arXiv subjects

P. M. Garnavich

Publications and source records attributed to P. M. Garnavich.

At least 55 records · Page 3Linked to original sources

arXiv2007

Measured Metallicities at the Sites of Nearby Broad-Lined Type Ic Supernovae and Implications for the SN-GRB Connection

We compare the chemical abundances at the sites of 12 nearby (z <0.14) Type Ic supernovae (SN Ic) that showed broad lines, but had no observed Gamma-Ray Burst (GRB), with the chemical abundances in 5 nearby (z < 0.25) galaxies at the sites of GRB where broad-lined SN Ic were seen after the fireball had faded. It has previously been noted that GRB hosts are low in luminosity and low in their metal abundances. If low metallicity is sufficient to force the evolution of massive stars to end their lives as GRB with an accompanying broad-lined SN Ic, then we would expect higher metal abundances for the broad-lined SN Ic that have no detected GRB. This is what we observe, and this trend is independent of the choice of metallicity calibration we adopt, and the mode of SN survey that found the broad-lined SN. A unique feature of this analysis is that we present new spectra of the host galaxies and analyze all the measurements of both samples in the same set of ways, using the galaxy emission-line measurements corrected for extinction and stellar absorption, via independent metallicity diagnostics of Kewley & Dopita (2002), of McGaugh (1991) and of Pettini & Pagel (2004). In our small sample, the boundary between galaxies that have GRB accompanying their broad-lined SN Ic and those that have broad-lined SN Ic without a GRB lies at an oxygen abundance of 12+log(O/H)_KD02 ~ 8.5, which corresponds to 0.2-0.6 Z_sun depending on the adopted metallicity scale and solar abundance value. Even when we limit the comparison to SN Ic that were found in untargeted supernova surveys, the environment of every broad-lined SN Ic that had no GRB is more metal rich than the site of any broad-lined SN Ic where a GRB was detected.

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arXiv2007

LBT Discovery of a Yellow Supergiant Eclipsing Binary in the Dwarf Galaxy Holmberg IX

In a variability survey of M81 using the Large Binocular Telescope we have discovered a peculiar eclipsing binary (MV ~ -7.1) in the field of the dwarf galaxy Holmberg IX. It has a period of 272 days and the light curve is well-fit by an overcontact model in which both stars are overflowing their Roche lobes. It is composed by two yellow supergiants (V-I ~ 1 mag, T_eff = 4800 K), rather than the far more common red or blue supergiants. Such systems must be rare. While we failed to find any similar systems in the literature, we did, however note a second example. The SMC F0 supergiant R47 is a bright (MV ~ -7.5) periodic variable whose All Sky Automated Survey (ASAS) light curve is well-fit as a contact binary with a 181 day period. We propose that these systems are the progenitors of supernovae like SN 2004et and SN 2006ov, which appeared to have yellow progenitors. The binary interactions (mass transfer, mass loss) limit the size of the supergiant to give it a higher surface temperature than an isolated star at the same core evolutionary stage. We also discuss the possibility of this variable being a long-period Cepheid.

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arXiv2007

The Sloan Digital Sky Survey-II Supernova Survey: Search Algorithm and Follow-up Observations

The Sloan Digital Sky Survey-II Supernova Survey has identified a large number of new transient sources in a 300 sq. deg. region along the celestial equator during its first two seasons of a three-season campaign. Multi-band (ugriz) light curves were measured for most of the sources, which include solar system objects, Galactic variable stars, active galactic nuclei, supernovae (SNe), and other astronomical transients. The imaging survey is augmented by an extensive spectroscopic follow-up program to identify SNe, measure their redshifts, and study the physical conditions of the explosions and their environment through spectroscopic diagnostics. During the survey, light curves are rapidly evaluated to provide an initial photometric type of the SNe, and a selected sample of sources are targeted for spectroscopic observations. In the first two seasons, 476 sources were selected for spectroscopic observations, of which 403 were identified as SNe. For the Type Ia SNe, the main driver for the Survey, our photometric typing and targeting efficiency is 90%. Only 6% of the photometric SN Ia candidates were spectroscopically classified as non-SN Ia instead, and the remaining 4% resulted in low signal-to-noise, unclassified spectra. This paper describes the search algorithm and the software, and the real-time processing of the SDSS imaging data. We also present the details of the supernova candidate selection procedures and strategies for follow-up spectroscopic and imaging observations of the discovered sources.

