Rotating Radio Transients Research Articles

Follow-up Observations of Apparently One-off Sources from the Parkes Telescope

A small fraction of fast radio bursts (FRBs) have been observed with multiple bursts, whereas most Galactic sources emitting radio pulses are known to repeat. Here we present the results of follow-up observations of two FRBs and four rotating radio transients (RRATs). Among these, only one RRAT has been observed with repeating pulses, with an estimated period of around 1.297047 s. For comparison, we reanalysed the Parkes archival follow-up observations in CSIRO’s data archive for all apparently one-off sources discovered by the Parkes telescopes, including 13 RRATs and 29 FRBs. In total, 3 RRATs are suggested to be repeaters, but no repeating signals were detected from the other sources. Reporting details of the nondetection observations for the apparently one-off sources would help investigate their origins, and catastrophic scenarios are worth proposing for both extragalactic and Galactic sources.

Long-term evolutionary links between the isolated neutron star populations

ABSTRACT We have investigated the evolutionary connections of the isolated neutron star (NS) populations including radio pulsars (RPs), anomalous X-ray pulsars (AXPs), soft gamma repeaters (SGRs), dim isolated NSs (XDINs), ‘high-magnetic field’ RPs (‘HBRPs’), central compact objects (CCOs), rotating radio transients (RRATs), and long-period pulsars (LPPs) in the fallback disc model. The model can reproduce these NS families as a natural outcome of different initial conditions (initial period, disc mass, and dipole moment, μ) with a continuous μ distribution in the $\sim 10^{27} - 5 \times 10^{30}$ G cm$^3$ range. Results of our simulations can be summarized as follows: (1) A fraction of ‘HBRPs’ with relatively high μ evolve into the persistent AXP/SGR properties, and subsequently become LPPs. (2) Persistent AXP/SGRs do not have evolutionary links with CCOs, XDINs, and RRATs. (3) For a wide range of μ, most RRATs evolve passing through RP or ‘HBRP’ properties during their early evolutionary phases. (4) A fraction of RRATs which have the highest estimated birth rate seem to be the progenitors of XDINs. (5) LPPs, whose existence was predicted by the fallback disc model, are the sources evolving in the late stage of evolution before the discs become inactive. These results provide concrete support to the ideas proposing evolutionary connections between the NS families to account for the ‘birth rate problem’, the discrepancy between the cumulative birth rate estimated for these systems and the core-collapse supernova rate.

Search for rotating radio transients in three years of monitoring data

The search for rotating radio transients (RRATs) was carried out at a frequency of 111 MHz, as daily observations carried out on the Large Phased Array (LPA) radio telescope at declinations of −9° < δ < +42°. Overall, 19 new RRATs were discovered for dispersion measures (DMs) from 2.5 to 72.6 pc cm−3. Estimates of the periods were obtained for three RRATs, with two of them (J0408+28; J0440+35) located at distances of 134 and 136 pc from Sun, placing them among the closest of all known RRATs.

RRAT J1913+1330: An Extremely Variable and Puzzling Pulsar

Rotating radio transients (RRATs) are neutron stars that emit sporadic radio bursts. We detected 1955 single pulses from RRAT J1913+1330 using the 19 beam receiver of the Five-hundred-meter Aperture Spherical radio Telescope. These pulses were detected in 19 distinct clusters, with 49.4% of them occurring with a waiting time of one rotation period. The energy distribution of these individual pulses exhibited a wide range, spanning 3 orders of magnitude, reminiscent of repeating fast radio bursts (FRBs). Furthermore, we observed abrupt variations in pulse profile, width, peak flux, and fluence between adjacent sequential pulses. These findings suggest that this RRAT could be interpreted as a pulsar with extreme pulse-to-pulse modulation. The presence of sequential pulse trains during active phases, along with significant pulse variations in profile, fluence, flux, and width, should be intrinsic to a subset of RRATs. Our results indicate that J1913+1330 represents a peculiar source that shares certain properties with populations of nulling pulsars, giant pulses, and FRBs from different perspectives. The dramatic pulse-to-pulse variation observed in J1913+1330 could be attributed to unstable pair creation above the polar cap region and the variation of the site where streaming pairs emit coherently. Exploring a larger sample of RRATs exhibiting similar properties to J1913+1330 has the potential to significantly advance our understanding of pulsars, RRATs, and FRBs.

