[ Previous | Next | ADS ]

ANTARES neutrino detection: Optical/NIR spectroscopy of the Swift/XRT counterpart candidate from NOT

ATel #7994; A. de Ugarte Postigo (IAA-CSIC, DARK/NBI), H. Korhonen (U. Turku, NBI), M. I. Andersen (DARK/NBI), J. P.U. Fynbo (DARK/NBI), S. Schulze (PUC, MAS), Z. Cano (U. Iceland), D. Xu (NAOC/CAS), N. R. Tanvir (U. Leicester), D. Watson (DARK/NBI), D. Malesani (DARK/NBI), J. Hjorth (DARK/NBI), A. A. Djupvik (NOT)
on 4 Sep 2015; 15:28 UT
Credential Certification: Antonio de Ugarte Postigo (adeugartepostigo@gmail.com)

Subjects: Infra-Red, Optical, X-ray, Neutrinos, Star, Transient

Referred to by ATel #: 7995, 7999, 8000, 8027, 8034, 8124

We observed the star USNO-B1.0 0626-0501169, associated with the X-ray emission detected by Swift, within the error box of the high-energy neutrino detected by ANTARES (Dornic et al. 18231, ATel#7987, Smartt et al. ATel#7992, Dichiara et al. ATel#7993), with the 2.5 m NOT telescope at La Palma (Spain). Our observation consisted of 3x400 s spectra with the FIES high-resolution spectrograph in the visible, and 4x120 s spectra with NOTCam in the near-infrared K-band.

The FIES spectra were obtained at a resolution of R = 25000 and covered the range between 3700 and 7100 AA, although good S/N is only obtained above 4500 AA. The mean observing epoch was the 3rd September 2015 at 21:45 UT (2.59 days after the neutrino detection), and observation was performed at an airmass of 3. Reduction of the NIR data is still ongoing.

The visible spectrum shows a red continuum with multiple absorption features as well as hydrogen Balmer lines in emission. Emission lines of H-alpha and H-beta are resolved, having a FWHM of 75 km/s, and equivalent widths of -1.9 and -1.0 AA, respectively. We detect no emission from HeI or [SII]. The spectrum shows broad and strong absorption due to NaID with a combined equivalent width of 7.1 AA. Detection of a strong absorption at 6708 AA seems to indicate the presence of Li in the object. There is no convincing evidence of molecular bands.

All this points to USNO-B1.0 0626-0501169 being a young accreting G-K star, undergoing a flaring episode that produced the X-ray emission. We also note that this object is close to the nearby Rho Ophiuchi star forming region, being probably associated with it.

This is a resubmission of GCN 18236.