The fifth main-sequence magnetic B-type star showing coherent radio emission: Is this really a rare phenomenon?

Abstract

We report the discovery of intense, highly directional radio emission from the Bp star HD 35298, which we interpret as the consequence of Electron Cyclotron Maser Emission (ECME). The star was observed with the Giant Metrewave Radio Telescope near the rotational phases of both magnetic nulls in band 4 (550 − 750 MHz) and one of the nulls in band 5 (1060 − 1460 MHz). In band 4, we observed flux density enhancement in both circular polarizations near both magnetic nulls. The sequences of arrival of the left and right circularly polarized pulses are opposite near the two nulls. In band 5, we did not have circular polarization information and hence measured only the total intensity lightcurve, which also shows enhancement around the magnetic null. The observed sequence of the circular polarization signs in band 4, compared with the longitudinal magnetic field curve, is able to locate the hemisphere from which ECME arises. This observational evidence supports the scenario of ECME in the ordinary mode, arising in a magnetosphere shaped like an oblique dipole. HD 35298 is the most slowly rotating and most distant main sequence magnetic star from which ECME has been observed.

Ultra-Wideband, Multi-epoch Radio Study of the First Discovered `Main sequence Radio Pulse emitter' CU Vir

“…From Figure 12, one can readily see that there are multiple candidates for counterparts of higher-frequency ECME pulses at 0.7 GHz. We assume that the circular polarization of ECME pulses does not change with frequency (this need not be true, Das et al 2019a). Let us consider the RCP pulse observed between 0.2-0.4 rotation cycle at 1-3 GHz.…”

“…However, as the corresponding acronym 'MSP' is already in use for millisecond pulsars, we propose to call this class of objects 'Main-sequence Radio Pulse emitter' (MRP). Currently seven MRPs are known: CU Vir (Trigilio et al 2000), HD 133880 (Chandra et al 2015;Das et al 2018), HD 142990 (Lenc et al 2018;Das et al 2019a), HD 142301 (Leto et al 2019), HD 35298 (Das et al 2019b), ρ Oph A (Leto et al 2020a) and ρ Oph C (Leto et al 2020b).…”

Magnetic Fields of Chemically Peculiar and Related Stars. VII. Main Results of 2020 and Near-Future Prospects

“…In the paper by Das et al (2019), coherent radio emission from the magnetic star HD 35298 was found. This is the fifth hot Bp star with the detected radio emission.…”

A scaling relationship for non-thermal radio emission from ordered magnetospheres: from the top of the Main Sequence to planets

“…It was recently discovered by Das et al (2019b) that HD 35298 is a source of low frequency (ν 1.4 GHz) high strength (flux level approaching up to ≈ 10 mJy) coherent auroral radio emission. Such maser emission is constrained within a well defined range of phases and is superimposed above the basal emission produced by the incoherent gyro synchrotron mechanism.…”