More Like this

1. Searches for Prompt Low-frequency Radio Counterparts to Gravitational-wave Event S250206dm with the OVRO-LWA Time Machine

   https://doi.org/10.3847/1538-4357/ae2ea3  

   Kosogorov, Nikita; Hallinan, Gregg; Law, Casey; Hickish, Jack; Dowell, Jayce; Mooley, Kunal P; Anderson, Marin M; Bowman, Judd D; Byrne, Ruby; Catha, Morgan; et al (January 2026, The Astrophysical Journal)

   Abstract We report on a search for prompt, low-frequency radio emission from the gravitational-wave (GW) merger S250206dm using the Owens Valley Radio Observatory Long Wavelength Array (OVRO-LWA). Early alerts favored a neutron-star-containing merger, making this a compelling target. Motivated by theoretical predictions of coherent radio bursts from mergers involving a neutron star, we utilized the OVRO-LWA Time Machine system to analyze voltage data recorded around the time of the event. Time Machine is a two-stage voltage buffer and processing pipeline that continuously buffers raw data from all antennas across the array’s nearly full-hemisphere instantaneous field of view, enabling retrospective beamforming, dedispersion, and fast-transient candidate identification. For this event, we analyzed a 30 minute interval beginning 3.5 minutes after the merger, which included 2 minutes of pre-alert data recovered by the ring buffer. We searched the 50% localization probability region with millisecond time resolution in the 69–86 MHz frequency band. No radio counterpart was detected above a 7σfluence detection threshold of ∼150 Jy ms. Using Bayesian analysis, we place a 95% confidence upper limit on the source luminosity ofL₉₅= 4 × 10⁴¹erg s⁻¹. These constraints start to probe the bright end of the coherent-emission parameter space predicted by jet–interstellar medium shock processes, magnetar and blitzar-like mechanisms, and recent simulation-based scenarios for neutron-star-containing mergers. This study presents the first sensitive, large-area, millisecond-timescale search for prompt low-frequency radio emission from a GW merger with the OVRO-LWA, establishing a framework in which about 10 additional events will yield stringent population-level constraints. 

   more » « less
2. Spatially Resolved Observations of Meteor Radio Afterglows With the OVRO‐LWA

   https://doi.org/10.1029/2023JA032272  

   Varghese, S S; Dowell, J; Obenberger, K S; Taylor, G B; Anderson, M; Hallinan, G (February 2024, Journal of Geophysical Research: Space Physics)

   Abstract We conducted an all‐sky imaging transient search with the Owens Valley Radio Observatory Long Wavelength Array (OVRO‐LWA) data collected during the Perseid meteor shower in 2018. The data collection during the meteor shower was motivated to conduct a search for intrinsic radio emission from meteors below 60 MHz known as the meteor radio afterglows (MRAs). The data collected were calibrated and imaged using the core array to obtain lower angular resolution images of the sky. These images were input to a pre‐existing LWA transient search pipeline to search for MRAs as well as cosmic radio transients. This search detected 5 MRAs and did not find any cosmic transients. We further conducted peeling of bright sources, near‐field correction, visibility differencing and higher angular resolution imaging using the full array for these 5 MRAs. These higher angular resolution images were used to study their plasma emission structures and monitor their evolution as a function of frequency and time. With higher angular resolution imaging, we resolved the radio emission size scales to less than 1 km physical size at 100 km heights. The spectral index mapping of one of the long duration event showed signs of diffusion of plasma within the meteor trails. The unpolarized emission from the resolved radio components suggest resonant transition radiation as the possible radiation mechanism of MRAs. 

   more » « less
3. Time-Domain Science Pipelines for the OVRO-LWA

   https://doi.org/10.23919/at-ap-rasc54737.2022.9814199  

   Huang, Yuping; Laures, Mei-Ling; Anderson, Marin M.; Law, Casey J.; Hallinan, Gregg (May 2022, 2022 3rd URSI Atlantic and Asia Pacific Radio Science Meeting (AT-AP-RASC))

