Data analysis of continuous gravitational wave: all-sky search and study of templates

We have studied the problem of an all-sky search in reference to a continuous gravitational wave particularly for such sources whose wave-form are known in advance. We have made an analysis of the number of templates required for matched-filter analysis as applicable to these sources. We have employed the concept of fitting factor (FF); treating the source location as the parameters of the signal manifold and have studied the matching of the signal with templates corresponding to different source locations. We have investigated the variation of FF with source location and have noticed a symmetry in template parameters,  θ_T  and  φ_T  . It has been found that the two different template values in source location, each in  θ_T  and  φ_T  , have the same FF. We have also computed the number of templates required assuming the noise power spectral density   S _n ( f )  to be flat. It is observed that higher FF requires an exponentially increasing, large number of templates.     

A photometric and spectroscopic study of the brightest northern Cepheids — I. Observations

We present simultaneous UBV uvby photometry for the 18 brightest northern Cepheids carried out between 1995 and 1997. Additionally, two fainter stars have been observed in the Johnson system only. The whole photometric data base contains about 3500 individual data points for 20 stars. The accuracy has been carefully tested with different methods. A serious systematic difference has been found between the present data set and the Stro¨mgren photometry available in the literature, which has probably been caused by the peculiar filter set used in the earlier study.   As an extension to the photometry, we took high-resolution optical spectra at David Dunlap Observatory in the red spectral region (λ/Δλ≈ 40 000, in the interval of 6200 and 6600 Å including Hα). The spectroscopic programme contained 12 stars from the photometric programme, the newly discovered bright classical Cepheid CK Cam and two double-mode Cepheids (TU Cas and CO Aur). New radial velocities obtained with the cross-correlation technique are presented. We found significant velocity differences between two cross-correlated spectral regions (6188–6220 and 6405–6435 Å) as large as 0.8–1.2 km s⁻¹, which show very characteristic phase dependence in certain Cepheids.   Finally, recent period variations are briefly discussed in terms of phase jumps and duplicity.     

Optimal filters for the construction of the ensemble pulsar time

An algorithm of the ensemble pulsar time based on the optimal Wiener filtration method has been constructed. This algorithm allows the separation of the contributions to the post-fit pulsar timing residuals of the atomic clock and the pulsar itself. Filters were designed using the cross- and auto-covariance functions of the timing residuals. The method has been applied to the timing data of millisecond pulsars PSR B1855+09 and B1937+21 and allowed the filtering out of the atomic-scale component from the pulsar data. Direct comparison of the terrestrial time TT(BIPM06) and the ensemble pulsar time PT_ens revealed that the fractional instability of TT(BIPM06)−PT_ens is equal to  σ _z = (0.8 ± 1.9) × 10⁻¹⁵  . Based on the  σ _z   statistics of TT(BIPM06)−PT_ens, a new limit of the energy density of the gravitational wave background was calculated to be equal to  Ω_g h ²∼ 3 × 10⁻⁹  .     

The Swinburne intermediate-latitude pulsar survey

We have conducted a survey of intermediate Galactic latitudes using the 13-beam 21-cm multibeam receiver of the Parkes 64-m radio telescope. The survey covered the region enclosed by 5°<| b |<15° and −100°< l <50° with 4702 processed pointings of 265 s each, for a total of 14.5 d of integration time. 13 2×96‐channel filterbanks provided 288 MHz of bandwidth at a centre frequency of 1374 MHz, one-bit sampled every 125 μs and incurring ∼ DM/13.4 cm⁻³ pc samples of dispersion smearing. The system was sensitive to slow and most millisecond pulsars in the region with flux densities greater than approximately 0.3–1.1 mJy . Offline analysis on the 64-node Swinburne workstation cluster resulted in the detection of 170 pulsars of which 69 were new discoveries. Eight of the new pulsars, by virtue of their small spin periods and period derivatives, may be recycled and have been reported elsewhere. The slow pulsars discovered are typical of those already known in the volume searched, being of intermediate to old age. Several pulsars experience pulse nulling and two display very regular drifting subpulses. We discuss the new discoveries and provide timing parameters for the 48 slow pulsars for which we have a phase-connected solution.     

