PSR J0437-4715 Research Articles

X-ray non-detection of PSR J0250 + 5854

ABSTRACT We conducted a deep XMM–Newton observing campaign on the 23.5-s radio pulsar PSR J0250 + 5854 in order to better understand the connection between long-period, radio-emitting neutron stars and their high-energy-emitting counterparts. No X-ray emission was detected resulting in an upper limit in the bolometric luminosity of PSR J0250 + 5854 of <1031 erg s−1 for an assumed blackbody with a temperature of 85 eV, typical of an X-ray Dim Isolated Neutron Star (XDINS). We compared the upper limit in the bolometric luminosity of PSR J0250 + 5854 with the known population of XDINSs and found that the upper limit is lower than the bolometric luminosity of all but one XDINS. We also compared PSR J0250 + 5854 with SGR 0418+5729, the magnetar with low dipole magnetic field strength, where the upper limit suggests that if PSR J0250 + 5854 has a thermal hotspot like SGR 0418 + 5729, it would have a blackbody temperature of <200 eV, compared to 320 eV of the magnetar.

Gamma-ray flares from pulsar wind nebulae in the Large Magellanic Cloud

ABSTRACTHigh-energy radiation of young pulsar wind nebulae (PWNe) is known to be variable. This is exemplified by the Crab nebula, which can undergo both rapid brightenings and dimmings. Two pulsars in the Large Magellanic Cloud, PSR J0540–6919 and PSR J0537–6910, are evolutionally close to Crab, so one may expect the same kind of variability from the PWNe around them. In this work, we search for flaring activity in these PWNe in gamma-rays using the data from the Fermi Large Area Telescope in the range 100 MeV–10 GeV collected from 2008 August to 2021 December. We construct light curves of these sources in the three bands, 100–300 MeV, 300–1000 MeV, and 1–10 GeV, with one-week resolution. We find evidence of flaring activity in all the bands, in contrast with Crab, where no flares at E>1 GeV were observed. Analysis of the flaring episode in the 100–300 and 300–1000 MeV bands indicates that the flux of one of the PWNe could grow by a factor of ≈5–10, and the statistical significance of the flare detection reaches 6σ. We are not confident about which of the two PWNe flared because of their proximity in the sky. However, in the 1–10 GeV band, where the angular resolution of LAT is better, we find several episodes of enhanced brightness in both the PWNe. We check possible contaminants which could be responsible for the observed variability but find their contribution not to be relevant.

Relativistic Correction to the r-mode Frequency in Light of Multimessenger Constraints

The r-mode oscillations of rotating neutron stars are promising candidates for continuous gravitational-wave (GW) observations. The r-mode frequencies for slowly rotating Newtonian stars are well known and independent of the equation of state (EOS), but for neutron stars several mechanisms can alter the r-mode frequency for which the relativistic correction is dominant and relevant for most of the neutron stars. The most sensitive searches for continuous GWs are those for known pulsars for which GW frequencies are in targeted narrow frequency bands of a few hertz. In this study, we investigate the effect of several state-of-the-art multimessenger constraints on the r-mode frequency for relativistic, slowly rotating, barotropic stars. Imposing these recent constraints on the EOS, we find that the r-mode frequency range is slightly higher than that from the previous study and the narrowband frequency range can increase by up to 25% for the most promising candidate PSR J0537−6910 depending on the range of compactness. We also derive universal relations between r-mode frequency and dimensionless tidal deformability that can be used to estimate the dynamical tide of the r-mode resonant excitation during the inspiral signal. These results can be used to construct the parameter space for r-mode searches in GW data and also constrain the nuclear EOS following a successful r-mode detection.

An application of pulsar timing in dynamic reference frame transformation of solar system

AbstractThe establishment of pulsar space–time reference frame is of great significance for X‐ray pulsar deep space navigation. To demonstrate that the pulsar parameters are accurate enough to be used as a spatial reference, the transformation parameters, that is, α, β, and γ, of different reference frames determined based on pulsar timing are shown and compared with that of the heliocentric coordinates of Earth‐Moon barycenter. The JPL ephemerides such as DE421, DE200 and INPOP series, are mainly selected for conversion parameter calculation. For the best‐determined parameter γ, the discrepancy between the two different data is 0.38 mas/1.33σ. The timing positions of pulsars clearly show the frame‐tie of different ephemerides, indicating that MSPs have the potential to be a candidate for constructing time–space standard. It is also found that the rotation angles change linearly with time, and PSR J0437 − 4715 plays a critical role in the fitting of α. By employing a few high‐quality MSPs, the transformation precision of the right ascension is evaluated to be on the order of sub‐milliarcsecond, which is an order of magnitude higher than that of the declination.

