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Register a new userChandra and XMM Monitoring of the Black Hole X-ray Binary IC 10 X-1
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The massive black hole + Wolf-Rayet binary IC10 X-1 was observed in a series of 10 Chandra and 2 XMM-Newton observations spanning 2003-2012, showing consistent variability around 7 x10^37 erg/s, with a spectral hardening event in 2009. We phase-connected the entire light-curve by folding the photon arrival times on a series of trial periods spanning the known orbital period and its uncertainty, refining the X-ray period to P = 1.45175(1)d. The duration of minimum-flux in the X-ray eclipse is 5 hr which together with the optical radial velocity curve for the companion yields a radius for the eclipsing body of 8-10 Rsun for the allowed range of masses. The orbital separation of 18.5-22 Rsun then provides a limiting inclination i>63 degrees for total eclipses to occur. The eclipses are asymmetric (egress duration 0.9 hr) and show energy dependence, suggestive of an accretion-disk hotspot and corona. The eclipse is much (5X) wider than the 1.5-2 Rsun WR star, pointing to absorption/scattering in the dense wind of the WR star. The same is true of the close analog NGC 300 X-1. RV measurements of the He II [4686] line from the literature show a phase-shift with respect to the X-ray ephemeris such that the velocity does not pass through zero at mid-eclipse. The X-ray eclipse leads inferior conjunction of the RV curve by 90 degrees, so either the BH is being eclipsed by a trailing shock/plume, or the He II line does not directly trace the motion of the WR star and instead originates in a shadowed partially-ionized region of the stellar wind.
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Black-hole binary (BHB) systems comprise a stellar-mass black hole and a closely orbiting companion star. Matter is transferred from the companion to the black hole, forming an accretion disk, corona and jet structures. The resulting release of gravitational energy leads to emission of X-rays. The radiation is affected by special/general relativistic effects, and can serve as a probe of the properties of the black hole and surrounding environment, if the accretion geometry is properly identified. Two competing models describe the disk-corona geometry for the hard spectral state of BHBs, based on spectral and timing measurements. Measuring the polarization of hard X-rays reflected from the disk allows the geometry to be determined. The extent of the corona differs between the two models, affecting the strength of relativistic effects (e.g., enhancement of polarization fraction and rotation of polarization angle). Here, we report observational results on linear polarization of hard X-ray (19-181 keV) emission from a BHB, Cygnus X-1, in the hard state. The low polarization fraction, <8.6% (upper limit at 90% confidence level), and the alignment of the polarization angle with the jet axis show that the dominant emission is not influenced by strong gravity. When considered together with existing spectral and timing data, our result reveals that the accretion corona is either an extended structure, or is located far from the black hole in the hard state of Cygnus X-1.
We have monitored the Cassiopeia dwarf galaxy (IC 10) in a series of 10 Chandra ACIS-S observations to capture its variable and transient X-ray source population, which is expected to be dominated by High Mass X-ray Binaries (HMXBs). We present a sample of 21 X-ray sources that are variable between observations at the 3 sigma level, from a catalog of 110 unique point sources. We find 4 transients (flux variability ratio greater than 10) and a further 8 objects with ratio > 5. The observations span years 2003 - 2010 and reach a limiting luminosity of >10$^{35}$ erg/s, providing sensitivity to X-ray binaries in IC 10 as well as flare stars in the foreground Milky Way. The nature of the variable sources is investigated from light-curves, X-ray spectra, energy quantiles, and optical counterparts. The purpose of this study is to discover the composition of the X-ray binary population in a young starburst environment. IC 10 provides a sharp contrast in stellar population age (<10 My) when compared to the Magellanic Clouds (40-200 My) where most of the known HMXBs reside. We find 10 strong HMXB candidates, 2 probable background Active Galactic Nuclei, 4 foreground flare-stars or active binaries, and 5 not yet classifiable sources. Complete classification of the sample requires optical spectroscopy for radial velocity analysis and deeper X-ray observations to obtain higher S/N spectra and search for pulsations. A catalog and supporting dataset are provided.
