Why changing image link invokes controller asynchronously in asp.net mvc

Why changing image link invokes controller asynchronously in asp.net mvc

I'm changing the link of image on client side and it's invokes controller
asynchronously, I don't understand this behavior, could someone explain me
what happens? Why url adding actually invokes the controller by default,
moreover it happens asynchronously.
<script>
$("#refreshLnk").click(function () {
$("#cap").attr('src', '@Url.Action("CaptchaImage")?' + new
Date().getTime());
});
</script>
<img id="cap" alt="Captcha" src="@Url.Action("CaptchaImage")" style="" />
<a id="refreshLnk" href="#">refresh</a>
public ActionResult CaptchaImage()
{
}