We present a detailed study of the X-ray energy and power spectral properties of the neutron star transient IGR J17191-2821. We discovered four instances of pairs of simultaneous kilohertz quasi-periodic oscillations (kHz QPOs). The frequency difference between these kHz QPOs is between 315 Hz and 362 Hz. We also report on the detection of five thermonuclear type-I X-ray bursts and the discovery of burst oscillations at ~294 Hz during three of them. Finally, we report on a faint and short outburst precursor, which occurred about two months before the main outburst. Our results on the broadband spectral and variability properties allow us to firmly establish the atoll source nature of IGR J17191-2821.
The discovery of a type I X-ray burst from the faint unidentified transient source IGR J17445-2747 in the Galactic bulge by the JEM-X telescope onboard the INTEGRAL observatory is reported. Type I bursts are believed to be associated with thermonuclear explosions of accreted matter on the surface of a neutron star with a weak magnetic field in a low-mass X-ray binary. Thus, this observation allows the nature of this source to be established.
The observation of a pair of simultaneous twin kHz QPOs in the power density spectrum of a neutron star or a black hole allows its mass-angular-momentum relation to be constrained. Situations in which the observed simultaneous pairs are more than one allow the different models of the kHz QPOs to be falsified. Discrepancy between the estimates coming from the different pairs would call the used model into question. In the current paper the relativistic precession model is applied to the twin kHz QPOs that appear in the light curves of three groups of observations of the accreting millisecond X-…
Thermonuclear X-ray bursts from accreting neutron stars power brief but strong irradiation of their surroundings, providing a unique way to study accretion physics. We analyze MAXI/GSC and Swift/XRT spectra of a day-long flash observed from IGR J17062-6143 in 2015. It is a rare case of recurring bursts at a low accretion luminosity of 0.15% Eddington. Spectra from MAXI, Chandra, and NuSTAR observations taken between the 2015 burst and the previous one in 2012 are used to determine the accretion column. We find it to be consistent with the burst ignition column of 5x10^10 g cm^-2, which indicat…
We report on a spectroscopic analysis of the X-ray emission from IGR J17062-6143 in the aftermath of its June 2020 intermediate duration Type I X-ray burst. Using the Neutron Star Interior Composition Explorer, we started observing the source three hours after the burst was detected with MAXI/GSC, and monitored the source for the subsequent twelve days. We observed the tail end of the X-ray burst cooling phase, and find that the X-ray flux is severely depressed relative to its historic value for a three day period directly following the burst. We interpret this intensity dip as the inner accre…
Physical parameters of both the mass donor and compact object can be constrained in X-ray binaries with well-defined eclipses, as our survey of wind-fed supergiant X-ray binaries (SGXBs) IGR J16393-4643, IGR J16418-4532, IGR J16479-4514, IGR J18027-2016 and XTE J1855-026 reveals. Using the orbital period and Kepler's third law, we express the eclipse half-angle in terms of radius, inclination angle and the sum of the masses. Pulse-timing and radial velocity curves can give masses of both the donor and compact object as in the case of the "double-lined" binaries IGR J18027-2016 and XTE J1855-02…
A micronova burst in the intermediate polar IGR J17014-4306
Universidade do Vale do Paraíba（巴西谷大学）；Universidad Nacional de Hurlingham (UNAHUR)（乌尔希宁国立大学）；Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)（国家科学研究委员会）；Instituto Nacional de Pesquisas Espaciais (INPE/MCTI)（国家空间研究所）
IGR J00291+5934 is the fastest-known accretion-powered X-ray pulsar, discovered during a transient outburst in 2004. In this paper, we report on Integral and Swift observations during the 2015 outburst, which lasts for $\sim25$ d. The source has not been observed in outburst since 2008, suggesting that the long-term accretion rate has decreased by a factor of two since discovery. The averaged broad-band (0.1 - 250 keV) persistent spectrum in 2015 is well described by a thermal Comptonization model with a column density of $N_{\rm H} \approx4\times10^{21}$ cm$^{-2}$, a plasma temperature of $kT…
