Many people do not like registering for a website, so this article is about what you can do in Skyalert if you register and log in. Registration allows you to create an Alert. Or many of them. Each Alert is a filter on an event stream, executed whenever a new event appears — essentially a decision about whether the new event is “interesting”. One result of that filter is a “feed” of interesting events that can be read by many internet tools. In Yahoo Pipes, for example, feeds can be combined and selected, used to alert a mobile device, or other kinds of messaging. iGoogle will collect feeds and other gadgets on an attractive “home page”.

An Alert uses data not just from the event itself (first observation), but also from a portfolio of other data perhaps from archives, follow-up observation, comment, or classification. This is all available in order to build the alert, so it can be quite a precise selector. The Alert is written in the following syntax based on Python, for example this uses the MOA stream:

MOA["Paczynski model parameters"]["Ibase"] < 21

Which means that events from the MOA stream are “interesting” if they are brighter than 17th magnitude. The parameter names were chosen by the authors of that particular stream.

Let’s go through the process of building an alert. (First you need to register, return the email, and login). Click here to see the list of your current alerts. At the top, click on “For a New Alert Click Here” and select the event stream that you want, perhaps SWIFT, or CRTS3, or MOA. At this point, you can select secondary data that is necessary for your Alert — perhaps events where a human-written circular has also appeared and been added to the portfolio. Selecting secondary streams reduces the flow of your Alert filter by requiring additional data in the portfolio.

Click on “Continue to next step”. Give your alert a name, so you know which is which, and decide what should happen when the portfolio becomes interesting. To have an email sent, the action type should be “alert_email” and the email address below it. To just get the Atom feed of the events, make the action type blank.

The “trigger expression” is a piece of code that defines when an event is interesting. It uses the data from the portfolio to make a decision, of which more below. But for a first Alert, just put the word True in the trigger expression, meaning that all events are interesting and pass the filter.

Now click the “Save” button. You can also click the button “See past events”, which shows a table of recent events that satisfy your Trigger. If there is nothing in the table, then you may have chosen a stream that does not yet have any events, or your trigger criterion too strict.

Going back to the “My Alerts” page, and you can see your new alert three ways: for editing the alert or deleting it, and also a link to the corresponding Atom feed. This is what you can use in Yahoo Pipes or iGoogle, or other web applications that work with feeds.

Let’s do a more complicated alert example. Suppose a supernova hunter wants likely targets, meaning transients from the CRTS survey that are both bright and close to a galaxy from the SDSS survey, let’s say within 5 arcseconds. We use galaxy proximity as a proxy for likelihood the event is a supernova. From myAlerts click on New Alert, then select CRTS as the primary stream, and when you access the secondary streams, choose SDSS. Click “Continue” and you should see the Primary (CRTS) and Secondary (SDSS). Now we build the Trigger: clicking on the parameter names below will insert the right text into the Trigger Expression, so go ahead and click “First Detection params | magnitude” from CRTS and “nearest_gal | distance” from the SDSS, then go back to the Trigger Expression text. Edit things until it looks like this:

CRTS["First Detection params"]["magnitude"] < 19 and SDSS["nearest_gal"]["distance"] < 5.0

then click “Save”. You can see the feed from this alert, or something like it, at the “System Feeds” page.

You can also see the feed from your own alert: go back to myAlerts and click the relevant “feed” link. That URL is a representation of the feed from your personal definition of what is “interesting”. It can be used in iGoogle, Yahoo, or make you phone ping to say something interesting is happening in the cosmos.

This entry was posted on Friday, June 4th, 2010 at 10:21 pm and is filed under Uncategorized. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.