arXiv subjects

Vladimir V. Kouprianov

Publications and source records attributed to Vladimir V. Kouprianov.

At least 19 recordsLinked to original sources

arXiv2026

The October 2022 flare in OJ 287 and the mass of its primary black hole

The bright blazar OJ~287 has demonstrated a sequence of flares, which are well explained by a quasi-Keplerian orbit model. The flares are associated with the impact of the secondary on the accretion disk of the primary. The orbit must precess in order to produce the correct sequence of flares, and from the precession rate we calculate the mass of the primary. This precession rate gives the mass of the primary $M_{BH} = (18.35\pm0.05) \times 10^9 M_{\odot}$. Two kinds of flares have been identified: direct flares from the impacts, and tidal flares arising from an increased accretion flow into the jet. The precession rate and the primary black hole mass may be independently determined from both sets of flares; the tidal flare of October 2022 was recommended for an intense campaign for this reason. This paper describes these observations over a wide spectral range. We show that the October 2022 flare fits the expectations for a tidal flare and thus supports the earlier determination of the mass of the binary black hole system in OJ 287. The mass of the primary may also be deduced from secondary indicators such as the correlation with the hydrogen line strength and the black hole mass. These studies require that the mass is above $M_{BH} \sim 10^{10} M_{\odot}$, but do not specify the value more exactly.

astro-ph.HE↗

arXiv2026

An Extreme Scattering Event Toward PSR J2313+4253

We present evidence of an extreme scattering event (ESE) toward PSR J2313+4253 using high-cadence observations taken with the Green Bank Observatory 20m telescope. The high density of observations in time allow for detailed tracking of the event. We observe a pair of spikes along with the characteristic drop in scintillation bandwidth that is expected during an ESE. This pattern implies that the structures predominantly responsible for scattering occur at different distances than those from previous and subsequent epochs. A secondary spectrum processed during the event shows a detached feature similar to those found in double lensing events from previously observed ESEs. We measure this event as originating from a scattering region with a distance of 1.04(1) kpc, a transverse size of 15 AU, and a duration of approximately 220 days. These rare events provide opportunities to study the properties of small-scale structures in the ISM.

astro-ph.HE↗

arXiv2025

Identifying the secondary jet in the RadioAstron image of OJ~287

The 136 year long optical light curve of OJ~287 is explained by a binary black hole model where the secondary is in a 12 year orbit around the primary. Impacts of the secondary on the accretion disk of the primary generate a series of optical flares which follow a quasi-Keplerian relativistic mathematical model. The orientation of the binary in space is determined from the behavior of the primary jet. Here we ask how the jet of the secondary black hole projects onto the sky plane. Assuming that the jet is initially perpendicular to the disk, and that it is ballistic, we follow its evolution after the Lorentz transformation to the observer's frame. Since the orbital speed of the secondary is of the order of one-tenth of the speed of light, the result is a change in the jet direction by more than a radian during an orbital cycle. We match the theoretical jet line with the recent 12 $μ$as-resolution RadioAstron map of OJ~287, and determine the only free parameter of the problem, the apparent speed of the jet relative to speed of light. It turns out that the Doppler factor of the jet, $δ\sim5$, is much lower than in the primary jet. Besides following a unique shape of the jet path, the secondary jet is also distinguished by a different spectral shape than in the primary jet. The present result on the spectral shape agrees with the huge optical flare of 2021 November 12, also arising from the secondary jet.

