Browsing by Author "Guillot, S."
Now showing 1 - 12 of 12
Results Per Page
Sort Options
- ItemA HIGH BRAKING INDEX FOR A PULSAR(2016) Archibald, R. F.; Gotthelf, E. V.; Ferdman, R. D.; Kaspi, V. M.; Guillot, S.; Harrison, F. A.; Keane, E. F.; Pivovaroff, M. J.; Stern, D.; Tendulkar, S. P.; Tomsick, J. A.We present a phase-coherent timing solution for PSR. J1640-4631, a young 206 ms pulsar using X-ray timing observations taken with NuSTAR. Over this timing campaign, we have measured the braking index of PSR. J1640-4631 to be n = 3.15 +/- 0.03. Using a series of simulations, we argue that this unusually high braking index is not due to timing noise, but is intrinsic to the pulsar's spin-down. We cannot, however, rule out contamination due to an unseen glitch recovery, although the recovery timescale would have to be longer than most yet observed. If this braking index is eventually proven to be stable, it demonstrates that pulsar braking indices greater than three are allowed in nature; hence, other physical mechanisms such as mass or magnetic quadrupoles are important in pulsar spin-down. We also present a 3 sigma upper limit on the pulsed flux at 1.4 GHz of 0.018 mJy.
- ItemHubble Space Telescope Detection of the Millisecond Pulsar J2124-3358 and its Far-ultraviolet Bow Shock Nebula(2017) Reisenegger, Andreas; Rangelov, B.; Pavlov, G. G.; Kargaltsev, O.; Guillot, S.; Van Kerkwijk, M. H.
- ItemHubble Space Telescope Nondetection of PSR J2144-3933 : The Coldest Known Neutron Star(2019) Guillot, S.; Pavlov, G.G.; Reyes, C.; Reisenegger, Andreas; Rodríguez Pemjean, Luis Enrique; Rangelov, B.; Kargaltsev, O.
- ItemNICER Observes the Effects of an X-Ray Burst on the Accretion Environment in Aql X-1(2018) Keek, L.; Arzoumanian, Z.; Bult, P.; Cackett, E. M.; Chakrabarty, D.; Chenevez, J.; Fabian, A. C.; Gendreau, K. C.; Guillot, S.; Guver, T.; Homan, J.; Jaisawal, G. K.; Lamb, F. K.; Ludlam, R. M.; Mahmoodifar, S.; Markwardt, C. B.; Miller, J. M.; Prigozhin, G.; Soong, Y.; Strohmayer, T. E.; Wolff, M. T.Accretion disks around neutron stars regularly undergo sudden strong irradiation by Type-I X-ray bursts powered by unstable thermonuclear burning on the stellar surface. We investigate the impact on the disk during one of the first X-ray burst observations with the Neutron Star Interior Composition Explorer (NICER) on the International Space Station. The burst is seen from Aql X-1 during the hard spectral state. In addition to thermal emission from the neutron star, the burst spectrum exhibits an excess of soft X-ray photons below 1 keV, where NICER's sensitivity peaks. We interpret the excess as a combination of reprocessing by the strongly photoionized disk and enhancement of the pre-burst persistent flux, possibly due to Poynting-Robertson drag or coronal reprocessing. This is the first such detection for a short sub-Eddington burst. As these bursts are observed frequently, NICER will be able to study how X-ray bursts affect the disk and corona for a range of accreting neutron star systems and disk states.
