16608072
SDSS J124602.54+011318.8: A Highly Variable AGN, Not an Orphan GRB Afterglow
The optically variable source SDSS J124602.54+011318.8 first appears in Sloan Digital Sky Survey (SDSS) data as a bright point source with nonstellar colors. Subsequent SDSS imaging and spectroscopy showed that the point source declined or disappeared, revealing an underlying host galaxy at z = 0.385. Based on these properties, the source was suggested to be a candidate “orphan afterglow”: a moderately beamed optical transient, associated with a gamma-ray burst (GRB) whose highly beamed radiation cone does not include our line of sight. We present new imaging and spectroscopic observations of this source. When combined with a careful re-analysis of archival optical and radio data, the observations prove that SDSS J124602.54+011318.8 is in fact an unusual radioloud AGN, probably in the BL Lac class. The object displays strong photometric variability on time scales of weeks to years, including several bright flares, similar to the one initially reported. The SDSS observations are therefore almost certainly not related to a GRB. The optical spectrum of this object dramatically changes in correlation with its optical brightness. At the bright phase, weak, narrow oxygen emission lines and probably a broader Hα line are superposed on a blue continuum. As the flux decreases, the spectrum becomes dominated by the host galaxy light, with emerging stellar absorption lines. The narrow and broad emission lines persist. We briefly discuss the implications of this discovery on the study of AGNs and other optically variable or transient phenomena. Subject headings: galaxies: active, BL Lacertae objects: general, gamma rays: bursts
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.
119183379
Fourteen months of observations of the possible super-Chandrasekhar mass Type Ia Supernova 2009dc
In this paper, we present and analyse optical photometry and spectra of the extremely luminous and slowly evolving Type Ia supernova (SN Ia) 2009dc, and offer evidence that it is a super-Chandrasekhar mass (SC) SN Ia and thus has a SC white dwarf (WD) progenitor. Optical spectra of SN 2007if, a similar object, are also shown. SN 2009dc had one of the most slowly evolving light curves ever observed for a SN Ia, with a rise time of ~23 d and Δm 15 (B) = 0.72 mag. We calculate a lower limit to the peak bolometric luminosity of ~2.4 x 10 43 erg s -1 , though the actual value is likely almost 40 per cent larger. Optical spectra of SN 2009dc and SN 2007if obtained near maximum brightness exhibit strong C II features (indicative of a significant amount of unburned material), and the post-maximum spectra are dominated by iron-group elements (IGEs). All of our spectra of SN 2009dc and SN 2007if also show low expansion velocities. However, we see no strong evidence in SN 2009dc for a velocity 'plateau' near maximum light like the one seen in SN 2007if. The high luminosity and low expansion velocities of SN 2009dc lead us to derive a possible WD progenitor mass of more than 2 M ⊙ and a 56 Ni mass of about 1.4-1.7 M ⊙ . We propose that the host galaxy of SN 2009dc underwent a gravitational interaction with a neighbouring galaxy in the relatively recent past. This may have led to a sudden burst of star formation which could have produced the SC WD progenitor of SN 2009dc and likely turned the neighbouring galaxy into a 'post-starburst galaxy'. No published model seems to match the extreme values observed in SN 2009dc, but simulations do show that such massive progenitors can exist (likely as a result of the merger of two WDs) and can possibly explode as SC SNe Ia.
18546617
A High Intrinsic Peculiarity Rate among Type Ia Supernovae
We have compiled a sample of 45 Type Ia supernovae (SNe Ia) discovered by the Lick Observatory Supernova Search (LOSS) and the Beijing Astronomical Observatory Supernova Survey (BAOSS), and determined the rate of spectroscopically peculiar SNe Ia (i.e., SN 1986G-like, SN 1991bg-like, and SN 1991T-like objects) and the luminosity function of SNe Ia. Because of the nature of the two surveys (distance-limited with small baselines and deep limiting magnitudes), nearly all SNe Ia have been discovered in the sample galaxies of LOSS and BAOSS; thus, the observed peculiarity rate and luminosity function of SNe Ia are intrinsic. We find that 36% ± 9% of nearby SNe Ia are peculiar; specifically, the luminosity function of SNe Ia consists of 20% SN 1991T-like, 64% normal, and 16% SN 1991bg-like objects. We have compared our results to those found by earlier studies, and to those found at high redshift. The apparent dearth of SN 1991T-like objects at high redshift may be due to extinction, and especially to the difficulty of recognizing them from spectra obtained past maximum brightness or from spectra with low signal-to-noise ratios. Implications of the high peculiarity rate for the progenitor systems of SNe Ia are also briefly discussed.
