- ID:
- ivo://CDS.VizieR/J/A+A/635/A75
- Title:
- LOFAR census of non-recycled pulsars sample
- Short Name:
- J/A+A/635/A75
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results from the low-frequency (40-78MHz) extension of the first pulsar census of non-recycled pulsars carried out with the LOw-Frequency ARray (LOFAR). We used the low-band antennas of the LOFAR core stations to observe 87 pulsars out of 158 that had been previously detected using high-band antennas. We present flux densities and flux-calibrated profiles for the 43 pulsars we detected. Of this sample, 17 have not, to our knowledge, previously been detected at such low frequencies. Here we recalculate the spectral indices using the new low-frequency flux density measurements from the LOFAR census and discuss the prospects of studying pulsars at very low frequencies using current and upcoming facilities, such as the New Extension in Nancay Upgrading LOFAR (NenuFAR).
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- ID:
- ivo://CDS.VizieR/J/A+A/635/A76
- Title:
- LOFAR census of pulsars at low frequencies
- Short Name:
- J/A+A/635/A76
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To date, only 69 pulsars have been identified with a detected pulsed radio emission below 100MHz. A LOFAR-core LBA census and a dedicated campaign with the Nancay LOFAR station in stand-alone mode were carried out in the years 2014-2017 in order to extend the known population in this frequency range. In this paper, we aim to extend the sample of known radio pulsars at low frequencies and to produce a catalogue in the frequency range of 25-80 MHz. This will allow future studies to probe the local Galactic pulsar population, in addition to helping explain their emission mechanism, better characterising the low-frequency turnover in their spectra, and obtaining new information about the interstellar medium through the study of dispersion, scattering, and scintillation. We observed 102 pulsars that are known to emit radio pulses below 200MHz and with declination above -30{deg}. We used the the Low Band Antennas (LBA) of the LOw Frequency ARray (LOFAR) international station FR606 at the Nancay Radio Observatory in stand-alone mode, recording data between 25-80MHz. Out of our sample of 102 pulsars, we detected 64. We confirmed the existence of ten pulsars detected below 100 MHz by the LOFAR LBA census for the first time (Bilous et al., 2019, submitted) and we added two more pulsars that had never before been detected in this frequency range. We provided average pulse profiles, DM values, and mean flux densities (or upper limits in the case of non-detections). The comparison with previously published results allows us to identify a hitherto unknown spectral turnover for five pulsars, confirming the expectation that spectral turnovers are a widespread phenomenon.
- ID:
- ivo://CDS.VizieR/J/MNRAS/484/3646
- Title:
- LOFAR PSR low-frequency Faraday rotation measures
- Short Name:
- J/MNRAS/484/3646
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We determined Faraday rotation measures (RMs) towards 137 pulsars in the northern sky, using Low-Frequency Array (LOFAR) observations at 110-190MHz. This low-frequency RM catalogue, the largest to date, improves the precision of existing RM measurements on average by a factor of 20 - due to the low frequency and wide bandwidth of the data, aided by the RM synthesis method. We report RMs towards 25 pulsars for the first time. The RMs were corrected for ionospheric Faraday rotation to increase the accuracy of our catalogue to approximately 0.1rad/m^2^. The ionospheric RM correction is currently the largest contributor to the measurement uncertainty. In addition, we find that the Faraday dispersion functions towards pulsars are extremely Faraday thin - mostly less than 0.001rad/m^2^. We use these new precise RM measurements (in combination with existing RMs, dispersion measures, and distance estimates) to estimate the scale height of the Galactic halo magnetic field: 2.0(3)kpc for Galactic quadrants I and II above and below the Galactic plane (we also evaluate the scale height for these regions individually). Overall, our initial low-frequency catalogue provides valuable information about the 3-D structure of the Galactic magnetic field.
