No abstract

OJ287 is the best candidate active galactic nucleus (AGN) for hosting a supermassive binary black hole (SMBBH) at very close separation. We present 120 Very Long Baseline Array (VLBA) observations (at 15 GHz) covering the time between April 1995 and April 2017. We find that the OJ287 radio jet is precessing on a time-scale of ∼22 yr. In addition, our data are consistent with a jet-axis rotation on a yearly time-scale. We model the precession (24 ± 2 yr) and combined motion of jet precession and jet-axis rotation. The jet motion explains the variability of the total radio flux-density via viewing angle changes and Doppler beaming. Half of the jet-precession time-scale is of the order of the dominant optical periodicity time-scale. We suggest that the optical emission is synchrotron emission and related to the jet radiation. The jet dynamics and flux-density light curves can be understood in terms of geometrical effects. Disturbances of an accretion disc caused by a plunging BH do not seem necessary to explain the observed variability. Although the SMBBH model does not seem necessary to explain the observed variability, an SMBBH or Lense-Thirring precession (disc around single BH) seem to be required to explain the time-scale of the precessing motion. Besides jet rotation also nutation of the jet axis could explain the observed motion of the jet axis. We find a strikingly similar scaling for the time-scales for precession and nutation as indicated for SS433 with a factor of roughly 50 times longer in OJ287.

The quasar 0917ϩ624 has been one of the best-studied intraday variable radio sources. However, debate continues as to whether the underlying cause is intrinsic or extrinsic. Much previous work has assumed the intraday variability (IDV) to be intrinsic, which implies an extraordinarily compact source for the radio emission; in contrast, an extrinsic variation due to interstellar scintillation (ISS) implies a relatively larger source diameter, although at the smaller end of the range expected for relativistic jet models. Kraus et al. reported a marked slowing of the IDV at a wavelength of 6 cm in 1998 September and suggested that a change in the source was responsible. However, here we show that the slowing is consistent with the annual modulation in the scintillation timescale expected for ISS, under the assumption that the scattering medium moves with the local standard of rest (LSR). The ISS timescale is governed by the ISS spatial scale divided by the Earth's velocity relative to the scattering plasma. It happens that in the direction of 0917ϩ624, the transverse velocity of the Earth with respect to the LSR varies widely, with a deep minimum in the months of September-November. Hence, the slowing of the IDV in 1998 September strongly suggests that ISS rather than intrinsic variation of the source is the dominant cause of the IDV.

No abstract

No abstract

Pb isotope compositions of melt inclusions provide unique information about the composition of primary magmas and their source. In this study, we have developed a method for measuring Pb isotopes in small olivine-hosted melt inclusions (>40 mm) from young and old volcanoes by LA-MC-ICP-MS. We used a new interface cone assemblage consisting of a Jet sample cone and X skimmer cone. A small flow of N 2 gas was added to the carrier gas and passed through the assemblage to enhance the signal intensity. In addition the energy and repetition rate of the laser conditions were reduced and the signal integration time was shortened in order to lengthen the laser ablation time and to collect enough data. Mass bias and instrument drift were corrected using a standard-sample-standard bracketing method. The analysis routine employed eight ion counters to receive 238 basalts, but also from old samples that require correction for U-Th decay.

The search for periodic behavior in Blazars has been an important subject, which is helpful for providing significant clues to the structure and physical processes of their central energy engine. A binary black hole system has recently been suggested for causing precession of relativistic jets and rotation of the ejection position angle of VLBI knots in superluminal sources. It has been suggested that in QSO 3C345, the ejection direction of the superluminal knots rotates due to the precession of the central engine and thus the ejection position angle of the successive knots shows a periodic behavior. Some authors argue for a period of precession being ∼5.6 yr (Abraham & Caproni), ∼8-10 yr (Klare et al.) and ∼9.5 yr (Lobanov & Roland). Applying the helical model proposed by Qian et al. and selecting appropriate parameters to fit the initial trajectories (within 0.3 mas) of all the components (C4 to C10), we derive the relation between the ejection position angle of the components and their precession phase, and thus find a 6.9-year precession period (4.3 yr in the source frame), which can fit the ejection position angle of all these superluminal knots well. Since the VLBI observations have covered more than two precession periods, confirmation in one or more future periods would be important. In addition, we emphasize that the initial parts of the trajectories of these knots can be fitted by a common helical pattern (channel) through a precessing of its initial phase. This scenario (or helical precessing model) is different from the usual ballistic precessing model in which the individual superluminal knots move along straight-lines after ejection (Tateyama & Kingham).

No abstract