arXiv subjects

I. Pastor-Marazuela

Publications and source records attributed to I. Pastor-Marazuela.

13 recordsLinked to original sources

arXiv2026

Discovery of 27 new Rotating Radio Transients by MeerTRAP

We present the discovery of 27 new Galactic transients made by the commensal MeerTRAP single pulse search programme at the MeerKAT telescope. We determine the location of 14 of these discoveries with arcsecond accuracy by imaging the data captured in the dedicated transient buffer. A preliminary estimate of the period was made for 8 sources using the arrival times of several pulses detected by MeerTRAP. The periods of these transients range between 0.78 s and 4 s. For the previously published MeerTRAP source MTP0040 (PSR J1357-6507), we are able to provide the position and period using new pulses detected since it was reported. We also estimate the radio fluences and discuss the burst rates derived from the commensal search detections. The accurate image-domain localizations were used to conduct follow-up observations and timing analysis. Furthermore, some follow-up observations revealed ordinary pulsar-like pulsed behavior for four of the new sources, illustrating the blurred separation between rotating radio transients and canonical pulsars. We also present coherent timing solutions for 4 sources, providing insight into their rotational properties and their place within the Galactic neutron star population.

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arXiv2026

A bright wideband radio burst from the isolated neutron star 2XMM J104608.7$-$594306

We present the discovery of a second coherent radio burst from the thermally emitting neutron star 2XMM J104608.7$-$594306 in our follow-up observations with the Murriyang Ultra-Wideband Low receiver. This burst shows complex morphology with multiple components and wideband emission spanning from 704 to 4032MHz. We measured a steep spectral index of $α=-2.18\pm0.16$. Our polarimetric analysis demonstrates that the burst is highly polarised with a linear and circular polarisation fraction of 54% and 22%, respectively. We identified an orthogonal jump in the polarisation position angles of the burst, resembling those seen in radio pulsars. We compared this burst with the first radio burst detected from the source with MeerKAT. These two bursts detected in a total of 40 hours on source with MeerKAT and Murriyang, combined, show that 2XMM J104608.7$-$594306 can emit sporadic radio emission with luminosity jumps comparable to those seen in the bright bursts from SGR 1935+2154. This suggests that previously thought radio-quiet neutron stars such as X-ray dim isolated neutron stars and central compact objects could exhibit rare radio bursting activity.

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arXiv2025

Discovery of 30 Galactic radio transient pulsars with MeerTRAP

We present the discovery of 30 new Galactic sources from the MeerTRAP project, a commensal fast radio transient search programme using the MeerKAT telescope. These sources were all identified via a single pulse search. Most of them are likely to be rotating radio transients (RRATs) given their low pulse rates. Using data captured in our transient buffer we have localised nine sources in the image domain to arcsecond precision. This facilitates the timing of these sources and further follow-up with other telescopes. Using the arrival times of single pulses, we have constrained the periods of 14 sources, ranging from 121ms to 7.623s, and derived a phase-coherent timing solution for one of them. Follow-up observations of the MeerTRAP sources (including those published previously) performed with the Effelsberg telescope have detected regular but faint emission from three sources, confirming their long rotation period, including PSR J2218+2902 with a period of 17.5s, the fourth slowest in the radio pulsar population. A few of the sources exhibit interesting emission features, such as periodic microstructure in PSR J1243-0435 and possible nulling in PSR J1911-2020 and PSR J1243-0435. We find that the duty cycles of the three newly discovered pulsars are very low and follow the general trend for the duty cycle with period of known pulsars.

