infrared observations of eight x-ray sources from galactic plane surveys

ISSN 1063-7737, Astronomy Letters, 2013, Vol. 39, No. 8, pp. 523–531. c© Pleiades Publishing, Inc., 2013.Original Russian Text c© M.G. Revnivtsev, A. Kniazev, D.I. Karasev, L. Berdnikov, S. Barway, 2013, published in Pis’ma v Astronomicheskiı Zhurnal, 2013, Vol. 39, No. 8,pp. 591–600.

Infrared Observations of Eight X-ray Sources from Galactic PlaneSurveys

M. G. Revnivtsev1*, A. Kniazev2, 3, 4, D. I. Karasev1, L. Berdnikov4, and S. Barway2

1Space Research Institute, ul. Profsoyuznaya 84/32, Moscow, 117997 Russia2South African Astronomical Observatory, P.O. Box 9, Observatory, Cape Town 7935, South Africa

3South African Large Telescope, Cape Town, South Africa4Sternberg Astronomical Institute, Universitetskii pr. 13, Moscow, 119991 Russia

Received April 2, 2013

Abstract—Increasing the identification completeness of sources from new X-ray sky surveys is a necessarycondition for further works on analyzing the formation and long-term evolution of star systems in ourGalaxy. Infrared observations of several sources selected from Galactic plane surveys as candidatesfor low-mass X-ray binaries with the IRSF telescope at the South African Astronomical Observa-tory are presented. The infrared fluxes have been reliably measured from five of the eight sources(4U 1556-60, 4U 1708-40, AX J165901-4208, IGR J16287-5021, IGR J17350-2045, AX J171922-3703, SAX J1712.6-3739, 4U 1705-32). One of the objects (AX J165901-4208) may be a candidatefor symbiotic X-ray binaries, i.e., binaries in which the companion of a relativistic object is a giant star. Thedistances have been estimated for three sources and the orbital periods have been estimated for two.

DOI: 10.1134/S1063773713080082

Keywords: X-ray sources, sky surveys, neutron stars, cataclysmic variables, active galactic nuclei.

INTRODUCTION

Sky surveys in various parts of the electromag-netic spectrum provide a basis for almost all astro-physical studies. The sources that make it possibleto study the behavior of matter under the condi-tions of interest to us, allow their long-term (on timescales of millions and billions of years) evolution tobe understood, etc. can be selected precisely basedon the results of sky surveys. The advent of new-generation orbiting and ground-based observatorieshas allowed quite a few surveys of various sky regionsto be carried out. In particular, X-ray surveys oflarge parts of the sky have been conducted at a newsensitivity level with the ASCA (Sugizaki et al. 2001)and INTEGRAL (Krivonos et al. 2012) orbiting ob-servatories. The ASCA and INTEGRAL Galacticplane surveys were carried out in the 0.5–10 and 18–60 keV energy bands, respectively. The possibilityof scanning the Galaxy at energies above 2–5 keVgives big advantages—the X-ray absorption in theGalactic interstellar medium is essentially negligi-ble at these energies. At achieved sensitivities of∼5 × 10−12 erg s−1 cm−2, such sky surveys for thefirst time allow X-ray binaries with luminosities up to

*E-mail: [email protected]

1034−35 erg s−1 to be searched for in the entire Galaxy.This luminosity range is interesting in that neutronstars and black holes accreting matter from the stellarwinds of their companion stars should begin to appearhere (for evidence for the appearance of such objectsin the INTEGRAL Galactic plane survey, see Masettiet al. 2007). The transition from a predominanceof systems with accreting neutron stars to systemswith accreting white dwarfs should also occur in thisluminosity range.

