Abstract
Abstract Mrk 590 was originally classified as a Seyfert 1 galaxy, but then it underwent dramatic changes: the nuclear luminosity dropped by over two orders of magnitude and the broad emission lines all but disappeared from the optical spectrum. Here we present follow-up observations to the original discovery and characterization of this “changing-look” active galactic nucleus (AGN). The new Chandra and Hubble Space Telescope observations from 2014 show that Mrk 590 is awakening, changing its appearance again. While the source continues to be in a low state, its soft excess has re-emerged, though not to the previous level. The UV continuum is brighter by more than a factor of two and the broad Mg ii emission line is present, indicating that the ionizing continuum is also brightening. These observations suggest that the soft excess is not due to reprocessed hard X-ray emission. Instead, it is connected to the UV continuum through warm Comptonization. Variability of the Fe Kα emission lines suggests that the reprocessing region is within ∼10 lt-yr or 3 pc of the central source. The change in AGN type is neither due to obscuration nor due to one-way evolution from Type 1 to Type 2, as suggested in the literature, but may be related to episodic accretion events.
Highlights
Active galactic nuclei (AGNs) are characterized by continuum emission across the electromagnetic spectrum and strong emission lines in the UV, optical, and near-IR
D14 reported the low state of Mrk 590 with 0.5–10 keV flux of 1.1 × 10−12 erg s−1 cm−2, so compared to our Director’s Discretionary Time (DDT) Chandra observation in 2013, the source flux appears to have increased slightly, but as shown in Figure 1, the source continues to be in a low state
While the source continues to be in a low state, the UV continuum is re-emerging along with the soft excess
Summary
Active galactic nuclei (AGNs) are characterized by continuum emission across the electromagnetic spectrum and strong emission lines in the UV, optical, and near-IR. Intrinsic change, implying that “type” is not always associated with viewing angle This phenomenon has become of recent interest due to a combination of several serendipitous discoveries of changing-look AGNs (e.g., Shappee et al 2014; Denney et al 2014; LaMassa et al 2015) and the growing availability of large spectroscopic quasar databases with long time-baselines of multi-epoch photometry and spectroscopy. These rare occurrences have the potential to contribute to our limited understanding of the central engines of active galaxies. We argue that the changing-look phenomenon is a normal event in the duty cycle of “normal” quasars
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