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تسجيل مستخدم جديدObservation of burst activity from SGR1935+2154 associated to first galactic FRB with H.E.S.S
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Fast radio bursts (FRB) are enigmatic powerful single radio pulses with durations of several milliseconds and high brightness temperatures suggesting coherent emission mechanism. For the time being a number of extragalactic FRBs have been detected in the high-frequency radio band including repeating ones. The most plausible explanation for these phenomena is magnetar hyperflares. The first observational evidence of this scenario was obtained in April 2020 when an FRB was detected from the direction of the Galactic magnetar and soft gamma repeater SGR1935+2154. The FRB was preceded with a number of soft gamma-ray bursts observed by Swift-BAT satellite, which triggered the follow-up program of the H.E.S.S. imaging atmospheric Cherenkov telescopes (IACTs). H.E.S.S. has observed SGR1935+2154 over a 2 hour window few hours prior to the FRB detection by STARE2 and CHIME. The observations overlapped with other X-ray bursts from the magnetar detected by INTEGRAL and Swift-BAT, thus providing first observations of a magnetar in a flaring state in the very-high energy domain. We present the analysis of these observations, discuss the obtained results and prospects of the H.E.S.S. follow-up program for soft gamma repeaters and anomalous X-ray pulsars.
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Very recently, an extremely bright fast radio burst (FRB) 200428 with two sub-millisecond pulses was discovered to come from the direction of the Galactic magnetar SGR 1935+2154, and an X-ray burst (XRB) counterpart was detected simultaneously. These
observations favor magnetar-based interior-driven models. In this Letter, we propose a different model for FRB 200428 associated with an XRB from SGR 1935+2154, in which a magnetar with high proper velocity encounters an asteroid of mass $sim10^{20},$g. This infalling asteroid in the stellar gravitational field is first possibly disrupted tidally into a great number of fragments at radius $sim {rm a,,few}$ times $10^{10},$cm, and then slowed around the Alfv$acute{rm e}$n radius by an ultra-strong magnetic field and in the meantime two major fragments of mass $sim 10^{17},$g that cross magnetic field lines produce two pulses of FRB 200428. The whole asteroid is eventually accreted onto the poles along magnetic field lines, impacting the stellar surface, creating a photon-e$^pm$ pair fireball trapped initially in the stellar magnetosphere, and further leading to an XRB. We show that this gravitationally-powered model can interpret all of the observed features self-consistently.
Fast radio bursts (FRBs) are short pulses observed in radio band from cosmological distances. One class of models invoke soft gamma-ray repeaters (SGRs), or magnetars, as the sources of FRBs. Some radio pulses have been observed from some magnetars,
however, no FRB-like events had been detected in association any magnetar burst, including one giant flare. Recently, a pair of FRB-like bursts (FRB 200428 hereafter) separated by milliseconds (ms) were detected from the general direction of the Galactic magnetar SGR J1935+2154. Here we report the detection of a non-thermal X-ray burst in the 1-250 keV energy band with the Insight-HXMT satellite, which we identify as emitted from SGR J1935+2154. The burst showed two hard peaks with a separation of 34 ms, broadly consistent with that of the two bursts in FRB 200428. The delay time between the double radio and X-ray peaks is about 8.57 s, fully consistent with the dispersion delay of FRB 200428. We thus identify the non-thermal X-ray burst is associated with FRB 200428 whose high energy counterpart is the two hard peaks in X-ray. Our results suggest that the non-thermal X-ray burst and FRB 200428 share the same physical origin in an explosive event from SGR J1935+2154.
