XMM-Newton Detection and Spectrum of the Second Fastest Spinning Pulsar PSR J0952−0607

Abstract

With a spin frequency of 707 Hz, PSR J0952−0607 is the second fastest spinning pulsar known. It was discovered in radio by LOFAR in 2017 at an estimated distance of either 0.97 or 1.74 kpc and has a low-mass companion with a 6.42 hr orbital period. We report discovery of the X-ray counterpart of PSR J0952−0607 using XMM-Newton. The X-ray spectra can be well-fit by a single power law model (Γ ≈ 2.5) or by a thermal plus power law model (kT eff ≈ 40 eV and Γ ≈ 1.4). We do not detect evidence of variability, such as that due to orbital modulation from pulsar wind and companion star interaction. Because of its fast spin rate, PSR J0952−0607 is a crucial source for understanding the r-mode instability, which can be an effective mechanism for producing gravitational waves. Using the high end of our measured surface temperature, we infer a neutron star core temperature of ∼ 10 7 K, which places PSR J0952−0607 within the window for the r-mode to be unstable unless an effect such as superfluid mutual friction damps the fluid oscillation. The measured luminosity limits the dimensionless r-mode amplitude to be less than ∼ 1 × 10 −9 .

Return of the Big Glitcher: NICER timing and glitches of PSR J0537−6910

“…If correct, this suggests an active r-mode and the spin evolution of PSR J0537−6910 is determined by GW emission. Such a situation is examined in Andersson et al (2018), who conclude that an active r-mode is marginally possible, especially with uncertainties and discrepancies in our understanding of r-modes and their impact on observations (see, e.g., Ho et al 2019, and references therein).…”

Recent searches for continuous gravitational waves

“…The notion of a runaway rotational instability was first appreciated for high-frequency f -modes, (Chandrasekhar, 1970;Friedman and Schutz, 1978) (Chandrasekhar-Friedman-Schutz instability), but realistic viscosity effects seem likely to suppress the effect in conventional neutron star production (Lindblom and Detweiler, 1977;Lindblom and Mendell, 1995). Moreover, (Ho et al, 2019) set limits on the r-modes amplitude α for J0952−0607 below 10 −9 based on the absence of heating observed in its X-ray spectrum, despite its high rotation frequency (707 Hz) which places it in the nominal r-modes instability window. Similarly, (Boztepe et al, 2020) set limits on α as low as 3 × 10 −9 , based on observations of two other millisecond pulsars (PSR J1810+1744 and PSR J2241−5236) which also sit in the instability window.…”

Searches for continuous-wave gravitational radiation

“…The notion of a runaway rotational instability was first appreciated for highfrequency f-modes, (Chandrasekhar 1970;Friedman and Schutz 1978) (Chandrasekhar-Friedman-Schutz instability), but realistic viscosity effects seem likely to suppress the effect in conventional neutron star production (Lindblom and Detweiler 1977;Lindblom and Mendell 1995). Moreover, (Ho et al 2019) set limits on the rmodes amplitude a for J0952−0607 below 10 À9 based on the absence of heating observed in its X-ray spectrum, despite its high rotation frequency (707 Hz) which places it in the nominal r-modes instability window. Similarly, (Boztepe et al 2020) set limits on a as low as 3 Â 10 À9 , based on observations of two other millisecond pulsars (PSR J1810þ1744 and PSR J2241−5236) which also sit in the instability window.…”