arXiv subjects

R. W. Pogge

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

At least 73 records · Page 4Linked to original sources

arXiv2017

OGLE-2016-BLG-0596Lb: High-Mass Planet From High-Magnification Pure-Survey Microlensing Event

We report the discovery of a high mass-ratio planet $q=0.012$, i.e., 13 times higher than the Jupiter/Sun ratio. The host mass is not presently measured but can be determined or strongly constrained from adaptive optics imaging. The planet was discovered in a small archival study of high-magnification events in pure-survey microlensing data, which was unbiased by the presence of anomalies. The fact that it was previously unnoticed may indicate that more such planets lie in archival data and could be discovered by similar systematic study. In order to understand the transition from predominantly survey+followup to predominately survey-only planet detections, we conduct the first analysis of these detections in the observational $(s,q)$ plane. Here $s$ is projected separation in units of the Einstein radius. We find some evidence that survey+followup is relatively more sensitive to planets near the Einstein ring, but that there is no statistical difference in sensitivity by mass ratio.

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arXiv2017

Binary Source Microlensing Event OGLE-2016-BLG-0733: Interpretation of A Long-term Asymmetric Perturbation

In the process of analyzing an observed light curve, one often confronts various scenarios that can mimic the planetary signals causing difficulties in the accurate interpretation of the lens system. In this paper, we present the analysis of the microlensing event OGLE-2016-BLG-0733. The light curve of the event shows a long-term asymmetric perturbation that would appear to be due to a planet. From the detailed modeling of the lensing light curve, however, we find that the perturbation originates from the binarity of the source rather than the lens. This result demonstrates that binary sources with roughly equal-luminosity components can mimic long-term perturbations induced by planets with projected separations near the Einstein ring. The result also represents the importance of the consideration of various interpretations in planet-like perturbations and of high-cadence observations for ensuring the unambiguous detection of the planet.

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arXiv2017

Space Telescope and Optical Reverberation Mapping Project. V. Optical Spectroscopic Campaign and Emission-Line Analysis for NGC 5548

We present the results of an optical spectroscopic monitoring program targeting NGC 5548 as part of a larger multi-wavelength reverberation mapping campaign. The campaign spanned six months and achieved an almost daily cadence with observations from five ground-based telescopes. The H$β$ and He II $λ$4686 broad emission-line light curves lag that of the 5100 $Å$ optical continuum by $4.17^{+0.36}_{-0.36}$ days and $0.79^{+0.35}_{-0.34}$ days, respectively. The H$β$ lag relative to the 1158 $Å$ ultraviolet continuum light curve measured by the Hubble Space Telescope is roughly $\sim$50% longer than that measured against the optical continuum, and the lag difference is consistent with the observed lag between the optical and ultraviolet continua. This suggests that the characteristic radius of the broad-line region is $\sim$50% larger than the value inferred from optical data alone. We also measured velocity-resolved emission-line lags for H$β$ and found a complex velocity-lag structure with shorter lags in the line wings, indicative of a broad-line region dominated by Keplerian motion. The responses of both the H$β$ and He II $λ$4686 emission lines to the driving continuum changed significantly halfway through the campaign, a phenomenon also observed for C IV, Ly $α$, He II(+O III]), and Si IV(+O IV]) during the same monitoring period. Finally, given the optical luminosity of NGC 5548 during our campaign, the measured H$β$ lag is a factor of five shorter than the expected value implied by the $R_\mathrm{BLR} - L_\mathrm{AGN}$ relation based on the past behavior of NGC 5548.

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arXiv2016

Space Telescope and Optical Reverberation Mapping Project VI: reverberating Disk Models for NGC 5548

We conduct a multiwavelength continuum variability study of the Seyfert 1 galaxy NGC 5548 to investigate the temperature structure of its accretion disk. The 19 overlapping continuum light curves (1158 to 9157 angstroms) combine simultaneous HST , Swift , and ground-based observations over a 180 day period from 2014 January to July. Light-curve variability is interpreted as the reverberation response of the accretion disk to irradiation by a central time-varying point source. Our model yields the disk inclination, i, temperature T1 at 1 light day from the black hole, and a temperature-radius slope, alpha. We also infer the driving light curve and find that it correlates poorly with both the hard and soft X-ray light curves, suggesting that the X-rays alone may not drive the ultraviolet and optical variability over the observing period. We also decompose the light curves into bright, faint, and mean accretion-disk spectra. These spectra lie below that expected for a standard blackbody accretion disk accreting at L/LEdd = 0.1

