Search

The Lobster Eye Imager for Astronomy (LEIA) is the pathfinder of the wide-field X-ray telescope used in the Einstein Probe mission. In this study, we present an image of the Virgo Cluster taken by LEIA in the 0.5-4.5 keV band with an exposure time of $\sim$17.3 ks in the central region. This extended emission is generally consistent with the results obtained by ROSAT. However, the field is affected by bright point sources due to the instrument's Point Spread Function (PSF) effect. Through fitting of the LEIA spectrum of the Virgo Cluster, we obtained a temperature of $2.1^{+0.3}_{-0.1}$ keV, which is consistent with the XMM-Newton results ($\sim$2.3 keV). Above 1.6 keV, the spectrum is dominated by the X-ray background. In summary, this study validates LEIA's extended source imaging and spectral resolution capabilities for the first time., Comment: 9 pages, 6 figures, 1 table

We present a deep optical imaging campaign on the starburst galaxy NGC 4631 with CFHT/MegaCam. By supplementing the HST/ACS and Chandra/ACIS archival data, we search for the optical counterpart candidates of the five brightest X-ray sources in this galaxy, four of which are identified as ultraluminous X-ray sources (ULXs). The stellar environments of the X-ray sources are analyzed using the extinction-corrected color-magnitude diagrams and the isochrone models. We discover a highly asymmetric bubble nebula around X4 which exhibits different morphology in the H$\alpha$ and [O III] images. The [O III]/H$\alpha$ ratio map shows that the H$\alpha$-bright bubble may be formed mainly via the shock ionization by the one-sided jet/outflow, while the more compact [O III] structure is photoionized by the ULX. We constrain the bubble expansion velocity and interstellar medium density with the MAPPINGS V code, and hence estimate the mechanical power injected to the bubble as $P_w \sim 5\times10^{40}$ erg s$^{-1}$ and the corresponding bubble age of $\sim7\times 10^{5}$ yr. Relativistic jets are needed to provide such level of mechanical power with a mass-loss rate of $\sim10^{-7}\ M_{\odot}\ \rm yr^{-1}$. Besides the accretion, the black hole spin is likely an additional energy source for the super-Eddington jet power., Comment: 17 pages, 10 figures, accepted by ApJ

We study the giant outbursts of SMC X-3 and RX J0209.6-7427 to compare their super-Eddington accretion regime with that of Swift J0243.6+6124. The high double-peak profile of SMC X-3 is found to be 0.25 phase offset from that below $2.3\times10^{38}$erg\,s$^{-1}$, which is similar to Swift J0243 (happened around $0.9\times10^{38}$erg\,s$^{-1}$). The profile of RX J0209 shows a similar 0.25 phase offset between high double-peak and low double-peak around $1.25\times10^{38}$erg\,s$^{-1}$. The 0.25 phase offset corresponds to a 90 degree angle change of the emission beam and strongly supports for a transition from a fan beam to a pencil beam. Their critical luminosities imply a surface magnetic field $\sim4\times10^{13}$ G and $2\times10^{13}$ G for SMC X-3 and RX J0209, respectively, based on the recently measured cyclotron line of Swift J0243. The spin-up rate and luminosity of SMC X-3 follows a relation of $\dot{\nu}\propto L^{0.94\pm0.03}$, while that of RX J0209 follows $\dot{\nu}\propto L^{1.00\pm0.03}$, which are similar to Swift J0243 and consistent with the prediction of a radiation-pressure-dominated (RPD) disk. These results indicate that accretion columns are indeed formed above Eddington luminosity, and the population of ULXPs likely corresponds to X-ray pulsars of highest magnetic field., Comment: 9 pages, 5 figs, to appear on MNRAS

