arXiv subjects

C. W. Morgan

Publications and source records attributed to C. W. Morgan.

7 recordsLinked to original sources

arXiv2026

Joining forces: 30 years of optical monitoring of the Einstein Cross

We present an extended optical monitoring of the quadruply-imaged gravitationally lensed quasar QSO 2237+0305, the Einstein Cross, including observations from different observatories in both hemispheres and using a new photometric technique. This technique uses a region far enough from the lens system to determine accurately the sky background level, and minimises contamination from the lensing galaxy by combining analytical and numerical modeling of its structure. The resulting light curves of the four quasar images describe variations across practically the entire optical spectrum and span about 9000 days in the $VRI$ bands. The multi-band microlensing variability is captured with an unprecedented level of detail, and a preliminary microlensing analysis reveals an almost linear scaling of source radius with wavelength, providing direct evidence for the wavelength-dependent structure of the region contributing to optical passband fluxes. Specifically, assuming a mean microlens mass $\langle M \rangle$ = 0.3 $\rm{M_{\odot}}$ and concentric Gaussian sources that move according to the velocity distribution peaks (speed and direction) reported in a previous microlensing analysis, we find that the half-light radius of the $g$-band source is 9.6 $\pm$ 2.7 lt-day and the size of the sources grows with wavelength with a power-law index of $\alpha$ = 0.94 $\pm$ 0.05. We conclude that these long-term light curves set stringent empirical constraints on models of quasar emission and microlensing physics.

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arXiv2021

Resolving the inner accretion flow towards the central supermassive black hole in SDSS J1339+1310

We studied the accretion disc structure in the doubly imaged lensed quasar SDSS J1339+1310 using $r$-band light curves and UV-visible to near-IR (NIR) spectra from the first 11 observational seasons after its discovery. The 2009$-$2019 light curves displayed pronounced microlensing variations on different timescales, and this microlensing signal permitted us to constrain the half-light radius of the 1930 Å continuum-emitting region. Assuming an accretion disc with an axis inclined at 60 deg to the line of sight, we obtained log$_{10}$($r_{1/2}$/cm) = 15.4$^{+0.3}_{-0.4}$. We also estimated the central black hole mass from spectroscopic data. The width of the Civ, Mgii, and H$β$ emission lines, and the continuum luminosity at 1350, 3000, and 5100 Å, led to log$_{10}$($M_{BH}$/M$_{\odot}$) = 8.6 $\pm$ 0.4. Thus, hot gas responsible for the 1930 Å continuum emission is likely orbiting a 4.0 $\times$ 10$^8$ M$_{\odot}$ black hole at an $r_{1/2}$ of only a few tens of Schwarzschild radii.

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arXiv2017

Measuring the Innermost Stable Circular Orbits of Supermassive Black Holes

We present a promising new technique, the g-distribution method, for measuring the inclination angle (i), the innermost stable circular orbit (ISCO), and the spin of a supermassive black hole. The g-distribution method uses measurements of the energy shifts in the relativistic iron line emitted by the accretion disk of a supermassive black hole due to microlensing by stars in a foreground galaxy relative to the g-distribution shifts predicted from microlensing caustic calculations. We apply the method to the gravitationally lensed quasars RX J1131-1231 (z_s=0.658, z_l=0.295), QJ 0158-4325 (z_s=1.294, z_l=0.317), and SDSS 1004+4112 (z_s=1.734, z_l=0.68). For RX J1131-1231 our initial results indicate that r_ISCO<8.5 gravitational radii (r_g) and i > 76 degrees. We detect two shifted Fe lines, in several observations, as predicted in our numerical simulations of caustic crossings. The current DeltaE-distribution of RX J1131-1231 is sparsely sampled but further X-ray monitoring of RX J1131-1231 and other lensed quasars will provide improved constraints on the inclination angles, ISCO radii and spins of the black holes of distant quasars.

