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Register a new userPeculiar Lapse of Periodic Eclipsing Event at Low Mass X-ray Binary GRS 1747$-$312 during Suzaku Observation in 2009
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GRS 1747$-$312 is a neutron star Low-Mass X-ray Binary in the globular cluster Terzan 6, located at a distance of 9.5 kpc from the Earth. During its outbursts, periodic eclipses were known to occur. Observations for the outbursts were performed with Chandra in 2004 and Swift in 2013. XMM-Newton observed its quiescent state in 2004. In addition, when Suzaku observed it in 2009 as a part of Galactic center mapping observations, GRS 1747$-$312 was found to be in a low luminosity state with $L_{rm x} sim 1.2 times 10^{35}$ erg s$^{-1}$. All of the observations except for XMM-Newton included the time of the eclipses predicted. We analyzed archival data of these observations. During the Chandra and Swift observations, we found clear flux decreases at the expected time of the eclipses. During the Suzaku observation, however, there were no clear signs for the predicted eclipses. The lapse of the predicted eclipses during the Suzaku observation can be explained by a contaminant source quite close to GRS 1747$-$312. When GRS 1747$-$312 is in the quiescent state, we observe X-rays from the contaminant source rather than from GRS 1747$-$312. However, we have no clear evidence for the contaminant source in our data. The lapse might also be explained by thick material ($N_{rm H} > 10^{24}$ cm$^{-2}$ ) between the neutron star and the companion star, though the origin of the thick material is not clear.
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We report the serendipitous detection with the Rossi X-ray Timing Explorer of a long and peculiar X-ray burst whose localization is consistent with one known X-ray burster (GRS 1747-312) and which occurred when that source was otherwise quiescent. The peculiar feature concerns a strong radius expansion of the neutron star photosphere, which occurred not within a few seconds from the start of the burst, as is standard in radius-expansion bursts, but 20 s later. This suggests that two different layers of the neutron star may have undergone thermonuclear runaways: a hydrogen-rich and a hydrogen-poor layer. The reason for the delay may be related to the source being otherwise quiescent.
We studied the transient neutron-star low-mass X-ray binary GRS 1747-312, located in the globular cluster Terzan 6, in its quiescent state after its outburst in August 2004, using an archival XMM-Newton observation. A source was detected in this cluster and its X-ray spectrum can be fitted with the combination of a soft, neutron-star atmosphere model and a hard, power-law model. Both contributed roughly equally to the observed 0.5-10 keV luminosity (~4.8X10^33 erg/s). This type of X-ray spectrum is typically observed for quiescent neutron-star X-ray transients that are perhaps accreting in quiescence at very low rates. Therefore, if this X-ray source is the quiescent counterpart of GRS 1747-312, then this source is also accreting at low levels in-between outbursts. Since source confusion a likely problem in globular clusters, it is quite possible that part, if not all, of the emission we observed is not related to GRS 1747-312, and is instead associated with another source or conglomeration of sources in the cluster. Currently, it is not possible to determine exactly which part of the emission truly originates from GRS 1747-312, and a Chandra observation (when no source is in outburst in Terzan 6) is needed to be conclusive. Assuming that the detected emission is due to GRS 1747-312, we discuss the observed results in the context of what is known about other quiescent systems. We also investigated the thermal evolution of the neutron star in GRS 1747-312, and inferred that GRS 1747-312 can be considered a typical quiescent system under our assumptions.
In this paper, we report on the available X-ray data collected by INTEGRAL, Swift, and XMM-Newton during the first outburst of the INTEGRAL transient IGR J17451-3022, discovered in 2014 August. The monitoring observations provided by the JEM-X instruments on-board INTEGRAL and the Swift/XRT showed that the event lasted for about 9 months and that the emission of the source remained soft for the entire period. The source emission is dominated by a thermal component (kT~1.2 keV), most likely produced by an accretion disk. The XMM-Newton observation carried out during the outburst revealed the presence of multiple absorption features in the soft X-ray emission that could be associated to the presence of an ionized absorber lying above the accretion disk, as observed in many high-inclination low mass X-ray binaries. The XMM-Newton data also revealed the presence of partial and rectangular X-ray eclipses (lasting about 820 s), together with dips. The latter can be associated with increases in the overall absorption column density in the direction of the source. The detection of two consecutive X-ray eclipses in the XMM-Newton data allowed us to estimate the source orbital period at 22620.5(-1.8,+2.0) s (1{sigma} c.l.).
We observed IGR J16194-2810 in the low/hard state with the Suzaku X-ray satellite in 2009. The source is a Symbiotic X-ray Binary (SyXB) classified as a category of a Low-Mass X-ray Binary (LMXB), since the system is composed of an M-type giant and probably a neutron star (NS). We detected the 0.8-50 keV signal with the XIS and HXD-PIN. The 2-10 keV luminosity was L ~ 7 x 10^34 erg s^-1 corresponding to ~10^-3 L_Edd, where L_Edd is the Eddington Luminosity of a 1.4 M_o NS and a source distance of 3.7 kpc is assumed. The luminosity is similar to those of past observations. The spectral analysis showed that there are two emission components below and above ~2 keV. The hard emission component is represented by a Comptonized black-body emission model with the seed-photon temperature ~1.0 keV and the emission radius ~700 m. The seed photon is considered to come from a small fraction of the NS surface. The soft component is reproduced by either a raw black-body (~0.4 keV, ~1.7 km) or a Comptonized emission (~0.1 keV, ~75 km). We think the origin is the emission from other part of the NS surface or the accreting stream. The physical parameters of the hard emission component of IGR J16194-2810 are compared with those of an SyXB (4U 1700+24) and LMXBs (Aql X-1 and 4U 0614+091). This comparison reveals that these SyXBs in the low/hard state have a smaller radiation region (< 1 km) on the NS surface with a higher seed-photon temperature (~1 keV) than the compared LMXBs.
Spectroscopy of the low mass X-ray binary Ser X-1 using the Gran Telescopio Canarias have revealed a ~2 hr periodic variability that is present in the three strongest emission lines. We tentatively interpret this variability as due to orbital motion, making it the first indication of the orbital period of Ser X-1. Together with the fact that the emission lines are remarkably narrow, but still resolved, we show that a main sequence K-dwarf together with a canonical 1.4Msun neutron star gives a good description of the system. In this scenario the most likely place for the emission lines to arise is the accretion disk, instead of a localized region in the binary (such as the irradiated surface or the stream-impact point), and their narrowness is due instead to the low inclination (<10 degrees) of Ser X-1.
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