Ultraluminous X-ray bursts (hereafter ULXBs) are ultraluminous X-ray flares with a fast rise ($\sim$ one minute) and a slow decay ($\sim$ an hour), which are commonly observed in extragalactic globular clusters. Most ULXBs are observational one-off bursts, whereas five flares from the same source in NGC 5128 were discovered by Irwin et al. (2016). In this Letter, we propose a neutron star (NS)-white dwarf (WD) binary model with super-Eddington accretion rates to explain the repeating behavior of the ULXB source in NGC 5128. With an eccentric orbit, the mass transfer occurs at the periastron where the WD fills its Roche lobe. The ultraluminous X-ray flares can be produced by the accretion column around the NS magnetic poles. On the other hand, some repeating fast radio bursts (hereafter FRBs) were also found in extragalactic globular clusters. Repeating ULXBs and repeating FRBs are the most violent bursts in the X-ray and radio bands, respectively. We propose a possible association between the repeating ULXBs and the repeating FRBs. Such an association is worth further investigation by follow-up observations on nearby extragalactic globular clusters., Comment: 8 pages, 3 figures, accepted for publication in ApJ

LS I +61$^{\circ}$ 303 is one of the rare gamma-ray binaries, emitting most of their luminosity in photons with energies beyond 100 MeV. The $\sim$26.5 d orbital period is clearly detected at many wavelengths. Additional aspects of its multi-frequency behavior make it the most interesting example of the class. The morphology of high-resolution radio images changes with orbital phase displaying a cometary tail pointing away from the high-mass star. LS I +61$^{\circ}$ 303 also shows superorbital variability. A couple of energetic ($\sim 10^{37}$ erg s$^{-1}$), short, magnetar-like bursts have been plausibly ascribed to it. LS I +61$^{\circ}$ 303's phenomenology has been put under theoretical scrutiny for decades, but the lack of certainty regarding the nature of the compact object in the binary has prevented advancing our understanding of the source. Here, using observations done with the Five-hundred-meter Aperture Spherical radio Telescope (FAST), we report on the existence of transient radio pulsations from the direction of LS I +61$^{\circ}$ 303. We find a period $P=269.15508 \pm 0.00016$ ms at a significance of $> 20\sigma$. This is the first evidence for pulsations from this source at any frequency, and strongly argues for the existence of a rotating neutron star in LS I +61$^{\circ}$ 303., Comment: Published in Nature Astronomy; authors' version

Accretion is an essential physical process in black-hole X-ray binaries (BHXRBs) and active galactic nuclei. The properties of accretion flows and their radiation were originally considered to be uniquely determined by the mass accretion rate of the disk; however, the ``hysteresis effect'' observed during outbursts of nearly all BHXRBs seriously challenges this paradigm. The hysteresis effect is referred to that the hard-to-soft state transition in the fast-rise stage occurs at much higher luminosity than the soft-to-hard state transition in the slow-decay stage. That is, the same source can show different spectral/temporal properties at the same luminosity. Phenomenologically, this effect is also represented as the so-called ``q''-shaped hardness-intensity diagram, which has been proposed as a unified scene for BHXRBs. However, there is still a lack of quantitative theoretical interpretation and observational understanding on the ``q''-diagram. Here, we present a detailed time-lag analysis of a recently found BHXRB, MAXI J1348-630, intensively monitored by Insight-HXMT over a broad energy band (1-150 keV). We find the first observational evidence that the observed time-lag between radiations of the accretion disk and the corona leads naturally to the hysteresis effect and the ``q''-diagram. Moreover, complemented by the quasi-simultaneous Swift data, we achieve a panorama of the accretion flow: the hard X-ray outburst from the corona heats and subsequently induces the optical brightening in the outer disk with nearly no lag; thereafter, the enhanced accretion in the outer disk propagates inward, generating the delayed soft X-ray outburst at the viscous timescale of ~ 8-12 days., Comment: 8 pages, 7 figures, published in ApJL

