The X-Ray Pulsar XTE J1858+034 Observed with NuSTAR and Fermi/GBM: Spectral and Timing Characterization plus a Cyclotron Line (original) (raw)
Related papers
The Astrophysical Journal, 2008
We show that: (i) the long-term X-ray outburst light curve of the transient AXP XTE J1810-197 can be accounted for by a fallback disk that is evolving towards quiescence through a disk instability after having been heated by a soft gamma-ray burst, (ii) the spin-frequency evolution of this source in the same period can also be explained by the disk torque acting on the magnetosphere of the neutron star, (iii) most significantly, recently observed pulsed-radio emission from this source coincides with the epoch of minimum X-ray luminosity. This is natural in terms of a fallback disk model, as the accretion power becomes so low that it is not sufficient to suppress the beamed radio emission from XTE J1810-197.
Timing and spectral studies of the X-ray pulsar 2S 1417–624 during the outburst in 2021
Astrophysics and Space Science, 2021
We study the timing and spectral properties of the X-ray pulsar 2S 1417-624 during the recent outburst in January 2021 based on the Neutron Star Interior Composition Explorer (NICER) observation. We also used some early data from the 2018 outburst to compare different temporal and spectral properties. The evolution of the spin period and pulsed flux is studied with Fermi/GBM during the outburst and the spin-up rate is found to be varied between (0.8-1.8) × 10 −11 Hz s −1. The pulse profile shows energy dependence and variability. The pulse profile shows multiple peaks and dips which evolve with energy. The evolution of the spectral state of this source is also studied using the hardness intensity diagram (HID). The HID shows a transition from the horizontal to the diagonal branch, which implies the source went through a state transition from the subcritical to supercritical accretion regime. The NICER energy spectrum is well described by a composite model of a power-law with a higher cutoff energy and blackbody components along with a photo-electric absorption component. An iron emission line is detected near 6.4 keV in the NICER spectrum with an equivalent width of ∼0.05 keV. The photon index shows an anti-correlation with flux below the critical flux. The mass accretion rate is estimated to be 1.3 × 10 17 g s −1 near the peak of the outburst. We have found a positive correlation between the pulse frequency derivatives and luminosity. The Ghosh and Lamb model is applied to estimate the magnetic field at different spin-up rates, which is compared to the earlier estimated magnetic field at a relatively high mass accretion rate. The magnetic field is estimated to be 10 14 G from the torque-luminosity model using the distance estimated by Gaia, which is comparatively higher than most of the other Be/XBPs.
The Astrophysical Journal, 2010
Anomalous X-ray pulsars (AXPs) and soft gamma repeaters (SGRs) are two small classes of Xray sources strongly suspected to host a magnetar, i.e. an ultra-magnetized neutron star with B ≈ 10 14 -10 15 G. Many SGRs/AXPs are known to be variable, and recently the existence of genuinely "transient" magnetars was discovered. Here we present a comprehensive study of the pulse profile and spectral evolution of the two transient AXPs (TAXPs) XTE J1810-197 and CXOU J164710.2-455216. Our analysis was carried out in the framework of the twisted magnetosphere model for magnetar emission. Starting from 3D Monte Carlo simulations of the emerging spectrum, we produced a large database of synthetic pulse profiles which was fitted to observed lightcurves in different spectral bands and at different epochs. This allowed us to derive the physical parameters of the model and their evolution with time, together with the geometry of the two sources, i.e. the inclination of the line-ofsight and of the magnetic axis with respect to the rotation axis. We then fitted the (phase-averaged) spectra of the two TAXPs at different epochs using a model similar to that used to calculate the pulse profiles (ntzang in XSPEC) freezing all parameters to the values obtained from the timing analysis, and leaving only the normalization free to vary. This provided acceptable fits to XMM-Newton data in all the observations we analyzed. Our results support a picture in which a limited portion of the star surface close to one of the magnetic poles is heated at the outburst onset. The subsequent evolution is driven both by the cooling/varying size of the heated cap and by a progressive untwisting of the magnetosphere.
