0000000000368144
AUTHOR
Andrea Possenti
showing 12 related works from this author
Radio-ejection and bump-related orbital period gap of millisecond binary pulsars
2005
The monotonic increase of the radius of low mass stars during their ascent on the red giant branch halts when they suffer a temporary contraction. This occurs when the hydrogen burning shell reaches the discontinuity in hydrogen content left from the maximum increase in the convective extension, at the time of the first dredge up, and produces a well known "bump" in the luminosity function of the red giants of globular clusters. If the giant is the mass losing component in a binary in which mass transfer occurs on the nuclear evolution time scale, this event produces a temporary stop in the mass transfer, which we will name "bump related" detachment. If the accreting companion is a neutron …
Evolution in Recycling Scenario
2011
The recycling model argues the existence of an evolutionary connection between low mass X-ray binaries and radio millisecond pulsars. The main difficulties which this model finds in predict the parameters of the fully recycled millisecond pulsars, as mass and spin period, can be overcome by the onset of the so-called radio-ejection mechanism. This work is to provide observational support to the radio-ejection mechanism by inspecting the orbital and spin parameters of the known population of fully recycled radio pulsars and compare these with the expectation for the occurrence of this mechanism.
Search for radio pulsations in four Anomalous X-ray Pulsars and discovery of two new pulsars
2006
We report on observations of four southern Anomalous X-ray Pulsars, (1RXS J170849.0-400910, 1E 1048.1-5937, 1E 1841-045 and AX J1845-0258), obtained at 1.4 GHz using the Parkes radio telescope. Radio pulsations from these sources have been searched (i) by directly folding the time series at a number of trial periods centered on the value of the spin rate obtained from the X-ray observations; (ii) by performing a blind search; (iii) using a code sensitive to single dedispersed pulses, in the aim to detect signals similar to those of the recently discovered Rotating RAdio Transients. No evidence for radio pulsations with an upper limit of ~0.1 mJy for any of the four targets has been found. T…
Search for radio pulsations in four anomalous X-ray pulsars and discovery of two new pulsars
2007
We have performed deep searches for radio pulsations from four southern anomalous X-ray pulsars (AXPs) to investigate their physical nature in comparison with the rotation powered pulsars. The data were acquired using the Parkes radio telescope with the 1.4 GHz multibeam receiver. No pulsed emission with periodicity matching the X-ray ephemeris have been found in the observed targets down to a limit of ∼0.1 mJy. A blind search has also been performed on all the 13 beams of the multibeam receiver (the central beam being pointed on the target AXP), leading to the serendipitous discovery of two new radio pulsars and to the further detection of 18 pulsars. Also a search for single dispersed pul…
Neutron Stars with Submillisecond Periods: A Population of High‐Mass Objects?
