Optical Monitoring Data Research Articles

Multiwavelength XMM-Newton observations of the Laor et al. sample of PG quasars

We present XMM–Newton/EPIC spectra for the Laor et al. sample of Palomar Green (PG) quasars. We find that a power law provides a reasonable fit to the 2–5 keV region of the spectra. Excess soft X-ray emission below 2 keV is present for all objects, with the exception of those known to contain a warm absorber. However, a single power law is a poor fit to the 0.3–10.0 keV spectrum and instead we find that a simple model, consisting of a broken power law (plus an iron line), provides a reasonable fit in most cases. The equivalent width of the emission line is constrained in just 12 objects but with low (<2σ) significance in most cases. For the sources whose spectra are well fitted by the broken-power-law model, we find that various optical and X-ray line and continuum parameters are well correlated; in particular, the power-law photon index is well correlated with the FWHM of the Hβ line and the photon indices of the low- and high-energy components of the broken power law are well correlated with each other. These results suggest that the 0.3–10 keV X-ray emission shares a common (presumably non-thermal) origin, as opposed to suggestions that the soft excess is directly produced by thermal disc emission or via an additional spectral component. We present XMM–Newton Optical Monitor (OM) data, which we combine with the X-ray spectra so as to produce broad-band spectral energy distributions (SEDs), free from uncertainties due to long-term variability in non-simultaneous data. Fitting these optical–UV spectra with a Comptonized disc model indicates that the soft X-ray excess is independent of the accretion disc, confirming our interpretation of the tight correlation between the hard and soft X-ray spectra.

Characterization of seasonal variation of tropospheric aerosols in Chiba, Japan

Seasonal variations of tropospheric aerosol properties in Chiba, Japan, are investigated by means of optical monitoring (1999–2005), ground sampling (1998–2004), and wind data. The observation site at Chiba University is located in the urban Chiba area, about 30 km southeast of Tokyo. The aerosol optical thickness (AOT) and Angstrom exponent are derived from the data taken with a sun photometer. The value of AOT at the wavelength of 500 nm exhibits a seasonal variation, showing small values (<0.2) in fall and winter, and large values (∼0.5) in spring and summer. The variation of Angstrom exponent is in the range 0.5–1.8, showing negative correlation with the wind speed. This indicates that the influence of anthropogenic particles from local sources becomes relatively important when the wind is weak near the ground level. The influence of Asian dust particles is also detected during March and April. The seasonal variation is remarkable also in the chemical analysis data. For fine particles with diameters less than 2 μm, elemental carbon dominates in fall and winter, while (NH 4) 2SO 4 is prominent in spring and summer. For coarse particles, the fraction of sea salt particles increases in spring and summer.

Sliding mode-based microstructure torque and force estimations using MEMS optical monitoring

The determination of microstructure state is becoming of increasing importance for microelectromechanical system (MEMS) sensors and actuators. Sliding mode-based microtorque estimation for a rotary micromotor, assuming the availability of a MEMS optical monitoring data stream, is presented. The dynamic model of the rotating MEMS system and the electrostatic torque are identified. The technique uses the estimated position signal to approach the actual measured position signal, obtainable through optical monitoring, to simultaneously estimate the microtorque and load torque. The estimated microtorque and load torque are low-pass filtered to eliminate the switching behavior inherent in the sliding-mode estimator. The experimental setup of a lateral comb resonator with optical monitoring is presented and discussed. The simulation results of both electrostatic and load torque estimations are presented, as well as the experimental force estimation of a lateral comb resonator device.

