arXiv subjects

Hartmut Winkler

Publications and source records attributed to Hartmut Winkler.

At least 19 recordsLinked to original sources

arXiv2026

A Changing-Look Seyfert Discovered by eROSITA Reveals a Two-Component Broad-Line Region

Extreme sudden changes in the flow of accreting gas onto SMBHs manifest themselves via large-amplitude continuum variability and changes to broad Balmer emission profiles, driving changing-look AGN. X-ray flux monitoring with SRG/eROSITA revealed that in the Seyfert AGN HE 1237-2252 the soft X-ray flux dipped abruptly, by a factor of 17 within 18 months. We initiated a follow-up campaign that caught the luminosity recovery after the dip, and enabled us to study how the various accretion components responded during this flux recovery. Our campaign included multiband photometry, X-ray spectroscopy, and optical spectroscopy. We tracked as the accretion rate relative to Eddington increased by a factor of 7 in 3 years. Based on broad Hbeta variability, HE 1237-2252 was subtype 1.0-1.2 in 2002, transitioned to subtype 1.8 by the time of the luminosity dip, and then transitioned back to subtype 1.0 within 3 months as luminosity recovered. Both transitions saw broad Hbeta integrated line flux change by factors of 4-6. The broad Balmer profile is decomposed into a broad Gaussian consistent with virialized gas at 27+/-3 lt-dy, plus a double-peaked profile, consistent with a diskline structure at more than roughly 5 lt-dy. The diskline component's relative contribution to the total profile increases as continuum flux rises. The lack of obscuration in the X-ray spectra, as well as the IR continuum dip, point to an intrinsic pause in the accretion rate as opposed to variable line-of-sight obscuration. Candidates for the underlying mechanisms include propagating cold and warm fronts in the accretion disk. The increased prominence of the diskline BLR component's emission could be due to evolution in the physical extent of the X-ray corona, and in the fraction of >13.6 eV photons intercepted by the diskline, as the accretion rate increases.

astro-ph.GA↗

arXiv2026

The unusually red delay spectrum of the low-mass black hole AGN NGC\,4051 as revealed by intensive continuum reverberation mapping with the Las Cumbres Observatory

We present a two-year optical reverberation mapping campaign of NGC 4051, an active galactic nucleus (AGN) hosting a low-mass black hole ($8\times10^5 M_\odot$), using daily observations in seven photometric bands from Las Cumbres Observatory augmented by archival data from Swift XRT and UVOT. The light curves show correlated variability with wavelength-dependent lags broadly consistent with the standard accretion disc scaling, $\tau \propto \lambda^{4/3}$, and a pronounced u-band excess. However, the $i$ and $z_s$ lags are significantly larger than expected and cannot be explained by a combination of disc emission and diffuse continuum (DC) from the broad-line region (BLR), making NGC 4051 a notable lag-luminosity outlier. The spectral energy distribution (SED) of the variable AGN component is markedly redder than the canonical accretion disc prediction, $F_\nu \propto \nu^{1/3}$, typically observed in more massive systems. We explore two scenarios to account for the red UV-optical SED and the anomalously large $i$ and $z_s$ lags: (a) SMC-like dust reddening ($E(B-V)\sim0.18$) combined with optically thick emission from the inner edge of the dusty torus; and (b) a dominant diffuse continuum contribution. We discuss the implications of each scenario within a comprehensive multi-wavelength framework.

astro-ph.HE↗

arXiv2026

Extreme line profile variations in the repeating changing-look active galactic nucleus IRAS23226-3843