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arXiv2016

The First Circumbinary Planet Found by Microlensing: OGLE-2007-BLG-349L(AB)c

We present the analysis of the first circumbinary planet microlensing event, OGLE-2007-BLG-349. This event has a strong planetary signal that is best fit with a mass ratio of $q \approx 3.4\times10^{-4}$, but there is an additional signal due to an additional lens mass, either another planet or another star. We find acceptable light curve fits with two classes of models: 2-planet models (with a single host star) and circumbinary planet models. The light curve also reveals a significant microlensing parallax effect, which constrains the mass of the lens system to be $M_L \approx 0.7 M_\odot$. Hubble Space Telescope images resolve the lens and source stars from their neighbors and indicate excess flux due to the star(s) in the lens system. This is consistent with the predicted flux from the circumbinary models, where the lens mass is shared between two stars, but there is not enough flux to be consistent with the 2-planet, 1-star models. So, only the circumbinary models are consistent with the HST data. They indicate a planet of mass $m_c = 80\pm 13\,M_\oplus$, orbiting a pair of M-dwarfs with masses of $M_A = 0.41\pm 0.07 M_\odot$ and $M_B = 0.30\pm 0.07 M_\oplus$, which makes this the lowest mass circumbinary planet system known. The ratio of the separation between the planet and the center-of-mass to the separations of the two stars is $\sim 40$, so unlike most of the circumbinary planets found by Kepler, the planet does not orbit near the stability limit.

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arXiv2016

OGLE-2015-BLG-0479LA,B: Binary Gravitational Microlens Characterized by Simultaneous Ground-based and Space-based Observation

We present a combined analysis of the observations of the gravitational microlensing event OGLE-2015-BLG-0479 taken both from the ground and by the {\it Spitzer Space Telescope}. The light curves seen from the ground and from space exhibit a time offset of $\sim 13$ days between the caustic spikes, indicating that the relative lens-source positions seen from the two places are displaced by parallax effects. From modeling the light curves, we measure the space-based microlens parallax. Combined with the angular Einstein radius measured by analyzing the caustic crossings, we determine the mass and distance of the lens. We find that the lens is a binary composed of two G-type stars with masses $\sim 1.0\ M_\odot$ and $\sim 0.9\ M_\odot$ located at a distance $\sim 3$ kpc. In addition, we are able to constrain the complete orbital parameters of the lens thanks to the precise measurement of the microlens parallax derived from the joint analysis. In contrast to the binary event OGLE-2014-BLG-1050, which was also observed by {\it Spitzer}, we find that the interpretation of OGLE-2015-BLG-0479 does not suffer from the degeneracy between $(\pm,\pm)$ and $(\pm,\mp)$ solutions, confirming that the four-fold parallax degeneracy in single-lens events collapses into the two-fold degeneracy for the general case of binary-lens events. The location of the blend in the color-magnitude diagram is consistent with the lens properties, suggesting that the blend is the lens itself. The blend is bright enough for spectroscopy and thus this possibility can be checked from future follow-up observations.

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arXiv2016

A Super-Jupiter Microlens Planet Characterized by High-Cadence KMTNet Microlensing Survey Observations of OGLE-2015-BLG-0954

We report the characterization of a massive (m_p=3.9 +- 1.4 M_jup) microlensing planet (OGLE-2015-BLG-0954Lb) orbiting an M dwarf host (M=0.33 +- 0.12 M_sun) at a distance toward the Galactic bulge of 0.6 (+0.4,-0.2) kpc, which is extremely nearby by microlensing standards. The planet-host projected separation is a_perp ~ 1.2 AU. The characterization was made possible by the wide-field (4 sq. deg.) high cadence (Gamma = 6/hr) monitoring of the Korea Microlensing Telescope Network (KMTNet), which had two of its three telescopes in commissioning operations at the time of the planetary anomaly. The source crossing time t_* = 16 min is among the shortest ever published. The high-cadence, wide-field observations that are the hallmark of KMTNet are the only way to routinely capture such short crossings. High-cadence resolution of short caustic crossings will preferentially lead to mass and distance measurements for the lens. This is because the short crossing time typically implies a nearby lens, which enables the measurement of additional effects (bright lens and/or microlens parallax). When combined with the measured crossing time, these effects can yield planet/host masses and distance.