astro-ph.HE↗

arXiv2024

The Pulsar Science Collaboratory: Multi-Epoch Scintillation Studies of Pulsars

We report on findings from scintillation analyses using high-cadence observations of eight canonical pulsars with observing baselines ranging from one to three years. We obtain scintillation bandwidth and timescale measurements for all pulsars in our survey, scintillation arc curvature measurements for four, and detect multiple arcs for two. We find evidence of a previously undocumented scattering screen along the line of sight (LOS) to PSR J1645$-$0317, as well as evidence that a scattering screen along the LOS to PSR J2313$+$4253 may reside somewhere within the Milky Way's Orion-Cygnus arm. We report evidence of a significant change in the scintillation pattern in PSR J2022$+$5154 from the previous two decades of literature, wherein both the scintillation bandwidth and timescale decreased by an order of magnitude relative to earlier observations at the same frequencies, potentially as a result of a different screen dominating the observed scattering. By augmenting the results of previous studies, we find general agreement with estimations of scattering delays from pulsar observations and predictions by the NE2001 electron density model but not for the newest data we have collected, providing some evidence of changes in the ISM along various LOSs over the timespans considered. In a similar manner, we find additional evidence of a correlation between a pulsar's dispersion measure and the overall variability of its scattering delays over time. The plethora of interesting science obtained through these observations demonstrates the capabilities of the Green Bank Observatory's 20m telescope to contribute to pulsar-based studies of the interstellar medium.

astro-ph.HE↗

arXiv2024

MASTER OT J030227.28+191754.5: an unprecedentedly energetic dwarf nova outburst

We present a detailed study of the MASTER OT J030227.28+191754.5 outburst in 2021-2022, reaching an amplitude of 10.2 mag and a duration of 60 d. The detections of (1) the double-peaked optical emission lines, and (2) the early and ordinary superhumps, established that MASTER OT J030227.28+191754.5 is an extremely energetic WZ Sge-type dwarf nova (DN). Based on the superhump observations, we obtained its orbital period and mass ratio as 0.05986(1) d and 0.063(1), respectively. These are within a typical range of low-mass-ratio DNe. According to the binary parameters derived based on the thermal-tidal instability model, our analyses showed that (1) the standard disk model requires an accretion rate $\simeq$ 10$^{20}$ g s$^{-1}$ to explain its peak optical luminosity and (2) large mass was stored in the disk at the outburst onset. These cannot be explained solely by the impact of its massive ($\gtrsim$ 1.15 M$_\odot$) primary white dwarf implied by Kimura et al. (2023). Instead, we propose that the probable origin of this enormously energetic DN outburst is the even lower quiescence viscosity than other WZ Sge-type DNe. This discussion is qualitatively valid for most possible binary parameter spaces unless the inclination is low ($\lesssim 40^\circ$) enough for the disk to be bright explaining the outburst amplitude. Such low inclinations, however, would not allow detectable amplitude of early superhumps in the current thermal-tidal instability model. The optical spectra at outburst maximum showed the strong emission lines of Balmer, He I, and He II series whose core is narrower than $\sim 800$ km s$^{-1}$. Considering its binary parameters, a Keplerian disk cannot explain this narrow component, but the presumable origin is disk winds.

astro-ph.SR↗

arXiv2024

A Statistical Analysis of Crab Pulsar Giant Pulse Rates

A small number of pulsars are known to emit giant pulses, single pulses much brighter than average. Among these is PSR J0534+2200, also known as the Crab pulsar, a young pulsar with high giant pulse rates. Long-term monitoring of the Crab pulsar presents an excellent opportunity to perform statistical studies of its giant pulses and the processes affecting them, potentially providing insight into the behavior of other neutron stars that emit bright single pulses. Here, we present an analysis of a set of 24,985 Crab giant pulses obtained from 88 hours of daily observations at a center frequency of 1.55 GHz by the 20-meter telescope at the Green Bank Observatory, spread over 461 days. We study the effects of refractive scintillation at higher frequencies than previous studies and compare methods of correcting for this effect. We also search for deterministic patterns seen in other single-pulse sources, possible periodicities seen in several rotating radio transients and fast radio bursts, and clustering of giant pulses like that seen in the repeating fast radio burst FRB121102.

astro-ph.HE↗

arXiv2024

Evidence of jet activity from the secondary black hole in the OJ287 binary system