Temporal and spectral study of the X-ray pulsar 2S 1553-542 during the 2021 outburst
arXiv (Cornell University), 2021
We study the timing and spectral properties of the X-ray pulsar 2S 1553-542 using the NuSTAR, and NICER during the outburst in January-February 2021. During the outburst, the spin period of the neutron star was P ∼ 9.2822 s based on NuSTAR data. The pulse profiles are studied using different NICER observations, which implies that the profile is more or less sinusoidal with a single peak and the beaming patterns are mostly dominated by the pencil beam. The NICER spectra of the source are studied for different days of the outburst and can be well described by a model consisting of a blackbody emission and power law along with a photoelectric absorption component. The variation of spectral parameters with luminosity is studied over the outburst. The photon index shows anti-correlation with luminosity below the critical luminosity, which implies that the source was accreting in the sub-critical accretion regime during the NICER observations. We also report the anti-correlation between pulsed fraction (PF) and luminosity of the 2S 1553-542 using NICER observations. The evolution of spin-up rate with luminosity is studied during the outburst, which implies that both are strongly correlated. The torqueluminosity model is applied to estimate the magnetic field at different spin-up rates. The magnetic field is estimated to be ≃ 2.56 × 10 12 G from the torque-luminosity model using the source distance of 20 kpc. The magnetic field is also estimated using the critical luminosity, which is also consistent with our findings.
A study of the X-ray pulsars X1845-024 and XTE J1858+034 based on INTEGRAL observations
Astronomy Reports, 2008
We present an analysis of observations of the relatively unstudied X-ray pulsars X1845-024 and XTE J1858+034 carried out from May 2003 through November 2004 using the JEM-X and IBIS telescopes of the INTEGRAL international gamma-ray observatory at energies of 5-70 keV. The Xray spectra and light curves of the pulsars are constructed. During the observation period, outbursts at 18-70 keV at levels of 13 mCrab and 111 mCrab were detected for X1845-024 and XTE J1858+034, respectively. We refined the rotational period of the neutron star in XTE J1858+034 (220.4 s), measured its acceleration during the outburst, and derived a probable value of the orbital period ( 380 d).
The long-term evolution of the accreting millisecond X-ray pulsar Swift J1756.9−2508
Monthly Notices of the Royal Astronomical Society, 2010
We present a timing analysis of the 2009 outburst of the accreting millisecond Xray pulsar Swift J1756.9-2508, and a re-analysis of the 2007 outburst. The source shows a short recurrence time of only ∼ 2 years between outbursts. Thanks to the approximately 2 year long baseline of data, we can constrain the magnetic field of the neutron star to be 0.4 × 10 8 G < ∼ B < ∼ 9 × 10 8 G, which is within the range of typical accreting millisecond pulsars. The 2009 timing analysis allows us to put constraints on the accretion torque: the spin frequency derivative within the outburst has an upper limit of |ν| < ∼ 3 × 10 −13 Hz s −1 at the 95% confidence level. A study of pulse profiles and their evolution during the outburst is analyzed, suggesting a systematic change of shape that depends on the outburst phase.
2004
(Abridge) We observed the accreting millisecond X-ray pulsars XTE J0929-314 and XTE J1751-305 in their quiescent states using Chandra. From XTE J0929-314 we detected 22 photons (0.3-8 keV) in 24.4 ksec, resulting in a count rate of 9 x 10^{-4} c/s. The small number of photons detected did not allow for a detailed spectral analysis, but we can demonstrate that the spectrum is harder than simple thermal emission which is what is usually presumed to arise from a cooling neutron star that has been heated during the outbursts. Assuming a power-law model for the spectrum, we obtain a power-law index of ~1.8 and an unabsorbed flux of 6 x 10^{-15} ergs/s/cm^2 (0.5-10 keV), resulting in a luminosity of 7 x 10^{31} (d/10 kpc)^2 ergs/s, with d in kpc. No thermal component could be detected; such a component contributed at most 30% to the 0.5-10 keV flux. Variability in the count rate of XTE J0929-314 was observed at the 95% confidence level. We did not conclusively detect XTE J1751-305 in our 43 ksec observation, with 0.5-10 keV flux upper limits between 0.2 and 2.7 x 10^{-14} ergs/s/cm^2 depending on assumed spectral shape, resulting in luminosity upper limits of 0.2 - 2 x 10^{32} (d/8 kpc)^2 ergs/s. We compare our results with those obtained for other neutron-star X-ray transients in their quiescent state. Using simple accretion disk physics in combination with our measured quiescent luminosity of XTE J0929-314 and the luminosity upper limits of XTE J1751-305, and the known spin frequency of the neutron stars, we could constrain the magnetic field of the neutron stars in XTE J0929-314 and XTE J1751-305 to be less than 3 x 10^9 (d/10 kpc) and 3 - 7 x 10^8 (d/8 kpc) Gauss (depending on assumed spectral shape of the quiescent spectrum), respectively.
