174350
The Distance to SN 1999em in NGC 1637 from the Expanding Photosphere Method
ABSTRACT We present 30 optical spectra and 49 photometric epochs sampling the first 517 days after discovery of supernova (SN) 1999em and derive its distance through the expanding photosphere method (EPM). SN 1999em is shown to be a Type II‐plateau (II‐P) event, with a photometric plateau lasting until about 100 days after explosion. We identify the dominant ions responsible for most of the absorption features seen in the optical portion of the spectrum during the plateau phase. Using the weakest unblended absorption features to estimate photospheric velocity, we find the distance to SN 1999em to be \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfon...
16857223
SN 2006tf: Precursor Eruptions and the Optically Thick Regime of Extremely Luminous Type IIn Supernovae
SN 2006tf is the third most luminous supernova (SN) discovered so far, after SN 2005ap and SN 2006gy. SN 2006tf is valuable because it provides a link between two regimes: (1) luminous Type IIn supernovae powered by emission directly from interaction with circumstellar material (CSM), and (2) the most extremely luminous SNe where the CSM interaction is so optically thick that energy must diffuse out from an opaque shocked shell. As SN 2006tf evolves, it slowly transitions from the second to the first regime as the clumpy shell becomes more porous. This link suggests that the range in properties of the most luminous SNe is largely determined by the density and speed of hydrogen-rich material ejected shortly before they explode. The total energy radiated by SN 2006tf was at least -->7 ? 1050 ergs. If the bulk of this luminosity came from the thermalization of shock kinetic energy, then the star needs to have ejected ~18 -->M? in the 4-8 yr before core collapse, and another 2-6 -->M? in the decades before that. A Type Ia explosion is therefore excluded. From the H? emission-line profile, we derive a blast wave speed of 2000 km s?1 that does not decelerate, and from the narrow P Cygni absorption from preshock gas we deduce that the progenitor's wind speed was ~190 km s?1. This is reminiscent of the wind speeds of luminous blue variables (LBVs), but not of red supergiants or Wolf-Rayet stars. We propose that like SN 2006gy, SN 2006tf marked the death of a very massive star that retained a hydrogen envelope until the end of its life and suffered extreme LBV-like mass loss in the decades before it exploded.
17627678
SN 2008S: A Cool Super-Eddington Wind in a Supernova Impostor
We present visual-wavelength photometry and spectroscopy of supernova (SN) 2008S. Based on the low peak luminosity for a SN of MR = –13.9 mag, photometric and spectral evolution unlike that of low-luminosity SNe, a late-time decline rate slower than 56Co decay, and slow outflow speeds of 600-1000 km s–1, we conclude that SN 2008S is not a true core-collapse SN and is probably not an electron-capture SN. Instead, we show that SN 2008S more closely resembles an SN impostor event like SN 1997bs, analogous to the giant eruptions of luminous blue variables (LBVs). Its total radiated energy was ~1047.8 erg, and it may have ejected 0.05-0.2 M ☉ in the event. We discover an uncanny similarity between the spectrum of SN 2008S and that of the Galactic hypergiant IRC+10420, which is dominated by narrow Hα, [Ca II], and Ca II emission lines formed in an opaque wind. We propose a scenario where the vastly super-Eddington (Γ 40) wind of SN 2008S partly fails because of reduced opacity due to recombination, as suggested for IRC+10420. The range of initial masses susceptible to eruptive LBV-like mass loss was known to extend down to 20-25 M ☉, but estimates for the progenitor of SN 2008S (and the similar NGC 300 transient) may extend this range to 15 M ☉. As such, SN 2008S may have implications for the progenitor of SN 1987A.
73630268
Observed Fractions of Core-Collapse Supernova Types and Initial Masses of their Single and Binary Progenitor Stars
We analyse the observed fractions of core-collapse supernova (SN) types from the Lick Observatory Supernova Search (LOSS), and we discuss the corresponding implications for massive star evolution. For a standard initial mass function, observed fractions of SN types cannot be reconciled with the expectations of single-star evolution. The mass range of Wolf–Rayet (WR) stars that shed their hydrogen envelopes via their own mass-loss accounts for less than half of the observed fraction of Type Ibc supernovae (SNe Ibc). The true progenitors of SNe Ibc must extend to a much lower range of initial masses than classical WR stars, and we argue that most SN Ibc and SN IIb progenitors must arise from binary Roche lobe overflow. In this scenario, SNe Ic would still trace higher initial mass and metallicity, because line-driven winds in the WR stage remove the helium layer and propel the transition from SN Ib to Ic. Less massive progenitors of SNe Ib and IIb may not be classical WR stars; they may be underluminous with weak winds, possibly hidden by overluminous mass-gainer companions that could appear as B[e] supergiants or related objects having aspherical circumstellar material. The remaining SN types (II-P, II-L and IIn) need to be redistributed across the full range of initial masses, so that even some very massive single stars retain H envelopes until explosion. We consider the possibility of direct collapse to black holes without visible SNe, but find this hypothesis difficult to accommodate in most scenarios. Major areas of remaining uncertainty are (1) the detailed influence of binary separation, rotation and metallicity; (2) mass differences in progenitors of SNe IIn compared to SNe II-L and II-P; and (3) the fraction of SNe Ic arising from single stars with the help of eruptive mass-loss, how this depends on metallicity and how it relates to diversity within the SN Ic subclass. Continued studies of progenitor stars and their environments in nearby galaxies, accounting for SN types, may eventually test these ideas.
