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Title: Detection of Time Lags between Quasar Continuum Emission Bands Based On Pan-STARRS Light Curves

Abstract

We study the time lags between the continuum emission of quasars at different wavelengths, based on more than four years of multi-band ( g , r , i , z ) light curves in the Pan-STARRS Medium Deep Fields. As photons from different bands emerge from different radial ranges in the accretion disk, the lags constrain the sizes of the accretion disks. We select 240 quasars with redshifts of z ≈ 1 or z ≈ 0.3 that are relatively emission-line free. The light curves are sampled from day to month timescales, which makes it possible to detect lags on the scale of the light crossing time of the accretion disks. With the code JAVELIN , we detect typical lags of several days in the rest frame between the g band and the riz bands. The detected lags are ∼2–3 times larger than the light crossing time estimated from the standard thin disk model, consistent with the recently measured lag in NGC 5548 and microlensing measurements of quasars. The lags in our sample are found to increase with increasing luminosity. Furthermore, the increase in lags going from g − r to g − i and then to g − z ismore » slower than predicted in the thin disk model, particularly for high-luminosity quasars. The radial temperature profile in the disk must be different from what is assumed. We also find evidence that the lags decrease with increasing line ratios between ultraviolet Fe ii lines and Mg ii, which may point to changes in the accretion disk structure at higher metallicity.« less

Authors:
 [1]; ; ;  [2];  [3]; ;  [4]; ;  [5]; ;  [6];  [7];  [8];  [9]; ; ; ; ; ;  [10] more »; « less
  1. Kavli Institute for Theoretical Physics, University of California, Santa Barbara, CA 93106 (United States)
  2. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
  3. Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States)
  4. Department of Astronomy, University of Illinois at Urbana-Champaign, Urbana, IL 61801 (United States)
  5. Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States)
  6. Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802 (United States)
  7. Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany)
  8. Institute for Applied Computational Science, John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138 (United States)
  9. Astrophysics, Imperial College London, Blackett Laboratory, London SW7 2AZ (United Kingdom)
  10. Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu HI 96822 (United States)
Publication Date:
OSTI Identifier:
22667720
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 836; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCRETION DISKS; DETECTION; EMISSION; GALAXIES; GALAXY NUCLEI; LUMINOSITY; METALLICITY; PHOTONS; QUASARS; RED SHIFT; ULTRAVIOLET RADIATION; VISIBLE RADIATION; WAVELENGTHS

