OJ287 is a quasi-periodic quasar with roughly 12 year optical cycles. It displays prominent outbursts that are predictable in a binary black hole model. The model predicted a major optical outburst in 2015 December. 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, 0.313 0.01 c = . 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 10% accuracy during the present decade.
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 OJ287 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 OJ287. We develop an approach that incorporates this effect into the BBH model for OJ287. 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 OJ287ʼs 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.
OpenBU http://open.bu.edu Astronomy BU Open Access Articles 2018-08-20 Stochastic modeling of multiwavelength variability of the classical BL Lac Object OJ287...
We present analyses of archival X-ray data obtained from the XMM-Newton satellite and optical photometric data obtained from 1 m class telescopes of ARIES, Nainital of a magnetic cataclysmic variable (MCV) Paloma. Two persistent periods at 156 ± 1 minutes and 130 ± 1 minutes are present in the X-ray data, which we interpret as the orbital and spin periods, respectively. These periods are similar to those obtained from the previous as well as new optical photometric observations. The soft-X-ray excess seen in the X-ray spectrum of Paloma and the averaged X-ray spectra are well fitted by two-temperature plasma models with temperatures of 0.10 +0.02 −0.01 and 13.0 +0.5 −0.5 keV with an Fe Kα line and an absorbing column density of 4.6 × 10 22 cm -2 . This material partially covers 60 ± 2 % of the X-ray source. We also present the orbital and spin-phase-resolved spectroscopy of Paloma in the 0.3 − 10.0 keV energy band and find that the X-ray spectral parameters show orbital and spin-phase dependencies. New results obtained from optical and X-ray studies of Paloma indicate that it belongs to a class of a few magnetic CVs that seem to have the characteristics of both the polars and the intermediate polars.
Based on the X-ray observations from XMM-Newton and Suzaku satellites at four different epochs, we present temporal and spectral properties of an intermediate polar (IP) V2400 Oph (=RX J1712.6-2414). The X-ray variations are found to occur at the spin and synodic periods and are derived to be 929 s and 1003 s, respectively. The X-ray spectrum is strongly absorbed by a dense material with an average equivalent hydrogen column density of ∼5 × 1022 cm−2, which partially covers ∼46% of the X-ray source. Suzaku spectra in the 0.3–50 keV energy range are well explained by two temperature collisional equilibrium plasma emission models with its reflection from the cold matter. A soft X-ray emission is also seen in the X-ray spectrum of V2400 Oph and is well modeled by the blackbody with an average temperature of ∼98 eV. The partial covering absorbers and softness ratio are spin phase dependent indicating that the coverage of accretion curtains is variable. A strong emission line of fluorescent Fe Kα at 6.4 keV is also detected in the X-ray spectra. The central energy of Fe Kα appears to be redshifted and found to be modulated with the white dwarf (WD) rotation, where modulations are at minimum around the spin minimum, indicating that the redshifted line is originated from pre-shock accreting material via fluorescence. An attempt is also made to characterize the system and to understand the magnetic accretion flows using the present data of V2400 Oph.
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