Time-Domain Cosmology with Strong Gravitational Lensing

Contribution List

1. Welcome

Kenneth Wong

25/01/2021, 22:00

Talk

3. Cosmology and Stellar Physics with Lensed Supernovae

Sherry Suyu

25/01/2021, 22:05

Talk

Strongly lensed supernovae (SNe) provide great opportunities for constraining cosmological parameters and SN progenitors. The time delays between the multiple images of a lensed SN allow a measurement of the Hubble constant (H0), which is complementary to lensed-quasar studies. An independent measurement of H0 is important for assessing the current H0 tension and the possible need for new...

4. Lessons learned from iPTF16geu

Ariel Goobar

25/01/2021, 22:30

Talk

Wide-field time domain surveys are well-suited to find strongly lensed systems, without the need for high spatial resolution, as demonstrated by the discovery of the first multiply-imaged Type Ia supernova, iPTF16geu. Yet, in spite of significant efforts, four years have passed without a sequel. I will summarize the circumstances surrounding the discovery of SN2016geu using the Palomar...

5. Lens Searches for transients and variable sources

Anupreeta More

25/01/2021, 23:00

Talk

I will give an overview of systematic lens searches (including machine learning based approaches) being conducted in the ongoing imaging surveys to find transients or variable sources which can allow us to put constraints on cosmological parameters or often times, give insight into the astrophysics. I will also talk about new methods proposed to be used in upcoming surveys such as LSST, their ...

23. Lens searches with Gaia and variability

Cameron Lemon

25/01/2021, 23:25

Talk

Lens searches with Gaia and variability

9. Galaxy lens models with offset mass components: implications for time delays and H0.

Liliya Williams

25/01/2021, 23:35

Talk

Accurate determination of the Hubble parameter from strong lensing depends critically on the mass model of the lensing galaxy. There is evidence that the commonly used elliptically symmetric lenses may not adequately represent the lens galaxy population. I will discuss the recent modeling of the quad Supernova iPTF16geu. Simple models suffer from a few deficiencies: the center and the position...

8. Constraining the Hubble constant -- some lessons learnt from using lensing simulations

Dandan Xu

26/01/2021, 22:00

Talk

Time-domain lensing observations and modeling have turn out to serve an increasingly important role in providing independent constraints on the Hubble constant and cosmology. A couple of issues regarding the modeling technique remain not entirely clear and many good efforts have been made in order to understand various possible key systematics. In this talk, I will briefly discuss a few...

10. Where my DAEMON hides -- one explanation to rule all lens models

Jenny Wagner

26/01/2021, 22:25

Talk

"A big obstacle to efficiently determine H0 from time-delay cosmography is the lens modelling.
When choosing a mass density profile as lens model, we have to select from a multitude of lens model classes and ranges for the model parameter values. A specific choice may bias the confidence bounds on H0 low, a marginalisation over many model classes and parameter ranges is computationally very...

22. Auto-identification of unphysical source reconstructions in strong lens modelling

Jacob Maresca

26/01/2021, 22:35

Talk

With the advent of next-generation surveys and the expectation of discovering huge numbers of strong gravitational lens systems, much effort is being invested into developing automated procedures for handling the data. The several orders of magnitude increase in the number of strong galaxy-galaxy lens systems is an insurmountable challenge for traditional modelling techniques. Whilst machine...

16. Real-time cosmology with lensed repeating Fast Radio Bursts

Adi Zitrin

26/01/2021, 22:45

Talk

Real-time cosmology refers to measuring the evolution of the universe in real time. Given the short human lifetime compared to the age of the universe, measuring such changes is very challenging. Thanks to their short duration and the typical time delays involved, lensed repeating FRBs may offer a unique opportunity to do so. I will review this possibility and discuss its feasibility using...

7. Large-Scale Gravitational Lens Modeling with Bayesian Neural Networks for Accurate and Precise Inference of the Hubble Constant

Ji Won Park

26/01/2021, 22:55

Talk

We investigate the use of approximate Bayesian neural networks (BNNs) in modeling hundreds of time-delay gravitational lenses for Hubble constant (H0) determination. Our BNN was trained on synthetic HST-quality images of strongly lensed active galactic nuclei (AGN) with lens galaxy light included. The BNN can accurately characterize the posterior PDFs of model parameters governing the...

11. Panel Discussion: Time-Delay Cosmography

Tommaso Treu, Dominique Sluse, Liliya Williams, Nan Li, Sherry Suyu, Simon Birrer

26/01/2021, 23:10

12. Recent studies on the propagation velocity of lensed gravitational waves

Ryuichi Takahashi

01/02/2021, 22:00

Talk

In this talk, we briefly review the propagation velocity of lensed gravitational waves in general relativity, based on recent papers (listed below). We mainly discuss the velocity difference between GWs and electromagnetic waves (EMWs) in the presence of a lens. The lensing of EMWs is usually studied in geometrical optics, while the lensing of GWs should be studied in wave optics if the...

