arXiv subjects

F. Camilo

Publications and source records attributed to F. Camilo.

278 records · Page 16Linked to original sources

arXiv1998

Upper Limits on Radio Emission from the Young X-ray Pulsars in the Supernova Remnants G11.2-0.3 and N157B

Using the Parkes radio telescope, we have searched for pulsed radio emission from the recently discovered X-ray pulsars AX J1811.5-1926 and PSR J0537-6910 in the supernova remnants G11.2-0.3 and N157B, respectively. We detected no significant pulsed radio emission from these pulsars and have set an upper limit of 0.07 mJy on the 1374 MHz flux from AX J1811.5-1926 and upper limits of 0.18 mJy and 0.06 mJy for the flux from PSR J0537-6910 at 660 MHz and 1374 MHz, respectively. Assuming a power law radio spectral index of 2, these flux limits correspond to luminosity limits at 400 MHz of 20 mJy kpc^2 for AX J1811.5-1926 and 1100 mJy kpc^2 for PSR J0537-6910. Our luminosity limit for AX J1811.5-1926 is lower than the observed luminosities of other young radio pulsars. The upper limit on the luminosity for PSR J0537-6910 in N157B is not significantly constraining due to the large distance to the pulsar. We have also searched for giant radio pulses from both pulsars and have found no convincing candidates.

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arXiv1998

The 69 ms Radio Pulsar Near the Supernova Remnant RCW 103

We report the detection of the radio pulsar counterpart to the 69 ms X-ray pulsar discovered near the supernova remnant RCW 103 (G332.4-0.4). Our detection confirms that the pulsations arise from a rotation-powered neutron star, which we name PSR J1617-5055. The observed barycentric period derivative confirms that the pulsar has a characteristic age of only 8 kyr, the sixth smallest of all known pulsars. The unusual apparent youth of the pulsar and its proximity to a young remnant requires that an association be considered. Although the respective ages and distances are consistent within substantial uncertainties, the large inferred pulsar transverse velocity is difficult to explain given the observed pulsar velocity distribution, the absence of evidence for a pulsar wind nebula, and the symmetry of the remnant. Rather, we argue that the objects are likely superposed on the sky; this is reasonable given the complex area. Without an association, the question of where is the supernova remnant left behind following the birth of PSR J1617-5055 remains open. We also discuss a possible association between PSR J1617-5055 and the gamma-ray source 2CG 333+01. Though an association is energetically plausible, it is unlikely given that EGRET did not detect 2CG 333+01.

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arXiv1998

The characteristics of millisecond pulsar emission: I. Spectra, pulse shapes and the beaming fraction

We have monitored a large sample of millisecond pulsars using the 100-m Effelsberg radio telescope in order to compare their radio emission properties to the slowly rotating population. With some notable exceptions, our findings suggest that the two groups of objects share many common properties. A comparison of the spectral indices between samples of normal and millisecond pulsars demonstrates that millisecond pulsar spectra are not significantly different from those of normal pulsars. There is evidence, however, that millisecond pulsars are slightly less luminous and less efficient radio emitters compared to normal pulsars. We confirm recent suggestions that a diversity exists among the luminosities of millisecond pulsars with the isolated millisecond pulsars being less luminous than the binary millisecond pulsars. There are indications that old millisecond pulsars exhibit somewhat flatter spectra than the presumably younger ones. We present evidence that millisecond pulsar profiles are only marginally more complex than those found among the normal pulsar population. Moreover, the development of the profiles with frequency is rather slow, suggesting very compact magnetospheres. The profile development seems to anti-correlate with the companion mass and the spin period, again suggesting that the amount of mass transfer in a binary system might directly influence the emission properties. The angular radius of radio beams of millisecond pulsars does not follow the scaling predicted from a canonical pulsar model which is applicable for normal pulsars. Instead they are systematically smaller. The smaller inferred luminosity and narrower emission beams will need to be considered in future calculations of the birth-rate of the Galactic population.

