TITLE: GCN GRB OBSERVATION REPORT NUMBER: 2916 SUBJECT: NIR Observations of GRB 041219 DATE: 04/12/28 07:44:54 GMT FROM: Don Lamb at U.Chicago NIR Observations of GRB 041219 F. Hearty (Colorado), D. Q. Lamb (Chicago), J. Barentine (APO), P. A. Price (Hawaii), S. Beland (Colorado), E. L. Turner (Princeton), R. McMillan (APO), J. Dembicky (APO), B. Ketzeback(APO), and D. G. York (Chicago) report on behalf of the ARC team of the FUN GRB collaboration: We observed the NIR afterglow (Blake and Bloom, GCN Circular No. 2870) of GRB 041219, a burst localized by Integral (Gotz et al., GCN Circular No. 2866) and Swift-BAT (Barthelmy et al., GCN Circular No. 2874), on the night of December 20th, using C-NIC (formerly NIC-FPS) on the ARC 3.5-meter telescope at Apache Point Observatory. The observation began at 01.05 UT, 47.25 hours after the burst, and consisted of a series of 120, 20, and 20-second exposures in J, H, and Ks, respectively. We constructed stacked images corresponding to 20-minute exposures in J and H, and a 40-minute exposure in Ks. We detect the afterglow in all three filters; the magnitudes are J = 19.9 +/- 0.2, H = 18.9 +/- 0.1, and Ks = 17.6 +/- 0.2. We thus confirm that the afterglow is heavily reddened, as previously noted by Blake and Bloom (GCN Circular No. 2870). We also confirm that the afterglow had faded significantly in comparison with the earlier NIR observations reported by Blake and Bloom (GCN Circular No. 2870) and Moon, Cenko, and Adams (GCN Circular Nos. 2876 and 2884), in agreement with the conclusion of Bloom et al. (GCN Circular No. 2893). As noted by Bloom et al. (GCN Circular No. 2893), the IR afterglow is located 2.5 arcseconds south-south-west of a faint compact source that is visible in J, H, and Ks. Using Schlegel et al. (1998), the estimated extinction in the direction of GRB 041219 is E(B-V) = 1.8 mag, corresponding to A_lambda values of J = 1.6, H = 1.0, K = 0.65 mag. These values give J-H = 0.6, H-K = 0.4, and J-K = 1 mag, compared to our measured values of J-H = 1.0, H-K = 1.3, and J-K = 2.3 mag. Although our results indicate greater reddening than that estimated using Schlegel et al. (1998), the estimated value of E(B-V) is unreliable because GRB 041219 lies very close to the Galactic plane (b = 0.6 [deg]). We therefore cannot say that there is more reddening than can be accounted for by Galactic extinction. However, our results show that the drop-off with decreasing wavelength is gradual and therefore is unlikely to be due to absorption by hydrogen in the host galaxy or along the line of sight to the host galaxy. Consequently, the burst is unlikely to lie at a very high redshift (z > 5). This message may be cited.