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Abstract Coronagraphs allow for faint off-axis exoplanets to be observed, but are limited to angular separations greater than a few beam widths. Accessing closer-in separations would greatly increase the expected number of detectable planets, which scales inversely with the inner working angle. The vortex fiber nuller (VFN) is an instrument concept designed to characterize exoplanets within a single beam width. It requires few optical elements and is compatible with many coronagraph designs as a complementary characterization tool. However, the peak throughput for planet light is limited to about 20%, and the measurement places poor constraints on the planet location and flux ratio. We propose to augment the VFN design by replacing its single-mode fiber with a six-port mode-selective photonic lantern, retaining the original functionality while providing several additional ports that reject starlight but couple planet light. We show that the photonic lantern can also be used as a nuller without a vortex. We present monochromatic simulations characterizing the response of the photonic lantern nuller (PLN) to astrophysical signals and wavefront errors, and show that combining exoplanet flux from the nulled ports significantly increases the overall throughput of the instrument. We show using synthetically generated data that the PLN detects exoplanets more effectively than the VFN. Furthermore, with the PLN, the exoplanet can be partially localized, and its flux ratio constrained. The PLN has the potential to be a powerful characterization tool complementary to traditional coronagraphs in future high-contrast instruments. 

Inner working angle is a key parameter for enabling scientific discovery in direct exoplanet imaging and characterization. Approaches to improving the inner working angle to reach the diffraction limit center on the sensing and control of wavefront errors, starlight suppression via coronagraphy, and differential techniques applied in post-processing. These approaches are ultimately limited by the shot noise of the residual starlight, placing a premium on the ability of the adaptive optics system to sense and control wavefront errors so that the coronagraph can effectively suppress starlight reaching the science focal plane. Photonic lanterns are attractive for use in the science focal plane because of their ability to spatially filter light using a finite basis of accepted modes and effectively couple the results to diffraction-limited spectrometers, providing a compact and cost-effective means to implement post-processing based on spectral diversity. We aim to characterize the ability of photonic lanterns to serve as focal-plane wavefront sensors, allowing the adaptive optics system to control aberrations affecting the science focal plane and reject additional stellar photon noise. By serving as focal-plane wavefront sensors, photonic lanterns can improve sensitivity to exoplanets through both direct and coronagraphic observations. We have studied the sensing capabilities of photonic lanterns in the linear and quadratic regimes with analytical and numerical treatments for different lantern geometries (including non-mode-selective, mode-selective, and hybrid geometries) as a function of port number. In this presentation we report on the sensitivity of such lanterns and comment on the relative suitability and sensitivity impacts of different lantern geometries for focal-plane wavefront sensing. 

A focal plane wavefront sensor offers major advantages to adaptive optics, including removal of non-commonpath error and providing sensitivity to blind modes (such as petalling). But simply using the observed point spread function (PSF) is not sufficient for wavefront correction, as only the intensity, not phase, is measured. Here we demonstrate the use of a multimode fiber mode converter (photonic lantern) to directly measure the wavefront phase and amplitude at the focal plane. Starlight is injected into a multimode fiber at the image plane, with the combination of modes excited within the fiber a function of the phase and amplitude of the incident wavefront. The fiber undergoes an adiabatic transition into a set of multiple, single-mode outputs, such that the distribution of intensities between them encodes the incident wavefront. The mapping (which may be strongly non-linear) between spatial modes in the PSF and the outputs is stable but must be learned. This is done by a deep neural network, trained by applying random combinations of spatial modes to the deformable mirror. Once trained, the neural network can instantaneously predict the incident wavefront for any set of output intensities. We demonstrate the successful reconstruction of wavefronts produced in the laboratory with low-wind-effect, and an on-sky demonstration of reconstruction of low-order modes consistent with those measured by the existing pyramid wavefront sensor, using SCExAO observations at the Subaru Telescope. 

Efficiently coupling light from large telescopes to photonic devices is challenging. However, overcoming this challenge would enable diffraction-limited instruments, which offer significant miniaturization and advantages in thermo-mechanical stability. By coupling photonic lanterns with high performance adaptive optics systems, we recently demonstrated through simulation that high throughput diffraction-limited instruments are possible (Lin et al., Applied Optics, 2021). Here we build on that work and present initial results from validation experiments in the near-infrared to corroborate those simulations in the laboratory. Our experiments are conducted using a 19-port photonic lantern coupled to the state-of-the-art SCExAO instrument at the Subaru Telescope. The SCExAO instrument allows us to vary the alignment and focal ratio of the lantern injection, as well as the Strehl ratio and amount of tip/tilt jitter in the beam. In this work, we present experimental characterizations against the aforementioned parameters, in order to compare with previous simulations and elucidate optimal architectures for lantern-fed spectrographs. 

