CV & Publications

{Young} A  J, {Lee} J  C, {Fabian} A  C, {Reynolds} C  S, {Gibson} R  R, {Canizares} C  R. {A Chandra HETGS Spectral Study of the Iron K Bandpass in MCG-6-30-15: A Narrow View of the Broad Iron Line}, in The X-ray Universe 2005. Vol 604. ; 2006 :475.Abstract
{Evans} D  A, {Lee} J  C, {Kamenetska} M, {Gallagher} S  C, {Kraft} R  P, {Hardcastle} M  J, {Weaver} K  A. {The Chandra, Hubble Space Telescope, and VLA View of the Circumnuclear Extended Emission in the Narrow Emission Line Galaxy NGC 2110}. \apj. 2006;653 :1121-1128.Abstract

{We present results from new Chandra, archival Hubble Space Telescope (HST), and VLA imaging observations of the circumnuclear extended emission in the nearby Type 2 Seyfert galaxy NGC 2110. We find resolved soft-band X-ray emission \~{}4'' (\~{}160 pc) north of the nucleus, which is spatially coincident with [O III] emission, but lies just beyond the northern edge of the radio jet in the source. We find that shock heating of multiphase gas clouds can successfully account for this extended emission, although we cannot rule out alternative models, such as the scattering of nuclear radiation by ionized material, or pure photoionization from the nucleus. In addition, we detect kiloparsec-scale (\~{}30'') extended soft-band X-ray emission south of the nucleus. Finally, we compare our results for NGC 2110 with the prototypical type 2 Seyfert galaxy NGC 1068, and suggest that different physical processes could produce extended circumnuclear X-ray emission in Seyfert galaxies. }

{Lee} J  C, {Ravel} B. {Determining the Grain Composition of the Interstellar Medium with High-Resolution X-Ray Spectroscopy}. \apj. 2005;622 :970-976.Abstract

{We investigate the ability of high-resolution X-ray spectroscopy to directly probe the grain composition of the interstellar medium. Using iron K-edge experimental data of likely ISM dust candidates taken at the National Synchrotron Light Source at Brookhaven National Laboratory and the Advanced Photon Source at Argonne National Laboratory, we explore the prospects for determining the chemical composition of astrophysical dust and discuss a technique for doing so. Focusing on the capabilities of the Astro-E2 XRS microcalorimeters, we assess the limiting effects of spectral resolution and noise for detecting significant X-ray absorption fine structure signal in astrophysical environments containing dust. We find that given sufficient signal, the resolution of the XRS will allow us to definitively distinguish gas-phase from dust-phase absorption and certain chemical compositions. }

{Gibson} R  R, {Marshall} H  L, {Canizares} C  R, {Lee} J  C. {The High-Resolution X-Ray Spectrum of MR 2251-178 Obtained with the Chandra HETGS}. \apj. 2005;627 :83-96.Abstract

{The QSO MR 2251-178 was observed with the Chandra High Energy Transmission Grating Spectrometer (HETGS) at a 2-10 keV luminosity of 2.41{\times}10$^{44}$ ergs s$^{-1}$ (using H₀=72 km s$^{-1}$ Mpc$^{-1}$). We observe the source in a relatively low state. The light curve shows no evidence of variability. We present the zero-order image of MR 2251-178 and compare it to previous observations. We find evidence of a highly ionized, high-velocity outflow, which we detect in a resolved Fe XXVI Ly{$\alpha$} absorption line. The outflow appears to have a large mass and kinetic energy flux compared to the estimated nuclear accretion rate and luminosity. We examine the possibility that other absorption features in the spectrum are associated with the high-velocity outflow. We detect a narrow Fe K{$\alpha$} line and resolved forbidden line emission from Ne IX and O VII. Modeling the emitting material enables us to constrain its properties and conclude that it is not along our line of sight. }

{Scott} J  E, {Kriss} G  A, {Lee} J  C, {Quijano} J  K, {Brotherton} M, {Canizares} C  R, {Green} R  F, {Hutchings} J, {Kaiser} M  E, {Marshall} H, et al. {Intrinsic Absorption in the Spectrum of NGC 7469: Simultaneous Chandra, FUSE, and STIS Observations}. \apj. 2005;634 :193-209.Abstract

