Cl. Bennett et al., COSMIC TEMPERATURE-FLUCTUATIONS FROM 2 YEARS OF COBE DIFFERENTIAL MICROWAVE RADIOMETERS OBSERVATIONS, The Astrophysical journal, 436(2), 1994, pp. 423-442
The first two years of COBE Differential Microwave Radiometers (DMR) o
bservations of the cosmic microwave background (CMB) anisotropy are an
alyzed and compared with our previously published first year results.
The results are consistent, but the addition of the second year of dat
a increases the precision and accuracy of the detected CMB temperature
fluctuations. The 2 yr 53 GHz data are characterized by rms temperatu
re fluctuations of (Delta T)(rms)(7 degrees) = 44 +/- 7 mu K and (Delt
a T)(rms)(10 degrees) = 30.5 +/- 2.7 mu K at 7 degrees and 10 degrees
angular resolution, respectively. The 53 x 90 GHz cross-correlation am
plitude at zero lag is C(0)(1/2) = 36 +/- 5 mu K (68% CL) for the unsm
oothed (7 degrees resolution) DMR data. We perform a likelihood analys
is of the cross-correlation function, with Monte Carlo simulations to
infer biases of the method, for a power-law model of initial density f
luctuations, P(k) proportional to k(n). The Monte Carlo simulations in
dicate that derived estimates of n are biased by +0.11 +/- 0.0l, while
the subset of simulations with a low quadrupole (as observed) indicat
e a bias of +0.31 +/- 0.04. Derived values for 68% confidence interval
s are given corrected (and not corrected) for our estimated biases. In
cluding the quadrupole anisotropy, the most likely quadrupole-normaliz
ed amplitude is Q(rms-PS) = 14.3(-3.3)(+5.2) mu K (12.8(-3.3)(+5.2) mu
K) with a spectral index n = 1.42(0.55)(+0.49) (n = 1.53(-0.55)(+0.49
)). With n fixed to 1.0 the most likely amplitude is 18.2 +/- 1.5 mu K
(17.4 +/- 1.5 mu K). The marginal likelihood of n is 1.42 +/- 0.37 (1
.53 +/- 0.37). Excluding the quadrupole anisotropy, the most likely qu
adrupole-normalized amplitude is Q(rms-PS) = 17.4(-5.2)(+7.5) mu K (15
.8(-5.2)(+7.5) mu K) with a spectral index n = 1.11(-0.55)(+0.60) (n =
1.22(-0.55)(+0.60)) With n fixed to 1.0 the most likely amplitude is
18.6 +/- 1.6 mu K (18.2 +/- 1.6 mu K). The marginal likelihood of n is
1.11 +/- 0.40 (1.22 +/- 0.40). Our best estimate of the dipole from t
he 2 yr DMR data is 3.363 +/- 0.024 mK toward Galactic coordinates (l,
b) = (264 degrees.4 +/- 0 degrees.2, +48 degrees.1 +/- 0 degrees.4),
and our best estimate of the rms quadrupole amplitude in our sky is 6
+/- 3 mu K (68% CL).