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  • 1
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    A Suzaku view of IGR J16393-4643 (2014)
    Oxford University Press
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    Publication Date: 2014-12-12
    Description: The pulsar IGR J16393–4643 belongs to a class of highly absorbed supergiant high-mass X-ray binaries (HMXBs), characterized by a very high column density of absorbing matter. We present the results of simultaneous broad-band pulsation and spectrum analysis from a 44-ks Suzaku observation of the source. The orbital intensity profile created with the Swift Burst Alert Telescope ( Swift –BAT) light curve shows an indication of IGR J16393–4643 being an eclipsing system with a short eclipse semi-angle E  ~ 17°. For a supergiant companion star with a 20-R radius, this implies an inclination of the orbital plane in the range 39°–57°, whereas for a main-sequence B star as the companion with a 10-R radius, the inclination of the orbital plane is in the range 60°–77°. Pulse profiles created for different energy bands have complex morphology, which shows some energy dependence and increases in pulse fraction with energy. We have also investigated broad-band spectral characteristics, phase-averaged spectra and resolving the pulse phase into peak and trough phases. The phase-averaged spectrum has a very high N H (~ 3 10 23  cm –2 ) and is described by a power law ( ~ 0.9) with a high-energy cut-off above 20 keV. We find a change in the spectral index in the peak and trough phases, implying an underlying change in the source spectrum.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 2
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    Orbital evolution and search for eccentricity and apsidal motion in the eclipsing HMXB 4U 1700-37 (2016)
    Oxford University Press
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    Publication Date: 2016-07-02
    Description: In the absence of detectable pulsations in the eclipsing high-mass X-ray binary 4U 1700–37, the orbital period decay is necessarily determined from the eclipse timing measurements. We have used the earlier reported mid-eclipse time measurements of 4U 1700–37 together with the new measurements from long-term light curves obtained with the all sky monitors RXTE -ASM, Swift -BAT and MAXI -GSC, as well as observations with RXTE -PCA, to measure the long-term orbital evolution of the binary. The orbital period decay rate of the system is estimated to be ${\dot{P}}/P = -(4.7 \pm 1.9) \times 10^{-7}$  yr –1 , smaller compared to its previous estimates. We have also used the mid-eclipse times and the eclipse duration measurements obtained from 10-years-long X-ray light curve with Swift -BAT to separately put constraints on the eccentricity of the binary system and attempted to measure any apsidal motion. For an apsidal motion rate greater than 5 deg yr –1 , the eccentricity is found to be less than 0.008, which limits our ability to determine the apsidal motion rate from the current data. We discuss the discrepancy of the current limit of eccentricity with the earlier reported values from radial velocity measurements of the companion star.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 3
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    The transcriptional repressor HDAC7 promotes apoptosis and c-Myc downregulation in particular types of leukemia and lymphoma (2015)
    Springer Nature
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    Publication Date: 2015-02-13
    Description: The transcriptional repressor HDAC7 promotes apoptosis and c-Myc downregulation in particular types of leukemia and lymphoma Cell Death and Disease 6, e1635 (February 2015). doi:10.1038/cddis.2014.594 Authors: B Barneda-Zahonero, O Collazo, A Azagra, I Fernández-Duran, J Serra-Musach, A B M M K Islam, N Vega-García, R Malatesta, M Camós, A Gómez, L Román-González, A Vidal, N López-Bigas, A Villanueva, M Esteller & M Parra
    Electronic ISSN: 2041-4889
    Topics: Biology , Medicine
    Published by Springer Nature
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  • 4
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    Variability study of the high-mass X-ray binary IGR J18027-2016 with Swift-XRT (2016)
    Oxford University Press
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    Publication Date: 2016-09-24
    Description: We report the results from pulsations and spectral analysis of a large number of observations of the high-mass X-ray binary pulsar IGR J18027–2016 with Swift X-ray Telescope (XRT), carried out at different orbital phases. In some orbital phases, as seen in different XRT observations, the X-ray intensity is found to vary by a large factor, of about ~50. In all the observations with sufficient number of source X-ray photons, pulsations have been detected around the previously known pulse period of ~140 s. When detected, the pulse profiles do not show any significant variation over a flux difference of a factor of ~3. The absorption column density is found to be large before and after the eclipse. We discuss various possible reasons for intensity and spectral variations in IGR J18027–2016, such as clumpy wind and hydrodynamic instabilities.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 5
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    Orbital phase resolved spectroscopy of GX 301-2 with MAXI (2014)
    Oxford University Press
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    Publication Date: 2014-05-22
    Description: GX 301-2, a bright high-mass X-ray binary with an orbital period of 41.5 d, exhibits stable periodic orbital intensity modulations with a strong pre-periastron X-ray flare. Several models have been proposed to explain the accretion at different orbital phases, invoking accretion via stellar wind, equatorial disc, and accretion stream from the companion star. We present results from exhaustive orbital phase resolved spectroscopic measurements of GX 301-2 using data from the Gas Slit Camera onboard MAXI . Using spectroscopic analysis of the MAXI data with unprecedented orbital coverage for many orbits continuously, we have found a strong orbital dependence of the absorption column density and equivalent width of the iron emission line. A very large equivalent width of the iron line along with a small value of the column density in the orbital phase range 0.10–0.30 after the periastron passage indicates the presence of high density absorbing matter behind the neutron star in this orbital phase range. A low energy excess is also found in the spectrum at orbital phases around the pre-periastron X-ray flare. The orbital dependence of these parameters are then used to examine the various models about mode of accretion on to the neutron star in GX 301-2.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 6
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    Variations in the pulsation and spectral characteristics of OAO 1657-415 (2014)
    Oxford University Press
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    Publication Date: 2014-06-29
    Description: We present broad-band pulsation and spectral characteristics of the accreting X-ray pulsar OAO 1657–415 with a 2.2 d long Suzaku observation carried out covering its orbital phase range ~0.4–0.6, with respect to the mid-eclipse. During the last third of the observation, the X-ray count rate in both the X-ray Imaging Spectrometer (XIS) and the HXD-PIN instruments increased by a factor of more than 10. During this observation, the hardness ratio also changed by a factor of more than 5, uncorrelated with the intensity variations. In two segments of the observation, lasting for ~30–50 ks, the hardness ratio is very high. In these segments, the spectrum shows a large absorption column density and correspondingly large equivalent widths of the iron fluorescence lines. We found no conclusive evidence for the presence of a cyclotron line in the broad-band X-ray spectrum with Suzaku . The pulse profile, especially in the XIS energy band, shows evolution with time but not so with energy. We discuss the nature of the intensity variations, and variations of the absorption column density and emission lines during the duration of the observation as would be expected due to a clumpy stellar wind of the supergiant companion star. These results indicate that OAO 1657–415 has characteristics intermediate to the normal supergiant systems and the systems that show fast X-ray transient phenomena.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 7
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    Orbital phase resolved spectroscopy of GX 301-2 with MAXI (2014)
    Oxford University Press
    Details
    Publication Date: 2014-05-20
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press on behalf of The Royal Astronomical Society.
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