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G. Aldering - One of the best experts on this subject based on the ideXlab platform.
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SNEMO: Improved Empirical Models for Type Ia Supernovae
Astrophys.J., 2018Co-Authors: C. Saunders, P. Antilogus, G. Aldering, S. Bailey, C. Baltay, K. Barbary, D. Baugh, K. Boone, S. Bongard, C. ButonAbstract:SN Ia cosmology depends on the ability to fit and standardize observations of supernova magnitudes with an empirical model. We present here a series of new models of SN Ia spectral time series that capture a greater amount of supernova diversity than is possible with the models that are currently customary. These are entitled SuperNova Empirical MOdels (SNEMO; https://snfactory.lbl.gov/snemo). The models are constructed using spectrophotometric time series from 172 individual Supernovae from the Nearby Supernova Factory, comprising more than 2000 spectra. Using the available observations, Gaussian processes are used to predict a full spectral time series for each supernova. A matrix is constructed from the spectral time series of all the Supernovae, and Expectation Maximization Factor Analysis is used to calculate the principal components of the data. K-fold cross-validation then determines the selection of model parameters and accounts for color variation in the data. Based on this process, the final models are trained on Supernovae that have been dereddened using the Fitzpatrick and Massa extinction relation. Three final models are presented here: SNEMO2, a two-component model for comparison with current Type Ia models; SNEMO7, a seven-component model chosen for standardizing supernova magnitudes, which results in a total dispersion of 0.100 mag for a validation set of Supernovae, of which 0.087 mag is unexplained (a total dispersion of 0.113 mag with an unexplained dispersion of 0.097 mag is found for the total set of training and validation Supernovae); and SNEMO15, a comprehensive 15-component model that maximizes the amount of spectral time-series behavior captured.
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Improving Cosmological Distance Measurements Using Twin Type Ia Supernovae
The Astrophysical Journal, 2015Co-Authors: H. K. Fakhouri, P. Antilogus, G. Aldering, S. Bailey, C. Baltay, K. Barbary, D. Baugh, K. Boone, C. Aragon, S. BongardAbstract:We introduce a method for identifying "twin" Type Ia Supernovae, and using them to improve distance measurements. This novel approach to Type Ia supernova standardization is made possible by spectrophotometric time series observations from the Nearby Supernova Factory (SNfactory). We begin with a well-measured set of Supernovae, find pairs whose spectra match well across the entire optical window, and then test whether this leads to a smaller dispersion in their absolute brightnesses. This analysis is completed in a blinded fashion, ensuring that decisions made in implementing the method do not inadvertently bias the result. We find that pairs of Supernovae with more closely matched spectra indeed have reduced brightness dispersion. We are able to standardize this initial set of SNfactory Supernovae to 0.083 +/- 0.012 magnitudes, implying a dispersion of 0.072 +/- 0.010 magnitudes in the absence of peculiar velocities. We estimate that with larger numbers of comparison SNe, e.g, using the final SNfactory spectrophotometric dataset as a reference, this method will be capable of standardizing high-redshift Supernovae to within 0.06-0.07 magnitudes. These results imply that at least 3/4 of the variance in Hubble residuals in current supernova cosmology analyses is due to previously unaccounted-for astrophysical differences among the Supernovae
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Type Ia Supernova Distance Modulus Bias and Dispersion from K-correction Errors: A Direct Measurement Using Light Curve Fits to Observed Spectral Time Series
The Astrophysical Journal, 2015Co-Authors: C. Saunders, P. Antilogus, G. Aldering, S. Bailey, C. Baltay, S. Bongard, C. Buton, C. Aragon, A. Canto, F. Cellier-holzemAbstract:We estimate systematic errors due to K-corrections in standard photometric analyses of high-redshift Type Ia Supernovae. Errors due to K-correction occur when the spectral template model underlying the light curve fitter poorly represents the actual supernova spectral energy distribution, meaning that the distance modulus cannot be recovered accurately. In order to quantify this effect, synthetic photometry is performed on artificially redshifted spectrophotometric data from 119 low-redshift Supernovae from the Nearby Supernova Factory, and the resulting light curves are fit with a conventional light curve fitter. We measure the variation in the standardized magnitude that would be fit for a given supernova if located at a range of redshifts and observed with various filter sets corresponding to current and future supernova surveys. We find significant variation in the measurements of the same Supernovae placed at different redshifts regardless of filters used, which causes dispersion greater than ~0.05 mag for measurements of photometry using the Sloan-like filters and a bias that corresponds to a 0.03 shift in w when applied to an outside data set. To test the result of a shift in supernova population or environment at higher redshifts, we repeat our calculations with the addition of a reweighting of the Supernovae as a function of redshift and find that this strongly affects the results and would have repercussions for cosmology. We discuss possible methods to reduce the contribution of the K-correction bias and uncertainty.
