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Over the past six years, the Fermi Large Area Telescope has detected more than 150 γ-ray pulsars, discovering a variety of light curve trends and classes. Such diversity hints at distinct underlying magnetospheric and/or emission geometries. We implemented an offsetdipole magnetic field, with an offset characterised by parameters epsilon and magnetic azimuthal angle, in an existing geometric pulsar modelling code which already includes static and retarded vacuum dipole fields. We use these different B-field solutions in conjunction with standard emission geometries, namely the two-pole caustic and outer gap models (the latter only for non-offset dipoles), and construct intensity maps and light curves for several pulsar parameters. We compare our model light curves to the Vela data from the second pulsar catalogue of Fermi. We use a refined chi-square grid search method for finding best-fit light curves for each of the different models. Our best fit is for the retarded vacuum dipole field and the outer gap model

Millisecond pulsars (MSPs) are a growing class of gamma-ray emitters. Pulsed gamma-ray signals have been detected from more than 40 MSPs with the Fermi Large Area Telescope (LAT). The wider radio beams and more compact magnetospheres of MSPs enable studies of emission geometries over a broader range of phase space than non-recycled radio-loud gamma-ray pulsars. We have modeled the gamma-ray light curves of 40 LAT-detected MSPs using geometric emission models assuming a vacuum retarded-dipole magnetic field. We modeled the radio profiles using a single-altitude hollow-cone beam, with a core component when indicated by polarimetry; however, forMSPs with gamma-ray and radio light curve peaks occurring at nearly the same rotational phase, we assume that the radio emission is co-located with the gamma rays and caustic in nature. The best-fit parameters and confidence intervals are determined using amaximum likelihood technique.We divide the light curves into three model classes, with gamma-ray peaks trailing (Class I), aligned (Class II), or leading (Class III) the radio peaks. Outer gap and slot gap (two-pole caustic) models best fit roughly equal numbers of Class I and II, while Class III are exclusively fit with pair-starved polar cap models. Distinguishing between the model classes based on typical derived parameters is difficult. We explore the evolution of the magnetic inclination angle with period and spin-down power, finding possible correlations. While the presence of significant off-peak emission can often be used as a discriminator between outer gap and slot gap models, a hybrid model may be needed http://dx.doi.org/10.1088/0067-0049/213/1/6 http://iopscience.iop.org/0067-0049 theNational Aeronautics and Space Administration and theDepartment of Energy in theUnited States, theCommissariat `a l’EnergieAtomique and the Centre National de la Recherche Scientifique/Institut National de Physique Nucl´eaire et de Physique des Particules in France, the Agenzia Spaziale Italiana and the Istituto Nazionale di Fisica Nucleare in Italy, the Ministry of Education, Culture, Sports, Science and Technology (MEXT), High Energy Accelerator Research Organization (KEK) and Japan Aerospace Exploration Agency (JAXA) in Japan, and the K. A. Wallenberg Foundation, the Swedish Research Council and the Swedish National Space Board in Sweden. Istituto Nazionale di Astrofisica in Italy and the Centre National d’ ´ Etudes Spatiales in France. NASA DPR S-15633-Y. C.V. is supported by the South African National Research Foundation. A.K.H. acknowledges support from NASA Astrophysics Theory grants and Fermi Guest Investigator grants 10-Fermi10-C4- 0054 and 09-FERMI309-0076.

To obtain constraints on the inclination and observer angles, α and ζ, of a γ-ray pulsar from its observed light curve (LC), we make use of geometric models detailing the position and extent of emission regions (acceleration gaps) in the magnetosphere. We do this by generating a sky map of emission intensity for a range of α, and at each α extracting a complete set of LCs. This yields an atlas of LCs characterised by a specific set of model parameters, such as gap width, position, and radial extent. This atlas can then be used to obtain fits to observed LCs (including rough errors on α and ζ) by eye through a systematic search of the (α,ζ) solution space. For radio-loud γ-ray pulsars, significantly better constraints on the viewing geometry (α and ζ) can be obtained by doing this concurrently for the observed radio and γ-ray LCs. This multiwavelength approach has been used successfully to obtain constraints on the viewing geometries of 6 Fermi-LAT pulsars. It is crucial, however, to understand how the set of model parameters influence the shapes and properties of the LCs contained in a particular atlas, since such an understanding enables improved parameter constraints, and directs future model refinement. A first approach is to study the effect of these parameters on the LCs. This is useful in some respects (and is indeed adequate for the relatively simple radio models). However, due to the complex structure of many of the produced γ-ray LCs, this approach doesn't give a comprehensive enough understanding of how these are produced in terms of the underlying magnetospheric structure and accelerator geometry. In this talk we explore a second approach to investigating the interplay between the model parameters and the LC atlas. Here, we do not attempt to understand how the set of model parameters influence the LC shapes directly, but rather, more fundamentally, investigate how the model parameters affect the sky maps from which the latter are extracted. This allows us to recognise structure within the atlas itself, as we are able to attribute features of the LCs to specific features on the sky map, meaning we not only understand how single LCs come about, but how their structure changes as we move through (α,ζ)-space, and why. http://events.saip.org.za/contributionDisplay.py?contribId=229&sessionId=16&confId=14 South African National Research Foundation

