G. P. Garmire

Nanjing University, Nan-ching, Jiangsu Sheng, China

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Publications (416)1300.91 Total impact

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    ABSTRACT: We present an X-ray and multiwavelength study of 33 weak emission-line quasars (WLQs) and 18 quasars that are analogs of the extreme WLQ, PHL 1811, at z ~ 0.5-2.9. New Chandra 1.5-9.5 ks exploratory observations were obtained for 32 objects while the others have archival X-ray observations. Significant fractions of these luminous type 1 quasars are distinctly X-ray weak compared to typical quasars, including 16 (48%) of the WLQs and 17 (94%) of the PHL 1811 analogs with average X-ray weakness factors of 17 and 39, respectively. We measure a relatively hard ($\Gamma=1.16_{-0.32}^{+0.37}$) effective power-law photon index for a stack of the X-ray weak subsample, suggesting X-ray absorption, and spectral analysis of one PHL 1811 analog, J1521+5202, also indicates significant intrinsic X-ray absorption. We compare composite SDSS spectra for the X-ray weak and X-ray normal populations and find several optical-UV tracers of X-ray weakness; e.g., Fe II rest-frame equivalent width and relative color. We describe how orientation effects under our previously proposed "shielding-gas" scenario can likely unify the X-ray weak and X-ray normal populations. We suggest that the shielding gas may naturally be understood as a geometrically thick inner accretion disk that shields the broad line region from the ionizing continuum. If WLQs and PHL 1811 analogs have very high Eddington ratios, the inner disk could be significantly puffed up (e.g., a slim disk). Shielding of the broad emission-line region by a geometrically thick disk may have a significant role in setting the broad distributions of C IV rest-frame equivalent width and blueshift for quasars more generally.
    Full-text · Article · Mar 2015 · The Astrophysical Journal
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    ABSTRACT: In the cores of some clusters of galaxies the hot intracluster plasma is dense enough that it should cool radiatively in the cluster's lifetime, leading to continuous 'cooling flows' of gas sinking towards the cluster centre, yet no such cooling flow has been observed. The low observed star-formation rates and cool gas masses for these 'cool-core' clusters suggest that much of the cooling must be offset by feedback to prevent the formation of a runaway cooling flow. Here we report X-ray, optical and infrared observations of the galaxy cluster SPT-CLJ2344-4243 (ref. 11) at redshift z = 0.596. These observations reveal an exceptionally luminous (8.2 × 10(45) erg s(-1)) galaxy cluster that hosts an extremely strong cooling flow (around 3,820 solar masses a year). Further, the central galaxy in this cluster appears to be experiencing a massive starburst (formation of around 740 solar masses a year), which suggests that the feedback source responsible for preventing runaway cooling in nearby cool-core clusters may not yet be fully established in SPT-CLJ2344-4243. This large star-formation rate implies that a significant fraction of the stars in the central galaxy of this cluster may form through accretion of the intracluster medium, rather than (as is currently thought) assembling entirely via mergers.
    No preview · Article · Aug 2012 · Nature
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    ABSTRACT: In the cores of some galaxy clusters the hot intracluster plasma is dense enough that it should cool radiatively in the cluster's lifetime, leading to continuous "cooling flows" of gas sinking towards the cluster center, yet no such cooling flow has been observed. The low observed star formation rates and cool gas masses for these "cool core" clusters suggest that much of the cooling must be offset by astrophysical feedback to prevent the formation of a runaway cooling flow. Here we report X-ray, optical, and infrared observations of the galaxy cluster SPT-CLJ2344-4243 at z = 0.596. These observations reveal an exceptionally luminous (L_2-10 keV = 8.2 x 10^45 erg/s) galaxy cluster which hosts an extremely strong cooling flow (dM/dt = 3820 +/- 530 Msun/yr). Further, the central galaxy in this cluster appears to be experiencing a massive starburst (740 +/- 160 Msun/yr), which suggests that the feedback source responsible for preventing runaway cooling in nearby cool core clusters may not yet be fully established in SPT-CLJ2344-4243. This large star formation rate implies that a significant fraction of the stars in the central galaxy of this cluster may form via accretion of the intracluster medium, rather than the current picture of central galaxies assembling entirely via mergers.