- ItemNuSTAR OBSERVATIONS OF MAGNETAR 1E 1048.1-5937(2016) Yang, C.; Archibald, R. F.; Vogel, J. K.; An, H.; Kaspi, V. M.; Guillot, S.; Beloborodov, A. M.; Pivovaroff, M.We report on simultaneous Nuclear Spectroscopic Telescope Array (NuSTAR) and XMM-Newton observations of the magnetar 1E. 1048.1-5937, along with Rossi X-ray Timing Explorer (RXTE) data for the same source. The NuSTAR data provide a clear detection of this magnetar's persistent emission up to 20 keV. We detect a previously unreported small secondary peak in the average pulse profile in the 7-10 keV band, which grows to an amplitude comparable to that of the main peak in the 10-20 keV band. We show using RXTE data that this secondary peak is likely transient. We find that the pulsed fraction increases with energy from a value of similar to 0.55 at similar to 2. keV to a value of similar to 0.75 near 8. keV but shows evidence of decreasing at higher energies. After filtering out multiple bright X-ray bursts during the observation, we find that the phase-averaged spectrum from combined NuSTAR and XMM data is well described by an absorbed double blackbody plus power-law model, with no evidence for the spectral turn-up near similar to 10. keV as has been seen in some other magnetars. Our data allow us to rule out a spectral turn-up similar to those seen in magnetars 4U 0142+61 and 1E 2259+586 of Delta Gamma greater than or similar to 2, where Delta Gamma is the difference between the soft-band and hard-band photon indexes. The lack of spectral turn-up is consistent with what has been observed from an active subset of magnetars given previously reported trends suggesting that the degree of spectral turn-up is correlated with spin-down rate and/or spin-inferred magnetic field.
- ItemModelling of the surface emission of the low magnetic field magnetar SGR 0418+5729(2015) Guillot, S.; Perna, R.; Rea, N.; Vigano, D.; Pons, J. A.We perform a detailed modelling of the post-outburst surface emission of the low magnetic field magnetar SGR 0418+5729. The dipolar magnetic field of this source, B = 6 x 10(12) G estimated from its spin-down rate, is in the observed range of magnetic fields for normal pulsars. The source is further characterized by a high pulse fraction and a single-peak profile. Using synthetic temperature distribution profiles, and fully accounting for the general-relativistic effects of light deflection and gravitational redshift, we generate synthetic X-ray spectra and pulse profiles that we fit to the observations. We find that asymmetric and symmetric surface temperature distributions can reproduce equally well the observed pulse profiles and spectra of SGR 0418. None the less, the modelling allows us to place constraints on the system geometry (i.e. the angles. and. that the rotation axis makes with the line of sight and the dipolar axis, respectively), as well as on the spot size and temperature contrast on the neutron star surface. After performing an analysis iterating between the pulse profile and spectra, as done in similar previous works, we further employed, for the first time in this context, a Markov-Chain Monte Carlo approach to extract constraints on the model parameters from the pulse profiles and spectra, simultaneously. We find that, to reproduce the observed spectrum and flux modulation: (a) the angles must be restricted to 65 degrees less than or similar to psi + xi less than or similar to 125 degrees or 235 degrees less than or similar to psi + xi less than or similar to 295 degrees; (b) the temperature contrast between the poles and the equator must be at least a factor of similar to 6, and (c) the size of the hottest region ranges between 0.2 and 0.7 km (including uncertainties on the source distance). Lastly, we interpret our findings within the context of internal and external heating models.
- ItemNeutron star radius measurement from the ultraviolet and soft X-ray thermal emission of PSR J0437-4715(2019) González Caniulef, Denis; Guillot, S.; Reisenegger, Andreas
- ItemNew Constraints on the Nuclear Equation of State from the Thermal Emission of Neutron Stars in Quiescent Low-mass X-Ray Binaries(2019) D'Etivaux, N.B.; Guillot, S.; Margueron, J.; Webb, N.; Catelan, Márcio; Reisenegger, Andreas
- ItemOld but Still Warm: Far-UV Detection of PSR B0950+08(2017) Pavlov, G.; Rangelov, B.; Kargaltsev, O.; Reisenegger, Andreas; Guillot, S.; Reyes, C.
