We present the spectral and timing analysis of the X-ray pulsar GRO J1744-28 during its 2014 outburst using data collected with the X-ray satellites Swift, INTEGRAL, Chandra, and XMM-Newton. We derived, by phase-connected timing analysis of the observed pulses, an updated set of the source ephemeris. We were also able to investigate the spin-up of the X-ray pulsar as a consequence of the accretion torque during the outburst. Relating the spin-up rate and the mass accretion rate as $\dotν\propto\dot{M}^β$, we fitted the pulse phase delays obtaining a value of $β=0.96(3)$. Combining the results from the source spin-up frequency derivative and the flux estimation, we constrained the source distance to be between 3.4-4.1 kpc, assuming a disc viscous parameter $α$ to be in the range 0.1-1. Finally, we investigated the presence of a possible spin-down torque by adding a quadratic component to the pulse phase delay model. The marginal statistical improvement of the updated model does not allow us to firmly confirm the presence of this component.
The outburst and spin-down glitch of magnetars are modeled from the magnetospheric point of view. We try to discuss the following four questions: (1) Which pulsar on the period and peirod-derivative diagram are more likely to show magnetar outburst? (2) Which outburst will make the glitch that triggered the outburst to become a spin-down glitch? (3) Can we model the outburst and spin-down glitch in PSR J1119$-$6127 simultaneously? (4) Why the torque variation is delayed compared with the peak of the X-ray luminosity in 1E 1048.1$-$5937 and PSR J1119$-$6127? It is found that both the global and…
We report on two years of flux and spin evolution monitoring of 1E 1048.1$-$5937, a 6.5-s X-ray pulsar identified as a magnetar. Using {\it Swift} XRT data, we observed an X-ray outburst consisting of an increase in the persistent 1--10 keV flux by a factor of 6.3$\pm$0.2, beginning on 2011 December 31 (MJD 55926). Following a delay of $\sim100$ days, the magnetar entered a period of large torque variability, with $\dotν$ reaching a factor of $4.55\pm0.05$ times the nominal value, before decaying in an oscillatory manner over a time scale of months. We show by comparing to previous outbursts f…
To observationally study spin-period changes of accreting pulsars caused by the accretion torque, the present work analyzes X-ray light curves of 12 Be binary pulsars obtained by the MAXI/GSC all-sky survey and their pulse periods measured by the Fermi/GBM pulsar project, both covering more than 6 years from 2009 August to 2016 March. The 12 objects were selected because they are accompanied by clear optical identification, and accurate measurements of surface magnetic fields. The luminosity $L$ and the spin-frequency derivatives $\dotν$, measured during large outbursts with $L\gtrsim 1\times …
Since its discovery, 1E 1048.1$-$5937 has been one of the most active magnetars, both in terms of radiative outbursts, and changes to its spin properties. Here we report on a continuing monitoring campaign with the Neil Gehrels Swift Observatory X-ray Telescope in which we observe two new outbursts from this source. The first outburst occurred in 2016 July, and the second in 2017 December, reaching peak 0.5-10 keV absorbed fluxes of $3.2^{+0.2}_{-0.3}\times 10^{-11}$ erg s$^{-1}$ cm$^{-2}$ and $2.2^{+0.2}_{-0.2}\times10^{-11}$ erg s$^{-1}$ cm$^{-2}$, respectively, factors of $\sim$5 and $\sim …
We present the updated orbital solution for the transient Be X-ray binary V 0332+53 comple- menting historical measurements with the data from the gamma-ray burst monitor onboard Fermi obtained during the outburst in June-October 2015. We model the observed changes in the spin- frequency of the pulsar and deduce the orbital parameters of the system. We significantly improve existing constrains and show that contrary to the previous findings no change in orbital parameters is required to explain the spin evolution of the source during the outbursts in 1983, 2005 and 2015. The reconstructed intr…
We report the evolution of the X-ray pulsations of EXO 2030+375 during its 2021 outburst using the observations from \textit{Insight}-HXMT. Based on the accretion torque model, we study the correlation between the spin frequency derivatives and the luminosity. Pulsations can be detected in the energy band of 1--160 keV. The pulse profile evolves significantly with luminosity during the outburst, leading to that the whole outburst can be divided into several parts with different characteristics. The evolution of the pulse profile reveals the transition between the super-critical (fan-beam domin…
