Person: Soderberg, Alicia
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Soderberg
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Alicia
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Soderberg, Alicia
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Publication Cosmological Constraints from Measurements of Type Ia Supernovae Discovered during the First 1.5 yr of the Pan-STARRS1 Survey(IOP Publishing, 2014) Rest, Armin; Scolnic, D.; Foley, R. J.; Huber, M. E.; Chornock, R.; Narayan, Gautham; Tonry, J. L.; Berger, Edo; Soderberg, Alicia; Stubbs, Christopher; Riess, A.; Kirshner, Robert; Smartt, S. J.; Schlafly, E.; Rodney, S.; Botticella, M. T.; Brout, D.; Challis, P.; Czekala, Ian; Drout, Maria Rebecca; Hudson, M. J.; Kotak, R.; Leibler, C.; Lunnan, R; Marion, G. H.; McCrum, M.; Milisavljevic, D.; Pastorello, A.; Sanders, Nathan Edward; Smith, K.; Stafford, E.; Thilker, D.; Valenti, S.; Wood-Vasey, W. M.; Zheng, Z.; Burgett, W. S.; Chambers, K. C.; Denneau, L.; Draper, P. W.; Flewelling, H.; Hodapp, K. W.; Kaiser, N.; Kudritzki, R.-P.; Magnier, E. A.; Metcalfe, N.; Price, P. A.; Sweeney, W.; Wainscoat, R.; Waters, C.We present griz P1 light curves of 146 spectroscopically confirmed Type Ia supernovae (SNe Ia; 0.03 < z < 0.65) discovered during the first 1.5 yr of the Pan-STARRS1 Medium Deep Survey. The Pan-STARRS1 natural photometric system is determined by a combination of on-site measurements of the instrument response function and observations of spectrophotometric standard stars. We find that the systematic uncertainties in the photometric system are currently 1.2% without accounting for the uncertainty in the Hubble Space Telescope Calspec definition of the AB system. A Hubble diagram is constructed with a subset of 113 out of 146 SNe Ia that pass our light curve quality cuts. The cosmological fit to 310 SNe Ia (113 PS1 SNe Ia + 222 light curves from 197 low-z SNe Ia), using only supernovae (SNe) and assuming a constant dark energy equation of state and flatness, yields $w=-1.120^{+0.360}_{-0.206}\hbox{(Stat)} ^{+0.269}_{-0.291}\hbox{(Sys)}$. When combined with BAO+CMB(Planck)+H 0, the analysis yields $\Omega _{\rm M}=0.280^{+0.013}_{-0.012}$ and $w=-1.166^{+0.072}_{-0.069}$ including all identified systematics. The value of w is inconsistent with the cosmological constant value of –1 at the 2.3σ level. Tension endures after removing either the baryon acoustic oscillation (BAO) or the H 0 constraint, though it is strongest when including the H 0 constraint. If we include WMAP9 cosmic microwave background (CMB) constraints instead of those from Planck, we find $w=-1.124^{+0.083}_{-0.065}$, which diminishes the discord to <2σ. We cannot conclude whether the tension with flat ΛCDM is a feature of dark energy, new physics, or a combination of chance and systematic errors. The full Pan-STARRS1 SN sample with ~three times as many SNe should provide more conclusive results.Publication A Search for Fast Optical Transients in the Pan-STARRS1 Medium-Deep Survey: M-Dwarf Flares, Asteroids, Limits on Extragalactic Rates, and Implications for LSST(American Astronomical Society, 2013) Berger, Edo; Leibler, C. N.; Chornock, R; Rest, A.; Foley, R. J.; Soderberg, Alicia; Price, P. A.; Burgett, W. S.; Chambers, K. C.; Flewelling, H.; Huber, M. E.; Magnier, E. A.; Metcalfe, N.; Stubbs, Christopher; Tonry, J. L.We present a search for fast optical transients (τ ~ 0.5 hr-1 day) using repeated observations of the Pan-STARRS1 Medium-Deep Survey (PS1/MDS) fields. Our search takes advantage of the consecutive g P1 r P1 observations (16.5 minutes in each filter), by requiring detections in both bands, with non-detections on preceding and subsequent nights. We identify 19 transients brighter than 22.5 AB mag (S/N gsim 10). Of these, 11 events exhibit quiescent