ABSTRACT
We present spot properties on 32 periodic young stellar objects in IC 5070. Long term, ∼5 yr, light curves in the V, R, and I-bands are obtained through the HOYS (Hunting Outbursting Young ...Stars) citizen science project. These are dissected into 6 months long slices, with 3 months oversampling, to measure 234 sets of amplitudes in all filters. We fit 180 of these with reliable spot solutions. Two thirds of spot solutions are cold spots, the lowest is 2150 K below the stellar temperature. One third are warm spots that are above the stellar temperature by less than ∼2000 K. Cold and warm spots have maximum surface coverage values of 40 per cent, although only 16 per cent of warm spots are above 20 per cent surface coverage as opposed to 60 per cent of the cold spots. Warm spots are most likely caused by a combination of plages and low-density accretion columns, most common on objects without inner disc excess emission in K − W2. Five small hot spot solutions have <3 per cent coverage and are 3000–5000 K above the stellar temperature. These are attributed to accretion, and four of them occur on the same object. The majority of our objects are likely to be accreting. However, we observe very few accretion hot spots as either the accretion is not stable on our time-scale or the photometry is dominated by other features. We do not identify cyclical spot behaviour on the targets. We additionally identify and discuss a number of objects that have interesting amplitudes, phase changes, or spot properties.
Abstract
We present our photometric and spectroscopic observations of the peculiar transient AT2018cow. The multiband photometry covers from peak to ∼70 days, and the spectroscopy ranges from 5 to ...∼50 days. The rapid rise (
t
r
≲ 2.9 days), high luminosity (
M
V
,peak
∼ −20.8 mag), and fast decline after peak make AT2018cow stand out from any other optical transients, whereas we find that its light curves show a high resemblance to those of Type Ibn supernovae. Moreover, the spectral energy distribution remains at a high temperature of ∼14,000 K at
t
> 15 days after discovery. The spectra are featureless in the first 10 days, while some broad emission lines due to H, He, C, and O emerge later, with velocity declining from ∼14,000 to ∼3000 km s
−1
at the end of our observations. Narrow and weak He
I
emission lines emerge in the spectra at
t
> 20 days after discovery. These emission lines are reminiscent of the features seen in interacting supernovae like the Type Ibn and IIn subclasses. We fit the bolometric light curves with a model of circumstellar interaction and radioactive decay of
56
Ni and find a good fit with ejecta mass
M
ej
∼ 3.16
M
⊙
, circumstellar medium (CSM) mass
M
CSM
∼ 0.04
M
⊙
, and ejected
56
Ni mass
M
⊙
. The CSM shell might be formed in an eruptive mass ejection of the progenitor star. Furthermore, the host environment of AT2018cow implies a connection of AT2018cow with massive stars. Combining observational properties and the light-curve fitting results, we conclude that AT2018cow might be a peculiar interacting supernova that originated from a massive star.
Results from regular monitoring of relativistic compact binaries like PSR 1913+16 are consistent with the dominant (quadrupole) order emission of gravitational waves (GWs). We show that observations ...associated with the binary black hole (BBH) central engine of blazar OJ 287 demand the inclusion of gravitational radiation reaction effects beyond the quadrupolar order. It turns out that even the effects of certain hereditary contributions to GW emission are required to predict impact flare timings of OJ 287. We develop an approach that incorporates this effect into the BBH model for OJ 287. This allows us to demonstrate an excellent agreement between the observed impact flare timings and those predicted from ten orbital cycles of the BBH central engine model. The deduced rate of orbital period decay is nine orders of magnitude higher than the observed rate in PSR 1913+16, demonstrating again the relativistic nature of OJ 287's central engine. Finally, we argue that precise timing of the predicted 2019 impact flare should allow a test of the celebrated black hole "no-hair theorem" at the 10% level.
