© 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved. © 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.
Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast, Belfast, UK.
Tuorla Observatory, Department of Physics
and Astronomy, University of Turku, Piikkiö, Finland.
Finnish Centre for Astronomy with ESO (FINCA), University of Turku, Piikkiö, Finland.
Centre, Department of Astronomy, AlbaNova, Stockholm University, Stockholm, Sweden.
Department of Physics, Durham University, Durham, UK.
Institute of Astronomy, University of Cambridge, Cambridge, UK.
School of Physics, O’Brien Centre for Science North, University College Dublin, Dublin,
Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh, UK.
Imperial College of Science Technology and Medicine,
Department of Physics and Astronomy, University College London, London, UK.
Department of Physics and Astronomy, University of
Southampton, Southampton, UK.
INAF—Osservatorio Astronomico di Padova, Padua, Italy.
Nordic Optical Telescope, Santa Cruz de la Palma, Spain.
Millennium Institute of Astrophysics, Santiago, Chile.
Núcleo de Astronomía de la Facultad de Ingeniería y Ciencias, Universidad Diego Portales,
Department of Physics, University of California, Davis, CA, USA.
Institute for Astronomy, University of Hawaii at Manoa, Honolulu,
HI, USA. *e-mail: email@example.com
Recent all-sky surveys have led to the discovery of new
types of transients. These include stars disrupted by the
central supermassive black hole, and supernovae that are
10–100 times more energetic than typical ones. However,
the nature of even more energetic transients that appar-
ently occur in the innermost regions of their host galaxies
is hotly debated
. Here we report the discovery of the most
energetic of these to date: PS1-10adi, with a total radiated
energy of ~2.3 × 10
erg. The slow evolution of its light curve
and persistently narrow spectral lines over ∼ 3 yr are incon-
sistent with known types of recurring black hole variability.
The observed properties imply powering by shock interac-
tion between expanding material and large quantities of sur-
rounding dense matter. Plausible sources of this expanding
material are a star that has been tidally disrupted by the cen-
tral black hole, or a supernova. Both could satisfy the energy
budget. For the former, we would be forced to invoke a new
and hitherto unseen variant of a tidally disrupted star, while
a supernova origin relies principally on environmental effects
resulting from its nuclear location. Remarkably, we also dis-
cover that PS1-10adi is not an isolated case. We therefore
surmise that this new population of transients has previously
been overlooked due to incorrect association with underlying
central black hole activity.
We discovered the optical transient PS1-10adi at right ascen-
sion 20 h 42 min 44.74 s and declination 15° 30′ 32.1″ (equinox
J2000.0) in the Panoramic Survey Telescope and Rapid Response
System 1 (Pan-STARRS1, or PS1) 3π Faint Galaxy Supernova
on 2010 August 15. Within the root mean square errors,
PS1-10adi appeared to be coincident with the centre of Sloan
Digital Sky Survey (SDSS) J204244.74+ 153032.1, and was ≳ 2 mag
brighter at peak in all optical bands than the SDSS data release
reference magnitudes. Over a period of ∼ 1,000 d, its light
curves evolve slowly and smoothly (Fig. 1, Supplementary Fig.1);
after this phase the quiescent host galaxy starts to dominate the
brightness. The early spectra are dominated by a blue continuum
and narrow (900 km s
) Balmer lines, consistent with a redshift
z = 0.203 ± 0.001. The shape of the Balmer lines at early epochs is
indicative of broadening by electron scattering
. Around ∼ 200 d,
the Balmer line profiles show a pronounced asymmetry in the red
wing (Fig.2). Spectra taken at epochs ≳ 3 yr are dominated by the
quiescent host, and display signatures of both active galactic nuclei
(AGN) and star-forming galaxies (see Methods). Compared with
this quiescent level, the Balmer line and Mg λ λ 2796,2803 line
fluxes increased, without any corresponding change in the [O ] λ
5007 or other forbidden lines (Supplementary Fig.2).
The U- to M-band photometry of PS1-10adi are well described
by two blackbody components (see Methods). Over ∼ 1,000 d
of monitoring, the hot and warm components evolved from
∼ 11,000 K to ∼ 8,000 K, and from ∼ 2,500 K to ∼ 1,200 K, respec
tively. The blackbody radius of the hot and warm components
peaked at ∼ 8 × 10
cm and ∼ 1.3 × 10
cm, respectively. The total
blackbody luminosity (Fig. 3) declined slowly and exponentially.
Integrating over the blackbody evolution yields a radiated energy of
1.7 × 10
erg; however, this is an underestimate given the early ultra-
violet (UV) excess (∼ 20%), and a missing rise-time contribution
(∼ 10%) (see Methods and Supplementary Fig.3). Thus, we infer the
total radiated energy to be 2.3± 0.5 × 10
Spectroscopically, PS1-10adi bears similarities both to narrow-
line Seyfert 1 galaxies
and to certain types of supernovae (type
that show signatures of ejecta interacting with dense sur-
roundings. Mg emission (Supplementary Fig. 2) is commonly
observed in both AGN
and type IIn supernovae
and is therefore
not a discriminant.
We first explore whether PS1-10adi could be linked to reprocessed
emission from either an AGN or a tidal disruption event (TDE)
A population of highly energetic transient events
in the centres of active galaxies
*, R. Kotak
, S. Mattila
, P. Lundqvist
, M. J. Ward
, M. Fraser
, A. Lawrence
S. J. Smartt
, W. P. S. Meikle
, A. Bruce
, J. Harmanen
, S. J. Hutton
, C. Inserra
, A. Pastorello
, T. Reynolds
, C. Romero-Cañizales
, K. W. Smith
, S. Valenti
K. C. Chambers
, K. W. Hodapp
, M. E. Huber
, N. Kaiser
, R.-P. Kudritzki
, E. A. Magnier
J. L. Tonry
, R. J. Wainscoat
and C. Waters
NATURE ASTRONOMY | VOL 1 | DECEMBER 2017 | 865–871 | www.nature.com/natureastronomy