counterparts in the deep PS1/MDS templates that we identify as M4-M9 dwarfs at d ≈ 0.2-1.2 kpc. The remaining eight transients lack quiescent counterparts, exhibit mild but significant astrometric shifts between the g P1 and r P1 images, colors of (g – r)P1 ≈ 0.5-0.8 mag, non-varying light curves, and locations near the ecliptic plane with solar elongations of about 130°, which are all indicative of main-belt asteroids near the stationary point of their orbits. With identifications for all 19 transients, we place an upper limit of R FOT(τ ~ 0.5 hr) lsim 0.12 deg–2 day–1 (95% confidence level) on the sky-projected rate of extragalactic fast transients at lsim 22.5 mag, a factor of 30-50 times lower than previous limits; the limit for a timescale of ~1 day is R FOT lsim 2.4 × 10–3 deg–2 day–1. To convert these sky-projected rates to volumetric rates, we explore the expected peak luminosities of fast optical transients powered by various mechanisms, and find that non-relativistic events are limited to M ≈ –10 to ≈ – 14 mag for a timescale of ~0.5 hr to ~1 day, while relativistic sources (e.g., gamma-ray bursts, magnetar-powered transients) can reach much larger luminosities. The resulting volumetric rates are lsim 13 Mpc–3 yr–1 (M ≈ –10 mag), lsim 0.05 Mpc–3 yr–1 (M ≈ –14 mag), and lsim 10–6 Mpc–3 yr–1 (M ≈ –24 mag), significantly above the nova, supernova, and gamma-ray burst rates, respectively, indicating that much larger surveys are required to provide meaningful constraints. Motivated by the results of our search, we discuss strategies for identifying fast optical transients in the Large Synoptic Survey Telescope main survey, and reach the optimistic conclusion that the veil of foreground contaminants can be lifted with the survey data, without the need for expensive follow-up observations.Publication Slowly Fading Super-Luminous Supernovae That Are Not Pair-Instability Explosions(Nature Publishing Group, 2013) Nicholl, M.; Smartt, S. J.; Jerkstrand, A.; Inserra, C.; McCrum, M.; Kotak, R.; Fraser, M.; Wright, D.; Chen, T.-W.; Smith, K.; Young, D. R.; Sim, S. A.; Valenti, S.; Howell, D. A.; Bresolin, F.; Kudritzki, R. P.; Tonry, J. L.; Huber, M. E.; Rest, A.; Pastorello, A.; Tomasella, L.; Cappellaro, E.; Benetti, S.; Mattila, S.; Kankare, E.; Kangas, T.; Leloudas, G.; Sollerman, J.; Taddia, F.; Berger, E.; Chornock, R; Narayan, Gautham; Stubbs, Christopher; Foley, R. J.; Lunnan, R; Soderberg, Alicia; Sanders, Nathan Edward; Milisavljevic, Danny; Margutti, Raffaella; Kirshner, Robert; Elias-Rosa, N.; Morales-Garoffolo, A.; Taubenberger, S.; Botticella, M. T.; Gezari, S.; Urata, Y.; Rodney, S.; Riess, A. G.; Scolnic, D.; Wood-Vasey, W. M.; Burgett, W. S.; Chambers, K.; Flewelling, H. A.; Magnier, E. A.; Kaiser, N.; Metcalfe, N.; Morgan, J.; Price, P. A.; Sweeney, W.; Waters, C.Super-luminous supernovae that radiate more than 10\(^{44}\) ergs per second at their peak luminosity have recently been discovered in faint galaxies at redshifts of 0.1–4. Some evolve slowly, resembling models of ‘pair-instability’ supernovae. Such models involve stars with original masses 140–260 times that of the Sun that now have carbon–oxygen cores of 65–130 solar masses. In these stars, the photons that prevent gravitational collapse are converted to electron–positron pairs, causing rapid contraction and thermonuclear explosions. Many solar masses of \(^{56}\)Ni are synthesized; this isotope decays to \(^{56}\)Fe via \(^{56}\)Co, powering bright light curves. Such massive progenitors are expected to have formed from metal-poor gas in the early Universe. Recently, supernova 2007bi in a galaxy at redshift 0.127 (about 12 billion years after the Big Bang) with a metallicity one-third that of the Sun was observed to look like a fading pair-instability supernova. Here we report observations