Evidence for Extremely High Dust Polarization Efficiency in NGC 3184

Recent studies have found the Type II-plateau supernova (SN) 1999gi to be highly polarized (p_max = 5.8%, where p_max is the highest degree of polarization measured in the optical bandpass; Leonard & Filippenko 2001) and minimally reddened (E[B-V] = 0.21 +/- 0.09 mag; Leonard et al. 2002). From multiple lines of evidence, including the convincing fit of a ``Serkowski'' interstellar polarization (ISP) curve to the continuum polarization shape, we conclude that the bulk of the observed polarization is likely due to dust along the line of sight (l-o-s), and is not intrinsic to SN 1999gi. We present new spectropolarimetric observations of four distant Galactic stars close to the l-o-s to SN 1999gi (two are within 0.02 degrees), and find that all are null to within 0.2%, effectively eliminating Galactic dust as the cause of the high polarization. The high ISP coupled with the low reddening implies an extraordinarily high polarization efficiency for the dust along this l-o-s in NGC 3184: ISP / E(B-V) = 31^{+22}_{-9} % mag^{-1}. This is inconsistent with the empirical Galactic limit (ISP / E[B-V] < 9% mag^{-1}), and represents the highest polarization efficiency yet confirmed for a single sight line in either the Milky Way or an external galaxy.Comment: 27 pages, accepted for publication by the Astronomical Journa

Measurement of the Background Activities of a 100Mo-enriched powder sample for AMoRE crystal material using a single high purity germanium detector

The Advanced Molybdenum-based Rare process Experiment (AMoRE) searches for neutrino-less double-beta (0{\nu}\b{eta}\b{eta}) decay of 100Mo in enriched molybdate crystals. The AMoRE crystals must have low levels of radioactive contamination to achieve low background signals with energies near the Q-value of the 100Mo 0{\nu}\b{eta}\b{eta} decay. To produce low-activity crystals, radioactive contaminants in the raw materials used to form the crystals must be controlled and quantified. 100EnrMoO3 powder, which is enriched in the 100Mo isotope, is of particular interest as it is the source of 100Mo in the crystals. A high-purity germanium detector having 100% relative efficiency, named CC1, is being operated in the Yangyang underground laboratory. Using CC1, we collected a gamma spectrum from a 1.6-kg 100EnrMoO3 powder sample enriched to 96.4% in 100Mo. Activities were analyzed for the isotopes 228Ac, 228Th, 226Ra, and 40K. They are long-lived naturally occurring isotopes that can produce background signals in the region of interest for AMoRE. Activities of both 228Ac and 228Th were < 1.0 mBq/kg at 90% confidence level (C.L.). The activity of 226Ra was measured to be 5.1 \pm 0.4 (stat) \pm 2.2 (syst) mBq/kg. The 40K activity was found as < 16.4 mBq/kg at 90% C.L.Comment: 20 pages, 6 figures, 5 table

Evidence for the involvement of more than one mRNA species in controlling the inactivation process of rat and rabbit brain Na channels expressed in Xenopus oocytes

The properties of rat and rabbit brain sodium (Na) channels expressed in Xenopus oocytes following either unfractionated or high-molecular- weight mRNA injections were compared to assess the relative contribution of different size messages to channel function. RNA was size-fractionated on a sucrose gradient and a high-molecular-weight fraction (7–10 kilobase) encoding the α-subunit gave rise to functional voltage-dependent Na channels in the oocyte membrane. Single- channel conductance, mean open time, and time to first opening were all similar to the values for channels following injection of unfractionated RNA. In contrast, inactivation properties were markedly different; Na currents from high-molecular-weight RNA inactivated with a several-fold smaller macroscopic inactivation rate and showed a steady-state voltage dependence that was shifted in the depolarizing direction by at least 10 mV relative to that for unfractionated RNA. Single-channel recording revealed that the kinetic difference arose from a greater probability for high-molecular-weight RNA induced channels to reopen during a depolarizing voltage step. Pooling all gradient fractions and injecting this RNA into oocytes led to the appearance of Na channels with inactivation properties indistinguishable from those following injection of unfractionated RNA. These results suggest that mRNA species not present in the high- molecular-weight fraction can influence the inactivation process of rat brain Na channels expressed in Xenopus oocytes. This mRNA may encode β-subunits or other proteins that are involved in posttranslational processing of voltage-dependent Na channels

