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The Pine Hill thrust, a western frontal thrust of the Green Mountain massif in southern Vermont, is characterized by reverse faults that place Precambrian basement rocks over mid-Ordovician rocks. Based on cross-cutting relationships, it has been considered a late-stage Taconic thrust. However, recent investigations in the western front of the Sutton Mountains, Green Mountain massif, and Berkshire massif of southern Quebec, Vermont, and Massachusetts, respectively, suggest fault displacement at 420 Ma and younger. Therefore, motion on these faults may instead be associated with the late Salinic or early Acadian orogeny. This study investigates the hypothesis that the Pine Hill thrust records deformational events associated with the late Salinic and/or Acadian orogenies. Preliminary studies from fieldwork and microstructural analysis of slabbed samples from transects across the Pine Hill thrust, where the lower Cambrian Dalton Formation is mapped as thrust over the Upper Ordovician Ira Formation, reveal at least four generations of foliation. The oldest tectonic foliation, S1, is parallel to primary compositional layering (S0) and is associated with isoclinal F1 folds. Moving from the Dalton Formation in the hanging wall towards the fault zone, S1 becomes progressively transposed into S2, marked by metamorphic compositional layering. Closer to the fault, S2 is crenulated, and S3 emerges as the dominant foliation, becoming the only foliation exhibited by the phyllonites in the fault zone. Finally, the youngest foliation, S4, is a localized crenulation cleavage developed in more pelitic material. These preliminary results suggest a complex deformation history, possibly involving multiple phases of post-Taconic motion on the fault during subsequent orogeneses. Further microstructural analysis and geochronology of these deformation fabrics will help establish the timing of deformation and its tectonic significance, helping to correlate surface geology with results from New England Seismic Transect (NEST) imaging of crustal and mantle lithospheric structure in the northern New England Appalachians. 

The Taconic thrust belt in New England is the type locality of the Ordovician Taconic orogeny, the result of partial subduction of the rifted Laurentian margin beneath the Gondwanan-derived Moretown terrane (MT) and the Shelburne Falls arc. Evidence for Ordovician deformation and metamorphism is only preserved in rocks of the Laurentian margin; Taconic deformation and metamorphism in the MT and suture zone were overprinted by Devonian Acadian tectonism. New thermochronological data from the Taconic thrust belt indicate that many faults were active during the Silurian and Devonian, well after the Taconic orogeny. Crust under accreted terranes in New England is much thinner (~30 km) than below the Grenville belt along the Laurentian margin (~45 km), and Li et al. (2018) noted a particularly abrupt change in crustal thickness in southwestern New England near the suture between Laurentia and the MT. New seismic evidence indicates that the abrupt offset in Moho depth in CT and MA occurs east of an anisotropic region (~25 km wide and ~15 km thick) that lies between the shallow Moho of the MT and the deep Moho of Laurentia. The Taconic and Acadian orogens are narrower in southern New England than they are to the north, suggesting greater crustal shortening, and high-grade metamorphic rocks exposed in southern New England indicate greater erosion of overlying crust. Hillenbrand et al. (2021) proposed that an Acadian plateau existed in southern New England from 380 to 330 Ma and that plateau collapse after 330 Ma led to the abrupt Moho offset. We suggest that an indenter in southern New England focused the Acadian collision between Laurentia and Avalonia leading to greater crustal shortening and uplift than elsewhere the Appalachians. The east-dipping suture zone and Neoproterozoic normal faults cutting the leading edge of Laurentia were reactivated as west-directed thrust faults. Further, the diffuse fault zone that displaced the MT and the leading edge of the Laurentian margin penetrated the crust and displaced the Moho beneath the MT creating a double Moho near the suture. The anisotropic zone between the double Moho region is likely composed of crustal and mantle rocks bounded by faults. It is unclear how far east rifted Grenville crust extends under the MT; it is possible that the MT is no longer above its original lithospheric mantle. 