of two slow-to-fade super-luminous supernovae that show relatively fast rise times and blue colours, which are incompatible with pair-instability models. Their late-time light-curve and spectral similarities to supernova 2007bi call the nature of that event into question. Our early spectra closely resemble typical fast-declining super-luminous supernovae, which are not powered by radioactivity. Modelling our observations with 10–16 solar masses of magnetar-energized ejecta demonstrates the possibility of a common explosion mechanism. The lack of unambiguous nearby pair-instability events suggests that their local rate of occurrence is less than 6 × 10\(^{−6}\) times that of the core-collapse rate.Publication PS1-10afx at z = 1.388: Pan-STARRS1 Discovery of a New Type of Superluminous Supernova(American Astronomical Society, 2013) Chornock, R; Berger, Edo; Rest, A.; Milisavljevic, Danny; Lunnan, R; Foley, R. J.; Soderberg, Alicia; Smartt, S. J.; Burgasser, A. J.; Challis, Peter; Chomiuk, L.; Czekala, Ian; Drout, Maria Rebecca; Fong, W; Huber, M. E.; Kirshner, Robert; Leibler, C.; McLeod, Brian; Marion, G. H.; Narayan, Gautham; Riess, A. G.; Roth, K. C.; Sanders, Nathan Edward; Scolnic, D.; Smith, K.; Stubbs, Christopher; Tonry, J. L.; Valenti, S.; Burgett, W. S.; Chambers, K. C.; Hodapp, K. W.; Kaiser, N.; Kudritzki, R.-P.; Magnier, E. A.; Price, P. A.We present the Pan-STARRS1 discovery of PS1-10afx, a unique hydrogen-deficient superluminous supernova (SLSN) at redshift z = 1.388. The light curve peaked at z P1 = 21.7 mag, making PS1-10afx comparable to the most luminous known SNe, with Mu = –22.3 mag. Our extensive optical and near-infrared observations indicate that the bolometric light curve of PS1-10afx rose on the unusually fast timescale of ~12 days to the extraordinary peak luminosity of 4.1 × 1044 erg s–1 (M bol = –22.8 mag) and subsequently faded rapidly. Equally important, the spectral energy distribution is unusually red for an SLSN, with a color temperature of ~6800 K near maximum light, in contrast to previous hydrogen-poor SLSNe, which are bright in the ultraviolet (UV). The spectra more closely resemble those of a normal SN Ic than any known SLSN, with a photospheric velocity of ~11, 000 km s–1 and evidence for line blanketing in the rest-frame UV. Despite the fast rise, these parameters imply a very large emitting radius (gsim 5 × 1015 cm). We demonstrate that no existing theoretical model can satisfactorily explain this combination of properties: (1) a nickel-powered light curve cannot match the combination of high peak luminosity with the fast timescale; (2) models powered by the spindown energy of a rapidly rotating magnetar predict significantly hotter and faster ejecta; and (3) models invoking shock breakout through a dense circumstellar medium cannot explain the observed spectra or color evolution. The host galaxy is well detected in pre-explosion imaging with a luminosity near L*, a star formation rate of ~15 M ☉ yr–1, and is fairly massive (~2 × 1010 M ☉), with a stellar population age of ~108 yr, also in contrast to the young dwarf hosts of known hydrogen-poor SLSNe. PS1-10afx is distinct from known examples of SLSNe in its spectra, colors, light-curve shape, and host galaxy properties, suggesting that it resulted from a different channel than other hydrogen-poor SLSNe.Publication Rapidly-Evolving and Luminous Transients From Pan-Starrs1(IOP Publishing, 2014) Drout, M. R.; Chornock, R.; Soderberg, Alicia; Sanders, Nathan Edward; McKinnon, R.; Rest, A.; Foley, R. J.; Milisavljevic, Danny; Margutti, R.; Berger, Edo; Calkins, M.; Fong, W.; Gezari, S.; Huber, M. E.; Kankare, E.; Kirshner, R. P.; Leibler, C.; Lunnan, R.; Mattila, S.; Marion, G. H.; Narayan, G.; Riess, A. G.; Roth, K. C.; Scolnic, D.; Smartt, S. J.; Tonry, J. L.; Burgett, W. S.; Chambers, K. C.; Hodapp, K. W.; Jedicke, R.; Kaiser, N.; Magnier, E. A.; Metcalfe, N.; Morgan, J. S.; Price, P. A.; Waters, C.In