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arXiv2007

Constraining Cosmic Evolution of Type Ia Supernovae

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.

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arXiv2007

The Luminous and Carbon-Rich Supernova 2006gz: A Double Degenerate Merger?

Spectra and light curves of SN 2006gz show the strongest signature of unburned carbon and one of the slowest fading light curves ever seen in a type Ia event (Delta m_15 = 0.69 +/- 0.04). The early-time Si II velocity is low, implying it was slowed by an envelope of unburned material. Our best estimate of the luminosity implies M_V = -19.74 and the production of ~ 1.2 M_sun of 56Ni. This suggests a super-Chandrasekhar mass progenitor. A double degenerate merger is consistent with these observations.

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arXiv2007

The Sloan Digital Sky Survey-II Supernova Survey: Technical Summary

The Sloan Digital Sky Survey-II (SDSS-II) has embarked on a multi-year project to identify and measure light curves for intermediate-redshift (0.05 < z < 0.35) Type Ia supernovae (SNe Ia) using repeated five-band (ugriz) imaging over an area of 300 sq. deg. The survey region is a stripe 2.5 degrees wide centered on the celestial equator in the Southern Galactic Cap that has been imaged numerous times in earlier years, enabling construction of a deep reference image for discovery of new objects. Supernova imaging observations are being acquired between 1 September and 30 November of 2005-7. During the first two seasons, each region was imaged on average every five nights. Spectroscopic follow-up observations to determine supernova type and redshift are carried out on a large number of telescopes. In its first two three-month seasons, the survey has discovered and measured light curves for 327 spectroscopically confirmed SNe Ia, 30 probable SNe Ia, 14 confirmed SNe Ib/c, 32 confirmed SNe II, plus a large number of photometrically identified SNe Ia, 94 of which have host-galaxy spectra taken so far. This paper provides an overview of the project and briefly describes the observations completed during the first two seasons of operation.

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arXiv2007

Scrutinizing Exotic Cosmological Models Using ESSENCE Supernova Data Combined with Other Cosmological Probes

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.

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arXiv2007

A Study of the Type Ia/IIn Supernova 2005gj from X-ray to the Infrared: Paper I

We present extensive ugrizYHJK photometry and optical spectroscopy of SN 2005gj obtained by the SDSS-II and CSP Supernova Projects, which give excellent coverage during the first 150 days after the time of explosion. These data show that SN 2005gj is the second clear case, after SN 2002ic, of a thermonuclear explosion in a dense circumstellar environment. Both the presence of singly and doubly ionized iron-peak elements (FeIII and weak SII, SiII) near maximum light as well as the spectral evolution show that SN 2002ic-like events are Type Ia explosions. Independent evidence comes from the exponential decay in luminosity of SN 2005gj, pointing to an exponential density distribution of the ejecta. The interaction of the supernova ejecta with the dense circumstellar medium is stronger than in SN 2002ic: (1) the supernova lines are weaker; (2) the Balmer emission lines are more luminous; and (3) the bolometric luminosity is higher close to maximum light. The velocity evolution of the Halpha components suggest that the CSM around SN 2005gj is clumpy and it has a flatter density distribution compared with the steady wind solution, in agreement with SN 2002ic. An early X-ray observation with Chandra gives an upper-limit on the mass loss rate from the companion of < 2x10^{-4} Msun/yr.

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arXiv2007

The Peculiar SN 2005hk: Do Some Type Ia Supernovae Explode as Deflagrations?