IRAS23226-3843 has been identified as a highly variable Seyfert galaxy and even as a changing-look active galactic nucleus based on optical spectra. Here we present follow-up observations - taken over the past five years - for examining the ongoing photometric and spectral variations in this remarkable galaxy. We carried out SWIFT observations of IRAS23226-3843 together with new optical spectra taken in 2023 and 2024. In parallel we investigate ASAS-SN photometric data from 2014 till 2025. IRAS23226-3843 stayed on a high continuum flux level in the X-ray as well as in the optical since a historic outburst in 2019. However, it shows strong short-term variations on timescales of a few months. Densely sampled ASAS-SN V-band continuum data from 2014 till 2025 confirm that behavior. IRAS23226-3843 switched from a clear Seyfert 1 type in December 2019 to a Seyfert 1.9/2 type in July 2020 based on its optical spectra. Afterward, it again became a Seyfert 1 type with symmetric broad single-peaked Balmer line profiles in January 2023. These spectra prove the repeating changing-look character of the galaxy.IRAS23226-3843 exhibits extreme high Balmer decrements Ha\Hb based on their broad line components. The Balmer decrement values are on the order of 10. IRAS23226-3843 successively showed all types of broad line Balmer profiles during the past 25 years over periods of many years: asymmetric single-peaked, double-peaked, as well as single-peaked and symmetric profiles in addition to its Seyfert 1.9/2 transition. These variations are not clearly correlated with continuum and line intensity variations.

astro-ph.GA↗

arXiv2026

A Phenomenological Study of the Accretion Disk in the Super-Eddington AGN I Zw 1

The structure of the accretion disk in AGN is still an unsolved question, especially how it may change with Eddington ratio. Here we examine the accretion disk in the super-Eddington AGN I Zw 1 using reverberation mapping of the optical continuum. We use three years of optical monitoring with Las Cumbres Observatory at sub-day cadence in $uBgVriz_s$. The lag-wavelength spectrum, calculated using the cross correlation method and PyROA, shows a $u$-band excess. PyROA lags are equally well fitted with a thin and slim disk profile. The UV/optical AGN spectral energy distribution is consistent with a thin disk. The disk size at 4495 \r{A} for a thin disk model is $4.23\pm0.24\:\mathrm{ld}$ and for a slim disk model is $1.71\pm0.09\:\mathrm{ld}$, larger by a factor of $2-4$ than the fiducial disk size of $1.07\pm0.15\:\mathrm{ld}$ as determined using the Eddington ratio. We find evidence of different size scales probed with different variability timescales. Lags evaluated at longer variability timescales increase as do frequency-resolved lags at low frequencies, which we interpret as an additional secondary reprocessor at large radii consistent with the broad-line region (BLR) in I Zw 1. The high frequency lags, predicted well with just a disk, are fit with a thin disk profile and a size of $0.61\pm0.37\:\mathrm{ld}$. This indicates that the actual disk size may be on the order of the fiducial size. We also collate the most extensive set of directly measured internal sizes of an AGN, from optical to mid-infrared with reverberation mapping and optical interferometry. Assuming that the disk is indeed the fiducial size, these show little evidence that the accretion disk extends into the BLR significantly, tentatively disfavouring the failed radiatively accelerated dust driven outflow BLR formation model.

astro-ph.GA↗

arXiv2025

Supermassive Black Holes with High Accretion Rates in Active Galactic Nuclei. XII. Reverberation Mapping Results for 15 PG Quasars from a Long-Duration High-Cadence Campaign

We present the first results from long-term high-cadence spectroscopic monitoring of 15 PG quasars with relatively strong Fe II emission as a part of a broader reverberation mapping campaign performed with the Calar Alto Observatory 2.2m telescope. The $V$-band, 5100 \r{A} continuum, and H$\beta$ broad emission line light curves were measured for a set of quasars for between dozens to more than a hundred epochs from May 2017 to July 2020. Accurate time lags between the variations of the H$\beta$ broad line fluxes and the optical continuum strength are obtained for all 15 quasars, ranging from $17.0_{-3.2}^{+2.5}$ to $95.9_{-23.9}^{+7.1}$ days in the rest frame. The virial masses of the central supermassive black holes are derived for all 15 quasars, ranging between $0.50_{-0.19}^{+0.18}$ and $19.17_{-2.73}^{+2.98}$ in units of $10^7 M_\odot$. For 11 of the objects in our sample, this is the first reverberation analysis published. Of the rest, two objects have been the subject of previous reverberation studies, but we determine time lags for these that are only half as long as found in the earlier investigations, which had only been able to sample much more sparsely. The remaining two objects have previously been monitored with high sampling rates. Our results here are consistent with the earlier findings in the sense that the time lag and the line width vary inversely consistent with virialization.

