New technique recovers lost data from Crab Pulsar, sharpening cosmic X-ray maps
Astronomers recovered nearly all of a damaged satellite dataset using the Crab Pulsar as a natural clock, revealing clearer insights into high-energy radiation from space. The recovery method could help future space missions extract maximum value from flawed observations—important as imaging instruments become more sophisticated and costly.
Originaltitel: Refined Constraints on the Hard X-Ray Polarization of the Crab Pulsar and Nebula Derived from an Extended XL-Calibur Dataset
Abstract We present updated hard X-ray polarization measurements of the Crab pulsar and nebula obtained with the balloon-borne polarimeter XL-Calibur in the ∼19–64 keV energy range. During the flight, intermittent failure of the Global Positioning System (GPS) receiver resulted in poorly constrained timing for ∼38% of the Crab dataset. By implementing a new phase recovery method that reconstructs timing during extended GPS-off intervals, phase tag data are recovered for ∼95% of the GPS-off dataset, increasing the precision of the phase-resolved analysis. Phase information for the data is recovered by using the Crab pulsar, with its 33 ms period, as an external timing source. Using a Markov Chain Monte Carlo framework to jointly fit phase offsets and frequency derivatives, sufficient phase accuracy is achieved across multiple periods without GPS for a phase-resolved analysis. This enables inclusion of nearly the full dataset in the polarization study. The polarization degree of the nebular emission is found to be (27.7 ± 4.9)% at a polarization angle of 127 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover> <mml:mrow> <mml:mo>.</mml:mo> </mml:mrow> <mml:mrow> <mml:mtext>°</mml:mtext> </mml:mrow> </mml:mover> </mml:math> 2 ± 5 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover> <mml:mrow> <mml:mo>.</mml:mo> </mml:mrow> <mml:mrow> <mml:mtext>°</mml:mtext> </mml:mrow> </mml:mover> </mml:math> 1, confirming previous XL-Calibur results and remaining aligned with the Crab’s spin axis, consistent with synchrotron emission from the inner nebula. Phase-resolved measurements show that the off-pulse and bridge intervals exhibit a strong polarization, while the pulsar peaks, although weakly constrained, remain in agreement with the softer-energy trends of IXPE. These findings reinforce a scenario in which hard X-ray emission arises primarily in the nebular torus and wind regions. The successful recovery of precise phase tagging from GPS-off data demonstrates the capacity to use the pulsar as an external clock even in the case of sparsely populated data.