    Full-text · Article · Aug 2012
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    ABSTRACT: We present 35 ks Chandra ACIS observations of the 42 Myr old radio pulsar PSR B1451–68. A point source is detected 032 ± 073 from the expected radio pulsar position. It has ~200 counts in the 0.3-8 keV energy range. We identify this point source as the X-ray counterpart of the radio pulsar. PSR B1451–68 is located close to a Two Micron All Sky Survey point source for which we derive 7% as the upper limit on the flux contribution to the measured pulsar X-ray flux. The pulsar spectrum can be described by either a power-law model with photon index Γ = 2.4+0.4– 0.3 and a unrealistically high absorbing column density N H = (2.5+1.2– 1.3) × 1021 cm–2, or by a combination of a kT = 0.35+0.12– 0.07 keV blackbody and a Γ = 1.4 ± 0.5 power-law component for N DMH = 2.6 × 1020 cm–2, estimated from the pulsar dispersion measure. At the parallactic, a Lutz-Kelker bias corrected distance of 480 pc, the non-thermal X-ray luminosities in the 0.3-8 keV energy band are either L nonth0.3-8 keV = (11.3 ± 1.7) × 1029 erg s–1 or L nonth0.3-8 keV = (5.9+4.9– 5.0) × 1029 erg s–1, respectively. This corresponds to non-thermal X-ray efficiencies of either or 3 × 10–3, respectively.
    Full-text · Article · Feb 2012 · The Astrophysical Journal
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    D. Grupe · D. Burrows · X.-F. Wu · B. Zhang · G. Garmire
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    ABSTRACT: We summarize the results of the late-time Chandra observations of the X-ray afterglow of the Swift-discovered GRB 060729. These Chandra observations have been the latest X-ray detections of an afterglow, even up to 21 month after the trigger. The last two Chandra observations in December 2007 and May 2008 suggest a break at about a year after the burst, implying a jet half-opening angle of about 14 degrees, if interpreted as a jet break. As an alternative this break may have a spectral origin. In that case no jet break was observed and the half-opening angle is larger than 15 degrees for a wind medium. Comparing the X-ray afterglow of GRB 060729 with other bright X-ray afterglows we discuss why the afterglow of GRB 060729 was such an exceptionally long-lasting event. The detection by Chandra in May 2008 was the latest detection of an X-ray afterglow at cosmological distance ever. Figure 1: Swift XRT (black crosses) and Chandra ACIS-S (red triangles) light curve of the X-ray afterglow of GRB 060729. The solid line displays an initial decay slope of 1.32 ([2]), the dashed line the decay slope of 1.61 post-break at 1 Ms after the burst and the doted line the steep decay slope of 4.65 after the break at 41 Ms after the burst ([3]).
    Full-text · Article · Jan 2012
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    ABSTRACT: The South Pole Telescope (SPT) is currently surveying 2500 deg2 of the southern sky to detect massive galaxy clusters out to the epoch of their formation using the Sunyaev-Zel'dovich (SZ) effect. This paper presents a catalog of the 26 most significant SZ cluster detections in the full survey region. The catalog includes 14 clusters which have been previously identified and 12 that are new discoveries. These clusters were identified in fields observed to two differing noise depths: 1500 deg2 at the final SPT survey depth of 18 μK arcmin at 150 GHz and 1000 deg2 at a depth of 54 μK arcmin. Clusters were selected on the basis of their SZ signal-to-noise ratio (S/N) in SPT maps, a quantity which has been demonstrated to correlate tightly with cluster mass. The S/N thresholds were chosen to achieve a comparable mass selection across survey fields of both depths. Cluster redshifts were obtained with optical and infrared imaging and spectroscopy from a variety of ground- and space-based facilities. The redshifts range from 0.098 ≤ z ≤ 1.132 with a median of z med = 0.40. The measured SZ S/N and redshifts lead to unbiased mass estimates ranging from 9.8 × 1014M ☉h –170 ≤ M 200(ρmean) ≤ 3.1 × 1015M ☉h –170. Based on the SZ mass estimates, we find that none of the clusters are individually in significant tension with the ΛCDM cosmological model. We also test for evidence of non-Gaussianity based on the cluster sample and find the data show no preference for non-Gaussian perturbations.