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Initial Hubble Diagram Results from the Nearby Supernova Factory
2008Co-Authors: S. Bailey, P. Antilogus, G. Aldering, C. Baltay, S. Bongard, C. Buton, C. Aragon, M. Childress, Y. Copin, E. GanglerAbstract:The use of Type Ia Supernovae as distance indicators led to the discovery of the accelerating expansion of the universe a decade ago. Now that large second generation surveys have significantly increased the size and quality of the high-redshift sample, the cosmological constraints are limited by the currently available sample of ~50 cosmologically useful nearby Supernovae. The Nearby Supernova Factory addresses this problem by discovering nearby Supernovae and observing their spectrophotometric time development. Our data sample includes over 2400 spectra from spectral timeseries of 185 Supernovae. This talk presents results from a portion of this sample including a Hubble diagram (relative distance vs. redshift) and a description of some analyses using this rich dataset.
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Spectra of High-Redshift Type Ia Supernovae and a Comparison with their Low-Redshift Counterparts
Astronomical Journal, 2005Co-Authors: I. M. Hook, R Amanullah, M. S. Burns, G. Aldering, A. Conley, S. E. Deustua, R. Ellis, D. A. Howell, S. Fabbro, V. FadeyevAbstract:We present spectra for 14 high-redshift (0.17 < z < 0.83) Supernovae, which were discovered by the Supernova Cosmology Project as part of a campaign to measure cosmological parameters. The spectra are used to determine the redshift and classify the supernova type, essential information if the Supernovae are to be used for cosmological studies. Redshifts were derived either from the spectrum of the host galaxy or from the spectrum of the supernova itself. We present evidence that these Supernovae are of Type Ia by matching to spectra of nearby Supernovae. We find that the dates of the spectra relative to maximum light determined from this fitting process are consistent with the dates determined from the photometric light curves, and moreover the spectral time-sequence for SNe Type Ia at low and high redshift is indistinguishable. We also show that the expansion velocities measured from blueshifted CaHK are consistent with those measured for low-redshift Type Ia Supernovae. From these first-level quantitative comparisons we find no evidence for evolution in SNIa properties between these low- and high-redshift samples. Thus even though our samples may not be complete, we conclude that there is a population of SNe Ia at high redshift whose spectral properties match those at low redshift.
Mansi M. Kasliwal - One of the best experts on this subject based on the ideXlab platform.
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A strong ultraviolet pulse from a newborn type Ia supernova
Nature, 2015Co-Authors: Yi Cao, Avishay Gal-yam, D. Andrew Howell, A. Goobar, Mansi M. Kasliwal, R Amanullah, J. Johansson, S. R. Kulkarni, Stefano Valenti, Jesper SollermanAbstract:Type Ia Supernovae are destructive explosions of carbon-oxygen white dwarfs. Although they are used empirically to measure cosmological distances, the nature of their progenitors remains mysterious. One of the leading progenitor models, called the single degenerate channel, hypothesizes that a white dwarf accretes matter from a companion star and the resulting increase in its central pressure and temperature ignites thermonuclear explosion. Here we report observations with the Swift Space Telescope of strong but declining ultraviolet emission from a type Ia supernova within four days of its explosion. This emission is consistent with theoretical expectations of collision between material ejected by the supernova and a companion star, and therefore provides evidence that some type Ia Supernovae arise from the single degenerate channel.