Nanohertz gravitational wave astronomy during SKA era: An InPTA perspective

Decades long monitoring of millisecond pulsars, which exhibit highly stable rotational periods in pulsar timing array experiments is on the threshold of discovering nanohertz stochastic gravitational wave background. This paper describes the Indian pulsar timing array (InPTA) experiment, which employs the upgraded Giant Metrewave Radio Telescope (uGMRT) for timing an ensemble of millisecond pulsars for this purpose. We highlight InPTA’s observation strategies and analysis methods, which are relevant for a future PTA experiment with the more sensitive Square Kilometer Array (SKA) telescope. We show that the unique multi-sub-array multi-band wide-bandwidth frequency coverage of the InPTA, provides dispersion measure estimates with unprecedented precision for PTA pulsars, e.g., \(\sim 2 \times 10^{-5}\) pc cm\(^{-3}\) for PSR J1909-3744. Configuring the SKA-low and SKA-mid as two and four sub-arrays, respectively, it is shown that comparable precision is achievable, using observation strategies similar to those pursued by the InPTA, for a larger sample of 62 pulsars, requiring about 26 and 7 h per epoch for the SKA-mid and the SKA-low telescopes, respectively. We also review the ongoing efforts to develop PTA-relevant general relativistic constructs that will be required to search for nanohertz gravitational waves from isolated super-massive black hole binary systems like blazar OJ 287. These efforts should be relevant to pursue persistent multi-messenger gravitational wave astronomy during the forthcoming era of the SKA telescope, the thirty meter telescope, and the next-generation event horizon telescope.

LHAASO J2226+6057 as a pulsar wind nebula

Context. The Large High Altitude Air Shower Observatory has reported the detection of cosmic-ray sources in the Milky Way that can accelerate particles up to PeV (=1015 eV) energies. These sources, so-called “PeVatrons”, are mostly unidentified. Several classes of sources, such as supernova remnants, pulsar wind nebula, or young stellar clusters can potentially be the counterparts of these PeVatrons. Aims. The aim of this work is to study a pulsar wind nebula interpretation of one of these PeVatrons, LHAASO J2226+6057, which has a relatively well covered multifrequency spectrum. Methods. We have performed a leptonic, time-dependent modeling of the pulsar wind nebula (PWN) associated with PSR J2229+6114 considering a time-energy-dependent diffusion-loss equation. Injection, energy losses, as well as the escape of particles were considered to balance the time-dependent lepton population. We have also included the dynamics of the PWN and the associated supernova remnant and their interaction via the reverse shock to study the reverberation phase of the system. Results. We have considered different values of the braking index (n) and true age (tage) for the fitting of the MultiWaveLength (MWL) spectral energy distribution (SED) of LHAASO J2226+6057. The best-fit PWN model parameters and their 1σ confidence intervals have been evaluated. We have also demonstrated the impact of reverberation on the MWL SED with increasing time. Additionally, we have discussed the resultant large radius and low magnetic field associated with the PWN in question, as caveats for the possible physical connection of the pulsar as the origin of this high energy source.

Analysis of the ionized interstellar medium and orbital dynamics of PSR J1909-3744 using scintillation arcs

ABSTRACT Long-term studies of binary millisecond pulsars (MSPs) provide precise tests of strong-field gravity, and can be used to measure neutron-star masses. PSR J1909-3744, a binary MSP has been the subject of several pulsar timing analyses. The edge-on orbit enables measurement of its mass using the Shapiro delay; however, there is degeneracy in the sense of the inclination angle, i, and multiple solutions for the longitude of ascending node, Ω. Radio pulsars scintillate due to inhomogeneities in the ionized interstellar medium (IISM). This can result in scintillation arcs in the power spectrum of the dynamic spectrum that can use these to study the interstellar medium and constrain binary pulsar orbits. Here, we study the scintillation of PSR J1909-3744 using observations from the 64-m Parkes Radio Telescope (Murriyang) over ≈13 yr, using techniques to study scintillation in a lower signal-to-noise regime. By monitoring annual and orbital variations of the arc-curvature measurements, we are able to characterize the velocity of the IISM. We find that the statistics of the IISM remained stationary over this time and a slightly anisotropic model (axial ratio ≳1.2) is preferred. We measure the relative distance to a single dominant thin scattering screen at s = 0.49 ± 0.04, or Ds = 590 ± 50 pc, with an angle of anisotropy ζ = 85 ± 6° (East of North) and velocity in the direction of anisotropy VIISM,ζ = 14 ± 10 km s−1. By combining a physical model of the IISM and current pulsar timing results, we also constrain Ω = 225 ± 3° and i = 86.46 ± 0.05°.