An incomplete identification of detected sourcesstill remains a significant limitation of applying the re-sults of these surveys (ASCA, INTEGRAL). The na-ture of some of the objects remains unclear, althoughthe work on their identification is being actively car-ried out by various astrophysical teams worldwide,including our team (see, e.g., Combi et al. 2004;Karasev et al. 2010; Anderson et al. 2011; Degenaaret al. 2012; Anderson 2013). Extensive programsare conducted with optical and infrared (IR) ground-based telescopes to determine the nature of detectedX-ray objects. Within the framework of this work, aseries of IR observations of the fields around sourcesof the X-ray sky was performed in 2011 with theIRSF telescope at the South African AstronomicalObservatory (Glass and Nagata 2000). In this pa-

523

524 REVNIVTSEV et al.

per, we present the results obtained in this series ofobservations.

OBSERVATIONS

To identify the sources selected from the INTE-GRAL and ASCA sky surveys, observations wereperformed on May 12–14, 2011, at the 1.4-m IRSFtelescope (Sutherland, South Africa) (Glass and Na-gata 2000) with the SIRIUS camera (Nagayamaet al. 2003). The observations were carried out simul-taneously in three near-IR bands, J , H , and K. Eachof the three HgCdTe CCD detectors of the SIRIUScamera has a 7.7× 7.7 arcmin field of view with a pixelsize of 0.45 arcsec. The observations were performedin the mode of the telescope’s automatic shift with astep of∼20 arcsec after each 30 s exposure. One cycleconsisted of ten exposures during which the telescopemade a circle with the center at the initial coordinatesand was at the initial position after the tenth exposure.The total cycle time was ∼6 min. The observationswere carried out at seeing (FWHM) 1.1–1.5 arcsecin the K band.

The primary data reduction was done automati-cally, according to a standard technique, using theIRAF astronomical data reduction system. The re-duction included the standard steps of creating a flatfield from the shifted images of each cycle separatelyfor each band, correction for the flat field, automaticreduction of all images of each cycle to the commoncoordinates, and averaging all images of each cycle ineach band.

Our photometric analysis was carried out usingthe method of PSF photometry and the DAOPHOTsoftware (SCISOFT/ESO http://www.eso.org/sci/software/scisoft/). The photometric solutions wereobtained using 2MASS as a reference catalog: weselected about 100 sufficiently bright, not overex-posed stars that were then identified with 2MASSstars (using the WCStools 3.8.4 software package).Thus, we determined the photometric corrections forthe J , H , and Ks bands. Here, we use the extinctionlaw from Rieke and Lebofsky (1985) to recalculatethe interstellar extinction in different optical and IRbands.

RESULTS

4U 1556-60

The source 4U 1556-60 was discovered in theUHURU sky survey in the 1970s (Forman et al.1978). Subsequent observations allowed it to beidentified in the optical spectral range (Charles et al.1979). Smale (1991) hypothesized the existence of a9.1-h photometric period for the binary system. How-ever, it was not confirmed subsequently by Brammer

et al. (2001). Nelemans et al. (2006) tested thehypothesis that 4U 1556-60 was an ultracompactbinary system (i.e., it was checked whether the binarysystem could contain a white dwarf companion; inthis case, the orbital period of the binary could beconsiderably shorter than one hour). The detection ofhydrogen emission lines showed that the companionstar in the binary system is most likely not a carbon–oxygen white dwarf and the binary is not extremelyclose.

In our observations with the IRSF telescope, weobtained a series of photometric measurements (seeFigs. 1 and 2) that did not reveal any statisticallysignificant variability of the source’s brightness. Thesource’s color in IR bands is fairly blue (see Fig. 1),corresponding to the identification of the IR object asa low-mass X-ray binary.

However, we can attempt to estimate the orbitalperiod using the relationship between the luminosityof the X-ray source, the orbital period of the binarysystem (in fact, the size of the accretion disk in it),and the apparent IR brightness of the system (seeRevnivtsev et al. (2012), which is an outgrowth of thepaper by van Paradijs and McClintock (1994)).

