XTE J1739−302 as a Supergiant Fast X‐Ray Transient (original) (raw)
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The Optical Counterpart to the Peculiar X‐Ray Transient XTE J1739−302
The Astrophysical Journal, 2006
The weak X-ray transient XTE J1739−302, characterized by extremely short outbursts, has recently been identified with a reddened star. Here we present spectroscopy and photometry of the counterpart, identifying it as a O8 Iab(f) supergiant at a distance of ∼ 2.3 kpc. XTE J1739−302 becomes thus characterized as the prototype of the new class of Supergiant Fast X-ray Transients. The optical and infrared spectra of the counterpart to XTE J1739−302 do not reveal any obvious characteristics setting it apart from other X-ray binaries with supergiant companions, which display a very different type of X-ray lightcurve.
IGR J17544-2619: a new supergiant fast X-ray transient revealed by optical/infrared observations
Astronomy and Astrophysics, 2006
One of the most recent discoveries of the INTEGRAL observatory is the existence of a previously unknown population of X-ray sources in the inner arms of the Galaxy. IGR J17544−2619, IGR J16465−4507 and XTE J1739−302 are among these sources. Although the nature of these systems is still unexplained, the investigations of the optical/NIR counterparts of the two last sources, combined with high energy data, have provided evidence of them being highly absorbed high mass X-ray binaries with blue supergiant secondaries and displaying fast X-ray transient behaviour. In this work we present our optical/NIR observations of IGR J17544−2619, aimed at identifying and characterizing its counterpart. We show that the source is a high mass X-ray binary at a distance of 2-4 kpc with a strongly absorbed O9Ib secondary, and discuss the nature of the system.
X-ray behaviour of the Supergiant Fast X-ray Transient: XTE J1739-302
2008
An INTEGRAL long-term monitoring of XTE J1739-302, considered as the prototype source of the Supergiant Fast X-ray Transients (SFXTs), is presented in detail. The source follows a more complex behaviour than expected. Far from presenting a regular variability pattern, XTE J1739-3021 shows periods of high, intermediate, and low flaring activity. The X-ray behaviour of the source is analysed in the context of the clumpy structure of the supergiant wind.
Optical Observations of XTE J1118 + 480 during the 2000 Outburst
Publications of the Astronomical Society of Japan, 2002
We report on photometric and spectroscopic observations of a possible halo black-hole X-ray nova, XTE J1118 + 480 (= KV UMa) during outburst. Our photometric monitoring during the main outburst revealed that the optical maximum as well as the onset of the outburst precede those in the X-ray region. This indicates that the event was an "outside-in" type outburst and that its optical flux was dominated by viscous heating, itself, and not the effect of X-ray irradiation. Based on these results, we suggest an outburst scenario analogous to superoutbursts in SU UMa-type dwarf novae. This scenario predicts a superhump phenomenon, which we indeed detected throughout the outburst. We determined its period to be 0.170529 ± 0.000006 d, which is slightly longer than the orbital periods suggested from spectroscopic observations. We have furthermore revealed the first evidence of a continuous period decreasing in X-ray novae. The most prominent feature in our optical spectrum is a double-peak He II 4686Å emission line having an asymmetric profile with an outstanding blue side peak. Using a Doppler mapping method, we found that the He II emission originates from the accretion disk, which particularly concentrates on the hot spot. The time that the blue peak becomes strongest corresponds to a superhump peak. This implies that we see an elongated side of an eccentric disk at that time and, hence, it may cause an asymmetric emission profile. Substituting the observed fractional superhump excess for a theoretically expected relation between it and the mass ratio, we estimate that the black-hole mass is larger than 9.5 M. XTE J1118 + 480 thus has a large mass of a compact object compared with the typical black-hole X-ray novae.