    Full-text · Article · Aug 2011 · The Astrophysical Journal
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    ABSTRACT: We present results of X-ray observations of a sample of 15 clusters selected via their imprint on the cosmic microwave background from the thermal Sunyaev-Zel'dovich (SZ) effect. These clusters are a subset of the first SZ-selected cluster catalog, obtained from observations of 178 deg2 of sky surveyed by the South Pole Telescope (SPT). Using X-ray observations with Chandra and XMM-Newton, we estimate the temperature, TX , and mass, Mg , of the intracluster medium within r 500 for each cluster. From these, we calculate YX = MgTX and estimate the total cluster mass using an M 500-YX scaling relation measured from previous X-ray studies. The integrated Comptonization, Y SZ, is derived from the SZ measurements, using additional information from the X-ray-measured gas density profiles and a universal temperature profile. We calculate scaling relations between the X-ray and SZ observables and find results generally consistent with other measurements and the expectations from simple self-similar behavior. Specifically, we fit a Y SZ-YX relation and find a normalization of 0.82 ± 0.07, marginally consistent with the predicted ratio of Y SZ/YX = 0.91 ± 0.01 that would be expected from the density and temperature models used in this work. Using the YX -derived mass estimates, we fit a Y SZ-M 500 relation and find a slope consistent with the self-similar expectation of Y SZM 5/3 with a normalization consistent with predictions from other X-ray studies. We find that the SZ mass estimates, derived from cosmological simulations of the SPT survey, are lower by a factor of 0.78 ± 0.06 relative to the X-ray mass estimates. This offset is at a level of 1.3σ when considering the ~15% systematic uncertainty for the simulation-based SZ masses. Overall, the X-ray measurements confirm that the scaling relations of the SZ-selected clusters are consistent with the properties of other X-ray-selected samples of massive clusters, even allowing for the broad redshift range (0.29 < z < 1.08) of the sample.
    Full-text · Article · Aug 2011 · The Astrophysical Journal
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    ABSTRACT: Broos et al. (2011, Cat. J/ApJS/194/2) and citations therein describe the X-ray, visual, NIR, and MIR measurements available for CCCP sources. (1 data file).
    No preview · Article · May 2011
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    ABSTRACT: The Chandra Carina Complex Project (CCCP) is a 1.42deg2^ survey, at an assumed distance of 2.3kpc, of the Great Nebula in Carina with the Imaging array of the Advanced CCD Imaging Spectrometer (ACIS-I) on the Chandra X-ray Observatory, and is described in Townsley et al. (2011ApJS..194....1T). The Very Large Project (VLP) data were acquired over nine months, from 2008 February 12 through 2008 October 15 and were completed with Chandra archive ObsID 6402 (Trumpler 16, in 2006 Aug 30), ObsID 4495 (Trumpler 14, in 2004 Sep 21), and ObsID 6578 (Treasure Chest Cluster, in 2006 Apr 16). (3 data files).
    No preview · Article · May 2011
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    ABSTRACT: Trumpler 15 was observed as part of the CCCP (Townsley et al., 2011ApJS..194....1T), a large mosaic of Chandra Advanced CCD Imaging Spectrometer I-array (ACIS-I) observations. One CCCP pointing (ObsID 9484, a 60ks integration obtained on 2008 August 19) is centered on Trumpler 15; five other pointings cover the edges of the cluster (Figure 1(a)). (1 data file).
    No preview · Article · May 2011
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    ABSTRACT: The CCCP observations and their analysis are described in detail by Townsley et al. (2011ApJS..194....1T) and Broos et al. (2011, Cat. J/ApJS/194/2). Twenty-two overlapping pointings with the Chandra Advanced CCD Imaging Spectrometer (ACIS), each subtending 17'x17', were observed. They cover a 1.4deg2^ region. The X-ray data are aligned to the Two Micron All Sky Survey (2MASS)/Hipparcos frame and, in most cases, source positions have accuracies better than 0.5". Infrared counterparts are found by positional coincidences with 2MASS, VLT HAWK-I (Preibisch et al. 2011, Cat. J/ApJS/194/10), and other published catalogs. (3 data files).