Intrinsic Curvature in the X‐Ray Spectra of BL Lacertae Objects

We report results from XMM-Newton observations of 13 X-ray bright BL Lacertae objects, selected from the Einstein Slew Survey sample (SSS). The survey was designed to look for evidence of departures of the X-ray spectra from a simple power-law shape (i.e., curvature and/or line features) and to find objects worthy of deeper study. Our data are generally well fit by power-law models, with three cases having hard (Γ < 2; dN/dE ∝ E-Γ) spectra that indicate synchrotron peaks at E ≳ 5 keV. Previous data had suggested a presence of absorption features in the X-ray spectra of some BL Lac objects. In contrast, none of these spectra show convincing examples of line features in either absorption or emission, suggesting that such features are rare among BL Lac objects, or, more likely, are artifacts caused by instrumental effects. We find significant evidence for intrinsic curvature [steepening by dΓ/d(log E) = 0.4 ± 0.15] in 14 of the 17 X-ray spectra. This cannot be explained satisfactorily via excess absorption, since the curvature is essentially constant from 0.5-6 keV, an observation that is inconsistent with the modest amounts of absorption that would be required. We use the XMM-Newton Optical Monitor data with concurrent radio monitoring to derive broadband spectral energy distributions and peak frequency estimates. From these, we examine models of synchrotron emission and model the spectral curvature we see as the result of episodic particle acceleration.

Late‐Time X‐Ray, UV, and Optical Monitoring of Supernova 1979C

We present results from observations of supernova (SN) 1979C with the Newton X-Ray Multi-Mirror (XMM-Newton) mission in X-rays and in UV, archival X-ray, and Hubble Space Telescope (HST) data, and follow-up ground-based optical imaging. The XMM-Newton MOS spectrum shows the best-fit two-temperature thermal plasma emission characteristics of both the forward (kT(high) = 4:1(-2.4)(+76) keV) and reverse shock (kT(low) = 0.79(-0.17)(+0.24) keV) with no intrinsic absorption. The long-term X-ray light curve, constructed from all X-ray data available, reveals that SN 1979C is still radiating at a flux level similar to that detected by ROSAT in 1995, showing no sign of a decline over the last 6 years, some 16-23 yr after its outburst. The high inferred X-ray luminosity (L(0.3-2) = 8 x 10(38) ergs s(-1)) is caused by the interaction of the SN shock with dense circumstellar matter, likely deposited by a strong stellar wind from the progenitor with a high mass- loss rate of. M approximate to 1.5 x 10(-4) M(circle dot) yr(-1) (v(w)/10 km s(-1)). The X-ray data support a strongly decelerated shock and show a mass-loss rate history that is consistent with a constant progenitor mass-loss rate and wind velocity over the past greater than or similar to 16,000 yr in the stellar evolution of the progenitor. We find a best-fit circumstellar medium (CSM) density profile of rho(CSM) proportional to r(-s) with index s less than or similar to 1.7 and high CSM densities (greater than or similar to 10(4) cm(-3)) out to large radii from the site of the explosion (r greater than or similar to 4 x 10(17) cm). Using XMM-Newton Optical Monitor data, we further detect a pointlike optical/UV source consistent with the position of SN 1979C, with B-, U-, and UVW1-band luminosities of 5, 7, and 9 x 10(36) ergs s(-1), respectively. The young stellar cluster in the vicinity of the SN, as imaged by the HSTand follow- up ground- based optical imaging, can only provide a fraction of the total observed flux, so that a significant contribution to the output likely arises from the strong interaction of SN 1979C with dense CSM.

XMM-Newtonobservations of high-luminosity radio-quiet quasi-stellar objects

XMM-Newton observations of five high-luminosity radio-quiet quasi-stellar objects (QSOs; Q 0144-3938, UM 269, PG 1634+706, SBS 0909+532 and PG 1247+267) are presented. Spectral energy distributions were calculated from the XMM-Newton European Photon Imaging Camera (EPIC) and Optical Monitor (OM) data, with bolometric luminosities estimated in the range from 7 x 10 45 to 2 × 10 48 erg s -1 for the sample, peaking in the ultraviolet. At least four of the QSOs show a similar soft excess, which can be well modelled by either one or two blackbody components, in addition to the hard X-ray power law. The temperatures of these blackbodies (∼100-500 eV) are too high to be direct thermal emission from the accretion disc, so Comptonization is suggested. Two populations of Comptonizing electrons, with different temperatures, are needed to model the broad-band spectrum. The hotter of these produces what is seen as the hard X-ray power law, while the cooler (∼0.25-0.5 keV) population models the spectral curvature at low energies. Only one of the QSOs shows evidence for an absorption component, while three of the five show neutral iron emission. Of these, PG 1247+267 seems to have a broad line (with an equivalent width of ∼250eV), with a strong, associated reflection component (R ∼ 2), measured out to 30 keV in the rest frame of the QSO. Finally, it is concluded that the X-ray continuum shape of active galactic nuclei remains essentially constant over a wide range of black hole mass and luminosity.