astro-ph.GA↗

arXiv2025

Supermassive Black Holes with High Accretion Rates in Active Galactic Nuclei. XIV. Long-Duration High-Cadence Reverberation Mapping Results for 11 PG Quasars

We report the results of a long-duration high-cadence reverberation mapping campaign of a second batch of 11 PG quasars using the 2.2m telescope at the Calar Alto Observatory. This follows a similar earlier study of another sample of 15 objects reported by Hu et al. (2021). Among the 11 PG quasars, 8 objects have the H$\beta$ time lags measured for the first time, while the other 3 objects were observed in previous campaigns, but only had highly uncertain H$\beta$-lag measurements. Long-term light curves are presented of photometric $V$-band, spectroscopic 5100 \r{A} continuum, and the H$\beta$ emission line, lasting for $\sim$3--6 years with a cadence of $\sim$6--14 days. Accurate H$\beta$ time lags ranging from $\sim$20 to 150 days in the rest frame are obtained. The estimated virial masses of the central supermassive black holes range from $\sim$(3--300)$\times10^7 M_\odot$. Combining these results with those reported in Hu et al. (2021), we now have 26 PG quasars, with representative properties, having reliable H$\beta$ time-lag measurements from our long-duration high-cadence campaign. A tentative fit to the relation between the H$\beta$ time lag and the continuum luminosity for these 26 objects gives a slope of 0.53.

astro-ph.GA↗

arXiv2025

Monitoring AGNs with H$\beta$ Asymmetry. V. Long-term Variation and Evolution of the Broad H$\beta$ Emission-Line Profiles

The physical origins of the diverse emission-line asymmetries observed in the spectra of active galactic nuclei (AGNs) remain incompletely understood. Monitoring the temporal variations of line profiles offers a promising approach to investigating the underlying physics. In this study, we present an analysis of the broad H$\beta$ emission line profiles of eight AGNs observed from the end of 2016 to May 2023 as part of the reverberation mapping campaign titled "Monitoring AGNs with H$\beta$ Asymmetry" (MAHA), utilizing data obtained from the Wyoming Infrared Observatory (WIRO) 2.3-meter telescope. We measure the temporal variations of line asymmetry, width, and central velocity shift for the eight objects. Our findings reveal that the variation in asymmetry is positively correlated with H$\beta$ flux in five of the eight objects, while the remaining objects exhibit negative or complex correlations. Furthermore, we observe anti-correlations between line width and H$\beta$ flux for most objects, indicating the presence of the "breathing" phenomenon in their H$\beta$ emission lines. In contrast, two objects demonstrate an "anti-breathing" phenomenon or complex behavior. We discuss the physical origins of the temporal variations in line profiles and propose the possibility of decomposing the variations in H$\beta$ asymmetry and width into components: one that corresponds to short-term variations in H$\beta$ flux and another that reflects long-term variations in continuum light curves, perhaps driven by radiation pressure.

astro-ph.GA↗

arXiv2025

Spectroastrometry and Reverberation Mapping of Active Galactic Nuclei. II. Measuring Geometric Distances and Black Hole Masses of Four Nearby Quasars

