The twelfth accretion-powered millisecond pulsar, IGR J17511-3057, was discovered in September 2009. In this work we study its spectral and timing properties during the 2009 outburst based on Swift and RXTE data. Our spectral analysis of the source indicates only slight spectral shape evolution during the entire outburst. The equivalent width of the iron line and the apparent area of the blackbody emission associated with the hotspot at the stellar surface both decrease significantly during the outburst. This is consistent with a gradual receding of the accretion disc as the accretion rate drops. The pulse profile analysis shows absence of dramatic shape evolution with a moderate decrease in pulse amplitude. This behaviour might result from a movement of the accretion column footprint towards the magnetic pole as the disc retreats. The time lag between the soft and the hard energy pulses increase by a factor of two during the outburst. A physical displacement of the centroid of the accretion shock relative to the blackbody spot or changes in the emissivity pattern of the Comptonization component related to the variations of the accretion column structure could cause this evolution. We have found that IGR J17511-3057 demonstrates outburst stages similar to those seen in SAX J1808.4-3658. A transition from the "slow decay" into the "rapid drop" stage, associated with the dramatic flux decrease, is also accompanied by a pulse phase shift which could result from an appearance of the secondary spot due to the increasing inner disc radius.
We report the results of a high-energy multi-instrumental campaign with INTEGRAL, RXTE, and Swift of the recently discovered INTEGRAL source IGR J19294+1816. The Swift/XRT data allow us to refine the position of the source to RA= 19h 29m 55.9s Dec=+18deg 18' 38.4" (+- 3.5"), which in turn permits us to identify a candidate infrared counterpart. The Swift and RXTE spectra are well fitted with absorbed power laws with hard (Gamma ~ 1) photon indices. During the longest Swift observation, we obtained evidence of absorption in true excess to the Galactic value, which may indicate some intrinsic ab…
Rossi X-ray Timing Explorer (RXTE)/Proportional Counter Array (PCA) observations of IGR J19294+1816 covering two outburst episodes are reported. The first outburst happened during MJD 54921-54925 (2009 C.E.) and the second one happened during MJD 55499-55507 (2010 C.E.). In both the cases the PCA observations were made during the decay phase of the outburst, with the source exhibiting temporal and spectral evolution with the change in flux. At the bright flux level an absorption feature at 35.5 keV is detected in the spectra which may be attributed to Cyclotron Resonance Scattering Feature cor…
We present the results of the first four (quasi-)simultaneous radio (ATCA), X-ray (Swift, RXTE), and Gamma-ray (INTEGRAL) observations of the black hole candidate IGR J17091-3624, performed in February and March 2011. The X-ray analysis shows that the source was in the hard state, and then it transited to a soft intermediate state. We study the correlated radio/X-ray behaviour of this source for the first time. The radio counterpart to IGR J17091-3624 was detected during all four observations with the ATCA. In the hard state, the radio spectrum is typical of optically thick synchrotron emissio…
Aims. To establish the X-ray properties of the intermediate polar candidate IGR J15094-6649 and therefore confirm its inclusion into the class. Methods. 42 856 s of X-ray data from RXTE was analysed. Frequency analysis was used to constrain temporal variations and spectral analysis used to characterise the emission and absorption properties. Results. A spin period of 809.7+-0.6 s is present, revealed as a complex pulse profile whose modulation depth decreases with increasing X-ray energy. The spectrum is well fitted by either a 19+-4 keV Bremsstrahlung or Gamma=1.8+-0.1 power law, with an iron…
We present Karl G. Jansky Very Large Array radio frequency observations of the new accreting millisecond X-ray pulsar (AMXP), IGR J16597$-$3704, located in the globular cluster NGC 6256. With these data, we detect a radio counterpart to IGR J16597$-$3704, and determine an improved source position. Pairing our radio observations with quasi-simultaneous Swift/XRT X-ray observations, we place IGR J16597$-$3704 on the radio -- X-ray luminosity plane, where we find that IGR J16597$-$3704 is one of the more radio-quiet neutron star low-mass X-ray binaries known to date. We discuss the mechanisms tha…