2021
The results of the broadband spectral and timing study of the recently discovered transient X-ray pulsar MAXI J0903-531 in a wide range of luminosities differing by a factor of ~30 are reported. The observed X-ray spectrum in both states can be described as a classical pulsar-like spectrum consisting of the power-law with the high-energy cutoff. We argue that absence of the spectrum transformation to the two-hump structure expected at low fluxes points to a relatively weak magnetic field of the neutron star below (2-3)$\times10^{12}$ G. This estimate is consistent with other indirect constraints and non-detection of any absorption features which can be interpreted as a cyclotron absorption line. Timing analysis of the NuSTAR data revealed only slight variations of a single-peaked pulse profile of the source as a function of the energy band and mass accretion rate. In both intensity states the pulsed fraction increases from 40% to roughly 80% with the energy. Finally we were also abl...
Evidence of 1122 Hz X-Ray Burst Oscillations from the Neutron Star X-Ray Transient XTE J1739-285
The Astrophysical Journal, 2007
We report on millisecond variability from the X-ray transient XTE J1739-285. We detected six X-ray type I bursts and found evidence for oscillations at 1122 ± 0.3 Hz in the brightest X-ray burst. Taking into consideration the power in the oscillations and the number of trials in the search, the detection is significant at the 99.96% confidence level. If the oscillations are confirmed, the oscillation frequency would suggest that XTE J1739-285 contains the fastest rotating neutron star yet found. We also found millisecond quasiperiodic oscillations in the persistent emission with frequencies ranging from 757 Hz to 862 Hz. Using the brightest burst, we derive an upper limit on the source distance of about 10.6 kpc.
The double-peaked 2008 outburst of the accreting milli-second X-ray pulsar, IGR J00291+5934
Astronomy and Astrophysics, 2010
Context. In August 2008, the accreting milli-second X-ray pulsar (AMXP), IGR J00291+5934, underwent an outburst lasting ∼ 100 days, the first since its discovery in 2004. Aims. We present data from the 2008 double-peaked outburst of IGR J00291+5934 from Faulkes Telescope North, the Isaac Newton Telescope, the Keck Telescope, PAIRITEL, the Westerbork Synthesis Radio Telescope and the Swift, XMM-Newton and RXTE Xray missions. We study the outburst's evolution at various wavelengths, allowing us to probe accretion physics in this AMXP. Methods. We study the light curve morphology, presenting the first radio-X-ray Spectral Energy Distributions (SEDs) for this source and the most detailed UV-IR SEDs for any outbursting AMXP. We show simple models that attempt to identify the emission mechanisms responsible for the SEDs. We analyse short-timescale optical variability, and compare a medium resolution optical spectrum with those from 2004. Results. The outburst morphology is unusual for an AMXP, comprising two peaks, the second containing a 'plateau' of ∼ 10 days at maximum brightness within 30 days of the initial activity. This has implications on duty cycles of short-period X-ray transients. The X-ray spectrum can be fitted by a single, hard power-law. We detect optical variability of ∼ 0.05 magnitudes, on timescales of minutes, but find no periodic modulation. In the optical, the SEDs contain a blue component, indicative of an irradiated disc, and a transient near-infrared (NIR) excess. This excess is consistent with a simple model of an optically thick synchrotron jet (as seen in other outbursting AMXPs), however we discuss other potential origins. The optical spectrum shows a double-peaked Hα profile, a diagnostic of an accretion disc, but we do not clearly see other lines (e.g. He I, II) that were reported in 2004. Conclusions. Optical/IR observations of AMXPs appear to be excellent for studying the evolution of both the outer accretion disc and the inner jet, and may eventually provide us with tight constraints to model disc-jet coupling in accreting neutron stars.