Showing papers by "Brian P. Schmidt published in 2007"
Harvard University1, Fermilab2, Stanford University3, University of California, Berkeley4, Space Telescope Science Institute5, Johns Hopkins University6, University of Notre Dame7, University of Washington8, Australian National University9, Pontifical Catholic University of Chile10, University of Toronto11, University of Copenhagen12, Texas A&M University13, European Southern Observatory14, Ohio State University15, Stockholm University16, University of Hawaii17
TL;DR: In this paper, a set of constraints on the dark energy equation-of-state parameter w = P/(rho c(2)) were derived using 60 SNe Ia from the ESSENCE supernova survey.
Abstract: We present constraints on the dark energy equation-of-state parameter, w = P/(rho c(2)), using 60 SNe Ia fromthe ESSENCE supernova survey. We derive a set of constraints on the nature of the dark energy assuming a flat universe. By including constraints on (Omega(M), w) from baryon acoustic oscillations, we obtain a value for a static equation-of-state parameter w = -1:05(-0.12)(+0: 13) (stat 1 sigma) +/- 0: 13 (sys) and Omega(M) = 0:274(-0.020)(+0:033) (stat 1 sigma) with a bestfit chi(2)/dof of 0.96. These results are consistent with those reported by the Supernova Legacy Survey from the first year of a similar program measuring supernova distances and redshifts. We evaluate sources of systematic error that afflict supernova observations and present Monte Carlo simulations that explore these effects. Currently, the largest systematic with the potential to affect our measurements is the treatment of extinction due to dust in the supernova host galaxies. Combining our set of ESSENCE SNe Ia with the first-results Supernova Legacy Survey SNe Ia, we obtain a joint constraint of w = -1:07(-0: 09)(+0:09) (stat 1 sigma) +/- 0: 13 ( sys), Omega(M) 0:267(-0:028)(+0:028) (stat 1 sigma) with a best-fit chi(2)/dof of 0.91. The current global SN Ia data alone rule out empty (Omega(M) = 0), matter-only Omega(M) = 0: 3, and Omega(M) = 1 universes at > 4.5 sigma. The current SN Ia data are fully consistent with a cosmological constant.
989 citations
TL;DR: In this article, a set of constraints on the dark energy equation-of-state parameter w =P/(rho c^2) were derived for 60 Type Ia supernovae from the ESSENCE supernova survey.
Abstract: We present constraints on the dark energy equation-of-state parameter, w=P/(rho c^2), using 60 Type Ia supernovae (SNe Ia) from the ESSENCE supernova survey. We derive a set of constraints on the nature of the dark energy assuming a flat Universe. By including constraints on (Omega_M, w) from baryon acoustic oscillations, we obtain a value for a static equation-of-state parameter w=-1.05^{+0.13}_{-0.12} (stat; 1 sigma) +- 0.11 (sys) and Omega_M=0.274^{+0.033}_{-0.020} (stat; 1 sigma) with a best-fit chi^2/DoF of 0.96. These results are consistent with those reported by the SuperNova Legacy Survey in a similar program measuring supernova distances and redshifts. We evaluate sources of systematic error that afflict supernova observations and present Monte Carlo simulations that explore these effects. Currently, the largest systematic currently with the potential to affect our measurements is the treatment of extinction due to dust in the supernova host galaxies. Combining our set of ESSENCE SNe Ia with the SuperNova Legacy Survey SNe Ia, we obtain a joint constraint of w=-1.07^{+0.09}_{-0.09} (stat; 1 sigma) +- 0.12 (sys), Omega_M=0.267^{+0.028}_{-0.018} (stat; 1 sigma) with a best-fit chi^2/DoF of 0.91. The current SN Ia data are fully consistent with a cosmological constant.
863 citations
University of Copenhagen1, Stockholm University2, University of Washington3, Harvard University4, Pontifical Catholic University of Chile5, University of California, Berkeley6, University of Notre Dame7, Stanford University8, Texas A&M University9, European Southern Observatory10, Fermilab11, Space Telescope Science Institute12, Johns Hopkins University13, Australian National University14, University of Hawaii15, University of Illinois at Urbana–Champaign16
TL;DR: The first cosmological results from the ESSENCE supernova survey (Wood-Vasey and coworkers) are extended to a wider range of cosmology models including dynamical dark energy and nonstandard cosmologies as mentioned in this paper.
Abstract: The first cosmological results from the ESSENCE supernova survey (Wood-Vasey and coworkers) are extended to a wider range of cosmological models including dynamical dark energy and nonstandard cosmological models. We fold in a greater number of external data sets such as the recent Higher-z release of high-redshift supernovae (Riess and coworkers), as well as several complementary cosmological probes. Model comparison statistics such as the Bayesian and Akaike information criteria are applied to gauge the worth of models. These statistics favor models that give a good fit with fewer parameters. Based on this analysis, the preferred cosmological model is the flat cosmological constant model, where the expansion history of the universe can be adequately described with only one free parameter describing the energy content of the universe. Among the more exotic models that provide good fits to the data, we note a preference for models whose best-fit parameters reduce them to the cosmological constant model.
