Showing papers by "Brian P. Schmidt published in 2006"
TL;DR: Radio and X-ray observations of XRF 060218 (associated with supernova SN 2006aj), the second-nearest GRB identified until now, are reported, showing that this event is a hundred times less energetic but ten times more common than cosmological GRBs.
Abstract: Over the past decade, long-duration gamma-ray bursts (GRBs)--including the subclass of X-ray flashes (XRFs)--have been revealed to be a rare variety of type Ibc supernova. Although all these events result from the death of massive stars, the electromagnetic luminosities of GRBs and XRFs exceed those of ordinary type Ibc supernovae by many orders of magnitude. The essential physical process that causes a dying star to produce a GRB or XRF, and not just a supernova, is still unknown. Here we report radio and X-ray observations of XRF 060218 (associated with supernova SN 2006aj), the second-nearest GRB identified until now. We show that this event is a hundred times less energetic but ten times more common than cosmological GRBs. Moreover, it is distinguished from ordinary type Ibc supernovae by the presence of 10(48) erg coupled to mildly relativistic ejecta, along with a central engine (an accretion-fed, rapidly rotating compact source) that produces X-rays for weeks after the explosion. This suggests that the production of relativistic ejecta is the key physical distinction between GRBs or XRFs and ordinary supernovae, while the nature of the central engine (black hole or magnetar) may distinguish typical bursts from low-luminosity, spherical events like XRF 060218.
547 citations
California Institute of Technology1, Pennsylvania State University2, University of Hawaii at Manoa3, San Diego State University4, Australian National University5, Princeton University6, Carnegie Institution for Science7, Tel Aviv University8, National Radio Astronomy Observatory9, Hebrew University of Jerusalem10, Pomona College11, University of Virginia12, New York University13
TL;DR: In this paper, the authors report optical observations of GRB 060614 (duration ~100 s) that rule out the presence of an associated supernova, and also show that the properties of the host galaxy (redshift z = 0.125) distinguish it from other long-duration GRB hosts and suggest that an entirely new type of long-lived GRB progenitor may be required.
Abstract: Over the past decade, our physical understanding of gamma-ray bursts (GRBs) has progressed rapidly, thanks to the discovery and observation of their long-lived afterglow emission. Long-duration (≳2 s) GRBs are associated with the explosive deaths of massive stars ('collapsars', ref. 1), which produce accompanying supernovae; the short-duration (≲2 s) GRBs have a different origin, which has been argued to be the merger of two compact objects. Here we report optical observations of GRB 060614 (duration ~100 s, ref. 10) that rule out the presence of an associated supernova. This would seem to require a new explosive process: either a massive collapsar that powers a GRB without any associated supernova, or a new type of 'engine', as long-lived as the collapsar but without a massive star. We also show that the properties of the host galaxy (redshift z = 0.125) distinguish it from other long-duration GRB hosts and suggest that an entirely new type of GRB progenitor may be required.
403 citations
TL;DR: In this paper, the authors present detailed optical, X-ray, and radio observations of the bright afterglow of the short gamma-ray burst 051221a obtained with Gemini, Swift XRT, and the Very Large Array, as well as optical spectra from which they measure the redshift of the burst, z = 0.5464.
Abstract: We present detailed optical, X-ray, and radio observations of the bright afterglow of the short gamma-ray burst 051221a obtained with Gemini, Swift XRT, and the Very Large Array, as well as optical spectra from which we measure the redshift of the burst, z = 0.5464. At this redshift the isotropic-equivalent prompt energy release was about 1.5 × 10^(51) ergs, and using a standard afterglow synchrotron model, we find that the blast wave kinetic energy is similar, E_(K,iso) ≈ 8.4 × 10^(51) ergs. An observed jet break at t approx 5 days indicates that the opening angle is θ_j ≈ 7° and the total beaming-corrected energy is therefore ≈ 2.5 × 10^(49) ergs, comparable to the values inferred for previous short GRBs. We further show that the burst experienced an episode of energy injection by a factor of 3.4 between t = 1.4 and 3.4 hr, which was accompanied by reverse shock emission in the radio band. This result provides continued evidence that the central engines of short GRBs may be active significantly longer than the duration of the burst and/or produce a wide range of Lorentz factors. Finally, we show that the host galaxy is actively forming stars at a rate of about 1.6 M_☉ yr^(-1), yet exhibits evidence for an appreciable population of old stars (~1 Gyr) and near-solar metallicity. These properties are intermediate between those of long GRB hosts and previous short burst hosts. The lack of bright supernova emission and the low circumburst density (n ~ 10^(-3) cm^(-3)), however, continue to support the idea that short bursts are not related to massive stellar death. Given that the total energy release is larger than the predicted yield for a neutrino annihilation mechanism, this suggests that magnetohydrodynamic processes may be required to power the burst.