{We present simultaneous X-ray, far-ultraviolet, and near-ultraviolet spectra of the Seyfert 1 galaxy NGC 7469 obtained with the Chandra X-Ray Observatory, the Far Ultraviolet Spectroscopic Explorer, and the Space Telescope Imaging Spectrograph on the Hubble Space Telescope. Previous nonsimultaneous observations of this galaxy found two distinct UV absorption components, at -560 and -1900 km s$^{-1}$, with the former as the likely counterpart of the X-ray absorber. We confirm these two absorption components in our new UV observations, in which we detect prominent O VI, Ly{$\alpha$}, N V, and C IV absorption. In our Chandra spectrum we detect O VIII emission, but no significant O VIII or O VII absorption. We also detect a prominent Fe K{$\alpha$} emission line in the Chandra spectrum, as well as absorption due to hydrogen-like and helium-like neon, magnesium, and silicon at velocities consistent with the -560 km s$^{-1}$ UV absorber. The FUSE and STIS data reveal that the H I and C IV column densities in this UV- and X-ray-absorbing component have increased over time, as the UV continuum flux decreased. We use measured H I, N V, C IV, and O VI column densities to model the photoionization state of both absorbers self-consistently. We confirm the general physical picture of the outflow in which the low-velocity component is a highly ionized, high-density absorber with a total column density of 10$^{20}$ cm$^{-2}$, located near the broad emission-line region, although due to measurable columns of N V and C IV, we assign it a somewhat smaller ionization parameter than found previously, U\~{}1. The high-velocity UV component is of lower densit

{Lee} J  C, {Ravel} B. {Determining the Grain Composition of the Interstellar Medium with High-Resolution X-Ray Spectroscopy}. \apj. 2005;622 :970-976.Abstract

{We investigate the ability of high-resolution X-ray spectroscopy to directly probe the grain composition of the interstellar medium. Using iron K-edge experimental data of likely ISM dust candidates taken at the National Synchrotron Light Source at Brookhaven National Laboratory and the Advanced Photon Source at Argonne National Laboratory, we explore the prospects for determining the chemical composition of astrophysical dust and discuss a technique for doing so. Focusing on the capabilities of the Astro-E2 XRS microcalorimeters, we assess the limiting effects of spectral resolution and noise for detecting significant X-ray absorption fine structure signal in astrophysical environments containing dust. We find that given sufficient signal, the resolution of the XRS will allow us to definitively distinguish gas-phase from dust-phase absorption and certain chemical compositions. }

{Iwasawa} K, {Lee} J  C, {Young} A  J, {Reynolds} C  S, {Fabian} A  C. {The hard X-ray spectrum of the Seyfert galaxy IRAS 18325-5926: reflection from an ionized disc and variable iron K emission}. \mnras. 2004;347 :411-420.Abstract

{We report our analysis of the X-ray spectra of the Seyfert galaxy IRAS 18325-5926 (= Fairall 49) obtained from various X-ray observatories prior to XMM-Newton, including new results from two RXTE and one BeppoSAX observations. A relatively steep continuum slope ({$\Gamma$}\~{}= 2.2) in the 2-15 keV band is confirmed. The continuum spectrum observed with the BeppoSAX PDS shows a possible roll-over at energies above 30 keV, indicating a Comptonizing corona cooler than in other Seyfert nuclei. The X-ray spectrum above 2 keV is best explained with a model including reflection from a highly ionized disc with significant relativistic blurring. The iron K{$\alpha$} emission feature is then mainly due to FeXXV. The seven recent observations show that the iron K emission flux appears to follow the continuum between the observations separated by a few months to years, although some exceptions suggest that the linestrength may be determined in a more complex way. }

{Scott} J  E, {Kriss} G  A, {Lee} J  C, {Arav} N, {Ogle} P, {Roraback} K, {Weaver} K, {Alexander} T, {Brotherton} M, {Green} R  F, et al. {Intrinsic Absorption in the Spectrum of Markarian 279: Simultaneous Chandra, FUSE, and STIS Observations}. \apjs. 2004;152 :1-27.Abstract

