TITLE: GCN CIRCULAR NUMBER: 12170 SUBJECT: Swift J1822.3-1606: Transient Magnetar or Be X-ray Binary? DATE: 11/07/18 23:39:04 GMT FROM: Jules Halpern at Columbia U. Gogus et al. (GCN 12167) and Gorosabel et al. (ATel #3496) have proposed that the recently detected 8.43 s pulsar Swift J1822.3-1606 (Cummings et al., GCN 12159) may be a transient Be/X-ray binary like the 15.3 s pulsar Swift J1626.6-5156, rather than a magnetar. These suggestions were motivated by the large pulsed fraction of 41%, and a candidate 2MASS IR counterpart in the 1.8" radius X-ray error circle (as refined by Pagani et al., ATel #3493). However, the relatively small X-ray column of 3e21 cm^-2 for a power-law plus blackbody fit (Esposito et al., ATel #3490), together with the colors of the 2MASS star and lack of a bright optical detection, are incompatible with a B star companion. The intrinsic colors of an early B star, for example, type B1V, are J-K = -0.14, V-K = -0.76. In contrast, the 2MASS candidate has K = 11.63, J-K = 2.43, and V-K > 9 (from its absence on red and blue Sky Survey plates). The implied color excess E(V-K) > 10 for a B star is inconsistent with the X-ray column density 3e21 cm^-2, the latter corresponding to only ~1.7 magnitudes of extinction in V. A B1V star of absolute magnitude M_V = -3.14 at an assumed distance of 3 kpc should then have apparent V ~ 10.9, which is strongly contradicted by the non-detection. (See Reig et al., arXiv:1106.4671, for analogous discussion of the actual V = 15.5 optical counterpart of Swift J1626.6-5156, which has 3 times larger X-ray column than Swift J1822.3-1606.) Instead, the X-ray properties of Swift J1822.3-1606 may be similar to those of the 2003 outburst of the transient AXP XTE J1810-197 (Gotthelf & Halpern 2007, Ap&SS, 308, 79), including the latter's initial 2-10 keV flux of ~1e-10 erg cm^-2 s^-1, initial pulsed fraction of ~50%, X-ray column density of 6e21 cm^-2, distance of 3-4 kpc (Minter et al. 2008, ApJ, 676, 1189), and short (~1 s) bursts (Woods et al. 2005, ApJ, 629, 985).