Discovery of the Optical Counterparts to Four Energetic Fermi Millisecond Pulsars

In the last few years, over 43 millisecond radio pulsars have been discovered by targeted searches of unidentified gamma-ray sources found by the Fermi Gamma-Ray Space Telescope. A large fraction of these millisecond pulsars are in compact binaries with low-mass companions. These systems often show eclipses of the pulsar signal and are commonly known as black widows and redbacks because the pulsar is gradually destroying its companion. In this paper, we report on the optical discovery of four strongly irradiated millisecond pulsar companions. All four sources show modulations of their color and luminosity at the known orbital periods from radio timing. Light curve modelling of our exploratory data shows that the equilibrium temperature reached on the companion's dayside with respect to their nightside is consistent with about 10-30% of the available spin-down energy from the pulsar being reprocessed to increase the companion's dayside temperature. This value compares well with the range observed in other irradiated pulsar binaries and offers insights about the energetics of the pulsar wind and the production of gamma-ray emission. In addition, this provides a simple way of estimating the brightness of irradiated pulsar companions given the pulsar spin-down luminosity. Our analysis also suggests that two of the four new irradiated pulsar companions are only partially filling their Roche lobe. Some of these sources are relatively bright and represent good targets for spectroscopic follow-up. These measurements could enable, among other things, mass determination of the neutron stars in these systems.Comment: 11 pages, 5 tables, 1 figure, 4 online tables. ApJ submitted and referee

Long Term Study of the Double Pulsar J0737-3039 with XMM-Newton: pulsar timing

The relativistic double neutron star binary PSR J0737-3039 shows clear evidence of orbital phase-dependent wind-companion interaction, both in radio and X-rays. In this paper we present the results of timing analysis of PSR J0737-3039 performed during 2006 and 2011 XMM-Newton Large Programs that collected ~20,000 X-ray counts from the system. We detected pulsations from PSR J0737-3039A (PSR A) through the most accurate timing measurement obtained by XMM-Newton so far, the spin period error being of 2x10^-13 s. PSR A's pulse profile in X-rays is very stable despite significant relativistic spin precession that occurred within the time span of observations. This yields a constraint on the misalignment between the spin axis and the orbital momentum axis Delta_A ~6.6^{+1.3}_{-5.4} deg, consistent with estimates based on radio data. We confirmed pulsed emission from PSR J0737-3039B (PSR B) in X-rays even after its disappearance in radio. The unusual phenomenology of PSR B's X-ray emission includes orbital pulsed flux and profile variations as well as a loss of pulsar phase coherence on time scales of years. We hypothesize that this is due to the interaction of PSR A's wind with PSR B's magnetosphere and orbital-dependent penetration of the wind plasma onto PSR B closed field lines. Finally, the analysis of the full XMM-Newton dataset provided evidences of orbital flux variability (~7%) for the first time, involving a bow-shock scenario between PSR A's wind and PSR B's magnetosphere.Comment: Comments: 16 Pages, 6 Figures. Accepted for publication in Astrophysical Journal (Draft Version

Pulsar Wind Nebulae in the SKA era

Neutron stars lose the bulk of their rotational energy in the form of a pulsar wind: an ultra-relativistic outflow of predominantly electrons and positrons. This pulsar wind significantly impacts the environment and possible binary companion of the neutron star, and studying the resultant pulsar wind nebulae is critical for understanding the formation of neutron stars and millisecond pulsars, the physics of the neutron star magnetosphere, the acceleration of leptons up to PeV energies, and how these particles impact the interstellar medium. With the SKA1 and the SKA2, it could be possible to study literally hundreds of PWNe in detail, critical for understanding the many open questions in the topics listed above.Comment: Comments: 10 pages, 3 figures, to be published in: "Advancing Astrophysics with the Square Kilometre Array", Proceedings of Science, PoS(AASKA14

Phase segregation on electroactive self-assembled monolayers: a numerical approach for describing lateral interactions between redox centers

A numerical method is proposed in order to differentiate a random distribution from a phase segregation of redox centers on (mixed) SAMs. This approach is compared to Laviron’s interactions model and voltammetric data of nitroxylalkanethiolate SAMs

The SAMPIC Waveform and Time to Digital Converter

Sce ElectroniqueInternational audienceSAMPIC is a Waveform and Time to DigitalConverter (WTDC) multichannel chip. Each of its 16 channelsassociates a DLL-based TDC providing a raw time with an ultrafastanalog memory allowing fine timing extraction as well asother parameters of the pulse. Each channel also integrates adiscriminator that can trigger itself independently or participateto a more complex trigger. After triggering, analog data isdigitized by an on-chip ADC and only that corresponding to aregion of interest is sent serially to the DAQ. The association ofthe raw and fine timings permits achieving timing resolutions of afew ps rms. The paper describes the detailed SAMPIC0architecture and reports its main measured performances

Electrochemical Transduction on Self-Assembled Monolayers: Are Covalent Links Essential?

Electrochemical transduction without covalent links between redox and complexant units in a complexing self-assembled monolayer has been established. The results demonstrate that transduction depends on the crown ether/ferrocene ratio and appears to be tunable

Impact of the Nanoscale Organization of Nitroxyl Mixed Self-Assembled Monolayers on their Electrocatalytic Behaviour

Electrocatalysis: The molecular distribution of redox centers on mixed nitroxyl SAMs strongly influences the electrocatalytic reactivity

A protein conformational change associated with the photoreduction of the primary and secondary quinones in the bacterial reaction center

AbstractA comparison is made between the PQA → P+Q−A and PQAQB → P+QAQ−B transitions in Rps. viridis and Rb. sphaeroides reaction centers (RCs) by the use of light-induced Fourier transform infrared (FTIR) difference spectroscopy. In Rb. sphaeroides RCs, we identify a signal at 1650 cm−1 which is present in the P+QA-minus-PQA spectrum and not in the P+QAQ−B-minus-PQAQB spectrum. In contrast, this signal is present in both P+Q−A-minus-PQ−A and P+QAQ−B-minus-PQAQB spectra of Rps. viridis RCs. These data are interpreted in terms of a conformational change of the protein backbone near QA (possible at the peptide CO of a conserved alanine residue in the QA pocket) and of the different bonding interactions of QB with the protein in the RC of the two species