Universal afterglow of supernovaless gamma-ray bursts

The early-time afterglows of gamma-ray bursts (GRBs) not associated with a supernova (SN) explosion (SN-less GRBs) can be scaled down to a dimensionless, parameter-free universal behavior. This universal behavior is that expected from a pulsar wind nebula afterglow powered by the rotational energy loss of a newly born pulsar. Such SN-less GRBs include short-hard bursts produced by the merger of binary neutron stars and long bursts presumably produced by the accretion-induced collapse of neutron stars to quark stars in high-mass x-ray binaries, or in isolation due to energy and angular momentum loss.

Figure 1

Comparison between the observed x-ray afterglow of SHB150424A measured with Swift-XRT [19] and the best fit assuming the cannonball model for the prompt and extended emission [18] and Eq. (2) for their late-time afterglow.

Figure 2

Comparison between the scaled light curves of the well-sampled x-ray afterglow of 12 SGRBs measured with Swift-XRT [19] during the first couple of days after the burst and their universal behavior predicted by Eq. (3). The bolometric light curve of SHB170817A reported in Ref. [20] is also included. ${\chi }^2/\mathrm{d}.\mathrm{o}.\mathrm{f}.=761/534=1.43$.

Figure 3

Comparison between the observed afterglow of GRB990510 in the x-ray [21] and optical I, R, V, B bands [22] scaled according to Eq. (2) and plotted as function of $t/t_b$, and their predicted universal form as given by Eq. (3), which yields ${\chi }^2/\mathrm{d}.\mathrm{o}.\mathrm{f}.=45.52/54=0.84$.

Figure 4

Comparison between the predicted universal behavior given by Eq. (3) and the reduced x-ray afterglow of five SN-less GRBs with well-sampled x-ray light curves measured in 2018 with Swift-XRT [19] in the first couple of days after the burst, and their predicted universal behavior as given by Eq. (3). ${\chi }^2/\mathrm{d}.\mathrm{o}.\mathrm{f}.=352/339=1.04$.

Figure 5

Comparison between the predicted universal behavior given by Eq. (3) and the reduced light curves of the x-ray afterglow of SN-less GRBs with a well-sampled light curve of their x-ray afterglow measured within a few days after the burst with the SWIFT XRT (19) in the first 2 years (2005, 2006) after launch and in the past 5 years (2015–2019). The different colors indicate data points from different years. The dispersion of the data points has a ${\chi }^2/\mathrm{d}.\mathrm{o}.\mathrm{f}.=3927/3233=1.21$.

Figure 6

Comparison between the normalized light curves of well-sampled x-ray afterglows of LGRBs measured with the Swift-XRT [19] in the first couple of days after the burst in the years 2005 and 2006 and their predicted universal behavior as given by Eq. (3). ${\chi }^2/\mathrm{d}.\mathrm{o}.\mathrm{f}.=845/747=1.13$.

Figure 7

Comparison between the normalized light curves of well-sampled x-ray afterglows of LGRBs measured with Swift-XRT [19] in the first couple of days after burst in 2015 and 2016 and their predicted universal behavior as given by Eq. (3). ${\chi }^2/\mathrm{d}.\mathrm{o}.\mathrm{f}.=1780/1321=1.35$.

Figure 8

Comparison between the normalized light curves of well-sampled x-ray afterglows of LGRBs measured with Swift-XRT [19] in the first couple of days after burst in 2017 and their predicted universal behavior as given by Eq. (3). ${\chi }^2/\mathrm{d}.\mathrm{o}.\mathrm{f}.=600/480=1.25$.

Figure 9

Comparison between the normalized light curves of well-sampled X-ray afterglow of LGRBs measured with Swift-XRT [19] in the first couple of days after the burst in 2018 and 2019 before May and their predicted universal behavior as given by Eq. (3). ${\chi }^2/\mathrm{d}.\mathrm{o}.\mathrm{f}.=349/343=1.02$.