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

Abstract

We report detection of strong circularly polarized emission from the transient bursting source GCRT J1745-3009 based on new analysis of 325 MHz GMRT observations conducted on 28 September 2003. We place 8 R ⊙ as the upper limit on the size of the emission region. The implied high brightness temperature required for an object beyond 1 pc and the high fraction of circular polarization firmly establish the emission as coherent. Electron cyclotron or plasma emission from a highly subsolar magnetically dominated dwarf located ≤4 kpc away could have given rise to the GCRT radio emission.

Explosive and Radio-Selected Transients: Transient Astronomy with Square Kilometre Array and its Precursors

“…In the last decade, use of wide frequency imaging techniques have resulted in several reported detections. These include: (i) detection of a transient GCRT J1745−3009 with flux density ≤ 1 Jy at 325 MHz about a degree away from the Galactic centre emitting coherent emission (Hyman et al, 2005;Roy et al, 2010), (ii) ten transients from multi-epoch (22 years) observations of a single field from archival VLA data at 4.8 and 8.4 GHz at ∼a few hundred µJy or higher level of flux density (Bower et al, 2007), (iii) detection of a single transient at 1.4 GHz with ∼ 1 Jy flux density using Nasu observatory in Japan (Niinuma et al, 2007), (iv) detection of a single transient GCRT J1742−3001 at 240 MHz with flux density ∼ 0.1 Jy near the Galactic centre (Hyman et al, 2009), (v) detection of 15 transients at 843 MHz from a 22-yr survey with Molonglo observatory synthesis telescope (Bannister et al, 2011) at ∼ 10 mJy or higher, (vi) detection of a single transient from about 12 hours of observation at 325 MHz at a few mJy level (Jaeger et al, 2012), (vii) detection of a single transient from 4 months of observations at 60 MHz with LOFAR at ∼ 10 Jy level (Stewart et al, 2016).…”

“…However, coherent emission from stellar surface could occur from energetic processes (e.g., re-connection of magnetic flux tubes) like the electron cyclotron maser at the electron gyrofrequency and its harmonics, or the plasma emission at plasma frequency or its lower order harmonics. Though the bandwidth of such emission is quite small, but there can be multiple spots of emission with slightly different centre frequency (Roy et al, 2010). These emission could have high brightness temperature reaching ∼ 10 16 − 10 20 (Ergun et!al, 2000;Stepanov et al, 2001).…”

“…However, at metre wavelengths or larger, some of the flares recorded are ∼100 Jy (Abdul-Aziz et al, 1995). Therefore, occasional radio emission from magnetically dominated flare stars which are quite common in the Solar neighbourhood could explain some of these transient emission (Bower et al, 2007;Roy et al, 2010;Jaeger et al, 2012;Stewart et al, 2016) and could dominate the transient emissions at metre or decameter wavelengths.…”

VAST: An ASKAP Survey for Variables and Slow Transients

“…The identification of this source remains unclear (e.g. Kaplan et al 2008;Roy et al 2010), although The parameter space for radio transients, adapted from Cordes et al (2004). A quantity equivalent to absolute luminosity (observed flux density S multiplied by the square of the distance D 2 ) is plotted against the dimensionless product of the emission frequency ν and the transient duration or pulse width W .…”

Reliability of Radio Transients Detected in the Nasu Sky Survey

“…The bursts were emitted at 1 Jy flux density enduring for 10 min and with 77 min periodicity at 0.33 GHz. The origin or emission mechanism is unidentified, although a diversity of models have been proposed, including nulling pulsar (Kulkarni & Phinney 2005), double neutron star binary (Turolla et al 2005), white dwarf (Zhang & Gil 2005), precessing pulsar (Zhu & Xu 2006), and subsolar flare star (Roy et al 2010). Flare stars also constitute a class of long-duration radio transients.…”