In this study we present a method to estimate posterior distributions for standard accretion torque model parameters and binary orbital parameters for X-ray binaries using a nested sampling algorithm for Bayesian Parameter Estimation. We study the spin evolution of two Be X-ray binary systems in the Magellanic Clouds, RX J0520.5-6932 and RX J0209-7427, during major outbursts, in which they surpassed the Eddington-limit. Moreover, we apply our method to the recently discovered Swift J0243.6+6124; the only known Galactic pulsating ultra-luminous X-ray source. This is an excellent candidate for s…
GRO J1008-57, as a Be/X-ray transient pulsar, is considered to have the highest magnetic field in known neutron star X-ray binary systems. Observational data of the X-ray outbursts in GRO J1008-57 from 2017 to 2020 were collected by the Insight-HXMT satellite. In this work, the spin period of the neutron star in GRO J1008-57 was determined to be about 93.28 seconds in August 2017, 93.22 seconds in February 2018, 93.25 seconds in June 2019 and 93.14 seconds in June 2020. GRO J1008-57 evolved in the spin-up process with a mean rate of $-(2.10\pm 0.05)\times$10$^{-4}$ s/d from 2009 -- 2018, and t…
GRO J1750-27, discovered during an outburst in 1995 with CGRO-BATSE, is one of the farthest known galactic Be-X-ray binary systems. This relatively poorly studied system recently went into an outburst in September 2021. The source was observed during the latest outburst using the NuSTAR telescope during the rising phase of the outburst. We estimate the spin period of the source to be 4.45 s using which we produced energy-resolved pulse profiles between 3 and 65 keV. We find that the profile is double-peaked at low energies (<18 keV) while evolving into a single peak at higher energies (>18 keV…
In November 2019, MAXI detected an X-ray outburst from the known Be X-ray binary system RX J0209.6-7427 located in the outer wing of the Small Magellanic Cloud. We followed the outburst of the system with NICER which led to the discovery of X-ray pulsations with a period of 9.3 s. We analyzed simultaneous X-ray data obtained with NuSTAR and NICER allowing us to characterize the spectrum and provide an accurate estimate of its bolometric luminosity. During the outburst the maximum broadband X-ray luminosity of the system reached $1-2\times10^{39}$ erg/s, thus exceeding by about one order of mag…
We report on the aftermath of a magnetar outburst from the young, high-magnetic-field radio pulsar PSR J1119-6127 that occurred on 2016 July 27. We present the results of a monitoring campaign using the Neil Gehrels Swift X-ray Telescope, NuSTAR, and XMM-Newton. After reaching a peak luminosity of ~300 times the quiescent luminosity, the pulsar's X-ray flux declined by factor of ~50 on a time scale of several months. The X-ray spectra are well described by a blackbody and a hard power-law tail. After an initial rapid decline during the first day of the outburst, we observe the blackbody temper…
We present long term H$α$ monitoring results of five Be/X-ray binaries to study the Be disc size variations and their influence on Type II (giant) X-ray outbursts. The work is done in the context of the viscous decretion disc model which predicts that Be discs in binary systems are truncated by resonant torques induced by the neutron star in its orbit. Our observations show that type II outbursts are not correlated(nor anti-correlated) with the disc size, as they are seen to occur both at relatively small and large Be disc radii. We discuss these observations in context of alternate interpreta…
We present results of the first dedicated observation of the young X-ray pulsar SXP 1062 in the broad X-ray energy band obtained during its 2019 outburst with the NuSTAR and XMM-Newton observatories. The analysis of the pulse-phase averaged and phase-resolved spectra in the energy band from 0.5 to 70 keV did not reveal any evidence for the presence of a cyclotron line. The spin period of the pulsar was found to have decreased to 979.48+/-0.06 s implying a ~10% reduction compared to the last measured period during the monitoring campaign conducted about five years ago, and is puzzling consideri…