    No preview · Article · May 2011
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    ABSTRACT: We present a 1.42deg2^ mosaic of diffuse X-ray emission in the Great Nebula in Carina from the Chandra X-ray Observatory Advanced CCD Imaging Spectrometer camera. After removing >14000 X-ray point sources from the field, we smooth the remaining unresolved emission, tessellate it into segments of similar apparent surface brightness, and perform X-ray spectral fitting on those tessellates to infer the intrinsic properties of the X-ray-emitting plasma. By modeling faint resolved point sources, we estimate the contribution to the extended X-ray emission from unresolved point sources and show that the vast majority of Carina's unresolved X-ray emission is truly diffuse. Line-like correlated residuals in the X-ray spectral fits suggest that substantial X-ray emission is generated by charge exchange at the interfaces between Carina's hot, rarefied plasma and its many cold neutral pillars, ridges, and clumps. (2 data files).
    No preview · Article · May 2011
  • Bettina Posselt · G. G. Pavlov · G. P. Garmire
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    ABSTRACT: Very few old radio pulsars are detected in X-rays. These objects are in general very faint due to their cold surfaces and relatively low spin-down powers. Yet, old radio pulsars appear to convert their spin-down energy more efficiently into X-ray emission than their younger relatives. It is unclear how much of this X-ray emission can be attributed to thermally emitting, hot polar caps or to magnetospheric emission. The evolution of NS magnetospheres with age and the polar cap heating mechanism are both interesting for the entire NS population, but can be particularly well studied in the case of old X-ray detected radio pulsars. Here, we present recent Chandra observations of the 4.25e7 yrs old radio pulsar PSR B1451-68. The spectrum of the found X-ray source can be described by a power law with photon index ˜ 2.7. Its isotropic luminosity is L_X ˜ 1.7e30 d^2_450pc erg/s (0.3 keV to 8keV), which corresponds to a high X-ray efficiency of 8e-3. We discuss the influence of a nearby star on the detected X-ray emission.
    No preview · Article · May 2011
  • G. G. Pavlov · Z. Misanovic · O. Kargaltsev · G. P. Garmire
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    ABSTRACT: The Fermi LAT source 1FGL J1018.6-5856 has been recently identified as a high-mass gamma-ray binary (Corbet et al., ATel #3221). The source was observed with Chandra ACIS-I (ObsID 11831) on 2010-08-17 from 01:17 to 04:04 UTC, which corresponds to the binary phase interval from 0.312 to 0.319 (phase uncertainty ±0.024; zero phase corresponds to the gamma-ray flux maximum at the reference epoch MJD 55403.3+/-0.4, period 16.58+/-0.04 d, according to ATel #3221).
    No preview · Article · Mar 2011
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    ABSTRACT: Using the South Pole Telescope (SPT), we have discovered the most massive known galaxy cluster at z>1, SPT-CL J2106-5844. In addition to producing a strong Sunyaev-Zel'dovich (SZ) effect signal, this system is a luminous X-ray source and its numerous constituent galaxies display spatial and color clustering, all indicating the presence of a massive galaxy cluster. Very Large Telescope and Magellan spectroscopy of 18 member galaxies shows that the cluster is at z = 1.132+0.002–0.003. Chandra observations obtained through a combined HRC-ACIS GTO program reveal an X-ray spectrum with an Fe K line redshifted by z = 1.18 ± 0.03. These redshifts are consistent with the galaxy colors found in optical, near-infrared, and mid-infrared imaging. SPT-CL J2106-5844 displays extreme X-ray properties for a cluster having a core-excluded temperature of TX = 11.0+2.6–1.9 keV and a luminosity (within r 500) of LX(0.5-2.0 keV) = (13.9 ± 1.0) × 1044 erg s–1. The combined mass estimate from measurements of the SZ effect and X-ray data is M 200 = (1.27 ± 0.21) × 1015 h –170M ☉. The discovery of such a massive gravitationally collapsed system at high redshift provides an interesting laboratory for galaxy formation and evolution, and is a probe of extreme perturbations of the primordial matter density field. We discuss the latter, determining that, under the assumption of ΛCDM cosmology with only Gaussian perturbations, there is only a 7% chance of finding a galaxy cluster similar to SPT-CL J2106-5844 in the 2500 deg2 SPT survey region and that only one such galaxy cluster is expected in the entire sky.