665 citations
TL;DR: The first cosmological results from the ESSENCE supernova survey (Wood-Vasey et al. 2007) are extended to a wider range of cosmology models including dynamical dark energy and non-standard cosmologies.
Abstract: The first cosmological results from the ESSENCE supernova survey (Wood-Vasey et al. 2007) are extended to a wider range of cosmological models including dynamical dark energy and non-standard cosmological models. We fold in a greater number of external data sets such as the recent Higher-z release of high-redshift supernovae (Riess et al. 2007) as well as several complementary cosmological probes. Model comparison statistics such as the Bayesian and Akaike information criteria are applied to gauge the worth of models. These statistics favor models that give a good fit with fewer parameters.
Based on this analysis, the preferred cosmological model is the flat cosmological constant model, where the expansion history of the universe can be adequately described with only one free parameter describing the energy content of the universe. Among the more exotic models that provide good fits to the data, we note a preference for models whose best-fit parameters reduce them to the cosmological constant model.
546 citations
TL;DR: The SkyMapper telescope as mentioned in this paper is a 1.3m telescope with a 5.7-square-degree field-of-view Cassegrain imager, which is located at Siding Spring Observatory, Coonabarabran, NSW, Australia.
Abstract: This paper presents the design and science goals for the SkyMapper telescope. SkyMapper is a 1.3-m telescope featuring a 5.7-square-degree field-of-view Cassegrain imager commissioned for the Australian National University's Research School of Astronomy and Astrophysics. It is located at Siding Spring Observatory, Coonabarabran, NSW, Australia and will see first light in late 2007. The imager possesses 16 384 × 16 384 0.5-arcsec pixels. The primary scientific goal of the facility is to perform the Southern Sky Survey, a six-colour and multi-epoch (four-hour, one-day, one-week, one-month and one-year sampling) photometric survey of the southerly 2π sr to g ∼23 mag. The survey will provide photometry to better than 3% global accuracy and astrometry to better than 50 milliarcsec. Data will be supplied to the community as part of the Virtual Observatory effort. The survey will take five years to complete.
544 citations
TL;DR: The SkyMapper telescope as discussed by the authors is a 1.3m telescope featuring a 5.7 square degree field-of-view Cassegrain imager, designed for the Australian National University's Research School of Astronomy and Astrophysics.
Abstract: This paper presents the design and science goals for the SkyMapper telescope. SkyMapper is a 1.3m telescope featuring a 5.7 square degree field-of-view Cassegrain imager commissioned for the Australian National University's Research School of Astronomy and Astrophysics. It is located at Siding Spring Observatory, Coonabarabran, NSW, Australia and will see first light in late 2007. The imager possesses 16kx16k 0.5 arcsec pixels. The primary scientific goal of the facility is to perform the Southern Sky Survey, a six colour and multi-epoch (4 hour, 1 day, 1 week, 1 month, 1 year sampling) photometric survey of the southerly 2pi steradians to g~23 mag. The survey will provide photometry to better than 3% global accuracy and astrometry to better than 50 mas. Data will be supplied to the community as part of the Virtual Observatory effort. The survey will take five years to complete.
461 citations
Fermilab1, Pontifical Catholic University of Chile2, Harvard University3, Texas A&M University4, University of California, Berkeley5, University of Hawaii6, Australian National University7, University of Washington8, University of Copenhagen9, University of Notre Dame10, Stanford University11, European Southern Observatory12, Ohio State University13, Johns Hopkins University14, Space Telescope Science Institute15, Stockholm University16
TL;DR: In this paper, the authors describe the implementation and optimization of the ESSENCE supernova survey, which they have undertaken to measure the dark energy equation-of-state parameter, w = P/(rho c(2)).
Abstract: We describe the implementation and optimization of the ESSENCE supernova survey, which we have undertaken to measure the dark energy equation-of-state parameter, w = P/(rho c(2)). We present a meth ...
318 citations
Australia Telescope National Facility1, Swinburne University of Technology2, York University3, Durham University4, University of Calgary5, University of Sydney6, University of Colorado Boulder7, University of Tasmania8, University of California, Berkeley9, University of Adelaide10, Laval University11, McGill University12, Herzberg Institute of Astrophysics13, California Institute of Technology14, La Trobe University15, University of Toronto16, Australian National University17, University of British Columbia18, University of Western Australia19, Curtin University20
TL;DR: The Australian SKA Pathfinder (ASKAP) is a technology demonstrator aimed in the mid-frequency range, and achieves instantaneous wide-area imaging through the development and deployment of phased-array feed systems on parabolic reflectors as mentioned in this paper.