The Be X-ray pulsar (BeXRP) SXP 59 underwent a giant outburst in 2017 with a peak X-ray luminosity of $1.1\times10^{38}$ erg~s$^{-1}$. We report on the X-ray behaviour of SXP 59 with the XMM--Newton and NuSTAR observations collected at the outburst peak, decay, and the low luminosity states. The pulse profiles are energy dependent, the pulse fraction increases with the photon energy and saturates at $\sim$ 65% above 10 keV. It is difficult to constrain the change in the geometry of emitting region with the limited data. Nevertheless, because the pulse shape generally has a double-peaked profile at high luminosity and a single peak profile at low luminosity, we prefer the scenario that the source transited from the super-critical state to the sub-critical regime. This result would further imply that the neutron star (NS) in SXP 59 has a typical magnetic field. We confirm that the soft excess revealed below 2 keV is dominated by a cool thermal component. On the other hand, the NuSTAR spectra can be described as a combination of the non-thermal component from the accretion column, a hot blackbody emission, and an iron emission line. The temperature of the hot thermal component decreases with time, while its size remains constant ($R \sim 0.6$ km). The existence of the hot blackbody at high luminosity cannot be explained with the present accretion theories for BeXRPs. It means that either more sophisticated spectral models are required to describe the X-ray spectra of luminous BeXRPs, or there is non-dipole magnetic field close to the NS surface., Comment: 6 pages, 6 figures, 2 table, published in MNRAS

GRS 1915+105 has been active for more than 26 years since it was discovered in 1992. There are hundreds of RXTE pointed observations on this source, and the quasi-regular flares with a slow rise and a sharp decrease (i.e. the "heartbeat" state) were recorded in more than 200 observations. The connections among the disk/corona, jet, and the disk wind at the heartbeat state have been extensively studied. In this work, we firstly perform a statistical analysis of the light curves and the X-ray spectra to investigate this peculiar state. We calculate the parameters for heartbeat cycles, including the recurrence time, the maximum and the minimum count rate, the flare amplitude, and the cumulative radiation for each cycle. The recurrence time has a bimodal distribution ranging from $\sim 20$ to $\sim 200$ s. The minimum count rate increases with increasing recurrence time; while the maximum count rate remains nearly constant around 2 Crab. Fitting the averaged spectrum for each observation, we find the strong correlations among the recurrence time, the apparent inner radius of the accretion disk (or the color correction factor), and the (nonthermal) X-ray luminosity. We suggest that the true inner edge of the accretion disk might always extend to the marginally stable orbit, while the change in corona size should result in the observed correlations., Comment: 8 pages, 7 figurs, 1 tables, published in ApJ

3XMM J031820.8-663034, first detected by ROSAT in NGC 1313, is one of a few known transient ultraluminous X-ray sources (ULXs). In this paper, we present decades of X-ray data of this source from ROSAT, XMM-Newton, Chandra and the Neil Gehrels Swift Observatory. We find that its X-ray emission experienced four outbursts since 1992, with a typical recurrent time $\sim$ 1800 days, an outburst duration $\sim 240-300$ days, and a nearly constant peak X-ray luminosity $\sim 1.5 \times 10^{39}$ erg/s. The upper limit of X-ray luminosity at the quiescent state is $\sim 5.6 \times 10^{36}$ erg/s, and the total energy radiated during one outburst is $\sim 10^{46}$ erg. The spectra at the high luminosity states can be described with an absorbed disk black-body, and the disk temperature increases with the X-ray luminosity. We compare its outburst properties with other known transient ULXs including ESO 243-49 HLX-1. As its peak luminosity only marginally puts it in the category of ULXs, we also compare it with normal transient black hole binaries. Our results suggest that the source is powered by an accreting massive stellar-mass black hole, and the outbursts are triggered by the thermal-viscous instability., Comment: 9 pages, 7 figurs, 3 tables, accepted for publication in ApJ