Constraining the Selection-corrected Luminosity Function and Total Pulse Count for Radio Transients

Studying transient phenomena, such as individual pulses from pulsars, has garnered considerable attention in the era of astronomical big data. Of specific interest to this study are rotating radio transients (RRATs), nulling, and intermittent pulsars. This study introduces a new algorithm named LuNfit, tailored to correct the selection biases originating from the telescope and detection pipelines. Ultimately LuNfit estimates the intrinsic luminosity distribution and nulling fraction of the single pulses emitted by pulsars. LuNfit relies on Bayesian nested sampling so that the parameter space can be fully explored. Bayesian nested sampling also provides the additional benefit of simplifying model comparisons through the Bayes ratio. The robustness of LuNfit is shown through simulations and applying LuNfit onto pulsars with known nulling fractions. LuNfit is then applied to three RRATs, J0012+5431, J1538+1523, and J2355+1523, extracting their intrinsic luminosity distribution and burst rates. We find that their nulling fractions are 0.4(2), 0.749(5), and 0.995(2), respectively. We further find that a log-normal distribution likely describes the single pulse luminosity distribution of J0012+5431 and J1538+1523, while the Bayes ratio for J2355+1523 slightly favors an exponential distribution. We show the conventional method of correcting selection effects by “scaling up” the missed fraction of radio transients can be unreliable when the mean luminosity of the source is faint relative to the telescope sensitivity. Finally, we discuss the limitations of the current implementation of LuNfit while also delving into potential enhancements that would enable LuNfit to be applied to sources with complex pulse morphologies.

A Study of 10 Rotating Radio Transients Using Parkes Radio Telescope

Rotating Radio Transients (RRATs) are a relatively new subclass of pulsars that emit detectable radio bursts sporadically. We analyzed 10 RRATs observed using the Parkes telescope, with eight of these observed via the ultra-wide-bandwidth low-frequency (UWL) receiver. We measured the burst rate and produced integrated profiles spanning multiple frequency bands for three RRATs. We also conducted a spectral analysis on both integrated pulses and individual pulses of three RRATs. All of their integrated pulses follow a simple power law, consistent with the known range of pulsar spectral indices. Their average spectral indices of single pulses are −0.9, −1.2, and −1.0 respectively, which are within the known range of pulsar spectral indices. Additionally, we find that the spreads of single-pulse spectral indices for these RRATs (ranging from −3.5 to +0.5) are narrower compared to what has been observed in other RRATs. Notably, the average spectral index and scatter of single pulses are both relatively small. For the remaining five RRATs observed at the UWL receiver, we also provide the upper limits on fluence and flux density. In addition, we obtain the timing solution of PSR J1709-43. Our analysis shows that PSRs J1919+1745, J1709-43, and J1649-4653 are potentially nulling pulsars or weak pulsars with sparse strong pulses.

