Please read the following table in HTML format from a webpage and then answer the question in detail according to the table. Each table cell is defined by a <td> and a </td> tag. Each table row starts with a <tr> and ends with a </tr> tag. 'rowspan=m' and 'colspan=n' represents a cell spaning over 'm' rows and 'n' columns.

Webpage title:
Sarah Sjöström
Table title:
World records (50 m)
Table:
<table id='hittask' contenteditable='False'>
<tr> <th colspan=1 rowspan=1 > No. </th><th colspan=1 rowspan=1 > Event </th><th colspan=1 rowspan=1 > Time </th><th colspan=1 rowspan=1 > Date </th><th colspan=1 rowspan=1 > Meet </th><th colspan=1 rowspan=1 > Location </th><th colspan=1 rowspan=1 > Age </th></tr>
<tr> <td colspan=1 rowspan=1 > 1 </td><td colspan=1 rowspan=1 > 100 m butterfly </td><td class="highlighted"  colspan=1 rowspan=1 > 56.44 </td><td colspan=1 rowspan=1 > 26 July 2009 </td><td colspan=1 rowspan=1 > World Championships </td><td colspan=1 rowspan=1 > Rome, Italy </td><td colspan=1 rowspan=1 > 15 </td></tr>
<tr> <td colspan=1 rowspan=1 > 2 </td><td class="highlighted"  colspan=1 rowspan=1 > 100 m butterfly (2) </td><td class="highlighted"  colspan=1 rowspan=1 > 56.06 </td><td colspan=1 rowspan=1 > 27 July 2009 </td><td colspan=1 rowspan=1 > World Championships </td><td colspan=1 rowspan=1 > Rome, Italy </td><td colspan=1 rowspan=1 > 15 </td></tr>
<tr> <td colspan=1 rowspan=1 > 3 </td><td colspan=1 rowspan=1 > 50 m butterfly </td><td colspan=1 rowspan=1 > 24.43 </td><td colspan=1 rowspan=1 > 5 July 2014 </td><td colspan=1 rowspan=1 > Swedish Championships </td><td colspan=1 rowspan=1 > Borås, Sweden </td><td colspan=1 rowspan=1 > 20 </td></tr>
<tr> <td colspan=1 rowspan=1 > 4 </td><td colspan=1 rowspan=1 > 100 m butterfly (3) </td><td colspan=1 rowspan=1 > 55.74 </td><td colspan=1 rowspan=1 > 2 August 2015 </td><td colspan=1 rowspan=1 > World Championships </td><td colspan=1 rowspan=1 > Kazan, Russia </td><td colspan=1 rowspan=1 > 21 </td></tr>
<tr> <td colspan=1 rowspan=1 > 5 </td><td colspan=1 rowspan=1 > 100 m butterfly (4) </td><td colspan=1 rowspan=1 > 55.64 </td><td colspan=1 rowspan=1 > 3 August 2015 </td><td colspan=1 rowspan=1 > World Championships </td><td colspan=1 rowspan=1 > Kazan, Russia </td><td colspan=1 rowspan=1 > 21 </td></tr>
<tr> <td colspan=1 rowspan=1 > 6 </td><td colspan=1 rowspan=1 > 100 m butterfly (5) </td><td colspan=1 rowspan=1 > 55.48 </td><td colspan=1 rowspan=1 > 7 August 2016 </td><td colspan=1 rowspan=1 > Olympic Games </td><td colspan=1 rowspan=1 > Rio de Janeiro, Brazil </td><td colspan=1 rowspan=1 > 22 </td></tr>
<tr> <td colspan=1 rowspan=1 > 7 </td><td colspan=1 rowspan=1 > 100 m freestyle </td><td colspan=1 rowspan=1 > 51.71 </td><td colspan=1 rowspan=1 > 23 July 2017 </td><td colspan=1 rowspan=1 > World Championships </td><td colspan=1 rowspan=1 > Budapest, Hungary </td><td colspan=1 rowspan=1 > 23 </td></tr>
<tr> <td colspan=1 rowspan=1 > 8 </td><td colspan=1 rowspan=1 > 50 m freestyle </td><td colspan=1 rowspan=1 > 23.67 </td><td colspan=1 rowspan=1 > 29 July 2017 </td><td colspan=1 rowspan=1 > World Championships </td><td colspan=1 rowspan=1 > Budapest, Hungary </td><td colspan=1 rowspan=1 > 23 </td></tr>
</table>
Question:
In which swimming event did Sarah Sjöström improve her world record time?
Answer:
In the 100 m butterfly, Sarah Sjöström improved her world record time to 56.06.