We present the results of our power spectral density analysis for the BL Lac object OJ 287, utilizing the Fermi-LAT survey at high-energy γ-rays, Swift-XRT in X-rays, several ground-based telescopes ...and the Kepler satellite in the optical, and radio telescopes at GHz frequencies. The light curves are modeled in terms of continuous-time autoregressive moving average (CARMA) processes. Owing to the inclusion of the Kepler data, we were able to construct for the first time the optical variability power spectrum of a blazar without any gaps across ∼6 dex in temporal frequencies. Our analysis reveals that the radio power spectra are of a colored-noise type on timescales ranging from tens of years down to months, with no evidence for breaks or other spectral features. The overall optical power spectrum is also consistent with a colored noise on the variability timescales ranging from 117 years down to hours, with no hints of any quasi-periodic oscillations. The X-ray power spectrum resembles the radio and optical power spectra on the analogous timescales ranging from tens of years down to months. Finally, the γ-ray power spectrum is noticeably different from the radio, optical, and X-ray power spectra of the source: we have detected a characteristic relaxation timescale in the Fermi-LAT data, corresponding to ∼150 days, such that on timescales longer than this, the power spectrum is consistent with uncorrelated (white) noise, while on shorter variability timescales there is correlated (colored) noise.
The Hunting Outbursting Young Stars (HOYS) project performs long-term, optical, multi-filter, high cadence monitoring of 25 nearby young clusters and star forming regions. Utilising Gaia DR3 data we ...have identified about 17000 potential young stellar members in 45 coherent astrometric groups in these fields. Twenty one of them are clear young groups or clusters of stars within one kiloparsec and they contain 9143 Gaia selected potential members. The cluster distances, proper motions and membership numbers are determined. We analyse long term (about 7yr) V, R, and I-band light curves from HOYS for 1687 of the potential cluster members. One quarter of the stars are variable in all three optical filters, and two thirds of these have light curves that are symmetric around the mean. Light curves affected by obscuration from circumstellar materials are more common than those affected by accretion bursts, by a factor of 2-4. The variability fraction in the clusters ranges from 10 to almost 100 percent, and correlates positively with the fraction of stars with detectable inner disks, indicating that a lot of variability is driven by the disk. About one in six variables shows detectable periodicity, mostly caused by magnetic spots. Two thirds of the periodic variables with disk excess emission are slow rotators, and amongst the stars without disk excess two thirds are fast rotators - in agreement with rotation being slowed down by the presence of a disk.
OJ 287 is a BL Lacertae type quasar in which the active galactic nucleus (AGN) outshines the host galaxy by an order of magnitude. The only exception to this may be at minimum light when the AGN ...activity is so low that the host galaxy may make quite a considerable contribution to the photometric intensity of the source. Such a dip or a fade in the intensity of OJ 287 occurred in November 2017, when its brightness was about 1.75 magnitudes lower than the recent mean level. We compare the observations of this fade with similar fades in OJ 287 observed earlier in 1989, 1999, and 2010. It appears that there is a relatively strong reddening of the B\(-\)V colours of OJ 287 when its V-band brightness drops below magnitude 17. Similar changes are also seen V\(-\)R, V\(-\)I, and R\(-\)I colours during these deep fades. These data support the conclusion that the total magnitude of the host galaxy is \(V=18.0 \pm 0.3\), corresponding to \(M_{K}=-26.5 \pm 0.3\) in the K-band. This is in agreement with the results, obtained using the integrated surface brightness method, from recent surface photometry of the host. These results should encourage us to use the colour separation method also in other host galaxies with strongly variable AGN nuclei. In the case of OJ 287, both the host galaxy and its central black hole are among the biggest known, and its position in the black hole mass-galaxy mass diagram lies close to the mean correlation.
We present our photometric and spectroscopic observations on the peculiar transient AT2018cow. The multi-band photometry covers from peak to \(\sim\)70 days and the spectroscopy ranges from 5 to ...\(\sim\)50 days. The rapid rise ($t_{\mathrm{r}}$$\lesssim\(2.9 days), high luminosity (\)M_{V,\mathrm{peak}}\sim-\(20.8 mag) and fast decline after peak make AT2018cow stand out of any other optical transients. While we find that its light curves show high resemblance to those of type Ibn supernovae. Moreover, the spectral energy distribution remains high temperature of \)\sim\(14,000 K after \)\sim\(15 days since discovery. The spectra are featureless in the first 10 days, while some broad emission lines due to H, He, C and O emerge later, with velocity declining from \)\sim\(14,000 km s\)^{-1}\( to \)\sim\(3000 km s\)^{-1}\( at the end of our observations. Narrow and weak He I emission lines emerge in the spectra at \)t>\(20 days since discovery. These emission lines are reminiscent of the features seen in interacting supernovae like type Ibn and IIn subclasses. We fit the bolometric light curves with a model of circumstellar interaction (CSI) and radioactive decay (RD) of \Ni and find a good fit with ejecta mass \)M_{\mathrm{ej}}\sim\(3.16 M\)_{\odot}\(, circumstellar material mass \)M_{\mathrm{CSM}}\sim\(0.04 M\)_{\odot}\(, and ejected \Ni mass \)M_{^{56}\mathrm{Ni}}\sim\(0.23 M\)_{\odot}$. The CSM shell might be formed in an eruptive mass ejection of the progenitor star. Furthermore, host environment of AT2018cow implies connection of AT2018cow with massive stars. Combining observational properties and the light curve fitting results, we conclude that AT2018cow might be a peculiar interacting supernova originated from a massive star.