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Galaxy Zoo Supernovae
Monthly Notices of the Royal Astronomical Society, 2011Co-Authors: Arfon M. Smith, Mansi M. Kasliwal, Mark Sullivan, Stuart Lynn, Chris Lintott, Peter E. Nugent, János Botyánszki, R. M. Quimby, Steven P. Bamford, Lucy FortsonAbstract:This paper presents the first results from a new citizen science project: Galaxy Zoo Supernovae. This proof-of-concept project uses members of the public to identify supernova candidates from the latest generation of wide-field imaging transient surveys. We describe the Galaxy Zoo Supernovae operations and scoring model, and demonstrate the effectiveness of this novel method using imaging data and transients from the Palomar Transient Factory (PTF). We examine the results collected over the period 2010 April–July, during which nearly 14 000 supernova candidates from the PTF were classified by more than 2500 individuals within a few hours of data collection. We compare the transients selected by the citizen scientists to those identified by experienced PTF scanners and find the agreement to be remarkable – Galaxy Zoo Supernovae performs comparably to the PTF scanners and identified as transients 93 per cent of the ~130 spectroscopically confirmed Supernovae (SNe) that the PTF located during the trial period (with no false positive identifications). Further analysis shows that only a small fraction of the lowest signal-to-noise ratio detections (r > 19.5) are given low scores: Galaxy Zoo Supernovae correctly identifies all SNe with ≥8σ detections in the PTF imaging data. The Galaxy Zoo Supernovae project has direct applicability to future transient searches, such as the Large Synoptic Survey Telescope, by both rapidly identifying candidate transient events and via the training and improvement of existing machine classifier algorithms.
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relativistic ejecta from x ray flash xrf 060218 and the rate of cosmic explosions
Nature, 2006Co-Authors: A M Soderberg, S. R. Kulkarni, Ehud Naka, E Erge, P Camero, D A Frail, A Galyam, Reem Sari, S Cenko, Mansi M. KasliwalAbstract:Over the past decade, long-duration γ-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 (associated4 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.
E Pia - One of the best experts on this subject based on the ideXlab platform.
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an optical supernova associated with the x ray flash xrf 060218
Nature, 2006Co-Authors: E Pia, P A Mazzali, N Masetti, P Ferrero, S Klose, E Palazzi, Enrico Ramirezruiz, S E WoosleyAbstract:Long-duration gamma-ray bursts (GRBs) are associated with type Ic Supernovae(1) that are more luminous than average(2-5) and that eject material at very high velocities. Less-luminous Supernovae were not hitherto known to be associated with GRBs, and therefore GRB - Supernovae were thought to be rare events(6). Whether X-ray flashes - analogues of GRBs, but with lower luminosities and fewer gamma-rays - can also be associated with Supernovae, and whether they are intrinsically 'weak' events or typical GRBs viewed off the axis of the burst(7), is unclear. Here we report the optical discovery and follow-up observations of the type Ic supernova SN 2006aj associated with X-ray flash XRF 060218. Supernova 2006aj is intrinsically less luminous than the GRB - Supernovae, but more luminous than many Supernovae not accompanied by a GRB. The ejecta velocities derived from our spectra are intermediate between these two groups, which is consistent with the weakness of both the GRB output(8) and the supernova radio flux(9). Our data, combined with radio and X-ray observations(8-10), suggest that XRF 060218 is an intrinsically weak and soft event, rather than a classical GRB observed off-axis. This extends the GRB - supernova connection to X-ray flashes and fainter Supernovae, implying a common origin. Events such as XRF 060218 are probably more numerous than GRB - Supernovae.
P. Astier - One of the best experts on this subject based on the ideXlab platform.
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An Efficient Approach to Obtaining Large Numbers of Distant Supernova Host Galaxy Redshifts
Publications of the Astronomical Society of Australia, 2012Co-Authors: C. Lidman, P. Astier, C. Balland, V. Ruhlmann-kleider, M. Sullivan, J. Myzska, P. Dobbie, K. Glazebrook, J. Mould, M. BetouleAbstract:We use the wide-field capabilities of the 2dF fibre positioner and the AAOmega spectrograph on the Anglo-Australian Telescope (AAT) to obtain redshifts of galaxies that hosted Supernovae during the first three years of the Supernova Legacy Survey (SNLS). With exposure times ranging from 10 to 60 ksec per galaxy, we were able to obtain redshifts for 400 host galaxies in two SNLS fields, thereby substantially increasing the total number of SNLS Supernovae with host galaxy redshifts. The median redshift of the galaxies in our sample that hosted photometrically classified Type Ia Supernovae (SNe Ia) is 0.77, which is 25% higher than the median redshift of spectroscopically confirmed SNe Ia in the three-year sample of the SNLS. Our results demonstrate that one can use wide-field fibre-fed multi-object spectrographs on 4m telescopes to efficiently obtain redshifts for large numbers of supernova host galaxies over the large areas of sky that will be covered by future high-redshift supernova surveys, such as the Dark Energy Survey.