We report the study of a huge optical intraday flare on November 12, 2021, at 2 am UT, in the blazar OJ287. In the binary black hole model it is associated with an impact of the secondary black hole on the accretion disk of the primary. Our multifrequency observing campaign was set up to search for such a signature of the impact, based on a prediction made eight years earlier. The first I-band results of the flare have already been reported by \cite{2024ApJ...960...11K}. Here we combine these data with our monitoring in the R-band. There is a big change in the R-I spectral index by $1.0\pm0.1$ between the normal background and the flare, suggesting a new component of radiation. The polarization variation during the rise of the flare suggests the same. The limits on the source size place it most reasonably in the jet of the secondary black hole. We then ask why we have not seen this phenomenon before. We show that OJ287 was never before observed with sufficient sensitivity on the night when the flare should have happened according to the binary model. We also study the probability that this flare is just an oversized example of intraday variability, using the Krakow-dataset of intense monitoring between 2015 and 2023. We find that the occurrence of a flare of this size and rapidity is unlikely. In the Appendix, we give the full orbit-linked historical light curve of OJ287 as well as the dense monitoring sample of Krakow.

astro-ph.HE↗

arXiv2024

Accretion Funnel Reconfiguration during an Outburst in a Young Stellar Object: EX Lupi

EX Lupi, a low-mass young stellar object, went into an accretion-driven outburst in March of 2022. The outburst caused a sudden phase change of ~ 112$^{\circ}$ $\pm$ 5$^{\circ}$ in periodically oscillating multiband lightcurves. Our high resolution spectra obtained with HRS on SALT also revealed a consistent phase change in the periodically varying radial velocities, along with an increase in the radial velocity amplitude of various emission lines. The phase change and increase of radial velocity amplitude morphologically translates to a change in the azimuthal and latitudinal location of the accretion hotspot over the stellar surface, which indicates a reconfiguration of the accretion funnel geometry. Our 3D MHD simulations reproduce the phase change for EX Lupi. To explain the observations we explored the possibility of forward shifting of the dipolar accretion funnel as well as the possibility of an emergence of a new accretion funnel. During the outburst, we also found evidence of the hotspot's morphology extending azimuthally, asymmetrically with a leading hot edge and cold tail along the stellar rotation. Our high cadence photometry showed that the accretion flow has clumps. We also detected possible clumpy accretion events in the HRS spectra, that showed episodically highly blue-shifted wings in the Ca II IRT and Balmer H lines.

astro-ph.SR↗

arXiv2023

On the need of an ultramassive black hole in OJ 287

The highly variable blazar OJ~287 is commonly discussed as an example of a binary black hole system. The 130 year long optical light curve is well explained by a model where the central body is a massive black hole of 18.35$\times$10$^9$ solar mass that supports a thin accretion disc. The secondary black hole of 0.15$\times$10$^9$ solar mass impacts the disc twice during its 12 year orbit, and causes observable flares. Recently, it has been argued that an accretion disc with a typical AGN accretion rate and above mentioned central body mass should be at least six magnitudes brighter than OJ~287's host galaxy and would therefore be observationally excluded. Based on the observations of OJ~287's radio jet, detailed in Marscher and Jorstad (2011), and up-to-date accretion disc models of Azadi et al. (2022), we show that the V-band magnitude of the accretion disc is unlikely to exceed the host galaxy brightness by more than one magnitude, and could well be fainter than the host. This is because accretion power is necessary to launch the jet as well as to create electromagnetic radiation, distributed across many wavelengths, and not concentrated especially on the optical V-band. Further, we note that the claimed V-band concentration of accretion power leads to serious problems while interpreting observations of other Active Galactic Nuclei. Therefore, we infer that the mass of the primary black hole and its accretion rate do not need to be smaller than what is determined in the standard model for OJ~287.

astro-ph.HE↗

arXiv2023

Observational Implications of OJ 287's Predicted 2022 Disk Impact in the Black Hole Binary Model

