I am trying to prepare a Debian 8.9 boot disk following [these](http://verahill.blogspot.co.at/2013/03/361-installing-debian-on-usb-stick-from.html) instructions. Obtaining a kernel image via `apt` is part of this process. However, if I try

```
apt install linux-image-`uname -r`

```

I run into the following errors:

```
Reading package lists... Done
Building dependency tree       
Reading state information... Done
E: Unable to locate package linux-image-4.8.0-53-generic
E: Couldn't find any package by regex 'linux-image-4.8.0-53-generic'

```

My `/etc/apt/sources.list` is as follows:

```
deb http://ftp.au.debian.org/debian/ jessie main contrib non-free 

```

What is the appropriate way for obtaining `/boot/vmlinuz-4.8.0-53-generic` (or an equivalent) with a Debian package?