Astrophys. J., 889, 160-160 (2020/February-1)
Two new outbursts and transient hard X-rays from 1E 1048.1-5937.
ARCHIBALD R.F., SCHOLZ P., KASPI V.M., TENDULKAR S.P. and BEARDMORE A.P.
Abstract (from CDS):
Since its discovery, 1E 1048.1-5937 has been one of the most active magnetars, both in terms of radiative outbursts, and changes to its spin properties. Here we report on a continuing monitoring campaign with the Neil Gehrels Swift Observatory X-ray Telescope in which we observe two new outbursts from this source. The first outburst occurred in 2016 July, and the second in 2017 December, reaching peak 0.5-10 keV absorbed fluxes of 3.2–0.3+0.2×10–11 erg s–1 cm–2 and 2.2–0.2+0.2×10–11 erg s–1 cm–2, respectively, factors of ∼5 and ∼4 above the quiescent flux. Both new outbursts were accompanied by spin-up glitches with amplitudes of Δν=4.47(6)×10–7 Hz and Δν=4.32(5)×10–7 Hz, respectively. Following the 2016 July outburst, we observe, as for past outbursts, a period of delayed torque fluctuations, which reach a peak spin-down of 1.73 ± 0.01 times the quiescent rate, and which dominates the spin evolution compared to the spin-up glitches. We also report an observation near the peak of the first of these outbursts with NuSTAR in which hard X-ray emission is detected from the source. This emission is well characterized by an absorbed blackbody plus a broken power law, with a power-law index above 13.4 ± 0.6 keV of 0.5–0.2+0.3, similar to those observed in both persistent and transient magnetars. The hard X-ray results are broadly consistent with models of electron/positron cooling in twisted magnetic field bundles in the outer magnetosphere. However, the repeated outbursts and associated torque fluctuations in this source remain puzzling.
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Neutron stars - Magnetars - Pulsars - Compact objects - X-ray astronomy - X-ray transient sources - Transient sources
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