TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1657 SUBJECT: GRB 021023: Curious K-band Source(s) Just Outside of IPN Localization DATE: 02/10/27 19:42:40 GMT FROM: Josh Bloom at CIT GRB 021023: Curious K-band Source(s) Just Outside of IPN Localization J. S. Bloom and E. Falco (Harvard-Smithsonian Center for Astrophysics) report: "On 2002 Oct 25.5, we imaged the entire IPN error box of GRB 021023 (Hurley et al.; GCN #1653) at J and Ks-bands with the FLWO 1.2m equipped with STELIRCam. A comparison between the mosaiced Ks-band image and the 2MASS K-band QUICKLOOK image* reveals a bright new source (OBJ1) at (J2000) 07:24:39.49,-16:10:56.8 (+/- 0.1"). A second source (OBJ2), which appears to be just north of a faint counterpart in the 2MASS image, is located at 07:24:39.09,-16:11:02.62. OBJ1/OBJ2 was detected in each image in two separate pointing positions, consisting of ~10-20 dithered frames of 30 sec. Therefore, OBJ1/OBJ2 is clearly not an array defect nor a cosmic ray hit. See: http://www-cfa.harvard.edu/~jbloom/grb021023.ps.gz Curiously, there is no indication of OBJ1/OBJ2 in the simultaneous J-band images, which might suggest a high redshift source or heavily dust extincted source. However, given the proximity (66") of this OBJ1/OBJ2 to FW CMa (=HD58483; V=5.33mag, type B2.5IVe), the sources themselves may be a ghosting artifact. Two points weaken this possibility: 1) earlier standard star images of HD 22686 showed no indication of ghosting at similar separations in Ks and 2) though the optical path in the blue-channel (J-band) diverges from the red-channel, FW CMa is significantly brighter in J-band and no ghosts are detected in the J-band image. We encourage IR follow-up to help determine the nature of OBJ1/OBJ2." *Summed, mosaiced 2MASS images in J,H,K were constructed using the QUICKLOOK images from the 2MASS All-sky Data Release (see http://irsa.ipac.caltech.edu/applications/2MASS/Visualizer/). These images can be obtained by request (jbloom@tdc.harvard.edu). We thank K. Stanek. This message may be cited.