Universitat de - Departament d'Astronomia i Meteorologia ...

2.4. The radio counterpart: NVSS J182614−145054 43
Flux density [mJy]
Spectral index
50
40
30
20
10
0
0
−1
−2
GBI−NASA Monitoring Program (Set1 data)
2.25 GHz
8.3 GHz
−3
51050 51100 51150 51200 51250 51300 51350 51400 51450
Modified Julian Date [JD−2400000.5]
Figure 2.4: Top: GBI radio light curves of LS 5039 Set1 data at the frequencies of 2.25
and 8.3 GHz. Representative ± 1σ error bars have been plotted for the first data point.
Bottom: The corresponding spectral index. Error bars are also ± 1σ.
mJy and S8.3 GHz = 14.8 (±5.7) mJy. It must be noted that the 1σ errors of the
individual data points are 4 and 6 mJy, respectively. Hence, the source is detected
at the ∼ 8σ level at 2.25 GHz, and only at the ∼ 2.5σ level at 8.3 GHz. However,
the GBI is noise dominated below 10 mJy. Therefore, as pointed out by Clark
et al. (2001), the mean and standard deviation at 8.3 GHz should be estimated
with a Gaussian distribution truncated at 10 mJy. The result of this analysis is
S8.3 GHz = 13.7 (±6.7) mJy, indicating that LS 5039 is detected, on average, at the
∼ 2.0σ level at this frequency, preventing any reasonable variability analysis.
A careful inspection of the 2.25 GHz data in Fig. 2.4 reveals that the typical
day-to-day variability does not exceed ∼ 30 %. Ribó et al. (1999) noted that there
could be some exceptions to this behavior, for example around MJD 51075, 51086