340 citations
Pontifical Catholic University of Chile1, Australian National University2, University of California, Berkeley3, Harvard University4, University of Washington5, University of Notre Dame6, Space Telescope Science Institute7, European Southern Observatory8, California Institute of Technology9, Carnegie Institution for Science10, Ohio State University11, University of Hawaii12
TL;DR: In this paper, the authors presented observations of the Type Ia supernovae (SNe) 1999M, 1999N, 1999Q, 1999S, and 1999U, at redshift z ≈ 0.5.
Abstract: We present observations of the Type Ia supernovae (SNe) 1999M, 1999N, 1999Q, 1999S, and 1999U, at redshift z ≈ 0.5. They were discovered in early 1999 with the 4.0 m Blanco telescope at Cerro Tololo Inter-American Observatory by the High-z Supernova Search Team (HZT) and subsequently followed with many ground-based telescopes. SNe 1999Q and 1999U were also observed with the Hubble Space Telescope. We computed luminosity distances to the new SNe using two methods and added them to the high-z Hubble diagram that the HZT has been constructing since 1995. The new distance moduli confirm the results of previous work. At z ≈ 0.5, luminosity distances are larger than those expected for an empty universe, implying that a "cosmological constant," or another form of "dark energy," has been increasing the expansion rate of the universe during the last few billion years. Combining these new HZT SNe Ia with our previous results and assuming a ΛCDM cosmology, we estimate the cosmological parameters that best fit our measurements. For a sample of 75 low-redshift and 47 high-redshift SNe Ia with MLCS2k2 (Jha and coworkers) luminosity calibration we obtain Ω_M = 0.79^(+0.15)_(-0.18) and Ω_Λ = 1.57^(+0.24)_(-0.32) (1 σ uncertainties) if no constraints are imposed, or Ω_M = 0.29^(+0.06)_(-0.05) if Ω_M + Ω_Λ = 1 is assumed. For a different sample of 58 low-redshift and 48 high-redshift SNe Ia with luminosity calibrations done using the PRES method (a generalization of the Δ_m_15 method), the results are Ω_M = 0.43^(+0.17)_(-0.19) and Ω_Λ = 1.18^(+0.27)_(-0.28) (1 σ uncertainties) if no constraints are imposed, or Ω_M = 0.18^(+0.05)_(-0.04) if Ω_M + Ω_Λ = 1 is assumed.
190 citations
University of North Carolina at Chapel Hill1, University of Hertfordshire2, California Institute of Technology3, Pennsylvania State University4, University of Hawaii at Manoa5, Spanish National Research Council6, University of São Paulo7, University of California, Berkeley8, Space Telescope Science Institute9, University of Chicago10, Marshall Space Flight Center11, University of Amsterdam12, Australian National University13, Academy of Sciences of the Czech Republic14, Czech Technical University in Prague15, University of Geneva16, University of Wyoming17, Clemson University18, American Association of Variable Star Observers19, Lawrence Livermore National Laboratory20, University of Arizona21, University of Leicester22, Liverpool John Moores University23, University of Oxford24, Goddard Space Flight Center25
TL;DR: In this article, the authors reported the discovery of the bright near-infrared afterglow of GRB 050904 and determined the photometric redshift of the burst to be 6.29 ± 0.01, in agreement with their photometric estimate.