Map making in small field modulated CMB polarization experiments: approximating the maximum likelihood method

Map making presents a significant computational challenge to the next generation of kilopixel cosmic microwave background polarization experiments. Years worth of time ordered data (TOD) from thousands of detectors will need to be compressed into maps of the T , Q and U Stokes parameters. Fundamental to the science goal of these experiments, the observation of B modes, is the ability to control noise and systematics. In this paper, we consider an alternative to the maximum likelihood method, called destriping , where the noise is modelled as a set of discrete offset functions and then subtracted from the time stream. We compare our destriping code (Descart: the DEStriping CARTographer) to a full maximum likelihood mapmaker, applying them to 200 Monte Carlo simulations of TOD from a ground-based, partial-sky polarization modulation experiment. In these simulations, the noise is dominated by either detector or atmospheric  1/ f   noise. Using prior information of the power spectrum of this noise, we produce destriped maps of T , Q and U which are negligibly different from optimal. The method does not filter the signal or bias the E- or B-mode power spectra. Depending on the length of the destriping baseline, the method delivers between five and 22 times improvement in computation time over the maximum likelihood algorithm. We find that, for the specific case of single detector maps, it is essential to destripe the atmospheric  1/ f   in order to detect B modes, even though the Q and U signals are modulated by a half-wave plate spinning at 5 Hz.     

Periodicity search for possible X-ray counterparts to radio-quiet gamma-ray pulsar candidates

A periodicity search of gamma-ray data is usually difficult because of the small number of detected photons. A periodicity in the timing signal at other energy bands from the counterpart to the gamma-ray source may help to establish the periodicity in the gamma-ray emission and strengthen the identification of the source in different energy bands. However, it may still be difficult to find the period directly from X-ray data because of limited exposure. We have developed a procedure, by cross-checking two X-ray data sets, to find candidate periods for X-ray sources that are possible counterparts to gamma-ray pulsar candidates. Here, we report on the results of this method obtained with all the currently available X-ray data of eight X-ray sources. Some attractive periodicity features were found. These candidate periods can serve as the target periods for a future search when new data become available, so that a blind search with a huge number of trials can be avoided.     

Discovery of 10 pulsars in an Arecibo drift-scan survey

We present the results of a 430-MHz survey for pulsars conducted during the upgrade to the 305-m Arecibo radio telescope. Our survey covered a total of 1147 deg² of sky using a drift-scan technique. We detected 33 pulsars, 10 of which were not known prior to the survey observations. The highlight of the new discoveries is PSR J0407+1607, which has a spin period of 25.7 ms, a characteristic age of 1.5 Gyr and is in a 1.8-yr orbit about a low-mass  (>0.2 M_⊙)  companion. The long orbital period and small eccentricity  ( e = 0.0009)  make the binary system an important new addition to the ensemble of binary pulsars suitable to test for violations of the strong equivalence principle. We also report on our initially unsuccessful attempts to detect optically the companion to J0407+1607, which imply that its absolute visual magnitude is >12.1. If, as expected on evolutionary grounds, the companion is an He white dwarf, our non-detection implies a cooling age of least 1 Gyr.     

The energy loss of a rotating magnetized neutron star

The analysis of observations of pulsar B1931+24 shows that the mechanism of the spin-down of a rotating magnetized neutron star is due to the plasma generation in its magnetosphere and, consequently, the radio emission generation. The unique observation of the switch on and switch off of this pulsar allows us to distinguish between the energy loss in the absence of radio emission (the magnetodipole radiation) and the current loss due to the rotation energy expenditure to the relativistic plasma generation and acceleration in the pulsar magnetosphere. The inclination angle χ, the angle between the rotation axis and the magnetic dipole axis, can be stationary for this pulsar,  χ=χ_st  . From observations and theory it follows that  χ_st= 59°  .     

