On Some Geometric Properties of Slice Regular Functions of a Quaternion Variable

The goal of this paper is to introduce and study some geometric properties of slice regular functions of quaternion variable like univalence, subordination, starlikeness, convexity and spirallikeness in the unit ball. We prove a number of results, among which an Area-type Theorem, Rogosinski inequality, and a Bieberbach-de Branges Theorem for a subclass of slice regular functions. We also discuss some geometric and algebraic interpretations of our results in terms of maps from $\mathbb R^4$ to itself. As a tool for subordination we define a suitable notion of composition of slice regular functions which is of independent interest

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

The bumpy light curve of supernova iPTF13z

A Type IIn supernova (SN) is dominated by the interaction of SN ejecta with the circumstellar medium (CSM). Some SNe IIn (e.g., SN 2006jd) have episodes of re-brightening ("bumps") in their light curves. We present iPTF13z, a SN IIn discovered by the intermediate Palomar Transient Factory (iPTF) and characterised by several bumps in its light curve. We analyse this peculiar behaviour trying to infer the properties of the CSM and of the SN explosion, as well as the nature of its progenitor star. We obtained multi-band optical photometry for over 1000 days after discovery with the P48 and P60 telescopes at Palomar Observatory. We obtained low-resolution optical spectra in the same period. We did an archival search for progenitor outbursts. We analyse our photometry and spectra, and compare iPTF13z to other SNe IIn. A simple analytical model is used to estimate properties of the CSM. iPTF13z was a SN IIn showing a light curve with five bumps during its decline phase. The bumps had amplitudes between 0.4 and 0.9 mag and durations between 20 and 120 days. The most prominent bumps appeared in all our different optical bands. The spectra showed typical SN IIn characteristics, with emission lines of H$\alpha$ (with broad component FWHM ~$10^{3}-10^{4} ~{\rm ~km ~s^{-1}}$ and narrow component FWHM ~$10^2 \rm ~km ~s^{-1}$) and He I, but also with Fe II, Ca II, Na I D and H$\beta$ P-Cygni profiles (with velocities of ~$10^{3}$ ${\rm ~km ~s^{-1}}$). A pre-explosion outburst was identified lasting $\gtrsim 50$ days, with $M_r \approx -15$ mag around 210 days before discovery. Large, variable progenitor mass-loss rates (~> 0.01 $M_{\odot} \rm ~yr^{-1}$) and CSM densities (~> 10$^{-16}$ g cm$^{-3}$) are derived. We suggest that the light curve bumps of iPTF13z arose from SN ejecta interacting with denser regions in the CSM, possibly produced by the eruptions of a luminous blue variable star.Comment: Version 2: Update to match published paper. 21 pages, 14 figures, abstract abridged to comply with arXiv length limit. In version 1 of the paper on arXiv, Table 3 had some erroneous entries. Table 3 is now corrected and available via VizieR. Version 1 comment: Accepted for publication in Astronomy & Astrophysics (24 pages, 14 figures, abstract abridged by 20 % not to exceed the arXiv length limit

The Radio Afterglow and the Host Galaxy of the X-Ray Rich GRB 981226

We report the discovery of a radio transient VLA 232937.2-235553, coincident with the proposed X-ray afterglow for the gamma-ray burst GRB 981226. This GRB has the highest ratio of X-ray to gamma-ray fluence of all the GRBs detected by BeppoSAX so far and yet no corresponding optical transient was detected. The radio light curve of VLA 232937.2-235553 is qualitatively similar to that of several other radio afterglows. At the sub-arcsecond position provided by the radio detection, optical imaging reveals an extended R=24.9 mag object, which we identify as the host galaxy of GRB 981226. Afterglow models which invoke a jet-like geometry for the outflow or require an ambient medium with a radial density dependence, such as that produced by a wind from a massive star, are both consistent with the radio data. Furthermore, we show that the observed properties of the radio afterglow can explain the absence of an optical transient without the need for large extinction local to the GRB.Comment: Accepted for publication in the Astrophysical Journal Letters. Thirteen pages. Three Postscript figure

Supernova 2012ec: Identification of the progenitor and early monitoring with PESSTO

