Combine the vinegar, water, bay leaf, thyme and sugar in a 3-qt. saucepan, and bring to a simmer.Place the carrots, onion and jalapeños into the saucepan, cover and bring back to a boil. Watch carefully as this happens quickly. Pour vegetables and brine into a bowl.Cool to room temperature, and pour into a glass jar with a tight-fitting lid.The pickles will keep for up to two weeks in the refrigerator.