Simulating radio-off fractions in rotating radio transients

We aim to simulate the proportions of non-detectable emission, measured as radio-off fractions ($f_ off $), in rotating radio transients (RRATs). We also investigate the properties related to the underlying mechanism for such sporadic emission. From observations of intermittent pulsars, radio emission originates from two distinct emission states and it becomes non-detectable when the pulsar switches to an emission state characterized by magnetospheric plasma density of zero. We performed simulations of $f_ off $ based on 10,000 samples, each with 10,000 rotations and using a model that tracks changes in the plasma density in a pulsar magnetosphere with multiple emission states. We assumed that (i) RRATs are radio pulsars, (ii) radio pulse intensity is correlated with the emitting plasma density as stated in the conventional models, and (iii) a pulse emission corresponds to a change in the plasma density under favorable conditions. A best-fit distribution for $f_ off $ is obtained when emission from RRATs is defaulted to radio-off. The resulting wait time distribution can be fitted by two functions of an exponential and a Gaussian, which is consistent with the observations. We demonstrate that the switch rate is low and that the burst rate is dependent on rotation period. In addition, the switch rate is related to the obliquity angle, which implies that the mechanism varies over time. Our results suggest that switching to radio-on is a random process, which implies that the burst rate is different for different RRATs. We show that RRAT emission and pulse nulling may share similar origins, but with different default emission. We discuss how the emission may change from that of RRAT to pulse nulling (or vice versa) as a pulsar evolves.

Polarization and single-pulse micro-structure studies of Rotating Radio Transient J0139+3336 with FAST

ABSTRACT The study of polarization and micro-structure is very important for understanding the radiation mechanism of Rotating Radio Transients (RRATs). Due to the limitations of telescope sensitivity and time resolution, studies of the polarization and micro-structure of RRATs have been rare in the past. In this work, we report on a high-time resolution and full polarization observation of RRAT J0139+3336 with the Five-hundred-meter Aperture Spherical Radio Telescope (FAST). A total of 96 burst pulses were detected in the 3-h observation. The degrees of linear and circular polarization and the shape of the polarization position angle (PPA) of the single pulses vary significantly. The average profile displays a small degree of linear and circular polarization, and the PPA exhibits a remarkably smooth and steep S-shaped curve, which are also characteristics of pulsars. The circular polarization in some single pulses demonstrates a clear sign change. We discuss the geometric structure of the emission beam based on the results from fitting the RVM model to the changes in the PPA. Using an autocorrelation analysis, the quasi-periodic micro-structure in the single pulse emission is detected with a median period of about 0.91 ms. We show that the position of RRAT J0139+3336 on the P–Pμ diagram falls in the normal pulsar (NP) region . The radio emission of RRAT J0139+3336 shows unique properties, such as the sign change in the circular polarization and quasi-periodicity in the micro-structure, which will provide important clues to the emission mechanism of RRATs.

Wide-bandwidth Observations of PSR J0941–39 and PSR J1107–5907

We present a polarization analysis of PSR J0941–39 and PSR J1107–5907, which exhibit transitions between being pulsars and rotating radio transients (RRATs), using the ultrawide-bandwidth low-frequency receiver on Murriyang, the Parkes 64 m radio telescope. The spectral index of each pulsar was measured, revealing distinct variations among different states. By using the rotating vector model, we determined that the geometry of the magnetosphere remains consistent between the RRAT state and the pulsar state for PSR J0941–39, with emissions originating from the same height in the magnetosphere. The occurrence of the RRAT state could be attributed to variations in currents within the pulsar’s magnetosphere. Our results suggest that the emission mechanism of an RRAT may share similarities with that of a typical pulsar.

The FAST Galactic Plane Pulsar Snapshot Survey. II. Discovery of 76 Galactic Rotating Radio Transients and the Enigma of RRATs

