Soft X-ray Pulsations Research Articles

Discovery of Soft X-Ray Pulsations from PSR J1231–1411 using NICER

Abstract We report the discovery of soft X-ray pulsations from the nearby millisecond pulsar PSR J1231−1411 using the Neutron Star Interior Composition Explorer (NICER). The pulsed emission is characterized by a broad and asymmetric main pulse and a much fainter secondary interpulse, with a total pulsed count rate of 0.055 c s−1 in the 0.35–1.5 keV band. We analyzed Fermi Large Area Telescope (LAT) data to update the pulse timing model covering 10 yr of data and used that model to coherently combine NICER data over a year of observations. Spectral modeling suggests that the flux is dominated by thermal emission from a hot spot (or spots) on the neutron star surface. The phase relationship between the X-ray pulse and the radio and γ rays provides insight into the geometry of the system.

QUASI-PERIODIC PULSATIONS DURING THE IMPULSIVE AND DECAY PHASES OF AN X-CLASS FLARE

ABSTRACT Quasi-periodic pulsations (QPPs) are often observed in X-ray emission from solar flares. To date, it is unclear what their physical origins are. Here, we present a multi-instrument investigation of the nature of QPP during the impulsive and decay phases of the X1.0 flare of 2013 October 28. We focus on the character of the fine structure pulsations evident in the soft X-ray (SXR) time derivatives and compare this variability with structure across multiple wavelengths including hard X-ray and microwave emission. We find that during the impulsive phase of the flare, high correlations between pulsations in the thermal and non-thermal emissions are seen. A characteristic timescale of ∼20 s is observed in all channels and a second timescale of ∼55 s is observed in the non-thermal emissions. SXR pulsations are seen to persist into the decay phase of this flare, up to 20 minutes after the non-thermal emission has ceased. We find that these decay phase thermal pulsations have very small amplitude and show an increase in characteristic timescale from ∼40 s up to ∼70 s. We interpret the bursty nature of the co-existing multi-wavelength QPPs during the impulsive phase in terms of episodic particle acceleration and plasma heating. The persistent thermal decay phase QPPs are most likely connected with compressive magnetohydrodynamic processes in the post-flare loops such as the fast sausage mode or the vertical kink mode.

Discovery of soft X-ray pulsations from the γ-ray source Geminga

Soft X-ray observations of the Geminga field using Rosat have been used to detect coherent pulsations from 1E0630 + 178 at a period of 0.237 s. This result confirms suggestions that Geminga is, like Vela, a gamma-ray pulsar. It is speculated that Geminga is somewhat the older of the two.

The detection of photospheric X-ray pulsations from PG 1159-035 with EXOSAT

The detection of soft X-ray pulsations from the hot, helium-rich, degenerate object, PG 1159-035 is reported. These observations, obtained with the Low Energy experiment on EXOSAT, show the presence of large-amplitude soft X-ray (44-150 A) pulsations analogous to several of the low-amplitude, nonradial, g-mode pulsations which are observed in the optical. These soft X-ray pulsations, with periods of 516 s, 524 s, and 539 s, arise from the photosphere of PG 1159-035 and constitute the first observations of stellar atmospheric pulsational phenomena in the X-ray band.

Accretion onto the White Dwarf and X‐Ray Production in Nonmagnetic Cataclysmic Variables

Cataclysmic variables (CVs) are utilized to study the accretion processes in nonmagnetic systems. X-ray observations of the nonmagnetic CVs, SS Cyg and U Gem, in particular the two-component X-ray spectra and the dependence of X-ray production on accretion rate, are discussed, and these observations are related to current boundary layer theories. It is observed that the data support the existence of an X-ray emitting corona surrounding the white dwarf. The coronal model is described and applied to the explanation of quasi-periodic soft X-ray pulsations. 27 references.

