Near infrared studies of the massive X-ray binary 2S 0114+65

We present near-infrared spectroscopy of the massive X-ray binary 2S 0114+650. These observations covering the spectral range 1.08–2.35 μm span the region where Paschen and Brackett series recombination lines of hydrogen are expected to be seen, namely, Paβ , Brγ and Br 10–17 lines. The absence of any of these lines in emission supports earlier inferences that the optical component in 2S 0114+650 is unlikely to be a Be star but rather a B type supergiant. Near-IR photometry gives J = 8.78, H = 8.53 and K = 7.96; these values show marginal variations from earlier reported measurements.     

Phase resolved study of the CRSF in MX 0656-072

MXB 0656-072 is an accreting X-ray pulsar with a Be star companion, showing notable emission in H. In October 2003 this system exhibited a large and extended X-ray outburst. RXTE observations during this outburst indicated a pulse period of 160.4 s and a cyclotron resonance scattering feature in the spectrum at 32 keV. This paper presents pulse profile analysis and phase-resolved X-ray spectroscopy of RXTE observations during this outburst.     

Improved orbital parameters of accreting millisecond pulsar SAX J1808.4-3658

We analyze the three outbursts of the X-ray millisecond pulsar SAX J1808.4-3658 that occurred in 1998, 2000, and 2002 observed with RXTE. With a technique based on epoch folding search we find an unique orbital solution valid over the five years of high temporal resolution data available. We revise the estimate of the orbital period, P_orb = 7249.1569(1) s and of its error, which we decrease by one order of magnitude. We also give the first constraint on the orbital period derivative, . We find that in 2002 the pulse profile shape is clearly asymmetric, showing a secondary peak at about 145° from the main pulse, which is different from the sinusoidal shape reported at the beginning of the 1998 outburst.     

Measurement of neutron star parameters: A review of methods for low-mass X-ray binaries

Measurement of at least three independent parameters, for example, mass, radius and spin frequency, of a neutron star is probably the only way to understand the nature of its supranuclear core matter. Such a measurement is extremely difficult because of various systematic uncertainties. The lack of knowledge of several system parameter values gives rise to such systematics. Low mass X-ray binaries, which contain neutron stars, provide a number of methods to constrain the stellar parameters. Joint application of these methods has a great potential to significantly reduce the systematic uncertainties, and hence to measure three independent neutron star parameters accurately. Here, we review the methods based on: (1) thermonuclear X-ray bursts; (2) accretion-powered millisecond-period pulsations; (3) kilohertz quasi-periodic oscillations; (4) broad relativistic iron lines; (5) quiescent emissions; and (6) binary orbital motions.     

Spin parameters of nanosatellite BLITS determined from Graz 2 kHz SLR data

The nanosatellite BLITS (Ball Lens In The Space) is the first object designed as a passive, spherical retroreflector of the Luneburg type, dedicated for Satellite Laser Ranging (SLR). The 2 kHz SLR station Graz measures spin parameters of this satellite, providing information about the rotational dynamics of the body. The measurements obtained during the period from September 26, 2009 to November 24, 2010 show a significant change of the spin configuration. The spin axis was dynamically precessing since the launch and currently is sinus-like behaving between coordinates RA 120°…150°, Dec 30°…60° (J2000 inertial reference frame). The angle between the symmetry axis and the spin axis of BLITS is not constant, but is decreasing since the launch, while its spin period is rather stable with a mean value of 5.613 s (clockwise rotation). The satellite was dynamically changing its attitude during the first three months after deployment; after this time the spin parameters are relatively stable.     

Magnetar descendants in HMXBs?

We investigate the relation between the pulse and orbital periods in high-mass X-ray binaries (HMXBs), in order to find the candidates of magnetar descendants in HMXBs. We suggest that magnetar descendants can be found among the HMXBs with relatively shorter orbital periods and longer pulse periods.     