Abstract: Gamma-ray bursts (GRBs) and their afterglows are the most brilliant transient events in the Universe. Both the bursts themselves and their afterglows have been predicted to be visible out to redshifts of z approximately 20, and therefore to be powerful probes of the early Universe. The burst GRB 000131, at z = 4.50, was hitherto the most distant such event identified3. Here we report the discovery of the bright near-infrared afterglow of GRB 050904 (ref. 4). From our measurements of the near-infrared afterglow, and our failure to detect the optical afterglow, we determine the photometric redshift of the burst to be z = 6.29^(+0.11)_(-0.12) (refs 5–7). Subsequently, it was measured spectroscopically to be z = 6.29 ± 0.01, in agreement with our photometric estimate. These results demonstrate that GRBs can be used to trace the star formation, metallicity, and reionization histories of the early Universe.
121 citations
California Institute of Technology1, National Radio Astronomy Observatory2, Carnegie Institution for Science3, Princeton University4, Pennsylvania State University5, Pomona College6, University of Hawaii7, Australian National University8, University of Virginia9, Goddard Space Flight Center10, The Racah Institute of Physics11
TL;DR: In this paper, the authors present observations of the unusually bright and long γ-ray burst GRB 050820A, one of the best sampled broadband data sets in the Swift era.
Abstract: We present observations of the unusually bright and long γ-ray burst GRB 050820A, one of the best sampled broadband data sets in the Swift era. The γ-ray light curve is marked by a soft precursor pulse some 200 s before the main event; the lack of any intervening emission suggests that it is due to a physical mechanism distinct from the GRB itself. The large time lag between the precursor and the main emission enabled simultaneous observations in the γ-ray, X-ray, and optical bandpasses, something only achieved for a handful of events to date. While the contemporaneous X-rays are the low-energy tail of the prompt emission, the optical does not directly track the γ-ray flux. Instead, the early-time optical data appear consistent with the forward shock synchrotron peak passing through the optical and are therefore likely the beginning of the afterglow. On hour timescales after the burst, the X-ray and optical light curves are inconsistent with an adiabatic expansion of the shock into the surrounding region, but rather indicate that there is a period of energy injection. Observations at late times allow us to constrain the collimation angle of the relativistic outflow to 6°.8 ≾ θ ≾ 9°.3. Our estimates of both the kinetic energy of the afterglow (EKE = 5.2^(+7.9)_(4.1) × 10^(51) ergs) and the prompt γ-ray energy release (Eγ = 7.5^(+6.7)-(2.4) × 10^(51) ergs) make GRB 050820A one of the most energetic events for which such values could be determined.
114 citations
TL;DR: In this article, the gamma-ray light curve is marked by a soft precursor pulse some 200 s before the main event; the lack of any intervening emission suggests that it is due to a physical mechanism distinct from the GRB itself.
Abstract: We present observations of the unusually bright and long gamma-ray burst GRB 050820A, one of the best-sampled broadband data sets in the Swift era. The gamma-ray light curve is marked by a soft precursor pulse some 200 s before the main event; the lack of any intervening emission suggests that it is due to a physical mechanism distinct from the GRB itself. The large time lag between the precursor and the main emission enabled simultaneous observations in the gamma-ray, X-ray, and optical band-passes, something only achieved for a handful of events to date. While the contemporaneous X-rays are the low-energy tail of the prompt emission, the optical does not directly track the gamma-ray flux. Instead, the early-time optical data appear mostly consistent with the forward shock synchrotron peak passing through the optical, and are therefore likely the beginning of the afterglow. On hour time scales after the burst, the X-ray and optical light curves are inconsistent with an adiabatic expansion of the shock into the surrounding region, but rather indicate that there is a period of energy injection. Observations at late times allow us to constrain the collimation angle of the relativistic outflow to theta = 6.8 - 9.3 degrees. Our estimates of both the kinetic energy of the afterglow and the prompt gamma-ray energy release make GRB 050820A one of the most energetic events for which such values could be determined.
