ABSTRACT
Superluminous supernovae (SLSNe) and long gamma-ray bursts (LGRBs) have been proposed as progenitors of repeating fast radio bursts (FRBs). In this scenario, bursts originate from the ...interaction between a young magnetar and its surrounding supernova remnant (SNR). Such a model could explain the repeating, apparently non-Poissonian nature of FRB121102, which appears to display quiescent and active phases. This bursting behaviour is better explained with a Weibull distribution, which includes parametrization for clustering. We observed 10 SLSNe/LGRBs for 63 h, looking for repeating FRBs with the Effelsberg 100-m radio telescope, but have not detected any bursts. We scale the burst rate of FRB121102 to an FRB121102-like source inhabiting each of our observed targets, and compare this rate to our upper burst rate limit on a source by source basis. By adopting a fiducial beaming fraction of 0.6, we obtain 99.99 per cent and 83.4 per cent probabilities that at least one, and at least half of our observed sources are beamed towards us, respectively. One of our SLSN targets, PTF10hgi, is coincident with a persistent radio source, making it a possible analogue to FRB121102. We performed further observations on this source using the Effelsberg 100-m and Parkes 64-m radio telescopes. Assuming that PTF10hgi contains an FRB121102-like source, the probabilities of not detecting any bursts from a Weibull distribution during our observations are 14 per cent and 16 per cent for Effelsberg and Parkes, respectively. We conclude by showing that a survey of many short observations increases burst detection probability for a source with Weibull distributed bursting activity.
We report on the setup and initial discoveries of the Northern High Time Resolution Universe survey for pulsars and fast transients, the first major pulsar survey conducted with the 100-m Effelsberg ...radio telescope and the first in 20 years to observe the whole northern sky at high radio frequencies. Using a newly developed 7-beam receiver system combined with a state-of-the-art polyphase filterbank, we record an effective bandwidth of 240 MHz in 410 channels centred on 1.36 GHz with a time resolution of 54 μs. Such fine time and frequency resolution increases our sensitivity to millisecond pulsars and fast transients, especially deep inside the Galaxy, where previous surveys have been limited due to intrachannel dispersive smearing. To optimize observing time, the survey is split into three integration regimes dependent on Galactic latitude, with 1500, 180 and 90-s integrations for latitude ranges |b| < 3
5, |b| < 15° and |b| > 15°, respectively. The survey has so far resulted in the discovery of 15 radio pulsars, including a pulsar with a characteristic age of ∼18 kyr, PSR J2004+3429, and a highly eccentric, binary millisecond pulsar, PSR J1946+3417. All newly discovered pulsars are timed using the 76-m Lovell radio telescope at the Jodrell Bank Observatory and the Effelsberg radio telescope. We present timing solutions for all newly discovered pulsars and discuss potential supernova remnant associations for PSR J2004+3429.
ABSTRACT
Using data from the Large European Array for Pulsars, and the Effelsberg telescope, we study the scintillation parameters of the millisecond pulsar PSR J0613−0200 over a 7 yr timespan. The ...‘secondary spectrum’ – the 2D power spectrum of scintillation – presents the scattered power as a function of time delay, and contains the relative velocities of the pulsar, observer, and scattering material. We detect a persistent parabolic scintillation arc, suggesting scattering is dominated by a thin, anisotropic region. The scattering is poorly described by a simple exponential tail, with excess power at high delays; we measure significant, detectable scattered power at times out to ${\sim}5 \, \mu {\rm s}$, and measure the bulk scattering delay to be between 50 to 200 ns with particularly strong scattering throughout 2013. These delays are too small to detect a change of the pulse profile shape, yet they would change the times of arrival as measured through pulsar timing. The arc curvature varies annually, and is well fitted by a one-dimensional scattering screen ${\sim}40{{\ \rm per\ cent}}$ of the way towards the pulsar, with a changing orientation during the increased scattering in 2013. Effects of uncorrected scattering will introduce time delays correlated over time in individual pulsars, and may need to be considered in gravitational wave analyses. Pulsar timing programmes would benefit from simultaneously recording in a way that scintillation can be resolved, in order to monitor the variable time delays caused by multipath propagation.