- ID:
- ivo://CDS.VizieR/J/MNRAS/353/1311
- Title:
- Long-term timing observations of 374 pulsars
- Short Name:
- J/MNRAS/353/1311
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present pulsar timing solutions for 374 pulsars. Each ephemeris was obtained by analysing archival data stored at Jodrell Bank Observatory. This data archive contains over 5600yr of pulsar rotational history with individual data-spans of up to 34yr. A new method has been developed to mitigate the effects of timing noise by whitening the pulsar timing residuals.
- ID:
- ivo://CDS.VizieR/J/A+A/626/A104
- Title:
- LOTAAS pulsar discoveries
- Short Name:
- J/A+A/626/A104
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an overview of the LOFAR Tied-Array All-Sky Survey (LOTAAS) for radio pulsars and fast transients. The survey uses the high-band antennas of the LOFAR Superterp, the dense inner part of the LOFAR core, to survey the northern sky ({delta}>0{deg}) at a central observing frequency of 135MHz. A total of 219 tied-array beams (coherent summation of station signals, covering 12 square degrees), as well as three incoherent beams (covering 67 square degrees) are formed in each survey pointing. For each of the 222 beams, total intensity is recorded at 491.52 {mu}s time resolution. Each observation integrates for 1hr and covers 2592 channels from 119 to 151MHz. This instrumental setup allows LOTAAS to reach a detection threshold of 1-5mJy for periodic emission. Thus far, the LOTAAS survey has resulted in the discovery of 73 radio pulsars. Among these are two mildly recycled binary millisecond pulsars (P=13 and 33ms), as well as the slowest-spinning radio pulsar currently known (P=23.5s). The survey has thus far detected 311 known pulsars, with spin periods ranging from 4ms to 5.0s and dispersion measures from 3.0 to 217pc/cm^3^. Known pulsars are detected at flux densities consistent with literature values. We find that the LOTAAS pulsar discoveries have, on average, longer spin periods than the known pulsar population. This may reflect different selection biases between LOTAAS and previous surveys, though it is also possible that slower-spinning pulsars preferentially have steeper radio spectra. LOTAAS is the deepest all-sky pulsar survey using a digital aperture array; we discuss some of the lessons learned that can inform the approach for similar surveys using future radio telescopes such as the Square Kilometre Array.
- ID:
- ivo://CDS.VizieR/J/A+A/549/A23
- Title:
- MAGIC map of 1E 2259+586
- Short Name:
- J/A+A/549/A23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Magnetars are an extreme, highly magnetized class of isolated neutron stars whose large X-ray luminosity is believed to be driven by their high magnetic field. Study for the first time the possible very high energy {gamma}-ray emission above 100GeV from magnetars, observing the sources 4U 0142+61 and 1E 2259+586.
- ID:
- ivo://CDS.VizieR/J/AZh/94/598
- Title:
- Magnetic fields of radio pulsars
- Short Name:
- J/AZh/94/598
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The mechanism of magnetodipole braking of radio pulsars is used to calculate new values of the surface magnetic fields of neutron stars. The angles {beta} between the spin axes and magnetic moments of the neutron stars were estimated for 376 radio pulsars using three different methods. It is shown that small inclinations of magnetic axes dominate. The equatorial magnetic fields for the considered sample of pulsars are calculated using the {beta} values obtained. As a rule, these magnetic fields are a factor of a few higher than the corresponding values in known catalogs.
