Bursts before Burst: A Comparative Study on FRB 200428-associated and FRB-absent X-ray Bursts from SGR J1935+2154. (arXiv:2009.10342v2 [astro-ph.HE] UPDATED)

Bursts before Burst: A Comparative Study on FRB 200428-associated and FRB-absent X-ray Bursts from SGR J1935+2154. (arXiv:2009.10342v2 [astro-ph.HE] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Yang_Y/0/1/0/all/0/1">Yu-Han Yang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zhang_B/0/1/0/all/0/1">Bin-Bin Zhang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lin_L/0/1/0/all/0/1">Lin Lin</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zhang_B/0/1/0/all/0/1">Bing Zhang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zhang_G/0/1/0/all/0/1">Guo-Qiang Zhang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Yang_Y/0/1/0/all/0/1">Yi-Si Yang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Tu_Z/0/1/0/all/0/1">Zuo-Lin Tu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zou_J/0/1/0/all/0/1">Jin-Hang Zou</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ye_H/0/1/0/all/0/1">Hao-Yang Ye</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wang_F/0/1/0/all/0/1">Fa-Yin Wang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Dai_Z/0/1/0/all/0/1">Zi-Gao Dai</a>

Accompanied by an X-ray burst, the fast radio burst (FRB) FRB 200428 was
recently confirmed as originating from the Galactic magnetar soft gamma
repeater (SGR) SGR J1935+2154. Just before and after FRB 200428 was detected,
the Five-hundred-meter Aperture Spherical radio Telescope (FAST) had been
monitoring SGR J1935+2154 for eight hours. From UTC 2020 April 27 23:55:00 to
2020 April 28 00:50:37, FAST detected no pulsed radio emission from SGR
J1935+2154, while Fermi/Gamma-ray Burst Monitor registered 34 bursts in the
X/soft $gamma$-ray band, forming a unique sample of X-ray bursts in the
absence of FRBs. After a comprehensive analysis on light curves,
time-integrated, and time-resolved spectral properties of these FRB-absent
X-ray bursts, we compare this sample with the FRB-associated X-ray burst
detected by Insight-HXMT, INTEGRAL, and Konus-Wind. The FRB-associated burst
distinguishes itself from other X-ray bursts by its nonthermal spectrum and a
higher spectral peak energy, but otherwise is not atypical. We also compare the
cumulative energy distribution of our X-ray burst sample with that of first
repeating FRB source, FRB 121102, with the calibration of FRB 200428-X-ray
burst association. We find a similarity between the two, offering indirect
support of the magnetar origin of cosmological FRBs. The event rate density of
magnetar bursts is about $sim 150$ times higher than the FRB event rate
density at the energy of FRB 200428. This again suggests that, if all FRBs
originate from magnetars, only a small fraction of X-ray bursts are associated
with FRBs.

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