The origin of soft X-ray pulsations in dwarf novae at outburst and the DQ Herculis phenomenon

A recent study of X-ray emission from non-magnetic cataclysmic variables1 concludes that most of the hard (≳2 keV) flux is produced in a corona formed by the accreting material around the white dwarf. EXOSAT observations of SS Cygni (see accompanying paper)2 strongly support this model, confirming several of its detailed predictions. The model suggests that soft (≲2 keV) X-ray production is controlled largely by transport processes into the white-dwarf body which remove most of the energy from the accreting matter. I point out here that, because even weak magnetic fields can exert a marked influence on transport processes, tbere is a natural explanation for the quasi-periodic oscillations seen in soft X-ray observations of dwarf novae at outburst3–5. I suggest further that the puzzling behaviour of the ‘DQ Herculis’ system (DQ Her, V533 Her and AE Aqr) may be explained in this light.

Phase variability in the rapid optical oscillations of SS Cygni

High-speed photometry of SS Cygni on four nights during the 1978 September eruption revealed a small-amplitude optical oscillation with period 8.23 s and mean semiamplitude 0.0005 mag on September 21 and period 8.50 s and mean semiamplitude 0.0006 mag on September 23. If the observed periods present orbital periods near the surface of the white dwarf, then the white dwarf mass must exceed 0.92 solar mass. Phase variability of the oscillation is analyzed quantitatively and found to be less than that observed in 1978 June for soft X-ray pulsations from SS Cygni.

Soft X-ray pulsations from SS Cygni

view Abstract Citations (88) References (25) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Soft X-ray pulsations from SS Cyg. Cordova, F. A. ; Chester, T. J. ; Tuohy, I. R. ; Garmire, G. P. Abstract Pulsed soft X-rays (0.1 to 0.5 keV) with a period of 9 sec and a pulsed fraction that varies between 0 and 100% were detected from the dwarf nova SS Cygni at the peak of an optical outburst. This detection confirms for the first time the supposed high energy origin of optical pulsations seen in erupting dwarf novae. The pulse shape is remarkably sinusoidal for such a large-amplitude oscillation. The X-ray pulsation observed in this outburst is not coherent, in contrast to previous claims for the related optical oscillations. Publication: The Astrophysical Journal Pub Date: January 1980 DOI: 10.1086/157621 Bibcode: 1980ApJ...235..163C Keywords: Binary Stars; Dwarf Stars; Novae; Pulsed Radiation; Stellar Spectrophotometry; X Ray Sources; Black Body Radiation; Boundary Layer Stability; Heao; Light Curve; Pulse Duration; Stellar Luminosity; Stellar Models; X Ray Spectra; Astrophysics full text sources ADS | data products SIMBAD (2)

Analysis of the Soft X-Ray Pulsations of Dwarf Novae

Both SS Cyg and U Gem show enhanced soft X-ray emission (0.1–0.5 keV) during optical outbursts. In extended HEAO-1 pointings, it was discovered that a large fraction of this emission is pulsed (see Fig. 1). This confirms the general expectation that high energy pulsations are the ultimate source of the optical pulsations observed during outbursts of dwarf novae. For SS Cyg the average soft X-ray pulsation amplitude is 30%; this is to be contrasted with the upper limit of 10% to a hard X-ray (2–25 keV) pulsed component for the same observation (Swank 1979). Thus the origin of the oscillation is in soft X-rays, and the direct implication of such a large pulsed amplitude is that the oscillation itself must be an intrinsic part of the X-ray production mechanism.

Soft X-ray Pulsations from PSR 0833–45

THE radio pulsar PSR 0833–45 has the second fastest period of the presently known pulsars and was the first pulsar to be associated with a supernova remnant1. The SNR is the site of the nonthermal radio source2 Vela X and has also been observed to be a region of soft X-ray emission3. We have recently observed the X-ray structure of the Vela and Puppis SNRs in the energy range 0.1–1.5 keV with a scanning focusing collector that provided substantially better angular resolution than did the previous soft X-ray measurements of this region3. The instrument was an improved version of the device described by Gorenstein et al.4 and was flown aboard an Aerobee 170 sounding rocket fired from the White Sands Missile Range on April 1, 1972. We find the X-ray source in the Vela SNR to consist of a continuous extended region with structure plus a concentration of X-ray emission which is consistent with a point source at the position of PSR 0833–45. Here we report only results pertaining to PSR 0833–45.