ABSTRACT
We 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.
The stability of radio millisecond pulsars as celestial clocks allows for the possibility to detect and study the properties of gravitational waves (GWs) when the received pulses are timed jointly in ...a 'Pulsar Timing Array' (PTA) experiment. Here, we investigate the potential of detecting the GW from individual binary black hole systems using PTAs and calculate the accuracy for determining the GW properties. This is done in a consistent analysis, which at the same time accounts for the measurement of the pulsar distances via the timing parallax.
We find that, at low redshift, a PTA is able to detect the nano-hertz GW from super-massive black hole binary systems with masses of ∼108-1010 M⊙ less than ∼105 yrs before the final merger. Binaries with more than ∼103-104 yr before merger are effectively monochromatic GW, and those with less than ∼103-104 yr before merger may allow us to detect the evolution of binaries.
For our findings, we derive an analytical expression to describe the accuracy of a pulsar distance measurement via timing parallax. We consider 5 yr of bi-weekly observations at a precision of 15 ns for close-by (∼0.5-1 kpc) pulsars. Timing 20 pulsars would allow us to detect a GW source with an amplitude larger than 5 × 10−17. We calculate the corresponding GW and binary orbital parameters and their measurement precision. The accuracy of measuring the binary orbital inclination angle, the sky position and the GW frequency is calculated as functions of the GW amplitude. We note that the 'pulsar term', which is commonly regarded as noise, is essential for obtaining an accurate measurement for the GW source location.
We also show that utilizing the information encoded in the GW signal passing the Earth also increases the accuracy of pulsar distance measurements. If the GW is strong enough, one can achieve sub-parsec distance measurements for nearby pulsars with distance less than ∼0.5-1 kpc.
ABSTRACT
The shape and polarization properties of the radio pulse profiles of radio-loud magnetars provide a unique opportunity to investigate their magnetospheric properties. Gaussian process ...regression analysis was used to investigate the variation in the total intensity shape of the radio pulse profiles of the magnetar Swift J1818.0–1607. The observed profile shape was found to evolve through three modes between MJDs 59104 and 59365. The times at which these transitions occurred coincided with changes in the amplitude of modulations in the spin-down rate. The amount of linear and circular polarization was also found to vary significantly with time. Lomb–Scargle periodogram analysis of the spin-down rate revealed three possibly harmonically related frequencies. This could point to the magnetar experiencing seismic activity. However, no profile features exhibited significant periodicity, suggesting no simple correlations between the profile variability and fluctuations of the spin-down on shorter time-scales within the modes. Overall, this implies that the mode changes seen are a result of local magnetospheric changes, with other theories, such as precession, less able to explain these observations.
ABSTRACT
In this work, we study variations in the parabolic scintillation arcs of the binary millisecond pulsar PSR J1643−1224 over five years using the Large European Array for Pulsars (LEAP). The ...two-dimensional (2D) power spectrum of scintillation, called the secondary spectrum, often shows a parabolic distribution of power, where the arc curvature encodes the relative velocities and distances of the pulsar, ionized interstellar medium, and Earth. We observe a clear parabolic scintillation arc, which varies in curvature throughout the year. The distribution of power in the secondary spectra is inconsistent with a single scattering screen, which is fully 1D or entirely isotropic. We fit the observed arc curvature variations with two models: an isotropic scattering screen and a model with two independent 1D screens. We measure the distance to the scattering screen to be in the range 114–223 pc, depending on the model, consistent with the known distance of the foreground large-diameter H ii region Sh 2-27 (112 ± 17 pc), suggesting that it is the dominant source of scattering. We obtain only weak constraints on the pulsar’s orbital inclination and longitude of ascending node, since the scintillation pattern is not very sensitive to the pulsar’s motion and the screen is much closer to the Earth than the pulsar. More measurements of this kind – where scattering screens can be associated with foreground objects – will help to inform the origins and distribution of scattering screens within our galaxy.
