An international team of scientists, led by MeerTRAP’s Dr Manisha Caleb, have discovered a strange radio emitting neutron star, which rotates extremely slowly, completing one rotation every 76 seconds.
The source was initially found from a single flash, or pulse, by the MeerTRAP instrument whilst piggybacking on imaging observations being led by a different team, ThunderKAT. MeerTRAP and ThunderKAT then worked closely together to puzzle out its origin.
You can now read about this object in The Conversation.
Image credit: Danielle Futselaar
MeerTRAP is funded by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No 694745). The MeerKAT telescope is operated by the South African Radio Astronomy Observatory, which is a facility of the National Research Foundation, an agency of the Department of Science and Innovation (DSI). ThunderKAT is co-led by the Universities of Cape Town and Oxford. MeerTRAP collaborates closely with the Max-Planck Institut für Radioastronomie (MPIfR) and makes use of the beamforming and processing infrastructure funded and installed at MeerKAT by the MPIfR and the Max Planck Gesellschaft.
MeerTRAP is a project to continuously use the MeerKAT radio telescope to search the radio sky for pulsars and fast radio transients and to rapidly and accurately locate them. Utilising the excellent sensitivity and sky coverage of MeerTRAP the team will discover many rare and scientifically important pulsar types: relativistic binaries, intermittent emitters, and transitioning systems. Current radio telescopes have only explored the tip of the transients "iceberg" and MeerTRAP will transform our knowledge of these manifestations of extreme physics. It will detect hundreds of new bursts, which will all be well localised, allowing us to identify hosts and distances, greatly enhancing their use as cosmological probes. Localisation also enables measurement of their true fluxes, polarisation, and spectral indices; all of which are crucial to identify their origin. To achieve this we are designing, implementing, and exploiting state-of-the-art hardware and software. We will also use the MeerLICHT optical telescope, which will track MeerKAT, to give us a crucial glimpse of the optical sky immediately before and after any radio transient to further constrain their origin and the associated physics.
The MeerTRAP pipeline will detect fast radio transients, such as fast radio bursts, RRATs, and pulsars, in real-time.
Once a transient has been detected it can be rapidly localised using imaging. This enables rapid follow-up with MeerLICHT and other telescopes.
MeerTRAP is partnered with the MeerLICHT optical telescope, a fully robotic telescope that co-points with MeerKAT. This is essential for identifying optical counterparts of fast radio transients, particularly fast radio bursts.
Kaustubh Rajwade and co-authors are excited to share the first three fast radio bursts discovered using MeerTRAP. This paper was recently accepted by the Monthly Notices to the Royal Astronomical Society, and is now available Open Access on the ArXiv.
We report on the discovery and localization of fast radio bursts (FRBs) from the MeerTRAP project, a commensal fast radio transient-detection programme at MeerKAT in South Africa. Our hybrid approach combines a coherent search with an average field-of-view of 0.4 square degrees with an incoherent search utilizing a field-of-view of ~1.27 square degrees (both at 1284 MHz). Here, we present results on the first three FRBs: FRB 20200413A (DM=1990.05 pc cm-3), FRB 20200915A (DM=740.65 pc cm-3), and FRB 20201123A (DM=433.55 pc cm-3). FRB 20200413A was discovered only in the incoherent beam. FRB 20200915A (also discovered only in the incoherent beam) shows speckled emission in the dynamic spectrum which cannot be explained by interstellar scintillation in our Galaxy or plasma lensing, and might be intrinsic to the source. FRB 20201123A shows a faint post-cursor burst about 200 ms after the main burst and warrants further follow-up to confirm whether it is a repeating FRB. FRB 20201123A also exhibits significant temporal broadening consistent with scattering by a turbulent medium. The broadening exceeds that predicted for medium along the sightline through our Galaxy. We associate this scattering with the turbulent medium in the environment of the FRB in the host galaxy. Within the approximately1 degree localization region of FRB 20201123A, we identify one luminous galaxy (r ~ 15.67$; J173438.35-504550.4) that dominates the posterior probability for a host association. The galaxy's measured properties are consistent with other FRB hosts with secure associations.
Dynamic spectra and pulse profiles of all of the FRBs presented in this paper.
Tian Bezuidenhout and the MeerTRAP team present the first paper on Galactic fast transients discovered with MeerTRAP! This work also includes Tiaan's SeeKAT localisation software, full details of which will be presented in future work. You can read the full paper in the Monthly Notices of the Royal Astronomical Society and Open Access on the ArXiv.
