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The project MOMO (Multiwavelength Observations and Modelling of OJ 287) was set up to test predictions of binary supermassive black hole (SMBH) scenarios and to understand disc–jet physics of the blazar OJ 287. After a correction, the precessing binary (PB) SMBH model predicted the next main outburst of OJ 287 in 2022 October, making the outburst well observable and the model testable. We have densely covered this period in our ongoing multifrequency radio, optical, ultraviolet (UV), and X-ray monitoring. The predicted outburst was not detected. Instead, OJ 287 was at low optical–UV emission levels, declining further into November. The predicted thermal bremsstrahlung spectrum was not observed either, at any epoch. Further, applying scaling relations, we estimate an SMBH mass of OJ 287 of 108 M⊙. The latest in a sequence of deep low states that recur every 1–2 yr is used to determine an upper limit on the Eddington ratio and on the accretion-disc luminosity. This limit is at least a factor of 10 lower than required by the PB model with its massive primary SMBH of >1010 M⊙. All these results favour alternative binary SMBH models of OJ 287 that require neither strong orbital precession nor a very large mass of the primary SMBH.

 

In this paper, we discuss the outcomes of the follow-up campaign of SN 2018ijp, discovered as part of the Zwicky Transient Facility survey for optical transients. Its first spectrum shows similarities to broad-lined Type Ic supernovae around maximum light, whereas later spectra display strong signatures of interaction between rapidly expanding ejecta and a dense H-rich circumstellar medium, coinciding with a second peak in the photometric evolution of the transient. This evolution, along with the results of modeling of the first light-curve peak, suggests a scenario where a stripped star exploded within a dense circumstellar medium. The two main phases in the evolution of the transient could be interpreted as a first phase dominated by radioactive decays, and a later interaction-dominated phase where the ejecta collide with a pre-existing shell. We therefore discuss SN 2018jp within the context of a massive star depleted of its outer layers exploding within a dense H-rich circumstellar medium. 

ABSTRACT We present and discuss the optical spectrophotometric observations of the nearby (z = 0.087) Type I superluminous supernova (SLSN I) SN 2017gci, whose peak K-corrected absolute magnitude reaches Mg = −21.5 mag. Its photometric and spectroscopic evolution includes features of both slow- and of fast-evolving SLSN I, thus favoring a continuum distribution between the two SLSN-I subclasses. In particular, similarly to other SLSNe I, the multiband light curves (LCs) of SN 2017gci show two re-brightenings at about 103 and 142 d after the maximum light. Interestingly, this broadly agrees with a broad emission feature emerging around 6520 Å after ∼51 d from the maximum light, which is followed by a sharp knee in the LC. If we interpret this feature as Hα, this could support the fact that the bumps are the signature of late interactions of the ejecta with a (hydrogen-rich) circumstellar material. Then we fitted magnetar- and CSM-interaction-powered synthetic LCs on to the bolometric one of SN 2017gci. In the magnetar case, the fit suggests a polar magnetic field Bp ≃ 6 × 1014 G, an initial period of the magnetar Pinitial ≃ 2.8 ms, an ejecta mass $M_{\rm ejecta}\simeq 9\, \mathrm{M}_\odot $ and an ejecta opacity $\kappa \simeq 0.08\, \mathrm{cm}^{2}\, \rm{g}^{-1}$. A CSM-interaction scenario would imply a CSM mass $\simeq 5\, \mathrm{M}_\odot $ and an ejecta mass $\simeq 12\, \mathrm{M}_\odot $. Finally, the nebular spectrum of phase  + 187 d was modeled, deriving a mass of $\sim 10\, {\rm M}_\odot$ for the ejecta. Our models suggest that either a magnetar or CSM interaction might be the power sources for SN 2017gci and that its progenitor was a massive ($40\, {\rm M}_\odot$) star.