X-Ray Burst and Persistent Emission Properties of the Magnetar SGR 1830-0645 in Outburst

Abstract

We report on NICER X-ray monitoring of the magnetar SGR 1830−0645 covering 223 days following its 2020 October outburst, as well as Chandra and radio observations. We present the most accurate spin ephemerides of the source so far: ν = 0.096008680(2) Hz, ν ̇ = − 6.2 ( 1 ) × 10 − 14 Hz s−1, and significant second and third frequency derivative terms indicative of nonnegligible timing noise. The phase-averaged 0.8–7 keV spectrum is well fit with a double-blackbody (BB) model throughout the campaign. The BB temperatures remain constant at 0.46 and 1.2 keV. The areas and flux of each component decreased by a factor of 6, initially through a steep decay trend lasting about 46 days, followed by a shallow long-term one. The pulse shape in the same energy range is initially complex, exhibiting three distinct peaks, yet with clear continuous evolution throughout the outburst toward a simpler, single-pulse shape. The rms pulsed fraction is high and increases from about 40% to 50%. We find no dependence of pulse shape or fraction on energy. These results suggest that multiple hot spots, possibly possessing temperature gradients, emerged at outburst onset and shrank as the outburst decayed. We detect 84 faint bursts with NICER, having a strong preference for occurring close to the surface emission pulse maximum—the first time this phenomenon is detected in such a large burst sample. This likely implies a very low altitude for the burst emission region and a triggering mechanism connected to the surface active zone. Finally, our radio observations at several epochs and multiple frequencies reveal no evidence of pulsed or burst-like radio emission.

The 2022 High-energy Outburst and Radio Disappearing Act of the Magnetar 1E 1547.0–5408

“…Typically, the rate of hard X-ray bursts from an active magnetar is maximal at the start of an outburst, declining thereafter. This behavior is observed during burst storms, e.g., 1E 2259+596 ) and SGR 1935+2154 (Younes et al 2020), as well as over the course of weeks following the magnetar outburst onset, e.g., SGR 1830−0645 (Younes et al 2022a) and Swift J1818.0−1607 (Hu et al 2020). Hence, if the outburst indeed began at the time of the radio nondetection, more bursts should be detected from the direction of 1E 1547.0 −5408 by Fermi-GBM during the 20 day interval.…”

“…Generally, pulsed radio emission from magnetars is closely linked to the outburst mechanism: it switches on following the onset of an outburst before gradually fading into radio silence as the neutron star settles into X-ray quiescence (e.g., Camilo et al 2016;Scholz et al 2017; but see Zhu et al 2020;Younes et al 2023). Unlike other radio-loud magnetars, persistent radio pulses have been detected from 1E 1547.0−5408 since the quasi-stabilization of its X-ray flux to the current high state in ∼2013 (Coti Zelati et al 2020;F.…”

The 2022 high-energy outburst and radio disappearing act of the magnetar 1E 1547.0-5408

“…Typically, the rate of hard X-ray bursts from an active magnetar is maximal at the start of an outburst, declining thereafter. This behavior is observed during burst storms, e.g., 1E 2259+596 ), SGR 1935+2154 (Younes et al 2020, as well as over the course of weeks following the magnetar outburst onset, e.g., SGR 1830−0645 (Younes et al 2022b), Swift J1818.0−1607 (Hu et al 2020). Hence, if the outburst indeed began at the time of the radio nondetection, more bursts should be detected from the direction of 1E 1547.0−5408 by Fermi-GBM during the 20 day interval.…”

Advancing the Landscape of Multimessenger Science in the Next Decade

“…Both giant flares and short bursts exhibit as impulsive events transpiring on timescales much less than a second. Recent observations favor a very low altitude origin for both short bursts and giant flares, one that involves the neutron star crust such that these events can excite global seismic oscillations [e.g., [530][531][532][533][534][535][536]. If neutron star f-modes are excited in these bursts [537][538][539], third generational gravitational detectors observations of the nearby universe will attain highly constraining levels for magnetar models [540].…”