http://arxiv.org/abs/1801.00397
Using multi-wavelength observations of radio afterglows, we confirm the hypothesis that flux density of Gamma-Ray Bursts (GRBs) will become invariable as the GRBs locate far enough, that is to say the detection rate will be approximately independent of redshift. It is found that short and SN-associated GRBs marginally match the flux-redshift relationship in nearby universe and they could be outliers. We study this novel behavior theoretically and find that it can be well explained by the standard forward shock model involving a thin shell in both ISM and wind circumstances. A potential relation of medium density with redshift, namely $n\propto(1+z)^4$, has been ruled out according to the current measurements of $n$ and $z$ for short and long GRBs. In addition, the possible dependence of host flux on the redshift is also investigated. We discover the similar flux-redshift independence as well, which implies the detection rate of radio hosts might be also independent of the redshift. For the first time, we constrain the spectral index $\beta_h$ in $F_{\nu, h}\propto\nu^{\beta_h}$ of radio hosts statistically and obtain $\beta_h\sim2$ for the brighter hosts and $\beta_h<1$ for the dimmer ones, hinting two types of radio hosts. Finally, we predict the detection rates of radio afterglows by next-generation radio telescopes such as FAST, LOFAR, MeerKAT, ASKAP and SKA.
Z. Zhang, P. Chandra, Y. Huang, et. al.
Wed, 3 Jan 2018
32/59
Comments: Submitted to ApJ, comments are welcome
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