MeerTRAP is a real-time untargeted search project using the MeerKAT telescope to find single pulses from fast radio transients and pulsars. It is performed commensally with the MeerKAT large survey projects (LSPs), using data from up to 64 of MeerKAT's 13.96 m dishes to form hundreds of coherent beams on sky, each of which is processed in real time to search for millisecond-duration pulses. We present the first 12 Galactic sources discovered by MeerTRAP, with DMs in the range of 33-381 pc cm-3. One source may be Galactic or extragalactic depending on the Galactic electron density model assumed. Follow-up observations performed with the MeerKAT, Lovell, and Parkes radio telescopes have detected repeat pulses from 7 of the 12 sources. Pulse periods have been determined for four sources. Another four sources could be localized to the arcsecond-level using a novel implementation of the tied-array beam localization method.
Dynamic spectra of pulses/bursts from the 12 Galactic sources discovered using MeerTRAP.
Laura Driessen and ThunderKAT co-authors searched two years of weekly ThunderKAT observations of the low-mass X-ray binay, GX339-4, for other radio sources that change brightness over time. They found 21 new radio variable sources. You can read the full paper in the Monthly Notices of the Royal Astronomical Society and Open Access on the ArXiv.
We present 21 new long-term variable radio sources found commensally in 2 yr of weekly MeerKAT monitoring of the low-mass X-ray binary GX 339-4. The new sources are vary on time-scales of weeks to months and have a variety of light-curve shapes and spectral index properties. Three of the new variable sources are coincident with multiwavelength counterparts; and one of these is coincident with an optical source in deep MeerLICHT images. For most sources, we cannot eliminate refractive scintillation of active galactic nuclei as the cause of the variability. These new variable sources represent 2.2 ± 0.5 per cent of the unresolved sources in the field, which is consistent with the 1-2 per cent variability found in past radio variability surveys. However, we expect to find short-term variable sources in the field and these 21 new long-term variable sources. We present the radio light curves and spectral index variability of the new variable sources, as well as the absolute astrometry and matches to coincident sources at other wavelengths.
A deep MeerKAT radio image of the part of the sky observed weekly for two years. The 21 new variables sources and 3 known variable sources are labelled.
We present the results of two years of radio and X-ray monitoring of the magnetar XTE J1810 - 197 since the radio re-activation in late 2018. Single pulse analysis of radio observations from the Lovell and MkII telescopes at 1564 MHz and the Effelsberg telescope at 6 GHz has resulted in the detection of a total of 91 giant pulses (GPs) between MJDs 58858 and 59117. These GPs appear to be confined to two specific phase ranges (0.473 ≤ ϕ ≤ 0.502 and 0.541 ≤ ϕ ≤ 0.567). We also observe that the first detection of GP emission corresponds to a minimum in the spin-down rate. Simultaneous radio and X-ray observations were performed on MJDs 59009 and 59096. The 0.5-10 keV X-ray spectrum from NICER is well characterized by a two-component blackbody model that can be interpreted as two hot spots on the polar cap of the neutron star. The blackbody temperature decreases with time, consistent with the previous outburst, while the change in the pulsed fraction does not follow the same trend as was seen in the previous outburst. The radio and X-ray flux of XTE J1810 - 197 are correlated during the initial phase of the outburst (MJD 58450 - MJD 58550) and an increase in the radio flux is observed later that may be correlated to the onset of GPs. We argue that the disparity in the evolution of the current outburst compared to the previous one can be attributed to a change in geometry of the neutron star. You can read the full paper in the Monthly Notices of the Royal Astronomical Society and Open Access on the ArXiv.
Lovell Telescope and MkII Telescope total intensity profiles of XTE J1810-197 between 2018 and 2021. This plot shows how the profile has changed over time.
Vincent Morello, Kaustubh Rajwade and Ben Stappers present a new algorithm for masking radio frequency interefence in time-domain data. You can read the full article in the Monthly Notice for the Royal Astronomical Society or Open Access on the ArXiv.
In a search for short-time-scale astrophysical transients in time-domain data, radio-frequency interference (RFI) causes both large quantities of false positive candidates and a significant reduction in sensitivity if not correctly mitigated. Here, we propose an algorithm that infers a time-variable frequency channel mask directly from short-duration (~1 s) data blocks: the method consists of computing a spectral statistic that correlates well with the presence of RFI, and then finding high outliers among the resulting values. For the latter task, we propose an outlier detection algorithm called Inter-Quartile Range Mitigation (IQRM), which is both non-parametric and robust to the presence of a trend in sequential data. The method requires no training and can, in principle, adapt to any telescope and RFI environment; its efficiency is shown on data from both the MeerKAT and Lovell 76-m radio telescopes. IQRM is fast enough to be used in a streaming search and has been integrated into the MeerTRAP real-time transient search pipeline. Open-source PYTHON and C++ implementations are also provided.