The Be X-ray pulsar SMC X-3 underwent an extra long and ultraluminous giant outburst from 2016 August to 2017 March. The peak X-ray luminosity is up to $\sim 10^{39}$ erg/s, suggesting a mildly super-Eddington accretion onto the strongly magnetized neutron star. It therefore bridges the gap between the Galactic Be/X-ray binaries ($L_{\rm X}^{\rm peak} \leq 10^{38}$ erg/s) and the ultraluminous X-ray pulsars ($L_{\rm X}^{\rm peak} \geq 10^{40}$ erg/s) found in nearby galaxies. A number of observations were carried out to observe the outburst. In this paper, we perform a comprehensive phase-resolved analysis on the high quality data obtained with the Nustar and XMM-Newton, which were observed at a high and intermediate luminosity levels. In order to get a better understanding on the evolution of the whole extreme burst, we take the Swift results at the low luminosity state into account as well. At the early stage of outburst, the source shows a double-peak pulse profile, the second main peak approaches the first one and merges into the single peak at the low luminosity. The second main peak vanishes beyond 20 keV, and its radiation becomes much softer than that of the first main peak. The line widths of fluorescent iron line vary dramatically with phases, indicating a complicated geometry of accretion flows. In contrast to the case at low luminosity, the pulse fraction increases with the photon energy. The significant small pulse fraction detected below 1 keV can be interpreted as the existence of an additional thermal component located at far away from the central neutron star., Comment: 6 pages, 2 tables, 2 figures, Published in Astrophysics and Space Science

Most ultraluminous X-ray sources (ULXs) are thought to be supercritical accreting compact objects, where massive outflows are inevitable. Using the long-term monitoring data with the Swift X-ray Telescope, we identified a common feature in bright, hard ULXs: they display a quasi-periodic modulation in their hard X-ray band but not in their soft band. As a result, some sources show a bimodal distribution on the hardness intensity map. We argue that these model-independent results can be well interpreted in a picture that involves supercritical accretion with precession, where the hard X-ray emission from the central funnel is more or less beamed, while the soft X-rays may arise from the photosphere of the massive outflow and be nearly isotropic. It implies that precession may be ubiquitous in supercritical systems, such as the Galactic microquasar SS~433. How the hard X-rays are modulated can be used to constrain the angular distribution of the hard X-ray emission and the geometry of the accretion flow. We also find that two ULX pulsars (NGC 5907 ULX-1 and NGC 7793 P13) show similar behaviors but no bimodal distribution, which may imply that they have a different beaming shape or mechanism., Comment: 12 pages, 6 figures, 1 table, published in ApJ

The Be X-ray pulsar, SMC X-3 underwent a giant outburst from 2016 August to 2017 March, which was monitored with the Swift satellite. During the outburst, its broadband flux increased dramatically, and the unabsorbed X-ray luminosity reached an extreme value of $\sim 10^{39}$ erg/s around August 24. Using the Swift/XRT data, we measure the observed pulse frequency of the neutron star to compute the orbital parameters of the binary system. After applying the orbital corrections to Swift observations, we find that the spin frequency increases steadily from 128.02 mHz on August 10 and approach to spin equilibrium $\sim 128.74$ mHz in 2017 January with an unabsorbed luminosity of $L_{\rm X} \sim 2\times10^{37}$ erg/s, indicating a strong dipolar magnetic field $B \sim 6.8\times10^{12}$ G at the neutron star surface. The spin-up rate is tightly correlated with its X-ray luminosity during the super-Eddington outburst. The pulse profile in the Swift/XRT data is variable, showing double peaks at the early stage of outburst and then merging into a single peak at low luminosity. Additionally, we report that a low temperature ($kT \sim 0.2$ keV) thermal component emerges in the phase-averaged spectra as the flux decays, and it may be produced from the outer truncated disk or the boundary layer between the exterior flow and the magnetosphere., Comment: 8 pages, 5 figures, 2 table, conclusions unchanged, accepted for publication in ApJ