We present a summary of the results of the OJ 287 observational campaign, which was carried out during the 2021/2022 observational season. This season is special in the binary model because the major axis of the precessing binary happens to lie almost exactly in the plane of the accretion disc of the primary. This leads to pairs of almost identical impacts between the secondary black hole and the accretion disk in 2005 and 2022. In 2005, a special flare called "blue flash" was observed 35 days after the disk impact, which should have also been verifiable in 2022. We did observe a similar flash and were able to obtain more details of its properties. We describe this in the framework of expanding cloud models. In addition, we were able to identify the flare arising exactly at the time of the disc crossing from its photo-polarimetric and gamma-ray properties. This is an important identification, as it directly confirms the orbit model. Moreover, we saw a huge flare that lasted only one day. We may understand this as the lighting up of the jet of the secondary black hole when its Roche lobe is suddenly flooded by the gas from the primary disk. Therefore, this may be the first time we directly observed the secondary black hole in the OJ 287 binary system.

astro-ph.HE↗

arXiv2023

Multicolor and multi-spot observations of Starlink's Visorsat

This study provides the results of simultaneous multicolor observations for the first Visorsat (STARLINK-1436) and the ordinary Starlink satellite, STARLINK-1113 in the $U$, $B$, $V$, $g'$, $r$, $i$, $R_{\rm C}$, $I_{\rm C}$, $z$, $J$, $H$, and $K_s$ bands to quantitatively investigate the extent to which Visorsat reduces its reflected light. Our results are as follows: (1) in most cases, Virorsat is fainter than STARLINK-1113, and the sunshade on Visorsat, therefore, contributes to the reduction of the reflected sunlight; (2) the magnitude at 550 km altitude (normalized magnitude) of both satellites often reaches the naked-eye limiting magnitude ($<$ 6.0); (3) from a blackbody radiation model of the reflected flux, the peak of the reflected components of both satellites is around the $z$ band; and (4) the albedo of the near infrared range is larger than that of the optical range. Under the assumption that Visorsat and STARLINK-1113 have the same reflectivity, we estimate the covering factor, $C_{\rm f}$, of the sunshade on Visorsat, using the blackbody radiation model: the covering factor ranges from $0.18 \leq C_{\rm f} \leq 0.92$. From the multivariable analysis of the solar phase angle (Sun-target-observer), the normalized magnitude, and the covering factor, the phase angle versus covering factor distribution presents a moderate anti-correlation between them, suggesting that the magnitudes of Visorsat depend not only on the phase angle but also on the orientation of the sunshade along our line of sight. However, the impact on astronomical observations from Visorsat-designed satellites remains serious. Thus, new countermeasures are necessary for the Starlink satellites to further reduce reflected sunlight.

astro-ph.IM↗

arXiv2023

Refining the 2022 OJ 287 impact flare arrival epoch

The bright blazar OJ~287 routinely parades high brightness bremsstrahlung flares, which are explained as being a result of a secondary supermassive black hole (SMBH) impacting the accretion disc of a more massive primary SMBH in a binary system. The accretion disc is not rigid but rather bends in a calculable way due to the tidal influence of the secondary. Below we refer to this phenomenon as a variable disc level. We begin by showing that these flares occur at times predicted by a simple analytical formula, based on general relativity inspired modified Kepler equation, which explains impact flares since 1888. The 2022 impact flare, namely flare number 26, is rather peculiar as it breaks the typical pattern of two impact flares per 12-year cycle. This is the third bremsstrahlung flare of the current cycle that follows the already observed 2015 and 2019 impact flares from OJ~287. It turns out that the arrival epoch of flare number 26 is sensitive to the level of primary SMBH's accretion disc relative to its mean level in our model. We incorporate these tidally induced changes in the level of the accretion disc to infer that the thermal flare should have occurred during July-August 2022, when it was not possible to observe it from the Earth. Thereafter, we explore possible observational evidence for certain pre-flare activity by employing spectral and polarimetric data from our campaigns in 2004/05 and 2021/22. We point out theoretical and observational implications of two observed mini-flares during January-February 2022.