The second pulsar catalogue of the Fermi Large Area Telescope (LAT) will contain in excess of 100 gamma-ray pulsars. The light curves (LCs) of these pulsars exhibit a variety of shapes, and also different relative phase lags with respect to their radio pulses, hinting at distinct underlying magnetospheric geometries and emission properties for the individual pulsars. Detailed geometric modelling of the radio and gamma-ray LCs may provide constraints on the B-field structure and emission geometry. We used different B-field solutions in conjunction with an existing geometric modelling code, including the static vacuum dipole, the retarded vacuum dipole, and offset-dipole solutions, and constructed radiation sky maps and LCs for several different pulsar parameters. Standard emission geometries were assumed, namely the Two-Pole Caustic (TPC) and Outer Gap (OG) models. The sky maps and LCs of the various B-field and radiation model combinations were compared to study their effect on the resulting LCs. As an application, we compared our model LCs with Fermi LAT data for the Vela pulsar, and inferred the most probable configuration in this case, thereby constraining Vela’s high-altitude magnetic structure and system geometry. http://events.saip.org.za/contributionDisplay.py?contribId=127&sessionId=16&confId=14 South African National Research Foundation (NRF)

Guillemot et al. recently reported the discovery [1] of -ray pulsations from the 22.7 ms pulsar (pulsar A) in the famous double pulsar system J0737−3039A/B. The -ray light curve (LC) of pulsar A has two peaks separated by approximately half a rotation, and these are non-coincident with the observed radio and X-ray peaks. This suggests that the -ray emission originates in a part of the magnetosphere distinct from where the radio and X-ray radiation is generated. Thus far, three different methods have been applied to constrain the viewing geometry of pulsar A (its inclination and observer angles and ): geometric modelling of the radio and -ray light curves, modelling of the position angle sweep in phase seen in the radio polarisation data, and independent studies of the time evolution of the radio pulse profile of pulsar A. These three independent, complementary methods have yielded consistent results: pulsar A’s rotation axis is likely perpendicular to the orbital plane of the binary system, and its magnetic axis close to lying in the orbital plane (making this pulsar an orthogonal rotator). The observer is furthermore observing emission close to the magnetic axis. Thus far, however, current geometric models could not reproduce all the characteristics of the radio and -ray light curves, specifically the large radio-to- phase lag. In this paper we discuss some preliminary modelling attempts to address this problem, and offer ideas on how the LC fits may be improved by adapting the standard geometric models in order to reproduce the profile positions more accurately http://events.saip.org.za/getFile.py/access?contribId=245&sessionId=4&resId=0&materialId=paper&confId=32 South African National Research Foundation

The field of gamma-ray pulsars (rapidly spinning and highly magnetized neutron stars (NSs)) has been revolutionized by the launch of Fermi Large Area Telescope (LAT) in June 2008. Fermi LAT will soon release its second pulsar catalogue describing the properties of some 117 gamma-ray pulsars. The light curves (LCs) of these pulsars show great variety in profile shape, and may be divided into three general profile classes based on the relative phase differences between their radio and gamma-ray pulses. Such diversity hints at distinct underlying magnetospheric and / or emission geometries for the individual pulsar classes. Detailed geometric modelling of the radio and gamma-ray LCs may therefore provide constraints on the magnetospheric and emission characteristics. We implemented an offset-dipole magnetic field in an existing geometric pulsar modelling code which already includes static and retarded dipole fields. The magnetic field lines of an offset dipole undergo small distortions due to retardation and asymmetric currents, therefore shifting the NS's polar caps (PCs) by different amounts and directions. This offset is characterized by a parameter ε, which gives the relative shift in units of the stellar radius (with ε = 0 corresponding to the static dipole case). We constructed sky maps and LCs for several pulsar parameters, magnetic fields, and geometric models, studying their effect on the resulting LCs. Standard two-pole caustic (TPC) and outer gap (OG) emission geometries were used. As an application, we compared our model LCs with Fermi LAT data for the bright Vela pulsar, and inferred the most probable configuration based on the Fermi data, thereby constraining Vela's low-altitude magnetic structure and system geometry. http://events.saip.org.za/contributionDisplay.py?contribId=213&sessionId=4&confId=32