The Type IIn supernova (SN) 1978K in the nearby galaxy NGC 1313 has remained bright in multiwavelengths for more than $\sim 25$ yr. The archival data of SN 1978K collected with ROSAT, ASCA, XMM-Newton, and Chandra from 1990 to 2006 show no significant variation of the soft X-ray emission but a hint of flux decrease in hard X-rays. In this work, we perform a detailed analysis using more than 15 yr of XMM-Newton observations. Both the 0.5-2 keV and 2-10 keV light-curves decline as $t^{-1}$ from 2000 to 2015. The transition of light curve profiles can be explained in a way that the reverse shock was radiative at an early phase and then became adiabatic at late times. Such a scenario is also supported by the spectral analysis results. We also found a decrease in the absorption column density, which indicates the presence of a cool shell during the radiative phase., Comment: 5 pages, 1 figure, 3 tables, published in MNRAS

The spectral and temporal evolution during X-ray outbursts give important clues on the accretion process and radiation mechanism in black-hole X-ray binaries (BH XRBs). A set of Swift and RXTE observations were executed to monitor the 2008 outburst of the black-hole candidate Swift J1842.5-1124. We investigate these data to explore the accretion physics in BH XRBs. We carry out a comprehensive spectral and timing analysis on all the available pointing observations, including fitting both X-ray spectra and power density spectra, measuring the optical and near-ultraviolet flux density. We also search for correlations among the spectral and timing parameters. The observed properties of Swift J1842.5-1124 are similar to other BH XRBs in many respects, for example the hardness-intensity diagram and hardness-rms diagram. The type-C quasi-periodic oscillations (QPOs) were observed as the source started to transit from the low-hard state to the high-soft state. The frequency of QPOs correlate with intensity and the hard component index, and anti-correlate with the hardness and the total fractional rms. These relations are consistent with the Lense-Thirring precession model. The estimated U-band flux changed with the X-ray flux, while the flux density at the V band remained 0.26 mJy. These results imply that the X-ray reprocessing or the tail of thermal emission from the outer disk contributes a significant fraction of the U-band radiation; alternatively, the companion star or the jet dominates the flux at longer wavelengths., Comment: 6 pages, 5 figures, 3 tables, published in A&A

III Zw 2 is the prototype of radio-intermediate quasars. Although there is the evidence of possessing strong jet, significant $\gamma$-ray emission has not been reported before. In this work, we carry out a detailed analysis of the latest {\it Fermi}-LAT {\it Pass} 8 data. No significant $\gamma$-ray signal has been detected in the time-averaged 7-year {\it Fermi}-LAT data of III Zw 2, we however have identified two distinct $\gamma$-ray flares with isotropic luminosities of $\sim 10^{45}$ erg $\rm s^{-1}$. Multiwavelength data analysis (including also the optical photometric observations from Yunnan Observatories) are presented and the main finding is the simultaneous optical and $\gamma$-ray flares of III Zw 2 appearing in Nov. 2009. Violent $\gamma$-ray variability with doubling timescale of 2.5 hours was detected in another $\gamma$-ray flare in May 2010, for which the 3-hour $\gamma$-ray peak flux is $\sim 250$ times of the average flux in 7 years. Rather similar behaviors are observed in blazars and the blazar model can reasonably reproduce the spectral energy distribution of III Zw 2 in a wide energy range, strongly suggesting that its central engine resembles that of blazars. In view of its core which shares radio similarities with young radio sources together with the weak extended radio lobe emission, we suggest that III Zw 2 harbors a recurrent activity core and serves as a valuable target for investigating the fuelling and triggering of the activity in radio loud AGNs., Comment: ApJS in press, welcome any comments