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arXiv2025

MeerKAT discovery of a hyperactive repeating fast radio burst source

We present the discovery and localisation of a repeating fast radio burst (FRB) source from the MeerTRAP project, a commensal fast radio transient search programme using the MeerKAT telescope. FRB 20240619D was first discovered on 2024 June 19 with three bursts being detected within two minutes in the MeerKAT L-band (856 - 1712MHz). We conducted follow-up observations of FRB 20240619D with MeerKAT using the Ultra-High Frequency (UHF; 544 - 1088MHz), L-band and S-band (1968 - 2843MHz) receivers one week after its discovery, and recorded a total of 249 bursts. The MeerKAT-detected bursts exhibit band-limited emission with an average fractional bandwidth of 0.31, 0.34 and 0.48 in the UHF, L-band and S-band, respectively. We find our observations are complete down to a fluence limit of ~1Jy ms, above which the cumulative burst rate follows a power law $R (>F)\propto (F/1\,\text{Jy}\,\text{ms})^γ$ with $γ=-1.6\pm0.1$ and $-1.7\pm0.1$ in the UHF and L-band, respectively. The near-simultaneous L-band, UHF and S-band observations reveal a frequency dependent burst rate with $3\times$ more bursts being detected in the L-band than in the UHF and S-band, suggesting a spectral turnover in the burst energy distribution of FRB 20240619D. Our polarimetric analysis demonstrates that most of the bursts have $\sim100\%$ linear polarisation fractions and $\sim10\%\text{--}20\%$ circular polarisation fractions. We find no optical counterpart of FRB 20240619D in the MeerLICHT optical observations simultaneous to the radio observations and set a fluence upper limit in MeerLICHT's q-band of 0.76Jy ms and an optical-to-radio fluence ratio limit of 0.034 for a 15s exposure.

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arXiv2025

Slow and steady: long-term evolution of the 76-second pulsar J0901$-$4046

PSR J0901$-$4046, a likely radio-loud neutron star with a period of 75.88 seconds, challenges conventional models of neutron star radio emission. Here, we showcase results from 46 hours of follow-up observations of PSR J0901$-$4046 using the MeerKAT, Murriyang, GMRT, and MWA radio telescopes. We demonstrate the intriguing stability of the source's timing solution over more than three years, leading to an RMS arrival-time uncertainty of just $\sim$10$^{-4}$ of the rotation period. Furthermore, non-detection below 500 MHz may indicate a low-frequency turnover in the source's spectrum, while no secular decline in the flux density of the source over time, as was apparent from previous observations, has been observed. Using high time-resolution MeerKAT data, we demonstrate two distinct quasi-periodic oscillation modes present in single pulses, with characteristic time scales of 73 ms and 21 ms. We also observe a statistically significant change in the relative prevalence of distinct pulse morphologies compared to previous observations, possibly indicating a shift in the magnetospheric composition over time. Finally, we show that the W$_{50}$ pulse width is nearly constant from 544-4032 MHz, consistent with zero radius-to-frequency mapping. The very short duty cycle ($\sim$1.4$^{\circ}$) is more similar to radio pulsars with periods $>$5 seconds than to radio-loud magnetars. This, along with the lack of magnetar-like outbursts or timing glitches, complicates the identification of the source with ultra-long period magnetar models.

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arXiv2025

A coherent radio burst from an X-ray neutron star in the Carina Nebula

The neutron star zoo comprises several sub-populations that range from energetic magnetars and thermally emitting X-ray neutron stars to radio-emitting pulsars. Despite studies over the last five decades, it has been challenging to obtain a clear physical link between the various populations of neutron stars, vital to constrain their formation and evolutionary pathways. Here we report the detection of a burst of coherent radio emission from a known radio-quiet, thermally emitting neutron star 2XMM J104608.7$-$594306in the Carina Nebula. The burst has a distinctive sharp rise followed by a decay made up of multiple components, which is unlike anything seen from other radio-emitting neutron stars. It suggests an episodic event from the neutron star surface, akin to transient radio emission seen from magnetars. The radio burst confirms that the X-ray source is a neutron star and suggests a new link between these apparently radio-quiet X-ray emitting sources and other transient or persistent radio-emitting neutron stars. It also suggests that a common physical mechanism for emission might operate over a range of magnetic field strengths and neutron star ages. We propose that 2XMM J104608.7$-$594306 straddles the boundary between young, energetic neutron stars and their evolved radio-emitting cousins and may bridge these two populations. The detection of such a radio burst also shows that other radio-quiet neutron stars may also emit such sporadic radio emission that has been missed by previous radio surveys and highlights the need for regular monitoring of this unique sub-population of neutron stars.