We report a 5.4σ detection of pulsed gamma rays from PSR B1821−24 in the globular cluster M28 using ~44 months of Fermi Large Area Telescope (LAT) data that have been reprocessed with improved instrument calibration constants. We constructed a phase-coherent ephemeris, with post-fit residual rms of 3 μs, using radio data spanning ~23.2 yr, enabling measurements of the multi-wavelength light-curve properties of PSR B1821−24 at the milliperiod level. We fold RXTE observations of PSR B1821−24 from 1996 to 2007 and discuss implications on the emission zones. The gamma-ray light curve consists of two peaks separated by 0.41 ± 0.02 in phase, with the first gamma-ray peak lagging behind the first radio peak by 0.05 ± 0.02 in phase, consistent with the phase of giant radio pulses. We observe significant emission in the off-peak interval of PSR B1821−24 with a best-fit LAT position inconsistent with the core of M28. We do not detect significant gamma-ray pulsations at the spin or orbital periods from any other known pulsar in M28, and we place limits on the number of energetic pulsars in the cluster. The derived gamma-ray efficiency, ~2%, is typical of other gamma-ray pulsars with comparable spin-down power, suggesting that the measured spin-down rate (2.2 × 1036 erg s−1) is not appreciably distorted by acceleration in the cluster potential. This confirms PSR B1821−24 as the second very energetic millisecond pulsar in a globular cluster and raises the question of whether these represent a separate class of objects that only form in regions of very high stellar density http://iopscience.iop.org/0004-637X/778/2/106/article http://iopscience.iop.org/0004-637X http://dx.doi.org/10.1088/0004-637X/778/2/106

Two ion cyclotron range of frequencies (ICRF) heating schemes proposed for the half-field operation phase of ITER in hydrogen plasmas—fundamental H majority and second harmonic 3 He ICRF heating—were recently investigated in JET. Although the same magnetic field and RF frequencies ( f ≈ 42 MHz and f ≈ 52 MHz, respectively) were used, the density and particularly the plasma temperature were lower than those expected in the initial phase of ITER. Unlike for the well-performing H minority heating scheme to be used in 4 He plasmas, modest heating efficiencies ( η = P absorbed / P launched

Since the discovery of the first eight gamma-ray millisecond pulsars (MSPs) by the Fermi Large Area Telescope, this population has been steadily expanding. Four of the more recent detections, PSR J0034–0534, PSR J1939+2134 (B1937+21; the first MSP ever discovered), PSR J1959+2048 (B1957+20; the first discovery of a black widow system), and PSR J2214+3000, exhibit a phenomenon not present in the original discoveries: nearly phase-aligned radio and gamma-ray light curves (LCs). To account for the phase alignment, we explore models where both the radio and gamma-ray emission originate either in the outer magnetosphere near the light cylinder or near the polar caps. Using a Markov Chain Monte Carlo technique to search for best-fit model parameters, we obtain reasonable LC fits for the first three of these MSPs in the context of "altitude-limited" outer gap (alOG) and two-pole caustic (alTPC) geometries (for both gamma-ray and radio emission). These models differ from the standard outer gap (OG)/two-pole caustic (TPC) models in two respects: the radio emission originates in caustics at relatively high altitudes compared to the usual conal radio beams, and we allow both the minimum and maximum altitudes of the gamma-ray and radio emission regions to vary within a limited range (excluding the minimum gamma-ray altitude of the alTPC model, which is kept constant at the stellar radius, and that of the alOG model, which is set to the position-dependent null charge surface altitude). Alternatively, phase-aligned solutions also exist for emission originating near the stellar surface in a slot gap scenario ("low-altitude slot gap" (laSG) models). We find that the alTPC models provide slightly better LC fits than the alOG models, and both of these give better fits than the laSG models (for the limited range of parameters considered in the case of the laSG models). Thus, our fits imply that the phase-aligned LCs are likely of caustic origin, produced in the outer magnetosphere, and that the radio emission for these pulsars may come from close to the light cylinder. In addition, we were able to constrain the minimum and maximum emission altitudes with typical uncertainties of ~30% of the light cylinder radius. Our results therefore describe a third gamma-ray MSP subclass, in addition to the two previously found by Venter et al.: those with LCs fit by standard OG/TPC models and those with LCs fit by pair-starved polar cap models. http://dx.doi.org/10.1088/0004-637X/744/1/34 http://iopscience.iop.org/0004-637X/744/1/34/pdf/apj_744_1_34.pdf