{We present a study of the intrinsic X-ray and far-ultraviolet absorption in the Seyfert 1.5 galaxy Markarian 279 using simultaneous observations from the Chandra X-ray Observatory, the Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope, and the Far Ultraviolet Spectroscopic Explorer (FUSE). We also present FUSE observations made at three additional epochs. We detect the Fe K{$\alpha$} emission line in the Chandra spectrum, and its flux is consistent with the low X-ray continuum flux level of Mrk 279 at the time of the observation. Because of low signal-to-noise ratios (S/N) in the Chandra spectrum, no O VII or O VIII absorption features are observable in the Chandra data, but the UV spectra reveal strong and complex absorption from H I and high-ionization species such as O VI, N V, and C IV, as well as from low-ionization species such as C III, N III, C II, and N II in some velocity components. The far-UV spectral coverage of the FUSE data provides information on high-order Lyman series absorption, which we use to calculate the optical depths and line and continuum covering fractions in the intrinsic H I absorbing gas in a self-consistent fashion. The UV continuum flux of Mrk 279 decreases by a factor of \~{}7.5 over the time spanning these observations and we discuss the implications of the response of the absorption features to this change. From arguments based on the velocities, profile shapes, covering fractions and variability of the UV absorption, we conclude that some of the absorption components, particularly those showing prominent low-ionization lines, are likely associated with the host galaxy of Mrk 279, and possibly with its interaction with a close companion galaxy, while the remainder arises in a nuclear outflow. }

{Turner} A  K, {Fabian} A  C, {Vaughan} S, {Lee} J  C. {A softer look at MCG-6-30-15 with XMM-Newton}. Nuclear Physics B Proceedings Supplements. 2004;132 :135-140.Abstract

{We summarise the initial results from an analysis of a 320 ks observation of the Seyfert 1 galaxy MCG-6-30-15 with the Reflection Grating Spectrometer on-board XMM-Newton. }

{Turner} A  K, {Fabian} A  C, {Lee} J  C, {Vaughan} S. {The soft X-ray absorption lines of the Seyfert 1 galaxy MCG-6-30-15}. \mnras. 2004;353 :319-328.Abstract

{The absorption lines in the soft X-ray spectrum of MCG-6-30-15 are studied using the reflection grating spectrometer data from the 2001 XMM-Newton 320-ks observation. A line search of the full time-averaged spectrum reveals 51 absorption lines and one emission line. The equivalent widths of the lines are measured and the majority of the lines identified. We find lines produced by a broad range of charge states for several elements, including almost all the charge states of oxygen and iron, suggesting a broad range of ionization parameters is present in the warm absorber. The equivalent widths of the lines are broadly consistent with the best-fitting warm absorber models from Turner et al. The equivalent widths of the absorption lines allow confidence limits on the column density of the species to be determined. For OVII, a column density of 10$^{18.36}$-10$^{18.86}$ cm$^{-2}$ is found. This column density of OVII, when combined with the inferred FeI absorption, is sufficient to explain the drop in flux at 0.7 keV as being due to absorption from the warm absorber. Fitting OI K-edge absorption to the spectrum reveals a column of 10$^{17.51}$-10$^{17.67}$ cm$^{-2}$ of OI, suggesting an Fe:O ratio of \~{}1:2, consistent with the neutral iron being in the form of iron oxide dust. Variability is seen in a few absorption lines, but the majority of the absorption features, including the prominent absorption edges, stay constant throughout the observation despite variability in the continuum flux. }

{Ogle} P  M, {Brookings} T, {Canizares} C  R, {Lee} J  C, {Marshall} H  L. {Testing the Seyfert unification theory: Chandra HETGS observations of NGC 1068}. \aap. 2003;402 :849-864.Abstract

{We present spatially resolved Chandra HETGS observations of the Seyfert 2 galaxy NGC 1068. X-ray imaging and high resolution spectroscopy are used to test the Seyfert unification theory. Fe Kalpha emission is concentrated in the nuclear region, as are neutral and ionized continuum reflection. This is consistent with reprocessing of emission from a luminous, hidden X-ray source by the obscuring molecular torus and X-ray narrow-line region (NLR). We detect extended hard X-ray emission surrounding the X-ray peak in the nuclear region, which may come from the outer portion of the torus. Detailed modeling of the spectrum of the X-ray NLR confirms that it is excited by photoionization and photoexcitation from the hidden X-ray source. K-shell emission lines from a large range of ionization states of H-like and He-like N, O, Ne, Mg, Al, Si, S, and Fe Xvii-XXIV L-shell emission lines are modeled. The emission measure distribution indicates roughly equal masses at all observed ionization levels in the range log xi = 1-3. We separately analyze the spectrum of an off-nuclear cloud. We find that it has a lower column density than the nuclear region, and is also photoionized. The nuclear X-ray NLR column density, optical depth, outflow velocity, and electron temperature are all consistent with values predicted by optical spectropolarimetry for the region which provides a scattered view of the hidden Seyfert 1 nucleus. }

