Gravitational microlensing: A parallel, large-data implementation

Garsden, Hugh; Lewis, Geraint F.

doi:10.1016/j.newast.2009.06.006

Cited by 16 publications

(12 citation statements)

References 42 publications

(59 reference statements)

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“…We now describe our algorithm for computing the light curves of moving sources. There are several methods in the literature, the most popular one being inverse ray shooting, coupled with a hierarchical tree code to efficiently compute deflection angles (see, e.g., Garsden & Lewis 2010, and references within). This method does not solve the lens equation but gives a map of the magnification at any source position down to the pixel scale.…”

Section: Algorithm For Computing Light Curvesmentioning

confidence: 99%

Microlensing of Extremely Magnified Stars near Caustics of Galaxy Clusters

Venumadhav

Dai

Miralda-Escudé

2017

ApJ

111

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Recent observations of lensed galaxies at cosmological distances have detected individual stars that are extremely magnified when crossing the caustics of lensing clusters. In idealized cluster lenses with smooth mass distributions, two images of a star of radius R approaching a caustic brighten as t −1/2 and reach a peak magnification ∼ 10 6 (10 R /R) 1/2 before merging on the critical curve. We show that a mass fraction (κ 10 −4.5 ) in microlenses inevitably disrupts the smooth caustic into a network of corrugated microcaustics, and produces light curves with numerous peaks. Using analytical calculations and numerical simulations, we derive the characteristic width of the network, caustic-crossing frequencies, and peak magnifications. For the lens parameters of a recent detection and a population of intracluster stars with κ ∼ 0.01, we find a source-plane width of ∼ 20 pc for the caustic network, which spans 0.2 arcsec on the image plane. A source star takes ∼ 2 × 10 4 years to cross this width, with a total of ∼ 6 × 10 4 crossings, each one lasting for ∼ 5 hr (R/10 R ) with typical peak magnifications of ∼ 10 4 (R/10 R ) −1/2 . The exquisite sensitivity of caustic-crossing events to the granularity of the lens-mass distribution makes them ideal probes of dark matter components, such as compact halo objects and ultralight axion dark matter.

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Section: Algorithm For Computing Light Curvesmentioning

confidence: 99%

Microlensing of Extremely Magnified Stars near Caustics of Galaxy Clusters

Venumadhav

Dai

Miralda-Escudé

2017

ApJ

111

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“…We also fire rays in parallel, using multiple parallel processes. Using the method of Garsden & Lewis (2010), the map containing the largest number of masses can be generated in ∼14 d on a supercomputer using 16 parallel processes. For the maps with the least number of lens masses, the total time is ∼24 h. About 18 per cent of the compute time is used to generate the lens objects, and the rest is for firing the rays, with many rays fired in parallel.…”

Section: Methodsmentioning

confidence: 99%

“…It can be used as a probe of the source quasar because the quasar’s size and shape affect the microlensing variability (e.g. Mortonson, Schechter & Wambsganss 2005; Bate et al 2008; Garsden & Lewis 2010; Morgan et al 2010). For example, when the source is large, the changes in the light curve are not as prominent, since the larger source smooths out the variability.…”

Section: Introductionmentioning

confidence: 99%

Probing planetary mass dark matter in galaxies: gravitational nanolensing of multiply imaged quasars★

Garsden¹,

Bate²,

Lewis³

2012

Monthly Notices of the Royal Astronomical Society

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Gravitational microlensing of planetary-mass objects (or 'nanolensing', as it has been termed) can be used to probe the distribution of mass in a galaxy that is acting as a gravitational lens. Microlensing and nanolensing light curve fluctuations are indicative of the mass of the compact objects within the lens, but the size of the source is important, as large sources will smooth out a light curve. Numerical studies have been made in the past that investigate a range of source sizes and masses in the lens. We extend that work in two ways -by generating high-quality maps with over a billion small objects down to a mass of 2.5 × 10 −5 M , and by investigating the temporal properties and observability of the nanolensing events. The system studied is a mock quasar system similar to MG 0414+0534. We find that if a variability of 0.1 mag in amplitude can be observed, a source size of ∼0.1 Einstein radius (ER) would be needed to see the effect of 2.5 × 10 −5 M masses, and larger, in the microlensing light curve. Our investigation into the temporal properties of nanolensing events finds that there are two scales of nanolensing that can be observed -one due to the crossing of nanolensing caustic bands, and the other due to the crossing of nanolensing caustics themselves. The latter are very small, having crossing times of a few days and requiring sources of size ∼0.0001 ER to resolve. For sources of the size of an accretion disc, the nanolensing caustics are slightly smoothed out, but can be observed on time-scales of a few days. The crossing of caustic bands can be observed on time-scales of about three months.

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“…We generate 1,575 objects with 1 M⊙ masses for the lens, and no smooth matter, as the images are located in the bulge where stellar matter dominates. We use the inverse ray-tracing method developed by Wambsganss (1990Wambsganss ( , 1999 and Garsden & Lewis (2010) to fire the rays. The width of the map is 20 ER (1.2 pc) at a pixel resolution of 10000 2 pixels, or 0.002 ER (0.00012 pc) per pixel.…”

Section: Magnification Mapsmentioning

confidence: 99%

Gravitational microlensing of a reverberating quasar broad-line region - I. Method and qualitative results★

Garsden

Bate

Lewis

2011

Monthly Notices of the Royal Astronomical Society

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The kinematics and morphology of the broad emission‐line region (BELR) of quasars are the subject of significant debate. The two leading methods for constraining BELR properties are microlensing and reverberation mapping. Here we combine these two methods with a study of the microlensing behaviour of the BELR in Q2237+0305, as a change in continuum emission (a ‘flare’) passes through it. Beginning with some generic models of the BELR – sphere, bicones, disc – we slice in velocity and time to produce brightness profiles of the BELR over the duration of the flare. These are numerically microlensed to determine whether microlensing of reverberation mapping provides new information about the properties of BELRs. We describe our method and show images of the models as they are flaring, and the unlensed and lensed spectra that are produced. Qualitative results and a discussion of the spectra are given in this paper, highlighting some effects that could be observed. Our conclusion is that the influence of microlensing, while not strong, can produce significant observable effects that will help in differentiating the properties of BELRs.

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Gravitational microlensing: A parallel, large-data implementation

Cited by 16 publications

References 42 publications

Microlensing of Extremely Magnified Stars near Caustics of Galaxy Clusters

Microlensing of Extremely Magnified Stars near Caustics of Galaxy Clusters

Probing planetary mass dark matter in galaxies: gravitational nanolensing of multiply imaged quasars★

Gravitational microlensing of a reverberating quasar broad-line region - I. Method and qualitative results★

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