ASM Rapid Position Alerts

ASM Alert Number Date (UT) R.A. (J2000) Decl. (J2000) Comments/ID
Number 2403/02/14285.841+3.283No comment yet.
Number 2301/09/07252.137-50.047XTE J1650-500
Number 2201/03/25107.768+20.099No comment yet.
Number 2101/01/10154.575+68.666No comment yet.
Number 2000/12/27113.395-15.101No comment yet.
Number 1900/12/22 88.530+16.657No comment yet.
Number 1800/09/18 7.861+55.820No comment yet.
Number 1700/09/12251.151-44.897No comment yet.
Number 1600/09/11 83.559+21.528No comment yet.
Number 1500/09/11256.125-35.922No comment yet.
Number 1400/09/10 19.897+63.431No comment yet.
Number 1300/09/10351.279+58.698No comment yet.
Number 1200/09/09279.900+5.312False alarm due to bad calibration.
Number 1199/10/09284.634+22.640XTE J1859+226
Number 1099/02/15298.222+54.664Most likely solar contamination.
Number 998/09/15296.590+27.333XTE J1946+274 (= 3A 1942+274)
Number 898/09/07237.866-56.539XTE J1550-564
Number 798/08/27286.658+9.424SGR 1900+14
Number 698/07/03359.775+8.561GRB 980703
Number 598/06/27320.734-5.907XTE J2123-058
Number 498/06/09 82.106-65.442AB Dor
Number 398/06/04266.956-28.344XTE J1744-288
Number 298/05/26303.431+38.166XTE J2012+381
Number 198/03/31 64.859+55.959XTE J0421+560 ( = CI Cam)

The All-Sky Monitor scans the sky continuously in the 2-12 keV band, measuring the states of known X-ray sources and searching for the emergence of new Novae and other transients. Full-time telemetry connection to the satellite enables the data to arrive at MIT within 5 to 60 minutes of the observations. A single detection of a new X-ray source yields a line of position a few arcminutes wide. Multiple detections provide crossed lines of position, which constrain the location to a region of a few tens of square arcminutes. We maintain a catalog of known x-ray sources and recurrent transients. An alert is generated only if two positions overlap within a 300 s interval, and if this overlap region is inconsistent with any source in our catalog.

These alerts will report detections of both new X-ray Novae and GRBs. To aid users in distinguishing between the two, the alert system will check for a contemporaneous BATSE GRB detection. Since BATSE does not detect all GRBs, a lack of a corresponding BATSE burst should not be taken as proof that the event is not a GRB. The system also checks and reports on the ASM time-series data for evidence of variability on time-scales between 1/8-s and 90-s. GRBs tend to be highly variable at those timescales, while X-ray Novae vary much more slowly.

For each ASM alert, a web page that displays a sky map of the area around the crossed boxes, copies of alert messages, and plots of the time-series data is generated here. (See the list below.) As further data related to each event are accumulated, the web pages here are updated. No additional alerts are sent (remember on return visits to press RELOAD on your browser to make sure you have the most recent update). The web page will also provide a link to the DSS web site to generate a FITS-format image of the region around the ASM error box. A second link will query the SIMBAD database for a list of nearby catalogued sources. These links are provided for your convenience, and we have no offical connection to the groups that maintain these sites; see the external sites for their conditions of use.

Test runs on thirteen months of ASM data yielded nine alerts: five NEW transient X-ray sources, the re-emergence of a transient last detected in 1976, one GRB, one Soft Gamma-ray Repeater, and one nearby flare star. Two false alarms generated web pages (Numbers 2 and 8), but did not match the filter criteria used to generate email alerts to external sites. We are less strict for internal alerts, so that we can check borderline cases manually. Only observations that pass strict believability criteria will generate external email alerts. We are therefore confident, under the assumption that the ASM will continue to perform at its current ability, that even if an alert from this program is not generated by a GRB, there will be something new of Astronomical interest within the reported error box.

The alerts are produced in a standardized format, and they will be distributed via the Gamma-ray burst Coordinate Network (GCN), as well as direct emails to whomever requests them. This format is easily parsed by software to either alert the current working observer at your site or activate the automatic response of your instrument. The goal is to provide an accurate counterpart identification as soon as possible to enable spectroscopic measurements and broad-band monitoring of the event decay. Results should be reported via the GCN Circulars and any additional means of distribution you see fit to use. Please contact Scott Barthelmy for more information about the GCN. Please note that for security reasons, only registered users can submit GCN Circulars. It is trivial to join that list, merely contact Scott. If, however, it is the middle of the night and you wish to report a result, you may wish to try the Astronomer's Telegram for rapid result dissemination.

If you wish to be added to our mailing list, or if you have any questions or comments, please feel free to email Don Smith.