arXiv subjects

P. Moran

Publications and source records attributed to P. Moran.

29 records · Page 2Linked to original sources

arXiv2017

Technical Design Report for the Paul Scherrer Institute Experiment R-12-01.1: Studying the Proton "Radius" Puzzle with μp Elastic Scattering

The difference in proton radii measured with $μp$ atoms and with $ep$ atoms and scattering remains an unexplained puzzle. The PSI MUSE proposal is to measure $μp$ and $e p$ scattering in the same experiment at the same time. The experiment will determine cross sections, two-photon effects, form factors, and radii independently for the two reactions, and will allow $μp$ and $ep$ results to be compared with reduced systematic uncertainties. These data should provide the best test of lepton universality in a scattering experiment to date, about an order of magnitude improvement over previous tests. Measuring scattering with both particle polarities will allow a test of two-photon exchange at the sub-percent level, about a factor of four improvement on uncertainties and over an order of magnitude more data points than previous low momentum transfer determinations, and similar to the current generation of higher momentum transfer electron experiments. The experiment has the potential to demonstrate whether the $μp$ and $ep$ interactions are consistent or different, and whether any difference results from novel physics or two-photon exchange. The uncertainties are such that if the discrepancy is real it should be confirmed with $\approx$5$σ$ significance, similar to that already established between the regular and muonic hydrogen Lamb shift.

physics.ins-det↗

arXiv2016

Searching for the optical counterparts of two young gamma-ray pulsars

We report on the first deep optical observations of two $γ$-ray pulsars, both among the very first discovered by the {\em Fermi} Gamma-ray Space Telescope. The two pulsars are the radio-loud PSR\, J1907+0602 in the TeV pulsar wind nebula (PWN) MGRO\, J1908+06 and the radio-quiet PSR\, J1809$-$2332 in the "Taz" radio/X-ray PWN. These pulsars are relatively young and energetic and have been both detected in the X-rays by \xmm, which makes them viable targets for optical observations. We observed the pulsar fields in the B and V bands with the Very Large Telescope (VLT) in June/July 2015 to search for their optical counterparts. Neither of the two pulsars has been detected down to $3σ$ limiting magnitudes of $m_{\rm v} \sim 26.9$ and $m_{\rm v} \sim 27.6$ for PSR\, J1907+0602 and PSR\, J1809$-$2332, respectively. We discuss these results in the framework of the multi-wavelength emission properties of pulsars.

astro-ph.HE↗

arXiv2016

A candidate optical counterpart to the middle-aged gamma-ray pulsar PSR J1741-2054

We carried out deep optical observations of the middle-aged $γ$-ray pulsar PSR J1741-2054 with the Very Large Telescope (VLT). We identified two objects, of magnitudes $m_v=23.10\pm0.05$ and $m_v=25.32\pm0.08$, at positions consistent with the very accurate Chandra coordinates of the pulsar, the faintest of which is more likely to be its counterpart. From the VLT images we also detected the known bow-shock nebula around PSR J1741-2054. The nebula is displaced by $\sim 0\farcs9$ (at the $3σ$ confidence level) with respect to its position measured in archival data, showing that the shock propagates in the interstellar medium consistently with the pulsar proper motion. Finally, we could not find evidence of large-scale extended optical emission associated with the pulsar wind nebula detected by Chandra, down to a surface brightness limit of $\sim 28.1$ magnitudes arcsec$^{-2}$. Future observations are needed to confirm the optical identification of PSR J1741-2054 and characterise the spectrum of its counterpart.

astro-ph.HE↗

arXiv2015

VLT polarimetry observations of PSR B0656+14

Optical polarisation measurements are key tests for different models of the pulsar magnetosphere. Furthermore, comparing the relative orientation of the phase-averaged linear polarisation direction and the pulsar proper motion vector may unveil a peculiar alignment, clearly seen in the Crab pulsar. Our goal is to obtain the first measurement of the phase-averaged optical linear polarisation of the fifth brightest optical pulsar, PSR\, B0656+14, which has also a precisely measured proper motion, and verify a possible alignment between the polarisation direction and the proper motion vector. We carried out observations with the Very Large Telescope (VLT) to measure the phase-averaged optical polarisation degree (P.D.) and position angle (P.A.) of PSR B0656+14. We measured a P.D. of $11.9\%\pm5.5\%$ and a P.A. of $125.8\degr\pm13.2\degr$, measured East of North. Albeit of marginal significance, this is the first measurement of the phase-averaged optical P. D. for this pulsar. Moreover, we found that the P.A. of the phase-averaged polarisation vector is close to that of the pulsar proper motion ($93.12\degr\pm0.38\degr$).Deeper observations are needed to confirm our polarisation measurement of \psr, whereas polarisation measurements for more pulsars will better assess possible correlations of the polarisation degree with the pulsar parameters.