Abstract: The future of centimetre and metre-wave astronomy lies with the Square Kilometre Array (SKA), a telescope under development by a consortium of 17 countries that will be 50 times more sensitive than any existing radio facility. Most of the key science for the SKA will be addressed through large-area imaging of the Universe at frequencies from a few hundred MHz to a few GHz. The Australian SKA Pathfinder (ASKAP) is a technology demonstrator aimed in the mid-frequency range, and achieves instantaneous wide-area imaging through the development and deployment of phased-array feed systems on parabolic reflectors. The large field-of-view makes ASKAP an unprecedented synoptic telescope that will make substantial advances in SKA key science. ASKAP will be located at the Murchison Radio Observatory in inland Western Australia, one of the most radio-quiet locations on the Earth and one of two sites selected by the international community as a potential location for the SKA. In this paper, we outline an ambitious science program for ASKAP, examining key science such as understanding the evolution, formation and population of galaxies including our own, understanding the magnetic Universe, revealing the transient radio sky and searching for gravitational waves.
298 citations
University of Ferrara1, INAF2, Max Planck Society3, Space Sciences Laboratory4, California Institute of Technology5, University of California, Berkeley6, Queen's University Belfast7, Harvard University8, Hiroshima University9, Tel Aviv University10, University of Tokyo11, Japan Aerospace Exploration Agency12, Australian National University13
TL;DR: The results of a worldwide coordinated observational campaign on the broad-lined Type Ic supernova (SN Ic) 2003jd are presented in this paper, where the authors show that the V-band light curves of SNe Ic can be partially homogenized by introducing a time-stretch factor.
Abstract: The results of a worldwide coordinated observational campaign on the broad-lined Type Ic supernova (SN Ic) 2003jd are presented. In total, 74 photometric data points and 26 spectra were collected using 11 different telescopes. SN 2003jd is one of the most luminous SN Ic ever observed. A comparison with other Type Ic supernovae (SNe Ic) confirms that SN 2003jd represents an intermediate case between broad-line events (2002ap, 2006aj) and highly energetic SNe (1997ef, 1998bw, 2003dh, 2003lw), with an ejected mass of M_ej= 3.0 ± 1 M⊙ and a kinetic energy of E_k(tot) = 7^+3_−2 × 10^51 erg. SN 2003jd is similar to SN 1998bw in terms of overall luminosity, but it is closer to SNe 2006aj and 2002ap in terms of light-curve shape and spectral evolution. The comparison with other SNe Ic suggests that the V-band light curves of SNe Ic can be partially homogenized by introducing a time-stretch factor. Finally, because of the similarity of SN 2003jd to the SN 2006aj/XRF 060218 event, we discuss the possible connection of SN 2003jd with a gamma-ray burst (GRB).
241 citations
TL;DR: The results of a world-wide coordinated observational campaign on the broad-lined Type Ic SN 2003jd are presented in this article, which shows that the V-band light curves of SNe Ic can be partially homogenized by introducing a time stretch factor.
Abstract: The results of a world-wide coordinated observational campaign on the broad-lined Type Ic SN 2003jd are presented. In total, 74 photometric data points and 26 spectra were collected using 11 different telescopes. SN 2003jd is one of the most luminous SN Ic ever observed. A comparison with other Type Ic supernovae (SNe Ic) confirms that SN 2003jd represents an intermediate case between broad-line events (2002ap, 2006aj), and highly energetic SNe (1997ef, 1998bw, 2003dh, 2003lw), with an ejected mass of M_{ej} = 3.0 +/- 1 Mo and a kinetic energy of E_{k}(tot) = 7_{-2}^{+3} 10^{51} erg. SN 2003jd is similar to SN 1998bw in terms of overall luminosity, but it is closer to SNe 2006aj and 2002ap in terms of light-curve shape and spectral evolution. The comparison with other SNe Ic, suggests that the V-band light curves of SNe Ic can be partially homogenized by introducing a time stretch factor. Finally, due to the similarity of SN 2003jd to the SN 2006aj/XRF 060218 event, we discuss the possible connection of SN 2003jd with a GRB.
199 citations
Princeton University1, Carnegie Institution for Science2, Pennsylvania State University3, University of Hawaii4, California Institute of Technology5, Los Alamos National Laboratory6, University of Chicago7, Australian National University8, National Radio Astronomy Observatory9, Pomona College10, University of Oxford11, McGill University12
TL;DR: In this paper, the redshift distribution of short-duration gamma-ray bursts (GRBs) is studied and a conservative detection rate with the advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) of � 2 6 yr � 1.