For a distance to the source of 4 ± 1 kpc, its lumi-nosity of ∼1036 erg s−1 (Christian and Swank 1997),and its IR brightness corrected for extinction (AK ∼0.1, Marshall et al. 2006), mK ∼ 17.4, the formulafrom Revnivtsev et al. (2012) gives an estimate of theorbital period P ∼ 1−2 h. A binary system with aconsiderably longer orbital period should be brighterin the infrared due to the reradiation of its X-rayluminosity by a large accretion disk. The dimness ofthe binary system (its absolute magnitude is MK ∼4.3 for a distance of 4 kpc) implies its compactness.However, the presence of hydrogen emission lines inthe source’s spectrum suggests that the companionstar in the binary system is nondegenerate, i.e., theorbital period cannot be much shorter than 1–2 h.

4U 1708-40

4U 1708-40 is one of the persistent sources inthe X-ray sky with a flux from several to ten mCrab(Fx ∼ 10−11−10−10 erg s−1 cm−2). The source wasdetected in all sky surveys starting from the UHURUsurvey (Forman et al. 1978). A burst of nonsta-tionary thermonuclear burning was detected from thesource in 1999, which allowed the object to be confi-dently identified as a binary system with an accretingneutron star (Migliari et al. 2003). The absence ofevidence for photospheric expansion during burstsallowed only an upper limit for the distance to thesource to be estimated, D < 16 kpc. CHANDRAobservations gave the best astrometric position of theX-ray source to date (Wilson et al. 2003, see Table 1),

ASTRONOMY LETTERS Vol. 39 No. 8 2013

INFRARED OBSERVATIONS OF X-RAY SOURCES IN THE GALACTIC PLANE 525

10

1.00 0.5 1.5 2.0

12

14

16

18

K

J

–

K

4U1556-60

4U1556–60

(b)(‡)

Fig. 1. (a) K-band (2.2 μm) image of the sky around 4U 1556-60. The image size is about 1 arcmin. The source’s positionis indicated by the circle with a radius of 0.6 arcsec. The dotted line is an image processing artifact. (b) The color–magnitudediagram for stars in the 6-arcmin region around the source. The position of 4U 1556-60 on this diagram is indicated by theellipse whose size corresponds to the measurement uncertainty.

16.5

0.500.45 0.55 0.60 0.65Days since MJD 55694

17.0

17.5

18.0

K

17.0

0.500.45 0.55 0.60 0.65

H

17.2

0.500.45 0.55 0.60 0.65

J

17.417.617.818.018.2

17.2

17.4

17.6

17.818.0

4U1556–60

Fig. 2. Light curve of 4U 1556-60 in three spectral bands.

but an optical or infrared identification of the sourcehas never been made.

The highly accurate astrometric position of theX-ray source (with an accuracy of about 0.6 arcsec)allowed it to be identified in the images that we ob-tained with the IRSF telescope (see Fig. 3). TheJHK magnitudes of the source are given in the table.

The IR spectrum of low-mass X-ray binaries (pro-vided that the companion star is not a giant) is similar

in shape to the Rayleigh–Jeans part of the spectrumfor a blackbody (the IR colors of low-mass X-raybinaries were quantitatively estimated, for example,by Revnovtsev et al. (2012)). In fact, this implies thatan accreting low-mass X-ray binary with an X-rayluminosity above 1036 erg s−1 should have an IR colorJ − K ∼ 0. The considerably redder spectrum of4U 1708-40 (J −K ≈ 2.1) is most likely attributableto its reddening in the interstellar medium.



Astrometric positions and IR magnitudes of the investigated sources. The astrometric positional accuracy in X rays isabout 0.6 arcsec (the positions were determined using CHANDRA observations) for all sources, except IGR J17350-2045, whose position was determined with an accuracy of 2 arcsec using XMM-Newton observations. The astrometricpositional accuracy in the infrared is 0.3 arcsec

