Breakthrough Listen

Abstract:

Previous work detected transient ultraviolet outflow features for the short-period (P min), low-mass X-ray binary (LMXB) UW CrB, suggesting the presence of a disc wind in the system. However, because of the transient nature of the outflow features, and the limited amount of data available, the features were challenging to interpret. To follow up on this work, we present a comprehensive multiwavelength campaign on UW CrB. We observe complex phenomenology and find several features that could be naturally interpreted as being associated with a persistent disc wind. Moreover, we identify a blue-shifted absorption in the H line during one of the epochs, which might be the signature of such an outflow. We present an X-ray to radio campaign of the source, discuss our results in the context of accretion disc wind outflows, present a ‘toy model’ interpretation of the outflow scattering the X-ray emission into our line of sight, and explore the implications for binary evolution models. If correct, our preferred scenario of a persistent disc wind suggests that mass transfer for LMXBs can be non-conservative down to short orbital periods, and thereby opens an important parameter space for angular momentum loss in compact binaries.

Abstract:

We present the first multiepoch broadband radio and millimeter monitoring of an off-nuclear tidal disruption event (TDE) using the Very Large Array, the Atacama Large Millimeter/submillimeter Array, the Allen Telescope Array, the Arcminute Microkelvin Imager Large Array, and the Submillimeter Array. The off-nuclear TDE AT 2024tvd exhibits double-peaked radio light curves and the fastest-evolving radio emission observed from a TDE to date. With respect to the optical discovery date, the first radio flare rises faster than Fν ∼ t9 at Δt = 88–131 days and then decays as fast as Fν ∼ t−6. The emergence of a second radio flare is observed at Δt ≈ 194 days with an initial fast rise of Fν ∼ t18 and an optically thin decline of Fν ∼ t−12. We interpret these observations in the context of a self-absorbed and free–free absorbed synchrotron spectrum, while accounting for both synchrotron and inverse Compton cooling. We find that a single prompt outflow cannot easily explain these observations and that it is likely that either there is only one outflow that was launched at Δt ∼ 80 days or there are two distinct outflows, with the second launched at Δt ∼ 170–190 days. The nature of these outflows, whether sub-, mildly, or ultrarelativistic, is still unclear, and we explore these different scenarios. Finally, we find a temporal coincidence between the launch time of the first radio-emitting outflow and the onset of a power-law component in the X-ray spectrum, attributed to inverse Compton scattering of thermal photons.

Abstract:

A key science goal of large sky surveys such as those conducted by the Vera C. Rubin Observatory and precursors to the Square Kilometre Array is the identification of variable and transient objects. One approach is analyzing time series of the changing brightness of sources, namely, light curves. However, finding adequate statistical representations of light curves is challenging because of the sparsity of observations, irregular sampling, and nuisance factors inherent in astronomical data collection. The wide diversity of objects that a large-scale survey will observe also means that making parametric assumptions about the shape of light curves is problematic. We present a Gaussian process (GP) regression approach for characterizing light-curve variability that addresses these challenges. Our approach makes no assumptions about the shape of a light curve and, therefore, is general enough to detect a range of variable and transient source types. In particular, we propose using the joint distribution of GP amplitude hyperparameters to distinguish variable and transient candidates from nominally stable ones and apply this approach to 6394 radio light curves from the ThunderKAT survey. We compare our results with two variability metrics commonly used in radio astronomy, namely ην and Vν, and show that our approach has better discriminatory power and interpretability. Finally, we conduct a rudimentary search for transient sources in the ThunderKAT data set to demonstrate how our approach might be used as an initial screening tool. Computational notebooks in Python and R are available to help deploy this framework to other surveys.

Abstract:

We describe a resonant cavity search apparatus for axion dark matter constructed by the quantum sensors for the hidden sector collaboration. The apparatus is configured to search for QCD axion dark matter, though also has the capability to detect axion-like particles, dark photons, and some other forms of wave-like dark matter. Initially, a tuneable cylindrical oxygen-free copper cavity is read out using a low noise microwave amplifier feeding a heterodyne receiver. The cavity is housed in a dilution refrigerator (DF) and threaded by a solenoidal magnetic field, nominally 8 T. The apparatus also houses a magnetic field shield for housing superconducting electronics, and several other fixed-frequency resonators for use in testing and commissioning various prototype quantum electronic devices sensitive at a range of axion masses in the range 2.0– 40μeVc−2. The apparatus as currently configured is intended as a test stand for electronics over the relatively wide frequency band attainable with the TM010 cavity mode used for axion searches. We present performance data for the resonator, DF, and magnet, and plans for the first science run.

Abstract:

We present the detection of the binary system 2MASS J02132062+3648506 AB using the Karl G. Jansky Very Large Array archive data observed at 4–8 GHz. The system is a triple consisting of a tight binary () of two M dwarfs of spectral types M4.5 and M6.5 and a wide T3 brown dwarf companion (16.4 arcsec). The binary displays coronal and chromospheric activity as traced by previously measured X-ray flux and H emission. We detect the unresolved binary at a peak flux density of at a signal-to-noise ratio (SNR) of and determine a radio luminosity of . The radio emission is quiescent, polarized at a mean circular polarization fraction % and exhibits a spectral index . We probe the binary using the Enhanced Multi-Element Remotely Linked Interferometer Network (e-MERLIN) with an angular resolution of mas at 5 GHz and detect a component at a peak flux density of Jy at a SNR . We propose a gyrosynchrotron origin for the radio emission and estimate a magnetic field strength G, an emitting region of size times the radius of the M4.5 primary and a plasma number density . The brown dwarf companion is not detected. Additionally, we have analysed observations of 2MASS J04183483+213127, a chromospherically active L5 brown dwarf which is also not detected and can only place flux density upper limits at Jy and Jy for Stokes I and V, respectively.