We report on simultaneous observations of the magnetar SGR J1745−2900 at frequencies ν = 2.54–225 GHz using the Nançay 94-m equivalent, Effelsberg 100-m, and IRAM 30-m radio telescopes. We detect SGR ...J1745−2900 up to 225 GHz, the highest radio frequency detection of pulsed emission from a neutron star to date. Strong single pulses are also observed from 4.85 up to 154 GHz. At the millimetre band we see significant flux density and spectral index variabilities on time scales of tens of minutes, plus variability between days at all frequencies. Additionally, SGR J1745−2900 was observed at a different epoch at frequencies ν = 296–472 GHz using the APEX 12-m radio telescope, with no detections. Over the period MJD 56859.83-56862.93 the fitted spectrum yields a spectral index of 〈α〉 = −0.4 ± 0.1 for a reference flux density 〈S
154〉 = 1.1 ± 0.2 mJy (with S
ν ∝ να), a flat spectrum alike those of the other radio-loud magnetars. These results show that strongly magnetized neutron stars can be effective radio emitters at frequencies notably higher to what was previously known and that pulsar searches in the Galactic Centre are possible in the millimetre band.
Crab giant pulses at low frequencies Karuppusamy, R.; Stappers, B. W.; Lee, K. J.
Astronomy and astrophysics (Berlin),
02/2012, Letnik:
538
Journal Article
Recenzirano
Odprti dostop
We report observations of the Crab pulsar at frequencies in the range of 110–180 MHz. The combination of coherent dedispersion and the narrow synthesised beam of the Westerbork Synthesis Radio ...Telescope resulted in a sensitive observation. Our improved sensitivity and resolution allow us to confirm the presence of a precursor to the interpulse at these frequencies. We also detected more than 1000 giant pulses and find that the interpulse precursor component shows no giant pulse emission. Therefore, we attribute it to a similar emission source as the precursor to the mainpulse. Together these precursors might be the normal emission seen from the majority of radio pulsars. From the dispersion-free giant pulses, we find that the emission rate is ~10–20 × 10-3 s-1 and the scatter timescale in the range of ~1.5–5.6 ms. We further find that the radio flux of the pulsar is 6–11 Jy in this frequency range.
Abstract
We report the discovery and the results of follow-up timing observations of PSR J2045+3633 and PSR J2053+4650, two binary pulsars found in the Northern High Time Resolution Universe pulsar ...survey being carried out with the Effelsberg radio telescope. Having spin periods of 31.7 and 12.6 ms, respectively, and both with massive white dwarf companions, M
c > 0.8 M⊙, the pulsars can be classified as mildly recycled. PSR J2045+3633 is remarkable due to its orbital period (32.3 d) and eccentricity e = 0.017 212 44(5), which is amongst the largest ever measured for this class. After almost two years of timing, the large eccentricity has allowed the measurement of the rate of advance of periastron at the 5σ level, 0.0010(2)°yr− 1. Combining this with a detection of the orthometric amplitude of the Shapiro delay, we obtained the following constraints on the component masses (within general relativity):
$M_{\text{p}}\, = \, 1.33^{+0.30}_{-0.28}\, \mathrm{M}_{{\odot }}$
; and
$M_{\text{c}}\, = \, 0.94^{+0.14}_{-0.13}\, \mathrm{M}_{{\odot }}$
. PSR J2053+4650 has a 2.45 d circular orbit inclined to the plane of the sky at an angle
$i\, = \, 85.0^{+0.8}_{-0.9}\,{\rm deg}$
. In this nearly edge-on case the masses can be obtained from the Shapiro delay alone. Our timing observations resulted in a significant detection of this effect giving:
$M_{\text{p}}\, = \, 1.40^{+0.21}_{-0.18}\, \mathrm{M}_{{\odot }}$
; and
$M_{\text{c}}\, = \, 0.86^{+0.07}_{-0.06}\, \mathrm{M}_{{\odot }}$
.
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