13 research outputs found
Multi-Wavelength Monitoring of the Changing-Look AGN NGC 2617 during State Changes
Optical and near-infrared photometry, optical spectroscopy, and soft X-ray and UV monitoring of the changing-look active galactic nucleus NGC 2617 show that it continues to have the appearance of a type-1 Seyfert galaxy. An optical light curve for 2010-2017 indicates that the change of type probably occurred between 2010 October and 2012 February and was not related to the brightening in 2013. In 2016 and 2017 NGC 2617 brightened again to a level of activity close to that in 2013 April. However, in 2017 from the end of the March to end of July 2017 it was in very low level and starting to change back to a Seyfert 1.8. We find variations in all passbands and in both the intensities and profiles of the broad Balmer lines. A new displaced emission peak has appeared in Hβ. X-ray variations are well correlated with UV-optical variability and possibly lead by ̃2-3 d. The K band lags the J band by about 21.5 ± 2.5 d and lags the combined B + J bands by ̃25 d. J lags B by about 3 d. This could be because J-band variability arises predominantly from the outer part of the accretion disc, while K-band variability is dominated by thermal re-emission by dust. We propose that spectral-type changes are a result of increasing central luminosity causing sublimation of the innermost dust in the hollow bi-conical outflow. We briefly discuss various other possible reasons that might explain the dramatic changes in NGC 2617.Fil: Oknyansky, V. L.. Sternberg Astronomical Institute; RusiaFil: Gaskell, C. M.. Department of Astronomy and Astrophysics. University of California. Santa Cruz; Estados UnidosFil: Mikailov, K. M.. Shamakhy Astrophysical Observatory, National Academy of Sciences.
Pirkuli; AzerbaiyánFil: Lipunov, V. M.. Sternberg Astronomical Institute. M.V.Lomonosov Moscow State University ; RusiaFil: Shatsky, N. I.. Sternberg Astronomical Institute. M.V.Lomonosov Moscow State University; RusiaFil: Tsygankov, S. S.. Tuorla Observatory, Department of Physics and Astronomy. University of Turku.; FinlandiaFil: Gorbovskoy, E. S.. Sternberg Astronomical Institute. M.V.Lomonosov Moscow State University; RusiaFil: Tatarnikov, A. M.. Sternberg Astronomical Institute. M.V.Lomonosov Moscow State University; RusiaFil: Metlov, V. G.. Sternberg Astronomical Institute. M.V.Lomonosov Moscow State University; RusiaFil: Malanchev, K. L.. Sternberg Astronomical Institute. M.V.Lomonosov Moscow State University; RusiaFil: Brotherton, M.B.. University of Wyoming; Estados UnidosFil: Kasper, D.. University of Wyoming; Estados UnidosFil: Du, P.. Institute of High Energy Physics. Chinese Academy of Sciences; ChinaFil: Chen, X.. School of Space Science and Physics. Shandong University; ChinaFil: Burlak, M. A.. Sternberg Astronomical Institute. M.V.Lomonosov Moscow State University; RusiaFil: Buckley, D. A. H.. The South African Astronomical Observatory; SudáfricaFil: Rebolo, R.. Instituto de Astrofisica de Canarias; EspañaFil: Serra-Ricart, M.. Instituto de Astrofisica de Canarias; EspañaFil: Podestá, R.. Universidad Nacional de San Juan; ArgentinaFil: Levato, O. H.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio. Universidad Nacional de San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio; Argentin
A flare in the optical spotted in the changing-look Seyfert NGC 3516
We present observations from the short-term intensive optical campaign (from
Sep2019 to Jan2020) of the changing-look Seyfert NGC 3516. This active galactic
nucleus is known to have strong optical variability and has changed its type in
the past. It has been in the low-activity state in the optical since 2013, with
some rebrightening from the end of 2015 to the beginning of 2016, after which
it remained dormant. We aim to study the photometric and spectral variability
of NGC 3516 from the new observations in U- and B-bands and examine the
profiles of the optical broad emission lines in order to demonstrate that this
object may be entering a new state of activity. NGC 3516 has been monitored
intensively for the past 4 months with an automated telescope in U and B
filters, enabling accurate photometry of 0.01 precision. Spectral observations