We have carried out the Galactic Plane Pulsar Snapshot (GPPS) survey by using the Five-hundred-meter Aperture Spherical radio Telescope (FAST), the most sensitive systematic pulsar survey in the Galactic plane. In addition to more than 500 pulsars already discovered through normal periodical search, we report here the discovery of 76 new transient radio sources with sporadic strong pulses, detected by using the newly developed module for a sensitive single-pulse search. Their small DM values suggest that they all are Galactic rotating radio transients (RRATs). They show different properties in the follow-up observations. More radio pulses have been detected from 26 transient radio sources but no periods can be found due to a limited small number of pulses from all FAST observations. The follow-up observations show that 16 transient sources are newly identified as being the prototypes of RRATs with a period already determined from more detected sporadic pulses, and 10 sources are extremely nulling pulsars, and 24 sources are weak pulsars with sparse strong pulses. On the other hand, 48 previously known RRATs have been detected by the FAST, either during verification observations for the GPPS survey or through targeted observations of applied normal FAST projects. Except for one RRAT with four pulses detected in a session of 5-minute observation and four RRATs with only one pulse detected in a session, sensitive FAST observations reveal that 43 RRATs are just generally weak pulsars with sporadic strong pulses or simply very nulling pulsars, so that the previously known RRATs always have an extreme emission state together with a normal hardly detectable weak emission state. This is echoed by the two normal pulsars J1938+2213 and J1946+1449 with occasional brightening pulses. Though strong pulses of RRATs are very outstanding in the energy distribution, their polarization angle variations follow the polarization angle curve of the averaged normal pulse profile, suggesting that the predominant sparse pulses of RRATs are emitted in the same region with the same geometry as normal weak pulsars.

The second set of pulsar discoveries by CHIME/FRB/Pulsar: 14 rotating radio transients and 7 pulsars

ABSTRACT The Canadian Hydrogen Mapping Experiment (CHIME) is a radio telescope located in British Columbia, Canada. The large field of view allows CHIME/FRB to be an exceptional pulsar and rotating radio transient (RRAT) finding machine, despite saving only the metadata of incoming Galactic events. We have developed a pipeline to search for pulsar/RRAT candidates using density-based spatial clustering of applications with noise (dbscan), a clustering algorithm. Follow-up observations are then scheduled with the more sensitive CHIME/Pulsar instrument capable of near-daily high-time resolution spectra observations. We have developed the CHIME/Pulsar Single Pulse Pipeline to automate the processing of CHIME/Pulsar search-mode data. We report the discovery of 21 new Galactic sources, with 14 RRATs, 6 isolated long-period pulsars, and 1 binary system. Owing to CHIME/Pulsar’s observations, we have obtained timing solutions for 8 of the 14 RRATs along with all the regular pulsars and the binary system. Notably, we report that the binary system is in a long orbit of 412 d with a minimum companion mass of 0.1303 solar masses and no evidence of an optical companion within 10″ of the pulsar position. This highlights that working synergistically with CHIME/FRB’s large survey volume CHIME/Pulsar can obtain arc second localizations for low-burst rate RRATs through pulsar timing. We find that the properties of our newly discovered RRATs are consistent with those of the presently known population. They tend to have lower burst rates than those found in previous surveys, which is likely due to survey bias rather than the underlying population.

Detection of Two New RRATs at 111 MHz

At the LPA LPI radio telescope, a search was conducted for pulse signals in a specific area with declinations + 52^circ < delta < + 55^circ . The processing involved ten months of observations recorded in six frequency channels, each with a channel width of 415 kHz and a total bandwidth of 2.5 MHz. The analysis of the data revealed 22 000 events, exhibiting a pronounced dispersion delay of signals over the frequency channels, which are indicative of pulsar pulses. These pulses were found to belong to four known pulsars and two new rotating radio transients (RRAT). Additional pulse search was carried out in 32-channel data with a channel width of 78 kHz. This led to the discovery of 8 pulses for the transient J0249+52 and 7 pulses for the transient J0744+55. No periodic emission of transients was detected. The analysis of the observations indicates a high probability that the identified RRATs are pulsars with nullings, where the fraction of nullings is greater than 99.9%.

Detection of Two New RRATs at 111 MHz

At the LPA LPI radio telescope, a search was conducted for pulse signals in a specific area with declinations +52°δ+55°. The processing involved ten months of observations recorded in six frequency channels, each with a channel width of 415 kHz and a total bandwidth of 2.5 MHz. The analysis of the data revealed 22 000 events, exhibiting a pronounced dispersion delay of signals over the frequency channels, which are indicative of pulsar pulses. These pulses were found to belong to four known pulsars and two new rotating radio transients (RRAT). Additional pulse search was carried out in 32-channel data with a channel width of 78 kHz. This led to the discovery of 8 pulses for the transient J0249+52 and 7 pulses for the transient J0744+55. No periodic emission of transients was detected. The analysis of the observations indicates a high probability that the identified RRATs are pulsars with nullings, where the fraction of nullings is greater than 99.9%.