13. Using transients at extreme magnifications to constrain dark matter

Jose Diego

01/02/2021, 22:25

Talk

Events at cosmological distances, undergoing extreme magnifications have become a reality since the discovery of Icarus, the first strongly lensed star at redshift larger than 1. Since the discovery of Icarus, similar events have been observed in the last years, and many more are expected in the upcoming years. The large magnification factors present in these events allow to study not only the...

20. The effect of dark matter substructure on strong lensing measurements of the Hubble constant

Daniel Gilman

01/02/2021, 22:50

Talk

The particle nature of dark matter manifests in the abundance and density profiles of dark matter structure on sub galactic scales, both in the form of subhalos and field halos along the the line of sight. The lensing effects of these structures leaves subtle imprints on the arrival time delays and flux ratios between images in quadruply imaged quasars (quads). I will describe recent work that...

15. Beyond-WIMP DM models and constraints from anomalous strong-lens systems

Ayuki Kamada

01/02/2021, 23:05

Talk

"A weakly interacting massive particle (WIMP) from electroweak-scale new physics have been a promising candidate of cold dark matter (CDM).
Meanwhile beyond-WIMP DM models attract interests partially because they may explain the possible issues in CDM: tension between early and late cosmology in H0; and challenges in explaining the observed Galactic-scale structure.
I overview beyond-WIMP DM...

17. Phase shift of lensed gravitational waves

Liang Dai

01/02/2021, 23:30

Talk

Several gravitational wave signals of binary black hole coalescence in LIGO/Virgo O2 are found to show surprisingly coincident intrinsic and extrinsic parameters. Could they be multiple images of a gravitationally lensed source? Lensed gravitational waveforms are subject to a topological phase shift called the Morse phase shift. While the absolute Morse phase is degenerate with the source...

21. Gravitational Lensing of Gravitational Waves: Effect of Microlensing Population

Anuj Mishra

01/02/2021, 23:55

Talk

In this work, we investigate the effect of microlensing in strongly lensed gravitational wave signals due to the population of microlenses present in lensing galaxies. We consider a wide range of realistic strong lens magnification and the corresponding density values of the microlens population. We find that the effects of microlensing become increasingly significant with the increase in the...

18. Panel Discussion: Dark Matter Science with Upcoming Surveys/Telescopes

Kaiki Inoue, Ariel Goobar, Ayuki Kamada, Dandan Xu, Jose Diego, Thomas Collett

02/02/2021, 22:00

19. Microlensing in lensed quasars

Veronica Motta

02/02/2021, 23:00

Talk

"The observation of gravitationally microlensed quasars provides direct measurements of the accretion disk structure. The flux variations of the quasar images, induced by the source crossing through the microlens caustics, produce variations on timescales of years. There are two techniques to measure those variations: photometric monitoring and single epoch spectroscopy/photometry.
The...

6. Extremely Magnified Stars and Flashlights

Patrick Kelly

02/02/2021, 23:25

Talk

Observations with the Hubble Space Telescope (HST) have now definitively identified two blue supergiant stars, Icarus and Warhol, at cosmological distances which are extremely magnified by foreground Hubble Frontier Field (HFF) galaxy clusters. Moreover, several less well characterized stars have also been detected briefly when their magnification temporarily increased due to microlensing by...

2. Summary / closing

Masamune Oguri

02/02/2021, 23:50

Talk

33. Astrometric lensing signatures of IMBHs with the Gaia space mission

Zofia Kaczmarek

Talk

Intermediate mass black holes represent the apparent mass gap (10-10000 solar masses) between the well known populations of black holes: stellar-mass and supermassive black holes. They are thought to be the 'seeds' from which SMBHs grow, necessary to explain why there are SMBHs observed in the early Universe. There could be primordial black holes in the IMBH range; although observational...

30. Contribution of primordial black holes to quasar microlensing considering a bimodal mass-spectrum of BHs and stars

Ana Esteban Gutiérrez

Talk

The amplitude and frequency of gravitational microlensing can be used to detect Primordial Massive Black Holes (PBHs). However, they can be mixed with the normal stellar population that can also contribute to microlensing. To separate the contributions from both populations, we perform numerical simulations to study the possible degeneracy of a bimodal distribution of masses with a single-mass...

37. Extended continuum emission in quasars and its impact on time-delay lightcurves

Dominique Sluse

Talk

The accurate photometric monitoring of lensed quasars is instrumental to high precision cosmography from time-delay measurements, and to quasar continuum source size measurements with microlensing. We report recent evidence, from the microlensing spectroscopic study of two broad absorption line quasars, that the quasar continuum emission does not only originate from a compact accretion disc as...