XMM-Newton observations of faint X-ray sources in globular clusters

Using the new generation of X-ray observatories, we are now beginning to identify populations of close binaries in globular clusters, previously elusive in the optical domain because of the high stellar density. These binaries are thought to be, at least in part, responsible for delaying the inevitable core collapse of globular clusters and their identification is therefore essential in understanding the evolution of globular clusters, as well as being valuable in the study of the binaries themselves. Here, we present observations made with XMM-Newton of six globular clusters, in which we have identified neutron star low mass X-ray binaries and their descendants (millisecond pulsars), cataclysmic variables and other types of binaries. We discuss not only the characteristics of these binaries, but also their formation and evolution in globular clusters and their use in tracing the dynamical history of these clusters.     

改进S／DB提高FY—2A云图配准精度的方法

针对ＦＹ－２Ａ卫星因扫描辐射计步进引起卫星自旋周期变化从而造成图像精度恶化问题,根据扫描辐射计的运动规律,提出地面同步与数据缓冲系统（Ｓ／ＤＢ）预先补偿系统误差的解决方法;增强了Ｓ／ＤＢ的跟踪水平,使卫星图像的配准精度提高了近三倍,达到了内外先进卫星的水平,实际应用效果良好。     

22 Years of AJISAI spin period determination from standard SLR and kHz SLR data

Satellite Laser Ranging (SLR) is a powerful and efficient technique to measure spin parameters of satellites equipped with corner cube reflectors. We obtained spin period determination of the satellite AJISAI from SLR data only: 17246 pass-by-pass estimates from standard 1–15 Hz SLR data (14/Aug/1986–30/Dec/2008) and 1444 pass-by-pass estimates (9/Oct/2003–30/Dec/2008) from data of the first 2 kHz SLR system from Graz, Austria. A continuous history of the slowing down of AJISAI spin is derived from frequency analysis, and corrected for the apparent effects. The apparent corrections, elaborated here, allowed very accurate determination of AJISAI initial spin period: 1.4855 ± 0.0007 [s]. The paper identifies also non-gravitational effects as a source of the periodical changes in the rate of slowing down of the satellite.     

The peculiar X-ray source in NGC 5281

Recent observations with Chandra and XMM-Newton   have shown that the X-ray source 1WGA J1346.5–6255 is associated with the Be star HD 119682, a member of the open cluster NGC 5281, and displays all the characteristics of the new class of X-ray sources known as γ$\mathrm{\gamma }$-Cas analogues. We present a detailed spectroscopic study of this open cluster, finding an age of 40 Myr and a sequence of evolved stars. These results imply that HD 119682 is a blue straggler in NGC 5281, as it is much more massive than any other cluster member, and its membership is strongly suggested by proper motion analysis. This is the second γ$\mathrm{\gamma }$-Cas analogue found to be blue straggler in an open cluster, suggesting that evolution plays a role in the formation of these systems and that a supernova explosion has not occurred in them.     

Evolution of the temporal and the spectral properties in 2010 and 2011 outbursts of H 1743-322

The Galactic black hole candidate H 1743-322 exhibited two X-ray outbursts in rapid succession: one in August 2010 and the other in April 2011. We analyze archival data of this object from the PCA instrument on board RXTE (2–25 keV energy band) to study the evolution of its temporal and spectral characteristics during both the outbursts, and hence to understand the behavioral change of the accretion flow dynamics associated with the evolution of the various X-ray features. We study the evolution of QPO frequencies during the rising and the declining phases of both the outbursts. We successfully fit the variation of QPO frequency using the Propagating Oscillatory Shock (POS) model in each of the outbursts and obtain the accretion flow parameters such as the instantaneous shock locations, the shock velocity and the shock strength. Based on the degree of importance of the thermal (disk black body) and the non-thermal (power-law) components of the spectral fit and properties of the QPO (if present), the entire profiles of the 2010 and 2011 outbursts are subdivided into four different spectral states: hard, hard-intermediate, soft-intermediate and soft. We attempt to explain the nature of the outburst profile (i.e., hardness-intensity diagram) with two different types of mass accretion flow.     