IGR J17591-2342 is a recently INTEGRAL discovered accreting millisecond X-ray pulsar that went into outburst around July 21, 2018. To better understand the physics acting in these systems during the outburst episode we performed detailed temporal-, timing- and spectral analyses across the 0.3-300 keV band using data from NICER, XMM-Newton, NuSTAR and INTEGRAL. The hard X-ray 20-60 keV outburst profile is composed of four flares. During the maximum of the last flare we discovered a type-I thermonuclear burst in INTEGRAL JEM-X data. We derived a distance of 7.6+/-0.7 kpc, adopting Eddington lumi…
IGR~J18245--2452/PSR J1824--2452I is one of the rare transitional accreting millisecond X-ray pulsars, showing direct evidence of switches between states of rotation powered radio pulsations and accretion powered X-ray pulsations, dubbed transitional pulsars. IGR~J18245--2452 is the only transitional pulsar so far to have shown a full accretion episode, reaching an X-ray luminosity of $\sim10^{37}$~erg~s$^{-1}$ permitting its discovery with INTEGRAL in 2013. In this paper, we report on a detailed analysis of the data collected with the IBIS/ISGRI and the two JEM-X monitors on-board INTEGRAL at…
Low Mass X-Ray Binaries (LMXBs) are systems in which a compact object accretes from a binary companion star via an accretion disk. The X-ray properties of LMXBs show strong variability over timescales ranging from milliseconds to decades, much of which is tied to the extreme environment of the inner accretion disk, hence an understanding of this behaviour is key to understanding how matter behaves in such an environment. GRS 1915+105 and MXB 1730-335 are two LMXBs which show particularly unusual variability. GRS 1915+105 shows a large number of distinct classes of second-to-minute scale variab…
The intense radiation flux of Type I X-ray bursts is expected to interact with the accretion flow around neutron stars. High frequency quasiperiodic oscillations (kHz QPOs), observed at frequencies matching orbital frequencies at tens of gravitational radii, offer a unique probe of the innermost disk regions. In this paper, we follow the lower kHz QPOs, in response to Type I X-ray bursts, in two prototypical QPO sources, namely 4U 1636-536 and 4U 1608-522, as observed by the Proportional Counter Array of the Rossi X-ray Timing Explorer. We have selected a sample of 15 bursts for which the kHz …
Hard X-ray observations with the Neil Gehrels Swift Observatory Burst Alert Telescope (BAT) reveal superorbital modulation in the wind-accreting supergiant high-mass X-ray binary (HMXB) 4U 1538-52 at a period of 14.9130 +/- 0.0026 days that is consistent with four times the 3.73 day orbital period. These periods agree with a previously suggested correlation between superorbital and orbital periods in similar HMXBs. During the ~14 years of observations the superorbital modulation changes amplitude, and since ~MJD 57,650 it was no longer detected in the power spectrum, although a peak near the s…
Descalarization bursts from Galactic supramassive neutron stars: a kHz continuous-wave target
Eberhard Karls University of Tübingen（蒂宾根大学）；Universitat de València（瓦伦西亚大学）；Observatorio Astronómico, Universitat de València（瓦伦西亚大学天文台）；Sofia University（索非亚大学）；Institute of Mathematics and Informatics, Bulgarian Academy of Sciences（保加利亚科学院数学与计算机科学研究所）
IGR J16318-4848 is an X-ray binary with the highest known line of sight absorption column density among all known X-ray binary systems in our galaxy. In order to investigate the reason behind such a large absorption column, we looked at the variations in the X-ray intensity and spectral parameters as a function of the tentatively discovered $\sim$ 80 day orbit of this source. The orbital period is firmly confirmed in the long term ($\sim$ 12 year) Swift BAT lightcurve. Two peaks about half an orbit apart, one narrow and small, and the other broad and large are seen in the orbital intensity pro…
We investigate the correlation between the frequencies of the twin kilohertz quasi-periodic oscillations (kHz QPOs) and the neutron star (NS) spins in low mass X-ray binaries (LMXBs), based on the data sets of 12 sources with simultaneously detected twin kHz QPOs and NS spins, and find that the histogram of the ratio between the frequency difference of twin kHz QPOs (Δν = ν2 - ν1) and NS spin νs shows a non-uniform distribution with a gap at Δν/νs ~ 0.65. We try to classify the 12 sources into two categories according to this gap: (I) The slow rotators with <νs> ~ 311 Hz, XTE J1807.4-294, 4U 1…