A new accreting millisecond X-ray pulsar, IGR J17511-3057, was discovered in outburst on 2009 September 12 during the INTEGRAL Galactic bulge monitoring programme. To study the evolution of the source X-ray flux and spectral properties during the outburst, we requested a Swift monitoring of IGRJ17511-3057. In this paper we report on the results of the first two weeks of monitoring the source. The persistent emission of IGR J17511-3057 during the outburst is modeled well with an absorbed blackbody (kT~0.9 keV) and a power-law component (photon index~1-2), similar to what has been observed from …
We present the discovery of 163.65 Hz X-ray pulsations from IGR J17062-6143 in the only observation obtained from the source with the Rossi X-ray Timing Explorer. This detection makes IGR J17062-6143 the lowest-frequency accreting millisecond X-ray pulsar presently known. The pulsations are detected in the 2 - 12 keV band with an overall significance of 4.3 sigma, and an observed pulsed amplitude of 5.54 +- 0.67 % (in this band). Both dynamic power spectral and coherent phase timing analysis indicate that the pulsation frequency is decreasing during the 1.2 ks observation in a manner consisten…
IGR J17591$-$2342 is a 527-Hz accreting millisecond X-ray pulsar that was discovered in outburst in 2018 August. In this paper, we present quasi-simultaneous radio and X-ray monitoring of this source during the early part of the outburst. IGR J17591$-$2342 is highly absorbed in X-rays, with an equivalent hydrogen absorption along the line of sight, $N_{\rm H}$, of $\approx$4.4$\times$10$^{22}$\,cm$^{-2}$, where the Galactic column density is expected to be $\approx$1 -- 2$\times$10$^{22}$\,cm$^{-2}$. The high absorption suggests that the source is either relatively distant ($>$6\,kpc), or the …
We report the discovery of burst oscillations at the spin frequency in ten thermonuclear bursts from the accreting millisecond X-ray pulsar (AMXP) IGR J17511-3057. The burst oscillation properties are, like those from the persistent AMXPs SAX J1808.4-3658 and XTE J1814-338, anomalous compared to burst oscillations from intermittent pulsars or non-pulsing LMXBs. Like SAX J1808.4-3658 they show frequency drifts in the rising phase rather than the tail. There is also evidence for harmonic content. Where IGR J17511-3057 is unusual compared to the other two persistent pulsars is that oscillations a…
We report on the Neutron Star Interior Composition Explorer (NICER) monitoring campaign of the 468 Hz accreting millisecond X-ray pulsar IGR J17379-3747. From a detailed spectral and timing analysis of the coherent pulsations we find that they show a strong energy dependence, with soft thermal emission lagging about 640 microseconds behind the hard, Comptonized emission. Additionally, we observe uncommonly large pulse fractions, with measured amplitudes in excess of 20% sinusoidal fractional amplitude across the NICER passband and fluctuations of up to ~70%. Based on a phase-resolved spectral …
IGR J17591$-$2342 is a new accreting millisecond X-ray pulsar (AMXP) that was recently discovered in outburst in 2018. Early observations revealed that the source's radio emission is brighter than that of any other known neutron star low-mass X-ray binary (NS-LMXB) at comparable X-ray luminosity, and assuming its likely $\gtrsim 6$ kpc distance. It is comparably radio bright to black hole LMXBs at similar X-ray luminosities. In this work, we present the results of our extensive radio and X-ray monitoring campaign of the 2018 outburst of IGR J17591$-$2342. In total we collected 10 quasi-simulta…
We introduce a new method for analysing the aperiodic variability of coherent pulsations in accreting millisecond X-ray pulsars. Our method involves applying a complex frequency correction to the time-domain light curve, allowing for the aperiodic modulation of the pulse amplitude to be robustly extracted in the frequency domain. We discuss the statistical properties of the resulting modulation spectrum and show how it can be correlated with the non-pulsed emission to determine if the periodic and aperiodic variability are coupled processes. Using this method, we study the 598.88 Hz coherent p…
IGR J17511-3057 is a low mass X-ray binary hosting a neutron star and is one of the few accreting millisecond X-ray pulsars with X-ray bursts. We report on a 20ksec Chandra grating observation of IGR J17511-3057, performed on 2009 September 22. We determine the most accurate X-ray position of IGR J17511-3057, alpha(J2000) = 17h 51m 08.66s, delta(J2000) = -30deg 57' 41.0" (90% uncertainty of 0.6"). During the observation, a ~54sec long type-I X-ray burst is detected. The persistent (non-burst) emission has an absorbed 0.5-8keV luminosity of 1.7 x 10^36 erg/sec (at 6.9kpc) and can be well descri…