were triggered when an increase in brightness was spotted. We support our
analysis of past-episodes of violent variability with the UV and X-ray
long-term light curves constructed from the archival Swift data. An increase of
the photometric magnitude is seen in both U and B filters to a maximum
amplitude of 0.25mag and 0.1 mag, respectively. During the flare, we observe
stronger forbidden high-ionization iron lines than reported before, as well as
the complex broad Ha and Hb lines. This is especially seen in Ha which appears
to be double-peaked. It seems that a very broad component of ~10,000 km/s in
width in the Balmer lines is appearing. The trends in the optical, UV, and
X-ray light curves are similar, with the amplitudes of variability being
significantly larger in the case of UV and X-ray bands. The increase of the
continuum emission, the variability of the coronal lines, and the very broad
component in the Balmer lines may indicate that the AGN of NGC 3516 is finally
leaving the low-activity state in which it has been for the last ~3 years.Comment: 7 pages, 6 figures, accepted in A&A (corrected after receiving
comments from the language editor
Long-term multiwavelength monitoring and reverberation mapping of NGC 2617 during a changing-look event
We present the results of photometric and spectroscopic monitoring campaigns
of the changing look AGN NGC~2617 carried out from 2016 until 2022 and covering
the wavelength range from the X-ray to the near-IR. The facilities included the
telescopes of the SAI MSU, MASTER Global Robotic Net, the 2.3-m WIRO telescope,
Swift, and others. We found significant variability at all wavelengths and,
specifically, in the intensities and profiles of the broad Balmer lines. We
measured time delays of ~ 6 days (~ 8 days) in the responses of the H-beta
(H-alpha) line to continuum variations. We found the X-ray variations to
correlate well with the UV and optical (with a small time delay of a few days
for longer wavelengths). The K-band lagged the B band by 14 +- 4 days during
the last 3 seasons, which is significantly shorter than the delays reported
previously by the 2016 and 2017--2019 campaigns. Near-IR variability arises
from two different emission regions: the outer part of the accretion disc and a
more distant dust component. The HK-band variability is governed primarily by
dust. The Balmer decrement of the broad-line components is inversely correlated
with the UV flux. The change of the object's type, from Sy1 to Sy1.8, was
recorded over a period of ~ 8 years. We interpret these changes as a
combination of two factors: changes in the accretion rate and dust recovery
along the line of sight.Comment: 14 pages, 15 figures, accepted by the MNRA
Variability and the size-luminosity relation of the intermediate mass AGN in NGC 4395
We present the variability study of the lowest-luminosity Seyfert 1 galaxy
NGC 4395 based on the photometric monitoring campaigns in 2017 and 2018. Using
22 ground-based and space telescopes, we monitored NGC 4395 with a 5
minute cadence during a period of 10 days and obtained light curves in the UV,
V, J, H, and K/Ks bands as well as the H narrow-band. The RMS
variability is 0.13 mag on \emph{Swift}-UVM2 and V filter light curves,
decreasing down to 0.01 mag on K filter. After correcting for continuum
contribution to the H narrow-band, we measured the time lag of the
H emission line with respect to the V-band continuum as
to min. in 2017 and
to min. in 2018, depending on the assumption on the
continuum variability amplitude in the H narrow-band. We obtained no
reliable measurements for the continuum-to-continuum lag between UV and V bands
and among near-IR bands, due to the large flux uncertainty of UV observations
and the limited time baseline. We determined the AGN monochromatic luminosity
at 5100\AA\ , after subtracting the contribution of the
nuclear star cluster. While the optical luminosity of NGC 4395 is two orders of
magnitude lower than that of other reverberation-mapped AGNs, NGC 4395 follows
the size-luminosity relation, albeit with an offset of 0.48 dex
(2.5) from the previous best-fit relation of Bentz et al. (2013).Comment: Accepted for publication in ApJ (Feb. 23rd, 2020). 18 pages, 10
figure