ABSTRACT
The examination of long-term (1979–2020) photometric observations of SS433 enabled us to discover a non-zero orbital eccentricity of e = 0.05 ± 0.01. We have also found evidence for a ...secular increase in the orbital period at a rate of $\dot{P}_\mathrm{b}=(1.0\pm 0.3)\times 10^{-7}$ s s−1. The binary orbital period increase rate makes it possible to improve the estimate of the binary mass ratio q = MX/MV > 0.8, where MX and MV are the masses of the relativistic object and the optical star, respectively. For an optical star mass of 10 M⊙, the mass of the relativistic object (a black hole) is MX > 8 M⊙. A neutron star in SS433 is reliably excluded because in that case the orbital period should decrease, in contradiction to observations. The derived value of $\dot{P}_\mathrm{b}$ sets a lower limit on the mass-loss rate in the Jeans mode from the binary system ≳7 × 10−6 M⊙ yr−1. The discovered orbital ellipticity of SS433 is consistent with the model of the slaved accretion disc tracing the precession of the misaligned optical star’s rotational axis.
ABSTRACT
We present the first sample of tidal disruption events (TDEs) discovered during the SRG all-sky survey. These 13 events were selected among X-ray transients detected in the 0° < l < 180° ...hemisphere by eROSITA during its second sky survey (2020 June 10 to December 14) and confirmed by optical follow-up observations. The most distant event occurred at z = 0.581. One TDE continued to brighten at least 6 months. The X-ray spectra are consistent with nearly critical accretion on to black holes of a few ×103 to $10^8\, \mathrm{ M}_\odot$, although supercritical accretion is possibly taking place. In two TDEs, a spectral hardening is observed 6 months after the discovery. Four TDEs showed an optical brightening apart from the X-ray outburst. The other nine TDEs demonstrate no optical activity. All 13 TDEs are optically faint, with Lg/LX < 0.3 (Lg and LX being the g band and 0.2–6 keV luminosity, respectively). We have constructed a TDE X-ray luminosity function, which can be fit by a power law with a slope of −0.6 ± 0.2, similar to the trend observed for optically selected TDEs. The total rate is estimated at (1.1 ± 0.5) × 10−5 TDEs per galaxy per year, an order of magnitude lower than inferred from optical studies. This suggests that X-ray bright events constitute a minority of TDEs, consistent with models predicting that X-rays can only be observed from directions close to the axis of a thick accretion disc formed from the stellar debris. Our TDE detection threshold can be lowered by a factor of ∼2, which should allow a detection of ∼700 TDEs by the end of the SRG survey.
In this paper we construct the Fermi coordinates along any arbitrary line in a simple analytical way without use of orthogonal frames and their transport. In this manner we extend the Eddington ...approach to the construction of the Fermi metric in terms of the Riemann tensor. In the second part of the present article we show how the proposed approach works practically by applying it for deriving the Fermi coordinates for the static observer in the Schwarzschild spacetime.
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CMK, CTK, FMFMET, IJS, NUK, PNG, UM
On masses of the components in SS433 Cherepashchuk, A M; Postnov, K A; Belinski, A A
Monthly Notices of the Royal Astronomical Society,
10/2018, Volume:
479, Issue:
4
Journal Article
Context.
We present observations from the short-term intensive optical campaign (from September 2019 to January 2020) of the changing-look Seyfert NGC 3516. This active galactic nucleus is known to ...have strong optical variability and has changed its type in the past. It has been in the low-activity state in the optical since 2013, with some rebrightening from the end of 2015 to the beginning of 2016, after which it remained dormant.
Aims.
We aim to study the photometric and spectral variability of NGC 3516 from the new observations in
U
- and
B
-bands and examine the profiles of the optical broad emission lines in order to demonstrate that this object may be entering a new state of activity.
Methods.
NGC 3516 has been monitored intensively for the past 4 months with an automated telescope in
U
and
B
filters, enabling accurate photometry of 0.01 precision. Spectral observations were triggered when an increase in brightness was spotted. We support our analysis of past-episodes of violent variability with the UV and X-ray long-term light curves constructed from the archival
Swift
/UVOT and
Swift
/XRT data.
Results.
An increase of the photometric magnitude is seen in both
U
and
B
filters to a maximum amplitude of 0.25 mag and 0.11 mag, respectively. During the flare, we observe stronger forbidden high-ionization iron lines (Fe
VII
and Fe
X
) than reported before, as well as the complex broad H
α
and H
β
lines. This is especially seen in H
α
, which appears to be double-peaked. It seems that a very broad component of ∼10 000 km s
−1
in width in the Balmer lines is appearing. The trends in the optical, UV, and X-ray light curves are similar, with the amplitudes of variability being significantly larger in the case of UV and X-ray bands.
Conclusions.
The increase of the continuum emission, the variability of the coronal lines, and the very broad component in the Balmer lines may indicate that the AGN of NGC 3516 is finally leaving the low-activity state in which it has been for the last ∼3 years.