We present our works in updating the spin and orbital parameters for the newly discovered accreting millisecond X-ray pulsar (AMXP) IGR J17591$-$2342 through pulsar timing and analyzing its energy dependent pulse behaviors. The data being analyzed were collected by Neutron Star Interior Composition ExploreR (NICER) that observed this AMXP from August to October 2018. Using the pulse arrival time delay technique, more accurate spin and orbital parameters were evaluated. From the measured spin frequency derivative, it is estimated that the magnetic field of the neutron star in IGR J17591$-$2342 …
We report on a coherent timing analysis of the 163 Hz accreting millisecond X-ray pulsar IGR J17062-6143. Using data collected with the Neutron Star Interior Composition Explorer and XMM-Newton, we investigated the pulsar evolution over a timespan of four years. We obtained a unique phase-coherent timing solution for the stellar spin, finding the source to be spinning up at a rate of $(3.77\pm0.09)\times 10^{-15}$ Hz/s. We further find that the $0.4-6$ keV pulse fraction varies gradually between 0.5% and 2.5% following a sinusoidal oscillation with a $1210\pm40$ day period. Finally, we supplem…
The accreting millisecond pulsars IGR J00291+5934 and SAX J1808.4-3658 are two compact binaries with very similar orbital parameters. The latter has been observed to evolve on a very short timescale of ~70 Myr which is more than an order of magnitude shorter than expected. There is an ongoing debate on the possibility that the pulsar spin-down power ablates the companion generating large amount of mass-loss in the system. It is interesting therefore to study whether IGR J00291+5934 does show a similar behaviour as its twin system SAX J1808.4-3658. In this work we present the first measurement …
We report on the aperiodic X-ray timing and color behavior of the accreting millisecond X-ray pulsar (AMXP) IGR J17511-3057, using all the pointed observations obtained with the Rossi X-ray Timing Explorer Proportional Counter Array since the source's discovery on 2009 September 12. The source can be classified as an atoll source on the basis of the color and timing characteristics. It was in the hard state during the entire outburst. In the beginning and at the end of the outburst, the source exhibited what appear to be twin kHz quasi periodic oscillations (QPOs). The separation Δνbetween the…
This work presents an investigation of the stochastic X-ray variability from the 164 Hz accreting millisecond pulsar IGR J17062-6143, based on regular observations collected with the Neutron Star Interior Composition Explorer between 2017 July and 2020 August. Over this period, the power density spectrum showed a stable morphology, with broad $\sim25\%$ rms band-limited noise below 16 Hz. Quasi-periodic oscillations (QPOs) were occasionally observed, with the most notably detections including a low-frequency QPO centered at 2.7 Hz and a sharp QPO centered at 115 Hz that may be a 2:3 resonance …
IGR J17591-2342 is an accreting millisecond X-ray pulsar discovered in 2018 August in scans of the Galactic bulge and center by the INTEGRAL X-ray and gamma-ray observatory. It exhibited an unusual outburst profile with multiple peaks in the X-ray, as observed by several X-ray satellites over three months. Here we present observations of this source performed in the X-ray/gamma-ray and near infrared domains, and focus on a simultaneous observation performed with the Chandra-High Energy Transmission Gratings Spectrometer (HETGS) and the Neutron Star Interior Composition Explorer (NICER). HETGS …
We report the detection of 376.05 Hz (2.66 ms) coherent X-ray pulsations in NICER observations of a transient outburst of the low-mass X-ray binary IGR J17494-3030 in 2020 October/November. The system is an accreting millisecond X-ray pulsar in a 75 minute ultracompact binary. The mass donor is most likely a $\simeq 0.02 M_\odot$ finite-entropy white dwarf composed of He or C/O. The fractional rms pulsed amplitude is 7.4%, and the soft (1-3 keV) X-ray pulse profile contains a significant second harmonic. The pulsed amplitude and pulse phase lag (relative to our mean timing model) are energy-de…
We report on the phase-coherent timing analysis of the accreting millisecond X-ray pulsar IGR J17591-2342, using Neutron Star Interior Composition Explorer (NICER) data taken during the outburst of the source between 2018 August 15 and 2018 October 17. We obtain an updated orbital solution of the binary system. We investigate the evolution of the neutron star spin frequency during the outburst, reporting a refined estimate of the spin frequency and the first estimate of the spin frequency derivative ($\dotν \sim -7\times 10^{-14}$ Hz s$^{-1}$), confirmed independently from the modelling of the…