The gamma-ray population of millisecond pulsars (MSPs) detected by the Fermi Large Area Telescope (LAT) has been steadily increasing. A number of the more recent detections, including PSR J0034−0534, PSR J1939+2134 (B1937+21; the first MSP ever discovered), PSR J1959+2048 (B1957+20; the first black widow system), and PSR J2214+3000, exhibit an unusual phenomenon: nearly phase-aligned radio and gammaray light curves (LCs). To account for the phase alignment, we explore geometric models where both the radio and gamma-ray emission originate either in the outer magnetosphere near the light cylinder (RLC) or near the polar caps (PCs). We obtain reasonable fits for the first three of these MSPs in the context of “altitudelimited” outer gap (alOG) and two-pole caustic (alTPC) geometries. The outer magnetosphere phase-aligned models differ from the standard outer gap (OG) / two-pole caustic (TPC) models in two respects: first, the radio emission originates in caustics at relatively high altitudes compared to the usual low-altitude conal radio beams; second, we allow the maximum altitude of the gamma-ray emission region as well as both the minimum and maximum altitudes of the radio emission region to vary within a limited range. Alternatively, there also exist phase-aligned LC solutions for emission originating near the stellar surface in a slot gap (SG) scenario (“low-altitude slot gap” (laSG) models). We find best-fit LCs using a Markov chain Monte Carlo (MCMC) maximum likelihood approach [30]. Our fits imply that the phase-aligned LCs are likely of caustic origin, produced in the outer magnetosphere, and that the radio emission may come from close to RLC. We lastly constrain the emission altitudes with typical uncertainties of ∼ 0.3RLC. Our results describe a third gamma-ray MSP subclass, in addition to the two (with non-aligned LCs) previously found [50]: those with LCs fit by standard OG / TPC models, and those with LCs fit by pair-starved polar cap (PSPC) models

Pulsed gamma rays have been detected with the Fermi Large Area Telescope (LAT) from more than 20 millisecond pulsars (:\ISPs), some of which were discovered in radio observations of bright, unassociated LAT sources. We have fit the radio and gamma-ray light curves of 19 LAT-detected MSPs in the context of geometric, outermagnetospheric emission models assuming the retarded vacuum dipole magnetic field using a Markov chain Monte Carlo maximum likelihood technique. We find that, in many cases, the models are able to reproduce the observed light curves well and provide constraints on the viewing geometries that are in agreement with those from radio polarization measurements. Additionally, for some MSPs we constrain the altitudes of both the gamma-ray and radio emission regions. The best-fit magnetic inclination angles are found to cover a broader range than those of non-recycled gamma-ray pulsars

The Fermi Large Area Telescope (LAT) has revolutionized high-energy (HE) astronomy, and is making enormous contributions particularly to γ-ray pulsar science. As a result of the many new pulsar discoveries, the γ-ray pulsar population is now approaching 100. Some very famous millisecond pulsars (MSPs) have also been detected: J1939+2134 (a.k.a. B1937+21), the first MSP ever discovered, as well as J1959+2048 (a.k.a. B1957+20), the first black widow pulsar system. These, along with other MSPs such as PSR J0034−0534 and J2214+3000, are rare among the pulsar population in that they exhibit nearly phase-aligned radio and γ-ray light curves (LCs). Traditionally, pulsar LCs have been modelled using standard HE models in conjunction with low-altitude conal beam radio models. However, a different approach is needed to account for phase-aligned LCs. We explored two scenarios: one where both the radio and γ-ray emission originate in the outer magnetosphere, and one where the emission comes from near the polar caps (PCs) on the stellar surface. We find best-fit LCs using a Markov chain Monte Carlo (MCMC) technique for the first class of models. The first scenario seems to be somewhat preferred, as is also hinted at by the radio polarization data. This implies that the phase-aligned LCs are possibly of caustic origin produced in the outer magnetosphere, in contrast to the usual lower-altitude conal beam radio models. We lastly constrain the emission altitudes with typical uncertainties of ∼ 10% of the light cylinder radius. The modelled pulsars are members of a third γ-ray MSP subclass, in addition to two others with non-aligned radio and γ-ray LCs