Abstract: The redshift distribution of the short-duration gamma-ray bursts (GRBs) is a crucial, but currently fragmentary, cluetothenatureoftheirprogenitors.HerewepresentopticalobservationsofnineshortGRBsobtainedwithGemini, Magellan, and the Hubble Space Telescope. We detect the afterglows and host galaxies of two short bursts, and host galaxiesfortwoadditionalburstswithknownopticalafterglowpositions,andfivewithX-raypositions(P6 00 radius).In eightoftheninecaseswefindthatthemostprobablehostgalaxiesarefaint,R � 23 26:5mag,andarethereforestarkly different from the first few short GRB hosts with R � 17 22 mag and z P0:5. Indeed, we measure spectroscopic redshifts ofz � 0:4 1:1for the four brightest hosts. A comparison to largefield galaxy samples, as well as the hosts of longGRBsandpreviousshortGRBs,indicatesthatthefainterhostslikelyresideatz k1. Ourmostconservativelimit is that at least half of the five hosts without a known redshift reside at z > 0:7 (97% confidence level), suggesting that about 1 to 2 of all short GRBs originate at higher redshifts than previously determined. This has two important implications: (1) we constrain the acceptable age distributions to a wide lognormal (� k1) with � � � 4 8G yr, or to a powerlaw,P(� ) / � n ,with � 1Pn P0;and(2)theinferredisotropicenergies,E�; iso � 1050 10 52 ergs,aresignificantly larger than � 10 48 ‐10 49 ergs for the low-redshift, short GRBs, indicating a large spread in energy release or jet opening angles. Finally, we reiterate the importance of short GRBs as potential gravitational-wave sources and find a conservative detection rate with the advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) of � 2‐6 yr � 1 .
University of Arizona1, Los Alamos National Laboratory2, Max Planck Society3, University of California, Santa Cruz4, Carnegie Institution for Science5, Princeton University6, Massachusetts Institute of Technology7, University of Amsterdam8, University of Oxford9, University of Tokyo10, University of Virginia11, Australian National University12, California Institute of Technology13
TL;DR: In this paper, the authors review the current set of progenitor scenarios for long-duration gamma-ray bursts and the observational constraints on these scenarios and find that single stars cannot be the only progenitors for longduration GRBs.
Abstract: Although there is strong support for the collapsar engine as the power source of long-duration gamma-ray bursts (GRBs), we still do not definitively know the progenitor of these explosions. Here we review the current set of progenitor scenarios for long-duration GRBs and the observational constraints on these scenarios. Examining these models, we find that single stars cannot be the only progenitor for long-duration GRBs. Several binary progenitors can match the solid observational constraints and also have the potential to match the trends that we are currently seeing in the observations. Type Ib/c supernovae are also likely to be produced primarily in binaries; we discuss the relationship between the progenitors of these explosions and those of the long-duration GRBs.
Max Planck Society1, Pontifical Catholic University of Chile2, INAF3, University of California, Berkeley4, Imperial College London5, University of Paris6, University of Padua7, University of Sydney8, University of La Laguna9, European Southern Observatory10, Queen's University Belfast11, Saint Petersburg State University12, Durham University13, Australian National University14, Stockholm University15, University of Szeged16, DSM17
TL;DR: In this paper, optical and infrared observations of the unusual Type Ia supernova (SN) 2004eo were presented, and the light curves and spectra closely resemble those of the prototypical SN 1992A.
Abstract: We present optical and infrared observations of the unusual Type Ia supernova (SN) 2004eo. The light curves and spectra closely resemble those of the prototypical SN 1992A, and the luminosity at ma ...
California Institute of Technology1, Pennsylvania State University2, National Radio Astronomy Observatory3, University of Hawaii4, Australian National University5, Princeton University6, Carnegie Institution for Science7, Tel Aviv University8, Pomona College9, University of Virginia10, Goddard Space Flight Center11, INAF12, Hebrew University of Jerusalem13
TL;DR: In this article, the optical afterglow of a gamma-ray burst (GRB) was observed, spatially associated with a z = 0.0894 galaxy, and its proximity to a star forming region suggests that the progenitor delay time from birth to explosion is smaller than about 10 Myr.
Abstract: On May 5, 2006 a four-second duration, low-energy, approximately 10(exp 59) erg, Gamma-Ray Burst (GRB) was observed, spatially associated with a z=0.0894 galaxy. Here, we report the discovery of the GRB optical afterglow and observations of its environment using gemini-south, Hubble Space Telescope (HST), Chandra, Swift and the Very Large Array. The optical afterglow of this GRB is spatially associated with a prominent star forming region in the Sc-type galaxy 2dFGRS S173Z112. Its proximity to a star forming region suggests that the progenitor delay time, from birth to explosion, is smaller than about 10 Myr. Our HST deep imaging rules out the presence of a supernova brighter than an absolute magnitude of about -11 (or -126 in case of 'maximal' extinction) at about two weeks after the burst, and limits the ejected mass of radioactive Nickel 56 to be less than about 2x10(exp -4) solar mass (assuming no extinction). Although it was suggested that GRB 060505 may belong to a new class of long-duration GRBs with no supernova, we argue that the simplest interpretation is that the physical mechanism for this burst is the same as for short-duration GRBs.