XTE J1810-189 underwent an outburst in 2008, and was observed over $\sim 100$ d by RXTE. Performing a time-resolved spectral analysis on the photospheric radius expansion burst detected on 2008 May 4, we obtain the source distance in the range of 3.5--8.7 kpc for the first time. During its outburst, XTE J1810-189 did not enter into the high/soft state, and both the soft and hard colours decreased with decreasing flux. The fractional rms remained at high values ($\sim 30$ per cent). The RXTE/PCA spectra for 3-25 keV can be described by an absorbed power-law component with an additional Gaussian component, and the derived photon index $\Gamma$ increased from $1.84\pm0.01$ to $2.25\pm0.04$ when the unabsorbed X-ray luminosity in 3-25 keV dropped from $4\times10^{36}$ ergs s$^{-1}$ to $6\times10^{35}$ ergs s$^{-1}$. The relatively high flux, dense observations and broadband spectra allow us to provide strong evidence that the softening behaviour detected in the outburst of XTE J1810-189 originates from the evolution of non-thermal component rather than the thermal component (i.e. neutron star surface emission)., Comment: 7 pages, 5 figures, 3 tables, published in MNRAS

Swift J1357.2-0933 underwent an episodic accretion in 2011 and provided very regular temporal and spectral evolution, making it an ideal source for exploring the nature of very faint X-ray transients (VFXTs). In this work, we present a detailed analysis on both X-ray and near-ultraviolet (NUV) light curves. The fluxes at all wavelengths display a near-exponential decays in the early phase and transits to a faster-decay at late times. The e-folding decay time-scales monotonically decrease with photon energies, and the derived viscous time-scale is $\tau_{\rm \dot{M}} \sim 60$ days. The time-scale in the late faster-decay stage is about a few days. The high ratio of NUV luminosity to X-ray luminosity indicates that the irradiation is unimportant in this outburst, while the near-exponential decay profile and the long decay time-scales conflict with the disc thermal-viscous instability model. We thus suggest that the disc is thermally stable during the observations. Adopting the truncated disc model, we obtain a lower limit of peak accretion rate of $0.03 \dot{M}_{\rm Edd}$ and the X-ray radiative efficiency $\eta < 5\times10^{-4}$, which decreases as the luminosity declines. The low X-ray radiative efficiency is caused by the combined action of advection and outflows, and naturally explains that the X-ray reprocessing is overwhelmed by the viscous radiation of the outer standard disc in the NUV regime. We also propose a possibility that the outer standard disc recedes from the central black hole, resulting in the faster-decay at late times., Comment: 6 pages, 4 figures, published in MNRAS

We have generated an extended version of rather simplified but physically oriented three-dimensional magnetar emission model, STEMS3D, to allow spectral investigations up to 100 keV. We have then applied it to the broadband spectral spectra of four magnetars: 4U 0142+61, 1E 1841-045, 1E 2259+586 and 1E 1048.1-5937, using data collected with Swift/XRT or XMM-Newton in soft X-rays, and Nuclear Spectroscopic Telescope Array in the hard X-ray band. We found that the hard X-ray emission of 4U 0142+61 was spectrally hard compared to the earlier detections, indicating that the source was likely in a transition to or from a harder state. We find that the surface properties of the four magnetars are consistent with what we have obtained using only the soft X-ray data with STEMS3D, implying that our physically motivated magnetar emission model is a robust tool. Based on our broadband spectral investigations, we conclude that resonant scattering of the surface photons in the magnetosphere alone cannot account for the hard X-ray emission in magnetars; therefore, an additional non-thermal process, or a population of relativistic electrons is required. We also discuss the implication of the non-detection of persistent hard X-ray emission in 1E 1048.1-5937., Comment: 8 pages, 3 figures, 2 Tables, ApJ in press

Narrow line Seyfert 1 galaxies (NLS1s) usually do not host relativistic jets and the detection of their $\gamma$-ray emissions is rarely reported. Evidences for strong relativistic beaming effect have been found in all $\gamma$-ray NLS1s to date and hence their jets are believed to be closely aligned. In this work we perform a systematic analysis of 7-year {\it Fermi} Large Area Telescope (LAT) data of 18 steep radio spectrum NLS1s (S-NLS1s) and report the {\it first} two detections of $\gamma$-ray emissions in this class, increasing the total number of known $\gamma$-ray NLS1s to 9. A strong and stable $\gamma$-ray signal (over 8$\sigma$) is produced by SDSS J144318.56+472556.7, and a significant $\gamma$-ray emission (4.5$\sigma$) of SDSS J130522.74+511640.2 has been detected in a monthly flare in November 2013. A thorough investigation of their multiwavelength properties from radio to X rays has been performed, finding no significant variability. Along with their spectral energy distributions and the radio morphology, these facts strongly suggest that these two sources harbor mis-aligned and possibly underdeveloped relativistic jets, which provides valuable targets to reveal the formation and evolution of relativistic jets under extreme circumstances., Comment: replacement of arXiv 1510.05584 (named as "Discovery of gamma-ray emission from a steep radio spectrum NLS1 B3 1441+476")