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Dark energy constraints from a space-based supernova survey
Astronomy and Astrophysics - A&A, 2010Co-Authors: P. Astier, J. Guy, R. Pain, C. BallandAbstract:We present a forecast of dark energy constraints that could be obtained from a large sample of distances to Type Ia Supernovae detected and measured from space. We simulate the supernova events as they would be observed by a EUCLID-like telescope with its two imagers, assuming those would be equipped with 4 visible and 3 near infrared swappable filters. We account for known systematic uncertainties affecting the cosmological constraints, including those arising through the training of the supernova model used to fit the Supernovae light curves. Using conservative assumptions and Planck priors, we find that a 18 month survey would yield constraints on the dark energy equation of state comparable to the cosmic shear approach in EUCLID: a variable two-parameter equation of state can be constrained to ~0.03 at z~0.3. These constraints are derived from distances to about 13,000 Supernovae out to z=1.5, observed in two cones of 10 and 50 deg^2. These constraints do not require measuring a nearby supernova sample from the ground. Provided swappable filters can be accommodated on EUCLID, distances to Supernovae can be measured from space and contribute to obtain the most precise constraints on dark energy properties.
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The core-collapse rate from the Supernova Legacy Survey
Astronomy and Astrophysics - A&A, 2009Co-Authors: G. Bazin, P. Astier, C. Balland, N. Palanque-delabrouille, J. Rich, V. Ruhlmann-kleider, E. Aubourg, L. Le Guillou, S. Basa, R. G. CarlbergAbstract:We use three years of data from the Supernova Legacy Survey (SNLS) to study the general properties of core-collapse and type Ia Supernovae. This is the first such study using the "rolling search" technique which guarantees well-sampled SNLS light curves and good efficiency for Supernovae brighter than i'~24. Using host photometric redshifts, we measure the supernova absolute magnitude distribution down to luminosities 4.5 mag fainter than normal SNIa. Using spectroscopy and light-curve fitting to discriminate against SNIa, we find a sample of 117 core-collapse supernova candidates with redshifts z < 0.4 (median redshift of 0.29) and measure their rate to be larger than the type Ia supernova rate by a factor 4.5±0.8(stat.)±0.6 (sys.). This corresponds to a core-collapse rate at z = 0.3 of [ 1.42±0.3(stat.)±0.3(sys.)] ×10-4 yr-1(h_70-1 Mpc)-3.
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Spectroscopic observations of eight Supernovae at intermediate redshift
Astronomy and Astrophysics - A&A, 2007Co-Authors: C. Balland, A. Goobar, R Amanullah, G. Garavini, P. Astier, S. Fabbro, G. Folatelli, M. Mouchet, D. Hardin, M. J. IrwinAbstract:We present spectra of six Type Ia and two Type II Supernovae obtained in June 2002 at the William Herschel Telescope during a search for Type Ia Supernovae (SNIa) at intermediate redshift. Supernova type identification and phase determination are performed using a fitting technique based on a Xi2 minimization against a series of model templates. The spectra range from z=0.033 to z=0.328, including one spectroscopically underluminous SNIa at z=0.033. This set of spectra significantly increases the sample of well-observed type SNIa Supernovae available in the range 0.15< z
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Spectroscopic confirmation of high-redshift Supernovae with the ESO VLT
Astronomy and Astrophysics - A&A, 2005Co-Authors: C. Lidman, R Amanullah, G. Garavini, Gaston Folatelli, P. Antilogus, G. Aldering, P. Astier, D. A. Howell, S. Nobili, G. BlancAbstract:We present VLT FORS1 and FORS2 spectra of 39 candidate high-redshift Supernovae that were discovered as part of a cosmological study using Type Ia Supernovae (SNe Ia) over a wide range of redshifts. From the spectra alone, 20 candidates are spectrally classified as SNe Ia with redshifts ranging from z=0.212 to z=1.181. Of the remaining 19 candidates, 1 might be a Type II supernova and 11 exhibit broad supernova-like spectral features and/or have supernova-like light curves. The candidates were discovered in 8 separate ground-based searches. In those searches in which SNe Ia at z ~ 0.5 were targeted, over 80% of the observed candidates were spectrally classified as SNe Ia. In those searches in which SNe Ia with z > 1 were targeted, 4 candidates with z > 1 were spectrally classified as SNe Ia and later followed with ground and space based observatories. We present the spectra of all candidates, including those that could not be spectrally classified as supernova.