astro-ph.HE↗

arXiv2022

Skynet's New Observing Mode: The Campaign Manager

Built in 2004, the Skynet robotic telescope network originally consisted of six 0.4 m telescopes located at the Cerro-Tololo Inter-American Observatory in the Chilean Andes. The network was designed to carry out simultaneous multi-wavelength observations of gamma-ray bursts (GRBs) when they are only tens of seconds old. To date, the network has been expanded to ~20 telescopes, including a 20 m radio telescope, that span four continents and five countries. The Campaign Manager (CM) is a new observing mode that has been developed for Skynet. Available to all Skynet observers, the CM semi-autonomously and indefinitely scales and schedules exposures on the observer's behalf while allowing for modification to scaling parameters in real time. The CM is useful for follow up to various transient phenomena including gravitational-wave events, GRB localizations, young supernovae, and eventually, sufficiently bright Argus Optical Array and Large Synoptic Survey Telescope events.

astro-ph.IM↗

arXiv2022

Optical variability of eight FRII-type quasars with 13-yr photometric light curves

We characterize the optical variability properties of eight lobe-dominated radio quasars (QSOs): B2 0709$+$37, FBQS J095206.3$+$235245, PG 1004$+$130, [HB89] 1156$+$631, [HB89] 1425$+$267, [HB89] 1503$+$691, [HB89] 1721$+$343, 4C $+$74.26, systematically monitored for a duration of 13 years since 2009. The quasars are radio-loud objects with extended radio lobes that indicate their orientation close to the sky plane. Five of the eight QSOs are classified as giant radio quasars. All quasars showed variability during our monitoring, with magnitude variations between 0.3 and 1 mag for the least variable and the most variable QSO, respectively. We performed both structure function (SF) analysis and power spectrum density (PSD) analysis for the variability characterization and search for characteristic timescales and periodicities. As a result of our analysis, we obtained relatively steep SF slopes ($α$ ranging from 0.49 to 0.75) that are consistent with the derived PSD slopes ($\sim$2--3). All the PSDs show a good fit to single power law forms, indicating a red-noise character of variability between $\sim$13 years and weeks timescales. We did not measure reliable characteristic timescales of variability from the SF analysis which indicates that the duration of the gathered data is too short to reveal them. The absence of bends in the PSDs (change of slope from $\geq$1 to $\sim$0) on longer timescales indicates that optical variations are most likely caused by thermal instabilities in the accretion disk.

astro-ph.GA↗

arXiv2022

Optical Time-Series Photometry of the Symbiotic Nova V1835 Aquilae

We present time-series CCD photometry in the $BVRI$ passbands of the recently identified symbiotic nova V1835 Aquilae (NSV 11749) over an interval of 5.1 years with 7-14 day cadence, observed during its quiescence. We find slow light variations with a range of $\sim$0.9 mag in $V$ and $\sim$0.3 mag in $I$. Analysis of these data show strong periodicity at $419 \pm 10$ days, which we interpret to be the system's orbital period. A dip in the otherwise-sinusoidal phased light curve suggests a weak ellipsoidal effect due to tidal distortion of the giant star, which in turn opens the possibility that V1835 Aql transfers some of its mass to the hot component via Roche lobe overflow rather than via a stellar wind. We also find evidence that V1835 Aql is an S-type symbiotic star, relatively free of circumstellar dust, and include it among the nuclear burning group of symbiotics. Finally, we provide photometry, periods, and light curve classifications for 22 variable stars in the field around V1835 Aql, about half of which are newly identified.

