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1. COOL-LAMPS. VI. Lens Model and New Constraints on the Properties of COOL J1241+2219, a Bright z = 5 Lyman Break Galaxy and its z = 1 Cluster Lens

   https://doi.org/10.3847/1538-4357/ad22de  

   Klein, Maxwell; Sharon, Keren; Napier, Kate; Gladders, Michael D; Khullar, Gourav; Bayliss, Matthew; Dahle, Håkon; Owens, M Riley; Stark, Antony; Brownsberger, Sasha; et al (February 2024, The Astrophysical Journal)

   Abstract We present a strong lensing analysis of COOL J1241+2219, the brightest known gravitationally lensed galaxy atz≥ 5, based on new multiband Hubble Space Telescope (HST) imaging data. The lensed galaxy has a redshift ofz= 5.043, placing it shortly after the end of the “Epoch of Reionization,” and an AB magnitudez_AB= 20.47 mag (Khullar et al.). As such, it serves as a touchstone for future research of that epoch. The high spatial resolution of HST reveals internal structure in the giant arc, from which we identify 15 constraints and construct a robust lens model. We use the lens model to extract the cluster mass and lensing magnification. We find that the mass enclosed within the Einstein radius of thez= 1.001 cluster lens is $M(<5.″77)={1.079}_{-0.007}^{+0.023}\times {10}^{13}{M}_{☉}$, significantly lower than other known strong lensing clusters at its redshift. The average magnification of the giant arc is 〈μ_arc〉 = ${76}_{-20}^{+40}$, a factor of ${2.4}_{-0.7}^{+1.4}$greater than previously estimated from ground-based data; the flux-weighted average magnification is 〈μ_arc〉 = ${92}_{-31}^{+37}$. We update the current measurements of the stellar mass and star formation rate (SFR) of the source for the revised magnification to $\log \left(M_{\star }/M_{\odot }\right)=$9.7 ± 0.3 and SFR = ${10.3}_{-4.4}^{+7.0}$M_⊙yr⁻¹, respectively. The powerful lensing magnification acting upon COOL J1241+2219 resolves the source and enables future studies of the properties of its star formation on a clump-by-clump basis. The lensing analysis presented here will support upcoming multiwavelength characterization with HST and JWST data of the stellar mass assembly and physical properties of this high-redshift lensed galaxy. 

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2. Strong-lensing Analysis of SPT-CL J2325−4111 and SPT-CL J0049−2440, Two Powerful Cosmic Telescopes ( R _E > 40″) from the SPT Clusters Sample

   https://doi.org/10.3847/1538-4357/ad9aa5  

   Mahler, Guillaume; Sharon, Keren; Bayliss, Matthew; Bleem, Lindsey E; Brodwin, Mark; Floyd, Benjamin; Gassis, Raven; Gladders, Michael D; Khullar, Gourav; Remolina_González, Juan D; et al (February 2025, The Astrophysical Journal)

   Abstract We report the results from a study of two massive (M_500c> 6.0 × 10¹⁴M_⊙) strong-lensing clusters selected from the South Pole Telescope cluster survey for their large Einstein radius (R_E> 40″), SPT-CL J2325−4111 and SPT-CL J0049−2440. Ground-based and shallow Hubble Space Telescope (HST) imaging indicated extensive strong-lensing evidence in these fields, with giant arcs spanning 18″ and 31″, respectively, motivating further space-based imaging follow-up. Here, we present multiband HST imaging and ground-based Magellan spectroscopy of the fields, from which we compile detailed strong-lensing models. The lens models of SPT-CL J2325−4111 and SPT-CL J0049−2440 were optimized using nine and eight secure multiply imaged systems with a final image-plane rms of 0 $\stackrel{″}{.}$63 and 0 $\stackrel{″}{.}$73, respectively. From the lensing analysis, we measure a projected mass density within 500 kpc ofM(<500 kpc) = (7.30 ± 0.07) × 10¹⁴M_⊙and $M(<500\mathrm{kpc})=7.12_{-0.19}^{+0.16}\times 10^{14}$M_⊙for these two clusters, and subhalo mass ratios of 0.12 ± 0.01 and $0.21_{-0.05}^{+0.07}$, respectively. Both clusters produce a large area with high magnification (μ≥ 3) for a source atz= 9, ${\mathcal{A}}_{\left|\mu \right|\ge 3}^{\mathrm{lens}}=4.93_{-0.04}^{+0.03}$arcmin²and ${\mathcal{A}}_{\left|\mu \right|\ge 3}^{\mathrm{lens}}=3.64_{-0.10}^{+0.14}$arcmin², respectively, placing them in the top tier of strong-lensing clusters. We conclude that these clusters are spectacular sightlines for further observations that will reduce the systematic uncertainties due to cosmic variance. This paper provides the community with two additional well-calibrated cosmic telescopes, as strong as the Frontier Fields and suitable for studies of the highly magnified background Universe. 

