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In search of short gamma-ray burst optical counterpart with the Zwicky Transient Facility
No full textThe 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
SRGA J181414.6-225604: A New Galactic Symbiotic X-Ray Binary Outburst Triggered by an Intense Mass-loss Episode of a Heavily Obscured Mira Variable
No full textWe present the discovery and multiwavelength characterization of SRGA J181414.6-225604, a Galactic hard X-ray transient discovered during the ongoing SRG/ART-XC sky survey. Using data from the Palomar Gattini-IR survey, we identify a spatially and temporally coincident variable infrared (IR) source, IRAS 18111-2257, and classify it as a very-late-type (M7–M8), long-period (1502 ± 24 days), and luminous (M_K ≈ −9.9 ± 0.2) O-rich Mira donor star located at a distance of ≈14.6^(+2.9)_(−2.3) kpc. Combining multicolor photometric data over the last ≈25 yr, we show that the IR counterpart underwent a recent (starting ≈800 days before the X-ray flare) enhanced mass-loss (reaching ≈2.1 × 10⁻⁵ M_⊙ yr⁻¹) episode, resulting in an expanding dust shell obscuring the underlying star. Multi-epoch follow-up observations from Swift, NICER, and NuSTAR reveal a ≈200 day long X-ray outburst reaching a peak luminosity of L_ₓ ≈ 2.5 × 10³⁶ erg s⁻¹, characterized by a heavily absorbed (N_H ≈ 6 × 10²² cm⁻²) X-ray spectrum consistent with an optically thick Comptonized plasma. The X-ray spectral and timing behavior suggest the presence of clumpy wind accretion, together with a dense ionized nebula overabundant in silicate material surrounding the compact object. Together, we show that SRGA J181414.6-225604 is a new symbiotic X-ray binary in outburst, triggered by an intense dust-formation episode of a highly evolved donor. Our results offer the first direct confirmation for the speculated connection between enhanced late-stage donor mass loss and the active lifetimes of symbiotic X-ray binaries
Searching for Life, Mindful of Lyfe’s Possibilities
No full textWe are embarking on a new age of astrobiology, one in which numerous interplanetary missions and telescopes will be designed, built, and launched with the explicit goal of finding evidence for life beyond Earth. Such a profound aim warrants caution and responsibility when interpreting and disseminating results. Scientists must take care not to overstate (or over-imply) confidence in life detection when evidence is lacking, or only incremental advances have been made. Recently, there has been a call for the community to create standards of evidence for the detection and reporting of biosignatures. In this perspective, we wish to highlight a critical but often understated element to the discussion of biosignatures: Life detection studies are deeply entwined with and rely upon our (often preconceived) notions of what life is, the origins of life, and habitability. Where biosignatures are concerned, these three highly related questions are frequently relegated to a low priority, assumed to be already solved or irrelevant to the question of life detection. Therefore, our aim is to bring to the fore how these other major astrobiological frontiers are central to searching for life elsewhere and encourage astrobiologists to embrace the reality that all of these science questions are interrelated and must be furthered together rather than separately. Finally, in an effort to be more inclusive of life as we do not know it, we propose tentative criteria for a more general and expansive characterization of habitability that we call genesity
The Large Dispersion and Scattering of FRB 20190520B Are Dominated by the Host Galaxy
No full textThe repeating fast radio burst FRB 20190520B is localized to a galaxy at z = 0.241, much closer than expected given its dispersion measure DM = 1205 ± 4 pc cm⁻³. Here we assess implications of the large DM and scattering observed from FRB 20190520B for the host galaxy’s plasma properties. A sample of 75 bursts detected with the Five-hundred-meter Aperture Spherical radio Telescope shows scattering on two scales: a mean temporal delay τ(1.41 GHz) = 10.9 ± 1.5 ms, which is attributed to the host galaxy, and a mean scintillation bandwidth Δν_d(1.41 GHz) = 0.21 ± 0.01 MHz, which is attributed to the Milky Way. Balmer line measurements for the host imply an Hα emission measure (galaxy frame) EMₛ = 620 pc cm⁻⁶ × (T/10⁴ K)^(0.9), implying DM_(Hα) of order the value inferred from the FRB DM budget, DMₕ = 1121_(−138)^(+89) pc cm⁻³ for plasma temperatures greater than the typical value 10⁴ K. Combining τ and DMₕ yields a nominal constraint on the scattering amplification from the host galaxy F^~G =1.5_(-0.3}){(0.8) pc² km^(-1/3), describes turbulent density fluctuations and G represents the geometric leverage to scattering that depends on the location of the scattering material. For a two-screen scattering geometry where τ arises from the host galaxy and Δν_d from the Milky Way, the implied distance between the FRB source and dominant scattering material is ≲100 pc. The host galaxy scattering and DM contributions support a novel technique for estimating FRB redshifts using the τ–DM relation, and are consistent with previous findings that scattering of localized FRBs is largely dominated by plasma within host galaxies and the Milky Way
When Do Stars Go Boom?