The interaction of a rotating star's magnetic field with a surrounding plasma disk lies at the heart of many questions posed by neutron stars in X-ray binaries. We consider the opening of stellar magnetic flux due to differential rotation along field lines coupling the star and disk, using a simple model for the disk-opened flux, the torques exerted on the star by the magnetosphere, and the power extracted by the electromagnetic wind. We examine the conditions under which the system enters an equilibrium spin state, in which the accretion torque is instantaneously balanced by the pulsar wind t…
We study the timing and spectral properties of the X-ray pulsar 2S 1417--624 during the recent outburst in January 2021 based on the Neutron Star Interior Composition Explorer (NICER) observation. We also used some early data from the 2018 outburst to compare different temporal and spectral properties. The evolution of the spin period and pulsed flux is studied with Fermi/GBM during the outburst and the spin-up rate is found to be varied between $\simeq(0.8-1.8)\times 10^{-11}$ Hz s$^{-1}$. The pulse profile shows energy dependence and variability. The pulse profile shows multiple peaks and di…
Probing accretion dynamics and spin evolution in the X-ray pulsar RX J0520.5-6932 during its 2024 Outburst
Inter-University Centre for Astronomy and Astrophysics (IUCAA)（大学间天文学与天体物理学中心）；Raman Research Institute（拉曼研究所）；Indian Institute of Science Education and Research (IISER) Mohali（印度科学教育与研究学院穆扎法尔纳加尔分校）；School of Physics & Astronomy, University of Southampton（南安普顿大学物理与天文学院）；Indian Institute of Astrophysics（印度天体物理研究所）；Universitá degli Studi di Cagliari, Dipartimento di Fisica（卡利亚里大学物理系）；Max-Planck-Institut für extraterrestrische Physik（马克斯·普朗克地外物理研究所）；National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；School of Astronomy and Space Science, University of Chinese Academy of Sciences（中国科学院大学天文与空间科学学院）
We probe the properties of the transient X-ray pulsar MAXI J1409$-$619 through \textit{RXTE} and \textit{Swift} follow up observations of the outburst in 2010. We are able to phase connect the pulse arrival times for the 25 days episode during the outburst. We suggest that either an orbital model (with $P_{\rm{orb}} \simeq 14.7(4)$ days) or a noise process due to random torque fluctuations (with $S_r \approx 1.3 \times 10^{-18}$ Hz$^2$ s$^{-2}$ Hz$^{-1}$) is plausible to describe the residuals of the timing solution. The frequency derivatives indicate a positive torque-luminosity correlation, …
We investigate timing and spectral characteristics of the transient X-ray pulsar 2S 1417$-$624 during its 2018 outburst with \emph{NICER} follow up observations. We describe the spectra with high-energy cut-off and partial covering fraction absorption (PCFA) model and present flux-dependent spectral changes of the source during the 2018 outburst. Utilizing the correlation-mode switching of the spectral model parameters, we confirm the previously reported sub-critical to critical regime transitions and we argue that secondary transition from the gas-dominated to the radiation pressure-dominated…
The Be X-ray binary GRO J2058+42 recently went through a Type-II outburst during March-April 2019 lasting for about 50 days. This outburst was detected with the operating all sky X-ray monitors like the Fermi-GBM, Swift-BAT and MAXI-GSC. Two NuSTAR observations were also made, one during the rise and other during the decay of the outburst. It gave us the unique opportunity to analyze the broadband characteristics of the pulsar for the first time and accretion torque characteristics of the pulsar over a range of X-ray luminosity. The pulse profiles are strongly energy dependent, with at least f…
Temporal evolution of the circumstellar disk orientation in the transient X-ray pulsar GRO J1008-57
University of Turku（图尔库大学）；Universität Tübingen（蒂宾根大学）；Institute of High Energy Physics, Chinese Academy of Sciences（中国科学院高能物理研究所）；Sun Yat-sen University（中山大学）
The Be X-ray binary pulsar EXO 2030+375, first detected in 1985, has shown a significant detected X-ray outburst at nearly every periastron passage of its 46-day orbit for the past ~25 years, with one low state accompanied by a torque reversal in the 1990s. In early 2015 the outbursts progressively became fainter and less regular while the monotonic spin-up flattened. At the same time a decrease in the H$α$ line equivalent width was reported, indicating a change in the disk surrounding the mass donor. In order to explore the source behaviour in the poorly explored low-flux state with a possibl…
