwarf (WD) by a 105-106M⊙ black hole located in the outskirts of galaxy Z 137-068 could provide an explanation for most of the characteristics shown in the multiwavelength observations. A blackbody-like emission is emitted from an opaque photosphere, formed by the debris of the WD disruption. Broad features showing up in the optical/infrared spectra in the early stage are probably velocity broadened lines produced in a transient high-velocity outward moving cocoon. The asymmetric optical/infrared lines that appeared at a later stage are emission from an atmospheric layer when it detached from thermal equilibrium with the photosphere, which undergoes more rapid cooling. The photosphere shrinks when its temperature drops, and the subsequent infall of the atmosphere produced asymmetric line profiles. Additionally, a non-thermal jet might be present, emitting X-rays in the 10-150 keV band.",
author = "Kuin, {N. Paul M.} and Kinwah Wu and Samantha Oates and Amy Lien and Sam Emery and Kennea, {Jamie A.} and {De Pasquale}, Massimiliano and Qin Han and Brown, {Peter J.} and Aaron Tohuvavohu and Alice Breeveld and Burrows, {David Nelson} and Cenko, {S. Bradley} and Sergio Campana and Andrew Levan and Craig Markwardt and Osborne, {Julian P.} and Page, {Mat J.} and Page, {Kim L.} and Boris Sbarufatti and Siegel, {Michael Hiram} and Eleonora Troja",
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Kuin, NPM, Wu, K, Oates, S, Lien, A, Emery, S, Kennea, JA, De Pasquale, M, Han, Q, Brown, PJ, Tohuvavohu, A, Breeveld, A, Burrows, DN, Cenko, SB, Campana, S, Levan, A, Markwardt, C, Osborne, JP, Page, MJ, Page, KL, Sbarufatti, B, Siegel, MH & Troja, E 2019, 'Swift spectra of AT2018cow: A white dwarf tidal disruption event?', Monthly Notices of the Royal Astronomical Society, vol. 487, no. 2, pp. 2505-2521. https://doi.org/10.1093/mnras/stz053

Swift spectra of AT2018cow : A white dwarf tidal disruption event? / Kuin, N. Paul M.; Wu, Kinwah; Oates, Samantha; Lien, Amy; Emery, Sam; Kennea, Jamie A.; De Pasquale, Massimiliano; Han, Qin; Brown, Peter J.; Tohuvavohu, Aaron; Breeveld, Alice; Burrows, David Nelson; Cenko, S. Bradley; Campana, Sergio; Levan, Andrew; Markwardt, Craig; Osborne, Julian P.; Page, Mat J.; Page, Kim L.; Sbarufatti, Boris; Siegel, Michael Hiram; Troja, Eleonora.

In: Monthly Notices of the Royal Astronomical Society, Vol. 487, No. 2, 01.01.2019, p. 2505-2521.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Swift spectra of AT2018cow

T2 - A white dwarf tidal disruption event?

AU - Kuin, N. Paul M.

AU - Wu, Kinwah

AU - Oates, Samantha

AU - Lien, Amy

AU - Emery, Sam

AU - Kennea, Jamie A.

AU - De Pasquale, Massimiliano

AU - Han, Qin

AU - Brown, Peter J.

AU - Tohuvavohu, Aaron

AU - Breeveld, Alice

AU - Burrows, David Nelson

AU - Cenko, S. Bradley

AU - Campana, Sergio

AU - Levan, Andrew

AU - Markwardt, Craig

AU - Osborne, Julian P.

AU - Page, Mat J.

AU - Page, Kim L.

AU - Sbarufatti, Boris

AU - Siegel, Michael Hiram

AU - Troja, Eleonora

PY - 2019/1/1

Y1 - 2019/1/1

N2 - The bright transient AT2018cow has been unlike any other known type of transient. Its high brightness, rapid rise and decay, and initially nearly featureless spectrum are unprecedented and difficult to explain using models for similar burst sources. We present evidence for faint γ-ray emission continuing for at least 8 d, and featureless spectra in the ultraviolet bands - both unusual for eruptive sources. The X-ray variability of the source has a burst-like character. The UV-optical spectrum does not show any CNO line but is well described by a blackbody. We demonstrate that a model invoking the tidal disruption of a 0.1-0.4M⊙ helium white dwarf (WD) by a 105-106M⊙ black hole located in the outskirts of galaxy Z 137-068 could provide an explanation for most of the characteristics shown in the multiwavelength observations. A blackbody-like emission is emitted from an opaque photosphere, formed by the debris of the WD disruption. Broad features showing up in the optical/infrared spectra in the early stage are probably velocity broadened lines produced in a transient high-velocity outward moving cocoon. The asymmetric optical/infrared lines that appeared at a later stage are emission from an atmospheric layer when it detached from thermal equilibrium with the photosphere, which undergoes more rapid cooling. The photosphere shrinks when its temperature drops, and the subsequent infall of the atmosphere produced asymmetric line profiles. Additionally, a non-thermal jet might be present, emitting X-rays in the 10-150 keV band.

AB - The bright transient AT2018cow has been unlike any other known type of transient. Its high brightness, rapid rise and decay, and initially nearly featureless spectrum are unprecedented and difficult to explain using models for similar burst sources. We present evidence for faint γ-ray emission continuing for at least 8 d, and featureless spectra in the ultraviolet bands - both unusual for eruptive sources. The X-ray variability of the source has a burst-like character. The UV-optical spectrum does not show any CNO line but is well described by a blackbody. We demonstrate that a model invoking the tidal disruption of a 0.1-0.4M⊙ helium white dwarf (WD) by a 105-106M⊙ black hole located in the outskirts of galaxy Z 137-068 could provide an explanation for most of the characteristics shown in the multiwavelength observations. A blackbody-like emission is emitted from an opaque photosphere, formed by the debris of the WD disruption. Broad features showing up in the optical/infrared spectra in the early stage are probably velocity broadened lines produced in a transient high-velocity outward moving cocoon. The asymmetric optical/infrared lines that appeared at a later stage are emission from an atmospheric layer when it detached from thermal equilibrium with the photosphere, which undergoes more rapid cooling. The photosphere shrinks when its temperature drops, and the subsequent infall of the atmosphere produced asymmetric line profiles. Additionally, a non-thermal jet might be present, emitting X-rays in the 10-150 keV band.

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U2 - 10.1093/mnras/stz053

DO - 10.1093/mnras/stz053

M3 - Article

VL - 487

SP - 2505

EP - 2521

JO - Monthly Notices of the Royal Astronomical Society: Letters

JF - Monthly Notices of the Royal Astronomical Society: Letters

SN - 1745-3925

IS - 2

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