Rotating Radio Transients Research Articles

Search for Dispersed Pulses at Declinations from +56° to +87°

The survey of northern hemisphere were made at a frequency of 111 MHz. The total accumulation time at each point of the sky was at least one hour. 75 sources of pulse emission were detected. More then 80% of these sources are known pulsars observed in the side lobes of the antenna. From one to several hundreds pulses were detected in twelve known pulsars. For four pulsars (J0157+6212, J1910+5655, J2337+6151, J2354+6155) the narrowness of the strongest pulses and the ratio of peak flux densities in the strongest pulse and in the average profile indicate that they can be pulsars with giant pulses. One new rotating radio transient (RRAT) J0812+8626 with a dispersion measure DM=40.25 pc/cm3 was detected.

A GPU based single-pulse search pipeline (GSP) with database and its application to the Commensal Radio Astronomy FAST Survey (CRAFTS)

We developed a GPU based single-pulse search pipeline (GSP) with a candidate-archiving database. Largely based upon the infrastructure of the open source PulsaR Exploration and Search Toolkit (PRESTO), GSP implements GPU acceleration of the de-dispersion and integrates a candidate-archiving database. We applied GSP to the data streams from the Commensal Radio Astronomy FAST Survey (CRAFTS), which resulted in quasi-real-time processing. The integrated candidate database facilitates synergistic usage of multiple machine-learning tools and thus improves efficient identification of radio pulsars such as rotating radio transients (RRATs) and fast radio bursts (FRBs). We first tested GSP on pilot CRAFTS observations with the FAST Ultra-Wide Band (UWB) receiver. GSP detected all pulsars known from the the Parkes multibeam pulsar survey in the corresponding sky area covered by the FAST-UWB. GSP also discovered 13 new pulsars. We measured the computational efficiency of GSP to be ∼120 times faster than the original PRESTO and ∼60 times faster than an MPI-parallelized version of PRESTO.

A single pulse study of PSR J1752+2359

The single pulse observation of PSR J1752+2359 at 1250 MHz made using the Five-hundred-meter Aperture Spherical radio Telescope (FAST) is presented. We show that the pulsar exhibits two distinct emission states: a normal state with continuous normal pulse emission and a rotating radio transient (RRAT)-like state with sporadic emission. This makes PSR J1752+2359 the third pulsar that exhibits switching between RRAT-like and pulsar-like states. Our data show that, during the observation, 20 per cent of the time for this pulsar was in the normal state and 80 per cent in the RRAT-like state. A quasi-periodic switching, with a periodicity of around 568 spin periods, between the two states was observed. The pulse energies for the two states both follow log-normal distributions. We demonstrate that the polarization profiles and the linear polarization position angle (PA) swings differ significantly between the two states. There is a phase offset of about 0°.35 between the pulse profile peaks of the two states. We argue that the emission geometry in the magnetosphere may be different for the two states.

Search for fast radio transients using Arecibo drift-scan observations at 1.4 GHz

ABSTRACT We conducted a drift-scan observation campaign using the 305-m Arecibo telescope in 2020 January and March when the observatory was temporarily closed during the intense earthquakes and the initial outbreak of the COVID-19 pandemic, respectively. The primary objective of the survey was to search for fast radio transients, including fast radio bursts (FRBs) and rotating radio transients (RRATs). We used the seven-beam ALFA receiver to observe different sections of the sky within the declination region ∼(10°–20°) on 23 nights and collected 160 h of data in total. We searched our data for single-pulse transients, of covering up to a maximum dispersion measure of 11 000 pc cm−3 at which the dispersion delay across the entire bandwidth is equal to the 13-s transit length of our observations. The analysis produced more than 18 million candidates. Machine learning techniques sorted the radio frequency interference and possibly astrophysical candidates, allowing us to visually inspect and confirm the candidate transients. We found no evidence for new astrophysical transients in our data. We also searched for emission from repeated transient signals, but found no evidence for such sources. We detected single pulses from two known pulsars in our observations and their measured flux densities are consistent with the expected values. Based on our observations and sensitivity, we estimated the upper limit for the FRB rate to be <2.8 × 105 sky−1 d−1 above a fluence of 0.16 Jy ms at 1.4 GHz, which is consistent with the rates from other telescopes and surveys.

