The integrated optical spectrum of the Crab nebula and evidence for its fading synchrotron continuum

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Abstract

A flux-calibrated optical spectrum integrated over the entire Crab nebula was obtained by making drift scans with a long-slit spectrograph. Compared to observations obtained over the past 40 years, these new data confirm an earlier controversial result that the [O III] λλ4959, 5007 equivalent width is increasing with time, although the rate of ∼0.9 per cent yr -1 is somewhat slower than that measured previously. Additionally, the Hβ equivalent width is increasing at a comparable rate, but the measured fluxes of both Hβ and [O III] have changed less than their respective equivalent widths. The different rates of change in the measured fluxes and equivalent widths of these lines suggest that the optical synchrotron continuum from the Crab nebula is indeed fading rapidly. The apparent decline is consistent with a rate around -0.5 (±0.2) per cent yr -1 at wavelengths near 5000 Å inferred independently from measurements of the optical continuum flux during the same time period.

Original languageEnglish (US)
Pages (from-to)885-889
Number of pages5
JournalMonthly Notices of the Royal Astronomical Society
Volume346
Issue number3
DOIs
StatePublished - Dec 11 2003
Externally publishedYes

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Crab nebula
fading
optical spectrum
crab
synchrotrons
continuums
spectrographs
slits
wavelength
rate
wavelengths

Keywords

  • ISM: individual: Crab nebula
  • Supernova remnants

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

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title = "The integrated optical spectrum of the Crab nebula and evidence for its fading synchrotron continuum",
abstract = "A flux-calibrated optical spectrum integrated over the entire Crab nebula was obtained by making drift scans with a long-slit spectrograph. Compared to observations obtained over the past 40 years, these new data confirm an earlier controversial result that the [O III] λλ4959, 5007 equivalent width is increasing with time, although the rate of ∼0.9 per cent yr -1 is somewhat slower than that measured previously. Additionally, the Hβ equivalent width is increasing at a comparable rate, but the measured fluxes of both Hβ and [O III] have changed less than their respective equivalent widths. The different rates of change in the measured fluxes and equivalent widths of these lines suggest that the optical synchrotron continuum from the Crab nebula is indeed fading rapidly. The apparent decline is consistent with a rate around -0.5 (±0.2) per cent yr -1 at wavelengths near 5000 {\AA} inferred independently from measurements of the optical continuum flux during the same time period.",
keywords = "ISM: individual: Crab nebula, Supernova remnants",
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