THE MAN BEHIND THE CURTAIN: X-RAYS DRIVE THE UV THROUGH NIR VARIABILITY IN THE 2013 ACTIVE GALACTIC NUCLEUS OUTBURST IN NGC 2617

By B. Shappee, J. Prieto, D. Grupe, C. Kochanek, Krzysztof Zbigniew Stanek, G. D. Rosa, S. Mathur, Y. Zu, B. Peterson, R. Pogge and 37 more. 2013

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After the All-Sky Automated Survey for SuperNovae discovered a significant brightening of the inner region of NGC 2617, we began a ∼70 day photometric and spectroscopic monitoring campaign from the X-ray through near-infrared (NIR) wavelengths. We report that NGC 2617 went through a dramatic outburst, during which its X-ray flux increased by over an order of magnitude followed by an increase of its optical/ultraviolet (UV) continuum flux by almost an order of magnitude. NGC 2617, classified as a Seyfert 1.8 galaxy in 2003, is now a Seyfert 1 due to the appearance of broad optical emission lines and a continuum blue bump. Such “changing look active galactic nuclei (AGNs)” are rare and provide us with important insights about AGN physics. Based on the Hβ line width and the radius–luminosity relation, we estimate the mass of central black hole (BH) to be (4 ± 1) × 107 M☉. When we cross-correlate the light curves, we find that the disk emission lags the X-rays, with the lag becoming longer as we move from the UV (2–3 days) to the NIR (6–9 days). Also, the NIR is more heavily temporally smoothed than the UV. This can largely be explained by a simple model of a thermally emitting thin disk around a BH of the estimated mass that is illuminated by the observed, variable X-ray fluxes.

Subfields: Astronomy and Astrophysics, Instrumentation

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In Astronomy and Astrophysics

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2. Jenny E. Greene
3. Luis C. Ho
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Citations in the corpus

• ASASSN-15oi: a rapidly evolving, luminous tidal disruption event at 216 Mpc (2016, methodology): “Here we describe the discovery and follow-up observations of ASASSN-15oi, the third TDE discovered by the All-Sky Automated Survey for SuperNovae (ASAS-SN1; Shappee et al. 2014).”
• The All-Sky Automated Survey for Supernovae (ASAS-SN) Light Curve Server v1.0 (2017, methodology): “Rarer extragalactic events are tidal disruption events (TDEs), where the majority of the best studied TDEs have been discovered by ASAS-SN (Holoien et al. 2014b, 2016a,b, Brown et al. 2016, 2017a) or are present in ASAS-SN (Brown et al. 2017b), and “changing-look” AGN (Shappee et al. 2014).”
• The diversity of Type II supernova versus the similarity in their progenitors (2016, methodology): “Four objects within the sample were discovered by the All-Sky Automated Survey for SuperNovae (ASASSN1, Shappee et al. 2014), two by the La Silla Quest Variability Survey2 (Baltay et al. 2013), and one by the Lick Observa- 1 www.astronomy.ohio-state.edu/∼assassin/index.shtml 2 LSQ,…”
• The ASAS-SN catalogue of variable stars I: The Serendipitous Survey (2018, methodology): “E-mail: jayasinghearachchilage.1@osu.edu the All-Sky Automated Survey for SuperNovae (ASAS-SN, Shappee et al. 2014; Kochanek et al. 2017) originated.”
• PESSTO: survey description and products from the first data release by the Public ESO Spectroscopic Survey of Transient Objects (2014, methodology): “The ASAS-SN project is now running two 14 cm telescopes in the northern and southern hemispheres, successfully finding transients brighter than V ∼ 17 (Shappee et al. 2014) with the aim of being all sky to approximately this flux limit.”
• The fast, luminous ultraviolet transient AT2018cow: extreme supernova, or disruption of a star by an intermediate-mass black hole? (2018, positive): “The ASAS-SN non-detection reported by Prentice et al. 2018 (g > 18.9 at 58284.13) provides an even tighter constraint: a rise of > 4.2 magnitudes over <1.3 days.”
• The Sloan Digital Sky Survey Reverberation Mapping Project: Hα and Hβ Reverberation Measurements from First-year Spectroscopy and Photometry (2017, background): “Recent work has indicated that the optical continuum-emitting region can have a significant lag relative to the UV (Collier et al. 1998; Sergeev et al. 15 2005; McHardy et al. 2014; Shappee et al. 2014; Edelson et al. 2015; Fausnaugh et al. 2016).”
• The ASAS-SN Catalog of Variable Stars II: Uniform Classification of 412,000 Known Variables (2018, background): “In the modern era, surveys such as the All-Sky Automated Survey for SuperNovae (ASAS-SN, Shappee et al. 2014; Kochanek et al. 2017; Jayasinghe et al. 2018a,c), the All-Sky Automated Survey (ASAS; Pojmanski 2002), the Optical Gravitational Lensing Experiment (OGLE; Udalski 2003), the Northern Sky…”
• Stellar Dynamics and Stellar Phenomena Near a Massive Black Hole (2017, background): “…et al. 2011), which is looking for low-mass stars on relativistic orbits around Sgr A? with unprecedented astrometric precision, and large scale transient source surveys (Pan-STARRS (Kaiser et al. 2002), PTF/ZTF (Law et al. 2009; Bellm 2014), ASAS-SN (Shappee et al. 2014)), which search for TDEs.”
• Modelling the coincident observation of a high-energy neutrino and a bright blazar flare (2018, methodology): “In addition to the above listed ATels, we inspected the publicly available light curves of the OVRO 15 GHz radio telescope (24), the ASAS-SN robotic optical telescope network (7,25) and the Fermi Full Sky Variability Analysis (FAVA) in the sub-GeV and GeV energy ranges (26).”
• Unifying Type II Supernova Light Curves with Dense Circumstellar Material (2016, methodology): “Surveys with rapid cadences, such as the Zwicky Transient Facility (Law et al. 2009) and the All-sky Automated Survey for Supernovae (Shappee et al. 2014) make this an ideal time to identify SNe early, so that these critical spectra can be taken.”
• A systematic search for changing-look quasars in SDSS (2015, background): “As a prime example, following an outburst in the X-ray emission in the local Seyfert NGC 2617, Shappee et al. (2014) were able to use the variability across several wavebands (spanning X-rays–NIR) to map out the structure of the accretion disk and argue for illumination of the disk by the X-ray…”