1. Detecting radio afterglows and host emissions of Gamma-Ray Bursts with FAST
Speaker: Longbiao Li
Collaborators: Yongfeng Huang, Zhibin Zhang,
Di Li, Xuefeng Wu, Siwei Kong,
Heonyoung Chang and Chulsung Choi
Guizhou University

2. Contents 1 Observations of GRB radio afterglows 2
Dynamical Model and FAST Sensitivity 2
Detecting Radio Afterglows of GRBs with FAST 3
Radio Afterglows and Host Galaxies of GRBs 4
LOGO

3. 1. Observations of GRB radio afterglows
Fig.1. GRB : First burst with an observed radio afterglow.
8.46 GHz
LOGO
Frail et al., 1997, Nature, 389, 261

4. A Radio-selected sample of GRB afterglows
(Frail & Chandra, 2012)
Fig.2. Histogram summarizing the distribution of the radio-selected sample.
In left panel, more than fifty percent measurements are taken in eight point five GHz band, and in right panel, radio afterglows can continue until one thousand days.
LOGO
Frail & Chandra, 2012, ApJ, 746, 156

5. Table 1. Multi-waveband Statistics of the GRB Afterglow Sample.
LOGO
Frail & Chandra, 2012, ApJ, 746, 156

6. 2. Dynamical Model and FAST Sensitivity
Huang, Dai & Lu , 1998, A&A, 336, L69
Huang, Dai & Lu, 1999a, Chin. Phys. Lett., 16, 775
Huang, Dai & Lu, 1999b, MNRAS, 309, 513
Huang, Dai & Lu, 2000a, MNRAS, 316, 943
Huang, Gou, Dai & Lu 2000b, ApJ, 543, 90
LOGO

7. the system temperatures of FAST
How to estimate the detect limiting
sensitivity of FAST ?
the effective area.
the system temperatures of FAST
ηA=0.65 (yue et al ) Ag=pi (300/2)^2 m^2
LOGO

8. Table 2. Parameters describing the Nine Sets of Receivers that are Part of FAST.
Nan et al., 2011, IJMPD, 20, 989
Zhang et al., 2015, RAA, 15, 237
LOGO

9. 3. Detecting Radio Afterglows of GRBs with FAST
LOGO

10. We calculate the radio afterglow light curves of standard, failed, high-luminosity, and low- luminosity GRBs in different observational bands of FAST.
Table 3. Initial physical parameters of these four types of GRBs.
LOGO

11. The GRBs are assumed to be located at different distances from us.
Notices:
The GRBs are assumed to be located at different distances from us.
Contributions of host galaxies have been neglected for simplification.
LOGO

12. The peak emissions of standard bursts at
Fig.3. Radio afterglow light curves at a redshift z = 0.5 in the observer frame within the FAST’s observational bands.
The peak emissions of standard bursts at
ν > 0.4 GHz can be easily
detected.
FAST can hardly detect radio emissions from low-luminosity GRBs.
LOGO
Zhang et al., 2015, RAA, 15, 237

13. Fig.4. Radio afterglow light curves at a redshift z = 1.0.
FAST can detect the radio emission of standard bursts at ν> 0.6 GHz.
LOGO
Zhang et al., 2015, RAA, 15, 237

14. Fig.5. Radio afterglow light curves at a redshift z = 5.0.
Radio afterglows of standard GRBs under 0.8 GHz are
undetectable by FAST.
LOGO
Zhang et al., 2015, RAA, 15, 237

15. Fig.6. Radio afterglow light curves at a redshift z = 10.0.
Only standard GRBs’ radio afterglows above 1.4 GHz can be marginally detected.
LOGO
Zhang et al., 2015, RAA, 15, 237

16. Radio afterglows of high- luminosity GRBs can be detected at
Fig.7. Radio afterglow light curves at a redshift z = 15.0.
Radio afterglows of high- luminosity GRBs can be detected at
0.4–2.5 GHz.
LOGO
Zhang et al., 2015, RAA, 15, 237

17. 4. Radio Afterglows and Host Galaxies of GRBs
LOGO

18. How to consider the contribution from the host galaxy?
The observed radio emission
the GRB afterglow component
the contribution from the host galaxy
Meanwhile, the host flux density should be a
constant at all stages of the afterglow.
LOGO

19. There’s a constant component in the observed emission,
Fig.8. Radio afterglow light curves of GRB
There’s a constant component in the observed emission,
which is interpreted as
the contribution from the host.
LOGO
Berger, Kulkarni & Frail, 2001, ApJ, 560, 652

20. The sample of radio afterglows：
50 GRBs whose radio afterglows are detected
10 GRBs associated with supernova (SN),
6 GRBs without known redshifts.
Three types of GRBs according to isotropic energy:
5 low-luminosity GRBs,
18 standard GRBs,
21 high-luminosity GRBs.
Radio observational bands:
1.4 – 9.0 GHz.
47 data GHz,
25 data GHz,
10 data GHz, …
LOGO

21. Table 4. Observational properties of 50 GRBs and their host galaxies
in radio bands.
LOGO
For more detailed data, please see Li L.B. et al., 2015, MNRAS, 451, 1815

22. RRF -- the Ratio of the radio fluxes of the host to the peak emission
A new parameter:
RRF -- the Ratio of the radio fluxes of the host to the peak emission
the observed peak flux density
the peak flux density of the pure radio afterglow component
the host flux density

23. The linear fitting method
The correlation between RRF and observational frequency ?
The linear fitting method

24. Fig.9. The best linear fits to RRF versus ν for the low-luminosity, standard, high-luminosity GRBs and all GRBs.
LOGO
Li et al., 2015, MNRAS, 451,1815

25. Table 5. Best-fitting parameters for the linear RRF–ν correlation.
LOGO

26. Using the fitting function, one can easily derive
and
LOGO

27. According to the relation, observed radio emission is dominated by the host component at lower frequencies.
It may explain why the low-frequency radio afterglows are usually difficult to be detected, in contrast with the high-frequency case.
LOGO

28. The RRF-predicted host fluxes are included.
Fig Predicted radio light curves for four kinds of GRBs lying at z = 1.0.
The RRF-predicted host fluxes are included.
LOGO
Li L.B. et al., 2015, MNRAS, 451, 1815

29. Thank You !