The Magnificent Seven X-ray Isolated Neutron Stars Revisited. I. Improved Timing Solutions and Pulse Profile Analysis

TL;DR

This study provides improved timing solutions and detailed pulse profile analysis for the Magnificent Seven neutron stars, revealing diverse behaviors and complex surface emission patterns that challenge simple models.

Contribution

It offers the first firm measurement of spin-down for RX J2143.0+0654 and extends timing ephemerides for all six stars, uncovering complex pulse morphologies and energy-dependent features.

Findings

Five stars show steady spin-down without anomalies.

Detection of a second spin derivative in RX J0720.4-3125.

Complex pulse profiles suggest multi-temperature surfaces and anisotropic emission.

Abstract

We present the first systematic X-ray pulse timing analysis of the six members of the so-called "Magnificent Seven" nearby thermally-emitting isolated neutron stars (XINS) with detected pulsations. Using the extensive collection of archival XMM-Newton, Chandra, and NICER observations spanning over two decades, we obtain the first firm measurement of the spin-down rate for RX J2143.0+0654, while for the rest we improve upon previously published spin ephemerides and extend them by up to an additional decade. Five of the XINS follow steady spin-down with no indication of major anomalies in their long-term timing behavior; the notable exception is RX J0720.4-3125, for which, in addition to confirming the previously identified glitch, we detect a second spin derivative. The high quality folded X-ray pulse profiles produced with the updated timing solutions exhibit diverse and complex morphologies, as well as striking energy dependence. These peculiarities cannot be readily explained by blackbody-like isotropic emission and simple hot spot configurations, hinting at the presence of complex multi-temperature surface heat distributions and highly anisotropic radiation patterns, such as may arise from a strongly magnetized atmospheric layer.