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3. JWST Photometric Time-delay and Magnification Measurements for the Triply Imaged Type Ia “SN H0pe” at z = 1.78

   https://doi.org/10.3847/1538-4357/ad3c43  

   Pierel, J_D_R; Frye, B_L; Pascale, M.; Caminha, G_B; Chen, W.; Dhawan, S.; Gilman, D.; Grayling, M.; Huber, S.; Kelly, P.; et al (May 2024, The Astrophysical Journal)

   Abstract Supernova (SN) SN H0pe is a gravitationally lensed, triply imaged, Type Ia SN (SN Ia) discovered in James Webb Space Telescope imaging of the PLCK G165.7+67.0 cluster of galaxies. Well-observed multiply imaged SNe provide a rare opportunity to constrain the Hubble constant (H₀), by measuring the relative time delay between the images and modeling the foreground mass distribution. SN H0pe is located atz= 1.783 and is the first SN Ia with sufficient light-curve sampling and long enough time delays for anH₀inference. Here we present photometric time-delay measurements and SN properties of SN H0pe. Using JWST/NIRCam photometry, we measure time delays of Δt_ab= $-{116.6}_{-9.3}^{+10.8}$observer-frame days and Δt_cb= $-{48.6}_{-4.0}^{+3.6}$observer-frame days relative to the last image to arrive (image 2b; all uncertainties are 1σ), which corresponds to a ∼5.6% uncertainty contribution forH₀assuming 70 km s⁻¹Mpc⁻¹. We also constrain the absolute magnification of each image toμ_a= ${4.3}_{-1.8}^{+1.6}$,μ_b= ${7.6}_{-2.6}^{+3.6}$,μ_c= ${6.4}_{-1.5}^{+1.6}$by comparing the observed peak near-IR magnitude of SN H0pe to the nonlensed population of SNe Ia. 

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4. Safety First: Stability and Dissipation of Line-tied Force-free Flux Tubes in Magnetized Coronae

   https://doi.org/10.3847/1538-4357/ad3206  

   Rugg, N.; Mahlmann, J. F.; Spitkovsky, A. (May 2024, The Astrophysical Journal)

   Abstract Magnetized plasma columns and extended magnetic structures with both footpoints anchored to a surface layer are an important building block of astrophysical dissipation models. Current loops shining in X-rays during the growth of plasma instabilities are observed in the corona of the Sun and are expected to exist in highly magnetized neutron star magnetospheres and accretion disk coronae. For varying twist and system sizes, we investigate the stability of line-tied force-free flux tubes and the dissipation of twist energy during instabilities using linear analysis and time-dependent force-free electrodynamics simulations. Kink modes (m= 1) and efficient magnetic energy dissipation develop for plasma safety factorsq≲ 1, whereqis the inverse of the number of magnetic field line windings per column length. Higher-order fluting modes (m> 1) can distort equilibrium flux tubes forq> 1 but induce significantly less dissipation. In our analysis, the characteristic pitch ${\tilde{\mu }}_0$of flux-tube field lines determines the growth rate ( $\propto {\tilde{\mu }}_0^3$) and minimum wavelength of the kink instability ( $\propto {\tilde{\mu }}_0^{-1}$). We use these scalings to determine a minimum flux tube length for the growth of the kink instability for any given ${\tilde{\mu }}_0$. By drawing analogies to idealized magnetar magnetospheres with varying regimes of boundary shearing rates, we discuss the expected impact of the pitch-dependent growth rates for magnetospheric dissipation in magnetar conditions. 

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5. Accretion Disk Size and Updated Time-delay Measurements in the Gravitationally Lensed Quasar SDSS J165043.44+425149.3

   https://doi.org/10.3847/1538-4357/ad3069  

   Rivera, A. B.; Morgan, C. W.; Florence, S. M.; Kniezewski, K.; Millon, M.; Courbin, F.; Dahm, S. E.; Vrba, F. J.; Tilleman, T. M.; Cornachione, M. A.; et al (March 2024, The Astrophysical Journal)

   Abstract We analyze variability in 15-season optical lightcurves from the doubly imaged lensed quasar SDSS J165043.44+425149.3 (SDSS1650), comprising five seasons of monitoring data from the Maidanak Observatory (277 nights in total, including the two seasons of data previously presented in Vuissoz et al.), five seasons of overlapping data from the Mercator telescope (269 nights), and 12 seasons of monitoring data from the US Naval Observatory, Flagstaff Station at lower cadence (80 nights). We update the 2007 time-delay measurement for SDSS1650 with these new data, finding a time delay of $\mathrm{\Delta }{t}_{\mathrm{AB}}=-{55.1}_{-3.7}^{+4.0}$days, with image A leading image B. We analyze the microlensing variability in these lightcurves using a Bayesian Monte Carlo technique to yield measurements of the size of the accretion disk atλ_rest= 2420 Å, finding a half-light radius of log(r_1/2/cm) = ${16.19}_{-0.58}^{+0.38}$assuming a 60° inclination angle. This result is unchanged if we model 30% flux contamination from the broad-line region. We use the width of the Mgiiline in the existing Sloan Digital Sky Survey spectra to estimate the mass of this system’s supermassive black hole, findingM_BH= 2.47 × 10⁹M_⊙. We confirm that the accretion disk size in this system, whose black hole mass is on the very high end of theM_BHscale, is fully consistent with the existing quasar accretion disk size–black hole mass relation. 

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