IGR J17511-3057 is the second X-ray transient accreting millisecond pulsar discovered by INTEGRAL. It was in outburst for about a month from September 13, 2009. The broad-band average spectrum is well described by thermal Comptonization with an electron temperature of kT_e ~ 25 keV, soft seed photons of kT_bb ~ 0.6 keV, and Thomson optical depth τ_T ~ 2 in a slab geometry. During the outburst the spectrum stays remarkably stable with plasma and soft seed photon temperatures and scattering optical depth being constant within errors. We fitted the outburst profile with the exponential model, and…
Accreting Millisecond X-ray Pulsars like IGR J00291+5934 are important because it is possible to test theories of pulsar formation and evolution. They give also the possibility to constrain gravitational wave emission theories and the equation of state of ultra dense matter. Particularly crucial to our understanding is the measurement of the long term spin evolution of the accreting neutron star. An open question is whether these accreting pulsars are spinning up during an outburst and spinning down in quiescence as predicted by the recycling scenario. Until now it has been very difficult to m…
We report on the discovery by the Nuclear Spectroscopic Telescope Array (NuSTAR) and the Neutron Star Interior Composition Explorer (NICER) of the accreting millisecond X-ray pulsar IGR J17591-2342, detecting coherent X-ray pulsations around 527.4 Hz (1.9 ms) with a clear Doppler modulation. This implies an orbital period of ~8.8 hours and a projected semi-major axis of ~1.23 lt-s. From the binary mass function, we estimate a minimum companion mass of 0.42 solar masses, obtained assuming a neutron star mass of 1.4 solar masses and an inclination angle lower than 60 degrees, as suggested by the…
We report on the detection of a 400.99018734(1) Hz coherent signal in the Rossi X-ray Timing Explorer light curves of the recently discovered X-ray transient, IGR J17498-2921. By analysing the frequency modulation caused by the orbital motion observed between August 13 and September 8, 2011, we derive an orbital solution for the binary system with a period of 3.8432275(3) hr. The measured mass function, f(M_2, M_1, i)=0.00203807(8) Msun, allows to set a lower limit of 0.17 Msun on the mass of the companion star, while an upper limit of 0.48 Msun is set by imposing that the companion star does …
We re-analysed the archival data of RXTE / INTEGRAL / Swift satellites at the onset phase of the 2011 outburst of the X-ray source IGR J17091-3624. The evolution of the spectral and temporal properties of the source in this phase clearly exhibits state transition as Hard (HS) to Hard-Intermediate (HIMS) to Soft-Intermediate (SIMS) to Soft (SS) state, before entering the variability phase (VP).We attempt to understand the evolution of X-ray features and the state transitions based on two different types of accreting material (i.e, the Keplerian and sub-Keplerian flow).
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-…
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…
IGR J17062-6143 is an ultra-compact X-ray binary (UCXB) with an orbital period of 37.96 min. It harbours a millisecond X-ray pulsar that is spinning at 163 Hz and and has continuously been accreting from its companion star since 2006. Determining the composition of the accreted matter in UCXBs is of high interest for studies of binary evolution and thermonuclear burning on the surface of neutron stars. Here, we present a multi-wavelength study of IGR J17062-6143 aimed to determine the detailed properties of its accretion disc and companion star. The multi-epoch photometric UV to near-infrared …
We present an optical (gri) study during quiescence of the accreting millisecond X-ray pulsar IGR J00291+5934 performed with the 10.4m Gran Telescopio Canarias (GTC) in August 2014. Despite the source being in quiescence at the time of our observations, it showed a strong optical flaring activity, more pronounced at higher frequencies (i.e. the g band). Once the flares were subtracted, we tentatively recovered a sinusoidal modulation at the system orbital period in all bands, even if a significant phase shift with respect to an irradiated star, typical of accreting millisecond X-ray pulsars is…
We analyze the spectral and timing properties of IGR J17498-2921 and the characteristics of X-ray bursts to constrain the physical processes responsible for the X-ray production in this class of sources. The broad-band average spectrum is well-described by thermal Comptonization with an electron temperature of kT_e ~ 50 keV, soft seed photons of kT_bb ~ 1 keV, and Thomson optical depth \taut ~ 1 in a slab geometry. The slab area corresponds to a black body radius of R_bb ~9 km. During the outburst, the spectrum stays remarkably stable with plasma and soft seed photon temperatures and scatterin…