TL;DR: In this paper, the authors review the current set of progenitor scenarios for long-duration gamma-ray bursts and the observational constraints on these scenarios and find that single-star models cannot be the only progenitors for longduration GRBs.
Abstract: Although there is strong support for the collapsar engine as the power source of long-duration gamma-ray bursts (GRBs), we still do not definitively know the progenitor of these explosions. Here we review the current set of progenitor scenarios for long-duration GRBs and the observational constraints on these scenarios. Examining these, we find that single-star models cannot be the only progenitor for long-duration GRBs. Several binary progenitors can match the solid observational constraints and also have the potential to match the trends we are currently seeing in the observations. Type Ib/c supernovae are also likely to be produced primarily in binaries; we discuss the relationship between the progenitors of these explosions and those of the long-duration GRBs.
TL;DR: The optical afterglow of a gamma-ray burst (GRB) was detected in this paper, which is spatially associated with a star forming region in the Sc-type galaxy 2dFGRS S173Z112.
Abstract: On 2006 May 5, a four second duration, low energy, ~10^49 erg, Gamma-Ray Burst (GRB) was observed, spatially associated with a z=0.0894 galaxy. Here, we report the discovery of the GRB optical afterglow and observations of its environment using Gemini-south, Hubble Space Telescope (HST), Chandra, Swift and the Very Large Array. The optical afterglow of this GRB is spatially associated with a prominent star forming region in the Sc-type galaxy 2dFGRS S173Z112. Its proximity to a star forming region suggests that the progenitor delay time, from birth to explosion, is smaller than about 10 Myr. Our HST deep imaging rules out the presence of a supernova brighter than an absolute magnitude of about -11 (or -12.6 in case of ``maximal'' extinction) at about two weeks after the burst, and limits the ejected mass of radioactive Nickel 56 to be less than about 2x10^-4 solar mass (assuming no extinction). Although it was suggested that GRB 060505 may belong to a new class of long-duration GRBs with no supernova, we argue that the simplest interpretation is that the physical mechanism responsible for this burst is the same as for short-duration GRBs.
TL;DR: In this paper, an early-time optical and near-infrared photometry of supernova (SN) 2005cf is presented, spanning a period from about 12 d before to 3 months after maximum.
Abstract: We present early-time optical and near-infrared photometry of supernova (SN) 2005cf. The observations, spanning a period from about 12 d before to 3 months after maximum, have been obtained through the coordination of observational efforts of various nodes of the European Supernova Collaboration and including data obtained at the 2-m Himalayan Chandra Telescope. From the observed light curve we deduce that SN 2005cf is a fairly typical SN Ia with a post-maximum decline [� m15(B)true = 1.12] close to the average value and a normal luminosity of MB,max =− 19.39 ± 0.33. Models of the bolometric light curve suggest a synthesized 56 Ni mass of about 0.7 M� . The negligible host galaxy interstellar extinction and its proximity make SN 2005cf a good Type Ia SN template.
TL;DR: The ESC-RTN optical spectroscopy data set for SN 2005cf is presented and analyzed in this article, which is characterized by the presence of high velocity Si ii and Ca ii features.
Abstract: The ESC-RTN optical spectroscopy data set for SN 2005cf is presented and analyzed. The observations range from −11. 6a nd +77.3 days with respect to B-band maximum light. The evolution of the spectral energy distribution of SN 2005cf is characterized by the presence of high velocity Si ii and Ca ii features. SYNOW synthetic spectra are used to investigate the ejecta geometry of silicon. Based on the synthetic spectra, the Si ii high-velocity feature appears detached at 19 500 km s −1 . We also securely establish the presence of such a feature in SN 1990N, SN 1994D, SN 2002er, and SN 2003du. In a morphological study both the Ca ii IR triplet and H&K absorption lines of SN 2005cf show high-velocity features centered around 24 000 km s −1 . When compared with other type Ia SNe based on the scheme presented in Benetti et al. (2005, ApJ, 623, 1011), SN 2005cf definitely belongs to the LVG group.
TL;DR: In this article, the optical spectroscopic properties of Type Ia supernova (SN Ia) 2004dt, focusing on the early epochs, were studied, which indicated the presence of clumps of high-velocity, intermediate-mass elements in the outermost layers of its ejecta.