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arXiv2025

An activity transition in FRB 20201124A: methodological rigor, detection of frequency-dependent cessation, and a geometric magnetar model

We report detections of fast radio bursts (FRBs) from the repeating source FRB 20201124A with Apertif/WSRT and GMRT, and measurements of basic burst properties, especially the dispersion measure (DM) and fluence. Based on comparisons of these properties with previously published larger samples, we argue that the excess DM reported earlier for pulses with integrated signal to noise ratio $\lesssim 1000$ is due to incompletely accounting for the so-called sad trombone effect, even when using structure-maximizing DM algorithms. Our investigations of fluence distributions next lead us to advise against formal power-law fitting, especially dissuading the use of the least-square method, and we demonstrate the large biases involved. A maximum likelihood estimator (MLE) provides a much more accurate estimate of the power law and we provide accessible code for direct inclusion in future research. Our GMRT observations were fortuitously scheduled around the end of the activity cycle as recorded by FAST. We detected several bursts (one of them very strong) at 400/600 MHz, a few hours after sensitive FAST non-detections already showed the 1.3 GHz FRB emission to have ceased. After FRB 20180916B, this is a second example of a frequency-dependent activity window identified in a repeating FRB source. Since numerous efforts have so-far failed to determine a spin period for FRB 20201124A, we conjecture it to be an ultra-long period magnetar, with a period on the scale of months, and with a very wide, highly irregular duty cycle. Assuming the emission comes from closed field lines, we use radius-to-frequency mapping and polarization information from other studies to constrain the magnetospheric geometry and location of the emission region. Our initial findings are consistent with a possible connection between FRBs and crustal motion events.

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arXiv2025

Contemporaneous optical-radio observations of a fast radio burst in a close galaxy pair

We present the MeerKAT discovery and MeerLICHT contemporaneous optical observations of the Fast Radio Burst (FRB) 20230808F, which was found to have a dispersion measure of $\mathrm{DM}=653.2\pm0.4\mathrm{\,pc\,cm^{-3}}$. FRB 20230808F has a scattering timescale $τ_{s}=3.1\pm0.1\,\mathrm{ms}$ at $1563.6$ MHz, a rotation measure $\mathrm{RM}=169.4\pm0.2\,\mathrm{rad\,m^{-2}}$, and a radio fluence $F_{\mathrm{radio}}=1.72\pm0.01\,\mathrm{Jy\,ms}$. We find no optical counterpart in the time immediately after the FRB, nor in the three months after the FRB during which we continued to monitor the field of the FRB. We set an optical upper flux limit in MeerLICHT's $q$-band of $11.7\,\mathrm{μJy}$ for a 60 s exposure which started $\sim3.4$ s after the burst, which corresponds to an optical fluence, $F_{\mathrm{opt}}$, of $0.039\,\mathrm{Jy\,ms}$ on a timescale of $\sim3.4$ s. We obtain an estimate for the $q-$band luminosity limit of $vL_{v}\sim 1.3\times10^{43}\,\mathrm{erg\,s^{-1}}$. We localise the burst to a close galaxy pair at a redshift of $z_{\mathrm{spec}}=0.3472\pm0.0002$. Our time delay of $\sim3.4$ s between the FRB arrival time and the start of our optical exposure is the shortest ever for an as yet non-repeating FRB, and hence the closest to simultaneous optical follow-up that exists for such an FRB.

