Table 4
Upper limits set with different PTAs to SGWB of different origins, ρcri = 100.
 |
 |
 |
|
|---|---|---|---|
| EPTA (Lentati et al. 2015) | 1.4×10−15(3×10−15) | 2.5 × 10−10 | 4.7 × 10−10(1.2× −9) |
| PPTA (Shannon et al. 2015) | 2.45×l0−15(1×l0−15) | 6.4 × 10−10 | 1.2 × 10−10 |
| NANOGrav (Arzoumanian et al. 2018) | 1.6×10−15(1.45×10−15) | 3.6 × 10−10 | 6.3×10−10(3.4×l0−10) |
| IPTA | 9.9 × 10−16 | 1.0 × 10−10 | 2.0 × 10−10 |
Notes. Numbers in parentheses are values in literature. The most recent reported upper limit on the GW originating from cosmic string are in terms of the cosmic-string tension (Gμ). The conversion from Gμ to 
depends on models and the reconnection probability p, and so we cannot give literature values.
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