the past decade, several rapidly-evolving transients have been discovered whose timescales and luminosities are not easily explained by traditional supernovae (SN) models. The sample size of these objects has remained small due, at least in part, to the challenges of detecting short timescale transients with traditional survey cadences. Here we present the results from a search within the Pan-STARRS1 Medium Deep Survey (PS1-MDS) for rapidly-evolving and luminous transients. We identify 10 new transients with a time above half-maximum (t1/2) of less than 12 days and −16.5 > M > −20 mag. This increases the number of known events in this region of SN phase space by roughly a factor of three. The median redshift of the PS1-MDS sample is z=0.275 and they all exploded in star forming galaxies. In general, the transients possess faster rise than decline timescale and blue colors at maximum light (gP1 − rP1 . −0.2). Best fit blackbodies reveal photospheric temperatures/radii that expand/cool with time and explosion spectra taken near maximum light are dominated by a blue continuum, consistent with a hot, optically thick, ejecta. We find it difficult to reconcile the short timescale, high peak luminosity (L > 1043 erg s−1), and lack of UV line blanketing observed in many of these transients with an explosion powered mainly by the radioactive decay of 56Ni. Rather, we find that many are consistent with either (1) cooling envelope emission from the explosion of a star with a low-mass extended envelope which ejected very little (<0.03 M⊙) radioactive material, or (2) a shock breakout within a dense, optically thick, wind surrounding the progenitor star. After calculating the detection efficiency for objects with rapid timescales in the PS1-MDS we find a volumetric rate of 4800 − 8000 events yr−1 Gpc−3 (4 − 7% of the core-collapse SN rate at z=0.2).Publication An Ultraviolet–Optical Flare from the Tidal Disruption of a Helium-Rich Stellar Core(Nature Publishing Group, 2012) Gezari, S.; Chornock, R; Rest, A.; Huber, M. E.; Forster, K.; Berger, Edo; Challis, Peter J.; Neill, J. D.; Martin, D. C.; Heckman, T.; Lawrence, A.; Norman, C.; Narayan, Gautham; Foley, R. J.; Marion, G. H.; Scolnic, D.; Chomiuk, Laura; Soderberg, Alicia; Smith, K.; Kirshner, Robert; Riess, A. G.; Smartt, S. J.; Stubbs, Christopher; Tonry, J. L.; Wood-Vasey, W. M.; Burgett, W. S.; Chambers, K. C.; Grav, T.; Heasley, J. N.; Kaiser, N.; Kudritzki, R.-P.; Magnier, E. A.; Morgan, J. S.; Price, P. A.The flare of radiation from the tidal disruption and accretion of a star can be used as a marker for supermassive black holes that otherwise lie dormant and undetected in the centres of distant galaxies1. Previous candidate flares2, 3, 4, 5, 6 have had declining light curves in good agreement with expectations, but with poor constraints on the time of disruption and the type of star disrupted, because the rising emission was not observed. Recently, two ‘relativistic’ candidate tidal disruption events were discovered, each of whose extreme X-ray luminosity and synchrotron radio emission were interpreted as the onset of emission from a relativistic jet7, 8, 9, 10. Here we report a luminous ultraviolet–optical flare from the nuclear region of an inactive galaxy at a redshift of 0.1696. The observed continuum is cooler than expected for a simple accreting debris disk, but the well-sampled rise and decay of the light curve follow the predicted mass accretion rate and can be modelled to determine the time of disruption to an accuracy of two days. The black hole has a mass of about two million solar masses, modulo a factor dependent on the mass and radius of the star disrupted. On the basis