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arXiv2016

First simultaneous microlensing observations by two space telescopes: $Spitzer$ & $Swift$ reveal a brown dwarf in event OGLE-2015-BLG-1319

Simultaneous observations of microlensing events from multiple locations allow for the breaking of degeneracies between the physical properties of the lensing system, specifically by exploring different regions of the lens plane and by directly measuring the "microlens parallax". We report the discovery of a 30-55$M_J$ brown dwarf orbiting a K dwarf in microlensing event OGLE-2015-BLG-1319. The system is located at a distance of $\sim$5 kpc toward the Galactic bulge. The event was observed by several ground-based groups as well as by $Spitzer$ and $Swift$, allowing the measurement of the physical properties. However, the event is still subject to an 8-fold degeneracy, in particular the well-known close-wide degeneracy, and thus the projected separation between the two lens components is either $\sim$0.25 AU or $\sim$45 AU. This is the first microlensing event observed by $Swift$, with the UVOT camera. We study the region of microlensing parameter space to which $Swift$ is sensitive, finding that while for this event $Swift$ could not measure the microlens parallax with respect to ground-based observations, it can be important for other events. Specifically, for detecting nearby brown dwarfs and free-floating planets in high magnification events.

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arXiv2016

The First Neptune Analog or Super-Earth with Neptune-like Orbit: MOA-2013-BLG-605Lb

We present the discovery of the first Neptune analog exoplanet or super-Earth with Neptune-like orbit, MOA-2013-BLG-605Lb. This planet has a mass similar to that of Neptune or a super-Earth and it orbits at $9\sim 14$ times the expected position of the snow-line, $a_{\rm snow}$, which is similar to Neptune's separation of $ 11\,a_{\rm snow}$ from the Sun. The planet/host-star mass ratio is $q=(3.6\pm0.7)\times 10^{-4}$ and the projected separation normalized by the Einstein radius is $s=2.39\pm0.05$. There are three degenerate physical solutions and two of these are due to a new type of degeneracy in the microlensing parallax parameters, which we designate "the wide degeneracy". The three models have (i) a Neptune-mass planet with a mass of $M_{\rm p}=21_{-7}^{+6} M_{Earth}$ orbiting a low-mass M-dwarf with a mass of $M_{\rm h}=0.19_{-0.06}^{+0.05} M_\odot$, (ii) a mini-Neptune with $M_{\rm p}= 7.9_{-1.2}^{+1.8} M_{Earth}$ orbiting a brown dwarf host with $M_{\rm h}=0.068_{-0.011}^{+0.019} M_\odot$ and (iii) a super-Earth with $M_{\rm p}= 3.2_{-0.3}^{+0.5} M_{Earth}$ orbiting a low-mass brown dwarf host with $M_{\rm h}=0.025_{-0.004}^{+0.005} M_\odot$ which is slightly favored. The 3-D planet-host separations are 4.6$_{-1.2}^{+4.7}$ AU, 2.1$_{-0.2}^{+1.0}$ AU and 0.94$_{-0.02}^{+0.67}$ AU, which are $8.9_{-1.4}^{+10.5}$, $12_{-1}^{+7}$ or $14_{-1}^{+11}$ times larger than $a_{\rm snow}$ for these models, respectively. The Keck AO observation confirm that the lens is faint. This discovery suggests that low-mass planets with Neptune-like orbit are common. So processes similar to the one that formed Neptune in our own Solar System or cold super-Earth may be common in other solar systems.

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arXiv2016

Mass Measurements of Isolated Objects from Space-based Microlensing

We report on the mass and distance measurements of two single-lens events from the 2015 \emph{Spitzer} microlensing campaign. With both finite-source effect and microlens parallax measurements, we find that the lens of OGLE-2015-BLG-1268 is very likely a brown dwarf. Assuming that the source star lies behind the same amount of dust as the Bulge red clump, we find the lens is a $45\pm7$ $M_{\rm J}$ brown dwarf at $5.9\pm1.0$ kpc. The lens of of the second event, OGLE-2015-BLG-0763, is a $0.50\pm0.04$ $M_\odot$ star at $6.9\pm1.0$ kpc. We show that the probability to definitively measure the mass of isolated microlenses is dramatically increased once simultaneous ground- and space-based observations are conducted.

