Detection of 25 new rotating radio transients at 111 MHz

et al. 2019

A&A

110

132

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 (δ > 0 • ) at a central observing frequency of 135 MHz. 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 µs time resolution. Each observation integrates for 1 hr and covers 2592 channels from 119 to 151 MHz. This instrumental setup allows LOTAAS to reach a detection threshold of 1 to 5 mJy 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 33 ms), as well as the slowest-spinning radio pulsar currently known (P = 23.5 s). The survey has thus far detected 311 known pulsars, with spin periods ranging from 4 ms to 5.0 s and dispersion measures from 3.0 to 217 pc 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.

Section: Discoveriessupporting

confidence: 57%

Section: Discoveriesmentioning

confidence: 99%

The LOFAR Tied-Array All-Sky Survey (LOTAAS): Survey overview and initial pulsar discoveries

Sanidas

et al. 2019

A&A

110

132

“…Brinkman et al (2018) recently presented a timing model for the source compatible with the one we obtain. PSR J0302+2252 was first reported by Tyul'bashev et al (2016); PSRs J0122+1416, J1635+2332 and J2051+1248 by Tyul'bashev et al (2017); and PSRs J0139+3336, J1404+1159 and J1848+1516 by Tyul'bashev et al (2018). These sources have been blindly detected by LOTAAS around the same time and we present their timing models for the first time.…”

Section: Introductionmentioning

confidence: 71%

The LOFAR Tied-Array All-Sky Survey (LOTAAS): Characterization of 20 pulsar discoveries and their single-pulse behavior

Michilli

Monthly Notices of the Royal Astronomical Society

et al. 2019

We are using the LOw-Frequency ARray (LOFAR) to perform the LOFAR Tied-Array All-Sky (LOTAAS) survey for pulsars and fast transients. Here we present the astrometric and rotational parameters of 20 pulsars discovered as part of LOTAAS. These pulsars have regularly been observed with LOFAR at 149 MHz and the Lovell telescope at 1532 MHz, supplemented by some observations with the Lovell telescope at 334 MHz and the Nançay Radio Telescope at 1484 MHz. Timing models are calculated for the 20 pulsars, some of which are among the slowest-spinning pulsars known. PSR J1236−0159 rotates with a period P ∼ 3.6 s, while 5 additional pulsars show P > 2 s. Also, the spin-down rates $\dot{P}$ are, on average, low, with PSR J0815+4611 showing $\dot{P} \sim 4\times 10^{-18}$. Some of the pulse profiles, generically single-peaked, present complex shapes evolving with frequency. Multi-frequency flux measurements show that these pulsars have generically relatively steep spectra but exceptions are present, with values ranging between ∼−4 and −1. Among the pulsar sample, a large fraction shows large single-pulse variability, with 4 pulsars being undetectable more than $15\%$ of the time and one tentatively classified as a Rotating Radio Transient. Two single-peaked pulsars show drifting sub-pulses.

“…The sample of pulsars includes PSR J1658+3630, the first binary pulsar discovered by the survey. PSRs J0421+3255, J1638+4005, J1643+1338 and J1657+3304 were first reported by Tyul'bashev et al (2016Tyul'bashev et al ( , 2017Tyul'bashev et al ( , 2018 and these pulsars were blindly detected by LOTAAS around the same time. As of September, 2019 there are no published timing models for these pulsars.…”

mentioning

confidence: 85%

The LOFAR Tied-Array all-sky survey: Timing of 21 pulsars including the first binary pulsar discovered with LOFAR

Tan

Monthly Notices of the Royal Astronomical Society

et al. 2020

We report on the multi-frequency timing observations of 21 pulsars discovered in the LOFAR Tied-Array All-Sky Survey (LOTAAS). The timing data were taken at central frequencies of 149 MHz (LOFAR) as well as 334 and 1532 MHz (Lovell Telecope). The sample of pulsars includes 20 isolated pulsars and the first binary pulsar discovered by the survey, PSR J1658+3630. We modelled the timing properties of the pulsars, which showed that they have, on average, larger characteristic ages. We present the pulse profiles of the pulsars across the three observing bands, where PSR J1643+1338 showed profile evolution that appears not to be well-described by the radius-to-frequencymapping model. Furthermore, we modelled the spectra of the pulsars across the same observing bands, using a simple power law, and found an average spectral index of −1.9 ± 0.5. Amongst the pulsars studied here, PSR J1657+3304 showed large flux density variations of a factor of 10 over 300 days, as well as mode changing and nulling on timescales of a few minutes. We modelled the rotational and orbital properties of PSR J1658+3630, which has a spin period of 33 ms in a binary orbit of 3.0 days with a companion of minimum mass of 0.87M , likely a Carbon-Oxygen or Oxygen-Neon-Magnesium type white dwarf. PSR J1658+3630 has a dispersion measure of 3.0 pc cm −3 , making it possibly one of the closest binary pulsars known.