arXiv subjects

R. W. Pogge

Publications and source records attributed to R. W. Pogge.

At least 163 records · Page 9Linked to original sources

arXiv2007

First Space-Based Microlens Parallax Measurement: Spitzer Observations of OGLE-2005-SMC-001

We combine Spitzer and ground-based observations to measure the microlens parallax of OGLE-2005-SMC-001, the first such space-based determination since S. Refsdal proposed the idea in 1966. The parallax measurement yields a projected velocity \tilde v ~ 230 km/s, the typical value expected for halo lenses, but an order of magnitude smaller than would be expected for lenses lying in the Small Magellanic Cloud (SMC) itself. The lens is a weak (i.e., non-caustic-crossing) binary, which complicates the analysis considerably but ultimately contributes additional constraints. Using a test proposed by Assef et al. (2006), which makes use only of kinematic information about different populations but does not make any assumptions about their respective mass functions, we find that the likelihood ratio is L_halo/L_SMC = 20. Hence, halo lenses are strongly favored but SMC lenses are not definitively ruled out. Similar Spitzer observations of additional lenses toward the Magellanic Clouds would clarify the nature of the lens population. The Space Interferometry Mission could make even more constraining measurements.

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arXiv2006

Planetary Detection Efficiency of the Magnification 3000 Microlensing Event OGLE-2004-BLG-343

OGLE-2004-BLG-343 was a microlensing event with peak magnification A_{max}=3000+/-1100, by far the highest-magnification event ever analyzed and hence potentially extremely sensitive to planets orbiting the lens star. Due to human error, intensive monitoring did not begin until 43 minutes after peak, at which point the magnification had fallen to A~1200, still by far the highest ever observed. As the light curve does not show significant deviations due to a planet, we place upper limits on the presence of such planets by extending the method of Yoo et al. (2004b), which combines light-curve analysis with priors from a Galactic model of the source and lens populations, to take account of finite-source effects. This is the first event so analyzed for which finite-source effects are important, and hence we develop two new techniques for evaluating these effects. Somewhat surprisingly, we find that OGLE-2004-BLG-343 is no more sensitive to planets than two previously analyzed events with A_{max}~100, despite the fact that it was observed at ~12 times higher magnification. However, we show that had the event been observed over its peak, it would have been sensitive to almost all Neptune-mass planets over a factor of 5 of projected separation and even would have had some sensitivity to Earth-mass planets. This shows that some microlensing events being detected in current experiments are sensitive to very low-mass planets. We also give suggestions on how extremely high-magnification events can be more promptly monitored in the future.

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arXiv2006

Microlens OGLE-2005-BLG-169 Implies Cool Neptune-Like Planets are Common

We detect a Neptune mass-ratio (q~8e-5) planetary companion to the lens star in the extremely high-magnification (A~800) microlensing event OGLE-2005-BLG-169. If the parent is a main-sequence star, it has mass M~0.5 M_sun implying a planet mass of ~13 M_earth and projected separation of ~2.7 AU. When intensely monitored over their peak, high-magnification events similar to OGLE-2005-BLG-169 have nearly complete sensitivity to Neptune mass-ratio planets with projected separations of 0.6 to 1.6 Einstein radii, corresponding to 1.6--4.3 AU in the present case. Only two other such events were monitored well enough to detect Neptunes, and so this detection by itself suggests that Neptune mass-ratio planets are common. Moreover, another Neptune was recently discovered at a similar distance from its parent star in a low-magnification event, which are more common but are individually much less sensitive to planets. Combining the two detections yields 90% upper and lower frequency limits f=0.37^{+0.30}_{-0.21} over just 0.4 decades of planet-star separation. In particular, f>16% at 90% confidence. The parent star hosts no Jupiter-mass companions with projected separations within a factor 5 of that of the detected planet. The lens-source relative proper motion is μ~7--10 mas/yr, implying that if the lens is sufficiently bright, I<23.8, it will be detectable by HST by 3 years after peak. This would permit a more precise estimate of the lens mass and distance, and so the mass and projected separation of the planet. Analogs of OGLE-2005-BLG-169Lb orbiting nearby stars would be difficult to detect by other methods of planet detection, including radial velocities, transits, or astrometry.