Name X-ray R.A. X-ray Dec. IR R.A. IR Dec. J H K

4U 1556-60 16:01:02.13 –60:44:18.8 16:01:02.150 –60:44:19.22 17.83 ± 0.06 17.52± 0.08 17.40 ± 0.14

4U 1708-40 17:12:23.83 –40:50:34.0 17:12:23.860 –40:50:34.20 18.84 ± 0.18 17.29± 0.09 16.67 ± 0.09

AXJ 165901-4208 16:59:05.65 –42:07:25.9 16:59:05.653 –42:07:25.84 18.33 ± 0.06 16.05± 0.03 14.91 ± 0.04

IGR J16287-5021 16:28:26.85 –50:22:39.7 16:28:26.859 –50:22:39.45 16.84 ± 0.04 16.25± 0.10 15.94 ± 0.09

IGR J17350-2045 17:34:58.82 –20:45:32.4 17:34:58.838 –20:45:31.98 15.35 ± 0.06 14.40± 0.10 13.80 ± 0.10

AX J171922-3703 17:19:20.88 –37:01:55.2 >19.5 >18.2 >17.7

SAX J1712.6-3739 17:12:36.77 –37:38:41.0 >20.6 >20.2 >19.5

4U 1705-32 17:08:54.27 –32:18:56.9 >20.8 >20.6 >20.1

Taking the reddening coefficients in the J and Kbands from Rieke and Lebofsky (1985), we can writeAK = 0.66[(J − K) − (J − K)0]. For 4U 1708-40,we obtain AK ∼ 1.4 from the colors from the tableand Fig. 3. Using the three-dimensional reddeningmap from Marshall et al. (2006), we can estimate thedistance to the source, about 10–15 kpc.

At this distance to the source, its luminosity inquiescence should be (1−2) × 1037 erg s−1. Usually,binary systems with neutron stars at such a highluminosity are in the so-called soft state, in whichtheir spectrum can be properly described by the sumof the emissions from an optically thick accretiondisk and an optically thick spreading layer on theneutron star surface (Mitsuda et al. 1984; Gilfanovet al. 2003; Revnivtsev and Gilfanov 2006). TheBeppoSAX and RXTE spectroscopic measurements(Wilson et al. 2003) are consistent with these predic-tions.

AX J165901-4208

The source AX J165901-4208 was detected dur-ing the ASCA Galactic plane survey conducted inthe 1990s (Sugizaki et al. 2001). The astrometricposition determined using CHANDRA observationsallowed the source to be reliably identified with anobject with a K magnitude of 14.9 (see Fig. 4).

On the color–magnitude diagram ((J − K)−K,Fig. 4, the right panel), the source is close to the bandproduced by red clump giants at various heliocentricdistances. If this is not a chance coincidence butactually stems from the fact that the companion ofthe X-ray source is a late-type giant star, then wecan assume two possible variants of the nature ofAX J165901-4208.

• First, it can be assumed that AX J165901-4208 is a low-mass X-ray binary with a com-pact object accreting from the wind of a late-type giant star, the so-called symbiotic X-raybinary (SymbXB).

At present, we know very few of such sys-tems (see, e.g., Masetti et al. 2007), al-though binary evolution calculations (e.g.,Lu et al. 2012) suggest that there shouldbe quite a few of them in our Galaxy. TheX-ray emission in symbiotic X-ray binariesemerges upon accretion onto the compactobject (a neutron star, a black hole, or awhite dwarf) from the stellar wind of thecompanion star. The mass accretion rate inthem is low and their X-ray luminosity cannotexceed 1034−1035 erg s−1, corresponding tofluxes of less than 10−11 erg s−1 cm−2 fortypical distances in the Galaxy (5–10 kpc).Therefore only now, with the appearance ofdeeper surveys of large sky fields, has it becomepossible to systematically find such systemsin our Galaxy. However, spectrometric mea-surements of the IR source should be made toultimately determine the type of the companionin this binary system.

If the companion star in the binary systemAX J165901-4208 is assumed to be a redclump giant (with approximately identical lu-minosities), then an approximate estimate ofthe distance to the source can be obtained. Theinterstellar reddening per unit distance towardthe source cK can be taken from Marshallet al. (2006): cK ∼ 0.18 magnitude kpc−1.The position of AX J165901-4208 on the bandproduced by red clump giants (see Fig. 4)



30

16

18

K

J

–

K

4U1708-40

4U1708–40

1 2 4 5

14

12

10

8(a)(b)

Fig. 3. (a)K-band (2.2 μm) image of the sky around 4U 1708-40. The image size is about 1 arcmin. The position of the X-raysource (from Wilson et al. 2003) is indicated by the circle with a radius of 0.6 arcsec. (b) The color–magnitude diagram forstars in the 6-arcmin region around the source. The source’s position on the diagram is indicated by the ellipse.

