Person: Challis, Peter
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Challis
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Peter
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Challis, Peter
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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 Optical Spectroscopy of Type Ia Supernovae(IOP Publishing, 2008) Matheson, T.; Kirshner, Robert; Challis, Peter; Jha, S.; Garnavich, P. M.; Berlind, Perry; Calkins, Michael; Blondin, S.; Balog, Z.; Bragg, A. E.; Caldwell, Nelson; Concannon, K. Dendy; Falco, E. E.; Graves, G. J. M.; Huchra, J. P.; Kuraszkiewicz, Joanna; Mader, J. A.; Mahdavi, A.; Phelps, Matthew; Rines, K.; Song, I.; Wilkes, BelindaWe present 432 low-dispersion optical spectra of 32 Type Ia supernovae (SNe Ia) that also have well-calibrated light curves. The coverage ranges from 6 epochs to 36 epochs of spectroscopy. Most of the data were obtained with the 1.5 m Tillinghast telescope at the F. L. Whipple Observatory with typical wavelength coverage of 3700-7400 Å and a resolution of ~7 Å. The earliest spectra are 13 days before B-band maximum; two-thirds of the SNe were observed before maximum brightness. Coverage for some SNe continues almost to the nebular phase. The consistency of the method of observation and the technique of reduction makes this an ideal data set for studying the spectroscopic diversity of SNe Ia.Publication Cosmology With Contaminated Samples: Methods of Measuring Dark Energy With Photometrically Classified Pan-Starrs Supernovae(2016) Berger, Edo; Jones, D.O.; Scolnic, D.M.; Riess, A.G.; Kessler, R.; Kirshner, Robert; Ortega, C.A.; Foley, R.J.; Chornock, R.; Challis, Peter; Burgett, W.S.; Chambers, K.C.; Draper, P.W.; Flewelling, H.; Huber, M.E.; Kaiser, N.; Kudritzki, R.-P.; Metcalfe, N.; Wainscoat, R.J.; Waters, C.The Pan-STARRS (PS1) Medium Deep Survey discovered over 5,000 likely supernovae (SNe) but obtained spectral classifications for just 10% of its SN candidates. We measured spectroscopic host galaxy redshifts for 3,073 of these likely SNe and estimate that ∼1,000 are Type Ia SNe (SNe Ia) with light-curve quality sufficient for a cosmological analysis. We use these data with simulations to determine the impact of core-collapse SN (CC SN) contamination on measurements of the dark energy equation of state parameter, w. Using the method of Bayesian Estimation Applied to Multiple Species (BEAMS), distances to SNe Ia and the contaminating CC SN distribution are simultaneously determined as a function of redshift. We test light-curve based SN classification priors for BEAMS as well as a new classification method that relies upon host galaxy spectra and the association of SN type with host type. By testing several SN classification methods and CC SN parameterizations on 1,000-SN simulations, we conservatively estimate that CC SN contamination gives a systematic error on w (σ CC w ) of 0.014, 30% of the statistical uncertainty. Our best method gives σ CC w = 0.005, just 11% of the statistical uncertainty, but could be affected by incomplete knowledge of the CC SN distribution. Our method determines the SALT2 color and shape coefficients, α and β, with ∼3% bias. Real PS1 SNe without spectroscopic classifications give measurements of w that are within 0.5σ of measurements from PS1 spectroscopically confirmed SNe. Finally, the inferred abundance of bright CC SNe in our sample is greater than expected based on measured CC SN rates and luminosity functions.Publication Zooming in on the progenitors of superluminous supernovae with the HST(IOP Publishing, 2015) Lunnan, R; Chornock, R; Berger, Edo; Rest, A.; Fong, W; Scolnic, D.; Jones, D. O.; Soderberg, Alicia; Challis, Peter; Drout, Maria Rebecca; Foley, R. J.; Huber, M. E.; Kirshner, Robert; Leibler, C.; Marion, G. H.; McCrum, M.; Milisavljevic, Danny; Narayan, Gautham; Sanders, Nathan Edward; Smartt, S. J.; Smith, K. W.; Tonry, J. L.; Burgett, W. S.; Chambers, K. C.; Flewelling, H.; Kudritzki, R.