Showing papers by "Peter Nugent published in 2006"

Long γ-ray bursts and core-collapse supernovae have different environments

Abstract: When massive stars exhaust their fuel, they collapse and often produce the extraordinarily bright explosions known as core-collapse supernovae. On occasion, this stellar collapse also powers an even more brilliant relativistic explosion known as a long-duration γ-ray burst. One would then expect that these long γ-ray bursts and core-collapse supernovae should be found in similar galactic environments. Here we show that this expectation is wrong. We find that the γ-ray bursts are far more concentrated in the very brightest regions of their host galaxies than are the core-collapse supernovae. Furthermore, the host galaxies of the long γ-ray bursts are significantly fainter and more irregular than the hosts of the core-collapse supernovae. Together these results suggest that long-duration γ-ray bursts are associated with the most extremely massive stars and may be restricted to galaxies of limited chemical evolution. Our results directly imply that long γ-ray bursts are relatively rare in galaxies such as our own Milky Way.

The type Ia supernova SNLS-03D3bb from a super-Chandrasekhar-mass white dwarf star

Abstract: The acceleration of the expansion of the universe, and theneed for Dark Energy, were inferred from the observations of Type Iasupernovae (SNe Ia) 1;2. There is consensus that SNeIa are thermonuclearexplosions that destroy carbon-oxygen white dwarf stars that accretematter from a companion star3, although the nature of this companionremains uncertain. SNe Ia are thought to be reliable distance indicatorsbecause they have a standard amount of fuel and a uniform trigger theyare predicted to explode when the mass of the white dwarf nears theChandrasekhar mass 4 - 1.4 solar masses. Here we show that the highredshift supernova SNLS-03D3bb has an exceptionally high luminosity andlow kinetic energy that both imply a super-Chandrasekhar mass progenitor.Super-Chandrasekhar mass SNeIa shouldpreferentially occur in a youngstellar population, so this may provide an explanation for the observedtrend that overluminous SNe Ia only occur in young environments5;6. Sincethis supernova does not obey the relations that allow them to becalibrated as standard candles, and since no counterparts have been foundat low redshift, future cosmology studies will have to considercontamination from such events.

Time-dependent Monte Carlo Radiative Transfer Calculations for Three-dimensional Supernova Spectra, Light Curves, and Polarization

Abstract: We discuss Monte Carlo techniques for addressing the three-dimensional time-dependent radiative transfer problem in rapidly expanding supernova atmospheres. The transfer code SEDONA has been developed to calculate the light curves, spectra, and polarization of aspherical supernova models. From the onset of free expansion in the supernova ejecta, SEDONA solves the radiative transfer problem self-consistently, including a detailed treatment of gamma-ray transfer from radioactive decay and with a radiative equilibrium solution of the temperature structure. Line fluorescence processes can also be treated directly. No free parameters need be adjusted in the radiative transfer calculation, providing a direct link between multidimensional hydrodynamic explosion models and observations. We describe the computational techniques applied in SEDONA and verify the code by comparison to existing calculations. We find that convergence of the Monte Carlo method is rapid and stable even for complicated multidimensional configurations. We also investigate the accuracy of a few commonly applied approximations in supernova transfer, namely, the stationarity approximation and the two-level atom expansion opacity formalism.

Nearby Supernova Factory Observations of SN 2005gj: Another Type Ia Supernova in a Massive Circumstellar Envelope.

