Optical variability of the Seyfert nucleus NGC 7469 in timescales from days to minutes

Dultzin‐Hacyan, D.; Schuster, W. J.; Parrao, L.; Peña, J. H.; Peniche, R.; Benítez, E.; Costero, R.

doi:10.1086/116194

Cited by 25 publications

(15 citation statements)

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“…4 in the paper by Merkulova 2000). The result of this guiding test is very near to the calculations that have been made by Dultzin-Hacyan et al (1992): the measured brightness has an appreciable error (more than 1%) at a distance more than 5 from the center of a 20 diaphragm.…”

Section: Observations and Reductionssupporting

confidence: 70%

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UBVRI simultaneous observations of the nucleus of Seyfert galaxy NGC 5548 in 1993–1999

Меркулова

2002

A&A

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Abstract. An ongoing program on photometric and spectral monitoring of some bright Seyfert galaxies has been carried out at the Crimean Astrophysical Observatory since 1989. Results of photometric observations of NGC 5548 obtained with the 1.25 m telescope are reported in this paper; it focuses on the analysis of intranight variations. During 44 observational nights in 1993-1999 in each spectral band of the Johnson UBV RI system, 672 measurements have been performed simultaneously through the round aperture (diameter 15 ) using differential photometry techniques. The estimated accuracy of each measurement is about 0.01 mag. The peak amplitude Rmax = Fmax/Fmin = 2.99 for the whole light curve was observed in the U band, while the minimum amplitude Fmax/Fmin = 1.37 occurred in the I band during the full observation period. UBV RI observations and good sampled data of international monitoring campaigns of NGC 5548, were used to calculate Structure Functions. A comparison is made of the characteristics of the long and short time scale variations of NGC 5548 with those of NGC 4151, NGC 7469 and NGC 1275. In order to examine the intranight variations of the nucleus of NGC 5548, standard deviations (SD) of the nightly averaged flux F , and a measure of intranight variability -SD/F were calculated for each night. Using this parameter, a probability characteristics is introduced, and duty cycles (the fraction of time when the galaxy is variable), characterizing the efficiency of the central energy source, were evaluated. It is concluded that intranight variability is really transient in character and manifests itself with different probabilities for different galaxies.

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Section: Observations and Reductionssupporting

confidence: 70%

“…The shortest time scale of variations in the optical was reported by Dultzin-Hacyan et al (1992) for the NGC 7469 galaxy nucleus. Using a Stromgren photometer, they investigated variations with a duration of ∼13 min and average amplitude ∼0.…”

Section: Introductionmentioning

confidence: 88%

UBVRI simultaneous observations of the nucleus of Seyfert galaxy NGC 5548 in 1993–1999

Меркулова

2002

A&A

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“…Variability of a few tenths of a magnitude are common on timescales from days to months. Optical broad-band variations with even shorter time-scales have been claimed by Dultzin-Hacyan et al (1992) and Lyutyi et al (1995). Westin (1984) analysed an extensive series of UV observations taken with the International Ultraviolet Explorer (IUE) from 1978 June to 1982 December, showing variations of a factor of two in the 1500-Å continuum and somewhat less in the Fine Error Sensor (ϳvisible) counts.…”

Section: Introductionmentioning

confidence: 68%

Variability of Seyfert galaxies in the near-infrared — II. The unusual starburst Seyfert NGC 7469

Glass

1998

Monthly Notices of the Royal Astronomical Society

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The bright Seyfert 1 and starburst galaxy NGC 7469 has been monitored at JHKL for 13 yr. Its variations have been small, amounting to less than 0.3 mag, except for an event in 1989 when the flux from its active nucleus declined to about one quarter of its normal level. Using the technique of flux variation gradients (FVGs), the variations have been analysed, taking into account the known JHK fluxes from the star‐forming ring surrounding the nucleus. By comparing the FVGs of NGC 7469 with those of other Seyfert galaxies, the nucleus of NGC 7469 is found to suffer very little reddening. The active nucleus normally contributes more than 50 per cent of the flux measured in the K and L bands through an aperture of 12 arcsec diameter. Infrared excesses (above the fluxes expected from stars) are observed from the circumnuclear ring at both K and L and it is suggested that they arise from warm, small particles that also emit the aromatic hydrocarbon features seen in this galaxy.

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“…However, different authors often use different variability criteria. Computing quantities such as the ‘amplitude of the variations’ A m = (Δ m 2 −σ 2 m ) 1/2 (Dultzin‐Hacyan et al 1992), the variability coefficient C eff =Δ m /σ m (Jang & Miller 1997; S03) or P (χ 2 ) (de Diego et al 1998; Webb & Malkan 2000) constitute different approaches that may lead to different conclusions on the presence of the variability, even applied to the same data. This is true especially when the variations are very small or negligible.…”

Section: Discussionmentioning

confidence: 99%

“…Earlier microvariability observations were performed on relatively small-aperture telescopes, equipped with single-channel photomultipliers. They supposedly revealed short-term variability of E-mail: bachevr@astro.bas.bg (RB); anton@astro.bas.bg (AS) about 0.1 mag in nearby Seyferts, monitored mainly in U and B bands (Lyutyi et al 1989;Dultzin-Hacyan et al 1992;Merkulova 2000). Unfortunately, with such equipment an adequate assessment of the photometric errors is hardly possible and, taking into account the photon noise, atmospheric instabilities, etc., the photometric errors may easily reach a value comparable to the variability amplitude claimed (see also Section 4).…”

Section: Introductionmentioning

confidence: 99%

Short-term optical variability of high-redshift quasi-stellar objects

Bachev

Strigachev

Semkov

2005

Monthly Notices of the Royal Astronomical Society

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In this paper we present the results of a search for short‐term variability in the optical band of selected high‐luminosity, high‐redshift radio‐quiet quasars. Each quasar has been monitored typically for 2–4 h with a time resolution of 2–5 min and a photometric accuracy of about 0.01–0.02 mag. As a result of the significant redshift (z > 2), the covered wavelength range falls into the ultraviolet region (typically 1500–2500 Å). We have found no statistical evidence for any continuum variations larger than 0.01–0.02 mag for any of the monitored objects. Our results suggest that the presence of a short‐term variability in radio‐quiet quasars is unlikely even in the ultraviolet region, contrary to reports by other authors. This conclusion holds true at least for high‐luminosity (large black hole mass and accretion rate?) objects. The results are consistent with the idea that significant short‐term (less than 1 h) variations in active galactic nuclei, where observed, should be attributed primarily to processes in a relativistic jet.

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Optical variability of the Seyfert nucleus NGC 7469 in timescales from days to minutes

Cited by 25 publications

References 0 publications

UBVRI simultaneous observations of the nucleus of Seyfert galaxy NGC 5548 in 1993–1999

UBVRI simultaneous observations of the nucleus of Seyfert galaxy NGC 5548 in 1993–1999

Variability of Seyfert galaxies in the near-infrared — II. The unusual starburst Seyfert NGC 7469

Short-term optical variability of high-redshift quasi-stellar objects

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