98 citations
European Southern Observatory1, University of Arizona2, University of Oklahoma3, University of Texas at Austin4, University of Hawaii5, University of California, Berkeley6, Harvard University7, Pontifical Catholic University of Chile8, University of Washington9, Australian National University10, University of Notre Dame11, Ohio State University12, Space Telescope Science Institute13
TL;DR: In this article, the authors used archival data of low-redshift (z 1.7] SNe Ia, which are also subluminous, and showed that the magnitude of the velocity location at maximum profile absorption may underestimate that at the photosphere, as observed in the optically thinner line S II λ5640.
Abstract: Using archival data of low-redshift (z 1.7] SNe Ia, which are also subluminous. In addition, we give the first direct evidence in two high-z SN Ia spectra of a double-absorption feature in Ca II λ3945, an event also observed, although infrequently, in low-redshift SN Ia spectra (6 out of 22 SNe Ia in our local sample). Moreover, echoing the recent studies of Dessart & Hillier in the context of Type II supernovae (SNe II), we see similar P Cygni line profiles in our large sample of SN Ia spectra. First, the magnitude of the velocity location at maximum profile absorption may underestimate that at the continuum photosphere, as observed, for example, in the optically thinner line S II λ5640. Second, we report for the first time the unambiguous and systematic intrinsic blueshift of peak emission of optical P Cygni line profiles in SN Ia spectra, by as much as 8000 km s-1. All the high-z SNe Ia analyzed in this paper were discovered and followed up by the ESSENCE collaboration and are now publicly available.
98 citations
TL;DR: In this paper, the authors are grateful for support under the Space Telescope grant HST-GO-10135.01-A under contract NAS 5-26555.01 awarded by the STScI, which is operated by the Association of Universities for Research in Astronomy, Inc.
Abstract: The authors are grateful for support under the Space Telescope
Science Institute grant HST-GO-10135. A. M. S. acknowledges
support by the NASA Graduate Student Researchers Program.
E. B. is supported by NASA through Hubble Fellowship grant
HST-HF-01171.01 awarded by the STScI, which is operated by
the Association of Universities for Research in Astronomy, Inc.,
for NASA, under contract NAS 5-26555. A. G. acknowledges
support by NASA through Hubble Fellowship grant HST-HF-
01158.01-A awarded by STScI. K. R. is supported by the Gemini
Observatory, which provided observations presented in this paper,
and which is operated by the Association of Universities
for Research in Astronomy, Inc., under a cooperative agreement
with the NSF on behalf of the Gemini partnership: the National
Science Foundation (United States), the Particle Physics and
Astronomy Research Council (United Kingdom), the National
Research Council (Canada), CONICYT (Chile), the Australian
Research Council (Australia), CNPq (Brazil), and CONICET
(Argentina).
79 citations
TL;DR: In this paper, the authors present the discovery of radio afterglow emission from the high-redshift (z = 6.295) burst GRB 050904, which is similar to typical low-red-shift gamma-ray bursts (GRBs).
Abstract: We present the discovery of radio afterglow emission from the high-redshift (z = 6.295) burst GRB 050904. The peak flux density for this burst is similar to typical low-redshift gamma-ray bursts (GRBs). We further show that beyond a redshift of order unity, the flux densities of radio afterglows are largely insensitive to redshift, consistent with predictions. By combining the existing X-ray, near-infrared, and radio measurements, we derive estimates for the kinetic energy and opening angle of the blast wave and for the density of the circumburst medium into which it expands. Both the kinetic and radiated energy indicate that GRB 050904 was an unusually energetic burst (10^52 ergs). More importantly, we are able to make an in situ measurement of the density structure of the circumburst medium. We conclude that GRB 050904 exploded into a constant-density medium with n0 = 680 cm^−3, which is 2 orders of magnitude above the nominal value for low-redshift GRBs. The next generation of centimeter (EVLA) and millimeter radio instruments (ALMA) will be able to routinely detect events such as GRB 050904 and use them to study magnetic fields and the atomic and molecular gas in the high-redshift universe.
78 citations
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, a 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 were presented.
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 10^51 erg, and using a standard afterglow synchrotron model we find that the blastwave kinetic energy is a factor of 10 larger, E_K,iso ~ 10^52 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 10^50 erg. We further show that the burst produced a strong radio flare at t ~ 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 ~ 0.5L* and metallicity of Z ~ 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: The results of the analysis of γ-ray and X-ray data of GRB 050401 taken with the Swift satellite, together with a series of ground-based follow-up optical observations suggest that the extinction law is different from the Galactic one.
