GCN Circular 1657

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
Loading...
 
 ) 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.