Exploring the single-pulse behaviours of PSR J0628+0909 with FAST

ABSTRACTMore than 100 rotating radio transients (RRATs) have been discovered since 2006. However, it is unclear whether RRATs radiate in nulling states. PSR J0628+0909 has been classified as an RRAT. In this paper, we study the single pulses and integrated pulse profile of PSR J0628+0909 to check whether we can detect pulsed radio emission in the nulling states. We also aim to study the polarization of the RRAT and its relationship to the general pulsar population. We used the Five-hundred-meter Aperture Spherical radio Telescope (FAST) to observe PSR J0628+0909 in the frequency range from 1.0 to 1.5 GHz. We searched for strong single pulses and looked for pulsed emission in the RRAT nulling states. Polarization profiles, the single-pulse energy distribution, and waiting-time statistics were measured. The Faraday rotation measure and dispersion measure values are updated with the current observation. The single-pulse polarization behaviours show great diversity, similar to the case of pulsars. Based on the integrated pulse profile and single-pulse energy statistics, we argue that continuous pulsar-like emission exists in addition to the transient-like burst emission for PSR J0628+0909. We find that the pulse waiting time is not correlated with the pulse energy and conclude that the strong transient emission of RRAT is not generated by the energy store–release mechanism.

The Emission Properties of RRAT J0139+3336 at 1.25 GHz

Rotating Radio Transients are a relatively new subclass of pulsar characterized by sporadic bursting emission of single pulses. Here, we present a single-pulse analysis of a rotating radio transient, RRAT J0139+3336, using Five-hundred-meter Aperture Spherical radio Telescope at 1250 MHz. Within 3.32 hr of continuous observation, 152 single pulses were detected in RRAT J0139+3336, with the pulse rate of 45 pulses per hour. We perform a spectral analysis on the single pulses of this pulsar for the first time, finding its mean spectral indices to be −3.2 ± 0.2, which is steeper than most known pulsars. On a single-pulse basis, we produce the first polarimetric profile of this pulsar, which fits well with the rotating vector model. The single pulses are clearly affected by diffractive scintillation with a characteristic scintillation bandwidth of v sc = 28 ± 9 MHz. The pulse energy distribution for RRAT J0139+3336 can be described by a log-normal model.

Radio pulsar sub-populations (II): The mysterious RRATs

Several conjectures have been put forward to explain rotating radio transients (RRATs), the newest subclass of neutron stars, and their connections to other radio pulsars. This work discusses these conjectures in the context of the characteristic properties of the RRAT population. Contrary to expectations, it is seen that: (a) the RRAT population is statistically un-correlated with the nulling pulsars and (b) the RRAT phenomenon is unlikely to be related to old age or death-line proximity. It is perhaps more likely that the special emission property of RRATs is a signature of them being later evolutionary phases of other types of neutron stars which may have resulted in restructuring their magnetic fields.

Pushchino multibeam pulsar search – II. Long-term variability of rotating radio transients

ABSTRACT Pulses from 16 previously known rotating radio transients (RRATs) have been searched for with the 111 MHz daily monitoring program for 4 to 5.5 yr using the Large Phased Array (LPA) at Pushchino. The total number of pulses detected in such a long observation interval is only 90 for RRAT J0640+07, but is as high as 10 751 for RRAT J0302+22. The number and amplitude of pulses vary on time-scales from 6 to 20 months for RRATs J1336+33, J1404+11, J1848+15, J2051+12 and J2105+22, and the pulse number can increase by one or two orders of magnitude in active phases. Long-term trends are found for RRATs J0139+33 and J0302+22, which show a 2–3 times increase in detected pulse number over 1959 d. Some RRATs show annual variations in both pulse number and pulse amplitude. It is hard to explain all these variation time-scales by refractive scintillation on the interstellar medium. The annual and semi-annual variations are probably caused by scintillations on the inhomogeneous interplanetary plasma. Our data show that the number of observational sessions with no pulse detection over the threshold decreases exponentially with the length of pulse silence.