Timing Six Energetic Rotation-powered X-Ray Pulsars, Including the Fast-spinning Young PSR J0058-7218 and Big Glitcher PSR J0537-6910

Measuring a pulsar’s rotational evolution is crucial to understanding the nature of the pulsar. Here, we provide updated timing models for the rotational evolution of six pulsars, five of which are rotation phase-connected using primarily NICER X-ray data. For the newly discovered fast energetic young pulsar, PSR J0058−7218, we increase the baseline of its timing model from 1.4 days to 8 months and not only measure more precisely its spin-down rate but also for the first time the second time derivative of its spin rate . For the fastest and most energetic young pulsar, PSR J0537−6910 (with a 16 ms spin period), we detect four more glitches, for a total of 15 glitches over 4.5 yr of NICER monitoring, and show that its spin-down behavior continues to set this pulsar apart from all others, including a long-term braking index n = −1.234 ± 0.009 and interglitch braking indices that asymptote to ≲7 for long times after a glitch. For PSR J1101−6101, we measure a much more accurate spin-down rate that agrees with a previous value measured without phase connection. For PSR J1412+7922 (also known as Calvera), we extend the baseline of its timing model from our previous 1 yr model to 4.4 yr, and for PSR J1849−0001, we extend the baseline from 1.5 to 4.7 yr. We also present a long-term timing model of the energetic pulsar PSR J1813−1749, by fitting previous radio and X-ray spin frequencies from 2009–2019 and new ones measured here using 2018 NuSTAR and 2021 Chandra data.

Multicolour optical light curves of the companion star to the millisecond pulsar PSR J2051−0827

ABSTRACT We present simultaneous, multicolour optical light curves of the companion star to the black-widow pulsar PSR J2051−0827, obtained approximately 10 yr apart using ULTRACAM and HiPERCAM, respectively. The ULTRACAM light curves confirm the previously reported asymmetry in which the leading hemisphere of the companion star appears to be brighter than the trailing hemisphere. The HiPERCAM light curves, however, do not show this asymmetry, demonstrating that whatever mechanism is responsible for it varies on time-scales of a decade or less. We fit the symmetrical HiPERCAM light curves with a direct-heating model to derive the system parameters, finding an orbital inclination of $55.9^{+4.8}_{-4.1}$ degrees, in good agreement with radio-eclipse constraints. We find that approximately half of the pulsar’s spin-down energy is converted to optical luminosity, resulting in temperatures ranging from approximately $5150^{+190}_{-190}$ K on the day side to $2750^{+130}_{-150}$ K on the night side of the companion star. The companion star is close to filling its Roche lobe ($f_{\rm RL} =0.88^{+0.02}_{-0.02}$) and has a mass of $0.039^{+0.010}_{-0.011}$ M⊙, giving a mean density of $20.24^{+0.59}_{-0.44}$ g cm−3 and an apsidal motion constant in the range 0.0036 < k2 < 0.0047. The companion mass and mean density values are consistent with those of brown dwarfs, but the apsidal motion constant implies a significantly more centrally condensed internal structure than is typical for such objects.