We present results of integrated 40Ar/39Ar geochronology and microstructural analyses of samples from Taconic thrust faults of the northern New England Appalachians that provide evidence for reactivation during the Acadian, Neo-Acadian, and Alleghenian orogenies. 40Ar/39Ar ages c. 420 Ma from western frontal thrusts of the Green Mountains and Berkshire Massif have been interpreted previously to reflect partial resetting of Taconic ages during Acadian metamorphism. In Massachusetts and southern Vermont, these W-directed thrusts transport Grenville basement and its cover sequences over Cambrian-to-Ordovician phyllites and graphitic schists. Our recent investigations of these faults, however, yield a suite of c. 420 Ma 40Ar/39Ar ages obtained from syn-tectonic mica in mylonites and footwall schist/phyllite that are interpreted, rather, to reflect a pulse of W-directed thrusting. This interpretation that these ages record the timing of deformation is based, in part, on the preservation of quartz and feldspar dislocation creep microstructures (i.e., lack of evidence for static recrystallization), as well as the regional distribution of these data relative to Acadian metamorphic isograds. These results align with recent findings for the timing of formation of the Green Mountain Anticlinorium in northern Vermont, as well as detrital zircon data that require isolation of the Catskill Basin from the Connecticut Valley-Gaspe Basin (CVGB) at the onset of deposition around that time. Mylonites and samples from the adjacent footwall schists and phyllites also locally record evidence for minor to wholesale resetting c. 355 Ma associated with a younger phase of ductile deformation. Further evidence for partial resetting of 40Ar/39Ar ages c. 250 is associated with hematite-rich seams parallel to the mylonitic foliation and cross-cutting fractures. We explore how these age populations relate to those obtained from, for example, the CVGB and Chester and Athens Domes, and their implications for correlating surface geology with results from seismic imaging of the lithospheric and mantle structure in the northern New England Appalachians. 

Abstract We present the results of a search for gravitational-wave transients associated with core-collapse supernova SN 2023ixf, which was observed in the galaxy Messier 101 via optical emission on 2023 May 19, during the LIGO–Virgo–KAGRA 15th Engineering Run. We define a five-day on-source window during which an accompanying gravitational-wave signal may have occurred. No gravitational waves have been identified in data when at least two gravitational-wave observatories were operating, which covered ∼14% of this five-day window. We report the search detection efficiency for various possible gravitational-wave emission models. Considering the distance to M101 (6.7 Mpc), we derive constraints on the gravitational-wave emission mechanism of core-collapse supernovae across a broad frequency spectrum, ranging from 50 Hz to 2 kHz, where we assume the gravitational-wave emission occurred when coincident data are available in the on-source window. Considering an ellipsoid model for a rotating proto-neutron star, our search is sensitive to gravitational-wave energy 1 × 10⁻⁴M_⊙c²and luminosity 2.6 × 10⁻⁴M_⊙c²s⁻¹for a source emitting at 82 Hz. These constraints are around an order of magnitude more stringent than those obtained so far with gravitational-wave data. The constraint on the ellipticity of the proto-neutron star that is formed is as low as 1.08, at frequencies above 1200 Hz, surpassing past results. 

Abstract Continuous gravitational waves (CWs) emission from neutron stars carries information about their internal structure and equation of state, and it can provide tests of general relativity. We present a search for CWs from a set of 45 known pulsars in the first part of the fourth LIGO–Virgo–KAGRA observing run, known as O4a. We conducted a targeted search for each pulsar using three independent analysis methods considering single-harmonic and dual-harmonic emission models. We find no evidence of a CW signal in O4a data for both models and set upper limits on the signal amplitude and on the ellipticity, which quantifies the asymmetry in the neutron star mass distribution. For the single-harmonic emission model, 29 targets have the upper limit on the amplitude below the theoretical spin-down limit. The lowest upper limit on the amplitude is 6.4 × 10⁻²⁷for the young energetic pulsar J0537−6910, while the lowest constraint on the ellipticity is 8.8 × 10⁻⁹for the bright nearby millisecond pulsar J0437−4715. Additionally, for a subset of 16 targets, we performed a narrowband search that is more robust regarding the emission model, with no evidence of a signal. We also found no evidence of nonstandard polarizations as predicted by the Brans–Dicke theory. 

