New Limits on Radio Emission From X-Ray Dim Isolated Neutron Stars

Abstract

We have carried out a search for radio emission at 820 MHz from six X-ray dim isolated neutron stars (XDINSs) with the Robert C. Byrd Green Bank Radio Telescope. No transient or pulsed emission was found using fast folding, fast Fourier transform, and single-pulse searches. The corresponding flux limits are about 0.01 mJy for pulsed emission, depending on the integration time for the particular source and assuming a duty cycle of 2%, and 20 mJy for single dispersed pulses. These are the most sensitive limits to date on radio emission from XDINSs. There is no evidence for isolated radio pulses, as seen in a class of neutron stars known as rotating radio transients. Our results imply that either the radio luminosities of these objects are lower than those of any known radio pulsars, or they could simply be long-period nearby radio pulsars with high magnetic fields beaming away from the Earth. To test the latter possibility, we would need around 40 similar sources to provide a 1σ probability of at least one of them beaming toward us. We also give a detailed description of our implementation of the Fast Folding Algorithm.

Arecibo Pulsar Survey Using Alfa. Iv. Mock Spectrometer Data Analysis, Survey Sensitivity, and the Discovery of 40 Pulsars

“…One suggested method of improving sensitivity to longperiod pulsars is by using the Fast-folding algorithm (FFA; see e.g., Lorimer & Kramer 2004, page 151;Kondratiev et al 2009, and references therein). The periodograms produced by the FFA, a time-domain algorithm, are generated from computing a significance metric from pulse profiles.…”

“…However it does have the advantage of coherently summing all harmonics of a given period and greater period resolution than the DFT. These two factors should make the FFA slightly more sensitive to long-period pulsars, especially those with narrow profiles, than the Fourier Transform techniques described in Section 3.3.2, which is limited in the number of harmonics that can be summed (typically incoherently; Kondratiev et al 2009). The FFA has only been used sparingly in large-scale pulsar searches (e.g., Kondratiev et al 2009).…”

Observing pulsars and fast transients with LOFAR

“…The potential 100-MHz detection of Geminga, a prominent rotation-powered pulsar visible at optical, X-ray and gamma-ray wavelengths (Malofeev & Malov 1997;Kuzmin & Losovskii 1997;Shitov & Pugachev 1997), could exemplify a population of neutron stars that may be only detectable at radio wavelengths with LOFAR. Also, the non-detection of radio emission from X-ray dim isolated neutron stars (XDINSs) thus far (Kondratiev et al 2009), could be due to the beams of these long-period sources being quite narrow at high frequencies and there may be a better chance to detect them in radio at LOFAR frequencies. In fact, weak radio emission from two XDINSs, RX J1308.6+2127 and RX J2143.0+0654, was reported by Malofeev et al (2005Malofeev et al ( , 2007 at 111 MHz, hence it would be important to confirm this detection with LOFAR.…”

Atmospheres and radiating surfaces of neutron stars

“…Observations have provided stringent upper limits ( 0.1 mJy) to their radio emission [165]. XDINSs have longer periods (> 3 s) than the majority of pulsars, and their magnetic field estimations by Eq.…”