Revisiting the Pushchino RRAT search using a neural network

The search for rotating radio transients (RRAT) at declinations from −9° to +42° was carried out based on the semi-annual monitoring data obtained on the Large Phased Array (LPA) radio telescope at a frequency of 111 MHz. A neural network was used to search for candidates. Four new RRATs were detected; they have dispersion measures of 5–16 pc cm−3. A comparison with an earlier RRAT search that was conducted using the same data shows that the neural network reduced the amount of interference by 80 times. It is now down to 1.3% of the initial amount of interference. The loss of real pulsar pulses does not exceed 6% of their total number.

The Discovery of a Rotating Radio Transient J1918–0449 with Intriguing Emission Properties with the Five-hundred-meter Aperture Spherical Radio Telescope

In this study, we report on a detailed single-pulse analysis of the radio emission from a rotating radio transient (RRAT) J1918−0449, which is discovered with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The sensitive observations were carried out on 2021 April 30 using the FAST with a central frequency of 1250 MHz and a short time resolution of 49.152 μs, which forms a reliable basis to probe single-pulse emission properties in detail. The source was successively observed for around 2 hr. A total of 83 dispersed bursts with significance above 6σ are detected over 1.8 hr. The source’s dispersion measure (DM) and rotational period are determined to be 116.1 ± 0.4 pc cm−3 and 2479.21 ± 0.03 ms, respectively. The share of registered pulses from the total number of observed periods is 3.12%. No underlying emission is detected in the averaged off-pulse profile. For bursts with fluence larger than 10 Jy ms, the pulse energy follows a power-law distribution with an index of −3.1 ± 0.4, suggesting the existence of bright pulse emission. We find that the distribution of time between subsequent pulses is consistent with a stationary Poisson process and find no evidence of clustering over the 1.8 hr observations, giving a mean burst rate of one burst every 66 s. Close inspection of the detected bright pulses reveals that 21 pulses exhibit well-defined quasiperiodicities. The subpulse drifting is present in nonsuccessive rotations with periodicity of 2.51 ± 0.06 periods. Finally, possible physical mechanisms are discussed.

Detection Statistics of Pulse Signals at Declinations from +42° to +52° at the Frequency 111 MHz

A search for pulse signals was carried out in a new sky area included in the monitoring program for the search for pulsars and transients. Processing of several months data recorded in six frequency channels with a total bandwidth of 2.5 MHz showed that, on average, 4 pulses per hour are observed in each of the 24 connected stationary beams. Of these pulses, 18.3% are similar to those of pulsars. They are visible in one or two neighboring beams and have a pronounced dispersion shift, that is, they are recorded first at a high and then at a low frequency, which indicates the possible passage of the signal through the interstellar medium. Almost 68% of such detected pulses belong to six known pulsars with dispersion measures from 9 to 141 $pc/cm^3$, and almost all of the remaining pulses are either noise of an unknown nature or artifacts of the proposed pulse separation technique. An additional study of the selected array of 3650 obvious pulsar pulses revealed 13 pulses belonging to four rotating radio transients (RRATs). Their dispersion measures are in the range of 17-51 $pc/cm^3$. A search for regular (periodic) RRAT emission was carried out using power spectra summed over 121 days. Periodic radiation was not detected, but for two RRATs, upper estimates of the periods were obtained from measurements of the time intervals between pulses. The upper estimates of the integrated flux density of the detected RRATs are in the range 2-4 mJy at the frequency 111 MHz.