Deep searches for decametre-wavelength pulsed emission from radio-quiet gamma-ray pulsars

Abstract

We report the results of extensive follow-up observations of the gamma-ray pulsar J1732−3131, which has recently been detected at decametre wavelengths, and the results of deep searches for the counterparts of nine other radio-quiet gamma-ray pulsars at 34 MHz, using the Gauribidanur radio telescope. No periodic signal from J1732−3131 could be detected above a detection threshold of 8σ, even with an effective integration time of more than 40 h. However, the average profile obtained by combining data from several epochs, at a dispersion measure of 15.44 pc cm−3, is found to be consistent with that from the earlier detection of this pulsar at a confidence level of 99.2 per cent. We present this consistency between the two profiles as evidence that J1732−3131 is a faint radio pulsar with an average flux density of 200–400 mJy at 34 MHz. Despite the extremely bright sky background at such low frequencies, the detection sensitivity of our deep searches is generally comparable to that of higher frequency searches for these pulsars, when scaled using reasonable assumptions about the underlying pulsar spectrum. We provide details of our deep searches, and put stringent upper limits on the decametre-wavelength flux densities of several radio-quiet gamma-ray pulsars.