4–8 GHz Spectrotemporal Emission from the Galactic Center Magnetar PSR J1745–2900

Abstract

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.

4–8 GHz Fourier-domain Searches for Galactic Center Pulsars

“…As illustrated in Figure 1, our central pointing A00 contains the GC magnetar. We refer readers to Suresh et al (2021) for a 4-8 GHz study of the GC magnetar using our A00 data.…”

“…We followed the methodology of Suresh et al (2021) to excise RFI from our data using the rfifind module of the pulsar software package PRESTO (Ransom 2011). Adopting an integration time of 1 s for our rfifind runs, we detected bright, persistent interference between 4.…”

Extraterrestrial Axion Search with the Breakthrough Listen Galactic Center Survey

“…Our calibration procedure follows that of [58]. In short, we model the various contributions to the net system temperature of GBT pointed at the GC, denoted T GC sys , from which we determine a system equivalent flux density and calibration factor, C(f ), at frequency f .…”

“…We also use T Rg = 25 K, which is the approximately expected GBT system temperature and, in particular, overestimates T Rg over the full 4-8 GHz band [58,88]. We estimate that the systematic error introduced by our calibration approach is at the level of ∼ 15%, corresponding to the variation in C(f, t) over the range of elevations for the observations considered in this work.…”

“…We calibrate the data following the procedure in [58] (see the SM). We then join the calibrated results of the two observing sessions using a joint likelihood to obtain flux density limits and detection significances.…”