Abstract We present results from a search for X-ray/gamma-ray counterparts of gravitational-wave (GW) candidates from the third observing run (O3) of the LIGO–Virgo–KAGRA network using the Swift Burst Alert Telescope (Swift-BAT). The search includes 636 GW candidates received with low latency, 86 of which have been confirmed by the offline analysis and included in the third cumulative Gravitational-Wave Transient Catalogs (GWTC-3). Targeted searches were carried out on the entire GW sample using the maximum-likelihood Non-imaging Transient Reconstruction and Temporal Search pipeline on the BAT data made available via the GUANO infrastructure. We do not detect any significant electromagnetic emission that is temporally and spatially coincident with any of the GW candidates. We report flux upper limits in the 15–350 keV band as a function of sky position for all the catalog candidates. For GW candidates where the Swift-BAT false alarm rate is less than 10⁻³Hz, we compute the GW–BAT joint false alarm rate. Finally, the derived Swift-BAT upper limits are used to infer constraints on the putative electromagnetic emission associated with binary black hole mergers. 

Abstract The magnetar SGR 1935+2154 is the only known Galactic source of fast radio bursts (FRBs). FRBs from SGR 1935+2154 were first detected by the Canadian Hydrogen Intensity Mapping Experiment (CHIME)/FRB and the Survey for Transient Astronomical Radio Emission 2 in 2020 April, after the conclusion of the LIGO, Virgo, and KAGRA Collaborations’ O3 observing run. Here, we analyze four periods of gravitational wave (GW) data from the GEO600 detector coincident with four periods of FRB activity detected by CHIME/FRB, as well as X-ray glitches and X-ray bursts detected by NICER and NuSTAR close to the time of one of the FRBs. We do not detect any significant GW emission from any of the events. Instead, using a short-duration GW search (for bursts ≤1 s) we derive 50% (90%) upper limits of 10⁴⁸(10⁴⁹) erg for GWs at 300 Hz and 10⁴⁹(10⁵⁰) erg at 2 kHz, and constrain the GW-to-radio energy ratio to ≤10¹⁴−10¹⁶. We also derive upper limits from a long-duration search for bursts with durations between 1 and 10 s. These represent the strictest upper limits on concurrent GW emission from FRBs. 

Abstract Despite the growing number of binary black hole coalescences confidently observed through gravitational waves so far, the astrophysical origin of these binaries remains uncertain. Orbital eccentricity is one of the clearest tracers of binary formation channels. Identifying binary eccentricity, however, remains challenging due to the limited availability of gravitational waveforms that include the effects of eccentricity. Here, we present observational results for a waveform-independent search sensitive to eccentric black hole coalescences, covering the third observing run (O3) of the LIGO and Virgo detectors. We identified no new high-significance candidates beyond those that have already been identified with searches focusing on quasi-circular binaries. We determine the sensitivity of our search to high-mass (total source-frame massM> 70M_⊙) binaries covering eccentricities up to 0.3 at 15 Hz emitted gravitational-wave frequency, and use this to compare model predictions to search results. Assuming all detections are indeed quasi-circular, for our fiducial population model, we place a conservative upper limit for the merger rate density of high-mass binaries with eccentricities 0 <e≤ 0.3 at 16.9 Gpc⁻³yr⁻¹at the 90% confidence level. 

Abstract Gravitational lensing by massive objects along the line of sight to the source causes distortions to gravitational wave (GW) signals; such distortions may reveal information about fundamental physics, cosmology, and astrophysics. In this work, we have extended the search for lensing signatures to all binary black hole events from the third observing run of the LIGO-Virgo network. We search for repeated signals from strong lensing by (1) performing targeted searches for subthreshold signals, (2) calculating the degree of overlap among the intrinsic parameters and sky location of pairs of signals, (3) comparing the similarities of the spectrograms among pairs of signals, and (4) performing dual-signal Bayesian analysis that takes into account selection effects and astrophysical knowledge. We also search for distortions to the gravitational waveform caused by (1) frequency-independent phase shifts in strongly lensed images, and (2) frequency-dependent modulation of the amplitude and phase due to point masses. None of these searches yields significant evidence for lensing. Finally, we use the nondetection of GW lensing to constrain the lensing rate based on the latest merger-rate estimates and the fraction of dark matter composed of compact objects.