IC 10 X-1 is a variable X-ray source in the Local Group starburst galaxy IC 10 whose optical counterpart is a Wolf-Rayet (WR) star. Prestwich et al. (2007) recently proposed that it contains the most massive known stellar-mass black hole (23-34 M_sun), but their conclusion was based on radial velocities derived from only a few optical spectra, the most important of which was seriously affected by a CCD defect. Here we present new spectra of the WR star, spanning one month, obtained with the Keck-I 10 m telescope. The spectra show a periodic shift in the He II 4686 Ang. emission line as compared with IC 10 nebular lines such as [O III] 5007 Ang. From this, we calculate a period of 34.93+/-0.04 hr (consistent with the X-ray period of 34.40+/-0.83 hr reported by Prestwich et al. 2007) and a radial-velocity semi-amplitude of 370+/-20 km/s. The resulting mass function is 7.64+/-1.26 M_sun, consistent with that of Prestwich et al. (2007) (7.8 M_sun). This, combined with the previously estimated (from spectra) mass of 35 M_sun for the WR star, yields a minimum primary mass of 32.7+/-2.6 M_sun. Even if the WR star has a mass of only 17 M_sun, the minimum primary mass is 23.1+/-2.1 M_sun. Thus, IC 10 X-1 is indeed a WR/black-hole binary containing the most massive known stellar-mass black hole.
We present simultaneous multi-band radio and X-ray observations of the black hole X-ray binary Cygnus X-1, taken with the Karl G. Jansky Very Large Array and the Nuclear Spectroscopic Telescope Array. With these data, we detect clear flux variability consistent with emission from a variable compact jet. To probe how the variability signal propagates down the jet flow, we perform detailed timing analyses of our data. We find that the radio jet emission shows no significant power at Fourier frequencies $fgtrsim0.03$ Hz (below $sim30$ sec timescales), and that the higher frequency radio bands (9/11 GHz) are strongly correlated over a range of timescales, displaying a roughly constant time lag with Fourier frequency of a few tens of seconds. However, in the lower frequency radio bands (2.5/3.5 GHz) we find a significant loss of coherence over the same range of timescales. Further, we detect a correlation between the X-ray/radio emission, measuring time lags between the X-ray/radio bands on the order of tens of minutes. We use these lags to solve for the compact jet speed, finding that the Cyg X-1 jet is more relativistic than usually assumed for compact jets, where $beta=0.92^{+0.03}_{-0.06}$, ($Gamma=2.59^{+0.79}_{-0.61}$). Lastly, we constrain how the jet size scale changes with frequency, finding a shallower relation ($propto u^{-0.4}$) than predicted by simple jet models ($propto u^{-1}$), and estimate a jet opening angle of $phisim0.4-1.8$ degrees. With this study, we have developed observational techniques designed to overcome the challenges of radio timing analyses and created the tools needed to connect rapid radio jet variability properties to internal jet physics.
The black hole MAXI J1820+070 was discovered during its 2018 outburst and was extensively monitored across the electromagnetic spectrum. Following the detection of relativistic radio jets, we obtained four Chandra X-ray observations taken between 2018 November and 2019 May, along with radio observations conducted with the VLA and MeerKAT arrays. We report the discovery of X-ray sources associated with the radio jets moving at relativistic velocities with a possible deceleration at late times. The broadband spectra of the jets are consistent with synchrotron radiation from particles accelerated up to very high energies (>10 TeV) by shocks produced by the jets interacting with the interstellar medium. The minimal internal energy estimated from the X-ray observations for the jets is $sim 10^{41}$ erg, significantly larger than the energy calculated from the radio flare alone, suggesting most of the energy is possibly not radiated at small scales but released through late-time interactions.
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