ABSTRACT
We report the results of an observational campaign using the Effelsberg 100-m telescope of the pulsars J1746−2849, J1746−2850, J1746−2856, and J1745−2912 located in the central molecular ...zone (CMZ) close to the Galactic Centre in order to study rotation measure (RM) variations. We report for the first time the RM value of PSR J1746−2850 to be −12234 ± 181 rad m−2. This pulsar shows significant variations of RM of 300–400 rad m−2 over the course of months to years that suggest a strongly magnetized environment. The structure function analysis of the RM of PSR J1746−2850 revealed a steep power-law index of $1.87_{-0.3}^{+0.4}$ comparable to the value expected for isotropic turbulence. This pulsar also showed large dispersion measure (DM) variation of ∼50 pc cm−3 in an event lasting a few months where the RM increased by ∼200 rad m−2. The large difference in RM between PSR J1746−2849 and PSR J1746−2850 despite the small angular separation reveals the presence of a magnetic field of at least 70 μG in the CMZ and can explain the lack of polarization in the radio images of the region. These results contribute to our understanding of the magnetic field in the CMZ and show similarities between the RM behaviours of these pulsars and some fast radio bursts.
In 2015, Torne et al. reported detections of the magnetar SGR J1745-2900 up to 225 GHz (1.33 mm), which was the highest radio frequency detection of pulsar emission at that time. In this work, we ...present the results of new observations of the same magnetar with detections up to 291 GHz (1.03 mm), together with evidence of linear polarization in its millimetre emission. SGR J1745-2900 continues to show variability and is, on average, a factor ~4 brighter in the millimetre band than in our observations of 2014 July. The new measured spectrum is slightly inverted, with ... However, the spectrum does not seem to be well described by a single power law, which might be due to the intrinsic variability of the source, or perhaps a turn-up somewhere between 8.35 and 87 GHz. These results may help us to improve our still incomplete model of pulsar emission and, in addition, they further support the search for and study of pulsars located at the Galactic Centre using millimetre wavelengths. (ProQuest: ... denotes formulae/symbols omitted.)
We report the discovery of nine previously unknown gamma-ray pulsars in a blind search of data from the Fermi Large Area Telescope (LAT). The pulsars were found with a novel hierarchical search ...method originally developed for detecting continuous gravitational waves from rapidly rotating neutron stars. Designed to find isolated pulsars spinning at up to kHz frequencies, the new method is computationally efficient and incorporates several advances, including a metric-based gridding of the search parameter space (frequency, frequency derivative, and sky location) and the use of photon probability weights. The nine pulsars have spin frequencies between 3 and 12 Hz, and characteristic ages ranging from 17 kyr to 3 Myr. Two of them, PSRs J1803-2149 and J2111+ 4606, are young and energetic Galactic-plane pulsars (spin-down power above 6 x 10 super(35) erg s super(-1) and ages below 100 kyr). The seven remaining pulsars, PSRs J0106+4855, J0622+3749, J1620-4927, J1746-3239, J2028+3332, J2030+4415, and J2139+4716, are older and less energetic; two of them are located at higher Galactic latitudes (b > 10degrees). PSR J0106+4855 has the largest characteristic age (3 Myr) and the smallest surface magnetic field (2 x 10 super(11) G) of all LAT blind-search pulsars. PSR J2139+4716 has the lowest spin-down power (3 x 10 super(33) erg s super(-1)) among all non-recycled gamma-ray pulsars ever found. Despite extensive multi-frequency observations, only PSR JO 106+4855 has detectable pulsations in the radio band. The other eight pulsars belong to the increasing population of radio-quiet gamma-ray pulsars.
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.
Using the 100-m Effelsberg radio telescope operating at 1.36 GHz, we have performed a targeted radio pulsar survey of 289 unassociated γ-ray sources discovered by the Large Area Telescope (LAT) ...aboard the Fermi satellite and published in the 1FGL catalogue (Abdo et al. 2010a). This survey resulted in the discovery of millisecond pulsar J1745+1017, which resides in a short-period binary system with a low-mass companion,
, indicative of 'black widow' type systems. A 2-yr timing campaign has produced a refined radio ephemeris, accurate enough to allow for phase-folding of the LAT photons, resulting in the detection of a dual-peaked γ-ray light curve, proving that PSR J1745+1017 is the source responsible for the γ-ray emission seen in 1FGL J1745.5+1018 (2FGL J1745.6+1015; Nolan et al. 2012). We find the γ-ray spectrum of PSR J1745+1017 to be well modelled by an exponentially cut-off power law with cut-off energy 3.2 GeV and photon index 1.6. The observed sources are known to contain a further 10 newly discovered pulsars which were undetected in this survey. Our radio observations of these sources are discussed and in all cases limiting flux densities are calculated. The reasons behind the seemingly low yield of discoveries are also discussed.