{Schulz} N  S, {Canizares} C  R, {Lee} J  C, {Sako} M. {The Ionized Stellar Wind in Vela X-1 during Eclipse}. \apjl. 2002;564 :L21-L25.Abstract

{We present a first analysis of a high-resolution X-ray spectrum of the ionized stellar wind of Vela X-1 during eclipse. The data were obtained with the High-Energy Transmission Grating Spectrometer on board the Chandra X-Ray Observatory. The spectrum is resolved into emission lines with fluxes between 0.02 and 1.04{\times}10$^{-4}$ photons cm$^{-2}$ s$^{-1}$. We identify lines from a variety of charge states, including fluorescent lines from cold material and a warm photoionized wind. We can exclude signatures from collisionally ionized plasmas. For the first time, we identify fluorescent lines from L-shell ions from lower Z elements. We also detect radiative recombination continua from a kT=10 eV (1.2{\times}10⁵ K) photoionized optically thin gas. The fluorescent line fluxes imly the existence of optically thick and clumped matter within or outside the warm photoionized plasma. }

{Schulz} N  S, {Cui} W, {Canizares} C  R, {Marshall} H  L, {Lee} J  C, {Miller} J  M, {Lewin} W  H  G. {The First High-Resolution X-Ray Spectrum of Cygnus X-1: Soft X-Ray Ionization and Absorption}. \apj. 2002;565 :1141-1149.Abstract

{We observed the black hole candidate Cyg X-1 for 15 ks with the High-Energy Transmission Grating Spectrometer aboard the Chandra X-Ray Observatory. The source was observed during a period of intense flaring activity, so it was about a factor of 2.5 brighter than usual, with a 0.5-10 keV (1-24 {\AA}) luminosity of 1.6{\times}10$^{37}$ ergs s$^{-1}$ (at a distance of 2.5 kpc). The spectrum of the source shows prominent absorption edges, some of which have a complicated substructure. We use the most recent results from laboratory measurements and calculations to model the observed substructure of the edges. From the model, we derive a total absorption column of (6.21+/-0.22){\times}10$^{21}$ cm$^{-2}$. Furthermore, the results indicate that there are \~{}10%-25% abundance variations relative to solar values for neon, oxygen, and iron. The X-ray continuum is well described by a two-component model that is often adopted for black hole candidates: a soft multicolor disk component (with kT=203 eV) and a hard power-law component (with a photon index of \~{}2). Comparing the fit results to those of the hard and soft states, we conclude that the source was in a transitional state. Finally, the spectrum also shows the presence of faint emission lines, which could be attributed to highly ionized species. }

{Lee} J  C, {Reynolds} C  S, {Remillard} R, {Schulz} N  S, {Blackman} E  G, {Fabian} A  C. {High-Resolution Chandra HETGS and Rossi X-Ray Timing Explorer Observations of GRS 1915+105: A Hot Disk Atmosphere and Cold Gas Enriched in Iron and Silicon}. \apj. 2002;567 :1102-1111.Abstract

{The time-averaged 30 ks Chandra AO1 High Energy Transmission Grating Spectrometer observation of the microquasar GRS 1915+105 in the low hard state reveals for the first time in this source neutral K absorption edges from iron, silicon, magnesium, and sulphur. Ionized resonance (r) absorption from H- and He-like species of Fe (XXV, XXVI) and possibly Ca XX are also seen as well as possible emission from neutral Fe K{$\alpha$} and ionized Fe XXV (forbidden or the resonance emission component of a P Cygni profile). We report the tentative detection of the first astrophysical signature of X-ray absorption fine structure in the photoelectric edge of Si (and possibly Fe and Mg) attributed to material in grains. The large column densities measured from the neutral edges reveal anomalous Si and Fe abundances and illustrate the importance of high-resolution X-ray measurements for assessing material that surrounds bright X-ray sources, especially if depletion onto grains plays a prominent role. Scenarios for which the anomalous abundances can be attributed to surrounding cold material associated with GRS 1915+105 and/or for which the enrichment may signify either a highly unusual supernova/hypernova or external supernova activity local to the binary are discussed. We attribute the ionized features to a hot disk, disk wind, or corona environment. Based on H- and He-like Fe (XXV, XXVI), we estimate constraints on the ionization parameter (log{$\xi$}{\gt}\~{}4.15), temperature (T{\gt}2.4{\times}10⁶ K), and hydrogen equivalent number density (n{\gt}\~{}10$^{12}$ cm$^{-3}$) for this region. Variability studies with the simultaneous RXTE data show that the light-curve count rate tracks the changes in the disk blackbody as well as the power-law flux, with the most significant variations observed in the former. The Chandra data show spectral changes that also track the behavior of the light curve and may point to changes in both the ionizing flux and density of the absorber. A 3.69 Hz quasi-periodic oscillation and weak first harmonic are seen in the RXTE data. }