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 is the fifteenth discovered accreting millisecond X-ray pulsar and the first source of this class showing direct evidence for transition between accretion and rotational powered emission states. These swing provided the strongest confirmation of the pulsar recycling scenario available so far. During the two XMM-Newton observations that were carried out while the source was in outburst in April 2013, IGR J18245-2452 displayed a unique and peculiar variability of its X-ray emission. In this work, we report on a detailed analysis of the XMM- Newton data and focus in particular on …
We present results of recent Neutron Star Interior Composition Explorer observations of the accreting millisecond X-ray pulsar IGR J17062-6143 that show that it resides in a circular, ultracompact binary with a 38 minute orbital period. NICER observed the source for approximately 26 ksec over a 5.3 day span in 2017 August, and again for 14 and 11 ksec in 2017 October and November, respectively. A power spectral analysis of the August exposure confirms the previous detection of pulsations at 163.656 Hz in Rossi X-ray Timing Explorer data, and reveals phase modulation due to orbital motion of th…
The low mass X-ray binary (LMXB) IGR J17480-2446 in the globular cluster Terzan 5 harbors an 11 Hz accreting pulsar. This is the first object discovered in a globular cluster with a pulsar spinning at such low rate. The accreting pulsar is anomalous because its characteristics are very different from the other five known slow accreting pulsars in galactic LMXBs. Many features of the 11 Hz pulsar are instead very similar to those of accreting millisecond pulsars, spinning at frequencies >100 Hz. Understanding this anomaly is valuable because IGR J17480-2446 can be the only accreting pulsar disc…
We report on INTEGRAL, Swift and XMM-Newton observations of IGR J17511-3057 performed during the outburst that occurred between March 23 and April 25, 2015. The source reached a peak flux of 0.7(2)E-9 erg/cm$^2$/s and decayed to quiescence in approximately a month. The X-ray spectrum was dominated by a power-law with photon index between 1.6 and 1.8, which we interpreted as thermal Comptonization in an electron cloud with temperature > 20 keV . A broad (σ ~ 1 keV) emission line was detected at an energy (E = 6.9$^{+0.2}_{-0.3}$ keV) compatible with the Kα transition of ionized Fe, suggesting a…
We report on an XMM-Newton observation of the accreting millisecond pulsar, IGR J17511-3057. Pulsations at 244.8339512(1) Hz are observed with an RMS pulsed fraction of 14.4(3)%. A precise solution for the P_orb=12487.51(2)s binary system is derived. The measured mass function indicates a main sequence companion with a mass between 0.15 and 0.44 Msun. The XMM-Newton spectrum of the source can be modelled by at least three components, multicoloured disc emission, thermal emission from the NS surface and thermal Comptonization emission. Spectral fit of the XMM-Newton data and of the RXTE data, t…
Two outbursts were observed by RXTE in the history of the atoll source IGR J17473-2721. During the most recent outburst in 2008, the source showed a complete series of spectral states/transitions. The neutron star system was prolific in type-I X-ray bursts, and we investigate them in the context of complete outbursts evolution. A total exposure of ~ 309 ks was collected by RXTE during the two outbursts of IGR J17473-2721. We carried out a systematic search for type-I bursts in this data set. For each burst found, we investigated the burst profile, the peak flux, and their dependence on the acc…
{Timing analysis of Accretion-powered Millisecond Pulsars (AMPs) is a powerful tool to probe the physics of compact objects. The recently discovered \newigrj is the 12 discovered out of the 13 AMPs known. The Rossi XTE satellite provided an extensive coverage of the 25 days-long observation of the source outburst.} {Our goal is to investigate the complex interaction between the neutron star magnetic field and the accretion disk, determining the angular momentum exchange between them. The presence of a millisecond coherent flux modulation allows us to investigate such interaction from the study…