18839902
Possible Recovery of SN 1961V in Hubble Space Telescope Archival Images
SN 1961V in NGC 1058 was originally classified by Fritz Zwicky as a "Type V" supernova. However, it has been argued that SN 1961V was not a genuine supernova, but instead the superoutburst of an η Carinae-like luminous blue variable star. In particular, Filippenko et al. used pre-refurbishment Hubble Space Telescope (HST) Wide Field Planetary Camera (WFPC) images and the known radio position of SN 1961V to conclude that the star survived the eruption and is likely coincident with a V ≈ 25.6, V–I ≈ 1.9 mag object. Recently, Stockdale et al. recovered the fading SN 1961V at radio wavelengths and argue that its behavior is similar that of some Type II supernovae. We have analyzed post-refurbishment archival HST WFPC2 data and find that the new radio position is still consistent with the Filippenko et al. object, which has not changed in brightness or color, but is also consistent with an adjacent, fainter (I ≈ 24.3 mag), and very red (V–I > 1.0 mag) object. We suggest that this fainter object could be the survivor of SN 1961V. Forthcoming HST observations may settle this issue.
55046954
Berkeley Supernova Ia Program - I. Observations, data reduction and spectroscopic sample of 582 low-redshift Type Ia supernovae
In this first paper in a series, we present 1298 low-redshift (z ≲ 0.2) optical spectra of 582 Type Ia supernovae (SNe Ia) observed from 1989 to 2008 as part of the Berkeley Supernova Ia Program (BSNIP). 584 spectra of 199 SNe Ia have well-calibrated light curves with measured distance moduli, and many of the spectra have been corrected for host-galaxy contamination. Most of the data were obtained using the Kast double spectrograph mounted on the Shane 3 m telescope at Lick Observatory and have a typical wavelength range of 3300–10 400 A, roughly twice as wide as spectra from most previously published data sets. We present our observing and reduction procedures, and we describe the resulting SN Database, which will be an online, public, searchable data base containing all of our fully reduced spectra and companion photometry. In addition, we discuss our spectral classification scheme (using the SuperNova IDentification code, snid; Blondin & Tonry), utilizing our newly constructed set of snid spectral templates. These templates allow us to accurately classify our entire data set, and by doing so we are able to reclassify a handful of objects as bona fide SNe Ia and a few other objects as members of some of the peculiar SN Ia subtypes. In fact, our data set includes spectra of nearly 90 spectroscopically peculiar SNe Ia. We also present spectroscopic host-galaxy redshifts of some SNe Ia where these values were previously unknown. The sheer size of the BSNIP data set and the consistency of our observation and reduction methods make this sample unique among all other published SN Ia data sets and complementary in many ways to the large, low-redshift SN Ia spectra presented by Matheson et al. and Blondin et al. In other BSNIP papers in this series, we use these data to examine the relationships between spectroscopic characteristics and various observables such as photometric and host-galaxy properties.
123211493
Exploring the feasibility of a separated function RFQ with mini-vane structure
The accelerating field in the conventional RFQ is originated by the surface modulation of the quadruple electrodes. However, the axial accelerating field generated in this way is quite limited. To enhance the energy gain as well as the focusing power, a post-RFQ accelerating structure called separated function RFQ (SFRFQ) was proposed (Progr. Nat. Sci. 12(1) (2002) 23), and its feasibility has been explored (Chin. Phys. 51(6) (2002)). The RF accelerating field in the SFRFQ structure mainly occurs at gaps between periodical cells, while the electrical quadruple field inside the cells provides the transverse focusing. It turns out that the overall performance can be improved considerably, comparing with that of conventional RFQ. The preliminary results of calculation and model measurements are presented and discussed in the paper.