Abstract: We present the results of the analysis of γ-ray and X-ray data of GRB 050401 taken with the Swift satellite, together with a series of ground-based follow-up optical observations. The Swift X-ray light curve shows a clear break at about 4900 s after the γ-ray burst (GRB). The decay indices before and after the break are consistent with a scenario of continuous injection of radiation from the 'central engine' of the GRB to the fireball. Alternatively, this behaviour could result if ejecta are released with a range of Lorentz factors, with the slower shells catching up the faster at the afterglow shock position. The two scenarios are observationally indistinguishable. The GRB 050401 afterglow is quite bright in the X-ray band, but weak in the optical, with an optical to X-ray flux ratio similar to those of 'dark bursts'. We detect a significant amount of absorption in the X-ray spectrum, with N H = (1.7 ± 0.2) × 10 22cm -2 at a redshift of z = 2.9, which is typical of a dense circumburst medium. Such high column density implies an unrealistic optical extinction of 30 mag if we adopt a Galactic extinction law, which would not be consistent with the optical detection of the afterglow. This suggests that the extinction law is different from the Galactic one. © 2005 RAS.
TL;DR: In this article, the authors identify a light echo candidate from HST imaging of NGC 2441, the host galaxy of the Type Ia supernova 1995E, and find a distance of 207? 35 pc between the dust and the site of the supernova.
Abstract: We identify a light echo candidate from Hubble Space Telescope (HST) imaging of NGC 2441, the host galaxy of the Type Ia supernova 1995E. From the echo's angular size and the estimated distance to the host galaxy, we find a distance of 207 ? 35 pc between the dust and the site of the supernova. If confirmed, this echo brings the total number of observed nonhistorical Type Ia light echoes to three?the others being SN 1991T and SN 1998bu?suggesting that they are not uncommon. We compare the properties of the known Type Ia supernova echoes and test models of light echoes developed by Patat and coworkers. HST photometry of the SN 1991T echo shows a fading, which is consistent with scattering by dust distributed in a sphere or shell around the supernova. Light echoes have the potential to answer questions about the progenitors of Type Ia supernovae, and more effort should be made for their detection, given the importance of Type Ia supernovae to measurements of dark energy.
TL;DR: In this article, the authors identify a light echo candidate from HST imaging of NGC 2441, the host galaxy of the Type Ia supernova 1995E, and find a distance of 207 +/- 35 pc between the dust and the site of the supernova.
Abstract: We identify a light echo candidate from Hubble Space Telescope (HST) imaging of NGC 2441, the host galaxy of the Type Ia supernova 1995E. From the echo's angular size and the estimated distance to the host galaxy, we find a distance of 207 +/- 35 pc between the dust and the site of the supernova. If confirmed, this echo brings the total number of observed non-historical Type Ia light echoes to three -- the others being SN 1991T and SN 1998bu -- suggesting they are not uncommon. We compare the properties of the known Type Ia supernova echoes and test models of light echoes developed by Patat et al. (2005). HST photometry of the SN 1991T echo shows a fading which is consistent with scattering by dust distributed in a sphere or shell around the supernova. Light echoes have the potential to answer questions about the progenitors of Type Ia supernovae and more effort should be made for their detection given the importance of Type Ia supernovae to measurements of dark energy.
TL;DR: In this paper, the authors presented deep Hubble Space Telescope and Spitzer Space Telescope observations of the host galaxy of GRB 050904 at z=6.5 micron and inferred an extinction-corrected absolute magnitude, M(UV)=-20.7 mag.
