Gravitational Lens System PS J0147+4630 (Andromeda’s Parachute): Main Lensing Galaxy and Optical Variability of the Quasar Images

Abstract

Because follow-up observations of quadruple gravitational lens systems are of extraordinary importance for astrophysics and cosmology, we present single-epoch optical spectra and r-band light curves of PS J0147+4630. This recently discovered system mainly consists of four images ABCD of a background quasar around a foreground galaxy G that acts as a gravitational lens. First, we use long-slit spectroscopic data in the Gemini Observatory Archive and a multi-component fitting to accurately resolve the spectra of A, D, and G. The spectral profile of G resembles that of an early-type galaxy at a redshift of 0.678 ± 0.001, which is about 20% higher than the previous estimate. Additionally, the stellar velocity dispersion is measured to ∼5% precision. Second, our early r-band monitoring with the Liverpool Telescope leads to accurate light curves of the four quasar images. Adopting time delays predicted by the lens model, the new lens redshift, and a standard cosmology, we report the detection of microlensing variations in C and D as large as ∼0.1 mag on timescales of a few hundred days. We also estimate an actual delay between A and B of a few days (B is leading), which demonstrates the big potential of optical monitoring campaigns of PS J0147+4630.

Tdcosmo

“…Among the eight lens systems, the deflector velocity dispersions of the J0147+4630, and J1433+6007 lens systems were previously measured. For the deflector in J0147+4630, the previous measurement is 313 ± 14 km s −1 using a 0.5 -width slit under subarcsecond seeing conditions (Goicoechea & Shalyapin 2019). This result is within the uncertainty of our measurement of 283 ± 30 ± 12 km s −1 (see Table 3).…”

“…The spectroscopic redshift of the quasar is 2.341 ± 0.001 (Lee 2017). The redshift of the deflector is also measured, z d = 0.678 ± 0.001, along with the velocity dispersion, 313±14 km s −1 , by Goicoechea & Shalyapin (2019). In this paper, we provide an independent measurement of the velocity dispersion of the deflector using a larger wavelength range than the one used in the previous measurement.…”

“…Traditional optimal extraction codes based on the algorithm of Horne (1986) are not up to the task as they do not account for the blending or cross-contamination. To overcome this challenge, we have implemented a forward modeling method (e.g., Sluse et al 2007;Shalyapin & Goicoechea 2017;Goicoechea & Shalyapin 2019). First, a global model is created that emulates the data in a 1D spatial profile of the 2D science spectrum.…”

“…The green dots show the residuals between the unsmoothed flux and the model fit for each wavelength normalized to the respective model fits. Unlike the optimal extraction-based methods, the extraction technique presented in this paper and others (e.g., Goicoechea & Shalyapin 2019;Melo et al 2021) doesn't require defining an aperture along the spatial direction. Thus, the measured velocity dispersions correspond to the integrated velocity dispersions within a rectangular spectroscopic aperture of the respective slit-widths and slit-lengths centered on the deflectors (see Table 1).…”

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

“…For each of the two epochs, we used the 2700 (3×900) s exposure and a three-component fitting to resolve the spectra of A, B, and G. Our multi-component extraction technique is robust and has been recently applied to some lens systems (e.g. Sluse et al 2007;Shalyapin & Goicoechea 2017;Goicoechea & Shalyapin 2019). The model we used can be described in a nutshell as follows: three 1D Moffat profiles in the spatial direction for each wavelength bin.…”