24 research outputs found
Reverberation measurement of the inner radius of the dust torus in NGC 4151 during 2008-2013
We investigate the correlation between infrared (JHKL) and optical (B) fluxes
of the variable nucleus of the Seyfert galaxy NGC 4151 using partially
published data for the last 6 years (2008-2013.). Here we are using the same
data as in Oknyansky et al. (2014), but include also optical (B) data from Guo
et al. We find that the lag of flux in all the infrared bands is the same, 40
+- 6 days, to within the measurement accuracy. Variability in the J and K bands
is not quite simultaneous, perhaps due to the differing contributions of the
accretion disk in these bands. The lag found for the K band compared with the B
band is not significantly different from earlier values obtained for the period
2000-2007. However, finding approximately the same lags in all IR bands for
2008-2013 differs from previous results at earlier epochs when the lag
increased with increasing wavelength. Examples of almost the same lag in
different IR bands are known for some other active nuclei. In the case of NGC
4151 it appears that the relative lags between the IR bands may be different in
different years. The available data, unfortunately, do not allow us to
investigate a possible change in the lags during the test interval. We discuss
our results in the framework of the standard model where the variable infrared
radiation is mainly due to thermal re-emission from the part of the dusty torus
closest to the central source. There is also a contribution of some IR emission
from the accretion disk, and this contribution increases with decreasing
wavelength. Some cosmological applications of obtained results are discussed.Comment: 3 pages, 2 figures, 14-th Odessa International Astronomical Gamow
Conference-School Astronomy and beyond: Astrophysics, Cosmology and
Gravitation, Cosmomicrophysics, Radio-astronomy and Astrobiolog
Recommended from our members
Photometric observations of the radio bright B[e]/X-ray binary CI Cam
We present multiwavelength (optical, IR, radio) observations of CI Cam, the optical counterpart to the transient X-ray source XTE J0421+560. Pre-outburst quiescent observations reveal the presence of a dusty envelope around the system. Pronounced short term variability is observed at all wavebands from U-K, but no indication of prior flaring of a similar magnitude to the 1998 April outburst is found in these data.
Data obtained during the 1998 April X-ray flare reveal pronounced optical-radio flaring. The optical flux was observed to quickly return to quiescent levels, while the radio flare was of much longer duration. The optical component is likely to result from a combination of free-free/free-bound emission, emission line and thermal dust emission, caused by re-radiation of the X-ray flux, while the behaviour of the multiwavelength radio data is consistent with emission from expanding ejecta emitting via the synchrotron mechanism.
Post-outburst (1998 August-1999 March) U-M broadband photometric observations reveal that while the optical (UBV) flux remains at pre-outburst quiescent levels, near IR (JHKLM) fluxes exceed the pre-outburst fluxes by ~0.5 magnitudes. Modelling the pre- and post-outburst spectral energy distribution of CI Cam reveals that the structure and/or composition of the dusty component of the circumstellar envelope appears to have changed. Due to a lack of information on the precise chemical composition of the dust within the system several explanations for this behaviour are possible, such as the production of new dust at the inner edge of the envelope, or modification of the composition of the dust due to X-ray irradiation
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
Optical Spectroscopy of Supernova 1993J During Its First 2500 Days
We present 42 low-resolution spectra of Supernova (SN) 1993J, our complete
collection from the Lick and Keck Observatories, from day 3 after explosion to
day 2454, as well as one Keck high-dispersion spectrum from day 383. SN 1993J
began as an apparent SN II, albeit an unusual one. After a few weeks, a
dramatic transition took place, as prominent helium lines emerged in the
spectrum. SN 1993J had metamorphosed from a SN II to a SN IIb. Nebular spectra
of SN 1993J closely resemble those of SNe Ib and Ic, but with a persistent
H_alpha line. At very late times, the H_alpha emission line dominated the
spectrum, but with an unusual, box-like profile. This is interpreted as an
indication of circumstellar interaction.Comment: 19 pages plus 13 figures, AASTeX V5.0. One external table in AASTeX
V4.0, in landscape format. Accepted for publication in A
The photometric and spectral investigation of CI Camelopardalis, an X-ray transient and B[e] star
We combined the results of UBVR photometry of CI Cam taken at Sternberg
Astronomical Institute in 1998--2001, and moderate resolution spectroscopy
taken at Special Astrophysical Observatory during the same time period.
Photometry as well as fluxes of Balmer emissions and of some Fe II emission
lines of CI Cam in quiet state reveal a cyclic variation with the period of
. The variation like this may be due to an orbital motion in a
wide pair with a giant star companion that exhibits the reflection effect on
its side faced to a compact companion.
The V-band photometry also confirms the pre-outburst 11.7 day period found by
Miroshnichenko earlier, but with a lower amplitude of 3 per cent. The
possibility of identity of this photometric period with the period of jet's
rotation in the VLA radio map of the object CI Cam was investigated. The radio
map modelling reveals the inclination of the jet rotation axis to the line of
sight, , the angle between the rotation axis and the direction of
ejection of the jet, , and jet's spatial velocity of
0.23--0.26c.
Equivalent widths and fluxes of various spectral lines show different
amplitudes of changes during the outburst, and essentially distinct behaviour
in quiescence. Five types of such behaviour were revealed, that indicates the
strong stratification of a gas and dust envelope round the system . The time
lag of strengthening of 50--250 in the forbidden line of nitrogen [N II]
was found relatively to the X-ray outburst maximum.Comment: 15 pages, 8 figures, 3 tables, Astron. Zh., 2002, (in press), vol.79,
number
A flare in the optical spotted in the changing-look Seyfert NGC 3516
Context. We present observations from the short-term intensive optical campaign (from September 2019 to January 2020) 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.Aims. 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.Methods. 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/UVOT and Swift/XRT data.Results. An increase of the photometric magnitude is seen in both U and B filters to a maximum amplitude of 0.25 mag and 0.11 mag, respectively. During the flare, we observe stronger forbidden high-ionization iron lines ([FeVII] and [FeX]) than reported before, as well as the complex broad H alpha and H beta lines. This is especially seen in H alpha, which appears to be double-peaked. It seems that a very broad component of similar to 10 000 km s(-1) 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.Conclusions. 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 similar to 3 years.</div