No full textThe maximum mass of a star that can produce a white dwarf (WD) is an important astrophysical quantity. One of the best approaches to establishing this limit is to search for WDs in young star clusters in which only massive stars have had time to evolve and where the mass of the progenitor can be established from the cooling time of the WD together with the age of the cluster. Searches in young Milky Way clusters have not thus far yielded WD members more massive than about 1.1 M_⊙, well below the Chandrasekhar mass of 1.38 M_⊙, nor progenitors with masses in excess of about 6 M_⊙. However, the hunt for potentially massive WDs that escaped their cluster environs is yielding interesting candidates. To expand the cluster sample further, we used HST to survey four young and massive star clusters in the Magellanic Clouds for bright WDs that could have evolved from stars as massive as 10 M_⊙. We located five potential WD candidates in the oldest of the four clusters examined, the first extragalactic single WDs thus far discovered. As these hot WDs are very faint at optical wavelengths, final confirmation will likely have to await spectroscopy with 30 m class telescopes
Next-to-leading order scalar contributions to μ → e conversion
No full textWithin a class of models in which lepton flavor violation is induced dominantly by scalar particle exchanges, we estimate the μ → e conversion rate in several nuclei. We include next-to-leading order (NLO) terms in the one- and two-nucleon interactions in chiral effective theory, rectifying some incorrect results in the previous literature. We provide an uncertainty budget for the conversion rates and we find that NLO contributions affect the amplitudes at the level of 10%, which could be larger than the uncertainty on the leading order couplings, dominated by the strange and nonstrange nucleon sigma terms. We study the implications of our results for testing Higgs-mediated charged lepton flavor violation (CLFV) in the future by combining results from various experimental searches, such as μ → e conversion in multiple target nuclei and μ → eγ
Physics of a strongly oscillating axisymmetric air-water interface with a fixed boundary condition
No full textIn this work, we experimentally investigate the physics of a strongly oscillating, millimeter-sized, axisymmetric air-water interface with a fixed contact line boundary condition. Many previous studies focused on the regime of small oscillation amplitude, e.g., R = d/D ≪ 1, where
d is the oscillation amplitude and D is the characteristic size of the air-water interface. The current investigation instead focuses on a less-studied oscillation regime with large R that is up to 0.33. The dynamic oscillations induce different steady streaming patterns, such as a low-speed streaming vortex or a fast-speed streaming jet. The steady streaming jet, in particular, was not much studied previously and is the major focus of this work. The streaming jet is only generated when the oscillating interface exhibits the higher-order axisymmetric oscillation modes with a large oscillation amplitude, which correspond to the regime with large R and large Weber number (We). The streaming jet has a larger Reynolds number [Re ∼ O(100)]
than the typical streaming motions induced by an oscillating interface [Re ∼ O(1)]. In addition, the streaming jet has a high ratio of the streaming velocity versus the oscillatory velocity, which suggests a high efficiency in generating steady streaming motion. The dynamic velocity and vorticity field of the streaming jet in both the initiation stage and the quasisteady stage are presented, which demonstrates that the streaming jet onset process is a consequence of vorticity generation, transportation, and accumulation happening at the oscillating interface. As a zero-mass-flux jet, the streaming jet is sustained by entraining fluid mass flux from the circumferential regions through a process similar to the classical Stokes drift. It is further found that a streaming jet can be induced by an oscillating elastic no-slip membrane as well, when the oscillation has large R and We. The extraordinary characters of the streaming jet can be employed in many engineering applications
Learning algorithm reflecting universal scaling behavior near phase transitions
