GECAM discovery of the second FRB-associated Magnetar X-ray Burst from SGR J1935+2154

TL;DR

The paper reports the discovery of MXB 221014, the second magnetar X-ray burst from SGR J1935+2154 associated with a Fast Radio Burst (FRB 221014) detected by CHIME (and GBT), using data from GECAM-B and GECAM-C. Temporal analysis reveals a narrow X-ray pulse (P2) that aligns with the FRB main pulse with a delay of about $\Delta t \approx 5.7\ \mathrm{ms}$, and a possible second alignment (P3) with a weaker radio component; the burst shows no significant $f_{\mathrm{QPO}}\sim40$ Hz feature. Spectral fitting favors a single non-thermal CPL model with $E_{\mathrm{peak}}\approx30\ \mathrm{keV}$ and $E_{\mathrm{iso}}\approx7.35\times10^{39}\ \mathrm{erg}$ at $D\approx9\ \mathrm{kpc}$, with thermal components constrained to upper limits, suggesting a relatively compact fireball. The event is compared with the first MXB-FRB case (MXB 200428), revealing both shared traits (narrow X-ray/pulse alignment) and important differences (timing and QPO behavior), thereby tightening constraints on FRB-magnetar models and highlighting the diversity of MXB-FRB morphologies.

Abstract

Fast radio burst (FRB) is mysterious phenomenon with millisecond-duration radio pulses observed mostly from cosmological distance. The association between FRB 200428 and a magnetar X-ray burst (MXB) from SGR J1935+2154 has significantly advanced the understanding of FRB and magnetar bursts. However, it is uncertain whether this association between MXB and FRB (i.e. MXB/FRB 200428) is genuine or just coincidental only based on this single event. Here we report the discovery of a bright ($\rm\sim7.6\times10^{-7}\,erg \cdot cm^{-2}$ in 1-250 keV) magnetar X-ray burst detected by GECAM on October 14th, 2022 (dubbed as MXB 221014) from SGR J1935+2154, which is associated with a FRB detected by CHIME and GBT. We conducted a detailed temporal and spectral analysis of MXB 221014 with GECAM data and find that it is a bright and typical ($T_{90}\sim$250 ms) X-ray burst from this magnetar. Interestingly, we find two narrow X-ray pulses in the MXB, one of which temporally aligns with the main pulse of the FRB 221014 $\sim5.70$ ms latter than the peak time of FRB 221014), resembling the feature found in MXB/FRB 200428. Furthermore, we did comprehensive comparison between MXB/FRB 221014 and MXB/FRB 200428, and find that while the two events share several common features, they also exhibit distinct differences, highlighting the variety of the MXB-FRB association morphology. This finding not only confirms the association between MXB and FRB but also provides new insights into the mechanism of and the relationship between FRB and MXB.

Figures (4)

• Figure 1: The temporal analysis result of MXB 221014 and FRB 221014. (a), lightcurve of MXB 221014 in different energy range. The dashed line represents the peak time of FRB 221014 CHIME_221014_arxiv. A spike coincided with FRB 221014 can be clearly seen at higher energy range. The inset figures are the lightcurve in the unit of counts rate for the same energy range, but with a higher time resolution. (b), comparison between MXB/FRB 221014 and MXB/FRB 200428. The $T_0$ of MXB/FRB 200428 is 2020-04-28T14:34:24.42650 (geocentric time) while the $T_0$ of MXB/FRB 221014 is 2022-10-14T19:21:39.100. The red dashed lines in top panels are peak time of the two pulse of FRB 200428 CHIME_200428. The lightcurve of MXB 200428 is replotted from HXMT_0428_re. Both the lightcurve of MXB 200428 and MXB 221014 are not background subtracted in this subfigure. The red dashed lines in bottom panel is the peak time of FRB 221014 CHIME_221014_arxiv. Both MXB/FRB 221014 and MXB/FRB 200428 exhibit alignment of narrow pulses, although the narrow x-ray pulses and radio pulses occur during the weak tail region of MXB 221014, while they are around the bright peak region of the MXB 200428. (c), fitting of the lightcurve of MXB 221014. The lightcurve of MXB 221014 is combined all the data from GECAM-B and GECAM-C with time aligned. The top panel is the fitting result by four Gaussian function while the bottom panel is the residual. The cyan line is the result of the superposition of the four Gaussian function. Two blue lines are broad pulses with no-radio association and two red lines are narrow pulses. The first narrow X-ray pulse (P2) well coincides with the bright main pulse of FRB 221014, while the second narrow X-ray pulse (P3) also aligns with a possible weak radio pulse in CHIME ligutcurve CHIME_221014_arxiv. (d), the soft X-ray pulse profiles of SGR J1935+2154 obtained with the NICER data before FRB 221014 and the location of MXB 221014 in the soft X-ray pulse profiles, which is roughly aligns with the valley. All the lightcurves are aligned in Barycentric Dynamical Time.
• Figure 2: The spectra and residual of MXB 221014 by utilizing the data from GECAM-B and GECAM-C. (a), the spectra are best fitted with the CPL model in the energy band of 15–300 keV from T$_0$-0.11 s to T$_0$+0.12 s. (b), the map of $\Delta$BIC for CPL+BB with different parameters of thermal component. The thermal component with parameters in left bottom region are reasonable for MXB 221014.
• Figure 3: The comparison of spectral properties of MXB 221014 with other MXB from SGR J1935+2154. (a), the position of MXB 221014 and MXB 200428 in the $\alpha-E_{peak}$ diagram, indicating MXB 221014 drawn from the same population as the other X-ray bursts from SGR J1935+2154. (b), the fluence of MXBs from SGR J1935+2154 compared with burst sample. The position of the two MXBs associated with FRB, ie. MXB 221014 and MXB 200428 are marked as red solid line and black dashed line.
• Figure 4: Distribution of the number of X-ray burst from SGR J1935+J2154 in different activate episode with FRB-associated-MXB. (a), the activate episode in 2020 April. (b), the activate episode in 2022 October. The top panels are X-ray burst number detected by GECAM-B, GECAM-C, Fermi/GBM and Insight-HXMT in each hour. The bottom panels are cumulative distribution. During the time period covered in gray, there was no radio monitoring of SGR J1935+2154 by CHIME due to block of Earth.