TY - JOUR
T1 - AT 2018cow VLBI
T2 - No long-lived relativistic outflow
AU - Bietenholz, Michael F.
AU - Margutti, Raffaella
AU - Coppejans, Deanne
AU - Alexander, Kate D.
AU - Argo, Megan
AU - Bartel, Norbert
AU - Eftekhari, Tarraneh
AU - Milisavljevic, Dan
AU - Terreran, Giacomo
AU - Berger, Edo
N1 - Publisher Copyright:
© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.
PY - 2020/2/1
Y1 - 2020/2/1
N2 - We report on Very Long Baseline Interferometry (VLBI) observations of the fast and blue optical transient (FBOT), AT 2018cow. At ∼62 Mpc, AT 2018cow is the first relatively nearby FBOT. The nature of AT 2018cow is not clear, although various hypotheses from a tidal disruption event to different kinds of supernovae have been suggested. It had a very fast rise time (3.5 d) and an almost featureless blue spectrum, although high photospheric velocities (40 000 km s-1) were suggested early on. The X-ray luminosity was very high, ∼1.4 × 1043 erg s-1, larger than those of ordinary supernovae (SNe), and more consistent with those of SNe associated with gamma-ray bursts. Variable hard X-ray emission hints at a long-lived 'central engine.' It was also fairly radio luminous, with a peak 8.4-GHz spectral luminosity of ∼4 × 1028 erg s-1 Hz-1, allowing us to make VLBI observations at ages between 22 and 287 d. We do not resolve AT 2018cow. Assuming a circularly symmetric source, our observations constrain the average apparent expansion velocity to be <0.49, c by t = 98 d (3σ limit). We also constrain the proper motion of AT 2018cow to be < 0.51, c. Since the radio emission generally traces the fastest ejecta, our observations make the presence of a long-lived relativistic jet with a lifetime of more than 1 month very unlikely.
AB - We report on Very Long Baseline Interferometry (VLBI) observations of the fast and blue optical transient (FBOT), AT 2018cow. At ∼62 Mpc, AT 2018cow is the first relatively nearby FBOT. The nature of AT 2018cow is not clear, although various hypotheses from a tidal disruption event to different kinds of supernovae have been suggested. It had a very fast rise time (3.5 d) and an almost featureless blue spectrum, although high photospheric velocities (40 000 km s-1) were suggested early on. The X-ray luminosity was very high, ∼1.4 × 1043 erg s-1, larger than those of ordinary supernovae (SNe), and more consistent with those of SNe associated with gamma-ray bursts. Variable hard X-ray emission hints at a long-lived 'central engine.' It was also fairly radio luminous, with a peak 8.4-GHz spectral luminosity of ∼4 × 1028 erg s-1 Hz-1, allowing us to make VLBI observations at ages between 22 and 287 d. We do not resolve AT 2018cow. Assuming a circularly symmetric source, our observations constrain the average apparent expansion velocity to be <0.49, c by t = 98 d (3σ limit). We also constrain the proper motion of AT 2018cow to be < 0.51, c. Since the radio emission generally traces the fastest ejecta, our observations make the presence of a long-lived relativistic jet with a lifetime of more than 1 month very unlikely.
KW - radio continuum: general
KW - supernovae: individual: AT 2018cow
KW - transients: supernovae
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U2 - 10.1093/mnras/stz3249
DO - 10.1093/mnras/stz3249
M3 - Article
AN - SCOPUS:85080097361
VL - 491
SP - 4735
EP - 4741
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
SN - 0035-8711
IS - 4
ER -