Modern pulsar surveys produce many millions of candidate pulsars, far more than can be individually inspected. Traditional methods for filtering these candidates, based upon the signal-to-noise ratio ...of the detection, cannot easily distinguish between interference signals and pulsars. We have developed a new method of scoring candidates using a series of heuristics which test for pulsar-like properties of the signal. This significantly increases the sensitivity to weak pulsars and pulsars with periods close to interference signals. By applying this and other techniques for ranking candidates from a previous processing of the Parkes Multi-beam Pulsar Survey, 28 previously unknown pulsars have been discovered. These include an eccentric binary system and a young pulsar which is spatially coincident with a known supernova remnant.
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BFBNIB, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
We present temporal scattering measurements of single pulses and average profiles of PSR J1745-2900, a magnetar recently discovered only 3 arcsec away from Sagittarius A* (Sgr A*), from 1.2 to 18.95 ...GHz using the Effelsberg 100 m Radio Telescope, the Nancay Decimetric Radio Telescope, and the Jodrell Bank Lovell Telescope. Single pulse analysis shows that the integrated pulse profile above 2 GHz is dominated by pulse jitter, while below 2 GHz the pulse profile shape is dominated by scattering. This is the first object in the Galactic center (GC) with both pulse broadening and angular broadening measurements. We measure a pulse broadening time scale at 1 GHz of tau sub(1GHz) = 1.3 + or - 0.2 and pulse broadening spectral index of alpha = -3.8 + or - 0.2, which is several orders of magnitude lower than predicted by the NE2001 model (Cordes & Lazio 2002). If this scattering time scale is representative of the GC as a whole, then previous surveys should have detected many pulsars. The lack of detections implies either our understanding of scattering in the GC is incomplete or there are fewer pulsars in the GC than previously predicted. Given that magnetars are a rare class of radio pulsar, there are likely many canonical and millisecond pulsars in the GC, and not surprisingly, scattering in the GC is spatially complex.
ABSTRACT
We report on the latest six pulsars discovered through our standard pipeline in the intermediate-latitude region (|b| < 15°) of the Parkes High Time Resolution Universe Survey (HTRU). We ...also present timing solutions for the new discoveries and for 19 further pulsars for which only discovery parameters were previously published. Highlights of the presented sample include the isolated millisecond pulsar J1826−2415, the long-period binary pulsar J1837−0822 in a mildly eccentric 98-d orbit with a >0.27 M⊙ companion, and the nulling pulsar J1638−4233, detected only 10 per cent of the time. Other interesting objects are PSR J1757−1500, exhibiting sporadic mode changes, and PSR J1635−2616 showing one glitch over 6 yr. The new discoveries bring the total count of HTRU intermediate-latitude pulsars to 113, 25 per cent of which are recycled pulsars. This is the highest ratio of recycled over ordinary pulsars discoveries of all recent pulsar surveys in this region of the sky. Among HTRU recycled pulsars, four are isolated objects. Comparing the characteristics of Galactic fully recycled isolated MSPs with those of eclipsing binaries (‘spiders’), from which the former are believed to have formed, we highlight a discrepancy in their spatial distribution. This may reflect a difference in the natal kick, hence, possibly, a different formation path. On the other hand, however, isolated fully recycled MSPs spin periods are, on average, longer than those of spiders, in line with what one would expect, from simple magnetic-dipole spin-down, if the former were indeed evolved from the latter.
We report the discovery of PSR J1753−2240 in the Parkes Multibeam Pulsar Survey data base. This 95-ms pulsar is in an eccentric binary system with a 13.6-d orbital period. Period derivative ...measurements imply a characteristic age in excess of 1 Gyr, suggesting that the pulsar has undergone an episode of accretion-induced spin-up. The eccentricity and spin period are indicative of the companion being a second neutron star, so that the system is similar to that of PSR J1811−1736, although other companion types cannot be ruled out at this time. The companion mass is constrained by geometry to lie above 0.48 solar masses, although long-term timing observations will give additional constraints. If the companion is a white dwarf or a main-sequence star, optical observations may yield a direct detection of the companion. If the system is indeed one of the few known double neutron star systems, it would lie significantly far from the recently proposed spin-period/eccentricity relationship.
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