Is the slope of the intrinsic Baldwin effect constant?

We investigate the relationship between emission-line strength and continuum luminosity in the best-studied nearby Seyfert 1 galaxy NGC5548. Our analysis of 13 years of ground-based optical monitoring data reveals significant year-to-year variations in the observed H-beta emission-line response in this source. More specifically, we confirm the result of Gilbert and Peterson (2003) of a non-linear relationship between the continuum and H-beta emission-line fluxes. Furthermore, we show that the slope of this relation is not constant, but rather decreases as the continuum flux increases. Both effects are consistent with photoionisation model predictions of a luminosity-dependent response in this line.

The Mass of the Central Black Hole in the Seyfert Galaxy NGC 3783

Improved analysis of ultraviolet and optical monitoring data on the Seyfert 1 galaxy NGC 3783 provides evidence for the existence of a supermassive, (8.7 +/- 1.1) x 10(exp 6) solar mass, black hole in this galaxy. By using recalibrated spectra from the International Ultraviolet Explorer satellite and ground-based optical data, as well as refined techniques of reverberation mapping analysis, we have reduced the statistical uncertainties in the response of the emission lines to variations in the ionizing continuum. The different time lags in the emission-line responses indicate a stratification in the ionization structure of the broad-line region and are consistent with the virial relationship suggested by the analysis of similar active galaxies.

Central Masses and Broad‐Line Region Sizes of Active Galactic Nuclei. I. Comparing the Photoionization and Reverberation Techniques

The masses and emission-line region sizes of active galactic nuclei (AGNs) can be measured by reverberation-mapping techniques, and we use these results to calibrate similar determinations made by photoionization models of the AGN line-emitting regions. Reverberation mapping uses the light travel-time delayed emission-line response to continuum variations to determine the size and kinematics of the emission-line region. We compile a sample of 17 Seyfert 1 galaxies and two quasars with reliable reverberation and spectroscopy data, twice the number available previously. The data provide strong evidence that the broad-line region (BLR) size (as measured by the lag of the emission-line luminosity after changes in the continuum) and the emission-line width measure directly the central mass: the virial assumption is tested with long-term UV and optical monitoring data on NGC 5548. Two methods are used to estimate the distance of the broad emission-line region from the ionizing source: the photoionization method (which is available for many AGNs but has large intrinsic uncertainties) and the reverberation method (which gives very reliable distances but is available for only a few objects). The distance estimate is combined with the velocity dispersion, derived from the broad Hβ line width (in the photoionization method) or from the variable part (rms) of the line profile, in the reverberation-rms method, to estimate the virial mass. Comparing the central masses calculated with the reverberation-rms method to those calculated using a photoionization model, we find a highly significant, nearly linear correlation. This provides a calibration of the photoionization method on the objects with presently available reverberation data, which should enable mass estimates for all AGNs with measured Hβ line width. We find that the correlation between the masses is significantly better than the correlation between the corresponding BLR sizes calculated by the two methods, which further supports the conclusion that both methods measure the mass of the central black hole . Comparing the BLR sizes given by the two methods also enables us to estimate the ionizing EUV luminosity Lion, which is not directly observable. Typically it is 10 times the monochromatic luminosity at 5100 A (Lv). The Eddington ratio for the objects in our sample is in the range Lv/LEdd ~ 0.001-0.03 and Lion/LEdd ≈ 0.01-0.3.

