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Changing looks of the nucleus of Seyfert galaxy NGC 3516 during 2016-2020

V. L. Oknyansky, Kh. M. Mikailov, N. A. Huseynov

TL;DR

This paper presents long-term optical spectroscopic observations of the Seyfert galaxy NGC 3516 to study changing-look behavior during 2016–2020. The authors track dramatic fluctuations in the broad Hβ component, documenting CL events with a high-state in early 2016 and again in mid-2020, following a low-activity period in 2017–2018. The May 2020 spectrum reveals a pronounced blue-wing in Hβ and detections of He II 4681 and [Fe X] 6374, aligning with a continuum flare and corroborated by photometry. These findings support luminosity-driven CL AGN scenarios and highlight possible mechanisms such as accretion-disk instabilities or tidal interactions around the central supermassive black hole.

Abstract

The results of spectral observations of NGC 3516 with the 2-m telescope of the Shamakhy Astrophysical Observatory during 2016-2020 are presented. In the first half of 2016, the intensive broad component Hbeta was found, which indicates a spectral type change compared to 2014, when the broad component was almost invisible. In the second half of 2016, the broad component H$β$ again was weakened and was practically not observed, remaining as weak until the end of 2019. At the end of 2019, the broad component Hbeta strengthened again, and in May 2020 reached a typical level for the high state of the object. During 2016-2020 we observed several changing looks of NGC 3516.

Changing looks of the nucleus of Seyfert galaxy NGC 3516 during 2016-2020

TL;DR

This paper presents long-term optical spectroscopic observations of the Seyfert galaxy NGC 3516 to study changing-look behavior during 2016–2020. The authors track dramatic fluctuations in the broad Hβ component, documenting CL events with a high-state in early 2016 and again in mid-2020, following a low-activity period in 2017–2018. The May 2020 spectrum reveals a pronounced blue-wing in Hβ and detections of He II 4681 and [Fe X] 6374, aligning with a continuum flare and corroborated by photometry. These findings support luminosity-driven CL AGN scenarios and highlight possible mechanisms such as accretion-disk instabilities or tidal interactions around the central supermassive black hole.

Abstract

The results of spectral observations of NGC 3516 with the 2-m telescope of the Shamakhy Astrophysical Observatory during 2016-2020 are presented. In the first half of 2016, the intensive broad component Hbeta was found, which indicates a spectral type change compared to 2014, when the broad component was almost invisible. In the second half of 2016, the broad component H again was weakened and was practically not observed, remaining as weak until the end of 2019. At the end of 2019, the broad component Hbeta strengthened again, and in May 2020 reached a typical level for the high state of the object. During 2016-2020 we observed several changing looks of NGC 3516.

Paper Structure

This paper contains 4 sections, 4 figures, 1 table.

Table of Contents

  1. Introduction
  2. Spectral observations
  3. Results
  4. Conclusion

Figures (4)

  • Figure 1: Calibrated spectra of NGC 3516 in relative intensities (shifted arbitrarily along the ordinate for optimal clarity) for 2016-2020.
  • Figure 2: The isolated nuclear non-stellar spectrum of NGC 3516 obtained on May 22, 2020.
  • Figure 3: Spectra of NGC 3516 in the H${\beta}$ region, normalized to the continuum at three dates: 10 May 2016, 16 May 2018 and 22 May 2020.
  • Figure 4: Upper panel: variability of the H${\beta}$ intensity, normalized to the [OIII]$\lambda$5007, in 2016-2020. Bottom panel: light curve of NGC 3516 in the $B$ with an aperture of 10 arc seconds according to published data: points - photometry at the Crimean Astronomical Station of SAI MSU, crosses - photometry carried out at SAO RAS, circles - photometry carried out at CMO SAI MSU (see text).