New constraints on a triaxial model of the Galaxy

We determine the most likely values of the free parameters of an N -body model for the Galaxy developed by Fux via a discrete–discrete comparison with the positions on the sky and line-of-sight velocities of an unbiased, homogeneous sample of OH/IR stars. Via Monte Carlo simulation, we find the plausibility of the best-fitting models, as well as the errors on the determined values. The parameters that are constrained best by these projected data are the total mass of the model and the viewing angle of the central bar, although the distribution of the latter has multiple maxima. The other two free parameters, the size of the bar and the (azimuthal) velocity of the Sun, are less well-constrained. The best model has a viewing angle of ∼ 44°, a semimajor axis of 2.5 kpc (corotation radius 4.5 kpc, pattern speed 46 km s⁻¹ kpc⁻¹), a bar mass of 1.7×10¹⁰ M_⊙ and a tangential velocity of the local standard of rest of 171 km s⁻¹. We argue that the lower values that are commonly found from stellar data for the viewing angle (∼25°) arise when too few coordinates are available, when the longitude range is too narrow or when low latitudes are excluded from the fit. The new constraints on the viewing angle of the Galactic bar from stellar line-of-sight velocities decrease further the ability of the distribution of the bar to account for the observed microlensing optical depth toward Baade's window: our model reproduces only half the observed value. The signal of triaxiality diminishes quickly with increasing latitude, fading within approximately 1 scaleheight (≲3°). This suggests that Baade's window is not a very appropriate region in which to sample bar properties.     

The Parkes Multibeam Pulsar Survey: PSR J1811−1736, a pulsar in a highly eccentric binary system

We are undertaking a high-frequency survey of the Galactic plane for radio pulsars, using the 13-element multibeam receiver on the 64-m Parkes radio telescope. We describe briefly the survey system and some of the initial results. PSR J1811−1736, one of the first pulsars discovered with this system, has a rotation period of 104 ms. Subsequent timing observations using the 76-m radio telescope at Jodrell Bank show that it is in an 18.8-d, highly eccentric binary orbit. We have measured the rate of advance of periastron which indicates a total system mass of 2.6±0.9 M_⊙, and the minimum companion mass is about 0.7 M_⊙. This, the high orbital eccentricity and the recycled nature of the pulsar suggest that this system is composed of two neutron stars, only the fourth or fifth such system known in the disc of the Galaxy.     

PSR J1453+1902 and the radio luminosities of solitary versus binary millisecond pulsars

We present 3 yr of timing observations for PSR J1453+1902, a 5.79-ms pulsar discovered during a 430-MHz drift-scan survey with the Arecibo telescope. Our observations show that PSR J1453+1902 is solitary and has a proper motion of  8 ±  2  mas yr⁻¹. At the nominal distance of 1.2 kpc estimated from the pulsar's dispersion measure, this corresponds to a transverse speed of  46 ± 11   km s⁻¹  , typical of the millisecond pulsar population. We analyse the current sample of 55 millisecond pulsars in the Galactic disc and revisit the question of whether the luminosities of isolated millisecond pulsars are different from their binary counterparts. We demonstrate that the apparent differences in the luminosity distributions seen in samples selected from 430-MHz surveys can be explained by small-number statistics and observational selection biases. An examination of the sample from 1400-MHz surveys shows no differences in the distributions. The simplest conclusion from the current data is that the spin, kinematic, spatial and luminosity distributions of isolated and binary millisecond pulsars are consistent with a single homogeneous population.     

Glitch monitoring in PSRs B1046−58 and B1737−30

Large glitches were recently observed in the spin rates of two pulsars, B1046−58 and B1737−30. The glitches were characterized by fractional increases in rotation rate of 0.77 and  1.44×10⁻⁶  respectively. PSR B1737−30 is the most frequently glitching pulsar and this is the largest glitch so far observed from it. Most of the jump in the spin-down rate accompanying these glitches decayed away on short time-scales of a few days. For PSR B1737−30, there appears to be a cumulative shift in spin-down rate resulting from its frequent glitches. This probably accounts for its braking index of  −4±2  suggested by the available data, while a value of  2.1±0.2  is obtained for B1046−58.     