   The Owens Valley Radio Observatory Long Wavelength Array is a low radio frequency all-sky imaging radio interferometer. The full 352-element array will generate more than 2 TB of visibility data per hour of observation. One of the array’s primary science cases, the search for variable radio emission from exoplanets and for transients, require fast and high dynamic range interferometric imaging. Here we detail the design and implementation of a two-pipeline infrastructure that minimizes development cost: an offline pipeline that facilitates experimentation with existing pack-ages, and a real-time pipeline that minimizes overhead. 

   more » « less
4. A VOEvent-based automatic trigger system for the Murchison Widefield Array

   https://doi.org/10.1017/pasa.2019.40  

   Hancock, P. J.; Anderson, G. E.; Williams, A.; Sokolowski, M.; Tremblay, S. E.; Rowlinson, A.; Crosse, B.; Meyers, B. W.; Lynch, C. R.; Zic, A.; et al (January 2019, Publications of the Astronomical Society of Australia)

   Abstract The Murchison Widefield Array (MWA) is an electronically steered low-frequency (<300 MHz) radio interferometer, with a ‘slew’ time less than 8 s. Low-frequency (∼100 MHz) radio telescopes are ideally suited for rapid response follow-up of transients due to their large field of view, the inverted spectrum of coherent emission, and the fact that the dispersion delay between a 1 GHz and 100 MHz pulse is on the order of 1–10 min for dispersion measures of 100–2000 pc/cm 3 . The MWA has previously been used to provide fast follow-up for transient events including gamma-ray bursts (GRBs), fast radio bursts (FRBs), and gravitational waves, using systems that respond to gamma-ray coordinates network packet-based notifications. We describe a system for automatically triggering MWA observations of such events, based on Virtual Observatory Event standard triggers, which is more flexible, capable, and accurate than previous systems. The system can respond to external multi-messenger triggers, which makes it well-suited to searching for prompt coherent radio emission from GRBs, the study of FRBs and gravitational waves, single pulse studies of pulsars, and rapid follow-up of high-energy superflares from flare stars. The new triggering system has the capability to trigger observations in both the regular correlator mode (limited to ≥0.5 s integrations) and using the Voltage Capture System (VCS, 0.1 ms integration) of the MWA and represents a new mode of operation for the MWA. The upgraded standard correlator triggering capability has been in use since MWA observing semester 2018B (July–Dec 2018), and the VCS and buffered mode triggers will become available for observing in a future semester. 

   more » « less
5. Anomaly Detection and Approximate Similarity Searches of Transients in Real-time Data Streams

   https://doi.org/10.3847/1538-4357/ad6869  

   Aleo, P D; Engel, A W; Narayan, G; Angus, C R; Malanchev, K; Auchettl, K; Baldassare, V F; Berres, A; de_Boer, T_J L; Boyd, B M; et al (October 2024, The Astrophysical Journal)

   Abstract We present Lightcurve Anomaly Identification and Similarity Search (LAISS), an automated pipeline to detect anomalous astrophysical transients in real-time data streams. We deploy our anomaly detection model on the nightly Zwicky Transient Facility (ZTF) Alert Stream via the ANTARES broker, identifying a manageable ∼1–5 candidates per night for expert vetting and coordinating follow-up observations. Our method leverages statistical light-curve and contextual host galaxy features within a random forest classifier, tagging transients of rare classes (spectroscopicanomalies), of uncommon host galaxy environments (contextualanomalies), and of peculiar or interaction-powered phenomena (behavioralanomalies). Moreover, we demonstrate the power of a low-latency (∼ms) approximate similarity search method to find transient analogs with similar light-curve evolution and host galaxy environments. We use analogs for data-driven discovery, characterization, (re)classification, and imputation in retrospective and real-time searches. To date, we have identified ∼50 previously known and previously missed rare transients from real-time and retrospective searches, including but not limited to superluminous supernovae (SLSNe), tidal disruption events, SNe IIn, SNe IIb, SNe I-CSM, SNe Ia-91bg-like, SNe Ib, SNe Ic, SNe Ic-BL, and M31 novae. Lastly, we report the discovery of 325 total transients, all observed between 2018 and 2021 and absent from public catalogs (∼1% of all ZTF Astronomical Transient reports to the Transient Name Server through 2021). These methods enable a systematic approach to finding the “needle in the haystack” in large-volume data streams. Because of its integration with the ANTARES broker,LAISSis built to detect exciting transients in Rubin data. 

   more » « less