Several New Active Galactic Nuclei Among X-ray Sources Detected by INTEGRAL and SWIFT Observatories
R. A. Burenin, A. V. Mescheryakov, M. G. Revnivtsev, S. Yu. Sazonov, I. F. Bikmaev, M. N. Pavlinsky, R. A. Sunyaev
aa r X i v : . [ a s t r o - ph ] F e b Astronomy Letters, 2008, Vol. 34, No. 0, p. 0–0. Translated from Pis’ma v Astronomicheskij Zhurnal.PAZHASTL.CLS 12.02.08
Several New Active Galactic Nuclei Among X-ray Sources Detected by
INTEGRAL and
SWIFT
Observatories c (cid:13) , A. V. Mescheryakov , M. G. Revnivtsev , S. Yu. Sazonov ,I. F. Bikmaev , M. N. Pavlinsky , R. A. Sunyaev Received December 26, 2007
We present the results of the optical identifications of a set of X-ray sources from the all-sky surveys of
INTEGRAL and
SWIFT observatories. Optical data were obtained with Russian-Turkish 1.5-m Tele-scope (RTT150). Nine X-ray sources were identified as active galactic nuclei (AGNs). Two of them arehosted by nearby, nearly exactly edge-on, spiral galaxies MCG − − −
047 and NGC 973. One source,IGR J16562 − Keywords:
X-ray sources — gamma-sources — active galactic nuclei — optical observations
INTRODUCTIONThe all-sky surveys in hard X-rays give a valuableinformation on the populations of objects, which aredifficult to observe due to the presence of absorptionin optical and soft X-rays. The most sensitive to dateare recently completed
RXTE (XSS, Revnivtsev et al.,2004) and
INTEGRAL (Krivonos et al., 2007) all-sky surveys, and on-going
SWIFT all-sky survey(Tueller et al., 2007).These surveys contains a large number of knownnearby active galactic nuclei (AGNs), cataclysmic vari-ables, X-ray binaries, located in Galactic plane. How-ever, it turns out, that a considerable number ofsources, up to 20–30% of their total number, can not beidentified with previously known objects. In order tomake a complete use of the capabilities of these surveysfor statistical studies, one need to identify all the X-ray sources with optical objects and to determine theirnature.The work on optical identifications of hard X-raysources from the all-sky surveys was started on Russian-Turkish 1.5-m Telescope (RTT150) (Bikmaev et al.,2006a,b). In this paper we present the resultson the extragalactic objects — active galactic nu-clei, obtained in frames of this work during Au-tumn 2006 – Spring 2007. Some of these resultswere immediately published in astronomical circulars * e-mail: [email protected] (Burenin et al., 2006a,b; Mescheryakov et al., 2006;Burenin et al., 2007). Here we discuss the results ofthese observations in more detail.OBSERVATIONSA characteristic property of X-ray telescopes onboard INTEGRAL and
SWIFT observatories is thattheir accuracy of the localization of X-ray sources, inmany cases, is insufficient to unambiguously associatethe X-ray source with a certain object in optical band.The error box of
INTEGRAL and
SWIFT hard X-raysources usually is about few arcminutes. When observ-ing in optical band, even at high Galactic latitudes, onewill find a considerable number of galaxies and stars inthe error box of that size. At low Galactic latitudes, thefield of that size contain so large number of stars, thatit is impossible to directly associate the X-ray sourcewith any optical object.In order to obtain more accurate positions of hardX-ray sources one can use the observations in softer X-ray band, where the positions of X-ray sources can bemeasured much more accurately. First, one can use thedata of
ROSAT
All-Sky Survey (Voges et al., 1999). Incase of strongly absorbed X-ray sources, which are notdetected in
ROSAT
All-Sky Survey, one can use thedata of pointed observation of
Chandra , XMM -Newtontelescopes or X-ray telescope aboard
SWIFT , in harderX-ray band.The data for some hard X-ray sources were obtained0ew AGNs among
INTEGRAL and
SWIFT
X-ray sources 1in dedicated Chandra observations (Sazonov et al.,2005, 2008). An extensive program of observations of
