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Spectroscopy of HD 3191, X-ray source and possible counterpart of Fermi J0035+6131

ATel #8789; U. Munari (INAF PAdova), P. Valisa (ANS Collaboration)
on 8 Mar 2016; 21:52 UT
Credential Certification: U. Munari (ulisse.munari@oapd.inaf.it)

Subjects: Radio, Infra-Red, Optical, X-ray, Gamma Ray, AGN, Binary

Fermi J0035+6131 was discovered by LAT instrument on Jan 14, 2016 as a new strong gamma-ray source (ATel #8554) close to the Milky Way plane (Galactic longitude = 121.1 and latitude = -01.4 deg). The location on the sky of the new source has a 95% containment radius of 0.08 deg. This Fermi-LAT error region was explored on Jan, 2016 by XMM-Newton and was found to contain two X-ray sources (ATel #8783): the variable radio source 87GB 003232.7+611352 and the B1IV star HD 3191, with X-ray fluxes in the 0.5-10 keV range of 8.6x10-13 and 8.3x10-14 erg cm-2 s-1, respectively.

The radio source was observed at various radio frequencies with RATAN-600 between Jan 20 and Feb 6, 2016 (ATel #8718). The current flux measured at 4.8 GHz (0.23 Jy) is similar to old catalog data (0.21 Jy, Gregory and Taylor, 1981, ApJ 248, 596). Some flux increase is limited to higher frequencies. The same radio source was detected in the near-IR on Jan 28, 2016 at J=16.81, H=15.64 and Ks = 14.86 mag (ATel #8706), where the 2MASS catalog does not list a corresponding entry. The near-IR detection, however, does not necessarily means an actual recent increase in the source near-IR flux. In fact, the detection completeness limit for normal quality 2MASS sources within a few arcmin is ~1.5 mag brighter than Fermi J0035+6131, and still ~0.5 mag brighter even including 2MASS sources of any data quality.

On 7 March, 2016 we have obtained an Echelle optical spectrum (range 4225-8250 Ang, resolving power 11,000) of HD 3191, the other X-ray source found by XMM-Newton within the Fermi-LAT error region. We used the Varese 0.61m telescope equipped with a mk.III Multi Mode Spectrograph. No significant peculiarity is noticeable on the spectrum of HD 3191, like the presence of emission lines or emission line cores, or duplicity and/or asymmetry in the profile of absorption lines. From the equivalent width of interstellar KI 7696 atomic line and 6614 DIB a reddening E(B-V)=0.73 is inferred (NaI D1,D2 are saturated as such a high value), well matching the E(B-V)=0.71 derived by comparing existing UBV photometry of HD 3191 with intrinsic colors for normal B1IV stars. Such a reddening is larger than that corresponding to the neutral hydrogen column density inferred in ATel #8783 from XMM-Newton X-ray observations. We measured an heliocentric radial velocity of -46.0 +/-0.5 km/s for HD 3191, of -24.9 +/-0.6 km/s for the interstellar lines, and a projected stellar rotational velocity of 265 +/-10 km/s. There is apparently only one previous measure of the radial velocity of HD 3161 by Petrie and Pearce (1961) who found -22 +/-3 km/s from photographic spectra obtained between 1945 and 1952. This argues for HD 3191 being a binary, with only one component visible on our spectrum.