    Full-text · Article · Jan 2011 · The Astrophysical Journal
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    ABSTRACT: The South Pole Telescope (SPT) is currently surveying 2500 deg^2 of the southern sky to detect massive galaxy clusters out to the epoch of their formation using the Sunyaev-Zel'dovich (SZ) effect. This paper presents a catalog of the 26 most significant SZ cluster detections in the full survey region. The catalog includes 14 clusters which have been previously identified and 12 that are new discoveries. These clusters were identified in fields observed to two differing noise depths: 1500 deg^2 at the final SPT survey depth of 18 uK-arcmin at 150 GHz, and 1000 deg^2 at a depth of 54 uK-arcmin. Clusters were selected on the basis of their SZ signal-to-noise ratio (S/N) in SPT maps, a quantity which has been demonstrated to correlate tightly with cluster mass. The S/N thresholds were chosen to achieve a comparable mass selection across survey fields of both depths. Cluster redshifts were obtained with optical and infrared imaging and spectroscopy from a variety of ground- and space-based facilities. The redshifts range from 0.098 \leq z \leq 1.132 with a median of z_med = 0.40. The measured SZ S/N and redshifts lead to unbiased mass estimates ranging from 9.8 \times 10^14 M_sun/h_70 \leq M_200(rho_mean) \leq 3.1 \times 10^15 M_sun/h_70. Based on the SZ mass estimates, we find that none of the clusters are individually in significant tension with the LambdaCDM cosmological model. We also test for evidence of non-Gaussianity based on the cluster sample and find the data show no preference for non-Gaussian perturbations.
    Full-text · Article · Jan 2011
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    ABSTRACT: We report the spectroscopic confirmation of SPT-CL J0546-5345 at z = 1.067. To date this is the most distant cluster to be spectroscopically confirmed from the 2008 South Pole Telescope (SPT) catalog, and indeed the first z>1 cluster discovered by the Sunyaev-Zel'dovich Effect (SZE). We identify 21 secure spectroscopic members within 0.9 Mpc of the SPT cluster position, 18 of which are quiescent, early-type galaxies. From these quiescent galaxies we obtain a velocity dispersion of 1179+232–167 km s–1, ranking SPT-CL J0546-5345 as the most dynamically massive cluster yet discovered at z>1. Assuming that SPT-CL J0546-5345 is virialized, this implies a dynamical mass of M 200 = 1.0+0.6–0.4× 1015M ☉, in agreement with the X-ray and SZE mass measurements. Combining masses from several independent measures leads to a best-estimate mass of M 200 = (7.95 ± 0.92) × 1014M ☉. The spectroscopic confirmation of SPT-CL J0546-5345, discovered in the wide-angle, mass-selected SPT cluster survey, marks the onset of the high-redshift SZE-selected galaxy cluster era.
    Full-text · Article · Jun 2010 · The Astrophysical Journal
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    ABSTRACT: We present initial results from our Chandra ACIS observation of the shell-type Galactic supernova remnant (SNR) G340.6+0.3. The high resolution Chandra image clearly resolves the bright northern and southern shells. We detect strong line emission from highly ionized Si, S, Ar, and Ca in the northern shell. Abundances of these elements are several times higher than solar, indicating ejecta material enriched in these high-Z metal species. The southern shell can be fitted by a thermal plasma with solar abundances, indicating its origin as the shocked interstellar medium. The small angular size (2.3' radius), the detection of overabundant metals, and the high plasma temperatures (kT 1-1.5 keV) suggest that G340.6+0.3 is a young, ejecta-dominated SNR, which provides a useful opportunity to study the supernova nucleosynthesis of intermediate metal elements.