The geometric distances of active galactic nuclei (AGNs) are challenging to measure because of their exceptionally compact structure yet vast cosmic distances. A combination of spectroastrometry and reverberation mapping (SARM) of broad-line regions (BLRs) constitutes a novel means to probe the geometric distance of AGNs, which has recently become practically feasible owing to successful interferometric observations with VLTI/GRAVITY. Here, we perform SARM analysis of four nearby quasars: Mrk 509, PDS 456, 3C 273, and NGC 3783. Results for the former two are reported for the first time and the latter two are revisited using our improved BLR dynamical modeling that includes the radial-dependent responsivity of BLRs. This allows us to self-consistently account for the emissivity weighting of the BLR in spectroastrometry and responsivity weighting in reverberation mapping. We obtain angular-diameter distances of the four quasars, from which we derive a Hubble constant of $H_0=69_{-10}^{+12}\,\rm km\,s^{-1}\,Mpc^{-1}$. Although this constitutes a large uncertainty for a measurement of $H_0$, it is anticipated that the precision will improve to a competitive level once a greater number of AGNs are accessible following the upgrade of GRAVITY in the near future. From SARM analysis, the black hole masses of the four quasars are also measured with the statistical uncertainty ranging from 0.06 to 0.23 dex, consistent with the correlations between black hole masses and properties of the host bulges.

astro-ph.GA↗

arXiv2025

Accretion disc reverberation mapping of the quasar 3C 273

We present accretion disc size measurements for the well-known quasar 3C 273 using reverberation mapping (RM) performed on high-cadence light-curves in seven optical filters collected with the Las Cumbres Observatory (LCO). Lag estimates obtained using Javelin and PyROA are consistent with each other and yield accretion disc sizes a factor of ~2-7 larger than `thin disc' theoretical expectations. This makes 3C 273 one of a growing number of active galactic nuclei (AGN) to display the so-called `accretion disc size' problem usually observed in low-luminosity AGN. Power-law fits of the form tau~lambda^beta to the lag spectrum, and nufnu ~ nu^beta to the spectral energy distribution (SED) of the variations, both give results consistent with the `thin disc' theoretical expectation of beta=4/3. The Starkey et al. `flat disc with a steep rim' model can fit both the lag estimates and the SED variations. Extrapolating the observed optical lags to putative dust-forming regions of the disc gives r~100-200 light-days. These radii are consistent with the size of the broad line region (BLR) as determined by near-infrared interferometric studies as well as with the best-fit location of the outer edge for the `flat disc with a steep rim' model. Therefore, the accretion disc in 3C 273 might be sufficiently extended to be dusty, allowing the BLR to emerge from it in a dusty outflow. A flux variation gradient analysis and the structure function of our LCO light-curves confirm that the optical variability in 3C 273 is dominated by the accretion disc rather than its radio jet.

astro-ph.GA↗

arXiv2024

Broad-line Region of the Quasar PG 2130+099. II. Doubling the Size Over Four Years?

Over the past three decades, multiple reverberation mapping (RM) campaigns conducted for the quasar PG 2130+099 have exhibited inconsistent findings with time delays ranging from $\sim$10 to $\sim$200 days. To achieve a comprehensive understanding of the geometry and dynamics of the broad-line region (BLR) in PG 2130+099, we continued an ongoing high-cadence RM monitoring campaign using the Calar Alto Observatory 2.2m optical telescope for an extra four years from 2019 to 2022. We measured the time lags of several broad emission lines (including He II, He I, H$\beta$, and Fe II) with respect to the 5100 {\AA} continuum, and their time lags continuously vary through the years. Especially, the H$\beta$ time lags exhibited approximately a factor of two increase in the last two years. Additionally, the velocity-resolved time delays of the broad H$\beta$ emission line reveal a back-and-forth change between signs of virial motion and inflow in the BLR. The combination of negligible ($\sim$10%) continuum change and substantial time-lag variation (over two times) results in significant scatter in the intrinsic $R_{\rm H\beta}-L_{\rm 5100}$ relationship for PG 2130+099. Taking into account the consistent changes in the continuum variability time scale and the size of the BLR, we tentatively propose that the changes in the measurement of the BLR size may be affected by 'geometric dilution'.

astro-ph.GA↗

arXiv2024

Spectroastrometry and Reverberation Mapping (SARM) of Active Galactic Nuclei. I. The H$\beta$ Broad-line Region Structure and Black Hole Mass of Five Quasars

