PS1-14bj: A Hydrogen-Poor Superluminous Supernova with a Long Rise and Slow Decay

We present photometry and spectroscopy of PS1-14bj, a hydrogen-poor superluminous supernova (SLSN) at redshift z = 0.5215 discovered in the last months of the Pan-STARRS1 Medium Deep Survey. PS1-14bj stands out because of its extremely slow evolution, with an observed rise of ≳ 125 rest-frame days, and exponential decline out to ~250 days past peak at a measured rate of 0.01 mag day^(-1), consistent with fully trapped ^(56)Co decay. This is the longest rise time measured in an SLSN to date, and the first SLSN to show a rise time consistent with pair-instability supernova (PISN) models. Compared to other slowly evolving SLSNe, it is spectroscopically similar to the prototype SN 2007bi at maximum light, although lower in luminosity (L_(peak) ≃ 4.6 x 10^(43) erg s(-1)) and with a flatter peak than previous events. PS1-14bj shows a number of peculiar properties, including a near-constant color temperature for >200 days past peak, and strong emission lines from [O III] λ5007 and [O III] λ4363 with a velocity width of ~3400 km s^(−1) in its late-time spectra. These both suggest there is a sustained source of heating over very long timescales, and are incompatible with a simple ^(56)Ni-powered/PISN interpretation. A modified magnetar model including emission leakage at late times can reproduce the light curve, in which case the blue continuum and [O III] features are interpreted as material heated and ionized by the inner pulsar wind nebula becoming visible at late times. Alternatively, the late-time heating could be due to interaction with a shell of H-poor circumstellar material

Characterization of a novel class of mutation (Short Patch Illegitimate Recombination) in Acinetobacter baylyi

In prokaryotes, genetic variability contributes to the adaptation to novel environmental conditions, to resistance against threats such as antimicrobial agents and viruses, and ultimately to bacterial evolution through selection and drift. Genetic variability is mainly generated through mutations, e.g. point mutations, deletions, insertions, inversions, and duplications/amplifications. In addition, horizontal gene transfer (HGT) can contribute to variability by enabling a cell to acquire genetic material from closely (or more rarely, from distantly) related organisms. DNA taken up by HGT can be recombined with the chromosome of the recipient cell by either homologous recombination or illegitimate recombination. In this study a novel type of illegitimate recombination where small patches of DNA are recombined at microhomologous DNA segments, termed short patch illegitimate recombination (SPIR) is described in Acinetobacter baylyi. The results suggests that SPIR events typically lead to a substitution of 2-8 base pairs alone or together with a 3-9 base pair deletion, or a larger deletion up to 168 base pairs. It was also shown that SPIR occurs both in transformable and non-transformable strains, and that SPIR frequency is decreased by presence of the 3’-5’ single strand specific exonuclease ExoX. It is conceivable that SPIR enables greater changes in a genome over the course of a single generation than earlier described mutation mechanisms, and can thus play a role in adaptive evolution

Avinoam Shalem (ed.): The Chasuble of Thomas Becket: A Biography.

Over the past years, textiles have again become subjects of a range of studies in the field of medieval studies: from ecclesiastical history, economics and trade, to the role of textiles in medieval literature and cultural and gendered identities. The recent exhibition of embroidered vestments at the Victoria and Albert Museum in London, with its beautifully illustrated exhibition catalogue, has likewise spurred new interest in medieval textile art (see Browne et al. 2017). Despite this reinvigoration of a topic long neglected in medieval studies, the book reviewed here represents one of very few art historical monographs on an ecclesiastical textile from the Middle Ages. With The Chasuble of Thomas Becket: A Biography, professor Avinoam Shalem presents us with a collection of essays discussing different aspects of a textile now preserved in the cathedral of Fermo in Italy, known as the Chasuble of Thomas Becket. Venerated as a relic believed to have been worn by Becket, the textile was an important part of the Fermo cathedral’s treasury. However, the textile was made in an Andalusian workshop and the authors argue that the textile was originally a tent for a Muslim ruler. At some point (probably around 1200) the textile reached Italy and was remade into a chasuble for the cathedral’s bishop

The 300km/s stellar stream near Segue 1: Insights From high-resolution spectroscopy of its brightest star

We present a chemical abundance analysis of 300S-1, the brightest likely member star of the 300 km/s stream near the faint satellite galaxy Segue 1. From a high-resolution Magellan/MIKE spectrum we determine a metallicity of [Fe/H] = -1.46 +- 0.05 +- 0.23 (random and systematic uncertainties) for star 300S-1, and find an abundance pattern similar to typical halo stars at this metallicity. Comparing our stellar parameters to theoretical isochrones, we estimate a distance of 18 +- 7 kpc. Both the metallicity and distance estimates are in good agreement with what can be inferred from comparing the SDSS photometric data of the stream stars to globular cluster sequences. While several other structures overlap with the stream in this part of the sky, the combination of kinematic, chemical and distance information makes it unlikely that these stars are associated with either the Segue 1 galaxy, the Sagittarius stream or the Orphan stream. Streams with halo-like abundance signatures, such as the 300 km/s stream, present another observational piece for understanding the accretion history of the Galactic halo.Comment: 13 pages, emulateapj, accepted for publication in Ap