Investigation of the properties of four rotating radio transients at 111 MHz

ABSTRACT We present an analysis of the individual pulses of four rotating radio transients (RRATs), previously discovered in a monitoring survey running for 5.5 yr at the frequency of 111 MHz. At a time interval equivalent to 5 d of continuous observations for each RRAT, 90, 389, 206 and 157 pulses were detected in J0640+07, J1005+30, J1132+25 and J1336+33, respectively. The investigated RRATs have different distributions of their pulse amplitudes. For J0640+07 and J1132+25, the distribution is described by a single exponent over the entire range of flux densities. For J1005+30 and J1336+33, it is a lognormal function with a power-law tail. For J0640+07 and J1005+30, we have detected pulses with a signal-to-noise ratio (S/N) of a few hundred. For J1132+25 and J1336+33, the S/N of the strongest pulses reaches several tens. These RRATs show a strong change in their emission. When the strengths of their pulse amplitudes are significantly changed, we see long intervals of absence of emission or its strong attenuation. The analysis carried out in this work shows that it is possible that all the studied RRATs are, apparently, pulsars with giant pulses.

Modelling spin evolution of magnetars

ABSTRACT The origin and fate of magnetars [young, extremely magnetized neutron stars (NSs)] remains unsolved. Probing their evolution is therefore crucial for investigating possible links to other species of isolated NSs, such as the X-ray dim NSs (XDINSs) and rotating radio transients (RRATs). Here, we investigate the spin evolution of magnetars. Two avenues of evolution are considered: one with exponentially decaying B-fields, the other with sub- and superexponential decay. Using Monte Carlo methods, we synthesize magnetar populations using different input distributions and physical parameters, such as for the initial spin period, its time derivative, and the B-field decay time-scale. Additionally, we introduce a fade-away procedure that can account for the fading of old magnetars, and we briefly discuss the effect of alignment of the B-field and spin axes. Imposing the Galactic core-collapse supernova rate of ∼20 kyr−1 as a strict upper limit on the magnetar birthrate and comparing the synthetic populations to the observed one using both manual and automatic optimization algorithms for our input parameter study, we find that the B-field must decay exponentially or superexponentially with a characteristic decay time-scale of 0.5−10 kyr (with a best value of ∼4 kyr). In addition, the initial spin period must be less than 2 s. If these constraints are kept, we conclude that there are multiple choices of input physics that can reproduce the observed magnetar population reasonably well. We also conclude that magnetars may well be evolutionary linked to the population of XDINSs, whereas they are in general unlikely to evolve into RRATs.

The FAST Galactic Plane Pulsar Snapshot survey: I. Project design and pulsar discoveries ⋆ ⋆News and views on this paper

Discovery of pulsars is one of the main goals for large radio telescopes. The Five-hundred-meter Aperture Spherical radio Telescope (FAST), that incorporates an L-band 19-beam receiver with a system temperature of about 20 K, is the most sensitive radio telescope utilized for discovering pulsars. We designed the snapshot observation mode for a FAST key science project, the Galactic Plane Pulsar Snapshot (GPPS) survey, in which every four nearby pointings can observe a cover of a sky patch of 0.1575 square degrees through beam-switching of the L-band 19-beam receiver. The integration time for each pointing is 300 seconds so that the GPPS observations for a cover can be made in 21 minutes. The goal of the GPPS survey is to discover pulsars within the Galactic latitude of ± 10° from the Galactic plane, and the highest priority is given to the inner Galaxy within ± 5°. Up to now, the GPPS survey has discovered 201 pulsars, including currently the faintest pulsars which cannot be detected by other telescopes, pulsars with extremely high dispersion measures (DMs) which challenge the currently widely used models for the Galactic electron density distribution, pulsars coincident with supernova remnants, 40 millisecond pulsars, 16 binary pulsars, some nulling and mode-changing pulsars and rotating radio transients (RRATs). The follow-up observations for confirmation of new pulsars have polarization-signals recorded for polarization profiles of the pulsars. Re-detection of previously known pulsars in the survey data also leads to significant improvements in parameters for 64 pulsars. The GPPS survey discoveries are published and will be updated at http://zmtt.bao.ac.cn/GPPS/.

