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X-ray/Radio Correlation of Crab Pulsar Giant Pulses

Submitter: Vlad Kondratiev
Description: The Crab Nebula is one of the most well-known and probably most studied astrophysical objects in our Galaxy. The remnant of a supernova explosion in 1054 AD, it was the first (after the Sun) identified source of X-ray emission and synchrotron optical emission. The nebula hosts the youngest pulsar B0531+21, a.k.a. the "Crab Pulsar", the continuous source of high-energy relativistic particles that makes the nebula shine. The Crab Pulsar was discovered owing to its extremely bright pulses, so-called "giant pulses" (GPs), an almost unique form of radio emission that only a few other radio pulsars have been shown to emit.

Are the energetic radio pulses from PSR B0531+21 and its X-ray photons related to the same physical emission mechanism? The radio and X-ray profiles are aligned quite well with each other (right plot), though the peak of the radio profile lags the X-ray profile by about 0.3 ms. This may indicate the same, or very nearby, emission regions in the pulsar magnetosphere. To search for correlations between the radio and X-ray emission, we have carried out simultaneous 5.4 hr observations between the Green Bank Telescope at 1.5 GHz and the Chandra X-ray Observatory. Our results and detailed analysis have been recently published in this ApJ paper. We did not find any apparent correlation between radio GPs and X-ray photons. Derived limits on the change of X-ray flux during the periods with radio GPs lie within 2σ fluctuations of the X-ray flux around simulated pulses with random arrival times. This result rules out strong correlation between radio giant pulses and non-thermal X-ray emission and suggests increased plasma coherence as being the origin of GPs.

On the left is the central part of the Chandra image of the Crab Nebula made with the HRC-S (High Resolution Camera - Spectroscopy). Photon extraction regions are shown for pulsar (red) and background (black) for both pulsar region (circles, 0th order spectrum) and dispersed spectra of higher orders (rectangles). Right plot shows the phase distribution of the extracted X-ray photons (magenta) and the average radio profile (green).
Copyright: Bilous, McLaughlin, Kondratiev, & Ransom, 2012, ApJ, 749, 24
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