We present extensive u'g'r'i'BVRIYJHKs photometry and optical spectroscopy of SN 2005hk. These data reveal that SN 2005hk was nearly identical in its observed properties to SN 2002cx, which has been called ``the most peculiar known type Ia supernova.'' Both supernovae exhibited high ionization SN 1991T-like pre-maximum spectra, yet low peak luminosities like SN 1991bg. The spectra reveal that SN 2005hk, like SN 2002cx, exhibited expansion velocities that were roughly half those of typical type Ia supernovae. The R and I light curves of both supernovae were also peculiar in not displaying the secondary maximum observed for normal type Ia supernovae. Our YJH photometry of SN 2005hk reveals the same peculiarity in the near-infrared. By combining our optical and near-infrared photometry of SN 2005hk with published ultraviolet light curves obtained with the Swift satellite, we are able to construct a bolometric light curve from ~10 days before to ~60 days after B maximum. The shape and unusually low peak luminosity of this light curve, plus the low expansion velocities and absence of a secondary maximum at red and near-infrared wavelengths, are all in reasonable agreement with model calculations of a 3D deflagration which produces ~0.25 M_sun of 56Ni.

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arXiv2007

Strongly Variable z=1.48 FeII and MgII Absorption in the Spectra of z=4.05 GRB 060206

We report on the discovery of strongly variable FeII and MgII absorption lines seen at z=1.48 in the spectra of the z=4.05 GRB 060206 obtained between 4.13 to 7.63 hours (observer frame) after the burst. In particular, the FeII line equivalent width (EW) decayed rapidly from 1.72+-0.25 AA to 0.28+-0.21 AA, only to increase to 0.96+-0.21 AA in a later date spectrum. The MgII doublet shows even more complicated evolution: the weaker line of the doublet drops from 2.05+-0.25 AA to 0.92+-0.32 AA, but then more than doubles to 2.47+-0.41 AA in later data. The ratio of the EWs for the MgII doublet is also variable, being closer to 1:1 (saturated regime) when the lines are stronger and becoming closer to 2:1 (unsaturated regime) when the lines are weaker, consistent with expectations based on atomic physics. We have investigated and rejected the possibility of any instrumental or atmospheric effects causing the observed strong variations. Our discovery of clearly variable intervening FeII and MgII lines lends very strong support to their scenario, in which the characteristic size of intervening patches of MgII ``clouds'' is comparable to the GRB beam size, i.e, about 10^16 cm. We discuss various implications of this discovery, including the nature of the MgII absorbers, the physics of GRBs, and measurements of chemical abundances from GRB and quasar absorption lines.

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arXiv2007

Observational Constraints on the Nature of the Dark Energy: First Cosmological Results from the ESSENCE Supernova Survey

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.

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arXiv2007

The ESSENCE Supernova Survey: Survey Optimization, Observations, and Supernova Photometry

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.

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arXiv2006

"Anomalous" Optical GRB Afterglows are Common: Two z~4 Bursts, GRB 060206 and 060210

We report on two recent z~4 gamma-ray bursts (GRBs), GRB 060206 and GRB 060210, for which we have obtained well-sampled optical light curves. Our data, combined with early optical data reported in the literature, shows unusual behavior for both afterglows. In R-band GRB 060206 (z=4.045) experienced a slow early decay, followed by a rapid increase in brightness by factor ~2.5 about 1 hour after the burst. Its afterglow then faded in a broken power-law fashion, with a smooth break at t_b=0.6 days, but with additional, less dramatic (~10%) ``bumps and wiggles'', well detected in the densely sampled light curve. The R-band afterglow of GRB 060210 (z=3.91) is also unusual: the light curves was more or less flat between 60 and 300 sec after the burst, followed by ~70% increase at ~600 sec after the burst, after which the light curve declined as a t^{-1.3} power-law. Despite earlier reports to the contrary, we find that for GRB 060206 X-rays also more or less follow the optical decay, but with significant variations on short timescales. However, the X-ray afterglow is contaminated by a nearby, variable source, which especially at late times obscures the behavior of the X-ray afterglow. We argue that ``anomalous'' optical afterglows are likely to be the norm, and that the rapid variations often seen in Swift-XRT data would also be seen in the optical light curves, given good enough sampling. As a result, some of the often employed procedures, such as deriving the jet opening angle using a smooth broken power-law fit to the optical light curves, in many cases might have a poor statistical significance. We argue that the early increase in brighness for both bursts might be due to the turn-on of the external shock. Existence of such features could provide valuable additional information about the burst. (Abridged)

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arXiv2006

A Light Echo from Type Ia Supernova 1995E?