The Effect of a Variable Anisotropic Continuum Source upon the Broad Emission-Line Profiles and Responses

Optical monitoring data over several years in combination with the reconstructed 1-d response function for C IV obtained from the 1993 HST monitoring campaign of NGC 5548, reveal that: (a) radial motion does not dominate the gas kinematics (Korista et al. 1995); (b) line-profile variations occur in fixed regions of velocity space, a core and two wing components, are stochastic in nature, and appear to be unrelated to reverberation effects (Wanders &amp; Peterson 1996). Wanders et al. (1995) showed that these variations are broadly consistent with a spherical BLR geometry populated with optically thick clouds following randomly inclined circular Keplerian orbits, and illuminated by an anisotropically emitting point source of ionizing continuum radiation. Here we provide a brief description of this model and summarize its basic properties. A more thorough analysis is presented in Goad &amp; Wanders (1996).

CCD Photometry of 12 BL Lacertae Objects

view Abstract Citations (38) References (19) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS CCD Photometry of 12 BL Lacertae Objects Xie, G. Z. ; Zhang, Y. H. ; Li, K. H. ; Liu, F. K. ; Wang, J. C. ; Wang, X. M. Abstract The optical (BVRI) monitoring data covering 5 years for 12 x-ray-selected BL Lac objects are presented in this paper. The main results are: (1) If 0317+178 has shown a variability of 0.53 mag in R band on a time scale of about 1.93 days. (2) A variability of 0.58 mag within 5 min was recorded in the V band for H 0548-322. Our results would be valuable to understand the relation between XBLs and RBLs. Publication: The Astronomical Journal Pub Date: March 1996 DOI: 10.1086/117852 Bibcode: 1996AJ....111.1065X Keywords: HBL LACERTAE OBJECTS: GENERAL; X-RAYS: GALAXIES; GALAXIES: PHOTOMETRY full text sources ADS | data products SIMBAD (12) NED (12)

The optical variability of the Seyfert galaxies NGC 4051 and NGC 1068

The optical (BV) monitoring data for the Seyfert galaxies NGC 4051 and NGC 1068 are presented in this paper. NGC 4051 showed a variation of 0.43 mag in 21 minutes in B band from its bright nucleus, and the nucleus of NGC 1068 exhibited a variability of 0.46 mag in B band in a timescale of 1.8 hours. These results argued that the optical emission from the nuclei of the two Seyfert galaxies could be dominated by the nonthermal radiation. The data in this paper, however, are only marginal evidence on the rapid optical variability of these two Seyferts, and further monitoring is needed to confirm this type of variability.

Multiwavelength monitoring of the BL Lacertae object PKS 2155-304. 4: Multiwavelength analysis

Simultaneous X-ray, ultraviolet, optical, infrared, and radio monitoring data were used to test and constrain models of continuum emission from the BL Lacertae object PKS 2155-304. Intensively sampled ultraviolet and soft X-ray light curves showed a clear temporal correlation with the X-rays leading the ultraviolet by 2-3 hr. This lag was found to be significantly different from zero after an exhaustive comparison of four different techniques for measuring temporal correlations. Variations in the ultraviolet trough optical wave bands were also strongly correlated, with no measurable lag down to limiting timescales of approximately less than 1-2 hr. This strong correlation extends to the near-infrared, but the less intensive sampling precludes measurement of any lag beyomnd an upper limit of approximately less than 1 day. These lags and limits of the order of hours are much shorter than most rapid observed single-band variations. Because of the very sparse radio sampling, it was not possible to measure quantitatively the correlation and lag with shorter wavelengths, but the data do suggest that the radio may lag the optical/ultraviolet by approximately 1 week, with longer delays and weaker variations to longer radio wavelengths. The epoch-folding Q(exp 2) statistic was used to test for periodicity, and no evidence for strict or quasi-periodicity was found in any of the light curves. Because they lead the lower frequencies, the soft X-rays (approximately less than 1 keV) cannot arise from synchrotron self-Compton scattering. These results also rule out the accretion disk model, which predicts a measurable lag between ultraviolet/optical wavelength bands and a correlation between hardness and brightness, neither of which were seen. They are consistent with the entire radio through X-ray continuum arising from direct synchrotron emission from a relativistic jet. However, the tapered jet model, in which the X-ray emission is produced closer in, has problems explaining the magnitude of the ultraviolet/X-ray lag, because the X-ray-emitting electrons have very short lifetimes (t(sub 1/2) much less than 1 s). The result that the lag is much smaller than the variability timescale suggests instead that the radiation may be produced in a flattened region such as a shock front.