{Lee} J  C, {Iwasawa} K, {Houck} J  C, {Fabian} A  C, {Marshall} H  L, {Canizares} C  R. {The Shape of the Relativistic Iron K{$\alpha$} Line from MCG -6-30-15 Measured with the Chandra High Energy Transmission Grating Spectrometer and the Rossi X-Ray Timing Explorer}. \apjl. 2002;570 :L47-L50.Abstract

{We confirm the detection of the relativistically broadened iron K{$\alpha$} emission at 6.4 keV with simultaneous Chandra High Energy Transmission Grating Spectrometer (HETGS) and Rossi X-Ray Timing Explorer Proportional Counter Array observations. Heavily binned HETGS data show a disk line profile with parameters very similar to those previously seen by ASCA. We observe a resolved narrow component with a velocity width of \~{}4700 km s$^{-1}$ (FWHM\~{}11,000 km s$^{-1}$) that is most prominent and is narrower (FWHM\~{}3600 km s$^{-1}$) when the continuum flux is high. It is plausibly just the blue wing of the broad line. We obtain a stringent limit on the equivalent width of an intrinsically narrow line in the source of 16 eV, indicating little or no contribution due to fluorescence from distant material, such as the molecular torus. Variability studies of the narrow component show a constant iron line flux and variable width indicating the line may be originating from different kinematic regions of the disk. }

{Fang} T, {Marshall} H  L, {Lee} J  C, {Davis} D  S, {Canizares} C  R. {Chandra Detection of O VIII Ly{$\alpha$} Absorption from an Overdense Region in the Intergalactic Medium}. \apjl. 2002;572 :L127-L130.Abstract

{We report the first detection of an O VIII Ly{$\alpha$} absorption line associated with an overdense region in the intergalactic medium along the sight line toward PKS 2155-304 with the Chandra Low Energy Transmission Grating Spectrometer. The absorption line is detected at the 4.5 {$\sigma$} level with cz\~{}16,600 km s$^{-1}$. At the same velocity, Shull et al. detected a small group of spiral galaxies (with an overdensity of {$δ$}$_{gal}$\~{}100) and low-metallicity H I Ly{$\alpha$} clouds. We constrain the intragroup gas that gives rise to the O VIII Ly{$\alpha$} line to a baryon density in the range 1.0{\times}10$^{-5}$ cm$^{-3}$łt}n$_{b}$łt}7.5{\times}10$^{-5}$ cm$^{-3}$ (50łt}{$δ$}$_{b}$łt}350) and a temperature of (4-5){\times}10⁶ K, assuming 0.1 Z$_{solar}$. These estimates are in accordance with those of the warm/hot intergalactic medium (WHIM) that are predicted from hydrodynamic simulations. Extrapolating from this single detection implies that a large fraction of the ``missing baryons'' (\~{}10%, or \~{}30%-40% of the WHIM) are probed by the O VIII absorber. }

{Chakrabarty} D, {Wang} Z, {Juett} A  M, {Lee} J  C, {Roche} P. {The X-Ray Position and Infrared Counterpart of the Eclipsing X-Ray Pulsar OAO 1657-415}. \apj. 2002;573 :789-793.Abstract

{We have measured the precise position of the 38 s eclipsing X-ray pulsar OAO 1657-415 with the Chandra X-Ray Observatory: {$\alpha$}(J2000)=17$^{h}$00$^{m}$48.90$^{s}$, {$δ$}(J2000)=-41$^{deg}$39$^{'}$21.6'

{Pain} R, {Fabbro} S, {Sullivan} M, {Ellis} R  S, {Aldering} G, {Astier} P, {Deustua} S  E, {Fruchter} A  S, {Goldhaber} G, {Goobar} A, et al. {The Distant Type Ia Supernova Rate}. \apj. 2002;577 :120-132.Abstract

