A new perspective on GCRT J1745-3009

Abstract

Context. Reports on a transient source about 1.25 • south of the Galactic Centre motivated these follow-up observations with the WSRT and the reinvestigation of archival VLA data. The source GCRT J1745-3009 was detected during a 2002 Galactic Centre monitoring programme with the VLA at 92 cm by five powerful 10-min bursts with a 77-min recurrence while apparently lacking any interburst emission. Aims. The WSRT observations were performed and archival VLA data reduced to detect GCRT J1745-3009 again at different epochs and frequencies, to constrain its distance, and to determine its nature. We attempted to extract a more accurate lightcurve from the discovery dataset of GCRT J1745-3009 to rule out some of the models that have been suggested. We also investigated the transient behaviour of a nearby source. Methods. The WSRT data were taken in the "maxi-short" configuration, using 10 s integrations, on 2005 March 24 at 92 cm and on 2005 May 14/15 at 21 cm. Five of the six VLA observations we reduced are the oldest of this field in this band. Results. GCRT J1745-3009 was not redetected. With the WSRT we reached an rms sensitivity of 0.21 mJy beam −1 at 21 cm and 3.7 mJy beam −1 at 92 cm. Reanalysis of the discovery observation data resulted in a more accurate and more complete lightcurve. The five bursts appear to have the same shape: a steep rise, a more gradual brightening, and a steep decay. We found variations in burst duration of order 3%. We improved the accuracy of the recurrence period of the bursts by an order of magnitude: 77.012 ± 0.021 min. We found no evidence of aperiodicity. We derived a very steep spectral index: α = −6.5 ± 3.4. We improved the 5σ upper limits for interburst emission and fractional circular polarisation to 31 mJy beam −1 and 8%, respectively. Any transient behaviour of a nearby source could not be established. Conclusions. Models that predict symmetric bursts can be ruled out, but rotating systems are favoured, because their periodicity is precise. Scattering constraints imply that GCRT J1745-3009 cannot be located far beyond the GC. If this source is an incoherent emitter and not moving at a relativistic velocity, it must be closer than 14 pc.

Exploring the Transient Radio Sky With Vlite: Early Results

“…At least one of the GCRT J1745−3009 bursts exhibits time-varying, highly circularly polarized emission that approaches 100% (Roy et al 2010). Several of the bursts appear to have a steep spectrum, in one case with α ∼ −13 (where S ν ∝ ν α ), derived across the 30 MHz GMRT bandpass (Hyman et al 2007;Spreeuw et al 2009).…”

Circularly Polarized Emission From the Transient Bursting Radio Source GCRT J1745 – 3009

“…Adopting their approach during our re-analysis yields a stokes V of 12%, consistent with their reported limit. More recent reanalysis of its 2002 outburst (Spreeuw et al 2009) yields an upper limit of 8% on the fraction of circular polarization averaged over the emission timescale. To study the variation of the circular polarization, we have also made maps of the GCRT in Stokes V, and a light curve made from these maps is shown in Fig.…”

Two Extreme Steep-Spectrum, Polarized Radio Sources Towards the Galactic Bulge

“…Both sources share some similarities with GCRT J1745−3009 (a.k.a. "The Burper"), i.e., high circular polarization, a steep spectrum, and the absence of quiescent counterpart at other wavelengths (Roy et al 2010;Spreeuw et al 2009;Hyman et al 2005). The similarities diverge from there, however, as GCRT J1745−3009 appears to be a unique transient (Polisensky et al 2016;Anderson et al 2019), discovered initially as five Jansky-like flares of 10-min duration with a 77-min recurrence timescale (Hyman et al 2005), followed by some additional bursts before fading away altogether (Hyman et al 2006(Hyman et al , 2007.…”