We conduct a reverberation mapping (RM) campaign to spectroscopically monitor a sample of selected bright active galactic nuclei with large anticipated broad-line region (BLR) sizes adequate for spectroastrometric observations by the GRAVITY instrument on the Very Large Telescope Interferometer. We report the first results for five objects, IC 4329A, Mrk 335, Mrk 509, Mrk 1239, and PDS 456, among which Mrk 1239 and PDS 456 are for the first time spectroscopically monitored. We obtain multi-year monitoring data and perform multi-component spectral decomposition to extract the broad H$\beta$ profiles. We detect significant time lags between the H$\beta$ and continuum variations, generally obeying the previously established BLR size-luminosity relation. Velocity-resolved H$\beta$ time lags illustrate diverse, possibly evolving BLR kinematics. We further measure the H$\beta$ line widths from mean and rms spectra and the resulting virial products show good consistency among different seasons. Adopting a unity virial factor and the full width at half maximum of the broad H$\beta$ line from the mean spectrum as the measure of velocity, the obtained black hole mass averaged over seasons is $\log M_\bullet/M_\odot=8.02_{-0.14}^{+0.09}$, $6.92_{-0.12}^{+0.12}$, $8.01_{-0.25}^{+0.16}$, $7.44_{-0.14}^{+0.13}$, and $8.59_{-0.11}^{+0.07}$ for the five objects, respectively. The black hole mass estimations using other line width measures are also reported (up to the virial factors). For objects with previous RM campaigns, our mass estimates are in agreement with earlier results. In a companion paper, we will employ BLR dynamical modeling to directly infer the black hole mass and thereby determine the virial factors.

astro-ph.GA↗

arXiv2024

eROSITA Detection of a Cloud Obscuration Event in the Seyfert AGN EC 04570-5206

Recent years have seen broad observational support for the presence of a clumpy component within the circumnuclear gas around SMBHs. In the X-ray band, individual clouds can manifest themselves when they transit the line of sight to the X-ray corona, temporarily obscuring the X-ray continuum and thereby indicating the characteristics and location of these clouds. X-ray flux monitoring with SRG/eROSITA has revealed that in the Seyfert 1 AGN EC 04570-5206, the soft X-ray flux dipped abruptly for about 10-18 months over 2020-2021, only to recover and then drop a second time by early 2022. Here, we investigate whether these flux dips and recoveries could be associated with cloud occultation events. We complemented the eROSITA scans with multiwavelength follow-up observations, including X-ray/UV observations with Swift, XMM-Newton, and NICER, along with ground-based optical photometric and spectroscopic observations to investigate the spectral and flux variability. XMM-Newton spectra confirm that the soft X-ray flux dips were caused by partial-covering obscuration by two separate clouds. The 2020-2021 event was caused by a cloud with column density near 1e22 /cm2 and a covering fraction near 0.6. The cloud in the 2022 event had a column density near 3e23 /cm2 and a covering fraction near 0.8. The optical/UV continuum flux varied minimally and the optical emission line spectra showed no variability in Balmer profiles or intensity. The transiting gas clouds are neutral or lowly-ionized, while the lower limits on their radial distances are commensurate with the dust sublimation zone (cloud 1) or the optical broad line region (cloud 2). One possible explanation is a dust-free, outflowing wind with embedded X-ray clumps. These events are the first cloud obscuration events detected in a Seyfert galaxy using eROSITA's X-ray monitoring capabilities.

astro-ph.HE↗

arXiv2023

Continuum Reverberation Mapping of Mrk 876 Over Three Years With Remote Robotic Observatories

Continuum reverberation mapping probes the sizescale of the optical continuum-emitting region in active galactic nuclei (AGN). Through 3 years of multiwavelength photometric monitoring in the optical with robotic observatories, we perform continuum reverberation mapping on Mrk~876. All wavebands show large amplitude variability and are well correlated. Slow variations in the light curves broaden the cross-correlation function (CCF) significantly, requiring detrending in order to robustly recover interband lags. We measure consistent interband lags using three techniques (CCF, JAVELIN, PyROA), with a lag of around 13~days from $u$ to $z$. These lags are longer than the expected radius of 12~days for the self-gravitating radius of the disk. The lags increase with wavelength roughly following $λ^{4/3}$, as would be expected from thin disk theory, but the lag normalization is approximately a factor of 3 longer than expected, as has also been observed in other AGN. The lag in the $i$ band shows an excess which we attribute to variable H$α$ broad-line emission. A flux-flux analysis shows a variable spectrum that follows $f_ν\propto λ^{-1/3}$ as expected for a disk, and an excess in the $i$ band that also points to strong variable H$α$ emission in that band.

