We report the results of a multi-band observing campaign on the famous blazar 3C 279 conducted during a phase of increased activity from 2013 December to 2014 April, including first observations of it with NuSTAR. The γ-ray emission of the source measured by Fermi-LAT showed multiple distinct flares reaching the highest flux level measured in this object since the beginning of the Fermi mission, with F(E > 100 MeV) of 10 −5 photons cm −2 s −1 , and with a flux doubling time scale as short as 2 hours. The γ-ray spectrum during one of the flares was very hard, with an index of Γ γ = 1.7 ± 0.1, which is rarely seen in flat spectrum radio quasars. The lack of concurrent optical variability implies a very high Compton dominance parameter L γ /L syn > 300. Two 1-day NuSTAR observations with accompanying Swift pointings were separated by 2 weeks, probing different levels of source activity. While the 0.5−70 keV X-ray spectrum obtained during the first pointing, and fitted jointly with Swift-XRT is well-described by a simple power law, the second joint observation showed an unusual spectral structure: the spectrum softens by ∆Γ X ≃ 0.4 at ∼ 4 keV. Modeling the broad-band SED during this flare with the standard synchrotron plus inverse Compton model requires: (1) the location of the γ-ray emitting region is comparable with the broad line region radius, (2) a very hard electron energy distribution index p ≃ 1, (3) total jet power significantly exceeding the accretion disk luminosity L j /L d 10, and (4) extremely low jet magnetization with L B /L j 10 −4 . We also find that single-zone models that match the observed γ-ray and optical spectra cannot satisfactorily explain the production of X-ray emission.

Context. Over the past few years, on several occasions, large, continuous rotations of the electric vector position angle (EVPA) of linearly polarized optical emission from blazars have been reported. These events are often coincident with high energy γ-ray flares and they have attracted considerable attention, since they could allow us to probe the magnetic field structure in the γ-ray emitting region of the jet. The flat-spectrum radio quasar 3C 279 is one of the most prominent examples showing this behaviour. Aims. Our goal is to study the observed EVPA rotations and to distinguish between a stochastic and a deterministic origin of the polarization variability. Methods. We have combined multiple data sets of R-band photometry and optical polarimetry measurements of 3C 279, yielding exceptionally well-sampled flux density and polarization curves that cover a period of [2008][2009][2010][2011][2012]. Several large EVPA rotations are identified in the data. We introduce a quantitative measure for the EVPA curve smoothness, which is then used to test a set of simple random walk polarization variability models against the data. Results. 3C 279 shows different polarization variation characteristics during an optical low-flux state and a flaring state. The polarization variation during the flaring state, especially the smooth ∼360• rotation of the EVPA in mid-2011, is not consistent with the tested stochastic processes. Conclusions. We conclude that, during the two different optical flux states, two different processes govern polarization variation, which is possibly a stochastic process during the low-brightness state and a deterministic process during the flaring activity.

In this paper, we present the results from spectroscopic and photometric observations of the M-type flare star YZ CMi in the framework of the Optical and Infrared Synergetic Telescopes for Education and Research (OISTER) collaborations during the Transiting Exoplanet Survey Satellite (TESS) observation period. We detected 145 white-light flares from the TESS light-curve and four Hα flares from the OISTER observations performed between 2019 January 16 and 18. Among them, three Hα flares were associated with white-light flares. However, one of them did not show clear brightening in the continuum; during this flare, the Hα line exhibited blue asymmetry which lasted for ∼60 min. The line-of-sight velocity of the blueshifted component is in the range from −80 to −100 km s−1. This suggests that there can be upward flows of chromospheric cool plasma even without detectable red/near-infrared (NIR) continuum brightening. By assuming that the blue asymmetry in the Hα line was caused by a prominence eruption on YZ CMi, we estimated the mass and kinetic energy of the upward-moving material to be 1016–1018 g and 1029.5–1031.5 erg, respectively. The estimated mass is comparable to expectations from the empirical relation between the flare X-ray energy and mass of upward-moving material for stellar flares and solar coronal mass ejections (CMEs). In contrast, the estimated kinetic energy for the non-white-light flare on YZ CMi is roughly two orders of magnitude smaller than that expected from the relation between flare X-ray energy and kinetic energy for solar CMEs. This could be understood by the difference in the velocity between CMEs and prominence eruptions.

We report observations of the Type Iax supernova (SN Iax) 2012Z at optical and near-infrared wavelengths from immediately after the explosion until ∼ 260 days after the maximum luminosity using the Optical and Infrared Synergetic Telescopes for Education and Research (OISTER) Targetof-Opportunity (ToO) program and the Subaru telescope. We found that the near-infrared (NIR) light curve evolutions and color evolutions are similar to those of SNe Iax 2005hk and 2008ha. The NIR absolute magnitudes (M J ∼ −18.1 mag and M H ∼ −18.3 mag) and the rate of decline of the light curve (∆ m 15 (B)= 1.6 ± 0.1 mag) are very similar to those of SN 2005hk (M J ∼ −17.7 mag, M H ∼−18.0 mag, and ∆ m 15 (B)∼ 1.6 mag), yet differ significantly from SNe 2008ha and 2010ae (M J ∼ −14 − −15 mag and ∆ m 15 (B)∼ 2.4 − 2.7 mag). The estimated rise time is 12.0 ± 3.0 days,which is significantly shorter than that of SN 2005hk or any other Ia SNe. The rapid rise indicates that the 56 Ni distribution may extend into the outer layer or that the effective opacity may be lower than that in normal SNe Ia. The late-phase spectrum exhibits broader emission lines than those of SN 2005hk by a factor of 6-8. Such high velocities of the emission lines indicate that the density profile of the inner ejecta extends more than that of SN 2005hk. We argue that the most favored explosion scenario is a 'failed deflagration' model, although the pulsational delayed detonations is not excluded. Subject headings: supernovae: general -supernovae: individual (SN 2012Z) -supernovae: individual (SNe 2005hk)

Here we report on the results of the WEBT photo-polarimetric campaign targeting the blazar S5 0716+71, organized in March 2014 to monitor the source simultaneously in BVRI and near IR filters. The campaign resulted in an unprecedented dataset spanning ∼ 110 h of nearly continuous, multi-band observations, including two sets of densely sampled polarimetric data mainly in R filter. During the campaign, the source displayed pronounced variability with peak-to-peak variations of about 30% and "bluer-when-brighter" spectral evolution, consisting of a day-timescale modulation with superimposed hourlong microflares characterized by ∼ 0.1 mag flux changes. We performed an in-depth search for quasi-periodicities in the source light curve; hints for the presence of oscillations on timescales of ∼ 3 h and ∼ 5 h do not represent highly significant departures from a pure rednoise power spectrum. We observed that, at a certain configuration of the optical polarization angle relative to the positional angle of the innermost radio jet in the source, changes in the polarization degree led the total flux variability by about 2 h; meanwhile, when the relative configuration of the polarization and jet angles altered, no such lag could be noted. The microflaring events, when analyzed as separate pulse emission components, were found to be characterized by a very high polarization degree (> 30%) and polarization angles which differed substantially from the polarization angle of the underlying background component, or from the radio jet positional angle. We discuss the results in the general context of blazar emission and energy dissipation models.