arXiv subjects

A. Corongiu

Publications and source records attributed to A. Corongiu.

42 records · Page 3Linked to original sources

arXiv2006

The binary pulsar PSR J1811-1736: evidence of a low amplitude supernova kick

Aims: The binary pulsar PSR J1811-1736 has been identified, since its discovery, as a member of a double neutron star system. Observations of such binary pulsars allow the measurement of general relativistic effects, which in turn lead to information about the orbiting objects and, in a few cases, to tests of theories of gravity. Methods: Regular timing observations have been carried out with three of the largest European radio telescopes involved in pulsar research. The prospects of continued observations were studied with simulated timing data. Pulse scattering times were measured using dedicated observations at 1.4 GHz and at 3.1 GHz, and the corresponding spectral index has also been determined. The possibility of detecting the yet unseen companion as a radio pulsar was also investigated. A study of the natal kick received by the younger neutron star at birth was performed. Results: We present an up to date and improved timing solution for the binary pulsar PSR J1811-1736. One post-Keplerian parameter, the relativistic periastron advance, is measured and leads to the determination of the total mass of this binary system. The pulse profile at 1.4 GHz is heavily broadened by interstellar scattering, limiting the timing precision achievable at this frequency and the measurability of other post-keplerian parameters. Interstellar scattering is unlikely to be the reason for the continued failure to detect radio pulsations from the companion of PSR J1811-1736. The probability distribution that we derive for the amplitude of the kick imparted on the companion neutron star at its birth indicates that the kick has been of low amplitude.

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arXiv2006

Timing of millisecond pulsars in NGC 6752 - II. Proper motions of the pulsars in the cluster outskirts

Exploiting a five-year span of data, we present improved timing solutions for the five millisecond pulsars known in the globular cluster NGC 6752. They include proper motion determinations for the two outermost pulsars in the cluster, PSR J1910-5959A and PSR J1910-5959C. The values of the proper motions are in agreement with each other within current uncertainties, but do not match (at 4 sigma and 2 sigma level respectively) with the value of the proper motion of the entire globular cluster derived in the optical band. Implications of these results for the cluster membership of the two pulsars are investigated. Prospects for the detection of the Shapiro delay in the binary system J1910-5959A are also discussed.

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arXiv2006

The Parkes multibeam pulsar survey: VI. Discovery and timing of 142 pulsars and a Galactic population analysis

[ABRIDGED] We present the discovery and follow-up observations of 142 pulsars found in the Parkes 20-cm multibeam pulsar survey of the Galactic plane. These new discoveries bring the total number of pulsars found by the survey to 742. In addition to tabulating spin and astrometric parameters, along with pulse width and flux density information, we present orbital characteristics for 13 binary pulsars which form part of the new sample. Combining these results from another recent Parkes multibeam survey at high Galactic latitudes, we have a sample of 1008 normal pulsars which we use to carry out a determination of their Galactic distribution and birth rate. We infer a total Galactic population of 30000 +/- 1100 potentially detectable pulsars (i.e. those beaming towards us) having 1.4-GHz luminosities above 0.1 mJy kpc squared. Using a pulsar current analysis, we derive the birth rate of this population to be 1.4 +/- 0.2 pulsars per century. An important conclusion from our work is that the inferred radial density function of pulsars depends strongly on the assumed distribution of free electrons in the Galaxy. As a result, any analyses using the most recent electron model of Cordes & Lazio predict a dearth of pulsars in the inner Galaxy. We show that this model can also bias the inferred pulsar scale height with respect to the Galactic plane. Combining our results with other Parkes multibeam surveys we find that the population is best described by an exponential distribution with a scale height of 330 pc.

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arXiv2003

Three Binary Millisecond Pulsars in NGC 6266

We present rotational and astrometric parameters of three millisecond pulsars located near the center of the globular cluster NGC 6266 (M62) resulting from timing observations with the Parkes radio telescope. Their accelerations toward the cluster center yield values of the cluster central density and mass-to-light ratio consistent with those derived from optical data. The three pulsars are in binary systems. One (spin period P=5.24 ms) is in a 3.5-day orbit around a companion of minimum mass 0.2 Msun. The other two millisecond pulsars (P=3.59 ms and 3.81 ms) have shorter orbital periods (3.4 hr and 5.0 hr) and lighter companions (minimum mass 0.12 Msun and 0.07 Msun respectively). The pulsar in the closest system is the fifth member of an emerging class of millisecond pulsars displaying irregular radio eclipses and having a relatively massive companion. This system is a good candidate for optical identification of the companion star. The lack of known isolated pulsars in NGC 6266 is also discussed.

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arXiv2003

The X-ray spectrum of the black hole candidate GX339-4 in a low state

We report on four observations of the black hole candidate GX 339-4 collected in the spectral range 0.4-140 keV with the BeppoSAX satellite during 1997. All our spectra are typical of a black hole candidate in its low-hard state, i.e. are dominated by the hard tail of the emission from the corona. Although the direct emission from the accretion disk in the soft X-ray range is weak, spectra are well described only with models that take into consideration the Compton reflection of hard X-rays from the corona onto the surface of an accretion disk of non negligible extent.

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arXiv2000

Broad-band X-ray spectra of the persistent black hole candidates LMC X-1 and LMC X-3

We report on observations of the two persistent black hole candidates LMC X-3 and LMCX-1 performed with \BS in October 1997. The flux of LMC X-1 was possibly measured up to 60 keV, but there is a possible confusion with PSR 0540-69. Fits with an absorbed multicolor disk black body are not satisfactory, while the superposition of this model with a power law is acceptable. The sources showed little variations during the observations. However in LMC X-1 some X-ray color dependence on intensity is apparent, indicating a hardening of the spectrum in the second half of the observation. The inner disk radius and temperature change, featuring the same (anti)correlation found in {\it RXTE} data (Wilms et al. 2000). QPOs were searched for. In LMC X-3 none was detected; in LMCX-1 a 3 sigma upper (9% rms) limit is given at 0.07 Hz, the frequency of the QPO discovered with Ginga.

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