Two New SN1987A Light Echo Structures at Large Distance
Session 39 -- SN1993J, SN1978K and SN1987A
Display presentation, Thursday, January 13, 9:30-6:45, Salons I/II Room (Crystal Gateway)

## [39.08] Two New SN1987A Light Echo Structures at Large Distance

Jun Xu, Arlin P. Crotts (Columbia University), W. Kunkel (Carnegie Observatories)

Two new light echoes, probably related, were discovered at distances twice as far away as any previously reported. We have observed them since 18 Sep 1991, at Las Campanas Observatory with the C-40 telescope. A 612nm filter was used, since in this band nebular emission lines are suppressed while echoed SN light is bright. The spreading of light echoes in time also enables us to single out echoes from other backgrounds.

These echoes are about 238 arcsec away from SN1987A as of 1 May 1993. The position angle of the south-eastern echo is $110^{0}$ to $140^{0}$ and the northern one is $-4^{0}$ to $10^{0}$. Their distances in the SN foreground are 3140 and 3240 lyr, respectively.

Adopting Graphite:Silicate=35:100 for typical LMC interstellar dust and the grain number distribution over size of $f(a)=G_{0}a^{-3.5}$, we formulate forward scattering light echo model \begin{eqnarray} \frac{B_{SC}(\lambda,t,\phi)}{F_{SN}(\lambda)}= n_{d}(r_{t},\theta_{t},\phi)\frac{c\:\Delta z}{4\pi r_{t}} \:\frac{1}{\rho\Delta \rho} \:ACS(\lambda,\theta) \end{eqnarray} where effective cross section $ACS(\lambda,\theta)$ was calculated. This model gives dust mass swept by the light echo so far to be $4.0\:M_{\odot}$ and $1.7\:M_{\odot}$, and extinction $A_{v}$ of 0.052 and 0.044 magnitude, respectively.

The changing behavior of both the geometry and inferred dust density suggest that the light echoes have just entered two huge dust clouds, and hence should remain there. We suspect these clouds are related to the large scale structures discovered by other means (for example see F. C. Bruhweiler et al, 1991).