36. Efficient mass modeling of strong lenses through deep learning

Stefan Schuldt

Talk

Strong gravitational lensing is a very powerful, widely used tool for understanding several open questions including properties of dark matter, dark energy, and the expansion of the universe (Hubble constant H0). For all of these applications one needs a mass model of the lens, which is currently often obtained with Markov-chain Monte-Carlo (MCMC) methods via likelihood sampling. This is a...

32. Imperfect models and constraints: stellar kinematic constraints fail to correctly break the mass sheet degeneracy at the 1% level

Matthew Gomer

Talk

Because of the mass sheet degeneracy (MSD), lensing information alone is incomplete to constrain H_0. To break the degeneracy, assumptions are made through the modeling process about the mass profile of a galaxy e.g. it follows a power law. If the actual galaxy does not perfectly match the model profile, the recovered value of H_0 can be biased. Common practice is to improve the fit using...

26. Line-of-sight Lensing -a New Window to Dark Matter and Distant Dwarf Galaxies

Kaiki Inoue

Talk

Kaiki Inoue

Matter fluctuations on scales of <10 kpc are important for understanding the nature of dark matter and dwarf galaxies residing at cosmological scales. Gravitational lensing is a powerful tool for directly probing the nature. However, the lensing signal is too small for current and near future observations. To circumvent the problem, I propose to use massive galaxy-scale strong...

25. Probing the nature of dark matter with galaxy-galaxy strong gravitational lensing

Dorota Bayer

Talk

While a direct detection of the dark-matter particle remains very challenging, the nature of dark matter can potentially be constrained indirectly -- by comparing the properties of substructure in galactic haloes with predictions from the phenomenological dark-matter models, such as the cold, warm or hot dark matter. Whereas these models are practically indistinguishable with respect to the...

31. Revealing the Structure of the Lensed Quasar Q 0957+561

Carina Fian

Talk

We use signatures of microlensing (induced by stars in the foreground lens galaxy) on different wavelength regions in the gravitationally lensed quasar Q 0957+561 to infer the size of the accretion disk and to study the structure and kinematics of the broad-line region (BLR). We analyze the well-sampled 21-year GLENDAMA optical light curves of the double-lensed quasar (which so far has...

28. Strategies for precise and accurate measurements of the Hubble constant with strong lensing

Simon Birrer

Talk

Strong lensing time delays can measure the Hubble constant H0 independent of any other probe. Assuming commonly used forms for the radial mass density profile of the lenses, a 2% precision has been achieved with 7 Time-Delay Cosmography (TDCOSMO) lenses, in tension with the H0 from the cosmic microwave background. However, without assumptions on the radial mass density profile -- and relying...

35. The COSMOGRAIL project: past, on-going and future lensed quasars monitoring campaigns

Martin Millon

Talk

I will present the latest release of the COSMOGRAIL lensed quasar light curves. This dataset constitutes a unique sample of decade long and well sampled light curves, useful for time-delay cosmography, to measure the size of the quasar accretion disk and to study the quasar variability. I will show how we robustly measure the time delays in the presence of microlensing and how this...

38. The H0 bias due to angular structures in lenses

Lyne Van de Vyvere

Talk

Time-delay cosmography studies generally assume axi-symmetry of the deflector. However, nearby elliptical galaxies show deviation from ellipticity that can be captured by expanding the ellipitical isphotes into higher order Fourier modes. Multipoles of order 4, corresponding to disky or boxy shapes, are the most commonly observed perturbations. We have studied how such azimuthal structures...

34. The impact of line-of-sight structures on measuring H0 with strong lensing time-delays

Nan Li

Talk

Measurements of The Hubble-Lemaitre constant from early- and local-universe observations show a significant discrepancy. In an attempt to understand the origin of this mismatch, independent techniques to measure H0 are required. One such technique, strong lensing time delays, is set to become a leading contender amongst the myriad methods due to forthcoming large strong lens samples. It is...

29. Time Delay Lens Modeling Challenge

Xuheng Ding

Talk

Strong gravitational lenses with measured time delay are a powerful tool to measure cosmological parameters, especially the Hubble constant (H0). Recent studies show that six multiply-imaged AGN systems can determine H0 to 2.4% precision in a flat LCDM. Furthermore, the number of time-delay lens systems is growing rapidly, enabling, in principle, the determination of H0 to 1% precision in the...

27. Variability of the lens quasar QJ0158 : microlensing or reverberation ?

Eric Paic

Talk

Microlensing of strongly lensed quasars offers a unique window into AGN structure and its connection to the physical mechanisms behind quasar variability. The extrinsic variability it adds to the different images can, for example, give constraints on the radius of the accretion disk.
The current state-of-the-art light curve fitting method of Kochanek 2004 tends to overlook high frequency...