Abstract: Aims. We study the optical spectroscopic properties of Type Ia Supernova (SN Ia) 2004dt, focusing our attention on the early epochs. Methods. Observation triggered soon after the SN 2004dt discovery allowed us to obtain a spectrophotometric coverage from day−10 to almost one year (∼353 days) after the B band maximum. Observations carried out on an almost daily basis allowed us a good sampling of the fast spectroscopic evolution of SN 2004dt in the early stages. To obtain this result, low‐resolution, long‐slit spectr oscopy was obtained using a number of facilities. Results. This supernova, which in some absorption lines of its early spectra showed the highest degree of polarization ever measured in any SN Ia, has a complex velocity structure in the outer layers of its ejecta. Unburnt oxygen is present, moving at velocities as high as ∼16,700 km s −1 , with some intermediate‐mass elements (Mg, Si, Ca) moving equally fast. Modeling of the spectra based on standard density profiles of the ejecta fails to reproduce the observed featur es, whereas enhancing the density of outer layers significan tly improves the fit. Our analysis indicates the presence of clumps of high‐velocity, intermediate‐mass elements in the outermost layers, which is also suggested by the spectropolarimetric data.
California Institute of Technology1, National Radio Astronomy Observatory2, Pennsylvania State University3, Princeton University4, Carnegie Institution for Science5, University of Hawaii6, Australian National University7, University of Virginia8, University of Texas at Austin9, Lawrence Livermore National Laboratory10
TL;DR: In this paper, the authors present detailed optical, near-infrared and radio observations of the X-ray flash 050416a obtained with Palomar and Siding Springs Observatories as well as HST and the VLA.
Abstract: We present detailed optical, near-infrared, and radio observations of the X-ray flash 050416a obtained with Palomar and Siding Springs Observatories as well as HST and the VLA, placing this event among the best-studied X-ray flashes to date. In addition, we present an optical spectrum from Keck LRIS from which we measure the redshift of the burst, Z=0.6528. At this redshift the isotropic-equivalent prompt energy release was about 10(exp 51) erg, and using a standard afterglow synchrotron model we find that the blastwave kinetic energy is a factor of 10 larger, E-K,iso approximately equals 10 (exp 52) erg. The lack of an observed jet break to t - 20 days indicates that the opening angle is larger than 7 deg and the total beaming-corrected relativistic energy is larger than 10 exp (50) erg. We further show that the burst produced a strong radio flare at t is similar to 40 days accompanied by an observed flattening in the X-ray band which we attribute to an abrupt circumburst density jump or an episode of energy injection (either from a refreshed shock or off-axis ejecta). Late-time observations with HST show evidence for an associated supernova with peak optical luminosity roughly comparable to that of SN 1998bw. Next, we show that the host galaxy of XRF 050416a is actively forming stars at a rate of at least 2 M-solar per year with a luminosity of L-B is similar to 0.5L* and metallicity of Z is similar to 0.2-0.8 Z-solar. Finally, we discuss the nature of XRF 050416a in the context of short-hard gamma-ray bursts and under the framework of off-axis and dirty fireball models for X-ray flashes.
TL;DR: In this article, the authors presented the first large-scale effort of creating composite spectra of high-redshift type Ia supernovae (SNe Ia) and comparing them to low-red-shift counterparts.
Abstract: We present the first large-scale effort of creating composite spectra of high-redshift type Ia supernovae (SNe Ia) and comparing them to low-redshift counterparts. Through the ESSENCE project, we have obtained 107 spectra of 88 high-redshift SNe Ia with excellent light-curve information. In addition, we have obtained 397 spectra of low-redshift SNe through a multiple-decade effort at Lick and Keck Observatories, and we have used 45 UV spectra obtained by HST/IUE. The low-redshift spectra act as a control sample when comparing to the ESSENCE spectra. In all instances, the ESSENCE and Lick composite spectra appear very similar. The addition of galaxy light to the Lick composite spectra allows a nearly perfect match of the overall spectral-energy distribution with the ESSENCE composite spectra, indicating that the high-redshift SNe are more contaminated with host-galaxy light than their low-redshift counterparts. This is caused by observing objects at all redshifts with the same slit width, which corresponds to different projected distances. After correcting for the galaxy-light contamination, subtle differences in the spectra remain. We have estimated the systematic errors when using current spectral templates for K-corrections to be ~0.02 mag. The variance in the composite spectra give an estimate of the intrinsic variance in low-redshift maximum-light SN spectra of ~3% in the optical and growing toward the UV. The difference between the maximum light low and high-redshift spectra constrain SN evolution between our samples to be < 10% in the rest-frame optical.
TL;DR: In this paper, the authors describe the properties of the host galaxy of the gamma-ray burst GRB 060510B based on a spectrum of the burst afterglow obtained with the Gemini North 8 m telescope.
Abstract: We describe the properties of the host galaxy of the gamma-ray burst GRB 060510B based on a spectrum of the burst afterglow obtained with the Gemini North 8 m telescope. The galaxy lies at a redshift of z = 4.941, making it the fourth highest spectroscopically identified burst host. However, it is the second highest redshift galaxy for which the quality of the spectrum permits a detailed metallicity analysis. The neutral hydrogen column density has a logarithmic value of 21.0-21.2 cm^-2, and the weak metal lines of Ni, S, and Fe show that the metallicity is in excess of a tenth of solar, which is far above the metallicities in damped Lyα absorbers at high redshift. The tightest constraint is from the Fe lines, which place [Fe/H] in excess of -0.8. We argue that the results suggest that metallicity bias could be a serious obstacle to inferring star formation from the GRB population, and we consider how future higher quality measurements could be used to resolve this issue.