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.

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arXiv2006

Early-Time Photometry and Spectroscopy of the Fast Evolving SN 2006AJ Associated with GRB 060218

We present early photometric and spectroscopic data on the afterglow of GRB 060218 and report the evolution of the underlying supernova 2006aj. Our data span a time-range of 4 days to 22 days after the GRB and clearly establish that SN 2006aj is a fast-evolving broad-lined Type Ic SN with an extremely short rise-time (~ 10 days) and a large optical luminosity (M_V = -18.7 mag). The SN properties are deduced well since the GRB afterglow does not contribute a significant amount to the total light output. The spectra show broad lines indicative of large expansion velocities, but are better matched by those of SN 2002ap and SN 1997ef (that are not associated with a GRB) than those of the proto-typical GRB-related SN 1998bw. We refine the redshift estimate to z = 0.0335 +/- 0.00007. The host-galaxy is a low-metallicity dwarf galaxy (with M_V \~ -16.0 mag), similar to host-galaxies of other GRB-associated SNe.

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arXiv2006

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

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

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arXiv2005

Chemistry and Star Formation in the Host Galaxies of Type Ia Supervovae

We study the effect of environment on the properties of type Ia supernovae by analyzing the integrated spectra of 57 local type Ia supernova host galaxies. We deduce from the spectra the metallicity, current star formation rate, and star formation history of the host and compare these to the supernova decline rates. Additionally, we compare the host properties to the Hubble residuals for each SN. Our results indicate a statistically insignificant correlation in the direction higher metallicity spiral galaxies host fainter type Ia supernovae. However, we present qualitative evidence suggesting progenitor age is more likely than metallicity to be the source of variability in supernova peak luminosities. We do not find a correlation between the supernova decline rate and both host galaxy absolute B magnitude and current/past host galaxy star formation rate. A tenuous correlation is observed between the supernova Hubble residuals and host galaxy metallicities. Finally, we characterize the environmental property distributions for type Ia supernova host galaxies through a comparison with two larger, more general galaxy distributions using Kolmogorov-Smirnov tests. The results show the host galaxy metallicity distribution to be similar to the metallicity distributions of the galaxies of the NFGS and SDSS. Significant differences are observed between the SN Ia distributions of absolute B magnitude and star formation histories and the corresponding distributions of galaxies in the NFGS and SDSS. Among these is an abrupt upper limit observed in the distribution of star formation histories of the host galaxy sample suggesting a type Ia supernovae characteristic delay time lower limit of approximately 2.0 Gyrs. Other distribution discrepancies are investigated and the effect on the supernova properties are discussed.

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arXiv2005

Deep Photometry of GRB 041006 Afterglow: Hypernova Bump at Redshift z=0.716

We present deep optical photometry of the afterglow of gamma-ray burst (GRB) 041006 and its associated hypernova obtained over 65 days after detection (55 R-band epochs on 10 different nights). Our early data (t<4 days) joined with published GCN data indicates a steepening decay, approaching F_nu ~t^{-0.6} at early times (<<1 day) and F_nu ~t^{-1.3} at late times. The break at t_b=0.16+-0.04 days is the earliest reported jet break among all GRB afterglows. During our first night, we obtained 39 exposures spanning 2.15 hours from 0.62 to 0.71 days after the burst that reveal a smooth afterglow, with an rms deviation of 0.024 mag from the local power-law fit, consistent with photometric errors. After t~4 days, the decay slows considerably, and the light curve remains approximately flat at R~24 mag for a month before decaying by another magnitude to reach R~25 mag two months after the burst. This ``bump'' is well-fitted by a k-corrected light curve of SN1998bw, but only if stretched by a factor of 1.38 in time. In comparison with the other GRB-related SNe bumps, GRB 041006 stakes out new parameter space for GRB/SNe, with a very bright and significantly stretched late-time SN light curve. Within a small sample of fairly well observed GRB/SN bumps, we see a hint of a possible correlation between their peak luminosity and their ``stretch factor'', broadly similar to the well-studied Phillips relation for the type Ia supernovae.

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