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arXiv2005

The Disappearing Act of KH 15D: Photometric Results from 1995 to 2004

We present results from the most recent (2002-2004) observing campaigns of the eclipsing system KH 15D, in addition to re-reduced data obtained at Van Vleck Observatory (VVO) between 1995 and 2000. Phasing nine years of photometric data shows substantial evolution in the width and depth of the eclipses. The most recent data indicate that the eclipses are now approximately 24 days in length, or half the orbital period. These results are interpreted and discussed in the context of the recent models for this system put forward by Winn et al. and Chiang & Murray-Clay. A periodogram of the entire data set yields a highly significant peak at 48.37 +/- 0.01 days, which is in accord with the spectroscopic period of 48.38 +/- 0.01 days determined by Johnson et al. Another significant peak, at 9.6 days, was found in the periodogram of the out-of-eclipse data at two different epochs. We interpret this as the rotation period of the visible star and argue that it may be tidally locked in pseudosynchronism with its orbital motion. If so, application of Hut's theory implies that the eccentricity of the orbit is e = 0.65 +/- 0.01. Analysis of the UVES/VLT spectra obtained by Hamilton et al. shows that the v sin(i) of the visible star in this system is 6.9 +/- 0.3 km/sec. Using this value of v sin(i) and the measured rotation period of the star, we calculate the lower limit on the radius to be R = (1.3 +/- 0.1), R_Sun, which concurs with the value obtained by Hamilton et al. from its luminosity and effective temperature. Here we assume that i = 90 degrees since it is likely that the spin and orbital angular momenta vectors are nearly aligned.

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arXiv2005

A Jovian-mass Planet in Microlensing Event OGLE-2005-BLG-071

We report the discovery of a several-Jupiter mass planetary companion to the primary lens star in microlensing event OGLE-2005-BLG-071. Precise (<1%) photometry at the peak of the event yields an extremely high signal-to-noise ratio detection of a deviation from the light curve expected from an isolated lens. The planetary character of this deviation is easily and unambiguously discernible from the gross features of the light curve. Detailed modeling yields a tightly-constrained planet-star mass ratio of q=m_p/M=0.0071+/-0.0003. This is the second robust detection of a planet with microlensing, demonstrating that the technique itself is viable and that planets are not rare in the systems probed by microlensing, which typically lie several kpc toward the Galactic center.

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arXiv2004

Constraints on Planetary Companions in the Magnification A=256 Microlensing Event: OGLE-2003-BLG-423

We develop a new method of modeling microlensing events based on a Monte Carlo simulation that incorporates both a Galactic model and the constraints imposed by the observed characteristics of the event. The method provides an unbiased way to analyze the event especially when parameters are poorly constrained by the observed lightcurve. We apply this method to search for planetary companions of the lens in OGLE-2003-BLG-423, whose maximum magnification A_max=256+-43 (or A_max=400+-115 from the lightcurve data alone) is the highest among single-lens events ever recorded. The method permits us, for the first time, to place constraints directly in the planet-mass/projected-physical-separation plane rather than in the mass-ratio/Einstein-radius plane as was done previously. For example, Jupiter-mass companions of main-sequence stars at 2.5 AU are excluded with 80% efficiency.