astro-ph.GA↗

arXiv2023

A complex dust morphology in the high-luminosity AGN Mrk 876

Recent models for the inner structure of active galactic nuclei (AGN) advocate the presence of a radiatively accelerated, dusty outflow launched from the outer regions of the accretion disk. Here we present the first near-infrared (near-IR) variable (rms) spectrum for the high-luminosity, nearby AGN Mrk 876. We find that it tracks the accretion disk spectrum out to longer wavelengths than the mean spectrum due to a reduced dust emission. The implied outer accretion disk radius is consistent with the infrared results predicted by a contemporaneous optical accretion disk reverberation mapping campaign and much larger than the self-gravity radius. The reduced flux variability of the hot dust could be either due to the presence of a secondary, constant dust component in the mean spectrum or introduced by the destructive superposition of the dust and accretion disk variability signals or some combination of both. Assuming thermal equilibrium for optically thin dust, we derive the luminosity-based dust radius for different grain properties using our measurement of the temperature. We find that in all cases considered the values are significantly larger than the dust response time measured by IR photometric monitoring campaigns, with the least discrepancy present relative to the result for a wavelength-independent dust emissivity law, i.e. a blackbody, which is appropriate for large grain sizes. This result can be well explained by assuming a flared, disk-like structure for the hot dust.

astro-ph.GA↗

arXiv2022

The outburst of the changing-look AGN IRAS23226-3843 in 2019

IRAS23226-3843 has previously been classified as a changing-look AGN based on X-ray and optical spectral variations. In 2019, Swift observations revealed a strong rebrightening in X-ray and UV fluxes in comparison to observations in 2017. We took follow-up Swift, XMM-Newton, and NuSTAR observations together with optical spectra (SALT and SAAO 1.9m telescope) from 2019 until 2021. IRAS23226-3843 showed a strong X-ray and optical outburst in 2019. It varied in the X-ray and optical continuum by a factor of 5 and 1.6, respectively, within two months. This corresponds to a factor of 3 in the optical after correction for the host galaxy contribution. The Balmer and FeII emission-line intensities showed comparable variability amplitudes. The Halpha profiles changed from a blue-peaked profile in the years 1997 and 1999 to a broad double-peaked profile in 2017 and 2019. However, there were no major profile variations in the extremely broad double-peaked profiles despite the strong intensity variations in 2019. One year after the outburst, the optical spectral type changed and became a Seyfert type 2 in 2020. Blue outflow components are present in the Balmer lines and in the Fe band in the X-rays. A deep broadband XMM-Newton/NuSTAR spectrum was taken during the maximum state in 2019. This spectrum is qualitatively very similar to a spectrum taken in 2017, but by a factor of 10 higher. The soft X-ray band appears featureless. The soft excess is well modeled with a Comptonization model. A broadband fit with a power-law continuum, Comptonized soft excess, and Galactic absorption gives a good fit to the combined EPIC-pn and NuSTAR spectrum. In addition, we see a complex and broadened Fe K emission-line profile in the X-rays. The changing-look character in IRAS23226-3843 is most probably caused by changes in the accretion rate -- based on the short-term variations on timescales of weeks to months.

astro-ph.HE↗

arXiv2022

Monitoring AGNs with H$β$ Asymmetry. III. Long-term Reverberation Mapping Results of 15 Palomar-Green Quasars

