TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1539 SUBJECT: IPN GCN Circulars now to be issued without restriction DATE: 02/09/10 17:48:03 GMT FROM: Kevin Hurley at UCBerkeley/SSL IPN GCN Circulars now to be issued without restriction ______________________________________________________ Up to now, the IPN collaboration has been filtering its GCN Circulars and Notices on GRBs to include only localizations which satisfy three criteria: 1. Relatively small error boxes (<~ 1000 arcmin2) 2. Relatively rapidly determined error boxes (<~100 hours) 3. Error boxes with relatively small maximum dimension in any direction (<~30 arcmin) These filters were tailored to the requirements of astronomers searching for long-wavelength GRB afterglows. The resulting GCN rate has been roughly one per week over the past several years, with large fluctuations in this rate due to solar activity and the start-up and shutdown of various missions. However, following discussions with members of the community, we believe that, in order to better serve the needs of astronomers searching for other GRB-related phenomena, including neutrinos, gravitational radiation, and VHE gamma-rays, it is worthwhile to remove all filters from IPN GRBs. Accordingly, we will proceed to issue GCN Circulars which give information on bursts localized to annuli, sections of annuli, double error boxes, and so on, regardless of the area, maximum dimension, or delay in obtaining the error box. These Circulars will be issued as soon as possible after receipt of the data. The removal of filters should at least double the GCN message rate; the majority of these Circulars will be issued within several days of a burst, although outliers will always be present. (We do not plan to issue this information as GCN Notices, unless the circumstances are exceptional, or a clear desire to have such Notices is expressed by members of the community.) As always, all such information should be understood to be preliminary and subject to refinement when final data (such as spacecraft ephemeris and timing) become available, which takes up to about one month, depending on the spacecraft. Apart from exceptional cases, we will not issue final localizations as GCN Circulars, but instead defer them to publications in the refereed literature. We will use several techniques in addition to arrival-time analysis to constrain GRB arrival directions as much as possible. They include Earth-blocking, Mars-blocking, and ecliptic latitude determination. A brief discussion of some of these techniques may be found at ssl.berkeley.edu/ipn3/statusreport.htm. Unconfirmed events (i.e., events observed by a single detector, or by several detectors on a single spacecraft) pose a particular problem. In many cases, such events can safely be assumed to be cosmic due to their energy spectra and time histories. However, some cases are harder to judge. We will treat unconfirmed events in such a way as to minimize the false positive rate, while maximizing the completeness of the sample. Roughly speaking, we expect the overall result to be a GRB sample that is over 90% complete, with an over 90% probability that any unconfirmed event is indeed cosmic. (Note that some unconfirmed events may be localized, and some confirmed events may be unlocalized, due to the nature of the IPN and its experiments.) We will attempt to specify the nature of the event and its localization in the subject line of the circular, as far as possible. Questions about specific events, or questions such as "did any spacecraft observe a burst on day X at time Y?", can be addressed to khurley@sunspot.ssl.berkeley.edu.