M. Chernyakova

INTEGRAL and XMM-Newton observations of LSI +61 303

LSI +61 ◦ 303 is one of the few X-ray binaries with Be star companion from which both radio and high-energy gamma-ray emission have been observed. We present XMM-Newton and INTEGRAL observations which reveal variability of the X-ray spectra l index of the system. The X-ray spectrum is hard (photon index ≃ 1.5) during the orbital phases of both high and low X-ray flux. However, the spectrum softens at the moment of transition from high to low X-ray state. The spectrum of the system in the hard X-ray band does not reveal the presence of a cut-off (or, at least a spectral break) at 10-60 keV energies, expect ed if the compact object is an accreting neutron star. The observed spectrum and spectral variability can be explained if the compact object in the system is a rotation powered pulsar.

INTEGRAL and XMM-Newton observations of the X-ray pulsar IGR J16320-4751/AX J1631.9-4752

We report on observations of the X-ray pulsar IGR J16320−4751 (a.k.a. AX J1631.9−4752) performed simultaneously with INTEGRAL and XMM-Newton. We refine the source position and identify the most likely infrared counterpart. Our simultaneous coverage allows us to confirm the presence of X-ray pulsations at ∼ 1300 s, that we detect above 20 keV with INTEGRAL for the first time. The pulse fraction is consistent with bein g constant with energy, which is compatible with a model of polar accretion by a pulsar. We study the spectral properties of IGR J16320−4751 during two major periods occurring during the simultaneous coverage with both satellites, namely a flare and a non-flare p eriod. We detect the presence of a narrow 6.4 keV iron line in both periods. The presence of such a feature is typical of supergiant wind accretors such as Vela X-1 or GX 301−2. We inspect the spectral variations with respect to the pulse phase during the non-flare period, a nd show that the pulse is solely due to variations of the X-ray flux emitted by the source and no t to variations of the spectral parameters. Our results are therefore compatible with the source being a pulsar in a High Mass X-ray Binary. We detect a soft excess appearing in the spectra as a blackbody with a temperature of∼0.07 keV. We discuss the origin of the X-ray emission in IGR J16320−4751: while the hard X-rays are likely the result of Compton emission produced in the close vicinity of the pulsar, based on energy argument we suggest that the soft excess is likely the emission by a collisionally energised cloud in which the compact object is embedded.

INTEGRAL and RXTE monitoring of GRS 1758-258 in 2003 and 2004 : A transition from the dim soft state to the hard state

The Galactic Center black hole candidate (BHC) GRS 1758-258 has been observed extensively within INTEGRALs Galactic Center Deep Exposure (GCDE) program in 2003 and 2004, while also being monitored with RXTE. We present quasi-simultaneous PCA, ISGRI, and SPI spectra from four GCDE observation epochs as well as the evolution of energy-resolved PCA and ISGRI light curves on time scales of days to months. We find that during the first epoch GRS 1758-258 displayed another of its peculiar dim soft states like the one observed in 2001, increasing the number of observed occurrences of this state to three. During the other epochs the source was in the hard state. The hard X-ray emission component in the epoch-summed spectra can be well described either by phenomenological models, namely a cutoff power law in the hard state and a pure power law in the dim soft state, or by thermal Comptonization models. A soft thermal component is clearly present in the dim soft state and might also contribute to the softer hard state spectra. We argue that in the recently emerging picture of the hardness-intensity evolution of black hole transient outbursts in which hard and soft states are observed to occur in a large overlapping range of luminosities (hysteresis), the dim soft state is not peculiar. As noted before for the 2001 dim soft state, these episodes seem to be triggered by a sudden decrease (within days) of the hard emission, with the soft spectral component decaying on a longer time scale (weeks). We discuss this behavior as well as additional flux changes observed in the light curves in terms of the existence of two accretion flows characterized by different accretion time scales, the model previously suggested for the 2001 episode.

PANGU: A High Resolution Gamma-Ray Space Telescope

PANGU (the PAir-productioN Gamma-ray Unit) is a small astrophysics mission with wide field of view optimized for spectro-imaging, timing and polarisation studies. It will map the gamma-ray sky from ...

Discovery and study of the accreting pulsar 2RXP J130159.6-635806

We report on analysis of the poorly studied source 2RXP J130159.6-635806 at different epochs with ASCA, BeppoSAX, XMM-Newton and INTEGRAL. The source shows coherent X-ray pulsations at a period ∼700 s with an average spin-up rate of about v ∼ 2 × 10 -13 Hz s -1 . A broad-band (1-60 keV) spectral analysis of 2RXP J130159.6-635806 based on almost simultaneous XMM-Newton and INTEGRAL data demonstrates that the source has a spectrum typical of an accretion-powered X-ray pulsar, i.e. an absorbed power law with a high-energy cut-off with a photon index Γ ∼ 0.5-1.0 and a cut-off energy of ∼25 keV. The long-term behaviour of the source, its spectral and timing properties, tend to indicate a high-mass X-ray binary with a Be companion. We also report on the identification of the likely infrared counterpart to 2RXP J130159.6-635806. The interstellar reddening does not allow us to strongly constrain the spectral type of the counterpart. The latter is, however, consistent with a Be star, the kind of which is often observed in accretion-powered X-ray pulsars.