16104319
The Lick AGN Monitoring Project: Broad-line Region Radii and Black Hole Masses from Reverberation Mapping of Hβ
We have recently completed a 64-night spectroscopic monitoring campaign at the Lick Observatory 3-m Shane telescope with the aim of measuring the masses of the black holes in 12 nearby (z < 0: 05) Seyfert 1 galaxies with expected masses in the range � 10 6 -10 7 Mand also the well-studied nearby active galactic nucleus (AGN) NGC 5548. Nine of the objects in the sample (including NGC 5548) showed optical variability of sufficient strength during the monitoring campaign to all ow for a time lag to be measured between the continuum fluctuations and the response to these fluctuation s in the broad Hemission. We present here the light curves for all the objects in this sample and the subseq uent Htime lags for the nine objects where these measurements were possible. The Hlag time is directly related to the size of the broad-line reg ion in AGNs, and by combining the Hlag time with the measured width of the Hemission line in the variable part of the spectrum, we determine the virial mass of the central sup ermassive black hole in these nine AGNs. The absolute calibration of the black hole masses is based on the normalization derived by Onken et al., which brings the masses determined by reverberation mapping into agreement with the local MBH -�? relationship for quiescent galaxies. We also examine the time lag response as a function of velocity across the Hline profile for six of the AGNs. The analysis of four leads to rather ambiguous results with relatively flat time lags as a function of velocity. However, SBS 1116+583A exhibits a symmetric time lag response around the line center reminiscent of simple models for circularly orbiting broad -line region (BLR) clouds, and Arp 151 shows an asymmetric profile that is most easily explained by a simple g ravitational infall model. Further investigation will be necessary to fully understand the constraints place d on physical models of the BLR by the velocity- resolved response in these objects. Subject headings:galaxies: active - galaxies: nuclei - galaxies: Seyfert
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...
109503889
EM Calorimeter in BESIII Experiment
BESIII EM Calorimeter (EMC) is based on CsI crystals, working at upgraded Beijing Electron Positron Collider (BEPC), called BEPCII. The overall BEPCII and BESIII design and current status are briefly described. The design and construction of EMC and its performance are presented. EMC works very well and its performances reach the design expectations, it plays an important roll in detector operation and in the BESIII trigger. There are some special features in the EMC construction and reconstruction: the crystals are assembled without support wall to reduce dead area; the time information of the EM clusters can help to suppress the machine background; the detector noise is smaller than similar detectors; the energy reconstruction with TOF signals helps to improve the energy resolution, especially for low energy showers. Several physics papers mainly based on EMC information have been published.
73568718
The Upgrade of the Hefei Light Source HLS Transport Line
To enhance the performance of Hefei Light Source, an upgrade project is undergoing. The magnet lattice of storage ring will be reconstructed with 4 DBA cells, whose advantages are lower beam emittance and more straight section available for insertion devices. In order to assure smooth beam accumulation process under new low emittance lattice, the injector, which is composed of electron linac and beam transfer line, would be updated. The detail upgrading of Hefei Light Source transport line will be described in this paper. It include the upgrading of lattice, the orbit control of beam transfer line and others. It is hopeful to realize a high transfer efficiency and high injection efficiency for new low beam emittance storage ring. INTRODUCTION HLS is a dedicated second generation VUV light source, whose main body is composed of 800MeV electron storage ring, 200MeV linac and beam transfer line. There are two factors affecting light source performance: large beam emittance and less number of straight sections. In order to improve HLS performance, an upgrading is undergoing now[1]. The main purpose of upgrading are increasing the number of insertion devices, lowering the ring’s beam emittance and improving the beam orbit stability. After upgrading, separate function DBA was adopted as the standard cell of ring. There are four 4.0m long straight section and four 2.3m long straight section. The emittance of lattice will be reduced to 36nm.rad in achromatic mode and to 20nm.rad in distributed dispersion mode. The orbit stability will be smaller than 5μm. After upgrading, the beam accumulation process