We report results of X-ray timing analyses for the low-field magnetar CXOU~J164710.2$-$455216 which exhibited multiple outbursts. We use data taken with NICER, NuSTAR, Chandra, and Neil-Gehrels-Swift telescopes between 2017 and 2018 when the source was in an active state. We perform semi-phase-coherent timing analyses to measure the spin parameters and a spin-inferred magnetic-field strength ($B_s$) of the magnetar. Using a semi-phase-coherent method, we infer the magnetic field strengths to be $3-4\times 10^{13}\rm \ G$ at the observation period ($\sim$MJD 58000), and by comparing with previo…
Swift J1818.0-1607 is a radio-loud magnetar with a spin period of 1.36 s and a dipolar magnetic field strength of B~3E14 G, which is very young compared to the Galactic pulsar population. We report here on the long-term X-ray monitoring campaign of this young magnetar using XMM-Newton, NuSTAR, and Swift from the activation of its first outburst in March 2020 until October 2021, as well as INTEGRAL upper limits on its hard X-ray emission. The 1-10 keV magnetar spectrum is well modeled by an absorbed blackbody with a temperature of kT_BB~1.1 keV, and apparent reduction in the radius of the emitt…
We review more than 10 years of continuous monitoring of accreting X-ray pulsars with the all-sky Gamma-ray Burst Monitor (GBM) aboard the Fermi Gamma-ray Space Telescope. Our work includes data from the start of GBM operations in August 2008, through to November 2019. Pulsations from 39 accreting pulsars are observed over an energy range of $10-50\,$keV by GBM. The GBM Accreting Pulsars Program (GAPP) performs data reduction and analysis for each accreting pulsar and makes histories of the pulse frequency and pulsed flux publicly available. We examine in detail the spin histories, outbursts a…
We present the orbital solution for the newly discovered transient Be X-ray binary Swift J0243.6+6124 based on the data from gamma-ray burst monitor onboard Fermi obtained during the Oct 2017 outburst. We model the Doppler induced and intrinsic spin variations of the neutron star assuming that the later is driven by accretion torque and discuss the implications of the observed spin variations for the parameters of the neutron star and the binary. In particular we conclude that the neutron star must be strongly magnetized, and estimate the distance to the source at $\sim$5 kpc.
Studies of Thermally Unstable Accretion Disks around Black Holes with Adaptive Pseudospectral Domain Decomposition Method. II. Limit-Cycle Behavior in accretion disks around Kerr black holes
The recently discovered neutron star transient Swift J0243.6+6124 has been monitored by {\it the Hard X-ray Modulation Telescope} ({\it Insight-\rm HXMT). Based on the obtained data, we investigate the broadband spectrum of the source throughout the outburst. We estimate the broadband flux of the source and search for possible cyclotron line in the broadband spectrum. No evidence of line-like features is, however, found up to $\rm 150~keV$. In the absence of any cyclotron line in its energy spectrum, we estimate the magnetic field of the source based on the observed spin evolution of the neutr…
Be star X-ray binaries are transient systems that show two different types of outbursts. Type I outbursts occur each orbital period while type II outbursts have a period and duration that are not related to any periodicity of the binary system. Type II outbursts may be caused by mass transfer to the neutron star from a highly eccentric Be star disk. A sufficiently misaligned Be star decretion disk undergoes secular Von Zeipel-Lidov-Kozai (ZLK) oscillations of eccentricity and inclination. Observations show that in some systems the type II outbursts come in pairs with the second being of lower …
We present results from AstroSat observation of the recent outburst of GRO J2058+42, an X-ray pulsar in a Be-binary system. The source was observed on April 10, 2019 by LAXPC and SXT instruments on AstroSat during its declining phase of the latest giant outburst. Light curves showed a strong pulsation of the pulsar with a period of 194.2201 \pm 0.0016 s, and a spin-up rate of (1.65\pm0.06)\times10^{-11} Hz s^{-1}. Intermittent flaring was detected in light curves between 3--80 keV energy band with increase in intensity by up to 1.8 times its average intensity. Pulse profiles obtained between 3…
