A line of sight toward the Galactic Center (GC) offers the largest number of potentially habitable systems of any direction in the sky. The Breakthrough Listen program is undertaking the most sensitive and deepest targeted SETI surveys toward the GC. Here, we outline our observing strategies with Robert C. Byrd Green Bank Telescope (GBT) and Parkes telescope to conduct 600 hr of deep observations across 0.7–93 GHz. We report preliminary results from our survey for extraterrestrial intelligence (ETI) beacons across 1–8 GHz with 7.0 and 11.2 hr of observations with Parkes and GBT, respectively. With our narrowband drifting signal search, we were able to place meaningful constraints on ETI transmitters across 1–4 GHz and 3.9–8 GHz with EIRP limits of ≥4 × 1018 W among 60 million stars and ≥5 × 1017 W among half a million stars, respectively. For the first time, we were able to constrain the existence of artificially dispersed transient signals across 3.9–8 GHz with EIRP ≥1 × 1014 W/Hz with a repetition period ≤4.3 hr. We also searched our 11.2 hr of deep observations of the GC and its surrounding region for Fast Radio Burst–like magnetars with the DM up to 5000 pc cm−3 with maximum pulse widths up to 90 ms at 6 GHz. We detected several hundred transient bursts from SGR J1745−2900, but did not detect any new transient bursts with the peak luminosity limit across our observed band of ≥1031 erg s−1 and burst rate of ≥0.23 burst hr−1. These limits are comparable to bright transient emission seen from other Galactic radio-loud magnetars, constraining their presence at the GC.

Low radio frequency solar observations using the Murchison Widefield Array have recently revealed the presence of numerous weakshort-livednarrowband emission features, even during moderately quiet solar conditions. These nonthermal features occur at rates of many thousands per hour in the 30.72 MHz observing bandwidth, and hencenecessarily require an automated approach for their detection and characterization. Here, we employ continuous wavelet transform using a mother Ricker wavelet for feature detection from the dynamic spectrum. We establish the efficacy of this approach and present the first statistically robust characterization of the properties of these features. In particular, we examine distributions of their peak flux densities, spectral spans, temporal spans, and peak frequencies. We can reliably detect features weaker than 1 SFU, making them, to the best of our knowledge, the weakest bursts reported in literature. The distribution of their peak flux densities follows a power law with an index of −2.23 in the 12-155 SFU range, implying that they can provide an energetically significant contribution to coronal and chromospheric heating. These features typically last for 1-2 s and possess bandwidths of about 4-5 MHz. Their occurrence rate remains fairly flat in the 140-210 MHz frequency range. At the time resolution of the data, they appear as stationary bursts, exhibiting no perceptible frequency drift. These features also appear to ride on a broadband background continuum, hinting at the likelihood of them being weak type-I bursts.

Birefringence in ionized, magnetized media is usually measured as Faraday rotation of linearly polarized radiation. However, pulses propagating through regions with very large Faraday rotation measures (RMs) can split into circularly polarized components with measurable differences in arrival times ∝ ν −3 RM, where ν is the radio frequency. Differential refraction from gradients in DM (dispersion measure) and RM can contribute a splitting time ∝ |∇ ⊥ DM||∇ ⊥ RM| ν −5 . Regardless of whether the emitted pulse is unpolarized or linearly polarized, net circular polarization will be measured when splitting is a significant fraction of the pulse width. However, the initial polarization may be inferable from the noise statistics of the bursts. Extreme multipath scattering that broadens pulses can mask splitting effects. We discuss particular cases such as the Galactic center magnetar, J1745−2900, and the repeating fast radio burst source, FRB 121102. Both lines of sight have |RM| ∼ 10 5 rad m −2 that yields millisecond splittings at frequencies well below ∼ 1 GHz. We also consider the splitting of nanosecond shot pulses in giant pulses from the Crab pulsar and the minimal effects of birefringence on precision pulsar timing. Finally, we explore the utility of two-dimensional coherent dedispersion with DM and RM as parameters.

The nearby star òEridani has been a frequent target of radio surveys for stellar emission and extraterrestrial intelligence. Using deep 2-4GHz observations with the Very Large Array, we have uncovered a 29 μJy compact, steady continuum radio source coincident with ò Eridani to within 0 06 (2σ; 0.2 au at the distance of the star). Combining our data with previous high-frequency continuum detections of ò Eridani, our observations reveal a spectral turnover at 6 GHz. We ascribe the 2-6GHz emission to optically thick, thermal gyroresonance radiation from the stellar corona, with thermal free-free opacity likely becoming relevant at frequencies below 1GHz. The steep spectral index (α;2) of the 2-6GHz spectrum strongly disfavors its interpretation as stellar-windassociated thermal bremsstrahlung (α;0.6). Attributing the entire observed 2-4GHz flux density to thermal free-free wind emission, we thus derive a stringent upper limit of 3×10 −11 M e yr −1 on the mass-loss rate from ò Eridani. Finally, we report the nondetection of flares in our data above a 5σ threshold of 95 μJy. Together with the optical nondetection of the most recent stellar maximum expected in 2019, our observations postulate a likely evolution of the internal dynamo of ò Eridani.

Radio magnetars are exotic sources noted for their diverse spectrotemporal phenomenology and pulse profile variations over weeks to months. Unusual for radio magnetars, the Galactic Center (GC) magnetar PSR J1745−2900 has been continually active since its discovery in 2013. We monitored the GC magnetar at 4–8 GHz for 6 hr in 2019 August–September using the Robert C. Byrd Green Bank Telescope. During our observations, the GC magnetar emitted a flat fluence spectrum over 5–8 GHz to within 2σ uncertainty. From our data, we estimate a 6.4 GHz period-averaged flux density, S ¯ 6.4 ≈ ( 240 ± 5 ) μJy. Tracking the temporal evolution of S ¯ 6.4 , we infer a gradual weakening of GC magnetar activity during 2016–2019 relative to that between 2013 and 2015.5. Typical single pulses detected in our study reveal marginally resolved subpulses with opposing spectral indices, a feature characteristic of radio magnetars but unseen in rotation-powered pulsars. However, unlike in fast radio bursts, these subpulses exhibit no perceptible radio frequency drifts. Throughout our observing span, ≃5 ms scattered pulses significantly jitter within two stable emission components of widths 220 ms and 140 ms, respectively, in the average pulse profile.