TL;DR: In this paper, the authors detect the afterglow in the H band more than 3 weeks after the burst and confirm the presence of a jet break at t ≈ 2:1 days, leading to an estimated opening angle of about 4° and a beaming-corrected energy of about 10^(51) ergs.
Abstract: We present deep Hubble Space Telescope (HST ) and Spitzer Space Telescope observations of GRB 050904 at z = 6:295. We detect the afterglow in the H band more than 3 weeks after the burst and confirm the presence of a jet break at t ≈ 2:1 days. This leads to an estimated opening angle of about 4° and a beaming-corrected energy of about 10^(51) ergs, similar to those of lower redshift gamma-ray bursts (GRBs). We do not detect an underlying host galaxy with either HST or Spitzer. From the upper limits we infer an extinction-corrected absolute magnitude M_(UV) ≳ -20:3 mag, or L ≾ L^*, a star formation rate of ≾ 5.7M_⊙ yr^(-1), and a stellar mass of ≾ few x 10^9 M_⊙. A comparison to spectroscopically confirmed galaxies at z > 5:5 reveals that the host of GRB 050904 is fainter and has a lower star formation rate than at least 80% of these objects. Finally, using our luminosity limits, and the metallicity of about 0.05 Z_⊙ inferred from the afterglow absorption spectrum, we place the first limit on the luminosity-metallicity relation at z > 6. Future afterglow and host galaxy observations of z ≳ 4 GRBs should elucidate whether the mass- and luminosity-metallicity relations continue to evolve beyond the present limits of z ≾ 2.
Fermilab1, Pontifical Catholic University of Chile2, Harvard University3, Texas A&M University4, University of California, Berkeley5, University of Hawaii6, Australian National University7, University of Washington8, University of Copenhagen9, University of Notre Dame10, Stanford University11, European Southern Observatory12, Ohio State University13, Johns Hopkins University14, Space Telescope Science Institute15, Stockholm University16
TL;DR: The ESSENCE supernova survey as mentioned in this paper has been used to measure the equation of state parameter of the dark energy for a given fixed amount of telescope time on the CTIO 4m telescope.
Abstract: We describe the implementation and optimization of the ESSENCE supernova survey, which we have undertaken to measure the equation of state parameter of the dark energy. We present a method for optimizing the survey exposure times and cadence to maximize our sensitivity to the dark energy equation of state parameter w=P/rho c^2 for a given fixed amount of telescope time. For our survey on the CTIO 4m telescope, measuring the luminosity distances and redshifts for supernovae at modest redshifts (z~0.5 +- 0.2) is optimal for determining w. We describe the data analysis pipeline based on using reliable and robust image subtraction to find supernovae automatically and in near real-time. Since making cosmological inferences with supernovae relies crucially on accurate measurement of their brightnesses, we describe our efforts to establish a thorough calibration of the CTIO 4m natural photometric system. In its first four years, ESSENCE has discovered and spectroscopically confirmed 102 type Ia SNe, at redshifts from 0.10 to 0.78, identified through an impartial, effective methodology for spectroscopic classification and redshift determination. We present the resulting light curves for the all type Ia supernovae found by ESSENCE and used in our measurement of w, presented in Wood-Vasey et al, 2007.
Max Planck Society1, Pontifical Catholic University of Chile2, INAF3, University of California, Berkeley4, Imperial College London5, University of Paris6, University of Padua7, University of Sydney8, University of La Laguna9, Queen's University Belfast10, European Southern Observatory11, Saint Petersburg State University12, Durham University13, Australian National University14, Stockholm University15, University of Szeged16, DSM17
TL;DR: In this article, the authors present optical and infrared observations of the unusual Type Ia supernova (SN) 2004eo, which shows a relatively rapid post-maximum decline in the light curve (Delta m_(B) = 1.46).
Abstract: We present optical and infrared observations of the unusual Type Ia supernova (SN) 2004eo. The light curves and spectra closely resemble those of the prototypical SN 1992A, and the luminosity at maximum (M_B = -19.08) is close to the average for a SN Ia. However, the ejected 56Ni mass derived by modelling the bolometric light curve (about 0.45 solar masses) lies near the lower limit of the 56Ni mass distribution observed in normal SNe Ia. Accordingly, SN 2004eo shows a relatively rapid post-maximum decline in the light curve (Delta m_(B) = 1.46), small expansion velocities in the ejecta, and a depth ratio Si II 5972 / Si II 6355 similar to that of SN 1992A. The physical properties of SN 2004eo cause it to fall very close to the boundary between the faint, low velocity gradient, and high velocity gradient subgroups proposed by Benetti et al. (2005). Similar behaviour is seen in a few other SNe Ia. Thus, there may in fact exist a few SNe Ia with intermediate physical properties.