4–8 GHz Fourier-domain Searches for Galactic Center Pulsars

The Galactic Center (GC), with its high density of massive stars, is a promising target for radio transient searches. In particular, the discovery and timing of a pulsar orbiting the central supermassive black hole (SMBH) of our galaxy will enable stringent strong-field tests of gravity and accurate measurements of SMBH properties. We performed multiepoch 4–8 GHz observations of the inner ≈15 pc of our galaxy using the Robert C. Byrd Green Bank Telescope in 2019 August–September. Our investigations constitute the most sensitive 4–8 GHz GC pulsar survey conducted to date, reaching down to a 6.1 GHz pseudo-luminosity threshold of ≈1 mJy kpc2 for a pulse duty cycle of 2.5%. We searched our data in the Fourier domain for periodic signals incorporating a constant or linearly changing line-of-sight pulsar acceleration. We report the successful detection of the GC magnetar PSR J1745−2900 in our data. Our pulsar searches yielded a nondetection of novel periodic astrophysical emissions above a 6σ detection threshold in harmonic-summed power spectra. We reconcile our nondetection of GC pulsars with inadequate sensitivity to a likely GC pulsar population dominated by millisecond pulsars. Alternatively, close encounters with compact objects in the dense GC environment may scatter pulsars away from the GC. The dense central interstellar medium may also favorably produce magnetars over pulsars.

VLA proper motion constraints on the origin, age, and potential magnetar future of PSR J1734−3333

Context.The characteristic age of PSR J1734−3333 estimated from its current spin down rate implies that it is a young pulsar (τc = 8.1 kyr). However, the time derivative of its spin-down rate differs markedly from that assumed for normal radio pulsars, meaning its actual age is uncertain. G354.8−0.8 is a supernova remnant (SNR) whose centre is located 21′ away from the pulsar, and which has a morphology that suggests an association with the pulsar.Aims.We aim to assess the likelihood of the association between PSR J1734−3333 and G354.8−0.8 or other nearby SNRs quantitatively, with the objective of shedding light on the real age of this pulsar.Methods.Observations with the Karl G. Jansky Very Large Array were carried out in 2015 and 2019 that allow precise astrometric measurements and consequently a proper motion estimate for the pulsar.Results.The proper motion was found to beμα = 10 ± 10 mas yr−1andμδ = −29 ± 11 mas yr−1(error bars are 1-σ). Though marginal, this detection rules out the association with G354.8−0.8 because it means the pulsar is not moving away from the centre of the SNR. No SNR consistent with the measured proper motion and an ageτccould be found. We also present the first measurement of the spectral index for this pulsar,α = −1.1 ± 0.3, measured between 1.5 and 3.0 GHz.Conclusions.The SNR produced by the birth supernova of PSR J1734−3333 could have already faded to undetectable brightness, estimates of which suggest timescales of 10 − 100 kyr. This and other considerations lead us to conclude that the pulsar is possibly older than 45 − 100 kyr. PSR J1734−3333 is a pulsar with rotational properties that place it between standard radio pulsars and magnetars, and we interpret our result in the context of a possible future life as a magnetar for this pulsar.

Glitches in four gamma-ray pulsars and inferences on the neutron star structure

ABSTRACT We present timing solutions from the Fermi-LAT observations of gamma-ray pulsars PSR J0835 − 4510 (Vela), PSR J1023−5746, PSR J2111+4606, and PSR J2229+6114. Data ranges for each pulsar extend over a decade. From data analysis, we have identified a total of 20 glitches, 11 of which are new discoveries. Among them, 15 glitches are large ones with Δν/ν ≳ 10−6. PSR J1023−5746 is the most active pulsar with glitch activity parameter being Ag = 14.5 × 10−7 yr−1 in the considered data span and should be a target for frequently glitching Vela-like pulsars in future observations. We have done fits within the framework of the vortex creep model for 16 glitches with Δν/ν ≳ 10−7. By theoretical analysis of these glitches, we are able to obtain important information on the structure of neutron star, including moments of inertia of the superfluid regions participated in glitches and coupling time-scales between various stellar components. The theoretical prediction for the time to the next glitch from the parameters of the previous one is found to be in qualitative agreement with the observed inter-glitch time-scales for the considered sample. Recoupling time-scales of the crustal superfluid are within the range of theoretical expectations and scale inversely with the spin-down rate of a pulsar. We also determined a braking index n = 2.63(30) for PSR J2229+6114 after glitch-induced contributions have been removed.