8468111
SN 1997bs in M66: Another Extragalactic η Carinae Analog?1
ABSTRACT We report on SN 1997bs in NGC 3627 (M66), the first supernova discovered by the Lick Observatory Supernova Search using the 0.75 m Katzman Automatic Imaging Telescope (KAIT). Based on its early‐time optical spectrum, SN 1997bs was classified as Type IIn. However, from the BVRI light curves obtained by KAIT early in the supernova’s evolution, and F555W and F814W light curves obtained from Hubble Space Telescope archival WFPC2 images at late times, we question the identification of SN 1997bs as a bona fide supernova. We believe that it is more likely a superoutburst of a very massive luminous blue variable star, analogous to η Carinae, and similar to SN 1961V in NGC 1058 (Filippenko et al. 1995 AJ, 110, 2261) and SN 1954J (“Variable 12”) in NGC 2403 (Humphreys & Davidson 1994 PASP, 106, 1025). The progenitor may have survived the outburst, since the SN is seen in early 1998 at \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs}...
118464345
Induced radioactivity analysis for the NSRL Linac in China using Monte Carlo simulations and gamma-spectroscopy
The 200-MeV electron linac of the National Synchrotron Radiation Laboratory (NSRL) located in Hefei is one of the earliest high-energy electron linear accelerators in China. The electrons are accelerated to 200 MeV by five acceleration tubes and are collimated by scrapers. The scraper aperture is smaller than the acceleration tube one, so some electrons hit the materials when passing through them. These lost electrons cause induced radioactivity mainly due to bremsstrahlung and photonuclear reaction. This paper describes a study of induced radioactivity for the NSRL Linac using FLUKA simulations and gamma-spectroscopy. The measurements showed that electrons were lost mainly at the scraper. So the induced radioactivity of the NSRL Linac is mainly produced here. The radionuclide types were simulated using the FLUKA Monte Carlo code and the results were compared against measurements made with a High Purity Germanium (HPGe) gamma spectrometer. The NSRL linac had been retired because of upgrading last year. The removed components were used to study induced radioactivity. The radionuclides confirmed by the measurement are: $^{57}$Ni, $^{52}$Mn, $^{51}$Cr, $^{58}$Co, $^{56}$Co, $^{57}$Co, $^{54}$Mn, $^{60}$Co and $^{22}$Na, the first eight nuclides of which are predicted by FLUKA simulation. The research will provide the theoretical basis for the similar accelerator decommissioning plan, and is significant for accelerator structure design, material selection and radiation protection design.
16051323
Comment on `Cosmological Topological Massive Gravitons and Photons'
In a recent paper (arXiv: 0801.4566) it was shown that all global energy eigenstates of asymptotically $AdS_3$ chiral gravity have non-negative energy at the linearized level. This result was questioned (arXiv: 0803.3998) by Carlip, Deser, Waldron and Wise (CDWW), who work on the Poincare patch. They exhibit a linearized solution of chiral gravity and claim that it has negative energy and is smooth at the boundary. We show that the solution of CDWW is smooth only on that part of the boundary of $AdS_3$ included in the Poincare patch. Extended to global $AdS_3$, it is divergent at the boundary point not included in the Poincare patch. Hence it is consistent with the results of (arXiv: 0801.4566).
18467777
Direct Analysis of Spectra of the Peculiar Type?Ia Supernova 2000cx
The Type Ia supernova (SN) 2000cx exhibited multiple peculiarities, including a lopsided B-band light-curve peak that does not conform to current methods for using shapes of light curves to standardize SN Ia luminosities. We use the parameterized SN synthetic-spectrum code SYNOW to study line identifications in the photospheric-phase spectra of SN 2000cx. Previous work established the presence of Ca II infrared triplet features forming above velocity ~20,000 km s-1, much higher than the photospheric velocity of ~10,000 km s-1. We find Ti II features forming at the same high velocity. High-velocity line formation is partly responsible for the photometric peculiarities of SN 2000cx: for example, B-band flux blocking by Ti II absorption features that decreases with time causes the B light curve to rise more rapidly and decline more slowly than it otherwise would. SN 2000cx contains an absorption feature near 4530 A that may be Hβ, forming at the same high velocity. The lack of conspicuous Hα and Paα signatures does not necessarily invalidate the Hβ identification if the high-velocity line formation is confined to a clump that partly covers the photosphere and the Hα and Paα source functions are elevated relative to that of resonance scattering. The Hβ identification is tentative. If it is correct, the high-velocity matter must have come from a nondegenerate companion star.