1ES 1927+654: an AGN Caught Changing Look on a Timescale of Months. (arXiv:1903.11084v1 [astro-ph.GA])

1ES 1927+654: an AGN Caught Changing Look on a Timescale of Months. (arXiv:1903.11084v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Trakhtenbrot_B/0/1/0/all/0/1">Benny Trakhtenbrot</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Arcavi_I/0/1/0/all/0/1">Iair Arcavi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+MacLeod_C/0/1/0/all/0/1">Chelsea L. MacLeod</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ricci_C/0/1/0/all/0/1">Claudio Ricci</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kara_E/0/1/0/all/0/1">Erin Kara</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Graham_M/0/1/0/all/0/1">Melissa L. Graham</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Stern_D/0/1/0/all/0/1">Daniel Stern</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Harrison_F/0/1/0/all/0/1">Fiona A. Harrison</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Burke_J/0/1/0/all/0/1">Jamison Burke</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hiramatsu_D/0/1/0/all/0/1">Daichi Hiramatsu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hosseinzadeh_G/0/1/0/all/0/1">Griffin Hosseinzadeh</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Howell_D/0/1/0/all/0/1">D. Andrew Howell</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Smartt_S/0/1/0/all/0/1">Stephen J. Smartt</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Rest_A/0/1/0/all/0/1">Armin Rest</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Prieto_J/0/1/0/all/0/1">Jose L. Prieto</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Shappee_B/0/1/0/all/0/1">Benjamin J. Shappee</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Holoien_T/0/1/0/all/0/1">Thomas W.-S. Holoien</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bersier_D/0/1/0/all/0/1">David Bersier</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Filippenko_A/0/1/0/all/0/1">Alexei V. Filippenko</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Brink_T/0/1/0/all/0/1">Thomas G. Brink</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zheng_W/0/1/0/all/0/1">WeiKang Zheng</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Li_R/0/1/0/all/0/1">Ruancun Li</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Remillard_R/0/1/0/all/0/1">Ronald A. Remillard</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Loewenstein_M/0/1/0/all/0/1">Michael Loewenstein</a>

We study the sudden optical and UV brightening of 1ES 1927+654, which until
now was known as a narrow-line active galactic nucleus (AGN). 1ES 1927+654 was
part of the small and peculiar class of “true Type-2” AGN, which lack broad
emission lines and line-of-sight obscuration. Our high-cadence spectroscopic
monitoring captures the appearance of a blue, featureless continuum, followed
several weeks later by the appearance of broad Balmer emission lines. This
timescale is broadly consistent with the expected light travel time between the
central engine and the broad line emission region in (persistent) broad-line
AGN. HST spectroscopy reveals no evidence for broad UV emission lines (e.g.,
CIV1549, CIII]1909, MgII2798), probably due to dust in the broad line emission
region. To the best of our knowledge, this is the first case where the lag
between the change in continuum and in broad line emission of a “changing-look”
AGN has been temporally resolved. The nature and timescales of the photometric
and spectral evolution disfavor both a change in line-of-sight obscuration and
a change of the overall rate of gas inflow as driving the drastic spectral
changes seen in this AGN. Although the peak luminosity and timescales are
consistent with those of tidal disruption events seen in inactive galaxies, but
the spectral properties are not. The X-ray emission displays a markedly
different behavior, with frequent flares on timescales of hours to days, and
will be presented in a companion publication.

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