Gamma-Ray Polarimetry of the Crab Pulsar Observed by POLAR

Abstract

The X/$\gamma$ ray polarimetry of the Crab pulsar/nebula is believed to hold crucial information on their emission models. In the past, several missions have shown evidence of polarized emission from the Crab. The significance of these measurements remains however limited. New measurements are therefore required. POLAR is a wide Field of View Compton-scattering polarimeter (sensitive in 50-500 keV) onboard the Chinese spacelab Tiangong-2 which took data from September 2016 to April 2017. Although not designed to perform polarization measurements of pulsars, we present here a novel method which can be applied to POLAR as well as that of other wide Field of View polarimeters. The novel polarimetric joint-fitting method for the Crab pulsar observations with POLAR, allows us to obtain constraining measurements of the pulsar component. The best fitted values and corresponding 1$\sigma$ deviations for the averaged phase interval: (PD=$14\begin{array}{c}+15\\ -10\end{array}$\%, PA=$108{\begin{array}{c}+33\\ -54\end{array}}^{\circ }$), for Peak 1: (PD=$17\begin{array}{c}+18\\ -12\end{array}$\%, PA=$174{\begin{array}{c}+39\\ -36\end{array}}^{\circ }$) and for Peak 2: (PD=$16\begin{array}{c}+16\\ -11\end{array}$\%, PA=$78{\begin{array}{c}+39\\ -30\end{array}}^{\circ }$). Further more, the 3$\sigma$ upper limits on the polarization degree are for the averaged phase interval (55\%), Peak 1 (66\%) and Peak 2 (57\%). Finally, to illustrate the capabilities of this method in the future, we simulated two years observation to the Crab pulsar with POLAR-2. The results show that POLAR-2 is able to confirm the emission to be polarized with $5\sigma$ and $4\sigma$ confidence level if the Crab pulsar is polarized at $20\%$ and $10\%$ respectively.

14 pages, 18 figures, 2 tables; accepted for publication in MNRAS

References in corpus (12)

• Polarization of the Crab pulsar and nebula as observed by the Integral/IBIS telescope
• POLAR, a compact detector for Gamma Ray Bursts photon polarization measurements
• Optical polarisation of the Crab pulsar: precision measurements and comparison to the radio emission
• Detailed polarization measurements of the prompt emission of five Gamma-Ray Bursts
• Re-detection and a Possible Time Variation of Soft X-ray Polarisation from the Crab
• The POLAR Gamma-Ray Burst Polarization Catalog
• Outer-gap vs. Slot-gap Models for Pulsar High Energy Emissions: The Case of the Crab Pulsar
• Design and construction of the POLAR detector
• The annular gap model for gamma-ray emission from young and millisecond pulsars
• Instrument Performance and Simulation Verification of the POLAR Detector
• POLAR-2: a large scale gamma-ray polarimeter for GRBs
• Phase-resolved gamma-ray spectroscopy of the Crab pulsar observed by POLAR

Cited by in corpus (4)

• Response of the first POLAR-2 Prototype to Polarized Beams
• Gamma-Ray Polarimetry
• Crab Pulsar: IXPE Observations Reveal Unified Polarization Properties Across Optical and Soft X-Ray Bands
• Performance of the X-Calibur Hard X-Ray Polarimetry Mission during its 2018/19 Long-Duration Balloon Flight