Optical classification of 3 Swift southern hard X-ray sources

ATel #785; L. Morelli (PUC, Santiago), N. Masetti, L. Bassani, R. Landi, A. Malizia (INAF-IASF, Bologna), A. J. Bird (Univ. Southampton), P. Ubertini (INAF-IASF, Rome) and G. Galaz (PUC, Santiago)
on 30 Mar 2006; 21:14 UT
Credential Certification: Nicola Masetti (masetti@iasfbo.inaf.it)

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In order to identify the nature of 3 hard X-ray sources recently discovered by Swift (see ATels #669 and #677), we acquired optical spectra of their counterparts at the 1.5m telescope of the Cerro Tololo Interamerican Observatory (Chile) using the R-C spectrograph on the nights of March 21 and 22, 2006. Total exposure times ranged from 15 to 40 minutes, depending on the object brightness.

In the following table, we report the classification of these sources:

  

  
      Source         Class     z    ATel ref.          
  

  
SWIFT J0601.9-8636    Sy2?   0.006    #677
  
SWIFT J1038.8-4942    Sy1    0.060    #669
  
SWIFT J1238.9-2720    Sy2    0.024    #669
  

  

Notes on individual sources.

SWIFT J0601.9-8636: from the proposed optical counterpart, the nucleus of galaxy LEDA 18394, we detect narrow emission lines of Halpha and [OIII] superimposed on a continuum resembling that typical of spiral galaxy. This possibly indicates that the nucleus might be a hidden Sy2 AGN. We however caution the reader about the certainty of the association between the high-energy source detected with Swift/BAT and the galaxy (Tueller et al., ATel #677). The measured redshift is z = 0.006 +- 0.001, consistent with that measured by Fisher et al. (1995, ApJS, 100, 69).

SWIFT J1038.8-4942: broad Halpha and Hbeta emissions plus narrow [OI] and [OIII] emission lines are detected on a relatively flat continuum in the optical spectrum of the counterpart, 2MASX J10384520-4946531 (Tueller et al., ATel #669). From the observed wavelengths of narrow features, we determine a redshift z = 0.060 +- 0.001. The overall spectral appearance allows us to classify this object as a Seyfert 1 galaxy.

SWIFT J1238.9-2720: the presence of Halpha, Hbeta, [NII] and [OIII] narrow emission lines are detected in the optical spectrum of the counterpart, galaxy ESO 506-G027. The overall spectrum indicates that this source is most likely a Seyfert 2 AGN. The features are at redshift z = 0.024+-0.001, consistently with Da Costa et al. (1998, AJ, 116, 1).

We thank C. Aguilera and A. Gomez for the assistance at the telescope