Orbital evolution studies of two HMXB pulsars

High mass X-ray binary (HMXB) pulsars are of two types, persistent and transient. 4U1538−52 is a persistent HMXB whose orbit was previously measured to be circular but the RXTE observations revealed an eccentric orbit. We observed this system with RXTE-PCA in August 2003 and our timing analysis supports the eccentric orbit of the system. However, we do not find any evidence for orbital evolution.

Rotational and tidal interactions between the stars of a closed binary system result in apsidal motion which can be measured in systems with eccentric orbit. 4U0115+63 is a Be-transient HMXB whose eccentric orbit was well-determined during its 1978 outburst. We report preliminary results from analysis of data obtained during the 1999 outburst of this source with the RXTE-PCA.     

‘Spectro-temporal’ characteristics and disk-jet connection of the outbursting black hole source XTE J1859+226

We re-investigated the ‘spectro-temporal’ behavior of the source XTE J1859+226 in X-rays during its outburst phase in 1999, by analysing the RXTE PCA/HEXTE data in 2–150 keV spectral band. Detailed analysis shows that the source evolves through different spectral states during its entire outburst as indicated by the variation in the spectral and temporal characteristics. Although the evolution pattern of the outburst followed the typical q-shaped profile, we observed an absence of ‘canonical’ soft state and a weak presence of ‘secondary’ emission during the decay phase of the outburst. The broad-band spectra, modeled with high energy cutoff, shows that the fold-energy increases monotonically in the hard and hard-intermediate states followed by a random variation in the soft-intermediate state. We attempted to estimate the mass of the source based on the evolution of Quasi-Periodic Oscillation (QPO) frequencies during rising phase modeled with the propagating oscillatory shock solution, and from the correlation of photon index and QPO frequency. It is also observed that during multiple ejections (observed as radio flares) the QPO frequencies are not present in the power spectra and there is an absence of lag in the soft to hard photons. The disk flux increases along with a decrease in the high energy flux, implying the soft nature of the spectrum. These results are the ‘possible’ indication that the inner part of the disk (i.e., Comptonized corona), which could be responsible for the generation of QPO and for the non-thermal Comptonized component of the spectrum, is disrupted and the matter gets evacuated in the form of jet. We attempted to explain the complex behavior of ‘spectro-temporal’ properties of the source during the entire outburst and the nature of the disk-jet connection before, during and after the ejection events in the context of two different types of accreting flow material, in presence of magnetic field.     

Detecting gravitational waves from accreting neutron stars

The gravitational waves emitted by neutron stars carry unique information about their structure and composition. Direct detection of these gravitational waves, however, is a formidable technical challenge. In a recent study we quantified the hurdles facing searches for gravitational waves from the known accreting neutron stars, given the level of uncertainty that exists regarding spin and orbital parameters. In this paper we reflect on our conclusions, and issue an open challenge to the theoretical community to consider how searches should be designed to yield the most astrophysically interesting upper limits. With this in mind we examine some more optimistic emission scenarios involving spin-down, and show that there are technically feasible searches, particularly for the accreting millisecond pulsars, that might place meaningful constraints on torque mechanisms. We finish with a brief discussion of prospects for indirect detection.     

Spin parameters of Low Earth Orbiting satellites Larets and Stella determined from Satellite Laser Ranging data

Satellite Laser Ranging (SLR) measurements contain information about the spin parameters of the fully passive, geodetic satellites. In this paper we spectrally analyze the SLR data of 5 geodetic satellites placed on the Low Earth Orbits: GFZ-1, WESTPAC, Larets, Starlette, Stella, and successfully retrieve the frequency signal from Larets and Stella only. The obtained signals indicate an exponential increase of the spin period of Larets: T = 0.860499·exp(0.0197066·D) [s], and Stella: T = 13.5582·exp(0.00431232·D) [s], where D is in days since launch. The initial spin periods calculated from the first month of the SLR observations are: Larets: T_initial = 0.8239 s, Stella: T_initial = 13.2048 s. Analysis of the apparent effects indicates the counter-clockwise spin direction of the satellites. The twice more heavy Stella lost its rotational energy more than four times slower than Larets. Fitting the spin model to the observed spin trends allows determination of the spin axis orientation evolution for Larets and Stella before their rotational period becomes equal to the orbital period.     