In this third paper of the series reporting on the reverberation mapping (RM) campaign of active galactic nuclei with asymmetric H$β$ emission-line profiles, we present results for 15 Palomar-Green (PG) quasars using spectra obtained between the end of 2016 to May 2021. This campaign combines long time spans with relatively high cadence. For 8 objects, both the time lags obtained from the entire light curves and the measurements from individual observing seasons are provided. Reverberation mapping of 9 of our targets has been attempted for the first time, while the results for 6 others can be compared with previous campaigns. We measure the H$β$ time lags over periods of years and estimate their black hole masses. The long duration of the campaign enables us to investigate their broad line region (BLR) geometry and kinematics for different years by using velocity-resolved lags, which demonstrate signatures of diverse BLR geometry and kinematics. The BLR geometry and kinematics of individual objects are discussed. In this sample, the BLR kinematics of Keplerian/virialized motion and inflow is more common than outflow.

astro-ph.GA↗

arXiv2022

A revised simplified scattering model for the moonlit sky brightness profile based on photometry at SAAO

This paper presents multi-filter measurements of the night sky brightness at the South African Astronomical Observatory (SAAO) in Sutherland in the presence of a bright moon. The observations cover a wide range of sky directions, lunar phases and lunar positions. A revised simplified scattering model is developed for estimating the sky brightness due to moonlight that more accurately reflects the atmospheric extinction of the lunar beam compared to models frequently applied in astronomical studies. Contributions to night sky brightness due to sources other than moonlight are quantified and subtracted from the total sky background radiation to determine the spectral intensity and angular distribution of scattered moonlight. The atmospheric scattering phase function is then derived by comparing the sky brightening to the strength of the incoming lunar beam, estimated using a novel approach. The phase function is shown to be an excellent match to the combined theoretical Rayleigh and Mie scattering functions, the latter with a Henyey--Greenstein form instead of the exponential angular relationship often used in previous studies. Where deviations between measured and model sky brightness are evident in some bands these are explained by contributions from multiple scattering or airglow, and are quantified accordingly. The model constitutes an effective tool to predict sky brightness at SAAO in optical photometric bands, especially with a bright moon present. The methodology can also be readily be adapted for use at other astronomical sites. The paper furthermore presents $UBV(RI)_c$ and Str{ö}mgren photometry for 49 stars, most with no prior such data.

astro-ph.IM↗

arXiv2020

Evidence for Two Distinct Broad-Line Regions from Reverberation Mapping of PG 0026+129

We report on the results of a new spectroscopic monitoring campaign of the quasar PG 0026+129 at the Calar Alto Observatory 2.2m telescope from July 2017 to February 2020. Significant variations in the fluxes of the continuum and broad-emission lines, including H$β$ and He II, were observed in the first and third years, and clear time lags between them are measured. The broad H$β$ line profile consists of two Gaussian components: an intermediate-width H$β_{\rm IC}$ with a full width at half-maximum (FWHM) of 1964$\pm$18 $\rm km~s^{-1}$ and another very broad H$β_{\rm VBC}$ with a FWHM of 7570$\pm$83 $\rm km~s^{-1}$. H$β_{\rm IC}$ has long time lags of $\sim$40--60 days in the rest frame, while H$β_{\rm VBC}$ shows nearly zero time delay with respect to the optical continuum at 5100 Å. The velocity-resolved delays show consistent results: lags of $\sim$30--50 days at the core of the broad H$β$ line and roughly zero lags at the wings. H$β_{\rm IC}$ has a redshift of $\sim$400 $\rm km~s^{-1}$ which seems to be stable for nearly 30 years by comparing with archived spectra, and may originate from an infall. The root mean square (rms) spectrum of H$β_{\rm VBC}$ shows a double-peaked profile with brighter blue peak and extended red wing in the first year, which matches the signature of a thin disk. Both the double-peaked profile and the near-zero lag suggest that H$β_{\rm VBC}$ comes from a region associated with the part of the accretion disc that emits the optical continuum. Adopting the FWHM (in the rms spectrum) and the time lag measured for the total H$β$ line, and a virial factor of 1.5, we obtain a virial mass of $2.89_{-0.69}^{+0.60} \times10^7 M_{\odot}$ for the central black hole in this quasar.

astro-ph.GA↗