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arXiv2004

Central Masses and Broad-Line Region Sizes of Active Galactic Nuclei. II. A Homogeneous Analysis of a Large Reverberation-Mapping Database

We present improved black hole masses for 35 active galactic nuclei (AGNs) based on a complete and consistent reanalysis of broad emission-line reverberation-mapping data. From objects with multiple line measurements, we find that the highest precision measure of the virial product is obtained by using the cross-correlation function centroid (as opposed to the cross-correlation function peak) for the time delay and the line dispersion (as opposed to full width half maximum) for the line width and by measuring the line width in the variable part of the spectrum. Accurate line-width measurement depends critically on avoiding contaminating features, in particular the narrow components of the emission lines. We find that the precision (or random component of the error) of reverberation-based black hole mass measurements is typically around 30%, comparable to the precision attained in measurement of black hole masses in quiescent galaxies by gas or stellar dynamical methods. Based on results presented in a companion paper by Onken et al., we provide a zero-point calibration for the reverberation-based black hole mass scale by using the relationship between black hole mass and host-galaxy bulge velocity dispersion. The scatter around this relationship implies that the typical systematic uncertainties in reverberation-based black hole masses are smaller than a factor of three. We present a preliminary version of a mass-luminosity relationship that is much better defined than any previous attempt. Scatter about the mass-luminosity relationship for these AGNs appears to be real and could be correlated with either Eddington ratio or object inclination.

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arXiv2004

OGLE-2003-BLG-238: Microlensing Mass Estimate of an Isolated Star

Microlensing is the only known direct method to measure the masses of stars that lack visible companions. In terms of microlensing observables, the mass is given by M=(c^2/4G)\tilde r_E θ_E and so requires the measurement of both the angular Einstein radius, θ_E, and the projected Einstein radius, \tilde r_E. Simultaneous measurement of these two parameters is extremely rare. Here we analyze OGLE-2003-BLG-238, a spectacularly bright (I_min=10.3), high-magnification (A_max = 170) microlensing event. Pronounced finite source effects permit a measurement of θ_E = 650 uas. Although the timescale of the event is only t_E = 38 days, one can still obtain weak constraints on the microlens parallax: 4.4 AU < \tilde r_E < 18 AU at the 1 σlevel. Together these two parameter measurements yield a range for the lens mass of 0.36 M_sun < M < 1.48 M_sun. As was the case for MACHO-LMC-5, the only other single star (apart from the Sun) whose mass has been determined from its gravitational effects, this estimate is rather crude. It does, however, demonstrate the viability of the technique. We also discuss future prospects for single-lens mass measurements.

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arXiv2004

MOA 2003-BLG-37: A Bulge Jerk-Parallax Microlens Degeneracy

We analyze the Galactic bulge microlensing event MOA-2003-BLG-37. Although the Einstein timescale is relatively short, t_e=43 days, the lightcurve displays deviations consistent with parallax effects due to the Earth's accelerated motion. We show that the chi^2 surface has four distinct local minima that are induced by the ``jerk-parallax'' degeneracy, with pairs of solutions having projected Einstein radii, \tilde r_e = 1.76 AU and 1.28 AU, respectively. This is the second event displaying such a degeneracy and the first toward the Galactic bulge. For both events, the jerk-parallax formalism accurately describes the offsets between the different solutions, giving hope that when extra solutions exist in future events, they can easily be found. However, the morphologies of the chi^2 surfaces for the two events are quite different, implying that much remains to be understood about this degeneracy.

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arXiv2004

Jet emission in NGC1052 at radio, optical, and X-ray frequencies

We present a combined radio, optical, and X-ray study of the nearby LINER galaxy NGC 1052. Data from a short (2.3 ksec) {\it CHANDRA} observation of NGC 1052 reveal the presence of various jet-related X-ray emitting regions, a bright compact core and unresolved knots in the jet structure as well as an extended emitting region inside the galaxy well aligned with the radio synchrotron jet-emission. The spectrum of the extended X-ray emission can best be fitted with a thermal model with $kT = (0.4-0.5)$ keV, while the compact core exhibits a very flat spectrum, best approximated by an absorbed power-law with $N_{\rm H} = (0.6-0.8) \times 10^{22} {\rm cm^{-2}}$. We compare the radio structure to an optical ``structure map'' from a {\it Hubble Space Telescope} ({\it HST}) observation and find a good positional correlation between the radio jet and the optical emission cone. Bright, compact knots in the jet structure are visible in all three frequency bands whose spectrum is inconsistent with synchrotron emission.