30

16

18

K

J

–

K

AX J165901-4208

AX J165901–4208

1 2 4 5

14

12

10

8

(b)(‡)

Fig. 4. Image of the sky region around AX J165901-4208 (a) and color–magnitude diagram for the stars detected in the regionwith a radius of 6 arcmin around the source (b). The curve on the color–magnitude diagram indicates the expected positionsof red clump giants at various heliocentric distances if the interstellar reddening is uniform in distance and is 0.18 kpc−1. Theellipse indicates the position of AX J165901-4208.

roughly corresponds to a distance of 8.5–9.5 kpc. The X-ray flux from the source6 × 10−12 erg s−1 cm−2 (Sugizaki et al. 2001)at such a distance corresponds to a luminosityLX ∼ 5 × 1034 erg s−1.

• The second possible variant of the source’snature is a binary system with a giant star anda white dwarf as the compact object. LongerX-ray observations should be carried out toreliably determine what compact object is inthe binary system under consideration. TheX-ray emission from accreting white dwarfs

is produced by the emission of an opticallythin plasma with a temperature close to thevirial one near their surface (6–20 keV) andexhibits strong emission lines of highly ionizedheavy elements, while the emission from ac-creting neutron stars is generally produced byComptonization and contains no strong emis-sion lines. Highly accurate measurements ofthe source’s spectrum at 6.7 keV will allowthis question to be answered. The statisticalquality of the currently existing observations isinsufficient for this purpose.



0

K

J

–

K

IGR J16287-5021

IGR J16287–5021

4

10

12

14

16

321

(b)

(‡)

Fig. 5. (a) Image of the sky region around IGR J16287-5021. The position of the X-ray source is marked by the circle with aradius of 0.6 arcsec. (b) Color–magnitude diagram for the stars detected in the 6-arcmin region around the source. The ellipseindicates the position of IGR J16287-5021.

IGR J16287-5021

The source was discovered during the INTE-GRAL Galactic plane surveys (Bird et al. 2007).A further improvement of the object’s astrometricposition (Rodriguez et al. 2009; Tomsick et al. 2009)allowed its optical identification to be made. Masettiet al. (2010) took an optical spectrum of the source,which led him to conclude that it is most likely a low-mass X-ray binary.

The results of our IR brightness measurements forthe source are presented in Fig. 5 and the table. Thesource has red colors probably due to the interstellarextinction in its direction. If the interstellar extinctionis assumed to be AV ∼ 3.1 (from Masetti et al. 2010),then the source’s intrinsic (dereddened) color can beestimated as (J −K)0 ≈ (J −K)− 1.51AK ≈ (J −

IGR J17350-2045

Fig. 6. K-band (2.2 μm) image of the sky aroundIGR J17350-2045. The image size is about 1 arcmin.The position of the X-ray source is indicated by the circlewith a size of 2 arcsec.

K) − 0.17AV ∼ 0.4. Such a color index is typical oflow-luminosity low-mass X-ray binaries (see, e.g.,Russell et al. 2012). Even redder spectra of low-massX-ray binaries are expected as the source’s luminositydecreases (see Revnivtsev et al. 2012).

If the three-dimensional IR extinction model forour Galaxy from Marshall et al. (2006) is assumedto be correct, then we can obtain an approximateestimate of the distance to the source, 2−4 kpc, usingan interstellar extinction AK ≈ 0.112AV ∼ 0.3 in itsspectrum (we assume that there is no local (associ-ated with the binary system) extinction, which is truefor low-mass X-ray binaries).