Abstract: Revision 2.6, 2006/06/01 00:20:07 Nearby Supernova Factory Observations of SN 2005gj: Another Type Ia Supernova in a Massive Circumstellar Envelope. The Nearby Supernova Factory G. Aldering, P. Antilogus, S. Bailey, 1 C. Baltay, 8 A. Bauer, 8 N. Blanc, 2 S. Bongard, 1,5 Y. Copin, 2 E. Gangler, 2 S. Gilles, 3 R. Kessler, 7 D. Kocevski, 1,6 B. C. Lee, 1 S. Loken, 1 P. Nugent, 1 R. Pain, 3 E. P´ contal, 4 R. Pereira, 3 S. Perlmutter, 1,6 D. Rabinowitz, 8 e G. Rigaudier, R. Scalzo, G. Smadja, 2 R. C. Thomas, 1 L. Wang, 1 B. A. Weaver 1,5 ABSTRACT We report the independent discovery and follow-up observations of supernova 2005gj by the Nearby Supernova Factory. This is the second confirmed case of a “hybrid” Type Ia/IIn supernova, which like the prototype SN 2002ic, we inter- pret as the explosion of a white dwarf interacting with a circumstellar medium. Our early-phase photometry of SN 2005gj shows that the strength of the inter- action between the supernova ejecta and circumstellar material is much stronger than for SN 2002ic. Our first spectrum shows a hot continuum with broad and narrow Hα emission. Later spectra, spanning over 4 months from outburst, show clear Type Ia features combined with broad and narrow Hγ, Hβ, Hα and He I λλ5876,7065 in emission. At higher resolution, P Cygni profiles are appar- ent. Surprisingly, we also observe an inverted P Cygni profile for [O III ] λ5007. Physics Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA, 94720 Institut de Physique Nucl´ aire de Lyon, UMR5822, CNRS-IN2P3; Universit´ Claude Bernard Lyon 1, e e F-69622 Villeurbanne France Laboratoire de Physique Nucl´ aire et des Hautes Energies IN2P3 - CNRS - Universit´ s Paris VI et Paris e e VII, 4 place Jussieu Tour 33 - Rez de chauss´ e 75252 Paris Cedex 05 e Centre de Recherche Astronomique de Lyon, 9, av. Charles Andr´ , 69561 Saint Genis Laval Cedex e University of California, Space Sciences Laboratory, Berkeley, CA 94720-7450 Department of Physics, University of California, Berkeley, CA 94720 Kavli Institute for Cosmological Physics, The University of Chicago, Chicago, IL 60637 Department of Physics, Yale University, New Haven, CT 06250-8121

Time Dependent Monte Carlo Radiative Transfer Calculations For 3-Dimensional Supernova Spectra, Lightcurves, and Polarization

Abstract: We discuss Monte-Carlo techniques for addressing the 3-dimensional time-dependent radiative transfer problem in rapidly expanding supernova atmospheres. The transfer code SEDONA has been developed to calculate the lightcurves, spectra, and polarization of aspherical supernova models. From the onset of free-expansion in the supernova ejecta, SEDONA solves the radiative transfer problem self-consistently, including a detailed treatment of gamma-ray transfer from radioactive decay and with a radiative equilibrium solution of the temperature structure. Line fluorescence processes can also be treated directly. No free parameters need be adjusted in the radiative transfer calculation, providing a direct link between multi-dimensional hydrodynamical explosion models and observations. We describe the computational techniques applied in SEDONA, and verify the code by comparison to existing calculations. We find that convergence of the Monte Carlo method is rapid and stable even for complicated multi-dimensional configurations. We also investigate the accuracy of a few commonly applied approximations in supernova transfer, namely the stationarity approximation and the two-level atom expansion opacity formalism.

Nearby Supernova Factory Observations of SN 2005gj: Another Type Ia Supernova in a Massive Circumstellar Envelope

Abstract: We report Nearby Supernova Factory observations of SN 2005gj, the second confirmed case of a "hybrid" Type Ia/IIn supernova. Our early-phase photometry of SN 2005gj shows that the interaction is much stronger than for the prototype, SN 2002ic. Our first spectrum shows a hot continuum with broad and narrow H-alpha emission. Later spectra, spanning over 4 months from outburst, show clear Type Ia features combined with broad and narrow H-gamma, H-beta, H-alpha and HeI 5876,7065 in emission. At higher resolution, P Cygni profiles are apparent. Surprisingly, we also observe an inverted P Cygni profile for [OIII] 5007. We find that the lightcurve and measured velocity of the unshocked circumstellar material imply mass loss as recently as 8 years ago. The early lightcurve is well-described by a flat radial density profile for the circumstellar material. However, our decomposition of the spectra into Type Ia and shock emission components allows for little obscuration of the supernova, suggesting an aspherical or clumpy distribution for the circumstellar material. We suggest that the emission line velocity profiles arise from electron scattering rather than the kinematics of the shock. This is supported by the inferred high densities, and the lack of evidence for evolution in the line widths. Ground- and space-based photometry, and Keck spectroscopy, of the host galaxy are used to ascertain that the host galaxy has low metallicity Z/Zsun < 0.3; (95% confidence) and that this galaxy is undergoing a significant star formation event that began roughly 200+/-70 Myr ago. We discuss the implications of these observations for progenitor models and cosmology using Type Ia supernovae.

