Although rejecting the notion she violated any ethical standards, a federal judge who exchanged e-mails with a prosecutor’s husband during a criminal trial stepped aside from the case today. In a written opinion, U.S. District Judge Virginia M. Kendall said defendant Marvin Chapman’s “frivolous” challenge to her integrity forced her to recuse herself from his case. A reasonable observer could question her ability to rule objectively in Chapman’s case in light of that challenge, she …