astro-ph.HE↗

arXiv2014

HST optical polarimetry of the Vela pulsar & nebula

Polarisation measurements of pulsars offer an unique insight into the geometry of the emission regions in the neutron star magnetosphere. Therefore, they provide observational constraints on the different models proposed for the pulsar emission mechanisms. Optical polarisation data of the Vela pulsar was obtained from the {\em Hubble Space Telescope} ({\em HST}) archive. The data, obtained in two filters (F606W; central wavelength = 590.70 nm, and F550M; central wavelength = 558.15 nm), consists of a series of observations of the pulsar taken with the {\em HST}/Advanced Camera for Surveys (ACS) and covers a time span of 5 days. This data have been used to carry out the first high-spatial resolution and multi-epoch study of the polarisation of the pulsar. We produced polarisation vector maps of the region surrounding the pulsar and measured the degree of linear polarisation (P.D.) and the position angle (P.A.) of the pulsar's integrated pulse beam. %This yielded We obtained $\rm P.D.=8.1\%\pm0.7\%$ and $\rm P.A.=146.3\degr\pm2.4\degr$, averaged over the time span covered by these observations. These results not only confirm those originally obtained by \citeauthor{Wagner00} and \citeauthor{Mignani07}, both using the Very Large Telescope (VLT), but are of greater precision. Furthermore, we confirm that the P.A. of the pulsar polarisation vector is aligned with the direction of the pulsar proper-motion. The pulsar wind nebula (PWN) is undetected in polarised light as is the case in unpolarised light, down to a flux limit of 26.8 magnitudes arcsec$^{-2}$.

astro-ph.HE↗

arXiv2013

Optical Observations of PSR J0205+6449 - the next optical pulsar?

PSR J0205+6449 is a young ({\approx} 5400 years), Crab-like pulsar detected in radio and at X and γ-ray energies and has the third largest spin-down flux among known rotation powered pulsars. It also powers a bright synchrotron nebula detected in the optical and X-rays. At a distance of {\approx} 3.2 kpc and with an extinction comparable to the Crab, PSR J0205+6449 is an obvious target for optical observations. We observed PSR J0205+6449 with several optical facilities, including 8m class ground-based telescopes, such as the Gemini and the Gran Telescopio Canarias. We detected a point source, at a significance of 5.5σ, of magnitude i {\approx} 25.5, at the centre of the optical synchrotron nebula, coincident with the very accurate Chandra and radio positions of the pulsar. Thus, we discovered a candidate optical counterpart to PSR J0205+6449. The pulsar candidate counterpart is also detected in the g ({\approx}27.4) band and weakly in the r ({\approx}26.2) band. Its optical spectrum is fit by a power law with photon index Γ0 = 1.9{\pm}0.5, proving that the optical emission if of non-thermal origin, is as expected for a young pulsar. The optical photon index is similar to the X-ray one (ΓX = 1.77{\pm}0.03), although the optical fluxes are below the extrapolation of the X-ray power spectrum. This would indicate the presence of a double spectral break between the X-ray and optical energy range, at variance with what is observed for the Crab and Vela pulsars, but similar to the Large Magellanic Cloud pulsar PSR B0540-69.

astro-ph.HE↗

arXiv2011

VLT observations of Fermi pulsars

Many energetic gamma-ray pulsars discovered by Fermi are promising candidates for optical follow-ups. We present the results of the first deep optical observations of the two Vela-like Fermi pulsars PSR J1357-6429 and PSR J1048-5832 performed with the VLT. However, they have not been detected down to V~27 and V~27.6, respectively (3 sigma). These upper limits suggest an efficiency in converting spin-down power into optical luminosity < 7x10d-7 and <6x10d-6, respectively, lower than the Crab pulsar and, possibly, more compatible with the spin-down age of these two pulsars.