Laura Driessen and ThunderKAT co-authors present the first novel detection of a radio star with MeerKAT. EXO 040830-7134.7 is a known X-ray flaring star, and it was found in ThunderKAT observations of the cataclysmic variable VW Hydri. You can read the full article in the Monthly Notices of the Royal Astronomical Society and Open Access on the ArXiv.
Laura and co-authors report the detection of radio emission from the known X-ray flaring star EXO 040830-7134.7 during Karoo Array Telescope (MeerKAT) observations of the nearby cataclysmic variable VW Hydri. We have three epochs of MeerKAT observations, where the star is not detected in the first epoch, is detected in the second epoch, and is marginally detected in the third epoch. We cannot distinguish whether the detection is quiescent emission or a transient radio burst. If we assume that the radio detection is quiescent emission, the source lies somewhat to the right of the Güdel-Benz relation; however, if we assume that the upper limit on the radio non-detection is indicative of the quiescent emission, then the source lies directly on the relation. Both cases are broadly consistent with the relation. We use archival spectral energy distribution data and new Southern African Large Telescope high-resolution spectroscopy to confirm that EXO 040830-7134.7 is a chromospherically active M-dwarf with a temperature of 4000 ± 200 K of spectral type M0V. We use All-Sky Automated Survey (ASAS), All-Sky Automated Survey for Supernovae (ASAS-SN), and Transiting Exoplanet Survey Satellite (TESS) optical photometry to derive an improved rotational period of 5.18 ± 0.04 d. This is the first radio detection of the source, and the first MeerKAT detection of an M-dwarf.
Images of EXO 040830-7134.7 (position marked with a magenta cross) made using MeerKAT observations.
You can read Manisha and Evan's review of fast radio burst astronomy in Universe.
Kaustubh Rajwade and co-authors report on the the long term monitoring campaign of the seemingly youngest magnetar Swift J1818.0-1607 at radio and X-ray wavelengths over a span of one year. We obtained a coherent timing solution for the magnetar over the same time span. The frequency derivative of the magnetar shows systematic variation with the values oscillating about a mean value of -1.37 × 10-11 Hz s-1. The magnitude of the variation in the frequency derivative reduces with time before converging on the mean value. This corresponds to a characteristic age of ~ 860 years, 2-4 times more than previously estimated. We were able to identify four states in the spin-frequency derivative that were quantified by the amount of modulation about the mean value and the transition between these states seem to be correlated with the change in the radio emission of the magnetar while no correlation is seen in the average radio profile variability on a shorter time-scale (days). The 0.5-12 keV X-ray flux shows a monotonic decrease that can be attributed to thermal emission from a hot spot on the surface of the neutron star that is reducing in size. Such decrease is consistent with what is seen in other magnetars. The potential correlation between the radio emission mode and the behaviour of the spin-down rate hints to a global change in the magnetopshere of the magnetar akin to the correlation seen in a subset of mode-changing radio pulsars and suggests a physical link between the two sub-populations. You can read the full paper in the Monthly Notices of the Royal Astronomical Society and Open Access on the ArXiv.
Radio profiles of magentar Swift J1818-1607 from Jodrell Bank Observatory Lovell Telescope and Mark II Telescope observations.
Fabian Jankowski, Evan Keane and Ben Stappers present high-sensitivity, wide-band observations (704-4032 MHz) of the young to middle-aged radio pulsar J1452-6036, taken at multiple epochs before and, serendipitously, shortly after a glitch occurred on 2019 April 27. We obtained the data using the new ultra-wide-bandwidth low-frequency (UWL) receiver at the Parkes radio telescope, and we used Markov chain Monte Carlo techniques to estimate the glitch parameters robustly. The data from our third observing session began 3 h after the best-fitting glitch epoch, which we constrained to within ~4 min. The glitch was of intermediate size, with a fractional change in spin frequency of 270.52(3) × 10-9. We measured no significant change in spin-down rate and found no evidence for rapidly decaying glitch components. We systematically investigated whether the glitch affected any radiative parameters of the pulsar and found that its spectral index, spectral shape, polarization fractions, and rotation measure stayed constant within the uncertainties across the glitch epoch. However, its pulse-averaged flux density increased significantly by about 10 per cent in the post-glitch epoch and decayed slightly before our fourth observation a day later. We show that the increase was unlikely caused by calibration issues. While we cannot exclude that it was due to refractive interstellar scintillation, it is hard to reconcile with refractive effects. The chance coincidence probability of the flux density increase and the glitch event is low. Finally, we present the evolution of the pulsar's pulse profile across the band. The morphology of its polarimetric pulse profile stayed unaffected to a precision of better than 2 per cent. You can read the full paper in the Monthly Notices of the Royal Astronomical Society and Open Access on the ArXiv.