Abstract: We present deep Hubble Space Telescope and Spitzer Space Telescope observations of the host galaxy of GRB 050904 at z=6.295. The host is detected in the H-band and marginally at 3.6 micron. From these detections, and limits in the z'-band and 4.5 micron, we infer an extinction-corrected absolute magnitude, M(UV)=-20.7 mag, or ~L*, a substantial star formation rate of 15 solar masses per year, and a stellar mass of a few 10^9 solar masses. A comparison to the published sample of spectroscopically-confirmed galaxies at z>5.5 reveals that the host of GRB 050904 would evade detection and/or confirmation in any of the current surveys due to the lack of detectable Ly-alpha emission, which is likely the result of dust extinction (A[1200]~1.5 mag). This suggests that not all luminous starburst galaxies at z~6 are currently being accounted for. Most importantly, using the metallicity of Z~0.05 solar inferred from the afterglow absorption spectrum, our observations indicate for the first time that the observed evolution in the mass- and luminosity-metallicity relations from z=0 to z~2 continues on to z>6. The ease of measuring redshifts and metallicities from the afterglow emission suggests that in tandem with the next generation ground- and space-based telescopes, a GRB mission with dedicated near-IR follow-up can provide unique information on the evolution of stars and galaxies through the epoch of re-ionization.
TL;DR: In this paper, near-simultaneous multicolor (RIYJHK) observations made with the MAGNUM 2 m telescope of the gamma-ray burst GRB 050904 detected by the Swift satellite are reported.
Abstract: We report near-simultaneous multicolor (RIYJHK) observations made with the MAGNUM 2 m telescope of the gamma-ray burst GRB 050904 detected by the Swift satellite. The spectral energy distribution shows a very large break between the I and J bands. Using intergalactic transmissions measured from high-redshift quasars, we show that the observations place a 95% confidence lower limit of z = 6.18 on the object, consistent with a later measured spectroscopic redshift of 6.29 obtained by Kawai et al. with the Subaru telescope. We show that the break strength in the R and I bands is consistent with that measured in the quasars. Finally, we consider the implications for the star formation history at high redshift.
TL;DR: In this article, the authors present detailed optical, X-ray and radio observations of the bright afterglow of the short gamma-ray burst 051221a obtained with Gemini, Swift/XRT, and the Very Large Array, as well as optical spectra from which they measure the redshift of the burst, z=0.5464.
Abstract: We present detailed optical, X-ray and radio observations of the bright afterglow of the short gamma-ray burst 051221a obtained with Gemini, Swift/XRT, and the Very Large Array, as well as optical spectra from which we measure the redshift of the burst, z=0.5464. At this redshift the isotropic-equivalent prompt energy release was about 1.5 x 10^51 erg, and using the standard afterglow synchrotron model we find that the blastwave kinetic energy is similar, E_K,iso ~ 8.4 x 10^51 erg. An observed jet break at t ~ 5 days indicates that the opening angle is ~ 7 degrees and the total beaming-corrected energy is therefore ~ 2.5 x 10^49 erg, comparable to the values inferred for previous short GRBs. We further show that the burst experienced an episode of energy injection by a factor of 3.4 between t=1.4 and 3.4 hours, which was accompanied by reverse shock emission in the radio band. This result provides continued evidence that the central engines of short GRBs may be active significantly longer than the duration of the burst and/or produce a wide range of Lorentz factors. Finally, we show that the host galaxy of GRB051221a is actively forming stars at a rate of about 1.6 M_solar/yr, but at the same time exhibits evidence for an appreciable population of old stars (~ 1 Gyr) and near solar metallicity. The lack of bright supernova emission and the low circumburst density (n ~ 10^-3 cm^-3) continue to support the idea that short bursts are not related to the death of massive stars and are instead consistent with a compact object merger. Given that the total energy release is a factor of ~ 10 larger than the predicted yield for a neutrino annihilation mechanism, this suggests that magnetohydrodynamic processes may be required to power the burst.
TL;DR: In this paper, the authors used published spectroscopic and photometric data for eight Type Ia supernovae (SNe Ia) to construct a dispersion spectrum for this class of object, showing their diversity over the wavelength range 3700-7100A.
Abstract: We use published spectroscopic and photometric data for eight Type Ia supernovae (SNe Ia) to construct a dispersion spectrum for this class of object, showing their diversity over the wavelength range 3700-7100A. We find that the B and V bands are the spectral regions with the least dispersion, while the U band below 4100A is more diverse. Some spectral features such as the Si line at 6150A are also highly diverse. We then construct two objective measures of `peculiarity' by (i) using the deviation of individual objects from the average SN Ia spectrum compared to the typical dispersion and (ii) applying principal component analysis. We demonstrate these methods on several SNe Ia that have previously been classified as peculiar.