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arXiv2016

Space Telescope and Optical Reverberation Mapping Project. IV. Anomalous behavior of the broad ultraviolet emission lines in NGC 5548

During an intensive Hubble Space Telescope (HST) Cosmic Origins Spectrograph (COS) UV monitoring campaign of the Seyfert~1 galaxy NGC 5548 performed from 2014 February to July, the normally highly correlated far-UV continuum and broad emission-line variations decorrelated for ~60 to 70 days, starting ~75 days after the first HST/COS observation. Following this anomalous state, the flux and variability of the broad emission lines returned to a more normal state. This transient behavior, characterised by significant deficits in flux and equivalent width of the strong broad UV emission lines, is the first of its kind to be unambiguously identified in an active galactic nucleus reverberation mapping campaign. The largest corresponding emission-line flux deficits occurred for the high-ionization collisionally excited lines, C IV and Si IV(+O IV]), and also He II(+O III]), while the anomaly in Ly-alpha was substantially smaller. This pattern of behavior indicates a depletion in the flux of photons with E_{\rm ph} > 54 eV, relative to those near 13.6 eV. We suggest two plausible mechanisms for the observed behavior: (i) temporary obscuration of the ionizing continuum incident upon BLR clouds by a moving veil of material lying between the inner accretion disk and inner BLR, perhaps resulting from an episodic ejection of material from the disk, or (ii) a temporary change in the intrinsic ionizing continuum spectral energy distribution resulting in a deficit of ionizing photons with energies > 54 eV, possibly due to a transient restructuring of the Comptonizing atmosphere above the disk. Current evidence appears to favor the latter explanation.

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arXiv2016

Space Telescope and Optical Reverberation Mapping Project. III. Optical Continuum Emission and Broad-Band Time Delays in NGC 5548

We present ground-based optical photometric monitoring data for NGC 5548, part of an extended multi-wavelength reverberation mapping campaign. The light curves have nearly daily cadence from 2014 January to July in nine filters (\emph{BVRI} and \emph{ugriz}). Combined with ultraviolet data from the \emph{Hubble Space Telescope} and \emph{Swift}, we confirm significant time delays between the continuum bands as a function of wavelength, extending the wavelength coverage from 1158\,Å to the $z$ band ($\sim\!9160$\,Å). We find that the lags at wavelengths longer than the {\it V} band are equal to or greater than the lags of high-ionization-state emission lines (such as He\,{\sc ii}\,$λ1640$ and $λ4686$), suggesting that the continuum-emitting source is of a physical size comparable to the inner broad-line region (BLR). The trend of lag with wavelength is broadly consistent with the prediction for continuum reprocessing by an accretion disk with $τ\propto λ^{4/3}$. However, the lags also imply a disk radius that is 3 times larger than the prediction from standard thin-disk theory, assuming that the bolometric luminosity is 10\% of the Eddington luminosity ($L = 0.1L_{\rm Edd}$). Using optical spectra from the Large Binocular Telescope, we estimate the bias of the interband continuum lags due to BLR emission observed in the filters. We find that the bias for filters with high levels of BLR contamination ($\sim\! 20\%$) can be important for the shortest continuum lags, and likely has a significant impact on the {\it u} and {\it U} bands owing to Balmer continuum emission.

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arXiv2016

Spitzer Observations of OGLE-2015-BLG-1212 Reveal a New Path to Breaking Strong Microlens Degeneracies

Spitzer microlensing parallax observations of OGLE-2015-BLG-1212 decisively breaks a degeneracy between planetary and binary solutions that is somewhat ambiguous when only ground-based data are considered. Only eight viable models survive out of an initial set of 32 local minima in the parameter space. These models clearly indicate that the lens is a stellar binary system possibly located within the bulge of our Galaxy, ruling out the planetary alternative. We argue that several types of discrete degeneracies can be broken via such space-based parallax observations.

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arXiv2016

OGLE-2012-BLG-0563Lb: a Saturn-mass Planet around an M Dwarf with the Mass Constrained by Subaru AO imaging

We report the discovery of a microlensing exoplanet OGLE-2012-BLG-0563Lb with the planet-star mass ratio ~1 x 10^{-3}. Intensive photometric observations of a high-magnification microlensing event allow us to detect a clear signal of the planet. Although no parallax signal is detected in the light curve, we instead succeed at detecting the flux from the host star in high-resolution JHK'-band images obtained by the Subaru/AO188 and IRCS instruments, allowing us to constrain the absolute physical parameters of the planetary system. With the help of a spectroscopic information about the source star obtained during the high-magnification state by Bensby et al., we find that the lens system is located at 1.3^{+0.6}_{-0.8} kpc from us, and consists of an M dwarf (0.34^{+0.12}_{-0.20} M_sun) orbited by a Saturn-mass planet (0.39^{+0.14}_{-0.23} M_Jup) at the projected separation of 0.74^{+0.26}_{-0.42} AU (close model) or 4.3^{+1.5}_{-2.5} AU (wide model). The probability of contamination in the host star's flux, which would reduce the masses by a factor of up to three, is estimated to be 17%. This possibility can be tested by future high-resolution imaging. We also estimate the (J-Ks) and (H-Ks) colors of the host star, which are marginally consistent with a low metallicity mid-to-early M dwarf, although further observations are required for the metallicity to be conclusive. This is the fifth sub-Jupiter-mass (0.2<m_p/M_Jup<1) microlensing planet around an M dwarf with the mass well constrained. The relatively rich harvest of sub-Jupiters around M dwarfs is contrasted with a possible paucity of ~1--2 Jupiter-mass planets around the same type of star, which can be explained by the planetary formation process in the core-accretion scheme.

