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Register a new userXMM-Newton and Swift spectroscopy of the newly discovered very-faint X-ray transient IGR J17494-3030
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Montserrat Armas Padilla
Publication date
2013
fields
Physics
and research's language is
English
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A growing group of low-mass X-ray binaries are found to be accreting at very-faint X-ray luminosities of <1E36 erg/s (2-10 keV). Once such system is the new X-ray transient IGR J17494-3030. We present Swift and XMM-Newton observations obtained during its 2012 discovery outburst. The Swift observations trace the peak of the outburst, which reached a luminosity of ~7 E35 (D/8 kpc)^2 erg/s (2-10 keV). The XMM-Newton data were obtained when the outburst had decayed to an intensity of ~ 8 E34 (D/8 kpc)^2 erg/s. The spectrum can be described by a power-law with an index of ~1.7 and requires an additional soft component with a black-body temperature of ~0.37 keV (contributing ~20% to the total unabsorbed flux in the 0.5-10 keV band). Given the similarities with high-quality spectra of very-faint neutron star low-mass X-ray binaries, we suggest that the compact primary in IGR J17494-3030 is a neutron star. Interestingly, the source intensity decreased rapidly during the ~12 hr XMM-Newton observation, which was accompanied by a decrease in inferred temperature. We interpret the soft spectral component as arising from the neutron star surface due to low-level accretion, and propose that the observed decline in intensity was the result of a decrease in the mass-accretion rate onto the neutron star.
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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-dependent, each having a local maximum at 4 keV and 1.5 keV, respectively. We also recovered the X-ray pulsations in archival 2012 XMM-Newton observations, allowing us to measure a long-term pulsar spin-down rate of $dot u = -2.1(7)times10^{-14}$ Hz/s and to infer a pulsar surface dipole magnetic field strength of $simeq 10^9$ G. We show that the mass transfer in the binary is likely non-conservative, and we discuss various scenarios for mass loss from the system.
We present the results of combined INTEGRAL and XMM-Newton observations of the supergiant fast X-ray transient (SFXT) IGR J17354$-$3255. Three XMM-Newton observations of lengths 33.4 ks, 32.5 ks and 21.9 ks were undertaken, the first an initial pointing to identify the correct source in the field of view and the latter two performed around periastron. Simultaneous INTEGRAL observations across $sim66%$ of the orbital cycle were analysed but the source was neither detected by IBIS/ISGRI nor by JEM-X. The XMM-Newton light curves display a range of moderately bright X-ray activity but there are no particularly strong flares or outbursts in any of the three observations. We show that the spectral shape measured by XMM-Newton can be fitted by a consistent model throughout the observation, suggesting that the observed flux variations are driven by obscuration from a wind of varying density rather than changes in accretion mode. The simultaneous INTEGRAL data rule out simple extrapolation of the simple powerlaw model beyond the XMM-Newton energy range.
We report the first broad-band (0.5-150 keV) simultaneous X-ray observations of the very faint X-ray transient IGRJ17285-2922/XTEJ1728-295 performed with XMM-Newton and INTEGRAL satellites during its last outburst, started on 2010, August 28. XMM-Newton observed the source on 2010 September 9-10, for 22ks. INTEGRAL observations were part of the publicly available Galactic Bulge program, and overlapped with the times covered by XMM-Newton. The broad-band spectroscopy resulted in a best-fit with an absorbed power law displaying a photon index of 1.61+/-0.01, an absorbing column density of (5.10+/-0.05)E21 cm-2, and a flux of 2.4E-10 erg/cm2/s (1-100 keV), corrected for the absorption. The data did not require either a spectral cut-off (E>50 keV) or an additional soft component. The slopes of the XMM-Newton and INTEGRAL separate spectra were compatible, within the uncertainties. The timing analysis does not show evidence either for X-ray pulsations or for type I X-ray bursts. The broad band X-ray spectrum as well as the power density spectrum are indicative of a low hard state in a low mass X-ray binary, although nothing conclusive can be said about the nature of the compact object (neutron star or black hole). The results we are reporting here allow us to conclude that IGRJ17285-2922 is a low mass X-ray binary, located at a distance greater than 4 kpc.
IGR J18483-0311 was discovered with INTEGRAL in 2003 and later classified as a supergiant fast X-ray transient. It was observed in outburst many times, but its quiescent state is still poorly known. Here we present the results of XMM-Newton, Swift, and Chandra observations of IGRJ18483-0311. These data improved the X-ray position of the source, and provided new information on the timing and spectral properties of IGR J18483-0311 in quiescence. We report the detection of pulsations in the quiescent X-ray emission of this source, and give for the first time a measurement of the spin-period derivative of this source. In IGRJ18483-0311 the measured spin-period derivative of -(1.3+-0.3)x10^(-9) s/s likely results from light travel time effects in the binary. We compare the most recent observational results of IGRJ18483-0311 and SAXJ1818.6-1703, the two supergiant fast X-ray transients for which a similar orbital period has been measured.
We report our multiwavelength study of the 2011 outburst evolution of the newly discovered black hole candidate X-ray binary Swift J1357.2-0933. We analysed the Swift X-ray telescope and Ultraviolet/Optical telescope (UVOT) data taken during the ~7 months duration of the outburst. It displayed a 2-10 keV X-ray peak luminosity of ~1E35(D/1.5 kpc)^2 erg s-1 which classifies the source as a very faint X-ray transient. We found that the X-ray spectrum at the peak was consistent with the source being in the hard state, but it softened with decreasing luminosity, a common behaviour of black holes at low luminosities or returning to quiescence from the hard state. The correlations between the simultaneous X-ray and ultraviolet/optical data suggest a system with a black hole accreting from a viscous disc that is not irradiated. The UVOT filters provide the opportunity to study these correlations up to ultraviolet wavelengths a regime so far unexplored. If the black hole nature is confirmed, Swift J1357.2-0933 would be one of the very few established black hole very-faint X-ray transients.
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