- ItemSpectral analysis of the quiescent low-mass X-ray binary in the globular cluster M30(2020) Echiburú, C. S.; Guillot, S.; Zhao, Y.; Heinke, C. O.; Ozel, F.; Web, N. A.We present a recent Chandra observation of the quiescent low-mass X-ray binary containing a neutron star (NS), located in the globular cluster M30. We fit the thermal emission from the NS to extract its mass and radius. We find no evidence of flux variability between the two observations taken in 2001 and 2017, nor between individual 2017 observations, so we analyse them together to increase the signal-to-noise ratio. We perform simultaneous spectral fits using standard light-element composition atmosphere models (hydrogen or helium), including absorption by the interstellar medium, correction for pile-up of X-ray photons on the detector, and a power law for count excesses at high photon energy. Using a Markov chain Monte Carlo approach, we extract mass and radius credible intervals for both chemical compositions of the atmosphere: $\mbox{$R_{\rm NS}$}=7.94\mbox{{$\scriptstyle ^{ + 0.76}_{- 1.21}$}}$ km and $\mbox{$M_{\rm NS}$}\lt 1.19$ M⊙ assuming pure hydrogen, and $\mbox{$R_{\rm NS}$}=10.50\mbox{{$\scriptstyle ^{ + 2.88}_{- 2.03}$}}$ km and $\mbox{$M_{\rm NS}$}\lt 1.78$ M⊙ for helium, where the uncertainties represent the 90 per cent credible regions. For H, the small radius is difficult to reconcile with most current nuclear physics models (especially for nucleonic equations of state) and with other measurements of NS radii, with recent preferred values generally in the 11–14 km range. Whereas for He, the measured radius is consistent with this range. We discuss possible sources of systematic uncertainty that may result in an underestimation of the radius, identifying the presence of surface temperature inhomogeneities as the most relevant bias. According to this, we conclude that either the atmosphere is composed of He or it is anH atmosphere with a significant contribution of hotspots to the observed radiation.
- ItemThe NuSTAR view of the non-thermal emission from PSR J0437-4715(OXFORD UNIV PRESS, 2016) Guillot, S.; Kaspi, V. M.; Archibald, R. F.; Bachetti, M.; Flynn, C.; Jankowski, F.; Bailes, M.; Boggs, S.; Christensen, F. E.; Craig, W. W.; Hailey, C. A.; Harrison, F. A.; Stern, D.; Zhang, W. W.We present a hard X-ray Nuclear Spectroscopic Telescope Array (NuSTAR) observation of PSR J0437-4715, the nearest millisecond pulsar. The known pulsations at the apparent pulse period similar to 5.76 ms are observed with a significance of 3.7 sigma, at energies up to 20 keV above which the NuSTAR background dominates. We measure a photon index Gamma = 1.50 +/- 0.25 (90 per cent confidence) for the power-law fit to the non-thermal emission. It had been shown that spectral models with two or three thermal components fit the XMM-Newton spectrum of PSR J0437-4715, depending on the slope of the power-law component, and the amount of absorption of soft X-rays. The new constraint on the high-energy emission provided by NuSTAR removes ambiguities regarding the thermal components of the emission below 3 keV. We performed a simultaneous spectral analysis of the XMM-Newton and NuSTAR data to confirm that three thermal components and a power law are required to fit the 0.3-20 keV emission of PSR J0437-4715. Adding a ROSAT-PSPC spectrum further confirmed this result and allowed us to better constrain the temperatures of the three thermal components. A phase-resolved analysis of the NuSTAR data revealed no significant change in the photon index of the high-energy emission. This NuSTAR observation provides further impetus for future observations with the NICER mission (Neutron Star Interior Composition Explorer) whose sensitivity will provide much stricter constraints on the equation of state of nuclear matter by combining model fits to the pulsar's phase-folded light curve with the pulsar's well-defined mass and distance from radio timing observations.
- ItemThermal X-ray emission identified from the millisecond pulsar PSR J1909-3744(2019) Webb, N. A.; Leahy, D.; Guillot, S.; d'Etivaux, N. Baillot; Barret, D.; Guillemot, L.; Margueron, J.; Miller, M. C.Context. Pulsating thermal X-ray emission from millisecond pulsars can be used to obtain constraints on the neutron star equation of state, but to date only five such sources have been identified. Of these five millisecond pulsars, only two have well-constrained neutron star masses, which improve the determination of the radius via modelling of the X-ray waveform.