of the spectroscopic signature of ionized helium from the unbound debris, we determine that the disrupted star was a helium-rich stellar core.Publication Pan-STARRS1 Discovery of Two Ultraluminous Supernovae at z ≈ 0.9(IOP Publishing, 2011) Chomiuk, Laura; Chornock, R; Soderberg, Alicia; Berger, Edo; Chevalier, R. A.; Foley, R. J.; Huber, M. E.; Narayan, Gautham; Rest, A.; Gezari, S.; Kirshner, Robert; Riess, A.; Rodney, S. A.; Smartt, S. J.; Stubbs, Christopher; Tonry, J. L.; Wood-Vasey, W. M.; Burgett, W. S.; Chambers, K. C.; Czekala, Ian; Flewelling, H.; Forster, K.; Kaiser, N.; Kudritzki, R.-P.; Magnier, E. A.; Martin, D. C.; Morgan, J. S.; Neill, J. D.; Price, P. A.; Roth, K. C.; Sanders, Nathan Edward; Wainscoat, R. J.We present the discovery of two ultraluminous supernovae (SNe) at z ≈ 0.9 with the Pan-STARRS1 Medium Deep Survey. These SNe, PS1-10ky and PS1-10awh, are among the most luminous SNe ever discovered, comparable to the unusual transients SN 2005ap and SCP 06F6. Like SN 2005ap and SCP 06F6, they show characteristic high luminosities (M bol ≈ –22.5 mag), blue spectra with a few broad absorption lines, and no evidence for H or He. We have constructed a full multi-color light curve sensitive to the peak of the spectral energy distribution in the rest-frame ultraviolet, and we have obtained time series spectroscopy for these SNe. Given the similarities between the SNe, we combine their light curves to estimate a total radiated energy over the course of explosion of (0.9-1.4) × 1051 erg. We find photospheric velocities of 12,000-19,000 km s–1 with no evidence for deceleration measured across ~3 rest-frame weeks around light curve peak, consistent with the expansion of an optically thick massive shell of material. We show that, consistent with findings for other ultraluminous SNe in this class, radioactive decay is not sufficient to power PS1-10ky, and we discuss two plausible origins for these events: the initial spin-down of a newborn magnetar in a core-collapse SN, or SN shock breakout from the dense circumstellar wind surrounding a Wolf-Rayet star.Publication Systematic Uncertainties Associated with the Cosmological Analysis of the First Pan-STARRS1 Type Ia Supernova Sample(IOP Publishing, 2014) Scolnic, D.; Rest, A.; Riess, A.; Huber, M. E.; Foley, R. J.; Brout, D.; Chornock, R.; Narayan, G.; Tonry, J. L.; Berger, Edo; Soderberg, Alicia; Stubbs, Christopher; Kirshner, Robert; Rodney, S.; Smartt, S. J.; Schlafly, E.; Botticella, M. T.; Challis, P.; Czekala, I.; Drout, M.; Hudson, M. J.; Kotak, R.; Leibler, C.; Lunnan, R.; Marion, G. H.; McCrum, M.; Milisavljevic, Danny; Pastorello, A.; Sanders, Nathan Edward; Smith, K.; Stafford, E.; Thilker, D.; Valenti, S.; Wood-Vasey, W. M.; Zheng, Z.; Burgett, W. S.; Chambers, K. C.; Denneau, L.; Draper, P. W.; Flewelling, H.; Hodapp, K. W.; Kaiser, N.; Kudritzki, R.-P.; Magnier, E. A.; Metcalfe, N.; Price, P. A.; Sweeney, W.; Wainscoat, R.; Waters, C.We probe the systematic uncertainties from the 113 Type Ia supernovae (SN Ia) in the Pan-STARRS1 (PS1) sample along with 197 SN Ia from a combination of low-redshift surveys. The companion paper by Rest et al. (2013) describes the photometric measurements and cosmological inferences from the PS1 sample. The largest systematic uncertainty stems from the photometric calibration of the PS1 and low-z samples. We increase the sample of observed Calspec standards from 7 to 10 used to define the PS1 calibration system. The PS1 and SDSS-II calibration systems are compared and discrepancies up to ∼ 0.02 mag are recovered. We find uncertainties in the proper way to treat intrinsic colors and reddening produce differences in the recovered value of w up to 3%. We estimate masses of host galaxies of PS1 supernovae and detect an insignificant difference in distance residuals