SWIFT and
INTEGRAL hard X-ray sources is alsocarried out with
SWIFT
X-ray telescope (XRT, see,e.g., Tueller et al., 2007). We downloaded all necessaryadditional open data from
HEASARC archive.For our optical observations we first selected the hardX-ray sources, with the positional accuracy enhancedin one or another way. All optical data were obtainedwith Russian-Turkish 1.5-m Telescope (RTT150), usingmedium and low resolution spectrometer TFOSC . Inmost cases we used 54 mkm slit, which corresponds to0.96 ′′ size in the sky. We mostly used grism ≈
12 ˚A (FWHM). In those cases, where weneeded higher spectral resolution, we used other grisms.The data were reduces using standard
IRAF software.RESULTSThe list of X-ray sources, which we were able to iden-tify in Autumn 2006 – Spring 2007, is presented in Ta-ble 1. In the Table for each X-ray source we give itsname, coordinates, R magnitude, type of the object andredshift. The coordinates are given in 2000 epoch, us-ing USNO B1.0 catalog (Monet et al., 2003) as a refer-ence frame. For nearby galaxies we give the coordinatesof active nuclei or the maximum of emission near thecenter of the galaxy, where the optical spectrum wasobtained. R band magnitudes are given for referenceand are taken from USNO-B1.0 catalog. The desig-nation of object types are as follows: Sy1,2 — Seyfertgalaxy of type 1 or 2; BL Lac — BL Lacertae object.The AGNs redshifts were measured using only narrowlines, like [OIII] 4959,5007, [NI] 5199, [OI] 6300, [SII]6716,6731, and also in some cases [OII] 3727, [NeIII]3869 and narrow parts of Balmer lines. The errors of z measurement should not be larger than 0 . − r ′ filter ( SDSS ), obtained with RTT150telescope. In case of X-ray source IGR J16562 − http://heasarc.nasa.gov/ http://astroa.physics.metu.edu.tr/tug/tfosc.html http://iraf.noao.edu list of Massey et al. (1988). In cases of nearby galax-ies MCG − − −
047 and NGC 973 (X-ray sourcesIGR J01528 − ′′ and12 ′′ correspondingly, where the angular sizes are takenso that we obtain the upper estimate of the flux in emis-sion lines. In other cases the slit size correction wasapplied, assuming that the source is point-like, whichis a good approximation, since all the other AGNs havethe stellar-like nuclei.Due to the uncertainty of photometrical conditionsduring our observations, photometric calibration maycontain significant systematic errors, especially in bluepart of the spectrum λ < − Notes on individual objects
IGR J01528 − − − − H α , [NII],6583 and [SII],6716. From the inten-sity ratio lg([NII] , /H α ) ≈
0, we conclude thatthis source most probably is a Seyfert 2 AGN(Veilleux and Osterbrock, 1987).IGR J02343+3229 — The source is identified withnearby edge-on spiral galaxy NGC973. Optical spec-trum of the central part of the galaxy shows nar-row emission lines [OIII],5007, H α , [NII],6583 and[SII],6716. The emission lines intensity ratios canbe estimated as lg([OIII] , /H β ) > . , /H α ) ≈ .
4. Therefore, this source is mostprobably a Seyfert 2 AGN (Veilleux and Osterbrock,1987).IGR J03334+3718 — The source was detected alsoin
ROSAT
All-Sky Survey (1RXS J033316.2+371815),which allow to measure more accurate position withthe error circle ≈ ′′ . After that this source is un-ambiguously identified with the galaxy with stellar-likenucleus. The optical spectrum of the nucleus containsredshifted emission lines — broad Balmer lines, andalso narrow lines [OIII] 4959,5007 and others, whichallow to identify it as Seyfert 1 AGN.IGR J13038+5348 — This source was observed bySWIFT XRT. Using these data, we determined the ASTRONOMY LETTERS Vol. 34 No. 0 2008
Burenin et al.
IGR J01528 − − DSS-II-r
SWIFT J1745.4+2906
Fig. 1. — Optical images of the fields of hard X-ray sources.
ASTRONOMY LETTERS Vol. 34 No. 0 2008 ew AGNs among
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X-ray sources 3
Table 1.