We report on timing and spectral analysis of transient Be X-ray pulsar GRO J1750-27 by using the Nuclear Spectroscopic Telescope Array (NuSTAR) observation from September 2021. This is the fourth outburst of the system since 1995. The NuSTAR observation was performed during the rising phase of the outburst. Pulsations at a period of 4.450710(1) s were observed in the 3-60 keV energy range. The average pulse profile comprised of a broad peak with a weak secondary peak which evolved with energy. We did not find any appreciable variation in the X-ray emission during this observation. The broad-ba…
Accreting X-ray pulsars (XRPs) undergo luminous X-ray outbursts during which the spectral and timing behavior of the neutron star can be studied in detail. We analyze a $NuSTAR$ observation of the XRP XTE J1858+034 during its outburst in 2019. The spectrum is fit with a phenomenological, a semi-empirical and a physical spectral model. A candidate cyclotron line is found at $48\,$keV, implying a magnetic field of $5.4\times10^{\rm 12}\,$G at the site of emission. This is also supported by the physical best-fit model. We propose an orbital period of about $81$ days based on the visual inspection…
We have investigated the complex multiwavelength evolution of GRO J1655-40 during the rise of its 2005 outburst. We detected two hard X-ray flares, the first one during the transition from the soft state to the ultra-soft state, and the second one in the ultra-soft state. The first X-ray flare coincided with an optically thin radio flare. We also observed a hint of increased radio emission during the second X-ray flare. To explain the hard flares without invoking a secondary emission component, we fit the entire data set with the eqpair model. This single, hybrid Comptonization model sufficien…
SXP4.78 was originally discovered in 2000 as a pulsar in the Small Magellanic Cloud (SMC) by the Rossi X-ray Timing Explorer (RXTE) but it was not spatially located at that time. A new detection in 2018 with the Neil Gehrels Swift Observatory during a Type II outburst permitted its position to be accurately located and its optical counterpart identified. We report X-ray and optical monitoring covering epochs before and during the outburst. Using photometric data we show the long-term variability of the Be disc where we present flux and colour changes associated with the disc growth and decay o…
We use the In data collected during the 2019 outburst from X-ray pulsar 4U 1901+03 to complement the orbital parameters reported by Fermi/GBM. Using the Insight-HXMT, we examine the correlation between the derivative of the intrinsic spin frequency and bolometric flux based on accretion torque models. It was found that the pulse profiles significantly evolve during the outburst. The existence of two types of the profile's pattern discovered in the Insight-HXMT data indicates that this source experienced transition between a super-critical and a sub-critical accretion regime during its 2019 out…
We present simultaneous, multi-wavelength observations of the Small Magellanic Cloud Be/XRB IGR J01217-7257 (=SXP 2.16) during outbursts in 2014, 2015 and 2016. We also present the results of RXTE observations of the Small Magellanic Cloud during which the source was initially discovered with a periodicity of 2.1652$\pm$0.0001 seconds which we associate with the spin period of the neutron star. A systematic temporal analysis of long term Swift/BAT data reveals a periodic signal of 82.5$\pm$0.7 days, in contrast with a similar analysis of long base line OGLE I-band light curves which reveals an…
Accreting millisecond X-ray pulsars are known to provide a wealth of physical information during their successive states of outburst and quiescence. Based on the observed spin-up and spin-down rates of these objects it is possible, among other things, to infer the stellar magnetic field strength and test models of accretion disc flow. In this paper we consider the three accreting X-ray pulsars (XTE J1751-305, IGR J00291+5934, and SAX J1808.4-3658) with the best available timing data, and model their observed spin-up rates with the help of a collection of standard torque models that describe a …
KL Dra as a Benchmark Laboratory for Accretion-Disk Physics: Constraints from TESS and Ground-Based Surveys
University of Michigan（密歇根大学）；University of Texas Rio Grande Valley（德克萨斯大学里奥格兰德河谷分校）；South Texas Space Science Institute, University of Texas Rio Grande Valley（南得克萨斯空间科学研究所，德克萨斯大学里奥格兰德河谷分校）；Université de Strasbourg（斯特拉斯堡大学）；CNRS（法国国家科学研究中心）；Observatoire astronomique de Strasbourg（斯特拉斯堡天文台）；University of Alberta（阿尔伯塔大学）；Jagiellonian University（雅盖隆大学）；Texas Tech University（德克萨斯理工大学）；Universidad Nacional Autónoma de México（墨西哥国立自治大学）