Multi-wavelength observations of the binary system PSR B1259−63/LS 2883 around the 2014 periastron passage

We report on the results of the extensive multi-wavelength campaign from optical to GeV γ-rays of the 2014 periastron passage of PSR B1259−63, which is a unique high-mass γ-ray emitting binary system with a young pulsar companion. Observations demonstrate the stable nature of the post-periastron GeV flare and prove the coincidence of the flare with the start of rapid decay of the Hα equivalent width, usually interpreted as a disruption of the Be stellar disc. Intensive X-ray observations reveal changes in the X-ray spectral behaviour happening at the moment of the GeV flare. We demonstrate that these changes can be naturally explained as a result of synchrotron cooling of monoenergetic relativistic electrons injected into the system during the GeV flare.

SUPERORBITAL MODULATION OF X-RAY EMISSION FROM GAMMA-RAY BINARY LSI +61 303

We report the discovery of a systematic constant time lag between the X-ray and radio flares of the gamma-ray binary LSI +61 303, persistent over a long, multi-year timescale. Using the data from the monitoring of the system by RXTE we show that the orbital phase of X-ray flares from the source varies from {phi}{sub X} {approx_equal} 0.35 to {phi}{sub X} {approx_equal} 0.75 on the superorbital 4.6 yr timescale. Simultaneous radio observations show that periodic radio flares always lag the X-ray flare by {Delta}{phi}{sub X-R} {approx_equal} 0.2. We propose that the constant phase lag corresponds to the time of flight of the high-energy particle-filled plasma blobs from inside the binary to the radio emission region at the distance of {approx}10 times the binary separation distance. We put forward a hypothesis that the X-ray bursts correspond to the moments of formation of plasma blobs inside the binary system.

INTEGRAL observations of the PSR B1259-63/SS2883 system after the 2004 periastron passage

The millisecond pulsar PSR B1259-63 and the Be star SS2883 are situated in a highly eccentric binary system, with orbital period ∼3.4 years. We report on hard X-ray observations obtained with the INTEGRAL satellite close to the 2004 perias- tron passage. These are the first imaging observations of this system in the hard X-ray range (>20 keV) and allow the emission of PSR B1259-63 to be separated from that of a nearby unidentified variable source which may have contaminated previous hard X-ray observations of this system. Using the IBIS/ISGRI instrument we measured a flux of ∼2-6 mCrab in the 20-200 keV range, with a power law spectrum of photon index Γ= 1.3 ± 0.5.

GAMMA-RAY FLARE ACTIVITY FROM PSR B1259–63 DURING 2014 PERIASTRON PASSAGE AND COMPARISON TO ITS 2010 PASSAGE

PSR B1259-63/LS 2883 is a gamma-ray binary system containing a radio pulsar in a highly elliptical ~3.4-year orbit around a Be star. In its 2010 periastron passage, multiwavelength emission from radio to TeV was observed, as well as an unexpected GeV flare measured by the Fermi Large Area Telescope (LAT). Here, we report the results of LAT monitoring of PSR B1259-63 during its most recent 2014 periastron passage. We compare the gamma-ray behavior in this periastron with the former in 2010 and find that PSR B1259-63 shows a recurrent GeV flare. The similarities and differences in the phenomenology of both periastron passages are discussed.

NuSTAR DISCOVERY OF AN UNUSUALLY STEADY LONG-TERM SPIN-UP OF THE Be BINARY 2RXP J130159.6–635806

We present spectral and timing analysis of NuSTAR observations of the accreting X-ray pulsar 2RXP J130159.6-635806. The source was serendipitously observed during a campaign focused on the gamma-ray binary PSR B1259-63 and was later targeted for a dedicated observation. The spectrum has a typical shape for accreting X-ray pulsars, consisting of a simple power law with an exponential cutoff starting at ~7 keV with a folding energy of E_fold=~18 keV. There is also an indication of the presence of a 6.4 keV iron line in the spectrum at the ~3 sigma significance level. NuSTAR measurements of the pulsation period reveal that the pulsar has undergone a strong and steady spin-up for the last 20 years. The pulsed fraction is estimated to be ~80%, and is constant with energy up to 40 keV. The power density spectrum shows a break towards higher frequencies relative to the current spin period. This, together with steady persistent luminosity, points to a long-term mass accretion rate high enough to bring the pulsar out of spin equilibrium.