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TOPIC: Pulsars
Blobrana


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Title: Resolving discrete pulsar spin-down states with current and future instrumentation
Author: B. Shaw, B.W. Stappers, P. Weltevrede

An understanding of pulsar timing noise offers the potential to improve the timing precision of a large number of pulsars as well as facilitating our understanding of pulsar magnetospheres. For some sources, timing noise is attributable to a pulsar switching between two different spin-down rates (\dot{\nu}). Such transitions may be common but difficult to resolve using current techniques. In this work, we use simulations of (\dot{\nu})-variable pulsars to investigate the likelihood of resolving individual (\dot{\nu}) transitions. We inject step-changes in the value of (\dot{\nu}) with a wide range of amplitudes and switching timescales. We then attempt to redetect these transitions using standard pulsar timing techniques. The pulse arrival-time precision and the observing cadence are varied. Limits on (\dot{\nu}) detectability based on the effects such transitions have on the timing residuals are derived. With the typical cadences and timing precision of current timing programs, we find we are insensitive to a large region of \Delta \dot{\nu} parameter space which encompasses small, short timescale switches. We find, where the rotation and emission states are correlated, that using changes to the pulse shape to estimate (\dot{\nu}) transition epochs, can improve detectability in certain scenarios. The effects of cadence on \Delta \dot{\nu} detectability are discussed and we make comparisons with a known population of intermittent and mode-switching pulsars. We conclude that for short timescale, small switches, cadence should not be compromised when new generations of ultra-sensitive radio telescopes are online.

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Blobrana


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Title: Modelling of the gamma-ray pulsed spectra of Geminga, Crab, and Vela with synchro-curvature radiation
Author: Daniele Viganò, Diego F. Torres

Gamma-ray spectra of pulsars have been mostly studied in a phenomenological way, by fitting them to a cut-off power-law function. Here, we analyze a model where pulsed emission comes from synchro-curvature processes in a gap. We calculate the variation of kinetic energy of magnetospheric particles along the gap and the associated radiated spectra, considering an effective particle distribution. We fit the phase-averaged and phase-resolved Fermi-LAT spectra of the three brightest gamma-ray pulsars: Geminga, Crab, and Vela, and constrain the three free parameters we leave free in the model. Our best-fit models well reproduce the observed data, apart from residuals above a few GeV in some cases, range for which the inverse Compton scattering likely becomes the dominant mechanism. In any case, the flat slope at low-energy (\lesssim GeV) seen by Fermi-LAT both in the phase-averaged and phase-resolved spectra of most pulsars, including the ones we studied, requires that most of the detected radiation below ~GeV is produced during the beginning of the particle trajectories, when radiation mostly come from the loss of perpendicular momentum.

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Blobrana


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Discovery of the 1000th Pulsar on the 13th November 1998

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Blobrana


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Title: Recycling Pulsars: spins, masses and ages
Authors: T. M. Tauris, M. Kramer, N. Langer (Bonn Uni./ MPIfR)

Although the first millisecond pulsars (MSPs) were discovered 30 years ago we still do not understand all details of their formation process. Here, we present new results from Tauris, Langer & Kramer (2012) on the recycling scenario leading to radio MSPs with helium or carbon-oxygen white dwarf companions via evolution of low- and intermediate mass X-ray binaries (LMXBs, IMXBs). We discuss the location of the spin-up line in the (P,Pdot)-diagram and estimate the amount of accreted mass needed to obtain a given spin period and compare with observations. Finally, we constrain the true ages of observed recycled pulsars via calculated isochrones in the (P,Pdot)-diagram.

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Blobrana


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Southampton researchers explain how pulsars slow down with age

Researchers at the University of Southampton have developed a model which explains how the spin of a pulsar slows down as the star gets older.
Pulsars rotate at very stable speeds, but slow down as they emit radiation and lose their energy. Professor Nils Andersson and Dr Wynn Ho, from the University of Southampton, have now found a way to predict how this 'slowing' process will develop in individual pulsars.
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Blobrana


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Title: On the nature of Off-pulse emission from pulsars
Authors: Rahul Basu, Dipanjan Mitra, Ramana Athreya

In Basu et al. 2011 we reported the detection of Off-pulse emission from two long period pulsars B0525+21 and B2045-16. The pulsars were observed at a single epoch using the 325 MHz frequency band of the Giant Meterwave Radio Telescope (GMRT). In this paper we report a detailed study of the Off-pulse emission from these two pulsars using multiple observations at two different frequencies, 325 MHz and 610 MHz bands of GMRT. We report detection of Off-pulse emission during each observation and based on the scintillation effects and spectral index of Off-pulse emission we conclude a magnetospheric origin. The magnetospheric origin of Off-pulse emission gives rise to various interesting possibilities about its emission mechanism and raises questions about the structure of the magnetosphere.

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Blobrana


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Title: Pulsar glitches: The crust is not enough
Authors: N. Andersson, K. Glampedakis, W. C. G. Ho, C. M. Espinoza

Pulsar glitches are traditionally viewed as a manifestation of vortex dynamics associated with a neutron superfluid reservoir confined to the inner crust of the star. In this Letter we show that the non-dissipative entrainment coupling between the neutron superfluid and the nuclear lattice leads to a less mobile crust superfluid, effectively reducing the moment of inertia associated with the angular momentum reservoir. Combining the latest observational data for prolific glitching pulsars with theoretical results for the crust entrainment we find that the required superfluid reservoir exceeds that available in the crust. This challenges our understanding of the glitch phenomenon, and we discuss possible resolutions to the problem.

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Title: On Pulsar Distance Measurements and their Uncertainties
Authors: J. P. W. Verbiest, J. M. Weisberg, A. A. Chael, K. J. Lee, D. R. Lorimer

Accurate distances to pulsars can be used for a variety of studies of the Galaxy and its electron content. However, most distance measures to pulsars have been derived from the absorption (or lack thereof) of pulsar emission by Galactic HI gas, which typically implies that only upper or lower limits on the pulsar distance are available. We present a critical analysis of all measured HI distance limits to pulsars and other neutron stars, and translate these limits into actual distance estimates through a likelihood analysis that simultaneously corrects for statistical biases. We also apply this analysis to parallax measurements of pulsars in order to obtain accurate distance estimates and find that the parallax and HI distance measurements are biased in different ways, because of differences in the sampled populations. Parallax measurements typically underestimate a pulsar's distance because of the limited distance to which this technique works and the consequential strong effect of the Galactic pulsar distribution (i.e. the original Lutz-Kelker bias), in HI distance limits, however, the luminosity bias dominates the Lutz-Kelker effect, leading to overestimated distances because the bright pulsars on which this technique is applicable are more likely to be nearby given their brightness.

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Blobrana


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Pulsars: The Universe's Gift to Physics

Pulsars, superdense neutron stars, are perhaps the most extraordinary physics laboratories in the Universe. Research on these extreme and exotic objects already has produced two Nobel Prizes. Pulsar researchers now are poised to learn otherwise-unavailable details of nuclear physics, to test General Relativity in conditions of extremely strong gravity, and to directly detect gravitational waves with a "telescope" nearly the size of our Galaxy.
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Cosmic Vibrations from Neutron Stars

In the collision of neutron stars, the extremely compact remnants of evolved and collapsed stars, two light stars merge to one massive star. The newly-born heavyweight vibrates, sending out characteristic waves in space-time. Model calculations at the Max Planck Institute for Astrophysics now show how such signals can be used to determine the size of neutron stars and how we can learn more about the interior of these exotic objects.
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