Full text
Available for:
FMFMET, NUK, UL, UM, UPUK
Mass ratio in SS433 revisited Cherepashchuk, A M; Postnov, K A; Belinski, A A
Monthly Notices of the Royal Astronomical Society,
05/2019, Volume:
485, Issue:
2
Journal Article
Peer reviewed
Open access
Abstract
We revisit the determination of binary mass ratio in the Galactic microquasar SS433 based on recent GRAVITY VLTI measurements of mass and angular momentum outflow through a circumbinary ...disc. The new observations combined with the constancy of the binary orbital period over ∼30 yr confirm that the mass ratio in SS433 is q = Mx/Mv ≳ 0.6. For the assumed optical star mass Mv ranging from ∼8 to 15 $\, \mathrm{M}_\odot$ such a mass ratio suggests a low limit of the compact object mass of $M_\mathrm{x}\sim 5\text{--}9 \, \mathrm{M}_\odot$, placing the compact object in SS433 as a stellar mass black hole.
ABSTRACT
We present the results of photometric and spectroscopic monitoring campaigns of the changing look AGN NGC 3516 carried out in 2018 to 2020 covering the wavelength range from the X-ray to the ...optical. The facilities included the telescopes of the CMO SAI MSU, the 2.3-m WIRO telescope, and the XRT and UVOT of Swift. We found that NGC 3516 brightened to a high state and could be classified as Sy1.5 during the late spring of 2020. We have measured time delays in the responses of the Balmer and He ii λ4686 lines to continuum variations. In the case of the best-characterized broad H β line, the delay to continuum variability is about 17 d in the blue wing and is clearly shorter, 9 d, in the red, which is suggestive of inflow. As the broad lines strengthened, the blue side came to dominate the Balmer lines, resulting in very asymmetric profiles with blueshifted peaks during this high state. During the outburst the X-ray flux reached its maximum on 2020 April 1 and it was the highest value ever observed for NGC 3516 by the Swift observatory. The X-ray hard photon index became softer, ∼1.8 in the maximum on 2020 April 21 compared to the mean ∼0.7 during earlier epochs before 2020. We have found that the UV and optical variations correlated well (with a small time delay of 1–2 d) with the X-ray until the beginning of 2020 April, but later, until the end of 2020 June, these variations were not correlated. We suggest that this fact may be a consequence of partial obscuration by Compton-thick clouds crossing the line of sight.
ABSTRACT
We present results from applying the SNAD anomaly detection pipeline to the third public data release of the Zwicky Transient Facility (ZTF DR3). The pipeline is composed of three stages: ...feature extraction, search of outliers with machine learning algorithms, and anomaly identification with followup by human experts. Our analysis concentrates in three ZTF fields, comprising more than 2.25 million objects. A set of four automatic learning algorithms was used to identify 277 outliers, which were subsequently scrutinized by an expert. From these, 188 (68 per cent) were found to be bogus light curves – including effects from the image subtraction pipeline as well as overlapping between a star and a known asteroid, 66 (24 per cent) were previously reported sources whereas 23 (8 per cent) correspond to non-catalogued objects, with the two latter cases of potential scientific interest (e.g. one spectroscopically confirmed RS Canum Venaticorum star, four supernovae candidates, one red dwarf flare). Moreover, using results from the expert analysis, we were able to identify a simple bi-dimensional relation that can be used to aid filtering potentially bogus light curves in future studies. We provide a complete list of objects with potential scientific application so they can be further scrutinised by the community. These results confirm the importance of combining automatic machine learning algorithms with domain knowledge in the construction of recommendation systems for astronomy. Our code is publicly available.1
ABSTRACT
We report the discovery of a nearby massive white dwarf with He–H atmosphere. The white dwarf is located at a distance of 74.5 ± 0.9 pc. Its radius, mass, effective temperature, H/He ratio, ...and age are R = 2500 ± 100 km, M = 1.33 ± 0.01 $\rm M_{\odot }$, Teff = 31 200 ± 1200 K, H/He ∼ 0.1, and 330 ± 40 Myr, respectively. The observed spectrum is redshifted by Vr = +240 ± 15 km s−1, which is mostly attributed to the gravitational redshift. The white dwarf shows a regular stable photometric variability with amplitude Δg ≈ 0.06m and period P = 353.456 s suggesting rapid rotation. This massive, hot, and rapidly rotating white dwarf is likely to originate from the merging of close binary white dwarf system that avoided explosion in a thermonuclear Type Ia supernova.
ABSTRACT
We present the results of our new observations of the young binary ZZ Tau with a circumbinary disc. The system was found to consist of two coeval (age < 2 Myr) classical T Tauri stars with ...the total mass 0.86 ± 0.09 M⊙, orbital period 46.8 ± 0.8 yr, semimajor axis 88.2 ± 2.1 mas, eccentricity 0.58 ± 0.02, and the orbital inclination 123${_{.}^{\circ}}$8 ± 1${_{.}^{\circ}}$0. The accretion rate of ZZ Tau A and ZZ Tau B is approximately 7 × 10−10 and 2 × 10−10 M⊙ yr−1, respectively. No correlation was found between the long-term photometric variability of ZZ Tau and orbital position of its components. The periodic light variations with P = 4.171 ± 0.002 d were observed in the BVRI bands presumably connected with an accretion (hot) spot on the surface of the primary (ZZ Tau A). At the same time, no periodicity was observed in the U band nor in the emission line profile variations probably, due to the significant contribution of ZZ Tau B’s emission, which dominates shortward of λ ≈ 0.4 $\mu$m. We argue that the extinction in the direction to the primary is noticeably larger than that to the secondary. It appeared that the rotation axis of the primary is inclined to the line of sight by ≈31° ± 4°. We also concluded that ZZ Tau is the source of a CO molecular outflow; however, ZZ Tau IRS rather than ZZ Tau is the source of the Herbig–Haro object HH393.
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