Pulse energy distribution for RRAT J0139+33 according to observations at the 111 MHz frequency

Using five-year-monitoring observations, we carried out a blind search for pulses for rotating radio transient (RRAT) J0139+33 and PSR B0320+39. At the interval ±1.5m of the time corresponding to the source passing through the meridian, we detected 39377 individual pulses for the pulsar B0320+39 and 1013 pulses for RRAT J0139+33. The share of registered pulses from the total number of observed periods for the pulsar B0320+39 is 74%, and for the transient J0139+33 it is 0.42%. The signal-to-noise ratio (S/N) for the strongest registered pulses is, approximately, the following: S/N = 262 (for B0320+39) and S/N = 154 (for J0139+33). We obtained distributions of the number of detected pulses in S/N units for the pulsar and for the rotating transient. The distributions could be approximated with lognormal and power dependences. For the B0320+39 pulsar, the dependence is lognormal, and it turns into a power dependence at high values of S/N; and for RRAT J0139+33, the distribution of pulses by energy is described by a broken (bimodal) power dependence with an exponent of about 0.4 and 1.8 (S/N ≤ 19 and S/N ≥ 19). We did not detect a regular (pulsar) emission of J0139+33. Analysis of the obtained data suggests that RRAT J0139+33 is a pulsar with giant pulses.

On the long-term evolution of rotating radio transients

ABSTRACT Investigation of the long-term evolution of rotating radio transients (RRATs) is important to understand the evolutionary connections between the isolated neutron star populations in a single picture. The X-ray luminosities of RRATs (except one source) are not known. In the fallback disc model, we have developed a method to estimate the dipole field strengths of RRATs without X-ray information. We have found that RRATs could have dipole field strengths, B0, at the poles ranging from ∼7 × 109 to ∼6 × 1011 G which fill the gap between the B0 ranges of central compact objects (CCOs) and dim isolated neutron stars (XDINs) estimated in the same model. In our model, most of RRATs are evolving at ages (∼2–6) × 105 yr, much smaller than their characteristic ages, such that, cooling luminosities of a large fraction of relatively nearby RRATs could be detected by the eROSITA all-sky survey. Many RRATs are located above the upper border of the pulsar death valley with the fields inferred from the dipole-torque formula, while they do not show strong, continuous radio pulses. The B0 values estimated in our model, place all RRATs either into the death valley or below the death line. We have tentatively proposed that RRATs could be the sources below their individual death points, and their short radio bursts could be ignited by the disc-field interaction occasionally enhancing the flux of open field lines through the magnetic poles. We have also discussed the evolutionary links between CCOs, RRATs, and XDINs.

Classification of Young Pulsars and Empirical Evolution of Regular Braking Index

Abstract—The distribution of young pulsars in the log(dP/dt)–log(tc) diagram that have a characteristic age tc ~10–16 is analyzed. Six clusters-stripes are revealed for the first time, along which the long-term evolution tracks of individual pulsars pass. The mean track in a stripe corresponds to the long-term regular evolution for a typical pulsar of this stripe. The clusters-stripes population composition is analyzed by object types. Rotating radio transients (RRATs) are present in all clusters-stripes at tc > 105 yr. It turns out that three stripes contain objects of only one of the three numerous (≥10) known types: magnetars, pulsars with a high magnetic field, and Vela-like pulsars. In three other clusters-stripes, objects of the indicated three types are not found. The following object classification in the composition of six clusters-stripes is proposed: magnetars (M), pulsars with a high magnetic field (HB), pulsars with a sub-high magnetic field (S-HB), Vela-type pulsars (V), sub-Vela pulsars (SV), and low magnetic field pulsars (LB). Four pulsars that are outside the stripes are referred to peculiar. Analytical formulas are presented for calculating evolution parameters in the log(dP/dt)–log(tc) diagram. As a result of the optimal fitting of the mean clusters-stripes track by the appropriate empirical function, long-term regular values of the braking index and the second derivative of the period are estimated for 327 pulsars for the first time. As a consequence of the clusters-stripes presence, the “striped” distribution of the dipole magnetic field at pulsar birth indicates the intervality in the mass distribution of pulsar progenitor stars. The recent supernovae explosion models (Pejcha & Thomson, 2015) also produce an interval mass distribution of progenitors generating neutron stars, which confirm that pulsar clusters-stripes do exist and their origin can be naturally explained.