Interstellar holography

The dynamic spectrum of a radio pulsar is an in-line digital hologram of the ionized interstellar medium. It has previously been demonstrated that such holograms permit image reconstruction, in the sense that one can determine an approximation to the complex electric field values as a function of Doppler shift and delay, but to date the quality of the reconstructions has been poor. Here we report a substantial improvement in the method which we have achieved by simultaneous optimization of the thousands of coefficients that describe the electric field. For our test spectrum of PSR B0834+06 we find that the model provides an accurate representation of the data over the full 63 dB dynamic range of the observations: residual differences between model and data are noise like. The advent of interstellar holography enables detailed quantitative investigation of the interstellar radio-wave propagation paths for a given pulsar at each epoch of observation. We illustrate this using our test data which show the scattering material to be structured and highly anisotropic. The temporal response of the medium exhibits a scattering tail which extends to beyond  100 μs  , and the centroid of the pulse at this frequency and this epoch of observation is delayed by approximately  15 μs  as a result of multipath propagation in the interstellar medium.     

Limits on radio emission from pulsar wind nebulae

We report on a sensitive survey for radio pulsar wind nebulae (PWN) towards 27 energetic and/or high-velocity pulsars. Observations were carried out at 1.4 GHz using the Very Large Array and the Australia Telescope Compact Array and utilized pulsar-gating to search for off-pulse emission. These observing parameters resulted in a considerably more sensitive search than previous surveys and could detect PWN over a much wider range of spatial scales (and hence ambient densities and pulsar velocities). However, no emission clearly corresponding to a PWN was discovered. Based on these non-detections we argue that the young and energetic pulsars in our sample have winds which are typical of young pulsars, but produce unobservable PWN because they reside in low-density ( n ∼0.003 cm⁻³) regions of the interstellar medium. However, non-detection of PWN around older and less energetic pulsars can only be explained if the radio luminosity of their winds is less than 10⁻⁵ of their spin-down luminosity, implying an efficiency at least an order of magnitude smaller than that seen for young pulsars.     

The structure of the Galactic bar

We present a deep near-infrared wide-angle photometric analysis of the structure of the inner Galactic bar and central disc. The presence of a triaxial structure at the centre of the Galaxy is confirmed, consistent with a bar inclined at  22°± 55  from the Sun—Galactic Centre line, extending to approximately 2.5 kpc from the Galactic Centre and with a rather small axis ratio. A feature at  ℓ=−98  not aligned with this triaxiality suggests the existence of a second structure in the inner Galaxy, a double triaxiality or an inner ring. We argue that this is likely to be the signature of the end of the Galactic bar, at approximately 2.5–3 kpc, which is circumscribed by an inner pseudo-ring. No thick dust lane preceding the bar is detected and a hole in the dust distribution of the disc inside the bar radius is inferred.     

Contribution to the search for binaries among Am stars – VIII. New spectroscopic orbits of eight systems and statistical study of a sample of 91 Am stars

Red clump giant (RCG) stars can be used as distance indicators to trace the mass distribution of the Galactic bar. We use RCG stars from 44 bulge fields from the OGLE-II microlensing collaboration data base to constrain analytic triaxial models for the Galactic bar. We find the bar major-axis is oriented at an angle of 24°–27° to the Sun–Galactic Centre line-of-sight. The ratio of semimajor and semiminor bar axis scalelengths in the Galactic plane   x ₀, y ₀  , and vertical bar scalelength z ₀, is   x ₀ :  y ₀ :  z ₀= 10 : 3.5 : 2.6  , suggesting a slightly more prolate bar structure than the working model of Gerhard which gives the scalelength ratios as   x ₀ :  y ₀ :  z ₀= 10 : 4 : 3  .     

Statistical studies of pulsar glitches

Shemar & Lyne have previously presented observations and an analysis of 32 glitches and their subsequent relaxations observed in a total of 15 pulsars. These data are brought together in this paper with those published by other authors. We show quantitatively how glitch activity decreases linearly with decreasing rate of slow-down. As indicated previously from studies of the Vela pulsar, the analysis suggests that 1.7 per cent of the moment of inertia of a typical neutron star is normally contained in pinned superfluid which releases its excess angular momentum at the time of a glitch. There is a broad range of glitch amplitude and there is a strong indication that pulsars with large magnetic fields suffer many small glitches while others show a smaller number of large glitches. Transient effects following glitches are very marked in young pulsars and decrease linearly with decreasing rate of slow-down, suggesting that the amount of loosely pinned superfluid decreases with age. We suggest that the low braking index of the Vela and Crab pulsars cannot be caused by a decreasing moment of inertia and should be attributed to step increases in the effective magnetic moment of the neutron star at the glitches.     