Multifrequency observations of BL Lacertae

We present 20 years of optical, infrared, and radio monitoring data for BL Lac as well as four simultaneous multifrequency spectra covering the 10^9-10^(18) Hz range. Although there is no time delay between the optical and infrared variability, the high-frequency radio variations precede lower frequency variations, but only by weeks. The optical variability precedes the radio variability by a few years. The structure function for the radio variations is nearly that of shot noise for time scales less than 600 days, in contrast to the optical variation, which is similar to flicker noise. These results indicate that, although there are fundamental differences between the optical and radio emitting regions, they are related, possibly by the propagation of shocks between regions. The multifrequency spectra show that the power per logarithmic bandwidth has a well-defined peak in the near-infrared and a sharp cutoff in the optical-ultraviolet region. This cutoff is like those seen in a few other blazars and is attributed to synchrotron losses that prevent particle acceleration from exceeding a critical energy. The X-ray continuum is not smoothly connected to the optical-ultraviolet emission and has a flatter slope, similar to that of the infrared-millimeter region. In addition, the X-ray emission varied in the same sense as the infrared-millimeter emission but opposite that of the optical-ultraviolet emission. These X-ray properties are those expected from the synchrotron-self-Compton process. The best model suggests that the plasma radiating at ~ 10^(11.5) Hz has a size of ~ 10^(-2·5) pc, a Doppler parameter δ>= 2-3, and a magnetic field of B = 2-40 G.

Multifrequency observation of the optically violent variable quasar 3C 446

Extensive optical and radio monitoring data and seven multifrequency spectra were obtained of the violently variable quasar 3C 446. The monitoring data suggest a correlation between the radio and optical outbursts, with the optical flare preceding the radio activity by 400-600 days. A difference in the statistical behavior of the optical and radio variability indicates that considerable processing occurs to the optical emitting plasma before it becomes radio emitting plasma. Within the radio band, outbursts proceed from high to low frequencies. An outburst in 1983 showed greater and more rapid variation in the optical than in the near-IR region. The 10-100 μm fluxes did not follow the higher frequency variation, suggesting a time delay between these spectral domains. During another time, the X-ray emission varied on a time scale of days and more rapidly than the UV or optical emission. On a time scale of weeks-months, the X-ray fluxes are well correlated with the UV-IR fluxes but not with the radio fluxes. The multifrequency data show that the flat radio spectrum turns over at 3-10 x 10^(11) Hz and the continuum steepens with frequency; ɑ(IR) = 1.1, ɑ(opt-UV) = -2 to -3. The X-ray emission lies an order of magnitude above an extrapolation of the optical-UV spectrum and has a harder spectrum. The power is primarily concentrated in the submillimeter and infrared region. When the source is faint, a blue bump may be present. The flux in the Lycx line is proportional to the UV continuum flux density when the source is bright but is independent of the continuum level when the source is faint. The data suggest that the X-rays are produced by the inverse Compton process from an emitting region (10^(16) cm) smaller than but related to the synchrotron emitting UV-IR region. The characteristic size of the emitting region increases with decreasing frequency from 10^(16) (X-ray region) to 1-3 x 10^(17) cm (far IR-submillimeter region) to 10^(19)-10^(20) cm (radio region). Plasma conditions are best constrained at the frequency when the source becomes transparent, the far IR-submillimeter band, where B ≈ 3-100 G, n ≈ 40-100 cm^(-3); and the Doppler boosting factor δ ≈ 1-5.