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supernova unit

A unit used in expressing the frequency with which supernova occur, late 20ᵗʰ century – present. One supernova unit is a rate of 1 supernova per century in a field of stars whose luminosity, measured in the B-band, is 100 billion times that of the sun. Symbol, SNu.

The B-band is a portion of the spectrum, in the blue, average wavelength 442 nm, defined by the Johnson-Morgan photometric system.¹

1. H. L. Johnson, and W. W. Morgan.
Fundamental stellar photometry for standards of spectral type on the revised system of the Yerkes spectral atlas.
The Astrophysical Journal, vol 117, no. 3, pages 313–352 (1953).
doi:10.1086/145697.

sources

* In the quotations the word “solar” has been substituted for the solar symbol, which is not available in most browsers' fonts.

These results confirm previous findings and make it possible to compute SN rates in the so-called SN units, i.e., 1 SNu = 1 SN (100 yr)⁻¹(10¹⁰L_B(*solar))⁻¹. We remind the reader that SN rates expressed in SNu depend on the adopted distance scale, i.e. in our case they scale as (H/75)².

E. Cappellaro, M. Turatto, S. Benetti, D. Yu. Tsvetkov, O. S. Bartunov and I. N. Makarova.
The rate of supernovae. II. The selection effects and the frequencies per unit blue luminosity.
Astronomy and Astrophysics, vol. 273, pages 383-392 (1993). Selection from page 386.

This allows us to estimate the intermediate redshift SN rate in SNu (1 SNu = 1 supernova per century per 10¹⁰ L_B(solar*)).

…

Local estimates of the SN Ia rate are often expressed in the “supernova unit” (SNu), the number of SNe per century per 10¹⁰ solar luminosities in the rest-frame B-band.

R. Pain, S. Fabbro, M. Sullivan, R. S. Ellis, G. Aldering, P. Astier, S. E. Deustua, A. S. Fruchter, G. Goldhaber, A. Goobar, E. Groom, D. Hardin, M. Hook, D. A. Howell, J. Irwin, A. G. Kim, M. Y. Kim, R. A. Knop, J. C. Lee, R. G. McMahon, P. E. Nugent, N. Panagia, C. R. Pennypacker, S. Perlmutter, P. Ruiz-Lapuente, K. Schahmaneche, B. Schaefer and N. A. Walton.
The distant Type Ia supernova rate.
The Astrophysical Journal, volume 577, Issue 1, pp. 120-132 (September 2002). Selections from pages 121 and 127.
arXiv:astro-ph/0205476 v1 28 May 2002