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We analysed photometry and spectroscopy of the peculiar core-collapse SN 2013gc. The light curve shows a fast decline, a plateau phase and a re-brightening of 1 mag. From archival images taken years before the explosion, a weak source is visible in several images at the supernova location. The early spectra show Balmer lines, with a narrow P-Cygni absorption superimposed on a broad component. Analysing the colour curves, absolute light curves and spectra of SN 2013gc, we conclude that SN 2013gc is a member of the type IIn SN group, more specifically it belongs to the type IId SNe subgroup [4]. The complex profile of the Hα line suggests a composite circumstellar medium geometry, with a spherically symmetric shell and an expanding bilobed feature. The modest luminosity of SN 2013gc, the small amount of ejected 56Ni and the major pre-supernova stellar activity support a fall-back core-collapse scenario for the massive progenitor of SN 2013gc. [ABSTRACT FROM AUTHOR]

The source of strong and broad emission of the Balmer-a line in mixed plasmas of hydrogen (or deuterium) and noble gases in front of metallic surfaces is a subject of controversial discussion of many plasma types. In this work the excitation source of the Balmer lines is investigated by means of optical emission spectroscopy in the plasma device PSI-2. Neutral fast non-Maxwellian hydrogen atoms are produced by acceleration of hydrogen ions towards an electrode immersed into the plasma. By variation of the electrode potential the energy of ions and in turn of reflected fast atoms can be varied in the range of 40-300 eV. The fast atoms in front of the electrode are observed simultaneously by an Echelle spectrometer (0.001 nm/channel) and by an imaging spectrometer (0.01 nm/channel) up to few cm in the plasma. Intense excitation channels of the Balmer lines are observed when hydrogen is mixed with argon or with krypton. Especially in Ar-H and Ar-D mixed plasmas the emission of fast hydrogen atoms is very strong. Intermixing hydrogen with other noble gases (He, Ne or Xe) one observes the same effect however the emission is one order of magnitude less compared to Kr-H or Kr-D plasmas. It is shown, that the key process, impacting this emission, is the binary collision between the fast neutral hydrogen atom and the noble gas atom. Two possible sources of excitation are discussed in details: one is the excitation of hydrogen atoms by argon atoms in the ground state and the second one is the process of the so-called excitation transfer between the metastable states of noble gases and hydrogen. In the latter case the atomic data for excitation of Balmer lines are still not available in literature. Further experimental investigations are required to conclude on the source process of fast atom emission. [ABSTRACT FROM AUTHOR]

In GAMMA 10/PDX, spatial distribution of the occurrence of molecular activated recombination (MAR) has been studied by measuring two dimensional distributions of Hα and Hβ line intensities of the divertor simulation plasma. The V-shaped target in the D-module which is installed in the west end region was exposed to the end loss plasma, and additional hydrogen gas was injected in the D-module. The electron temperature near the corner of the V-shaped target decreased to ~2 eV with increase in the neutral gas pressure in the D-module and the density roll over was observed, indicating the plasma was detached. The two dimensional distributions of the intensity ratio of Hα and Hβ line intensities indicates that MAR was enhanced with increase in the neutral gas pressure and the region of the MAR occurrence spread and moved to the upstream side. [ABSTRACT FROM AUTHOR]

Time structure of Balmer Hα line intensity in Linac4 RF plasma has been analyzed by the combined simulation model of atomic transport and Collisional-Radiative models. As a preliminary result, time variation of the line intensity in the ignition phase of RF plasma is calculated and compared with the experimental results by photometry. For the comparison, spatial distribution of the local Hα photon emission rate at each time is calculated from the numerical model. The contribution of the local photon emission rates to the observed line intensity via optical viewing port is also investigated by application of the mock-up of the optical viewing port and the known light source. It has been clarified from the analyses that the higher and the lower peaks of the Hα line intensity observed during 1 RF cycle is mainly due to the different spatial distributions in the electron energy distribution function and the resultant local photon emission rate. These results support previous suggestion that the existence of the capacitive electric field in axial direction leads to the higher/lower peaks of the line intensity. [ABSTRACT FROM AUTHOR]

Violent eruptions, and consequently major mass loss, are a common feature of the so-called Luminous Blue Variable (LBV) stars. During major eruptive episodes LBVs mimic the behavior of real type IIn supernovae (SNe), showing comparable radiated energy and similar spectroscopic properties. For this reason these events are frequently labelled as SN impostors. Type IIn SN spectra are characterized by the presence of prominent narrow Balmer lines in emission. In most cases, SNe IIn arise from massive stars (M>8⊙) exploding in a dense H-rich circumstellar medium (CSM), produced by progenitor's mass loss prior to the SN explosion. Although the mechanisms triggering these eruptions are still unknown, recently we had direct proofs of the connection between very massive stars, their eruptions and ejecta-CSM interacting SNe. SNe 2006jc, 2010mc, 2011ht and the controversial SN 2009ip are famous cases in which we observed the explosion of the star months to years after major outbursts. In this context, the case of a recent transient event, LSQ13zm, is extremely interesting since we observed an outburst just ~3 weeks before the terminal SN explosion. All of this may suggest that SN impostors occasionally herald true SN explosions. Nonetheless, there are several cases where major eruptions are followed by a quiescent phase in the LBV life. The impostor SN 2007sv is one of these cases, since it showed a single outburst event. Its photometric (a relatively faint absolute magnitude at the maximum) and spectroscopic properties (low velocity and temperature of the ejecta, and the absence of the typical elements produced in the explosive nucleosynthesis) strongly suggest that SN 2007sv was the giant eruption of an LBV, which has then returned in a quiescent stage. [ABSTRACT FROM AUTHOR]