Anomalous X-ray pulsars (AXPs) and soft gamma-ray repeaters (SGRs) are recognized as the most promising magnetar candidates, as indicated by their energetic bursts and rapid spin-downs. It is expected that the strong magnetic field leaves distinctive imprints on the emergent radiation both by affecting the radiative processes in atmospheres of magnetars and by scattering in the upper magnetospheres. We construct a self-consistent physical model that incorporates emission from the magnetar surface and its reprocessing in the three-dimensional (3D) twisted magnetosphere using a Monte Carlo technique. The synthetic spectra are characterized by four parameters: surface temperature kT, surface magnetic field strength $B$, magnetospheric twist angle $\Delta\phi$, and the normalized electron velocity $\beta$. We also create a tabular model (STEMS3D) and apply it to a large sample of XMM-Newton spectra of magnetars. The model successfully fits nearly all spectra, and the obtained magnetic field for 7 out of the 11 sources are consistent with the values inferred from the spin-down rates. We conclude that the continuum-fitting by our model is a robust method to measure the magnetic field strength and magnetospheric configuration of AXPs and SGRs. Investigating the multiple observations of variable sources, we also study the mechanism of their spectral evolution. Our results suggest that the magnetospheres in these sources are highly twisted ($\Delta\phi > 1$), and the behavior of magnetospheric twisting and untwisting is revealed in the 2002 outburst of 1E 2259+586., Comment: 20 pages, 12 figures, 9 tables, published in ApJ

We investigate the X-ray spectrum, variability and the surrounding ionized bubble of NGC1313 X-2 to explore the physics of super-Eddington accretion. Beyond the Eddington luminosity, the accretion disk of NGC1313 X-2 is truncated at a large radius ($\sim$ 50 times of innermost stable circular orbit), and displays the similar evolution track with both luminous Galactic black-hole and neutron star X-ray binaries. In super-critical accretion, the speed of radiatively driven outflows from the inner disk is mildly relativistic. Such ultra-fast outflows would be over ionized and might produce weak Fe K absorption lines, which may be detected by the coming X-ray mission {\it Astro-H}. If the NGC1313 X-2 is a massive stellar X-ray binary, the high luminosity indicates that an ephemeral feast is held in the source. That is, the source must be accreting at a hyper-Eddington mass rate to give the super-Eddington emission over $\sim 10^{4}-10^{5}$ yr. The expansion of the surrounding bubble nebula with a velocity of $\sim$ 100 km~s$^{-1}$ might indicate that it has existed over $\sim 10^{6}$ yr and is inflated by the radiatively driven outflows from the transient with a duty cycle of activity of $\sim$ a few percent. Alternatively, if the surrounding bubble nebula is produced by line-driven winds, less energy is required than the radiatively driven outflow scenario, and the radius of the Str\"{o}mgren radius agrees with the nebula size. Our results are in favor of the line-driven winds scenario, which can avoid the conflict between the short accretion age and the apparently much longer bubble age inferred from the expansion velocity in the nebula., Comment: 25 pages, 3 figures, 4 Tables, published in ApJ

