Giant Radio Pulses from the Crab Pulsar

Individual giant radio pulses (GRPs) from the Crab pulsar last only a few microseconds. However, during that time they rank among the brightest objects in the radio sky reaching peak flux densities of up to 1500 Jy even at high radio frequencies. Our observations show that GRPs can be found in all phases of ordinary radio emission including the two high frequency components (HFCs) visible only between 5 and 9 GHz (Moffett & Hankins 1996). This leads us to believe that there is no difference in the emission mechanism of the main pulse (MP), inter pulse (IP) and HFCs. High resolution dynamic spectra from our recent observations of giant pulses at the MPIfR 100-m radio telescope in Effelsberg at a centre frequency of 8.35 GHz show distinct spectral maxima within our observational bandwidth of 500 MHz for individual pulses. The higher frequencies around 8.6 GHz appear to be brighter than the lower 8.1 GHz part. Sometimes one observes two or three peaks following each other within a few 100 μs. There is evidence for spectral evolution within and between sub-pulses. High frequency features appear earlier than low frequency ones. Strong plasma turbulence appears to be a feasible mechanism for the creation of the high energy densities of ∼ 6.7× 10 erg cm and brightness temperatures of ∼ 10 K. Subject headings: pulsars – PSR B0531+21 – Crab pulsar – giant radio pulses 1. Observational Techniques Observations with the Effelsberg 100-m radio telescope began on 25 November 2003 and ended on the 28 November 2003. We used a secondary focus cooled HEMT receiver with a centre frequency of 8.35 GHz, providing two circularly polarised IF signals with a system temperature of 25 K on both channels. Together with the contribution of the part of the Crab nebula within the telescope beam, being on the level of 33 K, and with the sky temperature of ca 8 K we had an effective temperature of 70 K. Two detection systems were used. First a polarimeter with 1.1 GHz bandwidth detected total power of the left-hand and right-hand circularly polarised signals (LHC and RHC respectively) as well as cos∠( LHC,RHC) and sin∠( LHC,RHC). These four signals were then recorded by the standard Effelsberg Pulsar Observation System (EPOS). With the Crab pulsar’s dispersion measure of 56.8 pc cm we had an un–dedispersed time resolution of tsample = 740 μs. EPOS was therefore set to continuously record data blocks containing 20 periods divided into 1020 phase bins for all four signals (Fig. 1).