ABSTRACT
OJ 287 is a BL Lacertae type quasar in which the active galactic nucleus (AGN) outshines the host galaxy by an order of magnitude. The only exception to this may be at minimum light when the ...AGN activity is so low that the host galaxy may make quite a considerable contribution to the photometric intensity of the source. Such a dip or a fade in the intensity of OJ 287 occurred in 2017 November, when its brightness was about 1.75 mag lower than the recent mean level. We compare the observations of this fade with similar fades in OJ 287 observed earlier in 1989, 1999, and 2010. It appears that there is a relatively strong reddening of the B− V colours of OJ 287 when its V-band brightness drops below magnitude 17. Similar changes are also seen in V− R, V− I, and R− I colours during these deep fades. These data support the conclusion that the total magnitude of the host galaxy is V = 18.0 ± 0.3, corresponding to MK = −26.5 ± 0.3 in the K-band. This is in agreement with the results, obtained using the integrated surface brightness method, from recent surface photometry of the host. These results should encourage us to use the colour separation method also in other host galaxies with strongly variable AGN. In the case of OJ 287, both the host galaxy and its central black hole are among the biggest known, and its position in the black hole mass–galaxy mass diagram lies close to the mean correlation.
ABSTRACT
V392 Persei is a known dwarf nova (DN) that underwent a classical nova eruption in 2018. Here we report ground-based optical, Swift UV and X-ray, and Fermi-LAT γ-ray observations following ...the eruption for almost three years. V392 Per is one of the fastest evolving novae yet observed, with a t2 decline time of 2 d. Early spectra present evidence for multiple and interacting mass ejections, with the associated shocks driving both the γ-ray and early optical luminosity. V392 Per entered Sun-constraint within days of eruption. Upon exit, the nova had evolved to the nebular phase, and we saw the tail of the supersoft X-ray phase. Subsequent optical emission captured the fading ejecta alongside a persistent narrow line emission spectrum from the accretion disc. Ongoing hard X-ray emission is characteristic of a standing accretion shock in an intermediate polar. Analysis of the optical data reveals an orbital period of 3.230 ± 0.003 d, but we see no evidence for a white dwarf (WD) spin period. The optical and X-ray data suggest a high mass WD, the pre-nova spectral energy distribution (SED) indicates an evolved donor, and the post-nova SED points to a high mass accretion rate. Following eruption, the system has remained in a nova-like high mass transfer state, rather than returning to the pre-nova DN low mass transfer configuration. We suggest that this high state is driven by irradiation of the donor by the nova eruption. In many ways, V392 Per shows similarity to the well-studied nova and DN GK Persei.
OJ287 is a quasi-periodic quasar with roughly 12 year optical cycles. It displays prominent outbursts which are predictable in a binary black hole model. The model predicted a major optical outburst ...in December 2015. We found that the outburst did occur within the expected time range, peaking on 2015 December 5 at magnitude 12.9 in the optical R-band. Based on Swift/XRT satellite measurements and optical polarization data, we find that it included a major thermal component. Its timing provides an accurate estimate for the spin of the primary black hole, chi = 0.313 +- 0.01. The present outburst also confirms the established general relativistic properties of the system such as the loss of orbital energy to gravitational radiation at the 2 % accuracy level and it opens up the possibility of testing the black hole no-hair theorem with a 10 % accuracy during the present decade.
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