Toward a cosmological Hubble diagram for type II-P supernovae

Abstract: We present the first high-redshift Hubble diagram for Type II-P supernovae (SNe II-P) based on five events at redshift up to z ~ 0.3. This diagram was constructed using photometry from the Canada-France-Hawaii Telescope Supernova Legacy Survey and absorption-line spectroscopy from the Keck Observatory. The method used to measure distances to these supernovae is based on recent work by Hamuy & Pinto and exploits a correlation between the absolute brightness of SNe II-P and the expansion velocities derived from the minimum of the Fe II λ 5169 P Cygni feature observed during the plateau phases. We present three refinements to this method that significantly improve the practicality of measuring the distances of SNe II-P at cosmologically interesting redshifts. These are an extinction correction measurement based on the V-I colors at day 50, a cross-correlation measurement for the expansion velocity, and the ability to extrapolate such velocities accurately over almost the entire plateau phase. We apply this revised method to our data set of high-redshift SNe II-P and find that the resulting Hubble diagram has a scatter of only 0.26 mag, thus demonstrating the feasibility of measuring the expansion history, with present facilities, using a method independent of that based on supernovae of Type Ia.

Towards a Cosmological Hubble Diagram for Type II-P Supernovae

Abstract: We present the first high-redshift Hubble diagram for Type II-P supernovae (SNe II-P) based upon five events at redshift up to z~0.3. This diagram was constructed using photometry from the Canada-France-Hawaii Telescope Supernova Legacy Survey and absorption line spectroscopy from the Keck observatory. The method used to measure distances to these supernovae is based on recent work by Hamuy & Pinto (2002) and exploits a correlation between the absolute brightness of SNe II-P and the expansion velocities derived from the minimum of the Fe II 516.9 nm P-Cygni feature observed during the plateau phases. We present three refinements to this method which significantly improve the practicality of measuring the distances of SNe II-P at cosmologically interesting redshifts. These are an extinction correction measurement based on the V-I colors at day 50, a cross-correlation measurement for the expansion velocity and the ability to extrapolate such velocities accurately over almost the entire plateau phase. We apply this revised method to our dataset of high-redshift SNe II-P and find that the resulting Hubble diagram has a scatter of only 0.26 magnitudes, thus demonstrating the feasibility of measuring the expansion history, with present facilities, using a method independent of that based upon supernovae of Type Ia.

Photometric Selection of High-Redshift Type Ia Supernova Candidates

Abstract: We present a method for selecting high-redshift type Ia supernovae (SNe Ia) located via rolling SN searches. The technique, using both color and magnitude information of events from only 2-3 epochs of multi-band real-time photometry, is able to discriminate between SNe Ia and core collapse SNe. Furthermore, for the SNe Ia, the method accurately predicts the redshift, phase and light-curve parameterization of these events based only on pre-maximum-light data. We demonstrate the effectiveness of the technique on a simulated survey of SNe Ia and core-collapse SNe, where the selection method effectively rejects most core-collapse SNe while retaining SNe Ia. We also apply the selection code to real-time data acquired as part of the Canada-France-Hawaii Telescope Supernova Legacy Survey (SNLS). During the period May 2004 to January 2005 in the SNLS, 440 SN candidates were discovered of which 70 were confirmed spectroscopically as SNe Ia and 15 as core-collapse events. For this test dataset, the selection technique correctly identifies 100% of the identified SNe II as non-SNe Ia with only a 1-2% false rejection rate. The predicted parameterization of the SNe Ia has a precision of |delta_z|/(1+z_spec)<0.09 in redshift, and +/- 2-3 rest-frame days in phase, providing invaluable information for planning spectroscopic follow-up observations. We also investigate any bias introduced by this selection method on the ability of surveys such as SNLS to measure cosmological parameters (e.g., w and omega matter), and find any effect to be negligible.