We present the identification of the progenitor of the Type IIP SN 2012ec in archival pre-explosion HST WFPC2 and ACS/WFC F814W images. The properties of the progenitor are further constrained by non-detections in pre-explosion WFPC2 F450W and F606W images. We report a series of early photometric and spectroscopic observations of SN 2012ec. The r'-band light curve shows a plateau with M(r')=-17.0. The early spectrum is similar to the Type IIP SN 1999em, with the expansion velocity measured at Halpha absorption minimum of -11,700 km/s (at 1 day post-discovery). The photometric and spectroscopic evolution of SN 2012ec shows it to be a Type IIP SN, discovered only a few days post-explosion (<6d). We derive a luminosity for the progenitor, in comparison with MARCS model SEDs, of log L/Lsun = 5.15+/-0.19, from which we infer an initial mass range of 14-22Msun. This is the first SN with an identified progenitor to be followed by the Public ESO Spectroscopic Survey of Transient Objects (PESSTO).Comment: 6 pages, 3 figures, MNRAS accepte

Characterization of oligomers from methylglyoxal under dark conditions : a pathway to produce secondary organic aerosol through cloud processing during nighttime

Aqueous-phase oligomer formation from methylglyoxal, a major atmospheric photooxidation product, has been investigated in a simulated cloud matrix under dark conditions. The aim of this study was to explore an additional pathway producing secondary organic aerosol (SOA) through cloud processes without participation of photochemistry during nighttime. Indeed, atmospheric models still underestimate SOA formation, as field measurements have revealed more SOA than predicted. Soluble oligomers (n = 1-8) formed in the course of acid-catalyzed aldol condensation and acid-catalyzed hydration followed by acetal formation have been detected and characterized by positive and negative ion electrospray ionization mass spectrometry. Aldol condensation proved to be a favorable mechanism under simulated cloud conditions, while hydration/acetal formation was found to strongly depend on the pH of the system and only occurred at a pH < 3.5. No evidence was found for formation of organosulfates. The aldol oligomer series starts with a beta-hydroxy ketone via aldol condensation, where oligomers are formed by multiple additions of C3H4O2 units (72 Da) to the parent beta-hydroxy ketone. Ion trap mass spectrometry experiments were performed to structurally characterize the major oligomer species. A mechanistic pathway for the growth of oligomers under cloud conditions and in the absence of UV-light and OH radicals, which could substantially enhance in-cloud SOA yields, is proposed here for the first time

The CFHTLS Real Time Analysis System "Optically Selected GRB Afterglows"

We describe a wide and deep search for optical GRB afterglows on images taken with MegaCAM at the Canada France Hawaii Telescope, within the framework of the CFHT Legacy Survey. This search is performed in near real-time thanks to a Real Time Analysis System called "Optically Selected GRB Afterglows", which has been completely realized and installed on a dedicated computer in Hawaii. This pipeline automatically and quickly analyzes Megacam images and extracts from them a list of astrometrically and photometrically variable objects which are displayed on a web page for validation by a member of the collaboration. In this paper, we comprehensively describe the RTAS process. We also present statistical results based on nearly one full year of operation, showing the quality of the images and the performance of the RTAS. Finally, we compare the efficiency of this study with similar searches, propose an ideal observational strategy using simulations, and discuss general considerations on the searches for GRB afterglows independently of the prompt emission. This is the first of a series of two papers. A second paper will discuss the characterization of variable objects we have found, as well as the GRB afterglow candidates and their nature. We will also estimate or at least constrain the collimation factor of GRB using the totality of the Very Wide Survey observations.Comment: 11 pages, 10 Figures, 5 Table

Gravitational Microlensing Events from the First Year of the Northern Galactic Plane Survey by the Zwicky Transient Facility

The Zwicky Transient Facility (ZTF) (Bellm et al. 2019; Graham et al. 2019; Masci et al. 2019) is currently surveying the entire northern sky, including dense Galactic plane fields. Here, we present preliminary results of the search for gravitational microlensing events in the ZTF data collected from the beginning of the survey (2018 March 20) through 2019 June 30