A model of an ion-proton radio pulsar polar cap

Abstract A number of previous papers have developed an ion-proton theory of the pulsar polar cap. The basic equations summarizing this are given here with the results of sets of model step-to-step calculations of pulse-precursor profiles. The nature of step-to-step profile variations is described by calculated phase-resolved modulation indices. The conditions under which nulls are present in step sequences are analysed. The change of mean null length with neutron-star surface temperature shows a pathway ending in emission similar to the Rotating Radio Transients. The model accommodates exceptional pulsars, the millisecond pulsars (in principle), and the 8.5 s period PSR J2144-3933. These are considered separately and their emission mechanism discussed in some detail.

Polarization studies of rotating radio transients

ABSTRACT We study the polarization properties of 22 known rotating radio transients (RRATs) with the 64-m Parkes radio telescope and present the Faraday rotation measures (RMs) for the 17 with linearly polarized flux exceeding the off-pulse noise by 3σ. Each RM was estimated using a brute-force search over trial RMs that spanned the maximum measurable range $\pm 1.18 \times 10^5 \, \mathrm{rad \, m^2}$ (in steps of 1 $\mathrm{rad \, m^2}$), followed by an iterative refinement algorithm. The measured RRAT RMs are in the range |RM| 1–950 rad m−2 with an average linear polarization fraction of 40 per cent. Individual single pulses are observed to be up to 100 per cent linearly polarized. The RMs of the RRATs and the corresponding inferred average magnetic fields (parallel to the line of sight and weighted by the free electron density) are observed to be consistent with the Galactic plane pulsar population. Faraday rotation analyses are typically performed on accumulated pulsar data, for which hundreds to thousands of pulses have been integrated, rather than on individual pulses. Therefore, we verified the iterative refinement algorithm by performing Monte Carlo simulations of artificial single pulses over a wide range of S/N and RM. At and above an S/N of 17 in linearly polarized flux, the iterative refinement recovers the simulated RM value 100 per cent of the time with a typical mean uncertainty of 5 rad m−2. The method described and validated here has also been successfully used to determine reliable RMs of several fast radio bursts (FRBs) discovered at Parkes.

Study of three rotating radio transients with FAST

Rotating radio transients (RRATs) are peculiar astronomical objects whose emission mechanism remains under investigation. In this paper, we present observations of three RRATs, J1538+2345, J1854+0306 and J1913+1330, carried out with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Specifically, we analyze the mean pulse profiles and temporal flux density evolutions of the RRATs. Owing to the high sensitivity of FAST, the derived burst rates of the three RRATs are higher than those in previous reports. RRAT J1854+0306 exhibited a time-dynamic mean pulse profile, whereas RRAT J1913+1330 showed distinct radiation and nulling segments on its pulse intensity trains. The mean pulse profile variation with frequency is also studied for RRAT J1538+2345 and RRAT J1913+1330, and the profiles at different frequencies could be well fitted with a cone-core model and a conal-beam model, respectively.