Towards robust constraints on axion dark matter using PSR J1745-2900

We apply novel, recently developed plasma ray-tracing techniques to model the propagation of radio photons produced by axion dark matter in neutron star magnetospheres and combine this with both archival and new data for the Galactic center magnetar PSR J1745-2900. The emission direction to the observer and the magnetic orientation are not constrained for this object leading to parametric uncertainty. Our analysis reveals that ray-tracing greatly reduces the signal sensitivity to this uncertainty, contrary to previous calculations where there was no emission at all in some directions. Based on a Goldreich-Julian (GJ) model for the magnetosphere and a Navarro-Frenk-White model for axion density in the Galactic center, we obtain the most robust limits on the axion-photon coupling, to date. These are comparable to those from the CAST solar axion experiment in the mass range $\ensuremath{\sim}4.2--60\text{ }\text{ }\ensuremath{\mu}\mathrm{eV}$. If the dark matter density is larger, as might predicted by a ``spike'' model, the limits could be much stronger. For a fixed GJ magnetosphere model, we conclude that of the two principle uncertainties considered in this work---observing angle and dark matter density---the latter is the larger of the two in our present calculations.

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.

The influence of small-scale magnetic field on the heating of J0250+5854 polar cap

The influence of surface small-scale magnetic field on the heating of PSR J0250+5854 polar cap is considered. It is assumed that the polar cap is heated only by reverse positrons accelerated in pulsar diode. It is supposed that pulsar diode is located near the star surface (polar cap model) and operates in the steady state space charge-limited flow regime. The reverse positron current is calculated in the framework of two models: rapid and gradually screening. To calculate the production rate of electron-positron pairs we take into account only the curvature radiation of primary electrons and its absorption in magnetic field. It is assumed that some fraction of electron-positron pairs may be created in bound state that can later be photoionized by thermal photons from star surface.

Constraints from LIGO O3 Data on Gravitational-wave Emission Due to R-modes in the Glitching Pulsar PSR J0537–6910

Abstract We present a search for continuous gravitational-wave emission due to r-modes in the pulsar PSR J0537–6910 using data from the LIGO–Virgo Collaboration observing run O3. PSR J0537–6910 is a young energetic X-ray pulsar and is the most frequent glitcher known. The inter-glitch braking index of the pulsar suggests that gravitational-wave emission due to r-mode oscillations may play an important role in the spin evolution of this pulsar. Theoretical models confirm this possibility and predict emission at a level that can be probed by ground-based detectors. In order to explore this scenario, we search for r-mode emission in the epochs between glitches by using a contemporaneous timing ephemeris obtained from NICER data. We do not detect any signals in the theoretically expected band of 86–97 Hz, and report upper limits on the amplitude of the gravitational waves. Our results improve on previous amplitude upper limits from r-modes in J0537-6910 by a factor of up to 3 and place stringent constraints on theoretical models for r-mode-driven spin-down in PSR J0537–6910, especially for higher frequencies at which our results reach below the spin-down limit defined by energy conservation.

4–8 GHz Spectrotemporal Emission from the Galactic Center Magnetar PSR J1745–2900

Abstract Radio magnetars are exotic sources noted for their diverse spectrotemporal phenomenology and pulse profile variations over weeks to months. Unusual for radio magnetars, the Galactic Center (GC) magnetar PSR J1745−2900 has been continually active since its discovery in 2013. We monitored the GC magnetar at 4–8 GHz for 6 hr in 2019 August–September using the Robert C. Byrd Green Bank Telescope. During our observations, the GC magnetar emitted a flat fluence spectrum over 5–8 GHz to within 2σ uncertainty. From our data, we estimate a 6.4 GHz period-averaged flux density, S ¯ 6.4 ≈ ( 240 ± 5 ) μJy. Tracking the temporal evolution of S ¯ 6.4 , we infer a gradual weakening of GC magnetar activity during 2016–2019 relative to that between 2013 and 2015.5. Typical single pulses detected in our study reveal marginally resolved subpulses with opposing spectral indices, a feature characteristic of radio magnetars but unseen in rotation-powered pulsars. However, unlike in fast radio bursts, these subpulses exhibit no perceptible radio frequency drifts. Throughout our observing span, ≃5 ms scattered pulses significantly jitter within two stable emission components of widths 220 ms and 140 ms, respectively, in the average pulse profile.

