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Infrared and Optical Measurements of the Crab Pulsar NP 0532

1969; IOP Publishing; Volume: 156; Linguagem: Inglês

10.1086/180361

1538-4357

G. Neugebauer, E. E. Becklin, J. Kristian, Robert B. Leighton, Grant Snellen, J. A. Westphal,

Gamma-ray bursts and supernovae

Observations of the pulsating component of NP 0532 at 2.2 and 1.65 µ are given.The energy density per pulse at 2.2 µ is (3.2 ± 0.4) X 10-3 1 J m-2 Hz-1 and forms a smooth continuation of the visual data.Shortly after the radio pulsar NP 0532 in the Crab Nebula was identified with an optical object by Cocke, Disney, and Taylor (1969), the absolute spectral-energy distribution was measured by Oke (1969) between the wavelengths of 0.34 and 0.83 µand was found to be relatively flat.The average energy density in the main pulse was approximately 1.5 X 10-30 J m-2 Hz-1 • Oke's measurements were made on three nights; although the intensity varied by 0.5 mag, the spectral shape remained unchanged.Comella et al. (1969) have measured the energy density in the pulse at 150 cm and find it higher than that in the optical by a factor of approximately 10 3 • They also find a spectral index a (f, a: v-a) of +2; this slope is consistent with an upper limit of 7 X 10-29 J m-1 Hz-1 placed on the energy in the pulse at 13 cm by Ekers and Moffet (1969).This Letter describes measurements of the pulsar at 2.2, 1.65, and 0.55 µ.Although the results are preliminary, the current interest in the energy distribution of pulsars seems to warrant publication at this time. OBSERVATIONSThe observations of NP 0532 were made between 1900 and 2015 P.S.T. on March 14, 1969, using the infrared photometer described by Becklin and Neugebauer (1968), at the Cassegrain focus of the 200-inch Hale telescope with a focal-plane aperture 7 1 : 5 in diameter.The output of the PbS detector was a.c.amplified and analyzed with a 1024-channel signal-averager set to enhance signals with a period twice the radio and optical period of NP 0532 at the time of observation.The contents of the averager were displayed on an oscilloscope and photographed for later analysis.A digital tape recording of the output signal from the a.c.amplifier was also obtained, but only the results from the averager were used in this reduction.Two 10-min observations were made at 2.2 µand one 10-min and one 5-min observation at 1.65 µ.Calibration data were obtained by mechanically chopping the light from t Tauri with an asymmetric chopper designed to admit a 1.5-msec pulse of radiation every 38 msec.This star has a magnitude at 2.2 µof 2.94 (Johnson 1964), corresponding to a flux density of 4.2 X 10-25 W m-2 Hz-1 ; at 1.65 µ,its flux density, based on comparisons with a Lyrae, is 6.0 X 10-25 W m-2 Hz-1 •