of the full sample of 0.037±0.031 mag for host galaxies with high and low masses. Assuming flatness and including systematic uncertainties in our analysis of only SNe measurements, we find w =−1.120+0.360 −0.206(Stat)+0.269 −0.291(Sys). With additional constraints from BAO, CMB (Planck) and H0 measurements, we find w = −1.166+0.072 −0.069 and Ωm = 0.280+0.013 −0.012 (statistical and systematic errors added in quadrature). Significance of the inconsistency with w = −1 depends on whether we use Planck or WMAP measurements of the CMB: wBAO+H0+SN+WMAP = −1.124+0.083−0.065.Publication Metallicity in the Grb 100316d/sn 2010bh Host Complex(IOP Publishing, 2011) Levesque, Emily M.; Berger, Edo; Soderberg, Alicia; Chornock, RThe recent long-duration GRB 100316D, associated with supernova SN 2010bh and detected by Swift, is one of the nearest GRB-SNe ever observed (z = 0.059). This provides us with a unique opportunity to study the explosion environment on ∼ kpc scale in relation to the host galaxy complex. Here we present spatially-resolved spectrophotometry of the host galaxy, focusing on both the explosion site and the brightest star-forming regions. Using these data, we extract the spatial profiles of the relevant emission features (Hα, Hβ, [OIII]λ5007, and [NII]λ6584), and use these profiles to examine variations in metallicity and star formation rate as a function of position in the host galaxy. We conclude that GRB 100316D/SN2010bh occurred in a low-metallicity host galaxy, and that the GRB-SN explosion site corresponds to the region with the lowest metallicity and highest star formation rate sampled by our observations.Publication A photometric redshift of Z - 9.4 for GRB 090429B(IOP Publishing, 2011) Cucchiara, A.; Levan, A. J.; Fox, D. B.; Tanvir, N. R.; Ukwatta, T. N.; Berger, Edo; Krühler, T.; Yoldas, A. Küpcü; Wu, X. F.; Toma, K.; Greiner, J.; E. Olivares, F.; Rowlinson, A.; Amati, L.; Sakamoto, T.; Roth, K.; Stephens, A.; Fritz, Alexander; Fynbo, J. P. U.; Hjorth, J.; Malesani, D.; Jakobsson, P.; Wiersema, K.; O, P. T.; Soderberg, Alicia; Foley, R. J.; Fruchter, A. S.; Rhoads, J.; Rutledge, R. E.; Schmidt, B. P.; Dopita, M. A.; Podsiadlowski, P.; Willingale, R.; Wolf, C.; Kulkarni, S. R.; D’Avanzo, P.Gamma-ray bursts (GRBs) serve as powerful probes of the early Universe, with their luminous afterglows revealing the locations and physical properties of star forming galaxies at the highest redshifts, and potentially locating first generation (Population III) stars. Since GRB afterglows have intrinsically very simple spectra, they allow robust redshifts from low signal to noise spectroscopy, or photometry. Here we present a photometric redshift of z ∼ 9.4 for the Swift detected GRB 090429B based on deep observations with Gemini-North, the Very Large Telescope, and the GRB Optical and Near-infrared Detector. Assuming an Small Magellanic Cloud dust law (which has been found in a majority of GRB sight-lines), the 90% likelihood range for the redshift is 9.06 < z < 9.52, although there is a low-probability tail to somewhat lower redshifts. Adopting Milky Way or Large Magellanic Cloud dust laws leads to very similar conclusions, while a Maiolino law does allow somewhat lower redshift solutions, but in all cases the most likely redshift is found to be z > 7. The non-detection of the host galaxy to deep limits (Y (AB) ∼ 28, which would correspond roughly to 0.001L∗ at z = 1) in our late time optical and infrared observations with the Hubble Space Telescope, strongly supports the extreme redshift origin of GRB 090429B, since we would expect to have detected any low-z galaxy, even if it were highly dusty. Finally, the energetics of GRB 090429B are comparable to those of other GRBs, and suggest that its progenitor is not greatly different to those of lower redshift bursts.