Swift/XRT follow-up observations of unidentified INTEGRAL/IBIS sources

arXiv:1003.1214v1 [astro-ph.HE] 5 Mar 2010 Swift/XRT follow-up observations of unidentified INTEGRAL/IBIS sources R. Landi∗ INAF/IASF Bologna, Via P. Gobetti 101, 40129 Bologna, Italy E-mail: landi@iasfbo.inaf.it L. Bassani INAF/IASF Bologna, Via P. Gobetti 101, 40129 Bologna, Italy E-mail: bassani@iasfbo.inaf.it A. Malizia INAF/IASF Bologna, Via P. Gobetti 101, 40129 Bologna, Italy E-mail: malizia@iasfbo.inaf.it J. B. Stephen INAF/IASF Bologna, Via P. Gobetti 101, 40129 Bologna, Italy E-mail: stephen@iasfbo.inaf.it A. Bazzano INAF/IASF Roma, Via Fosso del Cavaliere 100, 00133 Roma, Italy E-mail: angela.bazzano@iasf-roma.inaf.it M. Fiocchi INAF/IASF Roma, Via Fosso del Cavaliere 100, 00133 Roma, Italy E-mail: mariateresa.fiocchi@iasf-roma.inaf.it A. J. Bird School of Physics and Astronomy, University of Southampton, Highfield, SO17 1BJ, UK E-mail: ajd@phys.soton.ac.uk Many sources listed in the 4th IBIS/ISGRI survey are still unidentified, i.e. lacking an X-ray counterpart or simply not studied at lower energies (< 10 keV). The cross-correlation between the list of IBIS sources in the 4th catalogue and the Swift/XRT data archive is of key importance to search for the X-ray counterparts; in fact, the positional accuracy of few arcseconds obtained with XRT allows us to perform more efficient and reliable follow-up observations at other wavelengths (optical, UV, radio). In this work, we present the results of the XRT observations for four new gamma-ray sources: IGR J12123–5802, IGR J1248.2–5828, IGR J13107–5626 and IGR J14080– 3023. For IGR J12123–5802 we find a likely counterpart, but further information are needed to classified this object, IGR J1248.2–5828 is found to be a Seyfert 1.9, for IGR J13107–5626 we suggest a possible AGN nature, while IGR J14080–3023 is classified as a Seyfert 1.5 galaxy. The Extreme sky: Sampling the Universe above 10 keV - extremesky2009, October 13-17, 2009 Otranto (Lecce) Italy ∗Speaker. c ⃝Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. http://pos.sissa.it/ Swift/XRT follow-up observations of unidentified INTEGRAL/IBIS sources R. Landi Table 1: XRT position and classification of the counterpart of the IBIS sources. Source R.A. Dec Error Counterpart Type (J2000) (J2000) (arcsec) IGR J12123–5802 12h12m25s.97 −58◦00′23′′.1 3.7 2MASS J12122623–5800204 unidentified IGR J1248.2–5828 12h47m57s.82 −58◦29′59′′.1 4.0 2MASX J12475784–5829599 Seyfert 1.9 IGR J13107–5626 13h10m37s.27 −56◦26′56′′.7 4.4 2MASX J13103701–5626551 AGN candidate IGR J14080–3023 14h08m06s.57 −30◦23′52′′.6 3.6 2MASX J14080674–3023537 Seyfert 1 Figure 1: Left panel: XRT 0.3–10 keV image of the region surrounding IGR J12123–5802. The larger green circle represents the IBIS position and uncertainty, while the two X-ray sources detected within it are labelled as #1 and #2. Also plotted is the position (smaller red circle) of a ROSAT Bright Survey source (1RXS J121222.7–580118) located ∼1′ away from source #1. Right panel: XRT spectrum of source #1, the likely counterpart of IGR J12123–5802, fitted with a power law passing through Galactic absorption. 1. IGR J12123–5802 Within the IBIS positional uncertainty (see Bird et al. 2010), XRT reveals two X-ray source (see Figure 1, left panel). Source #1 has a counterpart in the United States Naval Observatory (USNO–B1.0, Monet et al. 2003) catalogue with magnitude R ∼14.9–16.5, also listed in the 2MASS (2 Micron All Sky Survey, Skrutskie et al. 2006) survey, with magnitudes J ∼15.4, H ∼15.2 and K ∼15.1. For source #2 (located at R.A.(J2000) = 12h12m32s.40, Dec(J2000) = −58◦06′09′′.5, error radius 6′′.0 and only detected below 4 keV) we did not find a counterpart in any database, thus suggesting that deeper X-ray observations are needed to investigate its nature. As can be seen in the left panel of Figure 1, at ∼1′ away from source #1 there is also the ROSAT source 1RXS J121222.7–580118, which is detected at ∼3σ but only at soft energies (< 3 keV). Although this source belongs to the ROSAT Bright survey, during the XRT pointing appears weak, having a 2–10 keV flux of ∼3×10−13 erg cm−2 s−1 assuming a power law model with the photon index frozen to 1.8. This behaviour seems to indicate a variable nature for this source, thus making unlikely its association with the IBIS detections, which instead is listed as persistent in the 4th survey. From the above considerations, we conclude that source #1 is the likely candidate for 2 Swift/XRT follow-up observations of unidentified INTEGRAL/IBIS sources R. Landi Figure 2: Left panel: XRT 0.3–10 keV image of the region surrounding IGR J1248.2–5828. The green circle represents the 90% IBIS error circle, while the two X-ray sources detected by XRT within and at the border of it are labelled as #2 and #3. Source #1 is the fainter source detected by XRT within the 99% IBIS error circle. Right panel: XRT spectrum of source #3, the likely counterpart of IGR J1248.2–5828, fitted with an a

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