Evidence for the involvement of more than one mRNA species in controlling the inactivation process of rat and rabbit brain Na channels expressed in Xenopus oocytes

The properties of rat and rabbit brain sodium (Na) channels expressed in Xenopus oocytes following either unfractionated or high-molecular- weight mRNA injections were compared to assess the relative contribution of different size messages to channel function. RNA was size-fractionated on a sucrose gradient and a high-molecular-weight fraction (7–10 kilobase) encoding the α-subunit gave rise to functional voltage-dependent Na channels in the oocyte membrane. Single- channel conductance, mean open time, and time to first opening were all similar to the values for channels following injection of unfractionated RNA. In contrast, inactivation properties were markedly different; Na currents from high-molecular-weight RNA inactivated with a several-fold smaller macroscopic inactivation rate and showed a steady-state voltage dependence that was shifted in the depolarizing direction by at least 10 mV relative to that for unfractionated RNA. Single-channel recording revealed that the kinetic difference arose from a greater probability for high-molecular-weight RNA induced channels to reopen during a depolarizing voltage step. Pooling all gradient fractions and injecting this RNA into oocytes led to the appearance of Na channels with inactivation properties indistinguishable from those following injection of unfractionated RNA. These results suggest that mRNA species not present in the high- molecular-weight fraction can influence the inactivation process of rat brain Na channels expressed in Xenopus oocytes. This mRNA may encode β-subunits or other proteins that are involved in posttranslational processing of voltage-dependent Na channels

Tsunami awareness and preparedness in Aotearoa New Zealand:The evolution of community understanding

After catastrophic events such as the 2004 Indian Ocean tsunami and the 2011 Great East Japan earthquake and tsunami there is a clear need for vulnerable countries like Aotearoa New Zealand to get prepared for tsunami. In the last ten years, the New Zealand government initiated major efforts to raise awareness of tsunami risk among coastal residents. This study explores tsunami awareness, preparedness, and evacuation intentions among residents of the East Coast of the North Island in a 2015 survey. The ten chosen locations also participated in a tsunami survey in 2003, with results demonstrating that tsunami awareness rose in the twelve years between the surveys. The 2015 survey also included questions on preparedness and intended action. Even though coastal residents know they live in a tsunami prone area, preparedness is relatively low and high expectations of a formal warning remain, even for a local source tsunami scenario. Furthermore, survey respondents had unrealistic ideas of evacuation procedures. When asked about their evacuation intentions, respondents intended to undertake a number of different actions before evacuating their homes, which could cause significant delays in the evacuation process. Most respondents were also reluctant to evacuate on foot and prefer using their vehicles instead, which could create dangerous traffic congestion. These surveyed intentions are consistent with a study of actual evacuation behaviours in the subsequent 2016 Kaikōura earthquake and tsunami, providing validation for the survey indicators. This paper identifies the procedures least understood by the public and offers some solutions to improve tsunami preparedness.</p

Spectropolarimetry of SN 2011dh in M51: geometric insights on a Type IIb supernova progenitor and explosion

We present seven epochs of spectropolarimetry of the Type IIb supernova (SN) 2011dh in M51, spanning 86 days of its evolution. The first epoch was obtained 9 days after the explosion, when the photosphere was still in the depleted hydrogen layer of the stripped-envelope progenitor. Continuum polarization is securely detected at the level of P~0.5% through day 14 and appears to diminish by day 30, which is different from the prevailing trends suggested by studies of other core-collapse SNe. Time-variable modulations in P and position angle are detected across P-Cygni line features. H-alpha and HeI polarization peak after 30 days and exhibit position angles roughly aligned with the earlier continuum, while OI and CaII appear to be geometrically distinct. We discuss several possibilities to explain the evolution of the continuum and line polarization, including the potential effects of a tidally deformed progenitor star, aspherical radioactive heating by fast-rising plumes of Ni-56 from the core, oblique shock breakout, or scattering by circumstellar material. While these possibilities are plausible and guided by theoretical expectations, they are not unique solutions to the data. The construction of more detailed hydrodynamic and radiative-transfer models that incorporate complex aspherical geometries will be required to further elucidate the nature of the polarized radiation from SN 2011dh and other Type IIb supernovae.Comment: Post-proof edit. Accepted to MNRAS 2015 Aug 1