A broad-band radio study of PSR J0250+5854: the slowest spinning radio pulsar known

ABSTRACT We present radio observations of the most slowly rotating known radio pulsar PSR J0250+5854. With a 23.5-s period, it is close, or even beyond, the P-$\dot{P}$ diagram region thought to be occupied by active pulsars. The simultaneous observations with the Five-hundred-metre Aperture Spherical radio Telescope (FAST), the Chilbolton and Effelsberg Low Frequency Array (LOFAR) international stations, and New Extension in Nançay Upgrading loFAR (NenuFAR) represent a five-fold increase in the spectral coverage of this object, with the detections at 1250 (FAST) and 57 MHz (NenuFAR) being the highest and lowest frequency published, respectively, to date. We measure a flux density of 4 ± 2 $\mu$Jy at 1250 MHz and an exceptionally steep spectral index of $-3.5^{+0.2}_{-1.5}$, with a turnover below ∼95 MHz. In conjunction with observations of this pulsar with the Green Bank Telescope and the LOFAR Core, we show that the intrinsic profile width increases drastically towards higher frequencies, contrary to the predictions of conventional radius-to-frequency mapping. We examine polarimetric data from FAST and the LOFAR Core and conclude that its polar cap radio emission is produced at an absolute height of several hundreds of kilometres around 1.5 GHz, similar to other rotation-powered pulsars across the population. Its beam is significantly underfilled at lower frequencies, or it narrows because of the disappearance of conal outriders. Finally, the results for PSR J0250+5854 and other slowly spinning rotation-powered pulsars are contrasted with the radio-detected magnetars. We conclude that magnetars have intrinsically wider radio beams than the slow rotation-powered pulsars, and that consequently the latter’s lower beaming fraction is what makes objects such as PSR J0250+5854 so scarce.

Regular Bardeen Black Holes in Anti-de Sitter Spacetime versus Kerr Black Holes through Particle Dynamics

In this work, test particle dynamics around a static regular Bardeen black hole (BH) in Anti-de Sitter spacetime has been studied. It has been shown for neutral test particles that parameters of a regular Bardeen black hole in Anti-de Sitter spacetime can mimic the rotation parameter of the Kerr metric up to the value a≈0.9 providing the same innermost stable circular orbit (ISCO) radius. We have also explored the dynamics of magnetized particles with a magnetic dipole moment around a magnetically charged regular Bardeen black hole in Anti-de Sitter spacetime. As a realistic astrophysical scenario of the study, we have treated neutron stars orbiting a supermassive black hole (SMBH), in particular, the magnetar PSR J1745-2900 orbiting Sgr A* with the parameter β=10.2, as magnetized test particles. The magnetized particles dynamics shows that the parameter β, negative values of cosmological constant and magnetic charge parameter of the central BH cause a decrease in the ISCO radius. We have compared the effects of the magnetic charge of the Bardeen BH with the spin of rotating Kerr BH and shown that magnetic charge parameter can mimic the spin in the range a/M≃(0,0.7896) when Λ=0 at the range of its values g/M≃(0,0.648).

Multi-epoch searches for relativistic binary pulsars and fast transients in the Galactic Centre

ABSTRACT The high stellar density in the central parsecs around the Galactic Centre makes it a seemingly favourable environment for finding relativistic binary pulsars. These include pulsars orbiting other neutron stars, stellar-mass black holes, or the central supermassive black hole, Sagittarius A*. Here, we present multi-epoch pulsar searches of the Galactic Centre at four observing frequencies, $4.85,\, 8.35,\, 14.6,\, 18.95\, {\rm GHz}$, using the Effelsberg 100-m radio telescope. Observations were conducted 1 yr prior to the discovery of, and during monitoring observations of, the Galactic Centre magnetar PSR J1745−2900. Our data analysis features acceleration searches on progressively shorter time series to maintain sensitivity to relativistic binary pulsars. The multi-epoch observations increase the likelihood of discovering transient or nulling pulsars, or ensure orbital phases are observed at which acceleration search methods work optimally. In ${\sim}147\, {\rm h}$ of separate observations, no previously undiscovered pulsars have been detected. Through calibration observations, we conclude this might be due to insufficient instantaneous sensitivity, caused by the intense continuum emission from the Galactic Centre, its large distance, and, at higher frequencies, the aggregate effect of steep pulsar spectral indices and atmospheric contributions to the system temperature. Additionally, we find that for millisecond pulsars in wide circular orbits $({\lesssim}800\, {\rm d})$ around Sagittarius A*, linear acceleration effects cannot be fully corrected in deep observations $(9\, {\rm h})$ with existing software tools. Pulsar searches of the Galactic Centre with the next generation of radio telescopes – such as MeerKat, ngVLA, and SKA1-mid – will have improved chances of uncovering this elusive population.