arXiv subjects

Julia Speicher

Publications and source records attributed to Julia Speicher.

3 recordsLinked to original sources

arXiv2026

Joint XMM-Newton and NuSTAR Observations of Type I X-ray Bursts from the Dipping Low-Mass X-ray Binary 4U 1323-62

In this study, we report partly simultaneous XMM-Newton and NuSTAR observations of the bursting, dipping low mass X-ray binary, 4U 1323-62 obtained in 2024. 4U 1323-62 is one of the well-known persistent bursters, with bursts occurring roughly every three hours. It is also one of the few sources for which the orbital period is known, and shows dips in X-rays. In this paper, we report the detection of 12 unique bursts with XMM-Newton and NuSTAR, 6 of them observed jointly. We detected two double burst events, one with the NuSTAR and another one observed with both missions. During our observations we detected 10 X-ray dips with a periodicity of 2.942 hours, in line with previous measurements. We also present the results of the time resolved X-ray spectral analysis of the bursts and show the limits on the cooling of the corona heated by the burst emission. We also found a $0.898+/- 0.017 Hz quasi-periodic oscillation (QPO) during the non-bursting and non-dipping times confirming previous detections.

astro-ph.HE↗

arXiv2025

The 2020 Superburst of 4U 1608-522 and its impact on the accretion disk

Superbursts are rare events observed from bursting neutron star low mass X-ray binaries. They are thought to originate from unstable burning of the thick layer of Carbon on the surface of the neutron star, causing the observed X-ray flashes to last several hours. Given their fluence it has long been thought that superbursts may have significant effects on the accretion flow around the neutron star. In this paper, we first present evidence for a new superburst observed from 4U 1608-522 by MAXI during the 2020 outburst, around 00:45 UTC on 16 July 2020. We compare some of the properties of this superburst and the underlying outburst with the events recorded on May 5 2005 by RXTE and most recently in 2025 by MAXI. We then present our spectral analysis of NICER and Insight-HXMT data obtained before and after the 2020 superburst event. Our results indicate that the inner disk temperature and the radius show a systematic evolution in the following few days, which may be related to the superburst. We show that the timescale of the observed evolution can not be governed by viscous timescales unless the viscosity parameter is unrealistically low.

astro-ph.HE↗

arXiv2021

Cosmic Ray transport in mixed magnetic fields and their role on the observed anisotropies

There is a growing set of observational data demonstrating that cosmic rays exhibit small-scale anisotropies (5-30 deg) with amplitude deviations lying between 0.01-0.1 percent that of the average cosmic ray flux. A broad range of models have been proposed to explain these anisotropies ranging from finite-scale magnetic field structures to dark matter annihilation. The standard diffusion transport methods used in cosmic ray propagation do not capture the transport physics in a medium with finite-scale or coherent magnetic field structures. Here, we present a Monte Carlo transport method, applying it to a series of finite-scale magnetic field structures to determine the requirements of such fields in explaining the observed cosmic ray,small-scale anisotropies.

astro-ph.HE↗