astro-ph.HE↗

arXiv2009

The Sizes of the X-ray and Optical Emission Regions of RXJ1131-1231

We use gravitational microlensing of the four images of the z=0.658 quasar RXJ1131-1231 to measure the sizes of the optical and X-ray emission regions of the quasar. The (face-on) scale length of the optical disk at rest frame 400 nm is 1.3 10^15cm, while the half-light radius of the rest frame 0.3-17 keV X-ray emission is 2.3 10^14cm. The formal uncertainties are factors of 1.6 and 2.0, respectively. With the exception of the lower limit on the X-ray size, the results are very stable against any changes in the priors used in the analysis. Based on the Hbeta line-width, we estimate that the black hole mass is ~10^8 Msun, which corresponds to a gravitational radius of r_g~2 10^13 cm. Thus, the X-ray emission is emerging on scales of ~10r_g and the 400 nm emission on scales of ~70 r_g. A standard thin disk of this size should be significantly brighter than observed. Possible solutions are to have a flatter temperature profile or to scatter a large fraction of the optical flux on larger scales after it is emitted. While our calculations were not optimized to constrain the dark matter fraction in the lens galaxy, dark matter dominated models are favored. With well-sampled optical and X-ray light curves over a broad range of frequencies there will be no difficulty in extending our analysis to completely map the structure of the accretion disk as a function of wavelength.

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arXiv2007

The Rewards of Patience: An 822 Day Time Delay in the Gravitational Lens SDSS J1004+4112

We present 107 new epochs of optical monitoring data for the four brightest images of the gravitational lens SDSS J1004+4112 observed between October 2006 and June 2007. Combining this data with the previously obtained light curves, we determine the time delays between images A, B and C. We confirm our previous measurement finding that A leads B by dt_BA=40.6+-1.8 days, and find that image C leads image A by dt_CA=821.6+-2.1 days. The lower limit on the remaining delay is that image D lags image A by dt_AD>1250 days. Based on the microlensing of images A and B we estimate that the accretion disk size at a rest wavelength of 2300 angstrom is 10^{14.8+-0.3} cm for a disk inclination of cos{i}=1/2, which is consistent with the microlensing disk size-black hole mass correlation function given our estimate of the black hole mass from the MgII line width of logM_BH/M_sun=8.44+-0.14. The long delays allow us to fill in the seasonal gaps and assemble a continuous, densely sampled light curve spanning 5.7 years whose variability implies a structure function with a logarithmic slope of gamma = 0.35+-0.02. As C is the leading image, sharp features in the C light curve can be intensively studied 2.3 years later in the A/B pair, potentially allowing detailed reverberation mapping studies of a quasar at minimal cost.

astro-ph↗

arXiv2007

The Sloan Digital Sky Survey-II Supernova Survey: Technical Summary

The Sloan Digital Sky Survey-II (SDSS-II) has embarked on a multi-year project to identify and measure light curves for intermediate-redshift (0.05 < z < 0.35) Type Ia supernovae (SNe Ia) using repeated five-band (ugriz) imaging over an area of 300 sq. deg. The survey region is a stripe 2.5 degrees wide centered on the celestial equator in the Southern Galactic Cap that has been imaged numerous times in earlier years, enabling construction of a deep reference image for discovery of new objects. Supernova imaging observations are being acquired between 1 September and 30 November of 2005-7. During the first two seasons, each region was imaged on average every five nights. Spectroscopic follow-up observations to determine supernova type and redshift are carried out on a large number of telescopes. In its first two three-month seasons, the survey has discovered and measured light curves for 327 spectroscopically confirmed SNe Ia, 30 probable SNe Ia, 14 confirmed SNe Ib/c, 32 confirmed SNe II, plus a large number of photometrically identified SNe Ia, 94 of which have host-galaxy spectra taken so far. This paper provides an overview of the project and briefly describes the observations completed during the first two seasons of operation.

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arXiv2006

A Time Delay for the Largest Gravitationally Lensed Quasar: SDSS J1004+4112

We present 426 epochs of optical monitoring data spanning 1000 days from December 2003 to June 2006 for the gravitationally lensed quasar SDSS J1004+4112. The time delay between the A and B images is 38.4+/-2.0 days in the expected sense that B leads A and the overall time ordering is C-B-A-D-E. The measured delay invalidates all published models. The models failed because they neglected the perturbations from cluster member galaxies. Models including the galaxies can fit the data well, but strong conclusions about the cluster mass distribution should await the measurement of the longer, and less substructure sensitive, delays of the C and D images. For these images, a CB delay of 681+/-15 days is plausible but requires confirmation, while CB and AD delays of >560 days and > 800 days are required. We clearly detect microlensing of the A/B images, with the delay-corrected flux ratios changing from B-A=0.44+/-0.01 mag in the first season to 0.29+/-0.01 mag in the second season and 0.32+/-0.01 mag in the third season.

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