Optical identifications of hard X-ray sources
Name α δ m R Type z Other(J2000) nameIGR J01528 − −
03 26 47.9 9.3 Sy2 0.017197 ∗ MCG − − − ∗ NGC 973IGR J03334+3718 03 33 18.78 +37 18 11.4 13.5 Sy1 0.05583IGR J13038+5348 13 03 59.50 +53 47 30.2 12.9 Sy1 0.03016 MCG +09 − − − −
33 02 12.8 17.5 BL Lac ?SWIFT J1745.4+2906 17 45 38.28 +29 08 22.2 14.2 Sy1 0.11040SWIFT J1930.5+3414 19 30 13.81 +34 10 49.8 15.8 Sy1 0.063261RXS J193347.6+325422 19 33 47.16 +32 54 26.2 13.4 Sy1 0.05794RX J2135.9+4728 21 35 54.02 +47 28 22.3 13.2 Sy1 0.02523 SWIFT J2156.2+4728 ∗ Redshifts are taken from
NED
SWIFT J1930.5+3414 1RXS J193347.6+325422RX J2135.9+4728
Fig. 1. — Continued .ASTRONOMY LETTERS Vol. 34 No. 0 2008
Burenin et al.IGR J01528 − F λ , × − e r g s − c m λ , ˚A F λ , × − e r g s − c m λ , ˚AIGRJ03334+3718 IGRJ13038+5348 F λ , × − e r g s − c m λ , ˚A F λ , × − e r g s − c m λ , ˚AIGR J16562 − λ , ˚A F λ , × − e r g s − c m λ , ˚A Fig. 2. — Spectra of optical objects, which were identified with hard X-ray sources.
ASTRONOMY LETTERS Vol. 34 No. 0 2008 ew AGNs among
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X-ray sources 5SWIFT J1930.5+3414 1RXS J193347.6+325422 F λ , × − e r g s − c m λ , ˚A F λ , × − e r g s − c m λ , ˚ARX J2135.9+4728 F λ , × − e r g s − c m λ , ˚A Fig. 2. — Continued .ASTRONOMY LETTERS Vol. 34 No. 0 2008
Burenin et al.source position with the few arcseconds accuracy, whichallow to associate this source with bright nearby galaxyMCG +09 − − − α, δ : 16:56:16 . − . UCAC2 catalog). The positional error hereshould be almost purely statistical and is about 1 . ′′ .These coordinates agree with the position of verybright radio source NVSS J165616-330211 (the flux isabout 0.4 Jy at 1.4 GHz). The coordinates of the onlyoptical object, which is coincide with both X-ray andradio sources, are given in Table 1. In the optical spec-trum of this object there are no bright emission lines(Fig. 2). All these data allow to conclude, that thissource is a BL Lacertae object. In order to measure itsredshift, the spectrum with much higher signal-to-noiseratio is needed.SWIFT J1745.4+2906, SWIFT J1930.5+3414,1RXSJ193347.6+325422 — These hard X-ray sourceswere detected by SWIFT observatory. The SWIFTXRT data, available in public domain, allowed tounambiguously identify these objects with the galacticnuclei. The optical spectra, obtained with RTT150telescope, show that all of them are Seyfert 1 AGN(Fig. 2).RX J2135.9+472 — As Seyfert 1 AGN this object wasidentified earlier, in frames of the work on optical identi-fications of X-ray sources from ROSAT
All-Sky Survey(Motch et al., 1997). However, this object was not in-cluded in
NED database, and we identified this objectindependently. In Table 1 we provide more accurateredshift, as compared to that published by Motch et al.(1997). Apart of the galactic nucleus, there is anotherone stellar like object in the image of the galaxy (seeFig. 1). We obtained the spectrum of this source andshow that this is a chance projection of a star.
Table 2.
The AGN luminosities in X-ray 17–60 keV band andin [OIII],5007 emission line.
Name lg L X lg L [ OIII ] IGR J01528 − < . Thefluxes in X-rays are taken from the catalogs of IN-TEGRAL and SWIFT all-sky surveys (Krivonos et al.,2007; Tueller et al., 2007). In last case the fluxes wereconverted to 17–60 keV band assuming power law spec-trum with photon index Γ = 1 .