    No preview · Article · Jan 2010
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    ABSTRACT: Broad absorption lines (BALs) in quasars (QSOs) are traditionally defined as having velocity widths of at least 2,000 km/s, while "mini-BALs" are defined as having intermediate velocity widths between 1,000 and 2,000 km/s. We have compiled a sample of 14 of the optically brightest radio-quiet quasars in the Sloan Digital Sky Survey Data Release 5 QSO catalog for which a mini-BAL is present, with redshift z > 1.9 and BEST photometric apparent magnitude, mi
    No preview · Article · Jan 2010
  • George Chartas · W. N. Brandt · C. Saez · M. Giustini · G. P. Garmire
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    ABSTRACT: We present recent X-ray observations of the z = 3.91 quasar APM 08279+5255 that confirm the presence of near-relativistic outflows of ionized absorbing material with velocities of up to 0.76c in this object. The maximum outflow velocity constrains the angle between the wind velocity and our line of sight to be less than 22 degrees. The X-ray broad absorption lines (BALs) and 0.2-10 keV continuum of APM 08279+5255 show significant variability on timescales as short as 3.3 days (proper time) implying a source size-scale r_g, where r_g is the gravitational radius. Based on our spectral analysis we identify the following components of the outflow: (a) Highly ionized X-ray absorbing material with an ionization parameter in the range of 2.9 < log xi < 3.9 and a column density of log N_H 23 outflowing at velocities of up to 0.76 c. (b) Low-ionization X-ray absorbing gas with log N_H 22.8. We find a possible trend between the X-ray photon index and the maximum outflow velocity of the ionized absorber in the sense that flatter spectra appear to result in lower outflow velocities. Our studies indicate that these quasar winds may be important in regulating the growth of the supermassive black hole, controlling the formation of the host galaxy, and enriching the intergalactic medium. We acknowledge financial support from NASA via the Smithsonian Institution grant SAO SV4-74018 and from NNX08AB71G. WNB acknowledges financial support from NASA LTSA grant NAG5-13035.
    No preview · Article · Jan 2010

Publication Stats

11k Citations
1,300.91 Total Impact Points

Institutions

  • 2012
    • Nanjing University
      Nan-ching, Jiangsu Sheng, China
  • 1991-2012
    • Pennsylvania State University
      • Department of Astronomy and Astrophysics
      University Park, Maryland, United States
  • 1987-2012
    • William Penn University
      Worcester, Massachusetts, United States
  • 2010
    • University of Chicago
      • Kavli Institute for Cosmological Physics
      Chicago, Illinois, United States
  • 2005-2008
    • Harvard-Smithsonian Center for Astrophysics
      • Smithsonian Astrophysical Observatory
      Cambridge, Massachusetts, United States
  • 2006
    • Johns Hopkins University
      Baltimore, Maryland, United States
  • 2004
    • The Astronomical Observatory of Brera
      Merate, Lombardy, Italy
    • Los Alamos National Laboratory
      Los Alamos, California, United States
    • University of Santiago, Chile
      • Departamento de Economía
      CiudadSantiago, Santiago, Chile
  • 2001-2003
    • Honolulu University
      Honolulu, Hawaii, United States
  • 1974-2003
    • California Institute of Technology
      • Jet Propulsion Laboratory
      Pasadena, California, United States
  • 1965-2003
    • Massachusetts Institute of Technology
      • • Kavli Institute for Astrophysics and Space Research
      • • Laboratory for Nuclear Science
      Cambridge, Massachusetts, United States
  • 2001-2002
    • Portland State University
      Portland, Oregon, United States
  • 1980
    • Stanford University
      • Department of Applied Physics
      Palo Alto, California, United States
  • 1973-1980
    • Pasadena City College
      Pasadena, Texas, United States
  • 1979
    • University of California, Berkeley
      Berkeley, California, United States
  • 1977
    • Columbia University
      New York, New York, United States