Changes in radio emission from PSR J0737–3039B

The double pulsar system, J0737–3039, provides a unique probe of a pulsar magnetosphere due to its edge-on viewing geometry, a tight orbit and a significant rate of advance of the angle of periastron. In this paper, we report on the changes in radio emission from the long period pulsar in this system, J0737–3039B, over a period of 9 months. Observations of this system with Giant Metrewave Radio Telescope (GMRT) show that the duration of the first bright phase of the pulsar centered at 210° orbital longitude from the ascending node is shrinking. These observations will be useful to constrain the proposed models for this system.     

10 Years of LAGEOS-1 and 15 years of LAGEOS-2 spin period determination from SLR data

Satellite Laser Ranging (SLR) stations measure distance to the satellites equipped with Corner Cube Reflectors (CCRs). These range measurements contain information about spin parameters of the spacecraft. In this paper we present results of spin period determination of two passive satellites from SLR data only: 10 years of LAGEOS-1 (10426 values), and 15 years of LAGEOS-2 (15580 values). The measurements have been made by standard 10 Hz SLR systems and the first 2 kHz SLR system from Graz (Austria). The obtained data allowed calculation of the initial spin period of the satellites: 0.61 s for LAGEOS-1 and 0.906 s for LAGEOS-2. Long time series of the spin period values show that the satellite’s slowing down rate is not constant but is oscillating with a period of 846 days for LAGEOS-1 and 578 days for LAGEOS-2. The results presented here definitely prove that the SLR is a very efficient technique able to measure spin period of the geodetic satellites.     

Time dependent accretion onto a black hole in a disk plus corona system

Hard X-ray lightcurves exhibit delays of 1 s with respect to the soft X-ray lightcurves when the microquasar GRS 1915+105 is in the state of frequent, regular outbursts. Such outbursts are supposed to be driven by the radiation pressure instability of the inner disk parts. The hard X-ray delays are then caused by the time needed for the adjustment of the corona to changing conditions in the underlying disk. We support this claim by the computation of the time evolution of the disk, including a non-stationary evaporation of the disk and mass exchange with the corona.     

Late stages of stellar evolution – Herschel’s contributions

Cool objects glow in the infrared. The gas and solid-state species that escape the stellar gravitational attraction of evolved late-type stars in the form of a stellar wind are cool, with temperatures typically ?1500 K, and can be ideally studied in the infrared. These stellar winds create huge extended circumstellar envelopes with extents approaching 10¹⁹${10}^{19}$ cm. In these envelopes, a complex kinematical, thermodynamical and chemical interplay determines the global and local structural parameters. Unraveling the wind acceleration mechanisms and deriving the complicated structure of the envelopes is important to understand the late stages of evolution of ∼97% of stars in galaxies as our own Milky Way. That way, we can also assess the significant chemical enrichment of the interstellar medium by the mass loss of these evolved stars. The Herschel Space Observatory is uniquely placed to study evolved stars thanks to the excellent capabilities of the three infrared and sub-millimeter instruments on board: PACS, SPIRE and HIFI. In this review, I give an overview of a few important results obtained during the first two years of Herschel observations in the field of evolved low and intermediate mass stars, and I will show how the Herschel observations can solve some historical questions on these late stages of stellar evolution, but also add some new ones.     

Production and evolution of millisecond X-ray and radio pulsars

Observations using the Rossi X-ray Timing Explorer (RXTE) have discovered dozens of accreting neutron stars with millisecond spin periods in low-mass binary star systems. Eighteen are millisecond X-ray pulsars powered by accretion or nuclear burning or both. These stars have magnetic fields strong enough for them to become millisecond rotation-powered (radio) pulsars when accretion ceases. Few, if any, accretion- or rotation-powered pulsars have spin rates higher than 750 Hz. There is strong evidence that the spin-up of some accreting neutron stars is limited by magnetic spin-equilibrium whereas the spin-up of others is halted when accretion ends. Further study will show whether the spin rates of some accretion- or rotation-powered pulsars are or were limited by emission of gravitational radiation.