We analyze all of the available {\it RXTE} observations of Cyg X-3 in order to investigate the connection between the central X-ray source and its surrounding environment. The hardness--intensity diagram of Cyg X-3 displays a "shoe" shape rather than the Q-type shape commonly seen in other black hole X-ray binary, and exhibits no apparent hysteresis effect. During the $\gamma$-ray outbursts, no existing data are located in the hard and intermediate states, which suggest the absence of a significant population of non-thermal electrons when the source is in these states. For the first time, we present the orbital modulation of the X-ray light curve (LC) of all five states. The different energy band LCs are in phase with each other in all five states, and the modulation amplitude of both soft and hard X-ray LCs monotonously increases with decreasing hardness from hard to soft non-thermal states. We confirm that the modulation depth decreases with increasing energy in the hard, intermediate, and very high states, as originally reported by Zdziarski et al. However, in the soft non-thermal state, the hard X-ray modulation strength significantly increases and is even larger than the soft X-ray one. Our results rule out both wind absorption and jet origins of the hard X-ray LC modulation in the soft non-thermal state, and challenge our understanding of the states of Cyg X-3., Comment: 22 pages, 8 figures, 4 tables

Low-mass X-ray binaries (LMXBs) are systems in which a low-mass companion transfers mass via Roche-lobe overflow onto a black hole (BH) or a weakly magnetized neutron star (NS). It is believed that both the solid surface and the magnetic field of an NS can affect the accretion flow and show some observable effects. Using the disk emission dominant data, we compare the disk evolution of the two types of systems from low luminosity to super-Eddington luminosity. As the luminosity decreases the disk in the NS LMXB 4U1608--522 begins to leave the innermost stable circular orbit (ISCO) at much higher luminosity ($\sim$ 0.1 $L_{\mathrm{Edd}}$), compared with BH LMXBs at much lower luminosity ($\sim$ 0.03 $L_{\mathrm{Edd}}$), due to the interaction between the NS magnetosphere and accretion flow. However, as the luminosity increases above a critical luminosity, the disks in BH and NS LMXBs trace the same evolutionary pattern, because the magnetosphere is restricted inside ISCO, and then both the NS surface emission and (dipole) magnetic field do not significantly affect the secular evolution of the accretion disk, that is driven by the increased radiation pressure in the inner region. We further suggest that the NS surface emission provides additional information of accretion disk, not available in BH systems. Through the observed NS surface emission, we argue that the disk thickness $H/R$ is less than $0.3-0.4$, and that the significant outflow from inner disk edge exists at luminosity close to Eddington luminosity., Comment: 17 pages, 5 figures, 1 table, accepted for publication in ApJ

We provide a detailed analysis of 12 XMM observations of the nearest persistent extragalactic ultraluminous X-ray source (ULX), M33 X-8. No significant spectral evolution is detected between the observations, therefore we combine the individual observations to increase the signal-to-noise ratio for spectral fitting. The combined spectra are best fitted by the self-consistent p-free disk plus power-law component model with p = 0.571_{-0.030}^{+0.032}, kT_{in} = 1.38_{-0.08}^{+0.09} keV, and the flux ratio of the p-free disk component to the power-law component being 0.63:0.37 in the 0.3 -- 10 keV band. The fitting indicates that the black hole in M33 X-8 is of \sim 10 M_{\odot} and accretes at a super-Eddington rate (\sim 1.5 L_{Edd}), and the phase of the accretion disk is close to a slim disk (p = 0.5). We report, for the first time, that an extra power-law component is required in addition to the p-free disk model for ULXs. In super-Eddington cases, the power-law component may possibly result from the optically thin inner region f the disk or a comptonized corona similar to that of a standard thin disk., Comment: 11 pages, 1 table, 2 figures, accepted by PASJ

We present a unified description of all the three known classes of optically thick accretion disks around black holes, namely Shakura-Sunyaev disks, slim disks, and neutrino-dominated accretion flows (NDAFs). It is found that NDAFs have both a maximal and a minimal possible mass accretion rate at their each radius. This may be suggestive of an interpretation for the origin of X-ray flares observed in gamma-ray bursts., Comment: 13 pages, 3 figures, accepted by ApJ