Since their discovery more than 50 years ago, broad-band radio studies of pulsars have generated a wealth of information about the underlying physics of radio emission. In order to gain some further insights into this elusive emission mechanism, we performed a multifrequency study of two very well-known pulsars, PSR B0919+06 and PSR B1859+07. These pulsars show peculiar radio emission properties whereby the emission shifts to an earlier rotation phase before returning to the nominal emission phase in a few tens of pulsar rotations (also known as 'swooshes'). We confirm the previous claim that the emission during the swoosh is not necessarily absent at low frequencies and the single pulses during a swoosh show varied behaviour at 220 MHz. We also confirm that in PSR B0919+06, the pulses during the swoosh show a chromatic dependence of the maximum offset from the normal emission phase with the offset following a consistent relationship with observing frequency. We also observe that the flux density spectrum of the radio profile during the swoosh is inverted compared to the normal emission. For PSR B1859+07, we have discovered a new mode of emission in the pulsar that is potentially quasi-periodic with a different periodicity than is seen in its swooshes. We invoke an emission model previously proposed in the literature and show that this simple model can explain the macroscopic observed characteristics in both pulsars. We also argue that pulsars that exhibit similar variability on short time-scales may have the same underlying emission mechanism. You can read this work in the Monthly Notices of the Royal Astronomical Society or Open Access on the ArXiv.
Example of the swooshing events from PSR B0919+06 observed simultaneously at four radio frequencies.
Laura Driessen reviews the history of radio transient astronomy for Astronomy & Geophysics. Laura's review focus on current investigations of a wide range of radio transients with Square Kilometre Array pathfinder and precursor instruments, and looks forward to what the SKA will reveal about the changing radio sky.
Kaustubh Rajwade and co-authors find an 157 day pattern in the activity of the first repeating fast radio burst, FRB 121102! The team who worked on this kept an eye on FRB 121102 for 4 years using the Jodrell Bank Observatory 76-m Lovell Telescope. Over the 4 years, we detected 32 bursts from FRB 121102. We used these bursts, plus bursts detected by other telescopes in the past, to find out that FRB 121102 emits bursts in a 90-day window, then goes silent for the next 67 days, and then this pattern repeats. Before now, only one other repeating FRB, called FRB 180916.J0158+65, demonstrated such regular behaviour. But the pattern of FRB 180916 repeats every 16 days, instead of every 157 days like FRB 121102. This huge difference between the two repeating FRBs means that there’s a wide range of periodicity in repeating FRB behaviour. This helps us narrow in on theoretical models to explain repeating FRBs. An example of a theory to explain these sources is a compact object (the object making the FRB bursts) orbiting a second object. Another theory is that the bursts come from the magnetic pole of a neutron star, but that the neutron star wobbles (precesses) as it rotates. This new information about periodic bursting tells us about how strong that magnetic field around the star has to be. We still need to find lots more of these objects (lots of us are working on it! Including the MeerTRAP team!) to narrow down the theory and work out exactly what causes these cool, mysterious radio bursts! You can read more about this result in the Monthly Notices for the Royal Astronomical Society and Open Access on the ArXiv.
Artists impression by Kirsti Mickaliger of the possible mechanism behind the acticity cycle of FRB 121102.
We present 11 detections of FRB 121102 in ∼3 h of observations during its 'active' period on the 10th of 2019 September. The detections were made using the newly deployed MeerTRAP system and single pulse detection pipeline at the MeerKAT radio telescope in South Africa. Fortuitously, the Nançay radio telescope observations on this day overlapped with the last hour of MeerKAT observations and resulted in four simultaneous detections. The observations with MeerKAT's wide band receiver, which extends down to relatively low frequencies (900-1670 MHz usable L-band range), have allowed us to get a detailed look at the complex frequency structure, intensity variations, and frequency-dependent sub-pulse drifting. The drift rates we measure for the full-band and sub-banded data are consistent with those published between 600 and 6500 MHz with a slope of -0.147 ± 0.014 ms-1. Two of the detected bursts exhibit fainter 'precursors' separated from the brighter main pulse by ∼28 and ∼34 ms. A follow-up multi-telescope campaign on the 6th and 8th of 2019 October to better understand these frequency drifts and structures over a wide and continuous band was undertaken. No detections resulted, indicating that the source was 'inactive' over a broad frequency range during this time. You can read the paper in the Monthly Notices of the Royal Astronomical Society and Open Access on the ArXiv.
