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Daniel E. Reichart

Publications and source records attributed to Daniel E. Reichart.

At least 37 records · Page 2Linked to original sources
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↗
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

SN 2022acko: the First Early Far-Ultraviolet Spectra of a Type IIP Supernova

We present five far- and near-ultraviolet spectra of the Type II plateau supernova, SN 2022acko, obtained 5, 6, 7, 19, and 21 days after explosion, all observed with the Hubble Space Telescope/Space Telescope Imaging Spectrograph. The first three epochs are earlier than any Type II plateau supernova has been observed in the far-ultraviolet revealing unprecedented characteristics. These three spectra are dominated by strong lines, primarily from metals, which contrasts with the relatively featureless early optical spectra. The flux decreases over the initial time series as the ejecta cools and line-blanketing takes effect. We model this unique dataset with the non-local thermodynamic equilibrium radiation transport code CMFGEN, finding a good match to the explosion of a low mass red supergiant with energy Ekin = 6 x 10^50 erg. With these models we identify, for the first time, the ions that dominate the early UV spectra. We also present optical photometry and spectroscopy, showing that SN 2022acko has a peak absolute magnitude of V = -15.4 mag and plateau length of ~115d. The spectra closely resemble those of SN 2005cs and SN 2012A. Using the combined optical and UV spectra, we report the fraction of flux redwards of the uvw2, U, B, and V filters on days 5, 7, and 19. We also create a spectral time-series of Type II supernovae in the ultraviolet, demonstrating the rapid decline of UV flux over the first few weeks of evolution. Future observations of Type II supernovae will continue to explore the diversity seen in the limited set of high-quality UV spectra.

astro-ph.HE↗
arXiv2023

Early Spectroscopy and Dense Circumstellar Medium Interaction in SN 2023ixf

We present the optical spectroscopic evolution of SN~2023ixf seen in sub-night cadence spectra from 1.18 to 14 days after explosion. We identify high-ionization emission features, signatures of interaction with material surrounding the progenitor star, that fade over the first 7 days, with rapid evolution between spectra observed within the same night. We compare the emission lines present and their relative strength to those of other supernovae with early interaction, finding a close match to SN~2020pni and SN~2017ahn in the first spectrum and SN~2014G at later epochs. To physically interpret our observations we compare them to CMFGEN models with confined, dense circumstellar material around a red supergiant progenitor from the literature. We find that very few models reproduce the blended \NC{} emission lines observed in the first few spectra and their rapid disappearance thereafter, making this a unique diagnostic. From the best models, we find a mass-loss rate of $10^{-3}-10^{-2}$ \mlunit{}, which far exceeds the mass-loss rate for any steady wind, especially for a red supergiant in the initial mass range of the detected progenitor. These mass-loss rates are, however, similar to rates inferred for other supernovae with early circumstellar interaction. Using the phase when the narrow emission features disappear, we calculate an outer dense radius of circumstellar material $R_\mathrm{CSM, out}\sim5\times10^{14}~\mathrm{cm}$ and a mean circumstellar material density of $ρ=5.6\times10^{-14}~\mathrm{g\,cm^{-3}}$. This is consistent with the lower limit on the outer radius of the circumstellar material we calculate from the peak \Halpha{} emission flux, $R_\text{CSM, out}\gtrsim9\times10^{13}~\mathrm{cm}$.

astro-ph.HE↗
arXiv2023

Strong Carbon Features and a Red Early Color in the Underluminous Type Ia SN 2022xkq

We present optical, infrared, ultraviolet, and radio observations of SN 2022xkq, an underluminous fast-declining type Ia supernova (SN Ia) in NGC 1784 ($\mathrm{D}\approx31$ Mpc), from $<1$ to 180 days after explosion. The high-cadence observations of SN 2022xkq, a photometrically transitional and spectroscopically 91bg-like SN Ia, cover the first days and weeks following explosion which are critical to distinguishing between explosion scenarios. The early light curve of SN 2022xkq has a red early color and exhibits a flux excess which is more prominent in redder bands; this is the first time such a feature has been seen in a transitional/91bg-like SN Ia. We also present 92 optical and 19 near-infrared (NIR) spectra, beginning 0.4 days after explosion in the optical and 2.6 days after explosion in the NIR. SN 2022xkq exhibits a long-lived C I 1.0693 $μ$m feature which persists until 5 days post-maximum. We also detect C II $λ$6580 in the pre-maximum optical spectra. These lines are evidence for unburnt carbon that is difficult to reconcile with the double detonation of a sub-Chandrasekhar mass white dwarf. No existing explosion model can fully explain the photometric and spectroscopic dataset of SN 2022xkq, but the considerable breadth of the observations is ideal for furthering our understanding of the processes which produce faint SNe Ia.