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arXiv2003

The Spectral Energy Distribution and Emission-Line properties of the NLS1 Galaxy Arakelian 564

We present the intrinsic spectral energy distribution (SED) of the NLS1 Arakelian 564, constructed with contemporaneous data obtained during a multi-wavelength, multi-satellite observing campaign in 2000 and 2001. We compare it with that of the NLS1 Ton S180 and with those obtained for BLS1s to infer how the relative accretion rates vary among the Sy1 population. Although the peak of the SED is not well constrained, most of the energy is emitted in the 10-100 eV regime, constituting roughly half of the emitted energy in the optical/X-ray ranges. This is consistent with a primary spectral component peaking in the extreme UV/soft X-ray band, and disk-corona models, hence high accretion rates. Indeed, we estimate that \dot{m}~1. We examine the emission lines in its spectrum, and we constrain the physical properties of the line-emitting gas through photoionization modeling. The line-emitting gas is characterized by log n~11 and log U~0, and is stratified around log U~0. Our estimate of the radius of the Hβ-emitting region ~10 \pm 2 lt-days is consistent with the radius-luminosity relationships found for Sy1 galaxies. We also find evidence for super-solar metallicity in this NLS1. We show that the emission lines are not good diagnostics for the underlying SEDs and that the absorption line studies offer a far more powerful tool to determine the ionizing continuum of AGNs, especially if comparing the lower- and higher-ionization lines.

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arXiv2003

OGLE-2003-BLG-262: Finite-Source Effects from a Point-Mass Lens

We analyze OGLE-2003-BLG-262, a relatively short, t_E=12.5+-0.1day, microlensing event generated by a point-mass lens transiting the face of a K giant source in the Galactic bulge. We use the resulting finite-source effects to measure the angular Einstein radius, theta_E=195+-17muas, and so constrain the lens mass to the full-width half-maximum interval 0.08 < M/M_sun < 0.54. The lens-source relative proper motion is mu_rel = 27+-2 km/s/kpc. Both values are typical of what is expected for lenses detected toward the bulge. Despite the short duration of the event, we detect marginal evidence for a "parallax asymmetry", but argue that this is more likely to be induced by acceleration of the source, a binary lens, or possibly by statistical fluctuations. Although OGLE-2003-BLG-262 is only the second published event to date in which the lens transits the source, such events will become more common with the new OGLE-III survey in place. We therefore give a detailed account of the analysis of this event to facilitate the study of future events of this type.

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arXiv2003

High-Precicison Limb-Darkening Measurement of a K3 Giant Using Microlensing

We obtain high-precision limb-darkening measurements in five bands (V, V_E, I_E, I, and H) for the K3 III (Teff=4200 K, [Fe/H]=+0.3, log(g)=2.3) source of the Galactic bulge microlensing event EROS BLG-2000-5. These measurements are inconsistent with the predictions of atmospheric models at >10 sigma. While the disagreement is present in all bands, it is most apparent in I, I_E and V_E, in part because the data are better and in part because the intrinsic disagreement is stronger. We find that when limb-darkening profiles are normalized to have unit total flux, the I-band models for a broad range of temperatures all cross each other at a common point. The solar profile also passes through this point. However, the profile as measured by microlensing does not. We conjecture that the models have incorporated some aspect of solar physics that is not shared by giant atmospheres.

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arXiv2003

The Twin-Jet of NGC1052 at Radio, Optical, and X-ray Frequencies

We present results from a combined radio, optical, and X-ray study of the jet-associated emission features in NGC1052. We analyse the radio-optical morphology and find a good positional correlation between the radio jet and the optical emission cone. Two optical emission knots are directly associated with radio counterparts exhibiting a radio to X-ray broadband spectrum not compatible with synchrotron emission. We discuss the possibility that the thermal soft spectrum of the extended X-ray emission originates from jet driven shocks produced in the interaction between the jet-plasma and its surrounding medium.