8. There is no X-rayflux for the source 1RXS J193347.6+325422 in Table 2,because this source is not included in current versionof SWIFT survey catalog. The fluxes in [OIII],5007emission line are corrected for the Galactic interstellarextinction using data from Schlegel et al. (1998).In Fig. 3 we show the relation between the luminosi-ties in 17–60 keV X-ray band and in [OIII],5007 line.Here we also add the data for AGNs, which we op-tically identified earlier (Bikmaev et al., 2006a). Thedata for the main part of AGNs are well agree withthe known correlation (see, e.g., Heckman et al., 2005).Excluding three lower points in Fig. 3, we find thatthe mean and the dispersion of the luminosities ratiologarithm are equal 2 . ± .
08 and 0 .
27 respectively,in good agreement with the results for AGNs, selectedmainly in optical band (Heckman et al., 2005).In contrast to optically selected AGNs, our sam-ple contain AGNs with much lower luminosity [OIII]line, as should be expected for their X-ray lumi-nosities. First, these are two nearby AGNs inMCG − − −
047 and NGC 973, nearly exactly edge-on galaxies. As it was noted above, in the calibrationsof their spectra there is a considerable uncertainty, dueto the unknown angular size of the line emitting region.However, their spectra were calibrated so that to ob-tain an upper estimate of [OIII] line fluxes (see above)and the lack of luminosity in this line should exist any-way. Most probably, this lack of luminosity in [OIII]line is explained by the extinction in the disks of thegalaxies, since in these two cases the galaxies are turned To convert fluxes into the luminosities we use the cosmolog-ical model with Ω = 0 .
3, Λ = 0 . H = 71 km s − Mpc − . ASTRONOMY LETTERS Vol. 34 No. 0 2008 ew AGNs among
INTEGRAL and
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X-ray sources 7 l g L [ O III ] , lg L X, − keV Fig. 3.
The relation between the luminosities in X-ray 17–60 keVband and in [OIII],5007 emission line. Filled and open symbolsshow Seyfert galaxies of type 1 and 2 respectively. Circles showthe data from our present work, triangles — the data which weobtained earlier (Bikmaev et al., 2006a). Dashed line show thedependency lg L X /L [ OIII ] = 2 .
13 (see text). nearly exactly edge-on. From the observed thickness ofthe disk, we estimate that the size of absorbed regionshould not be larger than ≈ ≈ .
1. These objectsshould modify the selection of AGN using their flux in[OIII] line and change the form of the AGN luminosityfunction in [OIII] line as compared to that in hard X-rays. The fraction of these AGNs may be less than ∼
20% (as it follows from Fig. 3), since here we consideronly, probably, most absorbed AGNs, which were notknown earlier and were detected only using observationsin hard X-rays. CONCLUSIONSIn this paper we present our new results of theobservations of the fields of unidentified hard X-raysources, detected in statistically complete all-sky sur-veys. The observations were carried out using Russian-Turkish 1.5-m Telescope (RTT150). Nine X-ray sourceswere identified with the active galactic nuclei. Twoof them are hosted by nearby, nearly exactly edge-on, spiral galaxies MCG − − −
047 and NGC 973.One source, IGR J16562 − − z < .
1, as for the majority of AGNs in INTEGRALAll-Sky Survey. Almost all of them are located at highGalactic latitudes | b | > ◦ .Taking in account the data, which we obtained earlier(Bikmaev et al., 2006a), we show, that the luminositiesin hard X-rays (17–60 keV) and in [OIII],5007 emis-sion line, lg L X /L [ OIII ] ≈ .
