{
  "bibcode": "2016GCN.19708....1M",
  "body": "D. Malesani (DARK/NBI), A. de Ugarte Postigo (IAA-CSIC and DARK/NBI), M. \nDe Pasquale (UCL/MSSL), D. A. Kann (TLS Tautenburg), Z. Cano (Univ. \nIceland), D. A. Perley (DARK/NBI), L. Izzo (IAA-CSIC), C. C. Thoene \n(IAA-CSIC),\n\nN. Butler (ASU), A. M. Watson (UNAM), A. Kutyrev (GSFC), W. H. Lee \n(UNAM), M. G. Richer (UNAM), O. Fox (STScI), J. X. Prochaska (UCSC), J. \nS. Bloom (UCB), A. Cucchiara (GSFC/STScI), E. Troja (GSFC), O. \nLittlejohns (ASU), E. Ramirez-Ruiz (UCSC), J. A. de Diego (UNAM), L. \nGeorgiev (UNAM), J. Gonzalez (UNAM), C. Roman-Zuniga (UNAM), N. Gehrels \n(GSFC), H. Moseley (GSFC), J. Capone (UMD), V. Zach Golkhou (ASU), and \nV. Toy (UMD), on behalf of the RATIR collaboration,\n\nreport:\n\nWe observed the field of GRB 160623A (Vianello et al., GCN 19553; \nFrederiks et al., GCN 19554; Mailyan et al., GCN 19555) with the Nordic \nOptical Telescope (NOT) equipped with the AlFOSC imager. Our \nobservations had a mid time 2016 July 8.09 UT (14.88 days after the GRB \ntrigger) and consisted of 6x300 s in the SDSS i filter.\n\nClose to the position of the optical and X-ray afterglow (Mingo et al., \nGCN 19558; Pozanenko et al., GCN 19561; Butler et al., GCN 19567), we \ndetect a bright source at the following coordinates (J2000):\n\nRA = 21:01:11.65\nDec = +42:13:15.0\n\nWe measure I = 20.6 +- 0.2 (Vega) against several nearby USNO stars \n(error dominated by the calibration). To determine the relation of this \nobject with the GRB afterglow, we cross-registered our image with those \nfrom RATIR (Butler et al., GCN 19567), yielding an RMS of 0.02\". We find \nthat the NOT source is offset to the SE of the afterglow by 0.7\". This \nsource could thus be the host galaxy or an unrelated, foreground star. \nWe also note some faint emission in the RATIR image at the NOT \ncoordinates, despite being blended with the brighter afterglow.\n\nA picture showing the comparison of the two images is shown here:\n\nhttp://www.astro.ku.dk/~malesani/GRB/160623A/GRB160623A_NOT_RATIR.png\n\nA spectrum (3x1200 s exposure) was acquired using the Gran Telescopio \nCanarias (GTC) equipped with OSIRIS, covering the wavelength range \n5100-10,000 AA (grism R1000R), starting on 2016 July 10.163 UT (16.95 \ndays after the GRB). The slit was centered at the coordinates of the NOT \nobject, but also partially overlapped with the afterglow location.\n\nWe detect continuum over the whole wavelength range and two emission \nlines in the red part of the spectrum, which we interpret as Halpha and \n[N II] at a common redshift z = 0.367. At the same redshift we also \ndetect weak [O III] 5008 (dimmed by the large foreground extinction). \nThis is most likely the redshift of GRB 160623A.\n\nThe source detected in the NOT image is possibly a foreground star (the \nGalactic latitude is b = -2.7 deg). In the GTC acquisition image, the \nobject is pointlike with a seeing of 1.2\". On the other hand, inspecting \nthe 2D spectrum, the spatial profile of the emission lines is different \nfrom that of the continuum: the features are wider and elongated towards \nthe position of the afterglow. A compact host cannot however be excluded.\n\nAt z = 0.367, a SN as bright as SN 1998bw would only reach a peak \nmagnitude of I ~ 24.8 (Vega) given the large Galactic extinction (A_I = \n2.2 mag; Schlafly & Finkbeiner 2011). From ground, such a SN would be \ndifficult to distinguish against the brighter foreground object.\n\nWe acknowledge excellent support from the observers at the NOT (in \nparticular Roi Alonso and Diego Hidalgo) and at the GTC.",
  "circularId": 19708,
  "createdOn": 1468514772000,
  "email": "malesani@dark-cosmology.dk",
  "subject": "GRB 160623A: optical astrometry, photometry, and redshift",
  "submitter": "Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst  <malesani@dark-cosmology.dk>",
  "eventId": "GRB 160623A"
}