Person: Calkins, Michael
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Calkins
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Michael
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Calkins, Michael
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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 Rapidly evolving and luminous transients from Pan-STARRS1(IOP Publishing, 2014) Drout, Maria Rebecca; Chornock, R; Soderberg, Alicia; Sanders, Nathan Edward; McKinnon, R.; Rest, Armin; Foley, R. J.; Milisavljevic, Danny; Margutti, Raffaella; Berger, Edo; Calkins, Michael; Fong, W; Gezari, S.; Huber, M. E.; Kankare, E.; Kirshner, Robert; Leibler, C.; Lunnan, R; Mattila, S.; Marion, G. H.; Narayan, Gautham; 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 (SNe) 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 (t 1/2) 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 (g P1 – r P1 lesssim –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 that 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 X‐Ray and Optical Variability in NGC 4051 and the Nature of Narrow‐Line Seyfert 1 Galaxies(IOP Publishing, 2000) Peterson, B. M.; McHardy, I. M.; Wilkes, Belinda; Berlind, Perry; Bertram, R.; Calkins, Michael; Collier, S. J.; Huchra, J. P.; Mathur, S.; Papadakis, I.; Peters, J.; Pogge, R. W.; Romano, P.; Tokarz, S.; Uttley, P.; Vestergaard, M.; Wagner, R. M.We report on the results of a three-year program of coordinated X-ray and optical monitoring of the narrow-line Seyfert 1 galaxy NGC 4051. The rapid continuum variations observed in the X-ray spectra are not detected in the optical, although the time-averaged X-ray and optical continuum fluxes are well correlated. Variations in the flux of the broad Hβ line are found to lag behind the optical continuum variations by 6 days (with an uncertainty of 2-3 days), and combining this with the line width yields a virial mass estimate of ~1.1 × 106 M☉, at the very low end of the distribution of active galactic nucleus masses measured by line reverberation. Strong variability of He II λ4686 is also detected, and the response time measured is similar to that of Hβ but with a much larger uncertainty. The He II λ4686 line is almost 5 times broader than Hβ, and it is strongly blueward asymmetric, as are the high-ionization UV lines recorded in archival spectra of NGC 4051. The data are consistent with the Balmer lines arising in a low-to-moderate-inclination disklike configuration and the high-ionization lines arising in an outflowing wind, of which we observe preferentially the near side. Previous observations of the narrow-line region morphology of this source suggest that the system is inclined by ~50°, and if this is applicable to the broad Hβ-emitting region, a central mass of ~1.4 × 106 M☉ can be inferred. During the third year of monitoring, both the X-ray continuum and the He II λ4686 line went into extremely low states, although the optical continuum and the Hβ broad line were both still present and variable. We suggest that the inner part of the accretion disk may have gone into an advection-dominated state, yielding little radiation from the hotter inner disk.Publication Steps toward Determination of the Size and Structure of the Broad‐Line Region in Active Galactic Nuclei. XVI. A 13 Year Study of Spectral Variability in NGC 5548(IOP Publishing, 2002) Peterson, B. M.; Berlind, Perry; Bertram, R.; Bischoff, K.; Bochkarev, N. G.; Borisov, N.; Burenkov, A. N.; Calkins, Michael; Carrasco, L.; Chavushyan, V. H.; Chornock, R; Dietrich, M.; Doroshenko, V. T.; Ezhkova, O. V.; Filippenko, A. V.; Gilbert, A. M.; Huchra, J. P.; Kollatschny, W.; Leonard, D. C.; Li, W.; Lyuty, V. M.; Malkov, Yu. F.; Matheson, T.; Merkulova, N. I.; Mikhailov, V. P.; Modjaz, M.; Onken, C. A.; Pogge, R. W.; Pronik, V. I.; Qian, B.; Romano, P.; Sergeev, S. G.; Sergeeva, E. A.; Shapovalova, A. I.; Spiridonova, O. I.; Tao, J.; Tokarz, S.; Valdes, J. R.; Vlasiuk, V. V.; Wagner, R. M.; Wilkes, BelindaWe present the final installment of an intensive 13 year study of variations of the optical continuum and broad Hβ emission line in the Seyfert 1 galaxy NGC 5548. The database consists of 1530 optical continuum measurements and 1248 Hβ measurements. The Hβ variations follow the continuum variations closely, with a typical time delay of about 20 days. However, a year-by-year analysis shows that the magnitude of emission-line time delay is correlated with the mean continuum flux. We argue that the data are consistent with the simple model prediction between the size of the broad-line region and the ionizing luminosity, r ∝ Lion. Moreover, the apparently linear nature of the correlation between the Hβ response time and the nonstellar optical continuum Fopt arises as a consequence of the changing shape of the continuum as it varies, specifically Fopt ∝ FUV.