1999
Fast spinning neutron stars, recycled in low mass binaries, may have accreted a substantial amount of mass. The available relativistic measurements of neutron star masses, all clustering around 1.4 M_sun, however refer mostly to slowly rotating neutron stars which accreted a tiny amount of mass during evolution in a massive binary system. We develop a semi-analytical model for studying the evolution of the spin period P of a magnetic neutron star as a function of the baryonic mass load M_{ac}; evolution is followed down to submillisecond periods and the magnetic field is allowed to decay significantly before the end of recycling. We use different equations of state and include rotational de…
Search for pulsations at high radio frequencies from accreting millisecond X-ray pulsars in quiescence
2010
It is commonly believed that millisecond radio pulsars have been spun up by transfer of matter and angular momentum from a low-mass companion during an X-ray active mass transfer phase. A subclass of low-mass X-ray binaries is that of the accreting millisecond X-ray pulsars, transient systems that show periods of X-ray quiescence during which radio emission could switch on. The aim of this work is to search for millisecond pulsations from three accreting millisecond X-ray pulsars, XTE J1751-305, XTE J1814-338, and SAX J1808.4-3658, observed during their quiescent X-ray phases at high radio frequencies (5 - 8 GHz) in order to overcome the problem of the free-free absorption due to the matter…
Searching for pulsed emission from XTE J0929-314 at high radio frequencies
2009
The aim of this work is to search for radio signals in the quiescent phase of accreting millisecond X-ray pulsars, in this way giving an ultimate proof of the recycling model, thereby unambiguously establishing that accreting millisecond X-ray pulsars are the progenitors of radio millisecond pulsars. To overcome the possible free-free absorption caused by matter surrounding accreting millisecond X-ray pulsars in their quiescence phase, we performed the observations at high frequencies. Making use of particularly precise orbital and spin parameters obtained from X-ray observations, we carried out a deep search for radio-pulsed emission from the accreting millisecond X-ray pulsar XTE J0929-31…
Discovery of 105 Hz coherent pulsations in the ultracompact binary IGR J16597-3704
2018
We report the discovery of X-ray pulsations at 105.2 Hz (9.5 ms) from the transient X-ray binary IGR J16597-3704 using NuSTAR and Swift. The source was discovered by INTEGRAL in the globular cluster NGC 6256 at a distance of 9.1 kpc. The X-ray pulsations show a clear Doppler modulation implying an orbital period of ~46 minutes and a projected semi-major axis of ~5 lt-ms, which makes IGR J16597-3704 an ultra-compact X-ray binary system. We estimated a minimum companion mass of 0.0065 solar masses, assuming a neutron star mass of 1.4 solar masses, and an inclination angle of <75 degrees (suggested by the absence of eclipses or dips in its light-curve). The broad-band energy spectrum of the…
A model to interpret pulse phase shifts in AMXPs: SAX J1808.4-3658 as a proof of concept
2011
Abstract: Observational evidences of erratic 1(st) harmonic pulse phase shifts in accreting millisecond X-ray pulsars pulse phase evolution was reported by several authors. This effect always go together with much more stable 2(nd) harmonics pulse phase delays. Different possible explanations of these phase shifts have been given in literature. But all these interpretations do not explain why the 2(nd) harmonic are more stable than the 1(st) harmonic. The explanation of such a behaviour is of fundamental importance in order to gain an insight on the NS rotational behaviour and to remove the still present interpretative ambiguity on the results of timing analysis. We propose a simple toy-mod…
Dense matter with eXTP
2019
In this White Paper we present the potential of the Enhanced X-ray Timing and Polarimetry (eXTP) mission for determining the nature of dense matter; neutron star cores host an extreme density regime which cannot be replicated in a terrestrial laboratory. The tightest statistical constraints on the dense matter equation of state will come from pulse profile modelling of accretion-powered pulsars, burst oscillation sources, and rotation-powered pulsars. Additional constraints will derive from spin measurements, burst spectra, and properties of the accretion flows in the vicinity of the neutron star. Under development by an international Consortium led by the Institute of High Energy Physics o…
Population synthesis of millisecond and submillisecond pulsars
1998
Known millisecond pulsars have periods longer than 1.558 ms. Recycled in binary systems, neutron stars can attain very short spin periods. In this paper we investigate the expected properties of the millisecond pulsar distribution by simulating synthetic populations under different assumptions for the neutron star equation of state and decay of the magnetic field. We find evidence that a tail in the distribution of millisecond pulsars may exist at periods shorter than those observed.
Accretion in strong field gravity with eXTP
2019
In this paper we describe the potential of the enhanced X-ray Timing and Polarimetry (eXTP) mission for studies related to accretion flows in the strong field gravity regime around both stellar-mass and supermassive black-holes. eXTP has the unique capability of using advanced 'spectral-timing-polarimetry' techniques to analyze the rapid variations with three orthogonal diagnostics of the flow and its geometry, yielding unprecedented insight into the inner accreting regions, the effects of strong field gravity on the material within them and the powerful outflows which are driven by the accretion process.