Pulsars emerge in the Fermi era as a sizable population of gamma-ray sources. Millisecond pulsars (MSPs) constitute an older subpopulation whose sky distribution extends to high Galactic latitudes, and it has been suggested that unresolved members of this class may contribute a significant fraction of the measured large-scale isotropic gamma-ray background (IGRB). We investigate the possible energy-dependent contribution of unresolved MSPs to the anisotropy of the Fermi-measured IGRB. For observationally-motivated MSP population models, we show that the preliminary Fermi anisotropy measurement…
We present the discovery of IGR J18245-2452, the first millisecond pulsar observed to swing between a rotation-powered, radio pulsar state, and an accretion-powered X-ray pulsar state (Papitto et al. 2013, Nature, 501, 517). This transitional source represents the most convincing proof of the evolutionary link shared by accreting neutron stars in low mass X-ray binaries, and radio millisecond pulsars. It demonstrates that swings between these two states take place on the same time-scales of luminosity variations of X-ray transients, and are therefore most easily interpreted in terms of changes…
In this work we have estimated upper and lower limits to the strength of the magnetic dipole moment of all 14 accreting millisecond X-ray pulsars observed with the Rossi X-ray Timing Explorer (RXTE). For each source we searched the archival RXTE data for the highest and lowest flux levels with a significant detection of pulsations. We assume these flux levels to correspond to the closest and farthest location of the inner edge of the accretion disk at which channelled accretion takes place. By estimating the accretion rate from the observed luminosity at these two flux levels, we place upper a…
We report our search for γ-ray emission in the energy range from 100 MeV to 300 GeV from four Accreting Millisecond Pulsars (AMPs), SAX J1808.4-3658, IGR J00291+5934, XTE J1814-338, and XTE J0929-314. The data are from four-year observations carried out by Large Area Telescope (LAT) onboard the Fermi γ-ray Space Telescope. The AMPs were not detected, and their γ-ray luminosity upper limits we obtain are 5.1*10^33 ergs/s for SAX J1808.4-3658, 2.1*10^33 ergs/s for IGR J00291+5934, 1.2*10^34 ergs/s for XTE J1814-338, and 2.2*10^33 ergs/s for XTE J0929-314. We compare our results with γ-ray irradi…
In this work, we study the X-ray timing and spectral evolution of the transient low mass X-ray binary IGR J17091-3624 during first 66 days of its 2011 outburst. We present results obtained from observations with two instruments, Rossi X-ray Timing Explorer (RXTE)/Proportional Counter Array (PCA) and SWIFT/X-ray telescope (XRT), between 09 February, 2011 and 15 April, 2011. Using quasi-periodic oscillation classifications, power density spectrum characteristics, time-lag behavior and energy spectral properties, we determine source states and their transitions at different times of the outburst.…
Detection of low-luminosity X-ray pulsations from the accreting millisecond pulsar IGR J17511-3057: An ever-thinning thread between bright accretion and sub-luminous states
INAF–Osservatorio Astronomico di Brera（意大利国家天体物理研究所布雷拉天文台）；INAF-Osservatorio Astronomico di Roma（意大利国家天体物理研究所罗马天文台）；Institute of Space Sciences (ICE, CSIC)（空间科学研究所（加泰罗尼亚高等研究理事会））；Institut d’Estudis Espacials de Catalunya (IEEC)（加泰罗尼亚空间研究院）；INAF, Istituto di Astrofisica Spaziale e Fisica Cosmica（意大利国家天体物理研究所空间天体物理与宇宙学研究所）；ASI - Agenzia Spaziale Italiana（意大利航天局）
In this paper, we report on the analysis of the peculiar X-ray variability displayed by the accreting millisecond X-ray pulsar IGR J00291+5934 in a 80 ks-long joint NuSTAR and XMM-Newton observation performed during the source outburst in 2015. The light curve of the source was characterized by a flaring-like behavior, with typical rise and decay time scales of ~120 s. The flares are accompanied by a remarkable spectral variability, with the X-ray emission being generally softer at the peak of the flares. A strong quasi periodic oscillation (QPO) is detected at ~8 mHz in the power spectrum of …
We performed an analysis of all RXTE observations of the Low Mass X-ray Binary and Black Hole Candidate IGR J17091-3624 during the 2011-2013 outburst of the source. By creating lightcurves, hardness-intensity diagrams and power density spectra of each observation, we have created a set of 9 variability `classes' that phenomenologically describe the range of types of variability seen in this object. We compare our set of variability classes to those established by Belloni et al. (2000) to describe the similar behaviour of the LMXB GRS 1915+105, finding that some types of variability seen in IGR…
