We report optical photometric and polarimetric observations of the blazar OJ 287 gathered during 2016/17. The high level of activity, noticed after the General Relativity Centenary flare, is argued to be part of the follow-up flares that exhibited high levels of polarization and originated in the primary black hole jet. We propose that the follow-up flares were induced as a result of accretion disk perturbations, travelling from the site of impact towards the primary SMBH. The timings inferred from our observations allowed us to estimate the propagation speed of these perturbations. Additionally, we make predictions for the future brightness of OJ 287.

We present a detailed analysis of the X-ray point source population of M81. By identifying HST counterparts to Chandra sources, taking into account the chance coincidence probability, we classify a large fraction of the X-ray point source population with unique counterparts: high-mass X-ray binaries and low-mass X-ray binaries in globular clusters. We then compare the shapes of the uncontaminated X-ray luminosity functions and the X-ray properties of sources of different classes to models and other existing work. We also calculate scaling relations with the star formation rate and stellar mass between the different classes of sources in global and sub-galactic scales. One initial, primary result is that the more massive and dense globular clusters are more likely to be associated with X-ray binaries.

Haumea—one of the four known trans-Neptunian dwarf planets—is a very elongated and rapidly rotating body. In contrast to other dwarf planets, its size, shape, albedo and density are not well constrained. The Centaur Chariklo was the first body other than a giant planet known to have a ring system, and the Centaur Chiron was later found to possess something similar to Chariklo’s rings. Here we report observations from multiple Earth-based observatories of Haumea passing in front of a distant star (a multi-chord stellar occultation). Secondary events observed around the main body of Haumea are consistent with the presence of a ring with an opacity of 0.5, width of 70 kilometres and radius of about 2,287 kilometres. The ring is coplanar with both Haumea’s equator and the orbit of its satellite Hi’iaka. The radius of the ring places it close to the 3:1 mean-motion resonance with Haumea’s spin period—that is, Haumea rotates three times on its axis in the time that a ring particle completes one revolution. The occultation by the main body provides an instantaneous elliptical projected shape with axes of about 1,704 kilometres and 1,138 kilometres. Combined with rotational light curves, the occultation constrains the three-dimensional orientation of Haumea and its triaxial shape, which is inconsistent with a homogeneous body in hydrostatic equilibrium. Haumea’s largest axis is at least 2,322 kilometres, larger than previously thought, implying an upper limit for its density of 1,885 kilograms per cubic metre and a geometric albedo of 0.51, both smaller than previous estimates. In addition, this estimate of the density of Haumea is closer to that of Pluto than are previous estimates, in line with expectations. No global nitrogen- or methane-dominated atmosphere was detected.

We present 120 times of minima of 8 eclipsing binaries.

We present 110 times of minima of 7 ultra-short orbital period eclipsing binaries.

The occultation of the 14th mag star UCAC4 345-180315 by Pluto on the evening of the 19th of July, 2016 could be observed from large parts of Europe, middle east and northern Africa as well. A campaign had been organized with for many observers and observatories throughout Europe and other countries. Professional as well as amateur observatories and observers shared in a PRO-AM cooperation to achieve the highest possible degree of coverage. The scientific goal was the ongoing monitoring of Pluto's atmosphere, waiting for a possible shrinking of its pressure due to the increasing distance of Pluto from the sun.

We carried out a pilot campaign of radio and optical band intra-day variability (IDV) observations of five blazars (3C66A, S5 0716+714, OJ287, B0925+504 and BL Lacertae) on 2015 December 18-21 by using the radio telescope in Effelsberg (Germany) and several optical telescopes in Asia, Europe and America. After calibration, the light curves from both 5 GHz radio band and the optical R band were obtained, although the data were not smoothly sampled over the sampling period of about four days. We tentatively analyse the amplitudes and time-scales of the variabilities, and any possible periodicity. The blazars vary significantly in the radio (except 3C66A and BL Lacertae with only marginal variations) and optical bands on intra- and inter-day time-scales, and the source B0925+504 exhibits a strong quasi-periodic radio variability. No significant correlation between the radio- and optical-band variability appears in the five sources, which we attribute to the radio IDV being dominated by interstellar scintillation whereas the optical variability comes from the source itself. However, the radio- and optical-band variations appear to be weakly correlated in some sources and should be investigated based on well-sampled data from future observations.

The presence of a supermassive binary black hole (BBH) central engine in OJ287 is revealed by impact flares which arise from the secondary impacting the accretion disk of the primary. These flares have been observed since 1913 from the study of old photographic plates and from recent observational campaigns, 9 events in total. In addition, the secondary induces flares by affecting the accretion rate of the primary. The records for the latter events start in 1900, and they have been observed for each of the 10 cycles since then. Because of orbital precession, the impact flares times do not follow any simple rule. However, since the BBH - accretion disk impact model was proposed in 1995, the optical flux behavior of OJ287 has become highly predictable. The latest predictions were given for the late 2015 - early 2017 season. These have now been verified. The impact flare started on 2015 November 25, during the Centenary of Einstein’s General Relativity, followed by induced accretion flares which peaked on 2016 March and 2016 October. The nine impact flares specify the two parameters of the standard accretion disk and the 6 parameters of the BBH orbit uniquely. The main remaining uncertainty has to do with the exact way the gravitational wave (GW) emission affects the orbit. The impact flare observations demand that the GW emission is a combination of the instantaneous and hereditary effects appearing at the Post Newtonian orders 2.5PN, 3.5PN and 4PN, and all of them have to be incorporated while modeling the dynamics of the central engine BBH in OJ287. Previously, only the standard 2.5PN “Newtonian” GW terms have been used. We develop a simplified way of incorporating the higher order General Relativistic effects and obtain revised estimates for various BBH parameters. The improved BBH dynamics makes specific predictions for the occurrences of the expected impact flares in future and thereby provide additional strong field tests of General Relativity.