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arXiv2024

Detection and localisation of the highly active FRB 20240114A with MeerKAT

We report observations of the highly active FRB 20240114A with MeerKAT using the Ultra-High Frequency (UHF; $544\text{--}1088$ MHz) and L-band ($856\text{--}1712$ MHz) receivers. A total of 62 bursts were detected in coherent tied-array beams using the MeerTRAP real-time transient detection pipeline. We measure a structure-optimising dispersion measure of $527.65\pm0.01\,\text{pc}\,\text{cm}^{-3}$ using the brightest burst in the sample. We find the bursts of FRB 20240114A are generally detected in part of the broad band of MeerKAT, $\sim40\%$ in the UHF and $\sim30\%$ in the L-band, indicating the band limited nature. We analyse the fluence distribution of the 44 bursts detected at UHF, constraining the fluence completeness limit to $\sim1\,$Jy ms, above which the cumulative burst rate follows a power law $R (>F)\propto (F/1\,\text{Jy}\,\text{ms})^γ$ with $γ=-1.8\pm0.2$. Using channelised telescope data captured in our transient buffer we localise FRB 20240114A in the image domain to RA = 21h27m39.86s, Dec = +04d19m45.01s with an uncertainty of 1.4 arcsec. This localisation allows us to confidently identify the host galaxy of FRB 20240114A. Also using the transient buffer data we perform a polarimetric study and demonstrate that most of the bursts have $\sim100\%$ linear polarisation fractions and up to $\sim20\%$ circular polarisation fractions. Finally, we predict the flux density of a potential persistent radio source (PRS) associated with FRB 20240114A is $\backsimeq[0.6\text{--}60]\,μ\text{Jy}$ based on the simple relation between the luminosity of the PRS and the rotation measure arising from the FRB local environment.

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arXiv2024

A study of two FRBs with low polarization fractions localized with the MeerTRAP transient buffer system

Localisation of fast radio bursts (FRBs) to arcsecond and sub-arcsecond precision maximizes their potential as cosmological probes. To that end, FRB detection instruments are deploying triggered complex-voltage capture systems to localize FRBs, identify their host galaxy and measure a redshift. Here, we report the discovery and localisation of two FRBs (20220717A and 20220905A) that were captured by the transient buffer system deployed by the MeerTRAP instrument at the MeerKAT telescope in South Africa. We were able to localize the FRBs to a precision of $\sim$1 arc-second that allowed us to unambiguously identify the host galaxy for FRB 20220717A (posterior probability$\sim$0.97). FRB 20220905A lies in a crowded region of the sky with a tentative identification of a host galaxy but the faintness and the difficulty in obtaining an optical spectrum preclude a conclusive association. The bursts show low linear polarization fractions (10--17$\%$) that conform to the large diversity in the polarization fraction observed in apparently non-repeating FRBs akin to single pulses from neutron stars. We also show that the host galaxy of FRB 20220717A contributes roughly 15$\%$ of the total dispersion measure (DM), indicating that it is located in a plasma-rich part of the host galaxy which can explain the large rotation measure. The scattering in FRB 20220717A can be mostly attributed to the host galaxy and the intervening medium and is consistent with what is seen in the wider FRB population.

