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Register a new userLOFAR discovery of the fastest-spinning millisecond pulsar in the Galactic field
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We report the discovery of PSR J0952$-$0607, a 707-Hz binary millisecond pulsar which is now the fastest-spinning neutron star known in the Galactic field (i.e., outside of a globular cluster). PSR J0952$-$0607 was found using LOFAR at a central observing frequency of 135 MHz, well below the 300 MHz to 3 GHz frequencies typically used in pulsar searches. The discovery is part of an ongoing LOFAR survey targeting unassociated Fermi Large Area Telescope $gamma$-ray sources. PSR J0952$-$0607 is in a 6.42-hr orbit around a very low-mass companion ($M_mathrm{c}gtrsim0.02$ M$_odot$) and we identify a strongly variable optical source, modulated at the orbital period of the pulsar, as the binary companion. The light curve of the companion varies by 1.6 mag from $r^prime=22.2$ at maximum to $r^prime>23.8$, indicating that it is irradiated by the pulsar wind. Swift observations place a 3-$sigma$ upper limit on the $0.3-10$ keV X-ray luminosity of $L_X < 1.1 times 10^{31}$ erg s$^{-1}$ (using the 0.97 kpc distance inferred from the dispersion measure). Though no eclipses of the radio pulsar are observed, the properties of the system classify it as a black widow binary. The radio pulsed spectrum of PSR J0952$-$0607, as determined through flux density measurements at 150 and 350 MHz, is extremely steep with $alphasim-3$ (where $S propto u^{alpha}$). We discuss the growing evidence that the fastest-spinning radio pulsars have exceptionally steep radio spectra, as well as the prospects for finding more sources like PSR J0952$-$0607.
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We do not present the discovery of strong nearly coherent oscillations (NCOs) at 890.44 Hz for the low mass X-ray binary MXB 1659-298. We find that what we are detecting is dead time in the NuSTAR detectors. Instead consider this paper as further evidence for why standard timing methods should not be used with NuSTAR data.
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 (Gamma = 2.5) or by a thermal plus power law model (kTeff = 40 eV and Gamma = 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 ~1x10^-9.
We have discovered an extended X-ray feature which is apparently associated with millisecond pulsar (MSP) PSR J1911-1114 from a XMM-Newton observation, which extends for ~1 and the radio timing position of PSR J1911-1114 is in the mid point of the feature. The orientation of the feature is similar to the proper motion direction of PSR J1911-1114. Its X-ray spectrum can be well-modeled by an absorbed power-law with a photon index of $Gamma=1.8^{+0.3}_{-0.2}$. If this feature is confirmed to be a pulsar wind nebula (PWN), this will be the third case that an X-ray PWN found to be powered by a MSP.
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Anne M. Archibald
, Vladislav I. Kondratiev
, Jason W. T. Hessels andn Daniel R. Stinebring
2014
High-precision timing of millisecond pulsars (MSPs) over years to decades is a promising technique for direct detection of gravitational waves at nanohertz frequencies. Time-variable, multi-path scattering in the interstellar medium is a significant source of noise for this detector, particularly as timing precision approaches 10 ns or better for MSPs in the pulsar timing array. For many MSPs the scattering delay above 1 GHz is at the limit of detectability; therefore, we study it at lower frequencies. Using the LOFAR (LOw-Frequency ARray) radio telescope we have analyzed short (5-20 min) observations of three MSPs in order to estimate the scattering delay at 110-190 MHz, where the number of scintles is large and, hence, the statistical uncertainty in the scattering delay is small. We used cyclic spectroscopy, still relatively novel in radio astronomy, on baseband-sampled data to achieve unprecedented frequency resolution while retaining adequate pulse phase resolution. We detected scintillation structure in the spectra of the MSPs PSR B1257+12, PSR J1810+1744, and PSR J2317+1439 with diffractive bandwidths of $6pm 3$, $2.0pm 0.3$, and $sim 7$ kHz, respectively, where the estimate for PSR J2317+1439 is reliable to about a factor of 2. For the brightest of the three pulsars, PSR J1810+1744, we found that the diffractive bandwidth has a power-law behavior $Delta u_d propto u^{alpha}$, where $ u$ is the observing frequency and $alpha = 4.5pm 0.5$, consistent with a Kolmogorov inhomogeneity spectrum. We conclude that this technique holds promise for monitoring the scattering delay of MSPs with LOFAR and other high-sensitivity, low-frequency arrays like SKA-Low.
We present the discovery of PSR J0250+5854, a radio pulsar with a spin period of 23.5 s. This is the slowest-spinning radio pulsar known. PSR J0250+5854 was discovered by the LOFAR Tied-Array All-Sky Survey (LOTAAS), an all-Northern-sky survey for pulsars and fast transients at a central observing frequency of 135 MHz. We subsequently detected pulsations from the pulsar in the interferometric images of the LOFAR Two-metre Sky Survey, allowing for sub-arcsecond localization. This, along with a pre-discovery detection 2 years prior, allowed us to measure the spin-period derivative to be $dot{P}=2.7 times 10^{-14}$ s s$^{-1}$. The observed spin period derivative of PSR J0250+5854 indicates a surface magnetic field strength, characteristic age and spin-down luminosity of $2.6 times 10^{13}$G, $13.7$ Myr and $8.2 times 10^{28}$ erg s$^{-1}$ respectively, for a dipolar magnetic field configuration. This also places the pulsar beyond the conventional pulsar death line, where radio emission is expected to cease. The spin period of PSR J0250+5854 is similar to those of the high-energy-emitting magnetars and X-ray dim isolated neutron stars (XDINSs). However, the pulsar was not detected by the Swift/XRT in the energy band of 0.3-10 keV, placing a bolometric luminosity limit of $1.5 times 10^{32}$ erg s$^{-1}$ for an assumed $N_{rm H}=1.35times10^{21}$ cm$^{-2}$ and a temperature of 85 eV (typical of XDINSs). We discuss the implications of the discovery for models of the pulsar death line as well as the prospect of finding more similarly long-period pulsars, including the advantages provided by LOTAAS for this.
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