-P.; Wainscoat, R. J.; Waters, C.We present Hubble Space Telescope (HST) rest-frame ultraviolet imaging of the host galaxies of 16 hydrogen-poor superluminous supernovae (SLSNe), including 11 events from the Pan-STARRS Medium Deep Survey. Taking advantage of the superb angular resolution of HST, we characterize the galaxies' morphological properties, sizes, and star formation rate (SFR) densities. We determine the supernova (SN) locations within the host galaxies through precise astrometric matching and measure physical and host-normalized offsets as well as the SN positions within the cumulative distribution of UV light pixel brightness. We find that the host galaxies of H-poor SLSNe are irregular, compact dwarf galaxies, with a median half-light radius of just 0.9 kpc. The UV-derived SFR densities are high ($\langle {{{\Sigma }}_{{\rm SFR}}}\rangle \simeq 0.1{{M}_{\odot }}\;{\rm y}{{{\rm r}}^{-1}}\;{\rm kp}{{{\rm c}}^{-2}}$), suggesting that SLSNe form in overdense environments. Their locations trace the UV light of their host galaxies, with a distribution intermediate between that of long-duration gamma-ray bursts (LGRBs; which are strongly clustered on the brightest regions of their hosts) and a uniform distribution (characteristic of normal core-collapse SNe), though cannot be statistically distinguished from either with the current sample size. Taken together, this strengthens the picture that SLSN progenitors require different conditions than those of ordinary core-collapse SNe to form and that they explode in broadly similar galaxies as do LGRBs. If the tendency for SLSNe to be less clustered on the brightest regions than are LGRBs is confirmed by a larger sample, this would indicate a different, potentially lower-mass progenitor for SLSNe than LRGBs.Publication Toward Characterization of the Type IIP Supernova Progenitor Population: A Statistical Sample of Light Curves from Pan-STARRS1(IOP Publishing, 2015) Sanders, Nathan Edward; Soderberg, Alicia; Gezari, S.; Betancourt, M.; Chornock, R; Berger, Edo; Foley, R. J.; Challis, Peter; Drout, Maria Rebecca; Kirshner, Robert; Lunnan, R; Marion, G. H.; Margutti, Raffaella; McKinnon, R.; Milisavljevic, Danny; Narayan, G.; Rest, A.; Kankare, E.; Mattila, S.; Smartt, S. J.; Huber, M. E.; Burgett, W. S.; Draper, P.W.; Hodapp, K. W.; Kaiser, N.; Kudritzki, R. P.; Magnier, E. A.; Metcalfe, N.; Morgan, J. S.; Price, P. A.; Tonry, J. L.; Wainscoat, R. J.; Waters, C.In recent years, wide-field sky surveys providing deep multiband imaging have presented a new path for indirectly characterizing the progenitor populations of core-collapse supernovae (SNe): systematic light-curve studies. We assemble a set of 76 grizy-band Type IIP SN light curves from Pan-STARRS1, obtained over a constant survey program of 4 yr and classified using both spectroscopy and machine-learning-based photometric techniques. We develop and apply a new Bayesian model for the full multiband evolution of each light curve in the sample. We find no evidence of a subpopulation of fast-declining explosions (historically referred to as "Type IIL" SNe). However, we identify a highly significant relation between the plateau phase decay rate and peak luminosity among our SNe IIP. These results argue in favor of a single parameter, likely determined by initial stellar mass, predominantly controlling the explosions of red supergiants. This relation could also be applied for SN cosmology, offering a standardizable candle good to an intrinsic scatter of lesssim 0.2 mag. We compare each light curve to physical models from hydrodynamic simulations to estimate progenitor initial masses and other properties of the Pan-STARRS1 Type IIP SN sample. We show that correction of systematic discrepancies between modeled and observed SN IIP light-curve properties and an expanded grid of progenitor properties are needed to enable robust progenitor inferences from multiband light-curve samples of this kind. This work will serve as a pathfinder for photometric studies of core-collapse SNe to be conducted through future wide-field transient searches.Publication An Ultraviolet Excess in the Superluminous