IGR J17350-2045IGR J17350-2045 was detected during the

INTEGRAL sky survey (Krivonos et al. 2007).Since it is located in the Galactic bulge, the sourcewas considered as a possible candidate for low-massX-ray binaries and, in this capacity, was included inthe list of sources to be observed with the IRSF tele-scope in 2011. Subsequently, using XMM-Newtonobservations, along with IR and radio observations,Karsev et al. (2012) managed to show that thesource is most likely an active galactic nucleus. TheIRSF observations provided additional informationabout the source’s brightness. The results of ourmeasurements are presented in Fig. 6 and in the table.

It should be noted that the object’s IR brightnessin our observations with IRSF differs significantlyfrom its IR brightness measured from SOFI/NTTdata in May 2007 (Karasev et al. 2012). Brightnessvariations with such or even larger amplitudes areexpected if the object is actually an active galacticnucleus.



AX J171922-3703

Fig. 7. K-band (2.2 μm) image of the sky aroundAX J171922-3703. The image size is about 1 arcmin.The position of the X-ray source is indicated by the circlewith a size of 0.6 arcsec.

AX J171922-3703

AX J171922-3703 was discovered during theASCA Galactic plane survey (Sugizaki et al. 2001).The astrometric position of the source was improvedusing CHANDRA observations (Anderson 2013).The ISRF observations did not allow any infrared ob-ject to be identified with the X-ray source (see Fig. 7).Upper limits for the IR brightness of AX J171922-3703 are given in the table.

SAX J1712.6-3739

The low-mass X-ray binary SAX J1712.6-3739was discovered in 1999 as an X-ray transient(in’t Zand et al. 1999). However, further studiesshowed it to be more likely a persistent X-ray source(in’t Zand et al. 2007). The detection of type Ibursts (Cocchi et al. 2001; Chelovekov et al. 2006)suggested that the compact object in the binarysystem is a neutron star and that the distance tothe source is about 6–8 kpc (Cocchi et al. 2001;Strohmayer and Baumgartner 2010).

The astrometric position of the source determinedusing CHANDRA data with an accuracy of 0.6 arc-sec (Wiersema et al. 2009) allows optical and IRidentifications of the source to be made even in such adensely populated region as the Galactic plane.

Based on optical observations with the 3.6-mESO telescope, Wiersema et al. (2009) suggestedtwo possible candidates for optical counterparts ofthe X-ray object. However, their significant angulardistances, ∼1 and 2.1 arcsec from the position of theX-ray source, do not allow them to be unequivocallyassociated with the binary SAX J1712.6-3739.

In our observations with IRSF in the IR bands,in which the interstellar extinction is considerablylower than that in the optical bands, we detected

SAX J1712.6-3739

Fig. 8. K-band (2.2 μm) image of the sky aroundSAX J1712.6-3739. The image size is about 1 arcmin.The position of the X-ray source is indicated by the circlewith a size of 0.6 arcsec.

no object in the 0.6-arcsec circle around the po-sition of the X-ray source either (Fig. 8). Upperlimits for the source’s infrared brightness are givenin the table. If the interstellar extinction towardthe source located at a distance of 6–8 kpc is as-sumed to be AK ∼ 0.8 (Marshall et al. 2006), then theK-band absolute magnitude of SAX J1712.6-3739 isMK > 4.2, suggesting that the binary system is com-pact. Using the source’s luminosity of ∼1036 erg s−1

(Fiocchi et al. 2008) and the relationship between theIR brightness, size, and X-ray luminosity for low-mass X-ray binaries from Revnivtsev et al. (2012), wecan estimate the orbital period of the binary system,P � 1 h.

4U 1705-32

4U 1705-32 was detected already in the first skysurveys conducted in the 1970s by the UHURU,OSO-7, and HEAO1 observatories. Subsequentobservations of the source with focusing telescopesallowed its astrometric position to be determined,initially with an accuracy of about 8 arcsec (basedon ROSAT data) and subsequently with an accuracyof about 0.6 arcsec (CHANDRA data; in’t Zandet al. 2005). Despite the high accuracy of the source’sposition determination, the existing data from opticaland IR surveys of this region did not allow the X-raysource to be associated with an optical or IR object.