The luminous late-time emission of the type Ic supernova iPTF15dtg - evidence for powering from a magnetar?

iPTF15dtg is a Type Ic supernova (SN) showing a broad light curve around maximum light, consistent with massive ejecta if we assume a radioactive-powering scenario. We study the late-time light curve of iPTF15dtg, which turned out to be extraordinarily luminous for a stripped-envelope (SE) SN. We compare the observed light curves to those of other SE SNe and also with models for the $^{56}$Co decay. We analyze and compare the spectra to nebular spectra of other SE SNe. We build a bolometric light curve and fit it with different models, including powering by radioactivity, magnetar powering, as well as a combination of the two. Between 150 d and 750 d past explosion, iPTF15dtg's luminosity declined by merely two magnitudes instead of the six magnitudes expected from $^{56}$Co decay. This is the first spectroscopically-regular SE SN showing this behavior. The model with both radioactivity and magnetar powering provides the best fit to the light curve and appears to be the more realistic powering mechanism. An alternative mechanism might be CSM interaction. However, the spectra of iPTF15dtg are very similar to those of other SE SNe, and do not show signs of strong CSM interaction. iPTF15dtg is the first spectroscopically-regular SE SN whose light curve displays such clear signs of a magnetar contributing to the powering of the late time light curve. Given this result, the mass of the ejecta needs to be revised to a lower value, and therefore the progenitor mass could be significantly lower than the previously estimated $>$35 $M_{\odot}$.Comment: 9 pages, 8 figures, accepted for publication in Astronomy and Astrophysic

Timothy varieties for northern Norway and mountain districts

Timoteisortane ‘Engmo’, ‘Vega’ og ‘Noreng’ og foredlingslinjene ‘GpTi8905’, ‘LøTi8801’ og ‘LøTi9001’ er testa i reinbestand på åtte felt i Nord-Noreg og i fjellbygdene på Austlandet i tidsrommet 1999-2005. Alle sortane viste seg å vera tilstrekkeleg hardføre i prøvetida. Det var ikkje sikker forskjell mellom sortar i avling i førsteslåtten, medan ‘Vega’ og ‘Noreng’ hadde størst gjenvekst. Det var liten forskjell i fordøyelegheit mellom sortane. Fiberkvaliteten målt på NIRS kalibrert etter totalt ufordøyeleg NDF målt med in sacco-metoden var dårlegast hos ‘Vega’. ‘Noreng’ hadde bra fiberkvalitet, men lågare innhald av vassløyseleg karbohydrat enn ‘Engmo’. Forsøket viser at forskjellen mellom nordlege sortar og foredlingslinjer av timotei er liten, og at det derfor bør vera nok med ein nordleg sort i marknaden.Timoteisortar for Nord-Noreg og fjellbygdeneTimothy varieties for northern Norway and mountain districtspublishedVersio

iPTF16abc and the population of Type Ia supernovae: Comparing the photospheric, transitional and nebular phases

Key information about the progenitor system and the explosion mechanism of Type Ia supernovae (SNe~Ia) can be obtained from early observations, within a few days from explosion. iPTF16abc was discovered as a young SN~Ia with excellent early time data. Here, we present photometry and spectroscopy of the SN in the nebular phase. A comparison of the early time data with a sample of SNe~Ia shows distinct features, differing from normal SNe~Ia at early phases but similar to normal SNe~Ia at a few weeks after maximum light (i.e. the transitional phase) and well into the nebular phase. The transparency timescales ($t_0$) for this sample of SNe~Ia range between $\sim$ 25 and 41 days indicating a diversity in the ejecta masses. $t_0$ also weakly correlates with the peak bolometric luminosity, consistent with the interpretation that SNe with higher ejecta masses would produce more $^{56}$Ni. Comparing the $t_0$ and the maximum luminosity, L$_{max}$\, distribution of a sample of SNe~Ia to predictions from a wide range of explosion models we find an indication that the sub-Chandrasekhar mass models span the range of observed values. However, the bright end of the distribution can be better explained by Chandrasekhar mass delayed detonation models, hinting at multiple progenitor channels to explain the observed bolometric properties of SNe~Ia. iPTF16abc appears to be consistent with the predictions from the M$_{ch}$ models.Comment: 13 pages, 8 figures, accepted for publication in MNRA