26-30 June 2023
Centro Congressi Federico II
Europe/Rome timezone

The optically elusive, changing look active nucleus in NGC4156

29 Jun 2023, 16:00
Aula Magna (Centro Congressi Federico II)

Aula Magna

Centro Congressi Federico II

Via Partenope, 36, Napoli, Italy


Giulia Tozzi (Università di Firenze)


Despite the increasing number of newly discovered changing look active galactic nuclei (AGN), larger samples of known objects and multi-epoch observations are needed to shed light on this debated physical mechanism. In this talk, I will report on the changing look AGN in the galaxy NGC4156, as serendipitously discovered thanks to data acquired in 2019 at the Telescopio Nazionale Galileo (TNG) during a student observing program. Unlike previous optical spectra showing no signatures of broad-line emission, our 2019 TNG data unexpectedly revealed the appearance of broad components in both Hα and Hβ profiles, along with a rising continuum, overall pointing to a transition from a type 2 towards a (nearly) type 1 AGN. The broad-line emission has been then confirmed by our 2022 TNG follow-up observations, whereas the rising continuum is no longer detected, which hints at a further evolution backwards to a (nearly) type 2. I will discuss possible mechanisms at the origin of the observed optical variability of NGC4156, and briefly compare it to what observed in its X-ray multi-epoch observations. Approved optical (Asiago telescope) and X-ray (Swift) monitoring programs will provide us further insights into the variability of this source, possibly constraining the typical timescales of these changing look events.

Primary authors

Giulia Tozzi (Università di Firenze) Elisabeta Lusso (Università di Firenze) Lapo Casetti (Università di Firenze) Marco Romoli (Università di Firenze)

Presentation Materials

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