Our observations with IRSF yielded the deepestIR images for this part of the sky (Fig. 9) and an upperlimit for the source’s brightness in the J , H , and Kbands (see the table).



4U1705-32

Fig. 9. K-band (2.2 μm) image of the sky around4U 1705-32. The image size is about 1 arcmin. Theposition of the X-ray source is indicated by the circle witha size of 0.6 arcsec.

CONCLUSIONS

We presented the results of our IR observationswith the IRSF telescope at the South African As-tronomical Observatory for several X-ray sources se-lected as candidates for low-mass X-ray binaries. Wemanaged to reliably measure the IR brightnesses forfive of them.

Our results can be summarized as follows:

• 4U 1556-560—the IR brightness of the sourcehas been measured for the first time; based onthe correlation of the IR brightness of accretinglow-mass X-ray binaries with their X-ray lu-minosity and orbital period, we concluded thatthe orbital period of the binary system shouldbe ∼1−2 h.

• 4U 1708-40—the IR brightness of the sourcehas been measured for the first time; basedon the color index and existing maps of theabsorbing dust distribution in our Galaxy, weestimated the distance to the object to be 10–15 kpc.

• AX J165901-4208—the object was shown tobe a possible candidate for symbiotic X-raybinaries (a binary system in which the com-panion of a compact object is a giant star).The source’s position on the color–magnitudediagram suggests that the companion in thisbinary can be a late-type giant star. The dis-tance to the source was estimated under thisassumption to be 8.5–9.5 kpc.

• IGR J16287-5021—the IR brightness of thesource has been measured for the first time;based on the color index and existing maps of

the absorbing dust distribution in our Galaxy,we estimated the distance to the object to be2–4 kpc.

• IGR J17350-2045—the IR brightness of thesource was measured; the derived brightnesseswere compared with the previously presentedresults of SOFT/NTT observations and a sig-nificant change in brightness was detected.

• AX J171922-3703, SAX J1712.6-3739,4U 1705-32—upper limits for the IR bright-ness of the sources were obtained. ForSAX J1712.6-3739, these upper limits, alongwith the known distance to the source andits X-ray luminosity, suggest that this binarysystem is ultracompact, with an orbital periodof less than an hour.

ACKNOWLEDGMENTS

This study was supported by the National Re-search Foundation of the Republic of South Africa.We thank the administration of the South AfricanAstronomical Observatory for the allocation of ob-serving time on the IRSF telescope. This work wassupported by Program P21 of the Presidium of theRussian Academy of Sciences, the “Scientific andScientific–Pedagogical Personnel of InnovationalRussia” Program OFN 16, Activity 1.3.1 (Contract8629), grants NSh-5603.2012.2, MD-1832.2011.2,RFBR-12-02-01265, and RFBR-13-02-00741.

REFERENCES1. G. Anderson, PhD thesis (Univ. of Syndey, 2013).2. G. E. Anderson et al., Astrophys. J. 727, 105 (2011).3. A. J. Bird et al., Astrophys. J. Suppl. Ser. 120, 175

(2007).4. G. Brammer, S. Wachter, D. W. Hoard, and

A. P. Smale, Bull. Am. Astron. Soc. 33, 1311 (2001).5. P. A. Charles et al., Bull. Am. Astron. Soc. 11, 720

(1979).6. I. V. Chelovekov, S. A. Grebenev, and R. A. Sunyaev,

Astron. Lett. 32, 456 (2006).7. D. J. Christian and J. H. Swank, Astrophys. J. Suppl.

Ser. 109, 177 (1997).8. M. Cocchi, A. Bazzano, L. Natalucci, et al., Mem.

Soc. Astron. Ital. 72, 757 (2001).9. J. A. Combi, M. Ribo, I. F. Mirabel, et al., Astron.

Astrophys. 422, 1031 (2004).10. N. Degenaar et al., Astron. Astrophys. 540, A22

(2012).11. M. Fiocchi, A. Bazzano, P. Ubertini, and G. De Ce-

sare, Astron. Astrophys. 477, 239 (2008).12. W. Forman, C. Jones, L. Cominsky, et al., Astrophys.