The recent discovery of long-period, low magnetic field pulsars in low-mass X-ray binaries (LMXBs) represents a challenge for the standard evolutionary scenario. These pulsars have a magnetic field strength comparable to that of millisecond pulsars ($\sim 10^8 - 10^9$ G), but their period is at least an order of magnitude longer. We discuss the origin of this new class of pulsars within the standard picture of LMXBs formation and apply our results to the case of IGR J17480-2446. The magnetothermal evolution of the binary system is studied numerically by taking into account the effect of differ…
IGRJ17361-4441 is a hard transient recently observed by the INTEGRAL satellite. The source, close to the center of gravity of the globular cluster NGC 6388, quickly became the target of follow-up observations conducted by the Chandra, Swift/XRT and RXTE observatories. Here, we concentrate in particular on a set of observations conducted by the XMM-Newton satellite during two slews, in order to get the spectral information of the source and search for spectral variations. The spectral parameters determined by the recent XMM-Newton slew observations were compared to the previously known results.…
The burst-only Swift J1749.4-2807 source was discovered in a high X-ray-active state, while during an {INTEGRAL observations of the Galactic bulge on 2010 April 10. Pulsations at 518 Hz were discovered in the RXTE data, confirming previous suggestions of possible associations between burst-only sources and accreting millisecond X-ray pulsars. The subsequent discovery of X-ray eclipses made Swift J1749.4$-$2807 the first eclipsing accreting millisecond X-ray pulsar. We obtain additional information on Swift J1749.4-2807 and other burst-only sources. We report on the results of a monitoring camp…
IGR J17480$-$2446 is an accreting X-ray pulsar in a low-mass X-ray binary harbored in the Galactic globular cluster Terzan 5. Compared with other accreting millisecond pulsars, IGR J17480$-$2446 is peculiar in its low spin frequency (11 Hz), which suggests that it might be a mildly recycled neutron star at the very early phase of mass transfer. However, this model seems to be in contrast with the low field strength deduced from the kiloHertz quasi-periodic oscillations observed in IGR J17480$-$2446. Here we suggest an alternative interpretation, assuming that the current binary system was form…
A FAST search for radio pulsations during the dormant state of the AMSPs IGR J00291+5934 and MAXI J1957+032
Institute of Space Sciences (ICE, CSIC)（空间科学研究所）；Institut d’Estudis Espacials de Catalunya (IEEC)（加泰罗尼亚太空研究学院）；Universidad de Santiago de Chile (USACH)（智利圣地亚哥大学）；Center for Interdisciplinary Research in Astrophysics and Space Sciences (CIRAS)（天体物理学与空间科学跨学科研究中心）；INAF/IASF Palermo（意大利国家天体物理研究所巴勒莫天文台）；Université Grenoble Alpes, CNRS, IPAG（格勒诺布尔阿尔卑斯大学）；INAF–Osservatorio Astronomico di Brera（意大利国家天体物理研究所布雷拉天文台）；INAF Osservatorio Astronomico di Roma（意大利国家天体物理研究所罗马天文台）；Università degli Studi di Cagliari（卡利亚里大学）
We use the 2011 Rossi X-ray Timing Explorer (RXTE) proportional counter array (PCA) data of the 401 Hz accreting pulsar and burster IGR J17498-2921 to perform timing analysis and time-resolved spectroscopy of 12 thermonuclear X-ray bursts. We confirm previously reported burst oscillations from this source with a much higher significance (8.8σ). We notice that the bursts can be divided into three groups: big photospheric radius expansion (PRE) bursts are about ten times more luminous than medium bursts, while the latter are about ten times more luminous than small bursts. The PCA field-of-view …
We have investigated the outbursts of IGR J17473-2721. We analyzed all available observations carried out by RXTE on IGR J17473-2721 during its later outburst and as well all the available SWIFT/BAT data. The flux of the latter outburst rose in ~ one month and then kept roughly constant for the following ~ two months. During this time period, the source was in a low/hard state. The source moved to a high/soft state within the following three days, accompanied by the occurrence of an additional outburst at soft X-rays and the end of the preceding outburst in hard X-rays. During the decay of thi…
We report the discovery using data from the Swift Burst Alert Telescope (BAT) of superorbital modulation in the wind-accretion supergiant high-mass X-ray binaries 4U 1909+07 (= X 1908+075), IGR J16418-4532, and IGR J16479-4514. Together with already known superorbital periodicities in 2S 0114+650 and IGR J16493-4348, the systems exhibit a monotonic relationship between superorbital and orbital periods. These systems include both supergiant fast X-ray transients (SFXTs) and classical supergiant systems, and have a range of inclination angles. This suggests an underlying physical mechanism which…
