The Crab pulsar experienced a major flare in 2010 as observed by Fermi LAT. Observations by the Hubble Space Telescope indicate that the flare was accompanied by a structural change in the anvil region of the Crab Nebula. In the framework of a photometric analysis we reconstruct the energetics of this event. Reconnection zones near the light cylinder are expected to release energy by accelerating beams of electrons, leading to flares of varying amplitude. In this case the major flare would have reduced the magnetic energy stored in the reconnection zones, and would thus have had an impact on the properties of the giant radio flares presumably originating from these regions. We test this scenario by observing giant radio pulses with the Westerbork Synthesis Radio Telescope.
Providing apparently the central driving mechanism of the Crab Nebula makes the Crab pulsar a unique object among other pulsars. Being detected for the first time during balloon measurements of the Crab Nebula at hard X-rays ( [1]), it is the only pulsar known so far with a pulsed emission profile which prevails throughout the whole electromagnetic spectrum from radio to GeV energies ( [2]). The profile contains several components known as precursor, main pulse (P1), interpulse (P2) and the high frequency components HFC 1, HFC 2 among others. Although the precursor and both high frequency components are visible just at a certain wavelength range, P1 and P2 prevail from radio to gamma wavelengths. Apart from its regular pulse structure the Crab pulsar is also a powerful emitter of giant radio pulses (GPs). These pulses distinguish themselves by several characteristics which will be briefly summarized here. Since the detection of the Crab pulsar at radio wavelengths by its GPs ( [3]), several properties have been observed like flux densities higher by at least thousand times than regular pulses. Furthermore their widths are smaller in contrast with regular pulses. They vary from several microseconds down to 2 nanoseconds ( [4]) while the shortest ones have been observed to have the highest flux densities. Being observed at a frequency range from 23 MHz ( [5]) till 15.1 GHz ( [6], [7]) reveals GPs apparently as a broadband phenomenon. They have been observed mainly at the phases of P1 and P2 overlapped with regular pulses although they are apparently non-periodical (one GPs occuring every 0.803 seconds according to [8]), However, there seem to be differences in the phases at which they occur since they were detected at the phases of HFC 1 and HFC 2 ([6], [9]), but not at the precursor for instance. Deducing from this they are apparently phase-bounded. The characteristics of GPs have been studies largely by [10] who observed Crab radio GPs also at γ wavelengths. According to this study Crab GPs represent single events and follow Poisson statistics. A comparison of the arrival times of both regular pulses and GPs gives indicates no difference between the arrival times of both which on the other hand suggests the same location of formation. Simultaneous radio and optical observations of Crab GPs reveal by [11] an increase of the optical flux during occuring radio GPs by 3 %. Hence the emission mechanism which causes GPs is apparently noncoherent since it emits throughout different parts of the electromagnetic spectrum. Differences between GPs occuring at the phases of P1 and P2 were discovered by [12] resulting from observations with the Arecibo radio telescope above 4 GHz. They determined different dynamic spectra for GPs occuring at P1 in contrast with the ones detected at the phase of P2. While Giant main pulses (GMPs) consist in their substructure of narrow-band nanopulses, Giant interpulses (GIPs) reveal narrow emission bands of microsecond duration. These results indicate probable different emission mechanisms for the main and the interpulses and question current pulsar emission theories. Theoretical aspects of radio GPs have been broadely discussed ( [13], [14], [4], [15]). The current only model basing on observational data is the Lyutikov model ( [16]) which can reproduce the emission bands of the GIPs at frequencies above 4 GHz. Whereas regular pulses are thought to develop on open magnetic field lines, the Lyutikov model emanates from a higher particle density in contrast with the Goldreich-Julian standard model. GPs are produced near the last closed magnetic field line via magnetic reconnection events through which a high energy Lorentz beam is produced. The latter moves along the closed field line and dissipates via curvature radiation. Thus it also predicts the occurence of γ-ray emission during the emission of radio GPs. Although several other pulsars apart from the Crab have been found to emit GPs ( [17]), a uniform emission mechanism for radio GPs has not been found yet. Searching for a possible origin of this rather exotic form of pulsar emission, we examined the optical emission resulting from the Crab flare 2010 with a photometrical analysis of three exposures made by the Hubble Space Telescope (HST). The central motivation for this analysis was an estimation of the synchrotron power of the so called anvil region located approximately 5 arcseconds from the pulsar (see Figure 1) in which an increase of brightness was detected after the flare detected by AGILE in September 2010.
If we assume that the Crab Nebula is powered solely by the pulsar, it is interesting to ask if the latter also contributes energetically to the reappearing flares detected from the Crab Nebula. We test this idea with GPs observed after the Crab flare in September 2010, to test if their properties are affected by the flare.
We examined three exposures from the archive of the Hubble Space Telescope[26] made in combinatio
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