TL;DR: In this article, the authors investigate how to choose filter bandpasses to reduce the error caused by intrinsic inhomogeneities in the Type Ia supernova population, or through observational error.
Abstract: To use Type Ia supernovae as standard candles for cosmology, we need accurate broadband magnitudes. In practice the observed magnitude may differ from the ideal magnitude‐redshift relationship either through intrinsic inhomogeneities in the Type Ia supernova population, or through observational error. Here we investigate how we can choose filter bandpasses to reduce the error caused by both these effects. We find that bandpasses with large integral fluxes and sloping wings are best able to minimize several sources of observational error, and are also least sensitive to intrinsic differences in Type Ia supernovae. The most important feature of a complete filter set for Type Ia supernova cosmology is that each bandpass be a redshifted copy of the first. We design practical sets of redshifted bandpasses that are matched to typical high‐resistivity CCD and HgCdTe infrared detector sensitivities. These are designed to minimize systematic error in well‐observed supernovae; final designs for specific missions should also consider signal‐to‐noise ratio requirements and observing strategy. In addition, we calculate how accurately filters need to be calibrated in order to achieve the required photometric accuracy of future supernova cosmology experiments, such as the Supernova/Acceleration Probe (SNAP), which is one possible realization of the Joint Dark Energy Mission (JDEM). We consider the effect of possible periodic miscalibrations that may arise from the construction of an interference filter.
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 article, optical observations of nine short GRBs obtained with Gemini, Magellan, and the Hubble Space Telescope were used to constrain the acceptable age distributions to a wide lognormal (sigma>1) with tau~4-8 Gyr, or to a power law, P(tau)~tau^n, with -1
Abstract: The redshift distribution of the short-duration GRBs is a crucial, but currently fragmentary, clue to the nature of their progenitors. Here we present optical observations of nine short GRBs obtained with Gemini, Magellan, and the Hubble Space Telescope. We detect the afterglows and host galaxies of two short bursts, and host galaxies for two additional bursts with known optical afterglow positions, and five with X-ray positions ( 1. Our most conservative limit is that at least half of the five hosts without a known redshift reside at z>0.7 (97% confidence level), suggesting that about 1/3-2/3 of all short GRBs originate at higher redshifts than previously determined. This has two important implications: (i) We constrain the acceptable age distributions to a wide lognormal (sigma>1) with tau~4-8 Gyr, or to a power law, P(tau)~tau^n, with -1
TL;DR: The SkyMapper Imager as mentioned in this paper is a wide-field Cassegrain Imager for the new 1.3m Skymapper Survey Telescope under construction for Siding Spring Observatory, NSW, Australia.
Abstract: The Research School of Astronomy and Astrophysics (RSAA) of the Australian National University (ANU) at Mt Stromlo Observatory is developing a wide-field Cassegrain Imager for the new 1.3m SkyMapper Survey Telescope under construction for Siding Spring Observatory, NSW, Australia. The Imager features a fast-readout, low-noise 268 Million pixel CCD mosaic that provides a 5.7 square degree field of view. Given the close relative sizes of the telescope and Imager, the work is proceeding in close collaboration with the telescope's manufacturer, Electro Optics Systems Pty Ltd (Canberra, Australia).
The design of the SkyMapper Imager focal plane is based on E2V (Chelmsford, UK) deep depletion CCDs. These devices have 2048 x 4096 15 micron pixels, and provide a 91% filling factor in our mosaic configuration of 4 x 8 chips. In addition, the devices have excellent quantum efficiency from 300nm-950nm, near perfect cosmetics, and low-read noise, making them well suited to the all-sky ultraviolet through near-IR Southern Sky Survey to be conducted by the telescope.
The array will be controlled using modified versions of the new IOTA controllers being developed for Pan-STARRS by Onaka and Tonry et al. These controllers provide a cost effective, low-volume, high speed solution for our detector read-out requirements. The system will have an integrated 6-filter exchanger, and Shack-Hartmann optics, and will be cooled by closed-cycle helium coolers.