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arXiv1998

The characteristics of millisecond pulsar emission: II. Polarimetry

We have made polarimetric monitoring observations of millisecond pulsars visible from the northern hemisphere at 1410 MHz. Their emission properties are compared with those of normal pulsars. Although we demonstrated in paper I that millisecond pulsars exhibit the same flux density spectra and similar profile complexity, our results presented here suggest that millisecond pulsar profiles do not comply with the predictions of classification schemes based on ``normal'' pulsars. The frequency development of a large number of millisecond pulsar profiles is abnormal when compared with the development seen for normal pulsars. Moreover, the polarization characteristics suggest that millisecond-pulsar magnetospheres might not simply represent scaled versions of the magnetospheres of normal pulsars, supporting results of paper I. However, phenomena such as mode-changing activity in both intensity and polarization are recognized here for the first time (e.g., J1730--2304). This suggests that while the basic emission mechanism remains insensitive to rotational period, the conditions that, according to the canonical pulsar model, regulate the radio emission, might be satisfied at different regions in millisecond pulsar magnetospheres. At least three types of model have been proposed to describe the millisecond pulsar magnetospheres. A comparison of the predictions of these models with the observations suggests that individual cases are better explained by different processes. However, we show that millisecond pulsars can be grouped according to common emission properties, a grouping that awaits verification from future multifrequency observations.

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arXiv1998

A search for pulsars in supernova remnants

We have carried out a sensitive search for young pulsars associated with supernova remnants using the 76-m Lovell radio telescope at Jodrell Bank. The observations were made at 606 MHz using a system with a bandwidth of 8 MHz and a set noise temperature on cold sky of about 50 K. The survey targeted 33 remnants in the northern hemisphere and achieved a nominal sensitivity of ~1 mJy in most cases. Two pulsars were discovered in the course of this survey and the known pulsar PSR B1952+29 was detected. The new pulsars, J0215+6218 and J1957+2831, were found during searches of the supernova remnants G132.7+1.3 and G65.1+0.6 respectively. Based on a statistical analysis of the present sample of proposed pulsar-supernova remnant pairs, we conclude that at most 17 associations are likely to be real. We find no strong evidence for a genuine association between either of the two newly discovered pulsars and their target supernova remnants.

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arXiv1997

Measurement of Relativistic Orbital Decay in the PSR B1534+12 Binary System

We have made timing observations of binary pulsar PSR B1534+12 with radio telescopes at Arecibo, Green Bank, and Jodrell Bank. By combining our new observations with data collected up to seven years earlier, we obtain a significantly improved solution for the astrometric, spin, and orbital parameters of the system. For the first time in any binary pulsar system, no fewer than five relativistic or "post-Keplerian" orbital parameters are measurable with useful accuracies in a theory-independent way. We find the orbital period of the system to be decreasing at a rate close to that expected from gravitational radiation damping, according to general relativity, although the precision of this test is limited to about 15% by the otherwise poorly known distance to the pulsar. The remaining post-Keplerian parameters are all consistent with one another and all but one of them have fractional accuracies better than 1%. By assuming that general relativity is the correct theory of gravity, at least to the accuracy demanded by this experiment, we find the masses of the pulsar and companion star each to be 1.339+-0.003 Msun and the system's distance to be d = 1.1+-0.2 kpc, marginally larger than the d ~ 0.7 kpc estimated from the dispersion measure. The increased distance reduces estimates of the projected rate of coalescence of double neutron-star systems in the universe, a quantity of considerable interest for experiments with terrestrial gravitational wave detectors such as LIGO.

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arXiv1996

Timing Measurements and Their Implications for Four Binary Millisecond Pulsars

We present timing observations of four millisecond pulsars, using data obtained over three years at the ATNF Parkes and NRAL Jodrell Bank radio telescopes. Astrometric, spin, and binary parameters are updated, and substantially improved for three pulsars, PSRs J0613-0200, J1045-4509 and J1643-1224. We have measured the time variation of the projected semi-major axis of the PSR J0437-4715 orbit due to its proper motion, and use it to constrain the inclination of the orbit and the mass of the companion. Some evidence is found for changes in the dispersion measures of PSRs J1045-4509 and J1643-1224. Limits are placed on the existence of planetary mass companions, ruling out companions with masses and orbits similar to the terrestrial planets of the solar system for eight pulsars.

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arXiv1995

A Tighter Test of Local Lorentz Invariance using PSR J2317+1439

Gravity being a long-range force, one might {\it a priori} expect the Universe's global matter distribution to select a preferred rest frame for local gravitational physics. The phenomenology of preferred-frame effects, in the strong-gravitational field context of binary pulsars, is described by two parameters $\hatα_1$ and $\hatα_2$. These parameters vanish identically in general relativity, and reduce, in the weak-field limit, to the two parametrized post-Newtonian (PPN) parameters $α_1$ and $α_2$. We derive a limit of $|\hatα_1| < 1.7\times 10^{-4}$ (90\%~C.L.) using the very low eccentricity binary pulsar PSR J2317+1439, improving by a factor of 3 on previous limits.

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