arXiv subjects

Paulo C. C. Freire

Publications and source records attributed to Paulo C. C. Freire.

78 records · Page 5Linked to original sources

arXiv2005

The Millisecond Pulsars in NGC 6760

We present the results of recent Arecibo and Green Bank observations of the globular cluster NGC 6760. Using Arecibo, a phase-coherent timing solution has been obtained for the previously known binary pulsar in this cluster, PSR J1911+0102A. We have also discovered a new millisecond pulsar in NGC 6760, PSR J1911+0101B, an isolated object with a rotational period of 5.38 ms and a dispersion measure DM = 196.7 cm-3 pc. Both pulsars are located within 1.3 core radii of the cluster center and have negative period derivatives. The resulting lower limits for the accelerations of the pulsars are within the range expected given a simple model of the cluster. A search for eclipses in the PSR J1911+0102A binary system using both telescopes yielded negative results. The corresponding limits on the extra gas column density at superior conjunction are consistent with the hypothesis that the observational properties of ultra-low-mass binary pulsars like PSR J1911+0102A are strongly affected by the inclination of the orbital plane of the system. Among globular cluster pulsar populations, that of NGC 6760 exhibits one of the largest known spreads in DM. This quantity seems to be roughly proportional to a cluster's central DM; this suggests that the observed spread is caused by a turbulent interstellar medium at spatial scales of 1 pc.

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arXiv2005

Twenty-One Millisecond Pulsars in Terzan 5 Using the Green Bank Telescope

We have discovered 21 millisecond pulsars (MSPs) in the globular cluster Terzan 5 using the Green Bank Telescope, bringing the total of known MSPs in Terzan 5 to 24. These discoveries confirm fundamental predictions of globular cluster and binary system evolution. Thirteen of the new MSPs are in binaries, of which two show eclipses and two have highly eccentric orbits. The relativistic periastron advance for the two eccentric systems indicates that at least one of these pulsars has a mass >1.68 Msun at 95% confidence. Such large neutron star masses constrain the equation of state of matter at or beyond the nuclear equilibrium density.

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arXiv2004

Eclipsing Binary Pulsars

The first eclipsing binary pulsar, PSR B1957+20, was discovered in 1987. Since then, 13 other eclipsing low-mass binary pulsars have been found, 12 of these are in globular clusters. In this paper we list the known eclipsing binary pulsars and their properties, with special attention to the eclipsing systems in 47 Tuc. We find that there are two fundamentally different groups of eclipsing binary pulsars; separated by their companion masses. The less massive systems (M_c ~ 0.02 M_sun) are a product of predictable stellar evolution in binary pulsars. The systems with more massive companions (M_c ~ 0.2 M_sun) were formed by exchange encounters in globular clusters, and for that reason are exclusive to those environments. This class of systems can be used to learn about the neutron star recycling fraction in the globular clusters actively forming pulsars. We suggest that most of these binary systems are undetectable at radio wavelengths.

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arXiv2004

A 20 cm Search for Pulsars in Globular Clusters with Arecibo and the GBT

We are conducting deep searches for radio pulsations at L-band (~ 20cm) towards more than 30 globular clusters using the 305m Arecibo telescope in Puerto Rico and the 100m Green Bank Telescope in West Virginia. With roughly three quarters of our search data analyzed, we have discovered 12 new millisecond pulsars, 11 of which are in binary systems, and at least three of which eclipse. We have timing solutions for several of these systems.

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arXiv2004

PSR J2021+3651: A New Gamma-Ray Pulsar Candidate

The COS B high energy gamma-ray source 2CG 075+00, also known as GeV J2020+3658 or 3EG J2021+3716, has avoided identification with a low energy counterpart for over twenty years. We present a likely identification with the discovery and subsequent timing of a young and energetic pulsar, PSR J2021+3651, with the Wideband Arecibo Pulsar Processor at the Arecibo Observatory. PSR J2021+3651 has a rotation period P = 104ms and Pdot = 9.6 x 10^{-14}, implying a characteristic age T_c = 17kyr and a spin-down luminosity Edot = 3.4 x 10^{36} erg s^{-1}. The pulsar is also coincident with the ASCA source AX J2021.1+3651. The implied luminosity of the associated X-ray source suggests the X-ray emission is dominated by a pulsar wind nebula unresolved by ASCA. The pulsar's unexpectedly high dispersion measure DM = 371 pc cm^{-3} and the d > 10kpc DM distance pose a new question: is PSR J2021+3651 an extremely efficient gamma-ray pulsar at the edge of the Galaxy? This is a question for AGILE and GLAST to answer.

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arXiv2002

PSR J2021+3651: A Young Radio Pulsar Coincident with an Unidentified EGRET Gamma-ray Source

We report on a deep search for radio pulsations toward five unidentified ASCA X-ray sources coincident with EGRET gamma-ray sources. This search has led to the discovery of a young and energetic pulsar using data obtained with the new Wideband Arecibo Pulsar Processor. PSR J2021+3651 is likely associated with the X-ray source AX J2021.1+3651, which in turn is likely associated with the COS B high energy gamma-ray source 2CG 075+00, also known as GeV J2020+3658 or 3EG J2021+3716. PSR J2021+3651 has a rotation period P = 104 ms and P_dot = 9.6x10^{-14}, implying a characteristic age ~17 kyr and a spin-down luminosity E_dot ~ 3.4x10^{36}ergs/s. The dispersion measure DM ~ 371 pc cm^{-3} is by far the highest of any observed pulsar in the Galactic longitude range 55 < l < 80. This DM suggests a distance d > 10 kpc, and a high gamma-ray efficiency of \~15%, but the true distance may be closer if there is a significant contribution to the DM from excess gas in the Cygnus region. The implied luminosity of the associated X-ray source suggests the X-ray emission is dominated by a pulsar wind nebula unresolved by ASCA.

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