Pulsars, transients and relativistic astrophysics

Abstract:

We present an extremely simple derivation of the general relativistic periastron advance for Schwarzschild geometry. The method lends itself to iteration, and so in principle may achieve an arbitrary level of accuracy with relative ease. Our technique involves no analysis of differential equations beyond that of a simple harmonic oscillator. The practical utility of the calculation is limited by its neglect of frame-dragging rotational effects.

Abstract:

We present deep optical and near-infrared observations of the host galaxies of 34 fast radio bursts (FRBs) detected by the Commensal Real-time ASKAP Fast Transient (or CRAFT) survey on the Australian SKA Pathfinder (ASKAP) to compare the locations of FRBs relative to their host light distributions. Incorporating three additional FRBs from the literature, for a total of four repeating and 33 apparently nonrepeating FRBs, we determine their projected galactocentric offsets and find a median of 4.2−2.5+5.7 kpc ( 1.0−0.6+1.5re ). We model their host surface-brightness profiles and develop synthetic spatial distributions of their globular clusters (GCs) based on host properties. We calculate the likelihood the observed location of each FRB is consistent with the smooth light of its host galaxy, residual (primarily spiral) substructure, or GC distributions. The majority of FRBs favor locations within the disks of their galaxies, while only 11% ± 5% favor a GC origin, primarily those with galactocentric offsets ≳3re. At z < 0.15, where spiral structure is apparent in 86% of our sample of FRB hosts, we find ≈20%–46% of FRBs favor an association with spiral arms. Assuming FRBs derive from magnetars, our results support multiple formation channels, with the majority of progenitors associated with massive stars and a minority formed through dynamical channels. However, the moderate fraction of FRBs associated with spiral structure indicates that high star formation efficiency of the youngest and most massive stars is not a predominant driver in the production of FRB progenitors.

Abstract:

In this paper we present the science potential of the enhanced X-ray Timing and Polarimetry (eXTP) mission, in its new configuration, for studies of strongly magnetized compact objects. We discuss the scientific potential of eXTP for quantum electrodynamic (QED) studies, especially leveraging the recent observations made with the NASA IXPE mission. Given eXTP’s unique combination of timing, spectroscopy, and polarimetry, we focus on the perspectives for physics and astrophysics studies of strongly magnetized compact objects, such as magnetars and accreting X-ray pulsars. Developed by an international Consortium led by the Institute of High Energy Physics of the Chinese Academy of Sciences, the eXTP mission is expected to launch in early 2030.

Abstract:

We study three extraordinarily bright X-ray flares originating from Cyg X-1 seen on July 10, 2023, detected with INTEGRAL. The flares had a duration on the order of only ten minutes each, and within seconds reached a 1–100 keV peak luminosity of 1.1 − 2.6 × 10 38  erg s −1 . The associated INTEGRAL/IBIS count rate was approximately ten times higher than usual for the hard state. To our knowledge, this is the first time that such strong flaring has been seen in Cyg X-1, despite the more than 21 years of INTEGRAL monitoring – with almost ∼20 Ms of exposure – and the similarly deep monitoring with RXTE/PCA from 1997 to 2012. The flares were seen in all three X-ray and γ -ray instruments of INTEGRAL. Radio monitoring by the AMI Large Array with observations 6 h before and 40 h after the X-ray flares did not detect a corresponding increase in radio flux. The shape of the X-ray spectrum shows only marginal change during the flares, i.e., photon index and cut-off energy are largely preserved. The overall flaring behavior points toward a sudden and brief release of energy either due to the ejection of material in an unstable jet or due to the interaction of the jet with the ambient clumpy stellar wind.