We use a sample of 27 gamma-ray bursts (GRBs) at redshiftz= 2–6 to probe the outflows in their respective host galaxies (log(M_*/M_⊙) ∼ 9–11) and search for possible relations between the outflow properties and those of the host galaxies, such asM_*, the star formation rate (SFR), and the specific SFR (sSFR). First, we consider three outflow properties: outflow column density (N_out), maximum outflow velocity (V_max), and normalized maximum velocity (V_norm=V_max/V_circ,halo, whereV_circ,halois the halo circular velocity). We observe clear trends ofN_outandV_maxwith increasing SFR in high-ion-traced outflows, with a stronger (>3σ)V_max–SFR correlation. We find that the estimated mass outflow rate and momentum flux of the high-ion outflows scale with SFR and can be supported by the momentum imparted by star formation (supernovae and stellar winds). The kinematic correlations of high-ion-traced outflows with SFR are similar to those observed for star-forming galaxies at low redshifts. The correlations with SFR are weaker in low-ion outflows. This, along with the lower detection fraction in low-ion outflows, indicates that the outflow is primarily high-ion dominated. We also observe a strong (>3σ) trend of normalized velocity (V_norm) decreasing with halo mass and increasing with sSFR, suggesting that outflows from low-mass halos and high-sSFR galaxies are most likely to escape and enrich the outer circumgalactic medium (CGM) and intergalactic medium with metals. By comparing the CGM–GRB stacks with those of starbursts atz∼ 2 andz∼ 0.1, we find that over a broad redshift range, the outflow strength strongly depends on the main-sequence offset at the respective redshifts, rather than simply the SFR.

 

Abstract Tidal disruption events (TDEs) offer a unique way to study dormant black holes. While the number of observed TDEs has grown thanks to the emergence of wide-field surveys in the past few decades, questions regarding the nature of the observed optical, UV, and X-ray emission remain. We present a uniformly selected sample of 30 spectroscopically classified TDEs from the Zwicky Transient Facility Phase I survey operations with follow-up Swift UV and X-ray observations. Through our investigation into correlations between light-curve properties, we recover a shallow positive correlation between the peak bolometric luminosity and decay timescales. We introduce a new spectroscopic class of TDE, TDE-featureless, which are characterized by featureless optical spectra. The new TDE-featureless class shows larger peak bolometric luminosities, peak blackbody temperatures, and peak blackbody radii. We examine the differences between the X-ray bright and X-ray faint populations of TDEs in this sample, finding that X-ray bright TDEs show higher peak blackbody luminosities than the X-ray faint subsample. This sample of optically selected TDEs is the largest sample of TDEs from a single survey yet, and the systematic discovery, classification, and follow-up of this sample allows for robust characterization of TDE properties, an important stepping stone looking forward toward the Rubin era. 

Abstract The Fermi Gamma-ray Burst Monitor (GBM) triggers on-board in response to ∼40 short gamma-ray bursts (SGRBs) per year; however, their large localization regions have made the search for optical counterparts a challenging endeavour. We have developed and executed an extensive program with the wide field of view of the Zwicky Transient Facility (ZTF) camera, mounted on the Palomar 48 inch Oschin telescope (P48), to perform target-of-opportunity (ToO) observations on 10 Fermi-GBM SGRBs during 2018 and 2020–2021. Bridging the large sky areas with small field-of-view optical telescopes in order to track the evolution of potential candidates, we look for the elusive SGRB afterglows and kilonovae (KNe) associated with these high-energy events. No counterpart has yet been found, even though more than 10 ground-based telescopes, part of the Global Relay of Observatories Watching Transients Happen (GROWTH) network, have taken part in these efforts. The candidate selection procedure and the follow-up strategy have shown that ZTF is an efficient instrument for searching for poorly localized SGRBs, retrieving a reasonable number of candidates to follow up and showing promising capabilities as the community approaches the multi-messenger era. Based on the median limiting magnitude of ZTF, our searches would have been able to retrieve a GW170817-like event up to ∼200 Mpc and SGRB afterglows to z = 0.16 or 0.4, depending on the assumed underlying energy model. Future ToOs will expand the horizon to z = 0.2 and 0.7, respectively. 

Gamma-ray bursts (GRBs) are among the brightest and most energetic events in the universe. The duration and hardness distribution of GRBs has two clusters, now understood to reflect (at least) two different progenitors. Short-hard GRBs (SGRBs; T90 <2 s) arise from compact binary mergers, while long-soft GRBs (LGRBs; T90 >2 s) have been attributed to the collapse of peculiar massive stars (collapsars). The discovery of SN 1998bw/GRB 980425 marked the first association of a LGRB with a collapsar and AT 2017gfo/GRB 170817A/GW170817 marked the first association of a SGRB with a binary neutron star merger, producing also gravitational wave (GW). Here, we present the discovery of ZTF20abwysqy (AT2020scz), a fast-fading optical transient in the Fermi Satellite and the InterPlanetary Network (IPN) localization regions of GRB 200826A; X-ray and radio emission further confirm that this is the afterglow. Follow-up imaging (at rest-frame 16.5 days) reveals excess emission above the afterglow that cannot be explained as an underlying kilonova (KN), but is consistent with being the supernova (SN). Despite the GRB duration being short (rest-frame T90 of 0.65 s), our panchromatic follow-up data confirms a collapsar origin. GRB 200826A is the shortest LGRB found with an associated collapsar; it appears to sit on the brink between a successful and a failed collapsar. Our discovery is consistent with the hypothesis that most collapsars fail to produce ultra-relativistic jets.