Supernova Gaia16apd Reveals a Powerful Central Engine(American Astronomical Society, 2017) Nicholl, Matthew; Berger, Edo; Margutti, R; Blanchard, Peter; Milisavljevic, Danny; Challis, Peter; Metzger, B.D.; Chornock, R.Since the discovery of superluminous supernovae (SLSNe) in the last decade, it has been known that these events exhibit bluer spectral energy distributions than other supernova subtypes, with significant output in the ultraviolet. However, the event Gaia16apd seems to outshine even the other SLSNe at rest-frame wavelengths below ∼3000 \AA. Yan et al (2016) have recently presented HST UV spectra and attributed the UV flux to low metallicity and hence reduced line blanketing. Here we present UV and optical light curves over a longer baseline in time, revealing a rapid decline at UV wavelengths despite a typical optical evolution. Combining the published UV spectra with our own optical data, we demonstrate that Gaia16apd has a much hotter continuum than virtually any SLSN at maximum light, but it cools rapidly thereafter and is indistinguishable from the others by ∼10-15 days after peak. Comparing the equivalent widths of UV absorption lines with those of other events, we show that the excess UV continuum is a result of a more powerful central power source, rather than a lack of UV absorption relative to other SLSNe or an additional component from interaction with the surrounding medium. These findings strongly support the central-engine hypothesis for hydrogen-poor SLSNe. An explosion ejecting Mej=4(0.2/κ) M⊙, where κ is the opacity in cm2g−1, and forming a magnetar with spin period P=2 ms, and B=2×1014 G (lower than other SLSNe with comparable rise-times) can consistently explain the light curve evolution and high temperature at peak. The host metallicity, Z=0.18 Z⊙, is comparable to other SLSNe.Publication Metamorphosis of Sn 2014c: Delayed Interaction Between a Hydrogen Poor Core-Collapse Supernova and a Nearby Circumstellar Shell(IOP Publishing, 2015) Milisavljevic, Danny; Margutti, Raffaella; Kamble, Atish; Patnaude, Daniel; Raymond, John; Eldridge, J. J.; Fong, W.; Bietenholz, M.; Challis, Peter; Chornock, R; Drout, Maria Rebecca; Fransson, C.; Fesen, R. A.; Grindlay, Jonathan; Kirshner, Robert; Lunnan, R; Mackey, J.; Miller, George; Parrent, Jerod T.; Sanders, Nathan Edward; Soderberg, Alicia; Zauderer, BWe present optical observations of supernova SN 2014C, which underwent an unprecedented slow metamorphosis from H-poor type Ib to H-rich type IIn over the course of one year. The observed spectroscopic evolution is consistent with the supernova having exploded in a cavity before encountering a massive shell of the progenitor star's stripped hydrogen envelope. Possible origins for the circumstellar shell include a brief Wolf–Rayet fast wind phase that overtook a slower red supergiant wind, eruptive ejection, or confinement of circumstellar material by external influences of neighboring stars. An extended high velocity Hα absorption feature seen in near-maximum light spectra implies that the progenitor star was not completely stripped of hydrogen at the time of core collapse. Archival pre-explosion Subaru Telescope Suprime-Cam and Hubble Space Telescope Wide Field Planetary Camera 2 images of the region obtained in 2009 show a coincident source that is most likely a compact massive star cluster in NGC 7331 that hosted the progenitor system. By comparing the emission properties of the source with stellar population models that incorporate interacting binary stars we estimate the age of the host cluster to be 30–300 Myr, and favor ages closer to 30 Myr in light of relatively strong Hα emission. SN 2014C is the best observed member of a class of core-collapse supernovae that fill the gap between events that interact strongly with dense, nearby environments immediately after explosion and those that never show signs of interaction. Better understanding of the frequency and nature of this intermediate population can contribute valuable information about the poorly understood final stages of stellar evolution.