GCN/ALEXIS extreme-UV Transient Notices (No Longer Available)

  1. Introduction
  2. Error Boxes
  3. Sequence of Activities
  4. Distribution Methods and Filters
  5. Recognition
  6. Further Help
  7. E-mail, Pager, and Short-form Pager Examples
  8. Subject-only Example

The GCN system has been modified to incorporate the distribution of extreme-UV Transient locations detected by the ALEXIS spacecraft (http://alexis-www.lanl.gov link no longer active).

The ALEXIS spacecraft has 3 pairs of telescopes tuned to the 66, 71 and 95 eV bandpasses. The orbit plus the attitude of the spacecraft are such that the anti-solar hemisphere of the sky is scanned every orbit. Roughly 1-5 steady state sources are detected during each 12 hour period, and ~0-3 transient sources candidates are detected per week. These transients typically last 6 hrs to 2 days.

While the ALEXIS team has set a relatively high threshold for detecting these transients (significance of less than 10^-7 or approximately 5.2 sigma, and with additional sanity tests required to be met), they acknowledge that some of these alerts will be false triggers. However, they estimate that the true rate of these transients to be between 1 per week and 1 per month. In addition, outburst emission from known transient EUV sources such as the cataclysmic variable systems U Gem, VW Hyi, and AR UMa will show up in the GCN/ALEXIS distributions.

Error Boxes

The uncertainty in these locations is about a 0.23 degree statistical uncertainty plus an ~0.15 degree systematic. The current understanding of these transients is that they are NOT correlated with GRBs. However, they are an interesting unknown phenomenon with no known source objects.

Sequence of Activities

The data are available every 12 hours (TM downlinks) and are batch processed. Maps are accumulated over the previous 12, 24, and 48 hours worth of data. The output of this processing is sent to the GCN system where it is scanned for transients. If there are any, the location, detection significance, and a few other details are distributed to those sites that have requested the ALEXIS-source of information by the distribution method they have choosen.

The Transients are also tabulated in the GCN/ALEXIS Transients web page.

Distribution Methods and Filters

These new data sources will be distributed using the same media (Internet sockets, e-mail, long and short pagers, and dialed phones), the same formats (see examples attached below), the same filters (all, visible, night, intensity, source, and custom), as with all the other sources (notice types) in the GCN system. The GCN filtering scheme allows for "source" filtering as well as the regular types of filtering (eg. they could have ALEXIS and RXTE Notices each enabled, but have the BATSE-Original Notices disabled).


Sites should include Jeff Bloch and Diane Roussel-Dupre (LANL for ALEXIS); and Scott Barthelmy and Paul Butterworth (GSFC for GCN) in the author list of papers discussing follow-up observations using these new GCN/ALEXIS locations.

Further Help

See the ALEXIS web page ( http://nis-www.lanl.gov/nis-projects/alexis) for details of the ALEXIS spacecraft and explanation of these "transients". Detailed questions should be directed to Jeff Bloch (LANL, 505-665-2568, jblock@lanl.gov).

E-mail, Pager, and Short-form Pager Format Examples

The format is based on the same "TOKEN: " scheme that was developed for the original BACODINE notices. Examples of the E-mail, and Long- and Short-form Pagers of the GCN/ALEXIS notices are attached below.

The "Subject" line for the e-mail format (only) is:
There are no "Subject" lines for the e-mails to the pager companies (both the long- and short-forms) because the Subject line use up valuable character counts from the maximum displayable for the body of the message. And it was the very limited display character count of some companies that motivated the short-form pager method in the first place.

The Current epoch is used in the (regular) pager form. And the 1950 epoch is used in the short-form pager format.

NOTICE_DATE:  Wed 14 May 97 23:43:31 UT
TRANS_RA:     211.05d {+14h 04m 11s} (J2000),
              211.02d {+14h 04m 05s} (current),
              210.39d {+14h 01m 33s} (1950)
TRANS_DEC:     -7.23d {-07d 13' 46"} (J2000),
               -7.22d {-07d 13' 11"} (current),
               -6.99d {-06d 59' 24"} (1950)
TRANS_ERROR:  0.66 [deg radius, 3-sigma, statistical+systematic]
TRANS_ALPHA:  7.40 [-log10(probability)]
TRANS_TELE:   3B, 66eV
MAP_DATE:     10805 TJD;   357 DOY;   97/12/23
MAP_TIME:     23:28:13 UT (end of map accumulation)
MAP_DURATION: 12 [hrs]
SUN_POSTN:    272.38d {+18h 09m 32s}  -23.42d {-23d 25' 15"}
SUN_DIST:      60.91 [deg]
MOON_POSTN:   203.99d {+13h 35m 58s}   -6.45d {-06d 26' 45"}
MOON_DIST:      7.02 [deg]
COMMENTS:     ALEXIS Transient Coordinates.
COMMENTS:     ALEXIS URL: http://nis-www.lanl.gov/nis-projects/alexis

RA=211.02 DEC=-7.22d
TIME=23:28:13 UT
ALPHA=7.40 [-log10(probability)]
ALEXIS Tansient Coordinates.

RA=210.39 DEC=-6.99d

Subject-only Example

An example of the Subject-only pager/cell_phone format is shown below. Only the "Subject" line for these e-mails sent to the pager companies because that's the only part of the e-mail they display on the pager/cellphone.

ALEXIS RA=152.40 DEC=+3.26d

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This file was last modified on 13-Dec-1997.