{We present a measurement of the rate of distant Type Ia supernovae derived using four large subsets of data from the Supernova Cosmology Project. Within this fiducial sample, which surveyed about 12 deg$^{2}$, 38 supernovae were detected at redshifts 0.25-0.85. In a spatially flat cosmological model consistent with the results obtained by the Supernova Cosmology Project, we derive a rest-frame Type Ia supernova rate at a mean redshift z\~{}=0.55 of 1.53$^{+0.28}$$_{-0.25}$$^{+0.32}$$_{- 0.31}${\times}10$^{-4}$ h$^{3}$ Mpc$^{-3}$ yr$^{-1}$ or 0.58$^{+0.10}$$_{-0.09}$$^{+0.10}$$_{-0.09}$ h$^{2}$ SNu (1SNu=1 supernova per century per 10$^{10}$ L$_{Bsolar}$), where the first uncertainty is statistical and the second includes systematic effects. The dependence of the rate on the assumed cosmological parameters is studied and the redshift dependence of the rate per unit comoving volume is contrasted with local estimates in the context of possible cosmic star formation histories and progenitor models. }

{Fabian} A  C, {Vaughan} S, {Nandra} K, {Iwasawa} K, {Ballantyne} D  R, {Lee} J  C, {de Rosa} A, {Turner} A, {Young} A  J. {A long hard look at MCG-6-30-15 with XMM-Newton}. \mnras. 2002;335 :L1-L5.Abstract

{We present the first results from a 325-ks observation of the Seyfert 1 galaxy MCG-6-30-15 with XMM-Newton and BeppoSAX. The strong, broad, skewed iron line is clearly detected and is well characterized by a steep emissivity profile within 6r$_{g}$ (i.e. 6GM/c$^{2}$) and a flatter profile beyond. The inner radius of the emission appears to lie at about 2r$_{g}$, consistent with results reported from both an earlier XMM-Newton observation of MCG-6-30-15 by Wilms et al. and part of an ASCA observation by Iwasawa et al. when the source was in a lower flux state. The radius and steep emissivity profile do depend however on an assumed incident power-law continuum and a lack of complex absorption above 2.5 keV. The blue wing of the line profile is indented, either by absorption at about 6.7 keV or by a hydrogenic iron emission line. The broad iron line flux does not follow the continuum variations in a simple manner. }

{Goobar} A, {Perlmutter} S, {Aldering} G, {Goldhaber} G, {Knop} R  A, {Nugent} P, {Castro} P  G, {Deustua} S, {Fabbro} S, {Groom} D  E, et al. {The Acceleration of the Universe:. Measurements of Cosmological Parameters from Type Ia Supernovae}, in Particle Physics and the Universe. ; 2001 :47-58.Abstract

{The fate of the Universe, infinite expansion or a ''big crunch'', can be determined by measuring the redshifts and brightness of very distant supernovae. These provide a record of changes in the expansion rate of the Universe over the past several billion years. The mass density, {$Ømega$}$_{M}$, and cosmological-constant energy density, {$Ømega$}$_{Λ}$, are measured from a data-set consisting of 42 high-redshift Type Ia supernovae discovered by the Supernova Cosmology Project. The magnitude-redshift data for these supernovae, at redshifts between 0.18 and 0.83, are fit jointly with a set of supernovae from the Calán/Tololo Supernova Survey, at redshifts below 0.1, to yield values for the cosmological parameters. We find {$Ømega$} $_{M}$ flat = 0.28$_{-0.08}$$^{+0.09}$ (1{$\sigma$} $\backslash$ statistical)$_{-0.04}$$^{+0.05}$ (identified systematics). The data are strongly inconsistent with a {$Łambda$} = 0 flat cosmology, the simplest inflationary universe model. An open, {$Łambda$} = 0 cosmology also does not fit the data well: the data indicate that the cosmological constant is non-zero and positive, with a confidence of P({$Łambda$} {\gt} 0) = 99%, including the identified systematic uncertainties. Thus, the Universe is found to be accelerating, i.e., q₀ = {$Ømega$}$_{M}$/2 - {$Ømega$}$_{Λ}$ łt} 0. The best-fit age of the universe relative to the Hubble time is t₀ flat = 14.9$_{-1.1}$$^{+1.4}$ (0.63/h)$\backslash$ Gyr for a flat cosmology. }