astro-ph.HE↗
arXiv2023

Shock Cooling and Possible Precursor Emission in the Early Light Curve of the Type II SN 2023ixf

We present the densely sampled early light curve of the Type II supernova (SN) 2023ixf, first observed within hours of explosion in the nearby Pinwheel Galaxy (Messier 101; 6.7 Mpc). Comparing these data to recently updated models of shock-cooling emission, we find that the progenitor likely had a radius of $410 \pm 10\ R_\odot$. Our estimate is model dependent but consistent with a red supergiant. These models provide a good fit to the data starting about 1 day after the explosion, despite the fact that the classification spectrum shows signatures of circumstellar material around SN 2023ixf during that time. Photometry during the first day after the explosion, provided almost entirely by amateur astronomers, does not agree with the shock-cooling models or a simple power-law rise fit to data after 1 day. We consider the possible causes of this discrepancy, including precursor activity from the progenitor star, circumstellar interaction, and emission from the shock before or after it breaks out of the stellar surface. The very low luminosity ($-11\mathrm{\ mag} > M > -14\mathrm{\ mag}$) and short duration of the initial excess lead us to prefer a scenario related to prolonged emission from the SN shock traveling through the progenitor system.

astro-ph.HE↗
arXiv2023

The Early Light Curve of SN 2023bee: Constraining Type Ia Supernova Progenitors the Apian Way

We present very early photometric and spectroscopic observations of the Type Ia supernova (SN Ia) 2023bee, starting about 8 hr after the explosion, which reveal a strong excess in the optical and nearest UV (U and UVW1) bands during the first several days of explosion. This data set allows us to probe the nature of the binary companion of the exploding white dwarf and the conditions leading to its ignition. We find a good match to the Kasen model in which a main-sequence companion star stings the ejecta with a shock as they buzz past. Models of double detonations, shells of radioactive nickel near the surface, interaction with circumstellar material, and pulsational delayed detonations do not provide good matches to our light curves. We also observe signatures of unburned material, in the form of carbon absorption, in our earliest spectra. Our radio nondetections place a limit on the mass-loss rate from the putative companion that rules out a red giant but allows a main-sequence star. We discuss our results in the context of other similar SNe Ia in the literature.

astro-ph.HE↗
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

A comprehensive optical search for pre-explosion outbursts from the quiescent progenitor of SN~2023ixf

We perform a comprehensive search for optical precursor emission at the position of SN~2023ixf using data from the DLT40, ZTF and ATLAS surveys. By comparing the current data set with precursor outburst hydrodynamical model light curves, we find that the probability of a significant outburst within five years of explosion is low, and the circumstellar material (CSM) ejected during any possible precursor outburst is likely smaller than $\sim$0.015\msun. By comparing to a set of toy models, we find that, if there was a precursor outburst, the duration must have been shorter than $\sim$100 days for a typical brightness of $M_{r}\simeq-9$ mag or shorter than 200 days for $M_{r}\simeq-8$ mag; brighter, longer outbursts would have been discovered. Precursor activity like that observed in the normal type II SN~2020tlf ($M_{r}\simeq-11.5$) can be excluded in SN~2023ixf. If the dense CSM inferred by early flash spectroscopy and other studies is related to one or more precursor outbursts, then our observations indicate that any such outburst would have to be faint and only last for days to months, or it occurred more than five years prior to the explosion. Alternatively, any dense, confined CSM may not be due to eruptive mass loss from a single red supergiant (RSG) progenitor. Taken together, the results of SN~2023ixf and SN~2020tlf indicate that there may be more than one physical mechanism behind the dense CSM inferred around some normal type II SNe.

astro-ph.HE↗
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↗
arXiv2023

Next-Level, Robotic Telescope-Based Observing Experiences to Boost STEM Enrollments and Majors on a National Scale: Year 1 Report