J. Suppl. Ser. 38, 357 (1978).13. M. Gilfanov, M. Revnivtsev, and S. Molkov, Astron.

Astrophys. 410, 217 (2003).



14. I. S. Glass and T. Nagata, Mon. Not. R. Astron. Soc.Southern Africa 59, 110 (2000).

15. D. I. Karasev, A. A. Lutovinov, and R. A. Burenin,Mon. Not. R. Astron. Soc. 409, L69 (2010).

16. D. I. Karasev, A. A. Lutovinov, M. G. Revnivtsev,et al., Astron. Lett. 38, 629 (2012).

17. R. Krivonos, M. Revnivtsev, A. Lutovinov, et al., As-tron. Astrophys. 475, 775 (2007).

18. R. Krivonos, S. Tsygankov, A. Lutovinov, et al., As-tron. Astrophys. 545, A27 (2012).

19. G.-L. Lu, C.-H. Zhu, K. A. Postnov, et al., Mon. Not.R. Astron. Soc. 424, 2265 (2012).

20. D. J. Marshall, A. C. Robin, C. Reyle, et al., Astron.Astrophys. 453, 635 (2006).

21. N. Masetti et al., Astron. Astrophys. 470, 331 (2007).22. N. Masetti et al., Astron. Astrophys. 519, A96 (2010).23. S. Migliari et al., Mon. Not. R. Astron. Soc. 342, 909

(2003).24. K. Mitsuda et al., Publ. Astron. Soc. Jpn. 36, 741

(1984).25. T. Nagayama et al., Instrument Design and Perfor-

mance for Optical/Infrared Ground-Based Tele-scopes, Ed. M. Iye and A. F. M. Moorwood, Proc.SPIE 4841, 459 (2003).

26. G. Nelemans, P. G. Jonker, and D. Steeghs, Mon.Not. R. Astron. Soc. 370, 255 (2006).

27. J. van Paradijs and J. E. McClintock, Astron. Astro-phys. 290, 133 (1994).

28. M. G. Revnivtsev and M. R. Gilfanov, Astron. Astro-phys. 452, 253 (2006).

29. M. G. Revnivtsev, I. Y. Zolotukhin, and A. V. Meshch-eryakov, Mon. Not. R. Astron. Soc. 421, 2846 (2012).

30. G. H. Rieke and M. J. Lebofsky, Astrophys. J. 288,618 (1985).

31. J. Rodriguez, J. A. Tomsick, and S. Chaty, Astron.Astrophys. 494, 417 (2009).

32. D. M. Russell, K. O’Brien, T. Munoz-Darias, et al.,Astron. Astrophys. 539, A53 (2012).

33. A. P. Smale, Publ. Astron. Soc. Pacif. 103, 636(1991).

34. T. E. Strohmayer and W. H. Baumgartner, As-tronomer’s Telegram, No. 2717 (2010).

35. M. Sugizaki, K. Mitsuda, H. Kaneda, et al., Astro-phys. J. Suppl. Ser. 134, 77 (2001).

36. J. A. Tomsick, S. Chaty, J. Rodriguez, et al., Astro-phys. J. 701, 811 (2009).

37. K. Wiersema et al., Mon. Not. R. Astron. Soc. 397,L6 (2009).

38. C. A. Wilson, S. K. Patel, C. Kouveliotou, et al.,Astrophys. J. 596, 1220 (2003).

39. J. J. M. in’t Zand, R. Cornelisse, and M. Mendez,Astron. Astrophys. 440, 287 (2005).

40. J. in’t Zand, J. Heise, A. Bazzano, et al., IAU Circ.7243, 2 (1999).

41. J. J. M. in’t Zand, P. G. Jonker, and C. B. Markwardt,Astron. Astrophys. 465, 953 (2007).

Translated by V. Astakhov


infrared observations of eight x-ray sources from galactic plane surveys

Documents