Supergiant Fast X-ray Transients (SFXTs) are a sub-class of High Mass X-ray Binaries (HMXBs) associated with OB supergiant companions and displaying transient X-ray activity. This behaviour is quite surprising since HMXBs hosting supergiants were known to be persistent sources, until the INTEGRAL discoveries obtained by means of the monitoring of the Galactic plane. We have been performing a monitoring campaign with Swift of four SFXTs with the main aim of characterizing both the long-term behaviour of these transients and the properties during bright outbursts. Here we discuss the properties of the X-ray emission observed outside the outbursts as well as the flares observed from two SFXTs: IGR J17544-2916 and XTE J1739-302.
The Astrophysical Journal
IGR J16479−4514 is a Supergiant Fast X-ray Transient (SFXT), a new class of High Mass X-ray Binaries, whose number is rapidly growing thanks to the INTEGRAL observations of the Galactic plane. It was regularly monitored with Swift/XRT since November 2007, to study the quiescent emission, the outburst properties and their recurrence. A new bright outburst, reaching fluxes above 10 −9 erg cm −2 s −1 , was caught by the Swift/BAT. Swift immediately re-pointed at the target with the narrow-field instruments so that, for the first time, an outburst from a SFXT where a periodicity in the outburst recurrence is unknown could be observed simultaneously in the 0.2-150 keV energy band. The X-ray emission is highly variable and spans almost four orders of magnitude in count rate during the Swift/XRT observations covering a few days before and after the bright peak. The X-ray spectrum in outburst is hard and highly absorbed. The power-law fit resulted in a photon index of 0.98±0.07, and in an absorbing column density of ∼5×10 22 cm −2 . These observations demonstrate that in this source (similarly to what was observed during the 2007 outburst from the periodic SFXT IGR J11215−5952), the accretion phase lasts much longer than a few hours.
XTE J1739302: An Unusual New X-Ray Transient
The Astrophysical …, 1998
A new X-ray transient, designated XTE J1739-302, was discovered with the proportional counter array on the Rossi X-Ray Timing Explorer in data from 1997 August 12. Although it was the brightest source in the Galactic center region while active (about 3.0× 10− 9 ergs ...
Monthly Notices of the Royal Astronomical Society: Letters, 2011
Swift observed an outburst from the supergiant fast X-ray transient (SFXT) AX J1841.0−0536 on 2010 June 5, and followed it with XRT for 11 days. The X-ray light curve shows an initial flare followed by a decay and subsequent increase, as often seen in other SFXTs, and a dynamical range of ∼ 1600. Our observations allow us to analyse the simultaneous broad-band (0.3-100 keV) spectrum of this source, for the first time down to 0.3 keV, which can be fitted well with models usually adopted to describe the emission from accreting neutron stars in high-mass X-ray binaries, and is characterized by a high absorption (N H ∼ 2 × 10 22 cm −2 ), a flat power law (Γ ∼ 0.2), and a high energy cutoff. All of these properties resemble those of the prototype of the class, IGR J17544−2619, which underwent an outburst on 2010 March 4, whose observations we also discuss. We show how well AX J1841.0−0536 fits in the SFXT class, based on its observed properties during the 2010 outburst, its large dynamical range in X-ray luminosity, the similarity of the light curve (length and shape) to those of the other SFXTs observed by Swift, and the X-ray broad-band spectral properties.
X-ray observation of XTE J2012+381 during the 1998 outburst
Journal of Astrophysics and Astronomy, 2000
The outburst of X ray transient source XTE J2012+381 was detected by the RXTE All Sky Monitor on 1998 May 24th. Following the outburst, X ray observations of the source were made in the 2 18keV energy band with the Pointed Proportional Counters of the Indian X ray Astronomy Experiment (IXAE) on board the Indian satellite IRS P3 during 1998 June 2nd 10th. The X ray flux of the source in the main outburst decreased exponentially during the period of observation. No large amplitude short term variability in the intensity is detected from the source. The power density spectrum obtained from the timing analysis of the data shows no indication of any quasi periodic oscillations in 0.002 0.5 Hz band. The hardness ratio i.e. the ratio of counts in 6 18 keV to 2 6 keV band, indicates that the X ray spectrum is soft with spectral index >2. From the similarities of the X ray properties with those of other black hole transients, we conclude that the X ray transient XTE J2012+381 is likely to be a black hole.