This paper will present the specifications, and opto-mechanical and detector control design of the SkyMapper Imager, including the test results of the detector characterisation and manufacturing progress.
Posted Content•
18 Apr 2006
Journal Article•
Posted Content•
20 Jan 2006
TL;DR: In this paper, the authors present detailed optical, X-ray and radio observations of the bright afterglow of the short gamma-ray burst 051221a obtained with Gemini, Swift/XRT, and the Very Large Array, as well as optical spectra from which they measure the redshift of the burst, z=0.5464.
Abstract: We present detailed optical, X-ray and radio observations of the bright afterglow of the short gamma-ray burst 051221a obtained with Gemini, Swift/XRT, and the Very Large Array, as well as optical spectra from which we measure the redshift of the burst, z=0.5464. At this redshift the isotropic-equivalent prompt energy release was about 1.5 x 10^51 erg, and using the standard afterglow synchrotron model we find that the blastwave kinetic energy is similar, E_K,iso ~ 8.4 x 10^51 erg. An observed jet break at t ~ 5 days indicates that the opening angle is ~ 7 degrees and the total beaming-corrected energy is therefore ~ 2.5 x 10^49 erg, comparable to the values inferred for previous short GRBs. We further show that the burst experienced an episode of energy injection by a factor of 3.4 between t=1.4 and 3.4 hours, which was accompanied by reverse shock emission in the radio band. This result provides continued evidence that the central engines of short GRBs may be active significantly longer than the duration of the burst and/or produce a wide range of Lorentz factors. Finally, we show that the host galaxy of GRB051221a is actively forming stars at a rate of about 1.6 M_solar/yr, but at the same time exhibits evidence for an appreciable population of old stars (~ 1 Gyr) and near solar metallicity. The lack of bright supernova emission and the low circumburst density (n ~ 10^-3 cm^-3) continue to support the idea that short bursts are not related to the death of massive stars and are instead consistent with a compact object merger. Given that the total energy release is a factor of ~ 10 larger than the predicted yield for a neutrino annihilation mechanism, this suggests that magnetohydrodynamic processes may be required to power the burst.
Stockholm University1, University of Copenhagen2, University of Washington3, European Southern Observatory4, Harvard University5, Pontifical Catholic University of Chile6, University of California, Berkeley7, University of Notre Dame8, Space Telescope Science Institute9, Australian National University10, University of Hawaii at Manoa11
TL;DR: The ESSENCE project as mentioned in this paper is a ground-based supernova survey aimed at finding and characterizing 200 SNe Ia in the redshift domain z =[0.2-0.8].
Abstract: The proper usage of Type Ia supernovae (SNe Ia) as distance indicators has revolutionized cosmology, and added a new dominant component to the energy density of the Universe, dark energy. Following the discovery and confirmation era, the currently ongoing SNe Ia surveys aim to determine the properties of the dark energy. ESSENCE is a five year ground-based supernova survey aimed at finding and characterizing 200 SNe Ia in the redshift domain z =[0.2-0.8]. The goal of the project is to put constraints on the equation of state parameter, w, of the dark energy with an accuracy of ≲ 10%. This paper presents these ongoing efforts in the context of the current developments in observational cosmology.
TL;DR: In this paper, the authors presented a resolution R ≈ 6000 optical spectrum of the afterglow of GRB060210 obtained with GMOS spectrograph on the Gemini South Telescope.
Abstract: We present a resolution R ≈ 6000 optical spectrum of the afterglow of GRB060210 obtained with GMOS spectrograph on the Gemini South Telescope. The spectrum shows a main absorption system at redshift z = 3.9122 which we identify as the GRB host galaxy. We identify and characterise a Damped Lya system (DLA) at this redshift with N(HI) = 21.7 ± 0.2, and note the presence of two intervening absorption systems at z = 3.81 and z = 1.47, respectively. An array of metal absorption features is detected in the GRB host galaxy and we determine the column densities for these species. The host galaxy has metallicity Z ∼ 0.1Z ⊙ . We detect also the Sill* fine-structure transition.