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Register a new userBroad-line region configuration of the supermassive binary black hole candidate PG1302-102 in the relativistic Doppler boosting scenario
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PG1302-102 is thought to be a supermassive binary black hole (BBH) system according to the periodical variations of its optical and UV photometry, which may be interpreted as being due to the relativistic Doppler boosting of the emission mainly from the disk around the secondary black hole (BH) modulated by its orbital motion. In this paper, we investigate several broad emission lines of PG1302-102 using archived UV spectra obtained by IUE, GALEX, and Hubble, to reveal the broad-line region (BLR) emission properties of this BBH system under the Doppler boosting scenario. We find that the broad lines Ly$alpha$, NV, CIV, and CIII] all show Gaussian profiles, and none of these lines exhibits obvious periodical variation. Adopting a simple model for the BLR, we perform Markov chain Monte Carlo fittings to these broad lines, and find that the BLR must be viewed at an orientation angle of $sim33^{circ}$, close to face-on. If the Doppler boosting interpretation is correct, then the BLR is misaligned with the BBH orbital plane by an angle of $sim51^circ$, which suggests that the Doppler boosted continuum variation has little effect on the broad-line emission and thus does not lead to periodical line variation. We further discuss the possible implications for such a BLR configuration with respect to the BBH orbital plane.
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Graham et al. (2015a) reported a periodically varying quasar and supermassive black hole binary candidate, PG1302-102 (hereafter PG1302), which was discovered in the Catalina Real-Time Transient Survey (CRTS). Its combined Lincoln Near-Earth Asteroid Research (LINEAR) and CRTS optical light curve is well fitted to a sinusoid of an observed period of $approx 1,884$ days and well modeled by the relativistic Doppler boosting of the secondary mini-disk (DOrazio et al. 2015). However, the LINEAR+CRTS light curve from MJD $approx 52700$ to MJD $approx 56400$ covers only $sim 2$ cycles of periodic variation, which is a short baseline that can be highly susceptible to normal, stochastic quasar variability (Vaughan et al. 2016). In this Letter, we present a re-analysis of PG1302, using the latest light curve from the All-Sky Automated Survey for Supernovae (ASAS-SN), which extends the observational baseline to the present day (MJD $approx 58200$), and adopting a maximum likelihood method which searches for a periodic component in addition to stochastic quasar variability. When the ASAS-SN data are combined with the previous LINEAR+CRTS data, the evidence for periodicity decreases. For genuine periodicity one would expect that additional data would strengthen the evidence, so the decrease in significance may be an indication that the binary model is disfavored.
The photometric light curve of PG1302-102 shows periodic variability which makes this object one of the most plausible supermassive black hole binary candidate. Interestingly, the most recent study of its updated optical light curve reports a decrease in significance of periodicity which may suggest that the binary model is less favorable. Here, we model the PG 1302-102 light curve, spanning almost 20 years, with a supermassive black hole binary system in which a perturbation in the accretion disk of more massive component is present. Our model reproduces well the observed light curve with a slight perturbation of a sinusoidal feature and predicts that a slightly larger period than previously reported, of about 1899 days, could arise due to a cold spot in the disk of {bf more massive} component of a close, unequal-mass ($frac{mathrm{m}_{1}}{mathrm{m}_{2}}=0.1$) black hole binary system. The light curve resembles the pattern of sinusoid-like shape within a few years, which could be confirmed by future observations. In addition, using our hybrid method for periodicity detection, we show that the periods in the observed ($1972pm 254$ days) and modeled ($1873 pm 250$ days) light curves are within one-sigma, which is also consistent with our physical model prediction and with previous findings. Thus, both the periodic nature and its slight fluctuation of the light curve of PG1302-102 is evident from our physical model and confirmed by the hybrid method for periodicity detection.
The bright quasar PG1302-102 has been identified as a candidate supermassive black hole binary from its near-sinusoidal optical variability. While the significance of its optical periodicity has been debated due to the stochastic variability of quasars, its multi-wavelength variability in the ultraviolet (UV) and optical bands is consistent with relativistic Doppler boost caused by the orbital motion in a binary. However, this conclusion was based previously on sparse UV data which were not taken simultaneously with the optical data. Here we report simultaneous follow-up observations of PG1302-102 with the Ultraviolet Optical Telescope on the Neil Gehrels Swift Observatory in six optical + UV bands. The additional nine Swift observations produce light curves roughly consistent with the trend under the Doppler boost hypothesis, which predicts that UV variability should track the optical, but with a ~2.2 times higher amplitude. We perform a statistical analysis to quantitatively test this hypothesis. We find that the data are consistent with the Doppler boost hypothesis when we compare the the amplitudes in optical B-band and UV light curves. However, the ratio of UV to V-band variability is larger than expected and is consistent with the Doppler model, only if either the UV/optical spectral slopes vary, the stochastic variability makes a large contribution in the UV, or the sparse new optical data underestimate the true optical variability. We have evidence for the latter from comparison with the optical light curve from ASAS-SN. Additionally, the simultaneous analysis of all four bands strongly disfavors the Doppler boost model whenever Swift V-band is involved. Additional, simultaneous optical + UV observations tracing out another cycle of the 5.2-year proposed periodicity should lead to a definitive conclusion.
Relativistic jets in active galactic nuclei represent one of the most powerful phenomena in the Universe. They form in the surroundings of the supermassive black holes as a by-product of accretion onto the central black hole in active galaxies. The flow in the jets propagates at velocities close to the speed of light. The distance between the first part of the jet that is visible in radio images (core) and the black hole is still a matter of debate. Only very-long-baseline interferometry observations resolve the innermost compact regions of the radio jet. Those can access the jet base, and combining data at different wavelenghts, address the physical parameters of the outflow from its emission. We have performed an accurate analysis of the frequency-dependent shift of the VLBI core location for a multi-wavelength set of images of the blazar CTA 102 including data from 6 cm down to 3 mm. The measure of the position of the central black hole, with mass $sim 10^{8.93},M_odot$, in the blazar CTA 102 reveals a distance of $sim 8times10^4$ gravitational radii to the 86 GHz core, in agreement with similar measures obtained for other blazars and distant radio galaxies, and in contrast with recent results for the case of nearby radio galaxies, which show distances between the black hole and the radio core that can be two orders of magnitude smaller.
We identify SDSS J153636.22+044127.0, a QSO discovered in the Sloan Digital Sky Survey, as a promising candidate for a binary black hole system. This QSO has two broad-line emission systems separated by 3500 km/sec. The redder system at z=0.3889 also has a typical set of narrow forbidden lines. The bluer system (z=0.3727) shows only broad Balmer lines and UV Fe II emission, making it highly unusual in its lack of narrow lines. A third system, which includes only unresolved absorption lines, is seen at a redshift, z=0.3878, intermediate between the two emission-line systems. While the observational signatures of binary nuclear black holes remain unclear, J1536+0441 is unique among all QSOs known in having two broad-line regions, indicative of two separate black holes presently accreting gas. The interpretation of this as a bound binary system of two black holes having masses of 10^8.9 and 10^7.3 solar masses, yields a separation of ~ 0.1 parsec and an orbital period of ~100 years. The separation implies that the two black holes are orbiting within a single narrow-line region, consistent with the characteristics of the spectrum. This object was identified as an extreme outlier of a Karhunen-Loeve Transform of 17,500 z < 0.7 QSO spectra from the SDSS. The probability of the spectrum resulting from a chance superposition of two QSOs with similar redshifts is estimated at 2X10^-7, leading to the expectation of 0.003 such objects in the sample studied; however, even in this case, the spectrum of the lower redshift QSO remains highly unusual.
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