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arXiv2022

First release of Apertif imaging survey data

(Abridged) Apertif is a phased-array feed system for WSRT, providing forty instantaneous beams over 300 MHz of bandwidth. A dedicated survey program started on 1 July 2019, with the last observations taken on 28 February 2022. We describe the release of data products from the first year of survey operations, through 30 June 2020. We focus on defining quality control metrics for the processed data products. The Apertif imaging pipeline, Apercal, automatically produces non-primary beam corrected continuum images, polarization images and cubes, and uncleaned spectral line and dirty beam cubes for each beam of an Apertif imaging observation. For this release, processed data products are considered on a beam-by-beam basis within an observation. We validate the continuum images by using metrics that identify deviations from Gaussian noise in the residual images. If the continuum image passes validation, we release all processed data products for a given beam. We apply further validation to the polarization and line data products. We release all raw observational data from the first year of survey observations, for a total of 221 observations of 160 independent target fields, covering approximately one thousand square degrees of sky. Images and cubes are released on a per beam basis, and 3374 beams are released. The median noise in the continuum images is 41.4 uJy/bm, with a slightly lower median noise of 36.9 uJy/bm in the Stokes V polarization image. The median angular resolution is 11.6"/sin(Dec). The median noise for all line cubes, with a spectral resolution of 36.6 kHz, is 1.6 mJy/bm, corresponding to a 3-sigma HI column density sensitivity of 1.8 x 10^20 atoms cm^-2 over 20 km/s (for a median angular resolution of 24" x 15"). We also provide primary beam images for each individual Apertif compound beam. The data are made accessible using a Virtual Observatory interface.

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arXiv2021

The intermediate polar cataclysmic variable GK Persei 120 years after the nova explosion: a first dynamical mass study

We present a complete dynamical study of the intermediate polar and dwarf nova cataclysmic variable GK Per (Nova Persei 1901) based on a multi-site optical spectroscopy and $R$-band photometry campaign. The radial velocity curve of the evolved donor star has a semi-amplitude $K_2=126.4 \pm 0.9 \, \mathrm{km}\,\mathrm{s}^{-1}$ and an orbital period $P=1.996872 \pm 0.000009 \, \mathrm{d}$. We refine the projected rotational velocity of the donor star to $v_\mathrm{rot} \sin i = 52 \pm 2 \, \mathrm{km}\,\mathrm{s}^{-1}$ which, together with $K_2$, provides a donor star to white dwarf mass ratio $q=M_2/M_1=0.38 \pm 0.03$. We also determine the orbital inclination of the system by modelling the phase-folded ellipsoidal light curve and obtain $i=67^{\circ} \pm 5^{\circ}$. The resulting dynamical masses are $M_{1}=1.03^{+0.16}_{-0.11} \, \mathrm{M}_{\odot}$ and $M_2 = 0.39^{+0.07}_{-0.06} \, \mathrm{M}_{\odot}$ at $68$ per cent confidence level. The white dwarf dynamical mass is compared with estimates obtained by modelling the decline light curve of the $1901$ nova event and X-ray spectroscopy. The best matching mass estimates come from the nova light curve models and an X-ray data analysis that uses the ratio between the Alfvén radius in quiescence and during dwarf nova outburst.

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arXiv2020

A bright, high rotation-measure FRB that skewers the M33 halo

We report the detection of a bright fast radio burst, FRB\,191108, with Apertif on the Westerbork Synthesis Radio Telescope (WSRT). The interferometer allows us to localise the FRB to a narrow $5\arcsec\times7\arcmin$ ellipse by employing both multibeam information within the Apertif phased-array feed (PAF) beam pattern, and across different tied-array beams. The resulting sight line passes close to Local Group galaxy M33, with an impact parameter of only 18\,kpc with respect to the core. It also traverses the much larger circumgalactic medium of M31, the Andromeda Galaxy. We find that the shared plasma of the Local Group galaxies could contribute $\sim$10\% of its dispersion measure of 588\,pc\,cm$^{-3}$. FRB\,191108 has a Faraday rotation measure of +474\,$\pm\,3$\,rad\,m$^{-2}$, which is too large to be explained by either the Milky Way or the intergalactic medium. Based on the more moderate RMs of other extragalactic sources that traverse the halo of M33, we conclude that the dense magnetised plasma resides in the host galaxy. The FRB exhibits frequency structure on two scales, one that is consistent with quenched Galactic scintillation and broader spectral structure with $Δν\approx40$\,MHz. If the latter is due to scattering in the shared M33/M31 CGM, our results constrain the Local Group plasma environment. We found no accompanying persistent radio sources in the Apertif imaging survey data.

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