No full textMachine-learning-inspired techniques have emerged as a new paradigm for analysis of phase transitions in quantum matter. In this work, we introduce a supervised learning algorithm for studying critical phenomena from measurement data, “neural network scaling,” which is based on iteratively training convolutional networks of increasing (spatial) complexity and test it on the transverse field Ising chain and q = 6 Potts model. At the continuous Ising transition, our scaling procedure directly reflects the hallmark of a continuous (second-order) phase transition, divergence of a characteristic length scale. Specifically, we extract a classification length scale by measuring the response of the classification accuracy while varying the largest convolution size (architecture of the network). We observe empirically the scaling exponent of the classification length is consistent with a power law with the correlation length exponent ν = 1. Furthermore, we demonstrate the versatility of our algorithm by showing the universal scaling behaviors persist across a variety of measurement bases, including when the order parameter is nonlocal. Finally, we show that the classification length scale remains finite for the q = 6 Potts model, which has a first-order transition and lacks a divergent correlation length
GriddingMachine, a database and software for Earth system modeling at global and regional scales
No full textLand and Earth system modeling is moving towards more explicit biophysical representations, requiring increasing variety of datasets for initialization and benchmarking. However, researchers often have difficulties in identifying and integrating non-standardized datasets from various sources. We aim towards a standardized database and one-stop distribution method of global datasets. Here, we present the GriddingMachine as (1) a database of global-scale datasets commonly used to parameterize or benchmark the models, from plant traits to vegetation indices and geophysical information and (2) a cross-platform open source software to download and request a subset of datasets with only a few lines of code. The GriddingMachine datasets can be accessed either manually through traditional HTTP, or automatically using modern programming languages including Julia, Matlab, Octave, Python, and R. The GriddingMachine collections can be used for any land and Earth modeling framework and ecological research at the regional and global scales, and the number of datasets will continue to grow to meet the increasing needs of research communities
Energetic constraints on the pattern of changes to the hydrological cycle under global warming
No full textThe response of precipitation minus evaporation (P-E) to global warming is investigated using a moist energy balance model (MEBM) with a simple Hadley-Cell parameterization. The MEBM accurately emulates P-E changes simulated by a suite of global climate models (GCMs) under greenhouse-gas forcing. The MEBM also accounts for most of the intermodel differences in GCM P-E changes and better emulates GCM P-E changes when compared to the "wet-gets-wetter, dry-gets-drier" thermodynamic mechanism. The intermodel spread in P-E changes are attributed to intermodel differences in radiative feedbacks, which account for 60-70% of the intermodel variance, with smaller contributions from radiative forcing and ocean heat uptake. Isolating the intermodel spread of feedbacks to specific regions shows that tropical feedbacks are the primary source of intermodel spread in P-E changes. The ability of the MEBM to emulate GCM P-E changes is further investigated using idealized feedback patterns. A less negative and narrowly peaked feedback pattern near the equator results in more atmospheric heating, which strengthens the Hadley Cell circulation in the deep tropics through an enhanced poleward heat flux. This pattern also increases gross moist stability, which weakens the subtropical Hadley Cell circulation. These two processes in unison increase P-E in the deep tropics, decrease P-E in the subtropics, and narrow the Intertropical Convergence Zone. Additionally, a feedback pattern that produces polar-amplified warming reduces the poleward moisture flux by weakening the meridional temperature gradient and the Clausius-Clapeyron relation. It is shown that changes to the Hadley Cell circulation and the poleward moisture flux are crucial for understanding the pattern of GCM P-E changes under warming