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Kangaslampi, Finland

Villforth C.,University of Turku | Nilsson K.,University of Turku | Heidt J.,ZAH | Takalo L.O.,University of Turku | And 45 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2010

OJ 287 is a BL Lac object at redshift.z= 0.306 that has shown double-peaked bursts at regular intervals of ∼12 yr during the last ∼40 yr. We analyse optical photopolarimetric monitoring data from 2005 to 2009, during which the latest double-peaked outburst occurred. The aim of this study is twofold: firstly, we aim to analyse variability patterns and statistical properties of the optical polarization light curve. We find a strong preferred position angle in optical polarization. The preferred position angle can be explained by separating the jet emission into two components: an optical polarization core and chaotic jet emission. The optical polarization core is stable on time-scales of years and can be explained as emission from an underlying quiescent jet component. The chaotic jet emission sometimes exhibits a circular movement in the Stokes plane. We find six such events, all on the time-scales of 10-20 d. We interpret these events as a shock front moving forwards and backwards in the jet, swiping through a helical magnetic field. Secondly, we use our data to assess different binary black hole models proposed to explain the regularly appearing double-peaked bursts in OJ 287. We compose a list of requirements a model has to fulfil to explain the mysterious behaviour observed in OJ 287. The list includes not only characteristics of the light curve but also other properties of OJ 287, such as the black hole mass and restrictions on accretion flow properties. We rate all existing models using this list and conclude that none of the models is able to explain all observations. We discuss possible new explanations and propose a new approach to understanding OJ 287. We suggest that both the double-peaked bursts and the evolution of the optical polarization position angle could be explained as a sign of resonant accretion of magnetic field lines, a 'magnetic breathing' of the disc. © 2010 The Authors. Journal compilation © 2010 RAS. Source


Baluev R.V.,Saint Petersburg State University | Sokov E.N.,Russian Academy of Sciences | Shaidulin V.S.,Saint Petersburg State University | Sokova I.A.,Russian Academy of Sciences | And 15 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2015

We perform an analysis of ~80 000 photometric measurements for the following 10 stars hosting transiting planets:WASP-2, -4, -5, -52, Kelt-1, CoRoT-2, XO-2, TrES-1, HD 189733, GJ 436. Our analysis includes mainly transit light curves from the Exoplanet Transit Database, public photometry from the literature, and some proprietary photometry privately supplied by other authors. Half of these light curves were obtained by amateurs. From this photometry we derive 306 transit timing measurements, as well as improved planetary transit parameters. Additionally, for 6 of these 10 stars we present a set of radial velocity measurements obtained from the spectra stored in the HARPS, HARPS-N and SOPHIE archives using the HARPS- TERRA pipeline. Our analysis of these transit timing and radial velocity data did not reveal significant hints of additional orbiting bodies in almost all of the cases. In the WASP-4 case, we found hints of marginally significant TTV signals having amplitude 10-20 s, although their parameters are model dependent and uncertain, while radial velocities did not reveal statistically significant Doppler signals. © 2015 The Authors. Source


Inserra C.,University of Catania | Inserra C.,National institute for astrophysics | Inserra C.,University of Oklahoma | Turatto M.,National institute for astrophysics | And 21 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2012

We present photometry and spectroscopy of the Type IIP supernova (SN IIP) 2009bw in UGC 2890 from a few days after the outburst to 241d. The light curve of SN 2009bw during the photospheric phase is similar to that of normal SNe IIP but with a brighter peak and plateau (mag, mag). The luminosity drop from the photospheric to the nebular phase is one of the fastest ever observed, ∼2.2mag in about 13d. The radioactive tail of the bolometric light curve indicates that the amount of ejected 56Ni is ≈0.022M ⊙. The photospheric spectra reveal high-velocity lines of Hα and Hβ until about 105d after the shock breakout, suggesting a possible early interaction between the SN ejecta and pre-existent circumstellar material, and the presence of CNO elements. By modelling the bolometric light curve, ejecta expansion velocity and photospheric temperature, we estimate a total ejected mass of ∼8-12M ⊙, a kinetic energy of ∼0.3 foe and an initial radius of ∼3.6-7 × 10 13cm. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS. Source


Kankare E.,University of Turku | Mattila S.,University of Turku | Ryder S.,Australian Astronomical Observatory | Fraser M.,University of Cambridge | And 12 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

We present near-infrared and optical photometry, plus optical spectroscopy of two strippedenvelope supernovae (SNe) 2010O and 2010P that exploded in two different components of an interacting luminous infrared galaxy Arp 299 within only a few days of one another. SN 2010O is found to be photometrically and spectroscopically similar to many normal Type Ib SNe and our multiwavelength observations of SN 2010P suggest it to be a Type IIb SN. No signs of clear hydrogen features or interaction with the circumstellar medium are evident in the optical spectrum of SN 2010P. We derive estimates for the host galaxy line-of-sight extinctions for both SNe, based on both light curve and spectroscopic comparison finding consistent results. These methods are also found to provide much more robust estimates of the SN host galaxy reddening than the commonly used empirical relations between extinction and equivalent width of Na I D absorption features. The SN observations also suggest that different extinction laws are present in different components of Arp 299. For completeness, we study high-resolution pre-explosion images of Arp 299 and find both SNe to be close to, but not coincident with, extended sources that are likely massive clusters. A very simple model applied to the bolometric light curve of SN 2010O implies a rough estimate for the explosion parameters of Ek ≈ 3 × 1051 erg, Mej ≈ 2.9M⊙ and MNi ≈ 0.16M⊙. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Source


Zheng W.,University of Michigan | Shen R.F.,University of Toronto | Sakamoto T.,NASA | Sakamoto T.,University of Maryland Baltimore County | And 60 more authors.
Astrophysical Journal | Year: 2012

We present a comprehensive analysis of a bright, long-duration (T 90 257 s) GRB 110205A at redshift z = 2.22. The optical prompt emission was detected by Swift/UVOT, ROTSE-IIIb, and BOOTES telescopes when the gamma-ray burst (GRB) was still radiating in the γ-ray band, with optical light curve showing correlation with γ-ray data. Nearly 200 s of observations were obtained simultaneously from optical, X-ray, to γ-ray (1 eV to 5MeV), which makes it one of the exceptional cases to study the broadband spectral energy distribution during the prompt emission phase. In particular, we clearly identify, for the first time, an interesting two-break energy spectrum, roughly consistent with the standard synchrotron emission model in the fast cooling regime. Shortly after prompt emission (1100s), a bright (R = 14.0) optical emission hump with very steep rise (α 5.5) was observed, which we interpret as the reverse shock (RS) emission. It is the first time that the rising phase of an RS component has been closely observed. The full optical and X-ray afterglow light curves can be interpreted within the standard reverse shock (RS) + forward shock (FS) model. In general, the high-quality prompt and afterglow data allow us to apply the standard fireball model to extract valuable information, including the radiation mechanism (synchrotron), radius of prompt emission (R GRB 3 × 1013cm), initial Lorentz factor of the outflow (Γ0 250), the composition of the ejecta (mildly magnetized), the collimation angle, and the total energy budget. © 2012. The American Astronomical Society. All rights reserved.. Source

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