astro-ph.HE↗

arXiv2011

VLT observations of the two Fermi pulsars PSR J1357-6429 and PSR J1048-5832

Optical observations of pulsars are crucial to study the neutron star properties, from the structure and composition of the interior, to the properties and geometry of the magnetosphere. Historically, X and gamma-ray observations have paved the way to the pulsar optical identifications. The launch of Fermi opened new perspectives in the optical-to-gamma-ray studies of neutron stars, with the detection of more than 80 pulsars. Here, we aim to search for optical emission from two Fermi pulsars which are interesting targets on the basis of their spin-down age, energetics, and distance: PSR J1357-6429and PSR J1048-5832. The two pulsars and their pulsar wind nebulae (PWNe) are also detected in X-rays by Chandra and XMM. No deep optical observations of these two pulsars have been reported so far. We used multi-band optical images (V,R,I) taken with the VLT and available in the European Southern Observatory (ESO) archive to search for, or put tight constraints to, their optical emission. We re-assessed the positions of the two pulsars from the analyses of all the available Chandra observations and the comparison with the published radio coordinates. For PSR J1357-6429, this yielded a tentative proper motion mu=0.17+/-0.055 "/yr (70+/-15 deg position angle). We did not detect candidate counterparts to PSR J1357-6429 and PSR J1048-5832 down to V~27 and ~27.6, respectively, although for the former we found a possible evidence for a faint, unresolved object at the Chandra position. Our limits imply an efficiency in converting spin-down power into optical luminosity <7x10^{-7} and <6x10^{-6}, respectively, possibly close to that of the Vela pulsar.

astro-ph.HE↗

arXiv2008

The Realistic Lattice Determination of alpha_s(M_Z) Revisited

We revisit the earlier determination of alpha_s(M_Z) via perturbative analyses of short-distance-sensitive lattice observables, incorporating new lattice data and performing a modified version of the original analysis. We focus on two high-intrinsic-scale observables, log(W_11) and log(W_12), and one lower-intrinsic scale observable, log(W_{12}/u_0^6), finding improved consistency among the values extracted using the different observables and a final result, alpha_s(M_Z)=0.1192(11), 2 sigma higher than the earlier result, in excellent agreement with recent non-lattice determinations and, in addition, in good agreement with the results of a similar, but not identical, re-analysis by the HPQCD Collaboration. A discussion of the relation between the two re-analyses is given, focussing on the complementary aspects of the two approaches.

hep-lat↗

arXiv2008

The determination of alpha_s(M_z) from perturbative analyses of short-distance-sensitive lattice QCD observables revisited

The determination of alpha_s(M_Z) via perturbative analyses of short-distance-sensitive lattice observables is revisited, incorporating new lattice data and performing a modified version of the original analysis. The analysis employs two high-intrinsic-scale observables, log (W_11) and log(W_12), and one lower-intrinsic-scale observable, log(W_12/u_0^6). We find good consistency among the values extracted using the different observables and a final result, alpha_s(M_Z)=0.1192(11), in excellent agreement with various recent non-lattice determinations, as well as with the results of a similar, but not identical, re-analysis by the HPQCD collaboration. The relation between the two re-analyses is discussed, focussing on the complementarity of the two approaches.

hep-lat↗

arXiv2008

Vacuum structure revealed by over-improved stout-link smearing compared with the overlap analysis for quenched QCD

A detailed comparison is made between the topological structure of quenched QCD as revealed by the recently proposed over-improved stout-link smearing in conjunction with an improved gluonic definition of the topological density on one hand and a similar analysis made possible by the overlap-fermionic topological charge density both with and without variable ultraviolet cutoff $λ_{cut}$. The matching is twofold, provided by fitting the density-density two-point functions on one hand and by a point-by-point fitting of the topological densities according to the two methods. We point out the similar cluster structure of the topological density for moderate smearing and $200 \mathrm{MeV} < λ_{cut} < 600 \mathrm{MeV}$, respectively. We demonstrate the relation of the gluonic topological density for extensive smearing to the location of the overlap zero modes and the lowest overlap non-zero mode as found for the unsmeared configurations.

hep-lat↗