Citation Formats

Jiang, Yan-Fei, Green, Paul J., Pancoast, Anna, MacLeod, Chelsea L., Greene, Jenny E., Morganson, Eric, Shen, Yue, Anderson, Scott F., Ruan, John J., Brandt, W. N., Grier, C. J., Rix, H.-W., Protopapas, Pavlos, Scott, Caroline, Burgett, W. S., Hodapp, K. W., Huber, M. E., Kaiser, N., Kudritzki, R. P., Magnier, E. A., and and others. Detection of Time Lags between Quasar Continuum Emission Bands Based On Pan-STARRS Light Curves. United States: N. p., 2017. Web. doi:10.3847/1538-4357/AA5B91.
Jiang, Yan-Fei, Green, Paul J., Pancoast, Anna, MacLeod, Chelsea L., Greene, Jenny E., Morganson, Eric, Shen, Yue, Anderson, Scott F., Ruan, John J., Brandt, W. N., Grier, C. J., Rix, H.-W., Protopapas, Pavlos, Scott, Caroline, Burgett, W. S., Hodapp, K. W., Huber, M. E., Kaiser, N., Kudritzki, R. P., Magnier, E. A., & and others. Detection of Time Lags between Quasar Continuum Emission Bands Based On Pan-STARRS Light Curves. United States. doi:10.3847/1538-4357/AA5B91.
Jiang, Yan-Fei, Green, Paul J., Pancoast, Anna, MacLeod, Chelsea L., Greene, Jenny E., Morganson, Eric, Shen, Yue, Anderson, Scott F., Ruan, John J., Brandt, W. N., Grier, C. J., Rix, H.-W., Protopapas, Pavlos, Scott, Caroline, Burgett, W. S., Hodapp, K. W., Huber, M. E., Kaiser, N., Kudritzki, R. P., Magnier, E. A., and and others. Mon . "Detection of Time Lags between Quasar Continuum Emission Bands Based On Pan-STARRS Light Curves". United States. doi:10.3847/1538-4357/AA5B91.
@article{osti_22667720,
title = {Detection of Time Lags between Quasar Continuum Emission Bands Based On Pan-STARRS Light Curves},
author = {Jiang, Yan-Fei and Green, Paul J. and Pancoast, Anna and MacLeod, Chelsea L. and Greene, Jenny E. and Morganson, Eric and Shen, Yue and Anderson, Scott F. and Ruan, John J. and Brandt, W. N. and Grier, C. J. and Rix, H.-W. and Protopapas, Pavlos and Scott, Caroline and Burgett, W. S. and Hodapp, K. W. and Huber, M. E. and Kaiser, N. and Kudritzki, R. P. and Magnier, E. A. and and others},
abstractNote = {We study the time lags between the continuum emission of quasars at different wavelengths, based on more than four years of multi-band ( g , r , i , z ) light curves in the Pan-STARRS Medium Deep Fields. As photons from different bands emerge from different radial ranges in the accretion disk, the lags constrain the sizes of the accretion disks. We select 240 quasars with redshifts of z ≈ 1 or z ≈ 0.3 that are relatively emission-line free. The light curves are sampled from day to month timescales, which makes it possible to detect lags on the scale of the light crossing time of the accretion disks. With the code JAVELIN , we detect typical lags of several days in the rest frame between the g band and the riz bands. The detected lags are ∼2–3 times larger than the light crossing time estimated from the standard thin disk model, consistent with the recently measured lag in NGC 5548 and microlensing measurements of quasars. The lags in our sample are found to increase with increasing luminosity. Furthermore, the increase in lags going from g − r to g − i and then to g − z is slower than predicted in the thin disk model, particularly for high-luminosity quasars. The radial temperature profile in the disk must be different from what is assumed. We also find evidence that the lags decrease with increasing line ratios between ultraviolet Fe ii lines and Mg ii, which may point to changes in the accretion disk structure at higher metallicity.},
doi = {10.3847/1538-4357/AA5B91},
journal = {Astrophysical Journal},
number = 2,
volume = 836,
place = {United States},
year = {Mon Feb 20 00:00:00 EST 2017},
month = {Mon Feb 20 00:00:00 EST 2017}
}
  • We present a pre-survey study of using the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) high sampling rate video mode guide star images to search for trans-Neptunian objects (TNOs). Guide stars are primarily used by Pan-STARRS to compensate for image motion and hence improve the point-spread function. With suitable selection of the guide stars within the Pan-STARRS 7 deg{sup 2} field of view, the light curves of these guide stars can also be used to search for occultations by TNOs. The best target stars for this purpose are stars with high signal-to-noise ratio (S/N) and small angular size. Inmore » order to do this, we compiled a catalog using the S/N calculated from stars with m{sub V} < 13 mag in the Tycho2 catalog, then cross matched these stars with the Two Micron All Sky Survey catalog, and estimated their angular sizes from (V - K) color. We also outlined a new detection method based on matched filter that is optimized to search for diffraction patterns in the light curves due to occultation by sub-kilometer TNOs. A detection threshold is set to compromise between real detections and false positives. Depending on the theoretical size distribution model used, we expect to find up to a hundred events during the three-year lifetime of the Pan-STARRS-1 project. The high sampling (30 Hz) of the project facilitates detections of small objects (as small as 400 m), which are numerous according to power-law size distribution, and thus allows us to verify various models and further constrain our understanding of the structure in the outer reach of the solar system. We have tested the detection algorithm and the pipeline on a set of engineering data (taken at 10 Hz instead of 30 Hz). No events were found within the engineering data, which is consistent with the small size of the data set and the theoretical models. Meanwhile, with a total of {approx}22 star-hours video mode data (|{beta}| < 10{sup 0}), we are able to set an upper limit of N(>0.5 km) {approx} 2.47 x 10{sup 10} deg{sup -2} at 95% confidence limit.« less
  • We present the discovery of the first high-redshift (z > 5.7) quasar from the Panoramic Survey Telescope and Rapid Response System 1 (Pan-STARRS1 or PS1). This quasar was initially detected as an i{sub P1} dropout in PS1, confirmed photometrically with the SAO Wide-field InfraRed Camera at Arizona's Multiple Mirror Telescope (MMT) and the Gamma-Ray Burst Optical/Near-Infrared Detector at the MPG 2.2 m telescope in La Silla. The quasar was verified spectroscopically with the MMT Spectrograph, Red Channel and the Cassegrain Twin Spectrograph at the Calar Alto 3.5 m telescope. Its near-infrared spectrum was taken at the Large Binocular Telescope Observatorymore » (LBT) with the LBT Near-Infrared Spectroscopic Utility with Camera and Integral Field Unit for Extragalactic Research. It has a redshift of 5.73, an AB z{sub P1} magnitude of 19.4, a luminosity of 3.8 Multiplication-Sign 10{sup 47} erg s{sup -1}, and a black hole mass of 6.9 Multiplication-Sign 10{sup 9} M{sub Sun }. It is a broad absorption line quasar with a prominent Ly{beta} peak and a very blue continuum spectrum. This quasar is the first result from the PS1 high-redshift quasar search that is projected to discover more than 100 i{sub P1} dropout quasars and could potentially find more than 10 z{sub P1} dropout (z > 6.8) quasars.« less
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  • Microlensing perturbations to the magnification of gravitationally lensed quasar images are dependent on the angular size of the quasar. If quasar variability at visible wavelengths is caused by a change in the area of the accretion disk, it will affect the microlensing magnification. We derive the expected signal, assuming that the luminosity scales with some power of the disk area, and estimate its amplitude using simulations. We discuss the prospects for detecting the effect in real-world data and for using it to estimate the logarithmic slope of the luminosity's dependence on disk area. Such an estimate would provide a directmore » test of the standard thin accretion disk model. We tried fitting six seasons of the light curves of the lensed quasar HE 0435-1223 including this effect as a modification to the Kochanek et al. approach to estimating time delays. We find a dramatic improvement in the goodness of fit and relatively plausible parameters, but a robust estimate will require a full numerical calculation in order to correctly model the strong correlations between the structure of the microlensing magnification patterns and the magnitude of the effect. We also comment briefly on the effect of this phenomenon for the stability of time-delay estimates.« less