{
  "bibcode": "2011GCN.12170....1G",
  "body": "Gogus et al. (GCN 12167) and Gorosabel et al. (ATel #3496)\nhave proposed that the recently detected 8.43 s pulsar\nSwift J1822.3-1606 (Cummings et al., GCN 12159) may be a\ntransient Be/X-ray binary like the 15.3 s pulsar Swift J1626.6-5156,\nrather than a magnetar.  These suggestions were motivated by the\nlarge pulsed fraction of 41%, and a candidate 2MASS IR counterpart\nin the 1.8\" radius X-ray error circle (as refined by Pagani et al.,\nATel #3493).  However, the relatively small X-ray column of\n3e21 cm^-2 for a power-law plus blackbody fit (Esposito et al.,\nATel #3490), together with the colors of the 2MASS star and lack\nof a bright optical detection, are incompatible with a B star companion.\n\nThe intrinsic colors of an early B star, for example, type B1V,\nare J-K = -0.14, V-K = -0.76.  In contrast, the 2MASS candidate\nhas K = 11.63, J-K = 2.43, and V-K > 9 (from its absence on\nred and blue Sky Survey plates).  The implied color excess\nE(V-K) > 10 for a B star is inconsistent with the X-ray column\ndensity 3e21 cm^-2, the latter corresponding to only ~1.7 magnitudes\nof extinction in V.  A B1V star of absolute magnitude M_V = -3.14\nat an assumed distance of 3 kpc should then have apparent V ~ 10.9,\nwhich is strongly contradicted by the non-detection.  (See Reig et al.,\narXiv:1106.4671, for analogous discussion of the actual V = 15.5 optical\ncounterpart of Swift J1626.6-5156, which has 3 times larger X-ray\ncolumn than Swift J1822.3-1606.)\n\nInstead, the X-ray properties of Swift J1822.3-1606 may be similar\nto those of the 2003 outburst of the transient AXP XTE J1810-197\n(Gotthelf & Halpern 2007, Ap&SS, 308, 79), including the latter's\ninitial 2-10 keV flux of ~1e-10 erg cm^-2 s^-1, initial pulsed fraction\nof ~50%, X-ray column density of 6e21 cm^-2, distance of 3-4 kpc\n(Minter et al. 2008, ApJ, 676, 1189), and short (~1 s) bursts\n(Woods et al. 2005, ApJ, 629, 985).",
  "circularId": 12170,
  "createdOn": 1311032344000,
  "email": "jules@astro.columbia.edu",
  "subject": "Swift J1822.3-1606: Transient Magnetar or Be X-ray Binary?",
  "submitter": "Jules Halpern at Columbia U.  <jules@astro.columbia.edu>"
}