astro-ph.SR↗

arXiv2022

Refining the prediction for OJ 287 next impact flare arrival epoch

The bright blazar OJ~287 routinely parades high brightness bremsstrahlung flares which are explained as being a result of a secondary supermassive black hole (SMBH) impacting the accretion disk of a primary SMBH in a binary system. We begin by showing that these flares occur at times predicted by a simple analytical formula, based on the Kepler equation, which explains flares since 1888. The next impact flare, namely the flare number 26, is rather peculiar as it breaks the typical pattern of two impact flares per 12 year cycle. This will be the third bremsstrahlung flare of the current cycle that follows the already observed 2015 and 2019 impact flares from OJ~287. Unfortunately, astrophysical considerations make it difficult to predict the exact arrival epoch of the flare number 26. In the second part of the paper, we describe our recent OJ~287 observations. They show that the pre-flare light curve of flare number 22, observed in 2005, exhibits similar activity as the pre-flare light curve in 2022, preceding the expected flare number 26 in our model. We argue that the pre-flare activity most likely arises in the primary jet whose activity is modulated by the transit of the secondary SMBH through the accretion disk of the primary. Observing the next impact flare of OJ~287 in October 2022 will substantiate the theory of disk impacts in binary black hole systems.

astro-ph.HE↗

arXiv2021

Changing look AGN Mrk 590: Broad line region and black hole mass from photometric reverberation mapping

We present the results of photometric reverberation mapping observations on the changing look active galactic nucleus Mrk 590 at z = 0.026. The observations were carried out from July to December, 2018 using broad band B, R and narrow band Hα and S II filters. B-band traces the continuum emission from the accretion disk, R-band encompasses both the continuum emission from the accretion disk and the redshifted Hα line from the broad line region (BLR), S II band contains the redshifted Hα emission and the Hα band traces the continuum emission underneath the S II band. All the light curves showed strong variation with a fractional root-mean-square variation of 0.132 (+/-) 0.001 in B-band and 0.321 (+/-) 0.001 in Hα line. From cross-correlation function analysis, we obtained a delayed response of Hα line emission to the optical B-band continuum emission of 21.44(+1.49/-2.11) days in the rest-frame of the source, corresponding to a linear size of the BLR of 0.018 pc. This is consistent with previous estimates using Hβ. By combining the BLR size with the Hα line full width at half maximum of 6478 (+/-) 240 km/s measured from a single-epoch spectrum obtained with the Subaru telescope, we derived a black hole mass of 1.96 (+0.15 / -0.21) X 10^8 Msun.

astro-ph.GA↗

arXiv2019

A Multi-Year Search For Transits Of Proxima Centauri. II: No Evidence For Transit Events With Periods Between 1-30 Days

Using a global network of small telescopes, we have obtained light curves of Proxima Centauri at 329 observation epochs from 2006 - 2017. The planet Proxima b discovered by Anglada-Escude et al. (2016) with an orbital period of 11.186 d has an a priori transit probability of ~1.5%; if it transits, the predicted transit depth is about 5 millimagnitudes. In Blank et al. (2018), we analyzed 96 of our light curves that overlapped with predicted transit ephemerides from previously published tentative transit detections, and found no evidence in our data that would corroborate claims of transits with a period of 11.186 d. Here we broaden our analysis, using 262 high-quality light curves from our data set to search for any periodic transit-like events over a range of periods from 1 - 30 d. We also inject a series of simulated planet transits and find that our data are sufficiently sensitive to have detected transits of 5 millimagnitude depth, with recoverability ranging from ~100% for an orbital period of 1 d to ~20% for an orbital period of 20 d for the parameter spaces tested. Specifically at the 11.186 d period and 5 millimagnitude transit depth, we rule out transits in our data with high confidence. We are able to rule out virtually all transits of other planets at periods shorter than 5 d and depths greater than 3 millimagnitudes; however, we cannot confidently rule out transits at the period of Proxima b due to incomplete orbital phase coverage and a lack of sensitivity to transits shallower than 4 millimagnitudes.

astro-ph.EP↗