{
  "bibcode": "2017GCN.20795....1F",
  "body": "Johan P.U. Fynbo, Daniele Malesani, Lise Christensen (DARK/NBI), Giorgos \nLeloudas (WIS), and Elena Pian (SNS; INAF/IASF Bo) report on behalf of a \nlarger collaboration:\n\nWe observed the location of the X-ray \"source 1\" within the LVC error \nregion for the GW trigger G275697 (LVC Circ. 20763) reported by Swift \n(Evans et al., LVC Circ. 20773) using the Nordic Optical Telescope (NOT) \nequipped with the ALFOSC camera and spectrograph. Observations were \ncarried out in the r band, and started on 2017 Mar 1.25 UT (in twilight, \nat high airmass).\n\nWe clearly detect the 2MPZ galaxy mentioned by Evans et al. (LVC GCN \n20773) and coincident with the X-ray source. We measure a magnitude r = \n16.67 +- 0.01 AB (5\" aperture radius, calibrated against nearby stars \nfrom the Pan-STARRS catalog). This value is consistent with the (Kron) \nmagnitude r = 16.68 listed in the Pan-STARRS catalog, indicating no \nvariability compared with the archival value.\n\nA 900-s spectrum was obtained covering the wavelength range 3300-9500 \nAA, under non-photometric conditions. Several emission lines are \ndetected, corresponding to Halpha, Hbeta, the [O III] doublet, [N II] \nand [S II], all at a common redshift z = 0.0385, corresponding to a \n(luminosity) distance of 170 Mpc.\n\nThe width of the Halpha and Hbeta lines is around 1700 km s^-1, \nindicating the presence of a broad-line region typical of an AGN. Also, \nthe location of this object in the extinction-insensitive BPT diagram \n(e.g. Kewley et al. 2013, ApJ, 774, L10) is consistent with LINERs and \nAGN. We caution that the [N II] lines, used for the BPT diagram, falls \nat this redshift close to the telluric B band, but correcting for the \nflux loss should, if anything, move our target even more towards the AGN \nlocus. Finally, we note that the Halpha/Hbeta ratio indicates \nsignificant extinction, even after correcting for the non-negligible \nGalactic reddening (A_V ~ 1 mag).\n\nOur data thus indicate that the XRT source 1 is an AGN, which would \nnaturally explain the detected X-ray emission (at a level of ~10^43 erg \ns^-1).\n\nWe acknowledge excellent support from the NOT staff, in particular Pere \nBlay and Amanda Djupvik.",
  "circularId": 20795,
  "createdOn": 1488479968000,
  "email": "malesani@dark-cosmology.dk",
  "subject": "LIGO/Virgo G275697: optical spectroscopy of Swift/XRT source 1",
  "submitter": "Daniele Malesani at DARK/NBI  <malesani@dark-cosmology.dk>",
  "eventId": "LIGO/Virgo G275697"
}