TITLE: GCN CIRCULAR NUMBER: 15734 SUBJECT: GRB 140104B: Further Swift XRT observations DATE: 14/01/14 19:37:50 GMT FROM: Dirk Grupe at PSU/Swift-XRT Dirk Grupe (Swift MOC, PSU) and Phil Evans (U Leicester) report on behalf of the Swift team: We report on further Swift XRT observations of the field of the Fermi GBM and LAT detected GRB 140104B (Xiong, GCN Circ. 15687, G. Vianello GCN Circ. 15684, respectively). We detected an uncatalogued X-ray source in the first Swift observation of the field of GRB 140104B starting at 15.5 hours after the Fermi trigger (Grupe, GCN circ 15691) at Ra-2000 = 14 35 01.0 Dec-2000 = -09 01 40.7 with an uncertainty of 4.0". The XRT count rate of this source was (8.1+/-1.6)e-3 counts s^-1. Note that we misidentified this source in the previous circular (15691) with the star TYC 5564-19-1, which however, is 2.2' away from this X-ray position. We re-observed this source on 2014-01-14 for 4.6 ks again with Swift (9.5 days after the trigger). We do not detect this source in the XRT any more, suggesting that this may be the X-ray afterglow of GRB 140104B. The 3sigma upper limit at the position of this source is 1.3e-3 counts s^-1. Note, however, that this is not conclusive. This source can still be a highly variable background AGN (see e.g. Grupe et al. 2010, ApJS, 187, 64). If this source is the X-ray afterglow of GRB 140104B, the X-ray spectrum appears to be rather soft. A spectral analysis of the X-ray data shows that the X-ray photon index is Gamma = 2.7+/-0.68 which is rather steep (see Grupe et al. 2013, ApJS, 209, 20; Evans et al., 2009, MNRAS, 397, 1177). The absorption column density is consistent with the Galactic value (5.63e20 cm^-2). This steep X-ray spectral index and the steep energy spectral index and the high fluence in the 10-1000 keV band of the burst reported by Xiong (GCN circular 15687) suggests a low redshift nature of the burst (see Grupe et al. 2013, ApJ, 209, 20). However, the steep X-ray photon index of Gamma = 2.7 does not exclude a possible AGN nature of the source. In a matter of fact, if this is a background AGN then the steep X-ray spectrum suggest that this is most-likely a Narrow Line Seyfert 1 galaxy. This is also the type of AGN with the strongest X-ray variability (e.g. Boller et al. 1996, Leighly 1999, Grupe et al. 2010). This report is an official product of the Swift team.