We report on the detection of X-ray pulsations at 2.1 ms from the known X-ray burster IGR J17379-3747 using XMM-Newton. The coherent signal shows a clear Doppler modulation from which we estimate an orbital period of ~1.9 hours and a projected semi-major axis of ~8 lt-ms. Taking into account the lack of eclipses (inclination angle of < 75 deg) and assuming a neutron star mass of 1.4 Msun, we estimated a minimum companion star of ~0.06 Msun. Considerations on the probability distribution of the binary inclination angle make less likely the hypothesis of a main-sequence companion star. On the ot…
Supergiant fast X-ray transients (SFXTs) are high mass X-ray binaries (HMXBs) hosting a neutron star and an OB supergiant companion. We examine the available Swift data, as well as other new or archival/serendipitous data, on three sources: IGR J17407-2808, 2XMM J185114.3-000004, and IGR J18175-2419, whose X-ray characteristics qualify them as candidate SFXT, in order to explore their properties and test whether they are consistent with an SFXT nature. As IGR J17407-2808 and 2XMM J185114.3-000004 triggered the Burst Alert Telescope on board Swift, the Swift data allow us to provide their first…
We present an investigation of long-term modulation in the X-ray light curves of five little-studied candidate high-mass X-ray binaries using the Swift Burst Alert Telescope. IGR J14488-5942 and AX J1700.2-4220 show strong modulation at periods of 49.6 and 44 days, respectively, which are interpreted as orbital periods of Be star systems. For IGR J14488-5942, observations with Swift X-ray Telescope show a hint of pulsations at 33.4 s. For AX J1700.2-4220, 54 s pulsations were previously found with XMM. Swift J1816.7-1613 exhibits complicated behavior. The strongest peak in the power spectrum i…
As of 2014 August, the Nuclear Spectroscopic Telescope Array (NuSTAR) had observed ~30 X-ray binaries either as part of the planned program, as targets of opportunity, or for instrument calibration. The main science goals for the observations include probing the inner part of the accretion disk and constraining black hole spins via reflection components, providing the first observations of hard X-ray emission from quiescent Low Mass X-ray Binaries (LMXBs), measuring cyclotron lines from accreting pulsars, and studying type I X-ray bursts from neutron stars. Here, we describe the science object…
Broad band power density spectra offer a window to understanding turbulent behavior in the emission mechanism and, at the highest frequencies, in the putative inner engines powering long GRBs. We describe a chirp search method which steps aside Fourier analysis for signal detection in the Poisson noise-dominated 2 kHz sampled BeppoSAX light curves. An efficient numerical implementation is described in $O(Nn\log n)$ operations, where $N$ is the number of chirp templates and $n$ is the length of the light curve time series, suited for embarrassingly parallel processing. For detection of individu…
We report on Nuclear Spectroscopic Telescope Array (NuSTAR), Neil Gehrels Swift Observatory (Swift) X-ray Telescope (XRT) and Swift Burst Alert Telescope (BAT) observations of IGR J16493-4348, a wind-fed Supergiant X-ray Binary (SGXB) showing significant superorbital variability. From a discrete Fourier transform of the BAT light curve, we refine its superorbital period to be 20.058 $\pm$ 0.007 days. The BAT dynamic power spectrum and a fractional root mean square analysis both show strong variations in the amplitude of the superorbital modulation, but no observed changes in the period were fo…
We report the discovery of two new types of variability in the neutron star low-mass X-ray binary MXB 1730-335 (the 'Rapid Burster'). In one observation in 1999, it exhibits a large-amplitude quasi-periodic oscillation with a period of about 7 min. In another observation in 2008, it exhibits two 4-min long 75 per cent deep dips 44 min apart. These two kinds of variability are very similar to the so-called $ρ$ or 'heartbeat' variability and the $θ$ variability, respectively, seen in the black hole low-mass X-ray binaries GRS 1915+105 and IGR J17091-3624. This shows that these types of behavior …