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arXiv2016

The Evolved Main-Sequence Channel: HST and LBT observations of CSS120422:111127+571239

The "evolved main-sequence" channel is thought to contribute significantly to the population of AM CVn type systems in the Galaxy, and also to the number of cataclysmic variables detected below the period minimum for hydrogen rich systems. CSS120422:J111127+571239 was discovered by the Catalina Sky Survey in April 2012. Its period was found to be 56 minutes, well below the minimum, and the optical spectrum is clearly depleted in hydrogen relative to helium, but still has two orders of magnitude more hydrogen than AM CVn stars. Doppler tomography of the H$α$ line hinted at a spiral structure existing in the disk. Here we present spectroscopy of CSS120422:J111127+571239 using the COS FUV instrument on the Hubble Space Telescope and using the MODS spectrograph on the Large Binocular Telescope. The UV spectrum shows SiIV, NV and HeII, but no detectable CIV. The anomalous nitrogen/carbon ratio is seen in a small number of other CVs and confirms a unique binary evolution. We also present and compare the optical spectrum of V418 Ser and advocate that it is also an evolved main-sequence system.

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arXiv2015

Spitzer Microlens Measurement of a Massive Remnant in a Well-Separated Binary

We report the detection and mass measurement of a binary lens OGLE-2015-BLG-1285La,b, with the more massive component having $M_1>1.35\,M_\odot$ (80% probability). A main-sequence star in this mass range is ruled out by limits on blue light, meaning that a primary in this mass range must be a neutron star or black hole. The system has a projected separation $r_\perp= 6.1\pm 0.4\,{\rm AU}$ and lies in the Galactic bulge. These measurements are based on the "microlens parallax" effect, i.e., comparing the microlensing light curve as seen from $Spitzer$, which lay at $1.25\,{\rm AU}$ projected from Earth, to the light curves from four ground-based surveys, three in the optical and one in the near infrared. Future adaptive optics imaging of the companion by 30m class telescopes will yield a much more accurate measurement of the primary mass. This discovery both opens the path and defines the challenges to detecting and characterizing black holes and neutron stars in wide binaries, with either dark or luminous companions. In particular, we discuss lessons that can be applied to future $Spitzer$ and $Kepler$ K2 microlensing parallax observations.

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arXiv2015

Red noise versus planetary interpretations in the microlensing event OGLE-2013-BLG-446

For all exoplanet candidates, the reliability of a claimed detection needs to be assessed through a careful study of systematic errors in the data to minimize the false positives rate. We present a method to investigate such systematics in microlensing datasets using the microlensing event OGLE-2013-BLG-0446 as a case study. The event was observed from multiple sites around the world and its high magnification (A_{max} \sim 3000) allowed us to investigate the effects of terrestrial and annual parallax. Real-time modeling of the event while it was still ongoing suggested the presence of an extremely low-mass companion (\sim 3M_\oplus ) to the lensing star, leading to substantial follow-up coverage of the light curve. We test and compare different models for the light curve and conclude that the data do not favour the planetary interpretation when systematic errors are taken into account.

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arXiv2015

Spitzer IRAC Photometry for Time Series in Crowded Fields

We develop a new photometry algorithm that is optimized for $Spitzer$ time series in crowded fields and that is particularly adapted to faint and/or heavily blended targets. We apply this to the 170 targets from the 2015 $Spitzer$ microlensing campaign and present the results of three variants of this algorithm in an online catalog. We present detailed accounts of the application of this algorithm to two difficult cases, one very faint and the other very crowded. Several of $Spitzer$'s instrumental characteristics that drive the specific features of this algorithm are shared by $Kepler$ and $WFIRST$, implying that these features may prove to be a useful starting point for algorithms designed for microlensing campaigns by these other missions.

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