Funded by a $3M Department of Defense (DoD) National Defense Education Program (NDEP) award, we are developing and deploying on a national scale a follow-up curriculum to "Our Place In Space!", or OPIS!, in which approx. 3,500 survey-level astronomy students are using our global network of "Skynet" robotic telescopes each year. The goal of this new curriculum, called "Astrophotography of the Multi-Wavelength Universe!", or MWU!, is to boost the number of these students who choose STEM majors. During Y1, our participating educators have developed MWU!'s (now renumbered) 2nd and 4th modules, and are in the process of developing its 3rd and 7th modules (out of 7). Solid progress has also been made on the software front, (1) where we have developed new graphing/analysis/modeling interfaces in support of Modules 2 and 4, and in response to feedback from the participating educators; and (2) where we are in the process of developing and adding astrophotography capabilities to Afterglow Access (AgA), our student-level, web-based, image processing and analysis application, in support of Modules 1 - 3 and 5 - 7. On the hardware front, development of our first four signal-processing units proceeds on schedule; these are key to Skynet's integration of a global network of radio telescopes, capable of exploring the invisible universe. Preparations have also been made on the evaluation and accessibility fronts, for when the first MWU! modules are deployed in Spring 2023.

astro-ph.IM↗
arXiv2023

Circumstellar Medium Interaction in SN 2018lab, A Low-Luminosity II-P Supernova observed with TESS

We present photometric and spectroscopic data of SN 2018lab, a low luminosity type IIP supernova (LLSN) with a V-band peak luminosity of $-15.1\pm0.1$ mag. SN 2018lab was discovered by the Distance Less Than 40 Mpc (DLT40) SNe survey only 0.73 days post-explosion, as determined by observations from the Transiting Exoplanet Survey Satellite (TESS). TESS observations of SN 2018lab yield a densely sampled, fast-rising, early time light curve likely powered by circumstellar medium (CSM) interaction. The blue-shifted, broadened flash feature in the earliest spectra ($<$2 days) of SN 2018lab provide further evidence for ejecta-CSM interaction. The early emission features in the spectra of SN 2018lab are well described by models of a red supergiant progenitor with an extended envelope and close-in CSM. As one of the few LLSNe with observed flash features, SN 2018lab highlights the need for more early spectra to explain the diversity of flash feature morphology in type II SNe.

astro-ph.HE↗
arXiv2023

Robust Chauvenet Rejection: Powerful, but Easy to Use Outlier Detection for Heavily Contaminated Data Sets

In Maples et al. (2018) we introduced Robust Chauvenet Outlier Rejection, or RCR, a novel outlier rejection technique that evolves Chauvenet's Criterion by sequentially applying different measures of central tendency and empirically determining the rejective sigma value. RCR is especially powerful for cleaning heavily-contaminated samples, and unlike other methods such as sigma clipping, it manages to be both accurate and precise when characterizing the underlying uncontaminated distributions of data sets, by using decreasingly robust but increasingly precise statistics in sequence. For this work, we present RCR from a software standpoint, newly implemented as a Python package while maintaining the speed of the C++ original. RCR has been well-tested, calibrated and simulated, and it can be used for both one-dimensional outlier rejection and $n$-dimensional model-fitting, with or without weighted data. RCR is free to use for academic and non-commercial purposes, and the code, documentation and accompanying web calculator can be found and easily used online at https://github.com/nickk124/RCR

stat.CO↗
arXiv2022

Spin vectors in the Koronis family: IV. Completing the sample of its largest members after 35 years of study

An observational study of Koronis family members' spin properties was undertaken with two primary objectives: to reduce selection biases for object rotation period and lightcurve amplitude in the sample of members' known spin vectors, and to better constrain future modeling of spin properties evolution. Here we report rotation lightcurves of nineteen Koronis family members, and derived results that increase the sample of determined spin vectors in the Koronis family to include 34 of the largest 36 family members, completing it to $H \approx 11.3$ ($D \sim 16$ km) for the largest 32 members. The program observations were made during a total of 72 apparitions between 2005-2021, and are reported here along with several earlier unpublished lightcurves. All of the reported data were analyzed together with previously published lightcurves to determine the objects' sidereal rotation periods, spin vector orientations, and convex model shape solutions. The derived distributions of retrograde rotation rates and pole obliquities appear to be qualitatively consistent with outcomes of modification by thermal YORP torques. The distribution of spin rates for the prograde rotators remains narrower than that for the retrograde rotators; in particular, the absence of prograde rotators having periods longer than about 20 h is real, while among the retrograde rotators are several objects having longer periods up to about 65 h. None of the prograde objects newly added to the sample appear to be trapped in an $s_6$ spin-orbit resonance that is characteristic of most of the largest prograde objects; these smaller objects either could have been trapped previously and have already evolved out, or have experienced spin evolution tracks that did not include the resonance.

astro-ph.EP↗
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↗