1, are well correlated, asexpected, for the majority of AGNs selected in hardX-rays. However, few AGNs considerably deviate fromthis correlation. For example, the flux in [OIII] lineturns to be lower in AGNs in two nearby edge-on spiralgalaxies MCG − − −
047 and NGC 973, which canbe explained by the extinction in their galactic disk.The fraction of AGNs, for which the [OIII] line fluxesare significantly deviate from that correlation, may beabout 20%, which should significantly modify [OIII] lineAGN selection and the form of the AGN luminosityfunction in [OIII] line as compared to that in hard X-rays.In result of the recent works on optical identificationsof hard X-ray sources (e.g., Bikmaev et al., 2006a,b;Masetti et al., 2006, and also this work), the catalog ofINTEGRAL All-Sky Survey (Krivonos et al., 2007) isnow almost complete at high Galactic latitudes. Nowthere are only few X-ray sources, which remain opti-cally unidentified, in this catalog at Galactic latitudes | b | > ◦ . At the same time, only in subsample of AGNsfrom this survey, 33 out of 127 objects were unknownbefore the survey was started (Sazonov et al., 2007).At low Galactic latitudes there are few tens of hardX-ray sources from INTEGRAL survey, which are notoptically identified yet. We will continue our works ontheir optical identifications. Optical objects, associatedwith some of these objects turn to be too faint for theobservations with RTT150. Now we submitted the pro-posals to observe these fainter objects with larger tele-scopes.This work is supported by grants RFFI 05-02-16540, RFFI 07-02-01004, NSh-784.2006.2 and NSh-1100.2006.2, and also with programs of Russian ASTRONOMY LETTERS Vol. 34 No. 0 2008
Burenin et al.academy of sciences P-04 and OFN-17.Note: When this paper was already accepted for pub-lication we have noticed that one of our hard X-raysources IGR J16562 − z = 2 . et al. ,Astron. Astrophys. Suppl. Ser. , 169 (2000).Bikmaev I. F., Sunyaev R. A., Revnivtsev M. G.,Burenin R. A., Astronomy Letters , 221(2006a) [Pis’ma v Astron. Zhurn., , 250;astro-ph/0511405].Bikmaev I. F., Revnivtsev M. G., Burenin R. A.,Sunyaev R. A., Astronomy Letters , 588(2006b) [Pis’ma v Astron. Zhurn., , 665;astro-ph/0603715].Burenin R., Mescheryakov A., Revnivtsev M., Bik-maev I., Sunyaev R., The Astron. Circ. , 295 (1987).Krivonos R., Revnivtsev M., Lutovinov A., Sazonov S.,Churazov E., Sunyaev R., Astron. Astrophys. ,775 (2007).Masetti N., Morelli L., Palazzi E., et al. , Astron. As-trophys. , 21 (2006).Masetti N., Mason E., Landi R., et al. , Astron. Astro-phys., in press, (2008); arXiv:0801.2976.Massey P., Strobel K., Barnes J. V., Anderson E., As-trophys. J. , 315 (1988).Markaryan B. E., Lipovetskii V. A., Stepanyan D. A.,Astrophysics , 639 (1983), Astrophysics , 21(1984), Astrophysics , 513 (1984), Astrophysics , 439 (1985), Astrophysics , 345 (1985).Mescheryakov A., Burenin R., Sazonov S., Revnivt-sev M., Bikmaev I., Sunyaev R., The Astron.Circ. et al. , Astron. Astro-phys. Suppl. Ser. , 201 (1997).Monet D. G., Levine S. E., Canzian B., et al. , Astro-phys. J. , 984 (2003).Revnivtsev M., Sazonov S., Jahoda K., Gilfanov M.,Astron. Astrophys. , 927 (2004).SazonovS. , Churazov E., Revnivtsev M., Vikhlinin A.,Sunyaev R., Astron. Astrophys. (Letters) , L37(2005); astro-ph/0508593.Sazonov S., Revnivtsev M., Krivonos R., E. Churazov,R. Sunyaev, Astron. Astrophys. , 57 (2007). Sazonov S., Revnivtsev M., Burenin R., Churazov E.,Krivonos R., Sunyaev R., Forman W. R. and Mur-ray S. S., Astron. Astrophys., in press (2008);arXiv:0802.0928.Tueller J., Markwardt C., Ajello M., et al. , The Astron.Circ. et al. , inpress; arXiv:0711.4130.Voges W., Aschenbach B., Boller Th., et al. , Astron.Astrophys. , 389 (1999).Heckman T. M., Ptak A., Hornschemeier A., Kauff-mann G., Astrophys. J. , 161 (2005).Schlegel D. J., Finkbeiner D. P., Davis M., Astrophys.J. , 525 (1998)., 525 (1998).