R Amanullah - One of the best experts on this subject based on the ideXlab platform.
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A strong ultraviolet pulse from a newborn type Ia supernova
Nature, 2015Co-Authors: Yi Cao, Avishay Gal-yam, D. Andrew Howell, A. Goobar, Mansi M. Kasliwal, R Amanullah, J. Johansson, S. R. Kulkarni, Stefano Valenti, Jesper SollermanAbstract:Type Ia Supernovae are destructive explosions of carbon-oxygen white dwarfs. Although they are used empirically to measure cosmological distances, the nature of their progenitors remains mysterious. One of the leading progenitor models, called the single degenerate channel, hypothesizes that a white dwarf accretes matter from a companion star and the resulting increase in its central pressure and temperature ignites thermonuclear explosion. Here we report observations with the Swift Space Telescope of strong but declining ultraviolet emission from a type Ia supernova within four days of its explosion. This emission is consistent with theoretical expectations of collision between material ejected by the supernova and a companion star, and therefore provides evidence that some type Ia Supernovae arise from the single degenerate channel.
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Near-IR search for lensed Supernovae behind galaxy clusters. II. First detection and future prospects
Astronomy and Astrophysics - A&A, 2009Co-Authors: A. Goobar, R Amanullah, K. Paech, V. Stanishev, T. Dahlén, J. Jönsson, J. P. Kneib, C. Lidman, M. Limousin, E. MörtsellAbstract:Aims: Powerful gravitational telescopes in the form of massive galaxy clusters can be used to enhance the light collecting power over a limited field of view by about an order of magnitude in flux. This effect is exploited here to increase the depth of a survey for lensed Supernovae at near-IR wavelengths. Methods: We present a pilot supernova search programme conducted with the ISAAC camera at VLT. Lensed galaxies behind the massive clusters A1689, A1835, and AC114 were observed for a total of 20 h divided into 2, 3, and 4 epochs respectively, separated by approximately one month to a limiting magnitude J ≲ 24 (Vega). Image subtractions including another 20 h worth of archival ISAAC/VLT data were used to search for transients with lightcurve properties consistent with redshifted Supernovae, both in the new and reference data. Results: The feasibility of finding lensed Supernovae in our survey was investigated using synthetic lightcurves of Supernovae and several models of the volumetric type Ia and core-collapse supernova rates as a function of redshift. We also estimate the number of supernova discoveries expected from the inferred star-formation rate in the observed galaxies. The methods consistently predict a Poisson mean value for the expected number of Supernovae in the survey of between N_SN = 0.8 and 1.6 for all supernova types, evenly distributed between core collapse and type Ia Supernovae. One transient object was found behind A1689, 0.5 arcsec from a galaxy with photometric redshift z_gal = 0.6 ± 0.15. The lightcurve and colors of the transient are consistent with being a reddened type IIP supernova at z_SN = 0.59. The lensing model predicts 1.4 mag of magnification at the location of the transient, without which this object would not have been detected in the near-IR ground-based search described in this paper (unlensed magnitude J ~ 25). We perform a feasibility study of the potential for lensed Supernovae discoveries with larger and deeper surveys and conclude that the use of gravitational telescopes is a very exciting path for new discoveries. For example, a monthly rolling supernova search of a single very massive cluster with the HAWK-I camera at VLT would yield ≳ 10 lensed supernova lightcurves per year, where type Ia Supernovae would constitute about half of the expected sample. Based on observations made with ESO telescopes at the La Silla Paranal Observatory under programme ID 079.A-0192 and ID 081.A-0734.
