Q What should I do if I'm arrested while on probation
Even if they didn't tell you, you already know that you're not supposed to commit another offense while on probation. Every order granting probation (or community supervision) contains the condition that you commit no offense against the laws of the State, any other state or even the federal government. That even includes such minor crimes as speeding or other traffic offenses.
So what happens if you did get arrested for a new charge?
There are several things you need to know. The first is that it really makes no difference whether you are guilty or not. While that will be an issue later, it's not something that's important now. Every probation order I've ever seen has the condition that you report an arrest within a certain amount of time - generally 48 hours. That means that if you don't tell your probation officer you were arrested - even it's a bogus charge - you've committed a probation violation. So do it!! The worst thing you can do is nothing, and have your probation officer call you up and ask about it.
So what happens after you tell them you've been arrested, or they find out on their own? It depends on a lot of factors, such as how long you've been on probation, how you've done, and how serious the charge is. The options the probation officer has may be limited by the nature of the charge, and the office policy. In many places an arrest for a felony requires the officer to request a motion to revoke probation. In other places, and in other situations, they may be handle it within the probation system - such as modifying the conditions of probation to include additional classes or counseling, or even weekends in jail.
Most people are worried about whether they will be arrested if they go in and report an arrest. The short answer is not usually. A probationer is generally not arrested unless there is a warrant for your arrest. To obtain a warrant the probation officer will submit the case to the District Attorney's office, who will file a motion to revoke probation and request a warrant from the judge. That takes some amount of time, which means a warrant may not be issued for several days - or several weeks, depending on the practices of where you are at.
If an arrest warrant is issued, you will be taken to jail, and have to post bond to be released. Generally a bond amount is set when the judge issues a warrant. In some cases the judge may deny bond - especially if the arrest is for a serious offense. Your probation officer may or may not tell you a warrant has been issued. If you've always been cooperative with them they will usually let you know so you can make arrangements to post the bond. In other cases they may just wait until your next reporting date and have you arrested at the office.
You might wonder what happens if the arrest is not justified, and you aren't guilty of the new offense. If a motion to revoke is filed you will have a hearing, and have an opportunity to present evidence that you didn't commit the offense.
While a new arrest is not a good thing, the worst thing you can do is ignore it. It's not going away, and your probation officer will always find out about it. It's better that they find out from you. While it's difficult to do that, it's something that has to be done.