MeerKAT observations of FRB 121102 bursts showing the interesting frequency structure..
Fast radio bursts (FRBs) are bright, extragalactic radio pulses whose origins are still unknown. Until recently, most FRBs have been detected at frequencies greater than 1 GHz with a few exceptions at 800 MHz. The recent discoveries of FRBs at 400 MHz from the Canadian Hydrogen Intensity Mapping Experiment (CHIME) telescope have opened up possibilities for new insights about the progenitors while many other low-frequency surveys in the past have failed to find any FRBs. Here, we present results from an FRB survey recently conducted at the Jodrell Bank Observatory at 332 MHz with the 76-m Lovell telescope for a total of 58 d. We did not detect any FRBs in the survey and report a 90 per cent upper limit of 5500 FRBs per day per sky for a Euclidean Universe above a fluence threshold of 46 Jy ms. We discuss the possibility of absorption as the main cause of non-detections in low-frequency (<800 MHz) searches and invoke different absorption models to explain the same. We find that Induced Compton Scattering alone cannot account for absorption of radio emission and that our simulations favour a combination of Induced Compton Scattering and Free-Free Absorption to explain the non-detections. For a free-free absorption scenario, our constraints on the electron density are consistent with those expected in the post-shock region of the ionized ejecta in superluminous supernovae. You can read this article in the Monthly Notices of the Royal Astronomical Society, or Open Access on the ArXiv.
Vincent Morello and co-authors present the discovery of a pulsar that spins once every 12.6 seconds, the second slowest spinning pulsar. You can read the paper in the Monthly Notices of the Royal Astronomical Society or Open Access on the ArXiv.
We report the discovery of PSR J2251-3711, a radio pulsar with a spin period of 12.1 s, the second longest currently known. Its timing parameters imply a characteristic age of 15 Myr, a surface magnetic field of 1.3 × 10^13 G, and a spin-down luminosity of 2.9 × 10^29 erg s-1. Its dispersion measure of 12.12(1) pc cm^-3 leads to distance estimates of 0.5 and 1.3 kpc according to the NE2001 and YMW16 Galactic free electron density models, respectively. Some of its single pulses show an uninterrupted 180-deg sweep of the phase-resolved polarization position angle, with an S-shape reminiscent of the rotating vector model prediction. However, the fact that this sweep occurs at different phases from one pulse to another is remarkable and without straightforward explanation. Although PSR J2251-3711 lies in the region of the P−P-dot parameter space occupied by the X-ray isolated neutron stars (XINS), there is no evidence for an X-ray counterpart in our Swift XRT observation; this places a 99 per cent-confidence upper bound on its unabsorbed bolometric thermal luminosity of 1.1×1031 (d/1 kpc)2 ergs−11.1×1031 (d/1 kpc)2 ergs−1 for an assumed temperature of 85 eV, where d is the distance to the pulsar. Further observations are needed to determine whether it is a rotation-powered pulsar with a true age of at least several Myr, or a much younger object such as an XINS or a recently cooled magnetar. Extreme specimens like PSR J2251-3711 help bridge populations in the so-called neutron star zoo in an attempt to understand their origins and evolution.
Single pulses and the shape of the average pulse from pulsar PSR J2251-3711.
MeerTRAP PhD student Laura Driessen led work on the discovery and analysis of the first new transient to be discovered with the MeerKAT telescope! you can find out more here, and you can read the paper in the Monthly Notices of the Royal Astronomical Society, or open-access on ArXiv.
The light curve of the newly discovered flaring source MKT J170456.2-482100, and the images corresponding to the light curve (the position of MKT J170456.2-482100 is circled in pink). These images were taken weekly.
The detection plot of one of the bursts from the repeating fast radio burst FRB121102, as seen by our MeerTRAP team after the real time detection of the burst. The top plot shows the frequency time plot, and the bottom plot shows the dedispersed burst profile.
We’re excited to announce that we have been involved in the detection of bursts from the first repeating fast radio burst, FRB 121102!
Recently, it was reported by various facilities that FRB 121102 was active, so we took the opportunity (as part of a MeerKAT DDT proposal) to observe the source early on the morning of the 10th of September. We used the MeerTRAP real-time pulse detection pipeline and backend, with the Max Planck Institute for Radio Astronomy beam former, to search for bursts in real-time for three hours.
Check out the ATel announcing our detection of 12 bursts from FRB 121102 in real-time in the three hours of observing.
Duncan working hard with the MeerTRAP team to spot bursts from the repeating fast radio burst, FRB121102.