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Near-IR search for lensed Supernovae behind galaxy clusters. I. Observations and transient detection efficiency
Astronomy and Astrophysics - A&A, 2009Co-Authors: V. Stanishev, A. Goobar, R Amanullah, K. Paech, T. Dahlén, J. Jönsson, J. P. Kneib, C. Lidman, M. Limousin, E. MörtsellAbstract:Context: Massive galaxy clusters at intermediate redshift can magnify the flux of distant background sources by several magnitudes. Aims: We exploit this effect to search for lensed distant Supernovae that may otherwise be too faint to be detected. Methods: A supernova search was conducted at near infrared wavelengths using the ISAAC instrument at the VLT. The massive galaxy clusters Abell 1689, Abell 1835, and AC114 were observed for a total of 20 h to search for Supernovae in gravitationally magnified background galaxies. The observations were split into individual epochs of 2 h of exposure time, separated by approximately one month. Image-subtraction techniques were used to search for transient objects with light curve properties consistent with Supernovae, both in our new and archival ISAAC/VLT data. The limiting magnitude of the individual epochs was estimated by adding artificial stars to the subtracted images. Most of the epochs reach 90% detection efficiency at SZ(J) ≃ 23.8-24.0 mag (Vega). Results: Two transient objects, both in archival images of Abell 1689 and AC114, were detected. The transient in AC114 coincides - within the position uncertainty - with an X-ray source and is likely to be a variable AGN at the cluster redshift. The transient in Abell 1689 was found at SZ = 23.24 mag, ~0.5''away from a galaxy with photometric redshift z_gal = 0.6 ± 0.15. The light curves and the colors of the transient are consistent with a reddened type IIP supernova at redshift z = 0.59 ± 0.05. The lensing model of Abell 1689 predicts ~1.4 mag of magnification at the position of the transient, making it the most magnified supernova ever found and only the second supernova found behind a galaxy cluster. Conclusions: Our pilot survey has demonstrated the feasibility to find distant gravitationally magnified Supernovae behind massive galaxy clusters. One likely supernova was found behind Abell 1689, in accordance with the expectations for this survey, as shown in an accompanying analysis paper. Based on observations made with ESO telescopes at the Paranal Observatory under program IDs 079.A-0192 and 081.A-0734.
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Near-IR Search for Lensed Supernovae Behind Galaxy Clusters - II. First Detection and Future Prospects
2008Co-Authors: A. Goobar, R Amanullah, K. Paech, V. Stanishev, T. Dahlén, J. Jönsson, J. P. Kneib, C. Lidman, M. Limousin, E. MörtsellAbstract:Powerful gravitational telescopes in the form of massive galaxy clusters can be used to enhance the light collecting power over a limited field of view by about an order of magnitude in flux. This remarkable effect is exploited here to increase the depth of a survey for lensed Supernovae at near-IR wavelengths. A pilot supernova search programme conducted with the ISAAC camera at VLT is presented. Lensed galaxies behind the massive clusters A1689, A1835 and AC114 were observed for a total of 20 hours split into 2, 3 and 4 epochs respectively, separated by approximately one month to a limiting magnitude $J\lsim 24$ (Vega). Image subtractions including another 20 hours worth of archival ISAAC/VLT data were used to search for transients with lightcurve properties consistent with redshifted Supernovae, both in the new and reference data. The feasibility of finding lensed Supernovae in our survey was investigated using synthetic lightcurves of Supernovae and several models of the volumetric Type Ia and core-collapse supernova rates as a function of redshift. We also estimate the number of supernova discoveries expected from the inferred star formation rate in the observed galaxies. The methods consistently predict a Poisson mean value for the expected number of Supernovae in the survey between N$_{\rm SN}$=0.8 and 1.6 for all supernova types, evenly distributed between core collapse and Type Ia Supernovae. One transient object was found behind A1689, 0.5" from a galaxy with photometric redshift z_gal=0.6 +- 0.15. The lightcurve and colors of the transient are consistent with being a reddened Type IIP supernova at z_SN=0.62. The lensing model predicts 1.7 mag of amplification at the location of the transient, without which this object would have been hard to detected with a ground based search (abridged).
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Quantitative comparison between type Ia supernova spectra at low and high redshifts: A case study
Astronomy and Astrophysics - A&A, 2007Co-Authors: G. Garavini, R Amanullah, Gaston Folatelli, Serena Nobili, Greg Aldering, P. Antilogus, Pierre Astier, G. Blanc, J. Bronder, M. S. BurnsAbstract:We develop a method to measure the strength of the absorption features in Type Ia supernova (SN Ia) spectra and use it to make a quantitative comparison between the spectra of Type Ia Supernovae at low and high redshifts. In this case study, we apply the method to 12 high-redshift (0.212 < z < 0.912) SNe Ia observed by the Supernova Cosmology Project . Through measurements of the strengths of these features and of the blueshift of the absorption minimum in Ca II H&K, we show that the spectra of the high-redshift SNe Ia are quantitatively similar to spectra of nearby SNe Ia (z < 0.15). One supernova in our high redshift sample, SN 2002fd at z=0.279, is found to have spectral characteristics that are associated with peculiar SN 1991T/SN 1999aa-like Supernovae.