will be more difficult under low injection energy. Improving injection efficiency is essential to obtain high beam intensity. In order to improve injection efficiency, the injector should be upgraded also. The demanding to the injection beam is shown in table 1. As comparing, the old injector beam properties are shown in table 1 also. The injector of HLS was constructed twenty years ago, and poor beam properties cannot meet the requirements of new ring. Several upgrades were proposed. A new thermal-cathode gun will be constructed to reduce the beam emittance and to get ns pulse time structure. Cooperating with new time system, bunch by bunch filling would be realized in the future. A new phase control system also will adapt to promote the energy stability of injector. An new beam trajectory monitoring system and related steering magnet system will be applied. It will be helpful to control the position and angle of injected beam. Table 1: Demanding to the Injection Beam parameters demanding Old machine Charge 1nc/1ns 80mA&0.5μs Energy spread 0.5% 0.8% Energy stibility 0.5% 0.7% Normalized emittance (rms) 40mm•mrad 200mm•mrad
15020605
The type Ia supernova 1997br in ESO 576-G40
The peculiar type Ia supernova SN 1997br in ESO 576-G40 was extensively observed at Beijing Astronomical Observatory and Lick Observatory. In this paper, we present and discuss the BVRI photometry and the spectra collected over 3 months, beginning 9 days before maximum brightness. The light curves of SN 1997br are similar to those of SN 1991T, with slow decline rates after the B maximum. Well-sampled data before the B maximum show unambiguously that SN 1997br rises more slowly and has a wider peak than normal type Ia supernovae. The optical color evolution of SN 1997br is also similar to that of SN 1991T. We estimate the extinction of SN 1997br to be E(B-V) = 0.35 ± 0.10 mag by comparing its BVRI light curves with those of SN 1991T and by measuring the equivalent width of interstellar Na I D absorption lines. We have conducted a thorough comparison of the spectroscopic evolution of SN 1997br, SN 1991T, and SN 1994D. Although SN 1997br is generally very similar to SN 1991T, it shows some interesting differences at various epochs. Spectra of SN 1997br seem to indicate an earlier transition to the dominant phase of Fe-peak elements after the B maximum. Si II lines in SN 1997br show a very short duration after the B maximum. We discuss the implications of our observations of SN 1997br for models of type Ia supernovae. Specifically, we suggest that some SNe Ia may result from decelerated detonations of white dwarfs.
158654
SUBARU AND KECK OBSERVATIONS OF THE PECULIAR TYPE IA SUPERNOVA 2006GZ AT LATE PHASES
Recently, a few peculiar Type Ia supernovae (SNe Ia) that show exceptionally large peak luminosity have been discovered. Their luminosity requires more than 1 M ? of 56Ni to be ejected during the explosion, suggesting that they might have originated from super-Chandrasekhar mass white dwarfs. However, the nature of these objects is not yet well understood. In particular, no data have been taken at late phases, about one year after the explosion. We report on Subaru and Keck optical spectroscopic and photometric observations of the SN Ia 2006gz, which had been classified as being one of these overluminous SNe Ia. The late-time behavior is distinctly different from that of normal SNe Ia, reinforcing the argument that SN 2006gz belongs to a different subclass than normal SNe Ia. However, the peculiar features found at late times are not readily connected to a large amount of 56Ni; the SN is faint, and it lacks [Fe II] and [Fe III] emissions. If the bulk of the radioactive energy escapes the SN ejecta as visual light, as is the case in normal SNe Ia, the mass of 56Ni does not exceed ~0.3 M ?. We discuss several possibilities to remedy the problem. With the limited observations, however, we are unable to conclusively identify which process is responsible. An interesting possibility is that the bulk of the emission might be shifted to longer wavelengths, unlike the case in other SNe Ia, which might be related to dense C-rich regions as indicated by the early-phase data. Alternatively, it might be the case that SN 2006gz, though peculiar, was actually not substantially overluminous at early times.
119304446
Perturbations of W(infinity) CFTs
The holographic duals of higher spin theories on AdS_3 are described by the large N limit of a family of minimal model CFTs, whose symmetry algebra is equivalent to W(infinity)[lambda]. We study perturbations of these limit theories, and show that they possess a marginal symmetry-preserving perturbation that describes switching on the 1/N corrections. We also test our general results for the specific cases of lambda=0,1, where free field realisations are available.