We report on INTEGRAL observations of the soft $gamma$-ray repeater SGR 1935+2154 performed between 2020 April 28 and May 3. Several short bursts with fluence of $sim10^{-7}-10^{-6}$ erg cm$^{-2}$ were detected by the IBIS instrument in the 20-200 ke
V range. The burst with the hardest spectrum, discovered and localized in real time by the INTEGRAL Burst Alert System, was spatially and temporally coincident with a short and very bright radio burst detected by the CHIME and STARE2 radio telescopes at 400-800 MHz and 1.4 GHz, respectively. Its lightcurve shows three narrow peaks separated by $sim$29 ms time intervals, superimposed on a broad pulse lasting $sim$0.6 s. The brightest peak had a delay of 6.5$pm$1.0 ms with respect to the 1.4 GHz radio pulse (that coincides with the second and brightest component seen at lower frequencies). The burst spectrum, an exponentially cut-off power law with photon index $Gamma=0.7_{-0.2}^{+0.4}$ and peak energy $E_p=65pm5$ keV, is harder than those of the bursts usually observed from this and other magnetars. By the analysis of an expanding dust scattering ring seen in X-rays with the {it Neil Gehrels Swift Observatory} XRT instrument, we derived a distance of 4.4$_{-1.3}^{+2.8}$ kpc for SGR 1935+2154, independent of its possible association with the supernova remnant G57.2+0.8. At this distance, the burst 20-200 keV fluence of $(6.1pm 0.3)times10^{-7}$ erg cm$^{-2}$ corresponds to an isotropic emitted energy of $sim1.4times10^{39}$ erg. This is the first burst with a radio counterpart observed from a soft $gamma$-ray repeater and it strongly supports models based on magnetars that have been proposed for extragalactic fast radio bursts.
Owing to the detection of an extremely bright fast radio burst (FRB) 200428 associated with a hard X-ray counterpart from the magnetar soft gamma-ray repeater (SGR) 1935+2154, the distance of SGR 1935+2154 potentially hosted in the supernova remnant
(SNR) G57.2+0.8 can be revisited. Under the assumption that the SGR and the SNR are physically related, in this Letter, by investigating the dispersion measure (DM) of the FRB contributed by the foreground medium of our Galaxy and the local environments and combining with other observational constraints, we find that the distance of SGR 1935+2154 turns out to be $9.0pm2.5,$kpc and the SNR radius falls into $10$ to $18,$pc since the local DM contribution is as low as $0-18,$pc cm$^{-3}$. These results are basically consistent with the previous studies. In addition, an estimate for the Faraday rotation measure of the SGR and SNR is also carried out.
The Galactic magnetar SGR1935+2154 has been reported to produce the first known example of a bright millisecond duration radio burst (FRB 200428) similar to the cosmological population of fast radio bursts (FRBs), bolstering the association of FRBs t
o active magnetars. The detection of a coincident bright X-ray burst has revealed the first observed multi-wavelength counterpart of a FRB. However, the search for similar emission at optical wavelengths has been hampered by the high inferred extinction on the line of sight. Here, we present results from the first search for second-timescale emission from the source at near-infrared wavelengths using the Palomar Gattini-IR observing system in J-band, made possible by a recently implemented detector read-out mode that allowed for short exposure times of 0.84 s with 99.9% observing efficiency. With a total observing time of 12 hours (47728 images) on source, we place median $3,sigma$ limits on the second-timescale emission of $< 20$ mJy (13.1 AB mag). We present non-detection limits from epochs of four simultaneous X-ray bursts detected by the Insight-{it HXMT} and {it NuSTAR} telescopes during our observing campaign. The limits translate to an extinction corrected fluence limit of $< 125$ Jy ms for an estimated extinction of $A_J = 2.0$ mag. These limits provide the most stringent constraints to date on the fluence of flares at frequencies of $sim 10^{14}$ Hz, and constrain the ratio of the near-infrared (NIR) fluence to that of coincident X-ray bursts to $R_{rm NIR} < 2.5 times 10^{-2}$. Our observations were sensitive enough to easily detect a near-infrared counterpart of FRB 200428 if the NIR emission falls on the same power law as that observed across its radio to X-ray spectrum. The non-detection of NIR emission around the coincident X-ray bursts constrains the fluence index of the brightest burst to be steeper than $0.35$.
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