Unveiling the nature ofINTEGRALobjects through optical spectroscopy

Abstract

Hard X-ray surveys performed by the INTEGRAL satellite have discovered a conspicuous fraction (up to 30%) of unidentified objects among the detected sources. Here we continue our program of identification of these objects by (i) selecting probable optical candidates by means of positional cross-correlation of the INTEGRAL detections with soft X-ray, radio, and/or optical archives and (ii) performing optical spectroscopy on them. As a result, we pinpointed and identified, or more accurately characterized, 44 definite or likely counterparts of INTEGRAL sources. Among them, 32 are active galactic nuclei (AGNs; 18 with broad emission lines, 13 with narrow emission lines only, and one X-ray bright, optically normal galaxy) with redshift 0.019 < z < 0.6058, 6 cataclysmic variables (CVs), 5 high-mass X-ray binaries (2 of which in the Small Magellanic Cloud), and 1 low-mass X-ray binary. This was achieved by using 7 telescopes of various sizes and archival data from two online spectroscopic surveys. The main physical parameters of these hard X-ray sources were also determined using the multiwavelength information available in the literature. In general, AGNs are the most abundant population among hard X-ray objects, and our results confirm the tendency of finding AGNs more frequently than any other type of hard X-ray emitting object among unidentified INTEGRAL sources when optical spectroscopy is used as an identification tool. Moreover, the deeper sensitivity of the more recent INTEGRAL surveys enables one to begin detecting hard X-ray emission above 20 keV from sources such as LINER-type AGNs and non-magnetic CVs.

XMM-Newtonobservations of four high mass X-ray binaries and IGR J17348−2045

“…The measured fluxes of the source were 0.4 ± 0.1 mCrab in the 20−40 keV energy band and 0.7 ± 0.2 mCrab in the 40−100 keV energy range 1 (Bird et al 2010). Masetti et al (2010) tentatively associated the source to the OB-V star SS 188 located at a distance of 6.1 kpc, thus suggesting that IGR J08262−3736 was a new member of the HMXB class discovered with INTEGRAL. The association was later confirmed by Malizia et al (2011) using Swift/XRT data.…”

Optical and X-Ray Studies of 10 X-Ray-Selected Cataclysmic Binaries

“…Shortened names are used; "Swift 0732" is V667 Puppis. The chart for 1RX J0457 supersedes the chart in Masetti et al (2010). with the same dispersion. Wavelength calibrations were from Hg, Ne, and Xe comparison lamps taken during twilight, and we used the night-sky λ5577 feature to track spectrograph flexure during the night.…”

“…It was detected in the Swift/BAT survey (Voss & Ajello 2010;Cusumano et al 2010a) and by INTEGRAL/IBIS (Krivonos et al 2010), then classified as a CV when Masetti et al (2010) obtained a spectrum of the optical counterpart but give coordinates and a finding chart for the wrong star; Figure 1 and Table 1 give the correct identification. Our spectrum (Figure 2) appears nearly identical to theirs, but with a slightly lower continuum level and better signal-to-noise ratio.…”

Confirmation of 1RXS J165443.5–191620 as an intermediate polar and its orbital and spin periods

“…This Rosat detection has been also catalogued in the INTEGRAL/IBIS survey ; but remained unidentified until a tentative classification by Masetti et al (2010) based on optical (follow-up) spectroscopy. The spectra displayed clear Balmer and HeI emission lines, with HeII λ4686 Å/Hβ equivalent width ratios ≥0.5, suggesting an intermediate polar classification for this CV.…”

“…trip to the Observatorio del Teide organised by the university of Southampton. The motivation for the project was the tentative spectroscopic classification of RX J1654 as an mCV by Masetti et al (2010). The source was observed for a total of about 2 h, with variable exposures between 20 and 40 s to compensate for variable atmospheric conditions during the observation.…”