Observation of polarized hard X-ray emission from the Crab by the PoGOLite Pathfinder

Abstract

We have measured the linear polarisation of hard X-ray emission from the Crab in a previously unexplored energy interval, 20-120 keV. The introduction of two new observational parameters, the polarisation fraction and angle stands to disentangle geometrical and physical effects, thereby providing information on the pulsar wind geometry and magnetic field environment. Measurements are conducted using the PoGOLite Pathfinder -a balloon-borne polarimeter. Polarisation is determined by measuring the azimuthal Compton scattering angle of incident X-rays in an array of plastic scintillators housed in an anticoincidence well. The polarimetric response has been characterised prior to flight using both polarised and unpolarised calibration sources. We address possible systematic effects through observations of a background field. The measured polarisation fraction for the integrated Crab light-curve is (18.4 +9.8 −10.6 )%, corresponding to an upper limit (99% credibility) of 42.4%, for a polarisation angle of (149.2 ± 16.0)• .

Calibration and performance studies of the balloon-borne hard X-ray polarimeter PoGO+

“…Using this factor, the simulated modulation factor for the Crab M Crab,sim = (44.19 ± 0.12)% can be converted to an expected value of M Crab = (41.75 ± 0.85)%. This is a significant improvement over the PoGOLite Pathfinder where M Crab = (21.4 ± 1.5)% [12]. Figure 9 shows the simulated energy dependence of M 100 .…”

Origin of Terrestrial Bioorganic Homochirality and Symmetry Breaking in the Universe

“…In fact, high-energy polarized photons have been observed in the X-ray to gamma-ray region. In this high photon energy region, linearly polarized X-rays, which are principally generated by synchrotron radiation (SR) from relativistic kinetic electrons captured by the strong magnetic fields around neutron stars in supernova remnant, have been observed emanating from the Crab Nebula [19][20][21]. Gamma-ray bursts (GRBs) from supernova explosion areas have been successfully observed with highly linear polarization (up to 70-80%) by the ICAROS/GAP satellite project [22].…”

Optimising a balloon-borne polarimeter in the hard X-ray domain: From the PoGOLite Pathfinder to PoGO+

“…The aforementioned MDP of 17.6% for 6 hours of Crab observation is therefore achieved after a two-day flight. The MDP for Cygnus X-1 (black squares) is calculated assuming that the source is in the high state 6 and an observation window of 10 hours per day (Cygnus X-1 is higher in the sky than the Crab as seen from Esrange during the Summer). Both the Crab and Cygnus X-1 are simulated using their respective average column density from the 2013 flight elevation and altitude profiles.…”

“…Measuring the linear polarisation of X-ray emissions from astrophysical sources gives unique insight into the emission mechanisms at work and the geometry of the emitting region [1,2]. Due to the difficulties in making sensitive measurements in this energy domain, only a few instruments have been able to successfully detect polarisation [3,4,5,6]. The delicate control of systematic effects benefits from instruments specifically designed for polarimetric measurements.…”

“…For the Crab an observation window of 6 hours is assumed, for Cygnus X-1, 10 hours. The PoGOLite Pathfinder performance for the Crab (red triangles) is shown as a comparison and the red star shows the MDP for the Crab as observed during the 2013 flight[6].…”