TL;DR: In this paper, a search for RR Lyrae variable stars from archival observations of the Southern Edgeworth-Kuiper Belt Object survey is presented, which reveals a series of structures coincident with the leading and trailing arms of debris from the Sagittarius dwarf galaxy.
Abstract: We present a search for RR Lyrae variable stars from archival observations of the Southern Edgeworth-Kuiper Belt Object survey. The survey covers 1675 square degrees along the ecliptic to a mean depth of V=19.5, i.e. a heliocentric distance of ~50kpc for RR Lyrae stars. The survey reveals 2016 RR Lyrae candidates. Follow-up photometric monitoring of a subset of these candidates shows (24+/-12)% contamination by non-RR Lyrae variables. We derive a map of over-density of RR Lyraes in the halo that reveals a series of structures coincident with the leading and trailing arms of debris from the Sagittarius dwarf galaxy. One of the regions of over-density is found on the trailing arm, 200 deg. from the main body of the Sagittarius dwarf at a distance of ~45kpc. This distant detection of the stellar population of the outer trailing arm of Sagittarius offers a tight constraint on the motion of the dwarf galaxy. A distinctly separate region of over-density is seen towards the Virgo Over Density.
17 Aug 2007
TL;DR: In this paper, a preliminary analysis of an extensive set of optical observations of the Type Ia SN 2005hk is presented, which shows that the evolution of SN2005hk closely follows that of the peculiar SN 2002cx.
Abstract: We present a preliminary analysis of an extensive set of optical observations of the Type Ia SN 2005hk. We show that the evolution of SN 2005hk closely follows that of the peculiar SN 2002cx. SN 2005hk is more luminous than SN 2002cx, while still under‐luminous compared to normal Type Ia supernovae. The spectrum at 9 days before maximum is dominated by conspicuous Fe III and Ni III lines, and the Si II 6355 line is also clearly visible. All these features have low velocity (∼ 6000 km/s). The near maximum spectra show lines of Si II, S II, Fe II‐III, as well as other intermediate mass and iron group elements. Analysis with the code for synthetic spectra SYNOW indicates that all these spectral lines have similar velocities.
TL;DR: In this article, the cross-correlation between fluctuations in the surface brightness of the cumulative Ly-alpha emission (which serves as a proxy for the star formation rate) and the redshifted 21cm signal from neutral hydrogen in the intergalactic medium (IGM) was investigated.
Abstract: Reionization is thought to be dominated by low mass galaxies, while direct observations of resolved galaxies probe only the most massive, rarest objects The cross-correlation between fluctuations in the surface brightness of the cumulative Ly-alpha emission (which serves as a proxy for the star formation rate) and the redshifted 21cm signal from neutral hydrogen in the intergalactic medium (IGM), will directly probe the causal link between the production of ionizing photons in galaxies and the reionization of the IGM We discuss the prospects for detecting this cross-correlation for unresolved galaxies We find that on angular scales 3 arc-minutes, the measurement of cross-correlation will be limited by the accuracy of the foreground sky subtraction
TL;DR: In this paper, the optical spectroscopic properties of Type Ia supernova (SN Ia) 2004dt, focusing on the early epochs, were studied, and the presence of clumps of high-velocity, intermediate-mass elements in the outermost layers of its ejecta was also suggested.
Abstract: Aims. We study the optical spectroscopic properties of Type Ia Supernova (SN Ia) 2004dt, focusing our attention on the early epochs.
Methods. Observation triggered soon after the SN 2004dt discovery allowed us to obtain a spectrophotometric coverage from day -10 to almost one year (~353 days) after the B band maximum. Observations carried out on an almost daily basis allowed us a good sampling of the fast spectroscopic evolution of SN 2004dt in the early stages. To obtain this result, low-resolution, long-slit spectroscopy was obtained using a number of facilities.
Results. This supernova, which in some absorption lines of its early spectra showed the highest degree of polarization ever measured in any SN Ia, has a complex velocity structure in the outer layers of its ejecta. Unburnt oxygen is present, moving at velocities as high as ~16,700 km/s, with some intermediate-mass elements (Mg, Si, Ca) moving equally fast. Modeling of the spectra based on standard density profiles of the ejecta fails to reproduce the observed features, whereas enhancing the density of outer layers significantly improves the fit. Our analysis indicates the presence of clumps of high-velocity, intermediate-mass elements in the outermost layers, which is also suggested by the spectropolarimetric data.
TL;DR: The work in this paper was supported by the Australian Research Council (ARC), JSBW and BPS and Harvard University grants (AL) and was published in the journal Nature.
Abstract: The research was supported by the Australian Research Council
(JSBW and BPS) and Harvard University grants (AL).