Measurement of Ωm, ΩΛ from a Blind Analysis of Type Ia Supernovae with CMAGIC: Using Color Information to Verify the Acceleration of the Universe

Abstract: Measurement of Ω m , Ω Λ from a blind analysis of Type Ia supernovae with CMAGIC: Using color information to verify the acceleration of the Universe A. Conley 1,2,8 , G. Goldhaber 1,2 , L. Wang 1 , G. Aldering 1 , R. Amanullah 3 , E. D. Commins 2 , V. Fadeyev 1 , G. Folatelli 4 , G. Garavini 5 , R. Gibbons 6 , A. Goobar 3 , D. E. Groom 1 , I. Hook 7 , D. A. Howell 8 , A. G. Kim 1 , R. A. Knop 6 , M. Kowalski 1 , N. Kuznetsova 1 , C. Lidman 9 , S. Nobili 5 , P. E. Nugent 1 , R. Pain 5 , S. Perlmutter 1,2 , E. Smith 6 , A. L. Spadafora 1 , V. Stanishev 3 , M. Strovink 1,2 , R. C. Thomas 1 , and W. M. Wood-Vasey 1,2 (THE SUPERNOVA COSMOLOGY PROJECT) conley@astro.utoronto.ca ABSTRACT We present measurements of Ω m and Ω Λ from a blind analysis of 21 high redshift supernovae using a new technique (CMAGIC) for fitting the multi- color lightcurves of Type Ia supernovae, first introduced in Wang et al. (2003). CMAGIC takes advantage of the remarkably simple behavior of Type Ia su- pernovae on color-magnitude diagrams, and has several advantages over current techniques based on maximum magnitudes. Among these are a reduced sensi- tivity to host galaxy dust extinction, a shallower luminosity-width relation, and the relative simplicity of the fitting procedure. This allows us to provide a cross check of previous supernova cosmology results, despite the fact that current data E. O. Lawrence Berkeley National Laboratory, 1 Cyclotron Rd., Berkeley, CA 94720, USA Department of Physics, University of California Berkeley, Berkeley, 94720-7300 CA, USA Department of Physics, Stockholm University, Albanova University Center, S-106 91 Stockholm, Sweden Observatories of the Carnegie Institution of Washington, 813 Santa Barbara St., Pasadena, CA 91101 LPNHE, CNRS-IN2P3, University of Paris VI & VII, Paris, France Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37240, USA Department of Physics, University of Oxford, Nuclear & Astrophysics Laboratory, Keble Road, Oxford, OX1 3RH, UK Department of Astronomy and Astrophysics, University of Toronto, 60 St. George St., Toronto, Ontario M5S 3H8, Canada European Southern Observatory, Alonso de Cordova 3107, Vitacura, Casilla 19001, Santiago 19, Chile

Infrared and Optical Observations of GRB 030115 and its Extremely Red Host Galaxy: Implications for Dark Bursts*

Abstract: We present near-infrared (a) and optical observations of the afterglow of GRB 030115. Discovered in an infrared search at Kitt Peak 5 hours after the burst trigger, this afterglow is the faintest ever observed in the R-band at such an early epoch, and exhibits very red colors, with R-K approximately equal to 6. The magnitude of the optical afterglow of GRB 030115 is fainter than many upper limits for other bursts, suggesting that without early nIR observations it would have been classified as a "dark" burst. Both the color and optical magnitude of the afterglow are likely due to dust extinction and indicate that at least some optical afterglows are observations were also taken of the host galaxy and the surrounding field. Photometric redshifts imply that the host, and a substantial number of faint galaxies in the field are at z approximately 2.5. The overdensity of galaxies is sufficiently great that GRB 030115 may have occurred in a rich high-redshift cluster. The host galaxy shows extremely red colors (R-K=5) and is the first GRB host to be classified as an Extreme Red Object (ERO). Some of the galaxies surrounding the host also show very red colors, while the majority of the cluster are much bluer, indicating ongoing unobscured star formation. As it is thought that much of high redshift star formation occurs in highly obscured environments it may well be that GRB 030115 represents a transition object, between the relatively unobscured afterglows seen to date and a population which are very heavily extinguished, even in the nIR.

Nearby Supernova Factory Observations of SN 2006D: On Sporadic Carbon Signatures in Early Type Ia Supernova Spectra

Abstract: We present four spectra of the Type Ia supernova (SN Ia) 2006D extending from -7 to +13 days with respect to B-band maximum. The spectra include the strongest signature of unburned material at photospheric velocities observed in a SN Ia to date. The earliest spectrum exhibits C II absorption features below 14,000 km/s, including a distinctive C II \lambda 6580 absorption feature. The carbon signatures dissipate as the SN approaches peak brightness. In addition to discussing implications of photospheric-velocity carbon for white dwarf explosion models, we outline some factors that may influence the frequency of its detection before and around peak brightness. Two effects are explored in this regard, including depopulation of the C II optical levels by non-LTE effects, and line-of-sight effects resulting from a clumpy distribution of unburned material with low volume-filling factor.

