Type Ia supernova and Gamma Rays INTEGRAL satellite Type Ia supernova and Gamma Rays INTEGRAL satellite

Type Ia supernova frequency in the Virgo cluster

I've looked at the eventuality of observing a type Ia supernova in gamma rays using the INTEGRAL satellite. Before its launch (october 2002) the satellite was thought to have enough sensibility (see e.g. Gomez-Gomar et al. 1998) to catch a type Ia supernova up to the Virgo cluster of galaxies which is 15 to 20 Mpc away.

The Virgo cluster

This cluster lays between 15 and 20 Mpc. It harbors about 1800 galaxies (up to B ~ 20): 1277 are cluster members and 574 may be cluster members (Binggeli et al. 1985). It spreads on the sky more or less within a circle of radius 6° centered on RA(1950) = 12h25m and DEC(1950) = +13°. This map of the cluster comes from Binggeli et al. 1987.

In order to see if the satellite may have a chance to observe such an event during its lifetime, I computed the frequency of type Ia supernova within the Virgo cluster. I calculated the total luminosity of the cluster using the galaxies luminosity function as measured by Sandage et al. 1985. The total luminosities per galaxy type have been multiplied by the type Ia supernova rate as measured in the local Universe by Cappellaro et al. 1997.

The result is 0.25 ± 0.06 type Ia event per year. All type of supernovae provides 0.84 ± 0.13 event per year.

Surface density of the supernova rate in the Virgo cluster

Since Binggeli et al. 1987 have measured the galaxy luminosity surface distribution on the sky, we can easily translate their measurement into a supernova frequency per surface unit.

Iso-supernova frequency (all types) within the cluster per century and per square degree. For the type Ia supernovae, the contours stand for 2.4, 1.8, 1.2 and 0.6 event per century and per square degree respectively.

Are these supernovae discovered?

I noticed 41 supernovae in the IAUC list within the cluster boundary between 1952 and october 1999. That is 41 events in 48 years, that is an average of 0.85 explosion per year, which is close to the number we computed. The sample is too small to check accurately the spatial distribution.

Type Ia supernova frequency in the Galactic neighborhood

But now that the sensibility of the satellite has been measured, it appeared to be lower than expected. Then type Ia supernova could only be reached within typically a radius of 10 Mpc.

A lower limit of the average type Ia supernova number accessible can still be computed. Using the LEDA database with its useful SQL query form, I retrieved 75 extragalactic objects with a B magnitude, a B absolute magnitude and a distance modulus. The total B luminosity of these objects is then 8.33e+11 LsunB. Knowing that the type Ia local supernova rate is: 0.36+-0.11 h2 SNu (Cappellaro et al 1999), this gives a number of potential SNIa:

If the sample is complete (which is probably not), there would be only 0.6 SNIa during its 4 remaining years on duty in the Milky Way neighborhood... Not so bad, but not so good... Actually this number is a lower limit...


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Guillaume Blanc, august 2003.