The FRATS project: real-time searches for fast radio bursts and other fast transients with LOFAR at 135 MHz

Context. In the previous decade, two new classes of fast radio transients were detected: the Galactic, rotating radio transients (RRATs) and the extragalactic fast radio bursts (FRBs). If the detectable emission of these objects extends to lower radio frequencies, the LOw Frequency ARray (LOFAR) is ideally suited to seek and localize these transients at frequencies of 10–250 MHz. This is due to LOFAR’s sensitivity, diverse beamform capabilities, and transient buffers for the individual elements that allow post-event imaging of events, potentially at arcsecond resolution. Aims. Our aim is to identify and localize pulses at frequencies below 250 MHz and, in the case of nondetections, derive upper limits on the sky and volume rates of FRBs. Methods. A real-time search program for fast radio transients is installed on the LOFAR systems which runs commensally with other observations, and uses the wide incoherent LOFAR beam (11.25 deg2 at 150 MHz). Buffered data from hundreds of dipoles are used to reconstruct the direction and polarization information of the event, and to distinguish between celestial, terrestrial, and instrumental origins. Results. Observations were taken covering either the frequency range 119–151 MHz or in four frequency bands, each of 2 MHz in width, centered at 124, 149, 156, and 185 MHz. A first pilot survey covered a range of dispersion measures (DM) below 120 pc cm−3, focusing on Galactic sources, and resulted in an upper limit on the transient rate at LOFAR frequencies of less than 1500 events per sky per day above a fluency of 1.6 kJy ms for an 8-ms pulse. A second pilot survey covered a range of DMs below 500 pc cm−3, focusing on extragalactic sources to about 1 Gpc, and resulted in an upper limit of 1400 events per sky per day above a fluency of 6.0 kJy ms for an 8-ms pulse. Using a model for the distance-DM relationship, this equates to an upper limit of 134 events per Gpc3 per day.

PALFA Single-pulse Pipeline: New Pulsars, Rotating Radio Transients, and a Candidate Fast Radio Burst

Abstract We present a new single-pulse pipeline for the PALFA survey to efficiently identify single radio pulses from pulsars, rotating radio transients (RRATs), and fast radio bursts (FRBs). We conducted a sensitivity analysis of this new pipeline in which many single pulses were injected into PALFA data and run through the pipeline. We find that for single pulse widths <5 ms, the sensitivity of our new pipeline is at most a factor of ∼2 less sensitive than theoretically predicted. For pulse widths >10 ms, as the DM decreases, the degradation in sensitivity gets worse and can increase up to a factor of ∼4.5. Using this pipeline, we have discovered seven pulsars and two RRATs, and identified three candidate RRATs and one candidate FRB. The confirmed pulsars and RRATs have DMs ranging from 133 to 386 pc cm−3 and flux densities ranging from 20 to 160 mJy. The pulsar periods range from 0.4 to 2.1 s. We report on candidate FRB 141113, which is likely astrophysical and extragalactic, having DM ≃ 400 pc cm−3, which is over the Galactic maximum along this line of sight by ∼100–200 pc cm−3. We consider implications for the FRB population and show via simulations that if FRB 141113 is real and extragalactic, the slope α of the distribution of integral source counts as a function of flux density (N(>S) ∝ S −α ) is 1.4 ± 0.5 (95% confidence range). However, this conclusion is dependent on assumptions that require verification.

Radio Properties of Rotating Radio Transients: Single-pulse Spectral and Wait-time Analyses

Abstract Rotating radio transients (RRATs) are a sub-class of pulsars characterized by sporadic emission and thus can generally only be studied by analysis of their single pulses. Here we present a single-pulse analysis using 11 years of timing data at 1400 MHz of three RRATs, PSRs J1819−1458, J1317−5759, and J1913+1330. We perform a spectral analysis on the single pulses of these RRATs for the first time, finding their mean spectral indices to be −1.1 ± 0.1, −0.6 ± 0.1, and −1.2 ± 0.2 respectively, within the known range of pulsar spectral indices. We find no evidence for narrowband features as seen for FRB 121102. However, we find the spread of single-pulse spectral indices for these RRATs (ranging from −7 to +4) to be larger than has been seen in other pulsars, with the exception of the Crab pulsar. We also analyze the time between detected pulses, or wait time, and find that the pulses are not random and cluster around wait times of a few pulse periods as well as ∼25 pulse periods for PSRs J1819−1458 and J1317−5759. Additionally we find that there is no correlation between the wait time and pulse flux density. Finally we find that the distribution of the pulse energy for PSRs J1317−5759 and J1913+1330 are log-normal, while that of PSR J1819−1458 is log-normal with possible evidence of an additional power-law component.