Measurement of \Omega_m, \Omega_{\Lambda} from a blind analysis of Type Ia supernovae with CMAGIC: Using color information to verify the acceleration of the Universe

Abstract: We present measurements of \Omega_m and \Omega_{\Lambda} from a blind analysis of 21 high-redshift supernovae using a new technique (CMAGIC) for fitting the multi-color lightcurves of Type Ia supernovae, first introduced in Wang et al. (2003). CMAGIC takes advantage of the remarkably simple behavior of Type Ia supernovae on color-magnitude diagrams, and has several advantages over current techniques based on maximum magnitudes. Among these are a reduced sensitivity to host galaxy dust extinction, a shallower luminosity-width relation, and the relative simplicity of the fitting procedure. This allows us to provide a cross check of previous supernova cosmology results, despite the fact that current data sets were not observed in a manner optimized for CMAGIC. We describe the details of our novel blindness procedure, which is designed to prevent experimenter bias. The data are broadly consistent with the picture of an accelerating Universe, and agree with a flat Universe within 1.7\sigma, including systematics. We also compare the CMAGIC results directly with those of a maximum magnitude fit to the same SNe, finding that CMAGIC favors more acceleration at the 1.6\sigma level, including systematics and the correlation between the two measurements. A fit for w assuming a flat Universe yields a value which is consistent with a cosmological constant within 1.2\sigma.

Long gamma-ray bursts and core-collapse supernovae have different environments

Abstract: When massive stars exhaust their fuel they collapse and often produce the extraordinarily bright explosions known as core-collapse supernovae. On occasion, this stellar collapse also powers an even more brilliant relativistic explosion known as a long-duration gamma-ray burst. One would then expect that long gamma-ray bursts and core-collapse supernovae should be found in similar galactic environments. Here we show that this expectation is wrong. We find that the long gamma-ray bursts are far more concentrated on the very brightest regions of their host galaxies than are the core-collapse supernovae. Furthermore, the host galaxies of the long gamma-ray bursts are significantly fainter and more irregular than the hosts of the core-collapse supernovae. Together these results suggest that long-duration gamma-ray bursts are associated with the most massive stars and may be restricted to galaxies of limited chemical evolution. Our results directly imply that long gamma-ray bursts are relatively rare in galaxies such as our own MilkyWay.

K-corrections for Type Ia Supernovae

Abstract: The usefulness of type Ia supernovae as distance indicators is a metter of current study and discussion. The avaialbel data suggest that the intrinsic dispersion in the absolute B magnitudes of SNe Ia at maximum light is less than 0.4 mag. Hence, SNe Ia offer considerable potential for cosmological studies out to redshifts of z~0.1 or greater. At these distances, however, the effects of the redshift on the observed magnitudes are not negligible and must be taken into account in order to compare the magnitudes and light curves of objects of different redshifts. In this paper we make use of the best spectra avaialbe for type Ia supernovae in order to calculate the effect of theredshift on the observed B and V magnitudes. We present K-temrs in the redshift range z=0.005-0.50 from a collection of spectra of SNe 1990N, 1991T, and 1992A covering from day -14 to day +76, counted from the time of maximum light in the blue band. The K-terms calculated for the V band from the different spectra show a well defined trend as a function of time. In the B band the K-terms show some scatter before maximum light due to the spectroscopic differences displayed by the trhee SNe selected. These spectral differences tend ti disappear for later epochs and, consequently the K-term curves in the B band after maximum light are much tighter. Our calculations enable us to interpolate K-terms for SNe Ia at maximum light, which should prove useful to study the Hubble diagram for these objects.

Supernovae and Dark Energy

Abstract: Astronomers have begun to measure the fundamental parameters of cosmology through the observation of very distant Type Ia supernovae. Over the past decade more than 300 spectroscopically confirmed high‐redshift supernovae have been discovered. These supernovae are used as standardized candles to measure the history of the expansion of the universe. Under the current standard model for cosmology these measurements indicate the presence of a heretofore unknown dark energy causing a recent acceleration in the expansion of the universe.At this time supernova measurements of the cosmological parameters are no longer limited by statistical uncertainties, rather systematic uncertainties are the dominant source of error. These include the effects of evolution (further back in time do the supernovae behave the same way?), the effect of intergalactic dust on the brightness of the supernovae and the relationship between supernovae and their environments. Here I present exciting new developments in the field of cosmo...