Is it Round? Spectropolarimetry of the Type II-P Supernova 1999em

We present the first multi-epoch spectropolarimetry of a type II plateau supernova (SN II-P), with optical observations of SN 1999em on days 7, 40, 49, 159, and 163 after discovery. These data are used to probe the geometry of the electron-scattering atmosphere before, during, and after the plateau phase, which ended roughly 90 days after discovery. Weak continuum polarization with an unchanging polarization angle (theta ~ 160 deg) is detected at all epochs, with p ~ 0.2% on day 7, p ~ 0.3% on days 40 and 49, and p ~ 0.5% in the final observations. Distinct polarization modulations across strong line features are present on days 40, 49, 159, and 163. Uncorrected for interstellar polarization (which is believed to be quite small), polarization peaks are associated with strong P Cygni absorption troughs and nearly complete depolarization is seen across the H-alpha emission profile. The temporal evolution of the continuum polarization and sharp changes across lines indicate polarization intrinsic to SN 1999em. When modeled in terms of the oblate, electron-scattering atmospheres of Hoeflich, the observed polarization implies anasphericity of at least 7% during the period studied. The temporal polarization increase may indicate greater asphericity deeper into the ejecta. We discuss the implications of asphericity on the use of type II-P supernovae as primary extragalactic distance indicators through the expanding photosphere method (EPM). If asphericity produces directionally dependant flux and peculiar galaxy motions are characterized by sigma_v_rec = 300 km/s, it is shown that the agreement between previous EPM measurements of SNe II and distances to the host galaxies predicted by a linear Hubble law restrict mean SN II asphericity to values less than 30% (3-sigma) during the photospheric phase.Comment: 65 pages (29 Figures, 4 Tables), Accepted for publication in the June 1, 2001 edition of ApJ. Revised statistical analysis of scatter in Hubble diagram of previous EPM distances and the implications for mean SN II asphericit

Multi-Epoch Spectropolarimetry for a Sample of Type IIn Supernovae: Persistent Asymmetry in Dusty Circumstellar Material

We present multi-epoch spectropolarimetry and spectra for a sample of 14 Type IIn supernovae (SNe IIn). We find that after correcting for likely interstellar polarization, SNe IIn commonly show intrinsic continuum polarization of 1--3% at the time of peak optical luminosity, although a few show weaker or negligible polarization. While some SNe IIn have even stronger polarization at early times, their polarization tends to drop smoothly over several hundred days after peak. We find a tendency for the intrinsic polarization to be stronger at bluer wavelengths, especially at early times. While polarization from an electron scattering region is expected to be grey, scattering of SN light by dusty circumstellar material (CSM) may induce such a wavelength-dependent polarization. For most SNe IIn, changes in polarization degree and wavelength dependence are not accompanied by changes in the position angle, requiring that asymmetric pre-SN mass loss had a persistent geometry. While 2--3% polarization is typical, about 30% of SNe IIn have very low or undetected polarization. Under the simplifying assumption that all SN IIn progenitors have axisymmetric CSM (i.e. disk/torus/bipolar), then the distribution of polarization values we observe is consistent with similarly asymmetric CSM seen from a distribution of random viewing angles. This asymmetry has very important implications for understanding the origin of pre-SN mass loss in SNe IIn, suggesting that it was shaped by binary interaction.Comment: 76 pages, 54 figures (13 in main text, 41 in appendix A

On the Progenitors of Core-Collapse Supernovae

Theory holds that a star born with an initial mass between about 8 and 140 times the mass of the Sun will end its life through the catastrophic gravitational collapse of its iron core to a neutron star or black hole. This core collapse process is thought to usually be accompanied by the ejection of the star's envelope as a supernova. This established theory is now being tested observationally, with over three dozen core-collapse supernovae having had the properties of their progenitor stars directly measured through the examination of high-resolution images taken prior to the explosion. Here I review what has been learned from these studies and briefly examine the potential impact on stellar evolution theory, the existence of "failed supernovae", and our understanding of the core-collapse explosion mechanism.Comment: 7 Pages, invited review accepted for publication by Astrophysics and Space Science (special HEDLA 2010 issue