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arXiv2002

Morphological Classification of the OSU Bright Spiral Galaxy Survey

To quantify the distribution of bar shapes in spiral galaxies, we have analysed 113 H-band and 89 B-band galaxy images from the Ohio State University Bright Spiral Galaxy Survey. Parameters measuring bar shape and position along the Hubble sequence were obtained in each waveband. Evidence was found for a bimodality in the distribution of bar shape, implying that barred and unbarred galaxies are not just the extrema of a single distribution, and that any evolution between these two states must occur on a rapid timescale. Objective bar shapes measured in the H-band were found to be more closely related to visual classifications than B-band bar strengths, as the B-band images are somewhat compromised by localised star formation, especially in later-type systems. Galaxies were found to be more centrally concentrated in the infrared. Later type galaxies showed greater asymmetry in the optical than the infrared, presumably again due to localised star formation, but on average the bar strengths in the two bands were found to be the same.

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arXiv2002

FUSE Observations of the Narrow-Line Seyfert 1 Galaxy Arakelian 564

We present a 63 ks FUSE observation of the Narrow-Line Seyfert 1 galaxy Arakelian 564. The spectrum is dominated by the strong emission in the O VI λ\lambda1032, 1038 resonance doublet. Strong, heavily saturated absorption troughs due to Lyman series of Hydrogen, O VI and C III λ977 at velocities near the systemic redshift of Arakelian564 are also observed. We used the column densities of O VI and C III in conjunction with the published column densities of species observed in the UV and X-ray bands to derive constraints on the physical parameters of the absorber through photoionization modeling. The available data suggest that the UV and X-ray absorbers in Arakelian~564 are physically related, and possibly identical. The combination of constraints indicates that the absorber is characterized by a narrow range in total column density N_H and U, centered at log N_H ~ 21 and log U ~ -1.5, and may be spatially extended along the line of sight.

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arXiv2002

First microlens mass measurement: PLANET photometry of EROS BLG-2000-5

We analyze PLANET photometric observations of the caustic-crossing binary-lens microlensing event, EROS BLG-2000-5, and find that modeling the observed light curve requires incorporation of the microlens parallax and the binary orbital motion. The projected Einstein radius (~r_E = 3.61 +/- 0.11 AU) is derived from the measurement of the microlens parallax, and we are also able to infer the angular Einstein radius (theta_E = 1.38 +/- 0.12 mas) from the finite source effect on the light curve, combined with an estimate of the angular size of the source given by the source position in a color-magnitude diagram. The lens mass, M = 0.612 +/- 0.057 M_sun, is found by combining these two quantities. This is the first time that parallax effects are detected for a caustic-crossing event and also the first time that the lens mass degeneracy has been completely broken through photometric monitoring alone. The combination of the projected Einstein radius and the angular Einstein radius also allows us to conclude that the lens lies in the near side of the disk, within 2.6 kpc of the Sun, while the radial velocity measurement indicates that the source is a Galactic bulge giant.

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arXiv2002

A Short, Non-Planetary, Microlensing Anomaly: Observations and Lightcurve Analysis of MACHO 99-BLG-47

We analyze PLANET and MACHO observations of MACHO 99-BLG-47, the first nearly-normal microlensing event for which high signal-to-noise-ratio data reveal a well-covered, short-duration anomaly. This anomaly occurs near the the peak of the event. Short-duration anomalies near the peak of otherwise normal events are expected to arise both from extreme-separation (either very close or very wide), roughly equal-mass binary lenses, and from planetary systems. We show that the lens of MACHO 99-BLG-47 is in fact an extreme-separation binary, not a planetary system, thus demonstrating for the first time that these two important classes of events can be distinguished in practice. However, we find that the wide-binary and close-binary lens solutions fit the data equally well, and cannot be distinguished even at Delta-chi^2=1. This degeneracy is qualitatively much more severe than the one identified for MACHO 98-SMC-1 because the present degeneracy spans two rather than one dimension in the magnification field and does not require significantly different blending fractions. In the appendix, we explore this result, and show that it is related to the symmetry in the lens equation.

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