- ID:
- ivo://CDS.VizieR/J/ApJ/896/124
- Title:
- MAXI GSC X-ray LCs of the ULX Swift J0243.6+6124
- Short Name:
- J/ApJ/896/124
- Date:
- 03 Dec 2021 13:33:27
- Publisher:
- CDS
- Description:
- This paper reports on the X-ray emission evolution of the ultraluminous Galactic X-ray pulsar Swift J0243.6+6124 during the giant outburst from 2017 October to 2018 January as observed by the MAXI GSC all-sky survey. The 2-30keV light curve and the energy spectra confirm the source luminosity LX assuming an isotropic emission reached 2.5x10^39^erg/s, 10 times higher than the Eddington limit for a 1.4M_{sun}_ neutron star. When the source was luminous with L_X_>~0.9x10^38^erg/s, it generally exhibited a negative correlation on a hardness-intensity diagram. However, two hardness ratios, a soft color (=4-10keV/2-4keV) and a hard color (=10-20keV/4-10keV), showed somewhat different behavior across a characteristic luminosity of L_c_~5x10^38^erg/s. The soft color changed more than the hard color when L_X_<L_c_, whereas the opposite was observed above Lc. The spectral change above Lc was represented by a broad enhanced feature at ~6keV on top of the canonical cutoff power-law continuum. The pulse profiles, derived daily, made the transition from a single-peak to a double-peak as the source brightened across Lc. These spectral and pulse-shape properties can be interpreted by a scenario in which the accretion columns on the neutron-star surface, producing the Comptonized X-ray emission, gradually became taller as LX increases. The broad 6keV enhancement could be a result of cyclotron-resonance absorption at ~10keV, corresponding to a surface magnetic field B_s_~1.1x10^12^G. The spin-frequency derivatives calculated with the Fermi GBM data showed a smooth positive correlation with LX up to the outburst peak, and its linear coefficient is comparable to those of typical Be binary pulsars whose B_s_ are (1-8)x10^12^G. These results suggest that the B_s_ of Swift J0243.6+6124 is a few times 10^12^G.
- ID:
- ivo://CDS.VizieR/J/ApJ/804/23
- Title:
- 327MHz observations of 124 pulsars
- Short Name:
- J/ApJ/804/23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the measurements of scatter broadening timescales ({tau}_SC_) for 124 pulsars at 327MHz using the upgraded Ooty Radio Telescope (ORT). These pulsars lie in the dispersion measure range of 37-503pc/cm3 and declination ({delta}) range of -57{deg}<{sigma}<60{deg}. New {tau}_SC_ estimates for 58 pulsars are presented, increasing the sample of all such measurements by about 40% at 327MHz. Using all available {tau}_SC_ measurements in the literature, we investigate the dependence of {tau}_SC_ on dispersion measure. Our measurements, together with previously reported values for {tau}_SC_, affirm that the ionized interstellar medium up to 3kpc is consistent with the Kolmogorov spectrum, while it deviates significantly beyond this distance.
- ID:
- ivo://CDS.VizieR/J/ApJ/846/L19
- Title:
- 115-155MHz radio survey of Fermi sources
- Short Name:
- J/ApJ/846/L19
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using LOFAR, we have performed a very-low-frequency (115-155MHz) radio survey for millisecond pulsars (MSPs). The survey targeted 52 unidentified Fermi {gamma}-ray sources. Employing a combination of coherent and incoherent dedispersion, we have mitigated the dispersive effects of the interstellar medium while maintaining sensitivity to fast-spinning pulsars. Toward 3FGLJ1553.1+5437 we have found PSRJ1552+5437, the first MSP to be discovered (through its pulsations) at a radio frequency <200MHz. PSR J1552+5437 is an isolated MSP with a 2.43ms spin period and a dispersion measure of 22.9pc/cm^3^. The pulsar has a very steep radio spectral index ({alpha}-2.8+/-0.4). We obtain a phase-connected timing solution combining the 0.74yr of radio observations with {gamma}-ray photon arrival times covering 7.5yr of Fermi observations. We find that the radio and {gamma}-ray pulse profiles of PSR J1552+5437 appear to be nearly aligned. The very steep spectrum of PSR J1552+5437, along with other recent discoveries, hints at a population of radio MSPs that have been missed in surveys using higher observing frequencies. Detecting such steep spectrum sources is important for mapping the population of MSPs down to the shortest spin periods, understanding their emission in comparison to slow pulsars, and quantifying the prospects for future surveys with low-frequency radio telescopes like SKA-Low and its precursors.