Mechanism of generation of the emission bands in the dynamic spectrum of the Crab pulsar

We show that the proportionately spaced emission bands in the dynamic spectrum of the Crab pulsar fit the oscillations of the square of a Bessel function whose argument exceeds its order. This function has already been encountered in the analysis of the emission from a polarization current with a superluminal distribution pattern: a current whose distribution pattern rotates (with an angular frequency ω) and oscillates (with a frequency  Ω > ω  differing from an integral multiple of ω) at the same time. Using the results of our earlier analysis, we find that the dependence on frequency of the spacing and width of the observed emission bands can be quantitatively accounted for by an appropriate choice of the value of the single free parameter  Ω/ω  . In addition, the value of this parameter, thus implied by Hankins & Eilek's data, places the last peak in the amplitude of the oscillating Bessel function in question at a frequency  (∼Ω³/ω²)  that agrees with the position of the observed ultraviolet peak in the spectrum of the Crab pulsar. We also show how the suppression of the emission bands by the interference of the contributions from differing polarizations can account for the differences in the time and frequency signatures of the interpulse and the main pulse in the Crab pulsar. Finally, we put the emission bands in the context of the observed continuum spectrum of the Crab pulsar by fitting this broad-band spectrum (over 16 orders of magnitude of frequency) with that generated by an electric current with a superluminally rotating distribution pattern.     

Timing of the accreting millisecond pulsar XTE J1814−338

We present a precise timing analysis of the accreting millisecond pulsar XTE J1814−338 during its 2003 outburst, observed by RXTE . A full orbital solution is given for the first time; Doppler effects induced by the motion of the source in the binary system were corrected, leading to a refined estimate of the orbital period,   P _orb= 15 388.7229(2)  s, and of the projected semimajor axis,   a sin  i / c = 0.390633(9)  light-second. We could then investigate the spin behaviour of the accreting compact object during the outburst. We report here a refined value of the spin frequency  (ν= 314.356 108 79(1) Hz)  and the first estimate of the spin frequency derivative of this source while accreting     . This spin-down behaviour arises when both the fundamental frequency and the second harmonic are taken into consideration. We discuss this in the context of the interaction between the disc and the quickly rotating magnetosphere, at accretion rates sufficiently low to allow a threading of the accretion disc in regions where the Keplerian velocity is slower than the magnetosphere velocity. We also present indications of a jitter of the pulse phases around the mean trend, which we argue results from movements of the accreting hotspots in response to variations of the accretion rate.     

Timeline analysis and wavelet multiscale analysis of the AKARI All-Sky Survey at 90 μm

We present a careful analysis of the point-source detection limit of the AKARI All-Sky Survey in the WIDE-S 90-μm band near the North Ecliptic Pole (NEP). Timeline analysis is used to detect IRAS ( Infrared Astronomy Satellite ) sources and then a conversion factor is derived to transform the peak timeline signal to the interpolated 90-μm flux of a source. Combined with a robust noise measurement, the point-source flux detection limit at signal-to-noise ratio  (S/N) > 5  for a single detector row is  1.1 ± 0.1 Jy  which corresponds to a point-source detection limit of the survey of ∼0.4 Jy.
Wavelet transform offers a multiscale representation of the Time Series Data ( tsd ). We calculate the continuous wavelet transform of the tsd and then search for significant wavelet coefficients considered as potential source detections. To discriminate real sources from spurious or moving objects, only sources with confirmation are selected. In our multiscale analysis, IRAS sources selected above 4σ can be identified as the only real sources at the Point Source Scales. We also investigate the correlation between the non- IRAS sources detected in timeline analysis and cirrus emission using wavelet transform and contour plots of wavelet power spectrum. It is shown that the non- IRAS sources are most likely to be caused by excessive noise over a large range of spatial scales rather than real extended structures such as cirrus clouds.