Detection of 25 new rotating radio transients at 111 MHz

Nearly all fast rotating radio transients (RRAT) that are pulsars with rare pulses have previously been detected using decimeter wavelengths. We present here 34 transients detected at meter wavelengths in our daily monitoring at declinations −9° ≤ δ ≤ +42°. Twenty-five transients are new RRATs. We confirm the detection of 7 RRATs based on our early observations. One of the 34 detected transients was determined to be a new pulsar, J1326+3346. At the same time, of the 35 RRATs detected at the decimeter wavelengths in the studied area, only one was detected by us, J1848+1518. The periods of 6 RRATs were found from the arrival time of single pulses. Three quarters of all RRATs were observed more than once, and the total number of RRATs in the area we studied has doubled.

Long-term evolution of RRAT J1819–1458

At present, J1819-1458 is the only rotating radio transient (RRAT) detected in X-rays. We have studied the long-term evolution of this source in the fallback disc model. The model can reproduce the period, period derivative and X-ray luminosity of J1819-1458 simultaneously in the accretion phase at ages $\sim 2 \times 10^5$ yr. We obtained reasonable model curves with a magnetic dipole field strength $B_0 \sim 5 \times 10^{11}$ G on the pole of the neutron star, which is much weaker than the field inferred from the dipole-torque formula. With this $B_0$ and the measured period, we find J1819-1458 below and close to the radio pulsar death line. Our results are not sensitive to initial period, and the source properties can be produced with a large range of disc masses. Our simulations indicate that J1819-1458 is evolving towards the properties of dim isolated neutron stars at later phases of evolution. This implies a close evolutionary link between RRATs and dim isolated neutron stars. For other RRATs with measured period derivatives and unknown X-ray luminosities, we have estimated the lower limits on the $B_0$ values in the fallback disc model. These limits allow a dipole field distribution for RRATs that could fill the $B_0$ gap between the estimated $B_0$ ranges of dim thermal isolated neutron stars and central compact objects in the same model.

Detection of a Glitch in the Pulsar J1709−4429

We report the detection of a glitch event in the pulsar J1709$-$4429 (also known as B1706$-$44) during regular monitoring observations with the Molonglo Observatory Synthesis Telescope (UTMOST). The glitch was found during timing operations, in which we regularly observe over 400 pulsars with up to daily cadence, while commensally searching for Rotating Radio Transients, pulsars, and FRBs. With a fractional size of $\Delta\nu/\nu \approx 52.4 \times10^{-9}$, the glitch reported here is by far the smallest known for this pulsar, attesting to the efficacy of glitch searches with high cadence using UTMOST.

A study of single pulses in the Parkes Multibeam Pulsar Survey

We reprocessed the Parkes Multibeam Pulsar Survey, searching for single pulses out to a DM of 5000 pc cm$^{-3}$ with widths of up to one second. We recorded single pulses from 264 known pulsars and 14 Rotating Radio Transients. We produced amplitude distributions for each pulsar which we fit with log-normal distributions, power-law tails, and a power-law function divided by an exponential function, finding that some pulsars show a deviation from a log-normal distribution in the form of an excess of high-energy pulses. We found that a function consisting of a power-law divided by an exponential fit the distributions of most pulsars better than either log-normal or power-law functions. For pulsars that were detected in a periodicity search, we computed the ratio of their single-pulse signal-to-noise ratios to their signal-to-noise ratios from a Fourier transform and looked for correlations between this ratio and physical parameters of the pulsars. The only correlation found is the expected relationship between this ratio and the spin period. Fitting log-normal distributions to the amplitudes of pulses from RRATs showed similar behaviour for most RRATs. Here, however, there seem to be two distinct distributions of pulses, with the lower-energy distribution being consistent with noise. Pulse-energy distributions for two of the RRATS processed were consistent with those found for normal pulsars, suggesting that pulsars and RRATs have a common emission mechanism, but other factors influence the specific emission properties of each source class.