Nov. 22, 1996

Announcement for GBI-NASA Radio Monitoring Program

The Green Bank Interferometer (GBI) resumed operation as a radio monitoring instrument on Nov. 22, 1996. The GBI is a two telescope interferometer that operates simultaneously at 2.7 and 8.3 GHz. During the last two decades the GBI program has evolved from doing radio astrometry and interstellar scintillation towards X-ray binaries and X-ray active AGN's. Due to changes in funding, it was shut down at the end of March 1996, but has now resumed operation as an instrument operated by NRAO and supported by the NASA High Energy Astrophysics program.

The steering committee for Green Bank Interferometer radio monitoring has adopted some initial policies for the new GBI-NASA effort. Here we summarize the essential policies and indicate how sources can be added to the monitoring program.

There are three categories of sources to be included in the GBI-NASA program. The highest priority is observations of both transient and persistent galactic X-ray and Gamma-ray sources. The other two categories of sources are active stellar binary systems and extra galactic sources: AGN, blazars, etc. Amongst the prime sources are GRS1915+105, GRO J1655-40, Cyg X-3, Cyg X-1, GRS1716-249, SS433, and LSI+61 303. The observing program for GBI-NASA is expected to typically include about 20 sources in addition to those used for calibration and data quality checking. Preference will be given to radio sources proposed for high energy X-ray and gamma-ray simultaneous observations.

The GBI-NASA steering committee has adopted the policy that all GBI data will be made publicly available via anonymous ftp ( and cd to /pub/dist/data) and internet Web page ( gbint/gbint.html).

Researchers using X-ray and gamma-ray instruments to study sources that exhibit, or could exhibit, radio emission, can propose to include new sources in the GBI program by sending a short request for observations (RFO) via E-mail to the following people:

  Marco Tavani   Chair of steering Comm.
  Bob Hjellming           Executive Comm.
  Elizabeth Waltman  Executive Comm.
  Frank Ghigo             Executive Comm.
The proposer should be aware of the GBI capabilities:

i)   simultaneous observations at 2.3 and 8.3 GHz frequencies;
ii)  typical sensitivity of 15-20 mJy at 2.3 GHz;
iii) possibility of multiple pointings per day;
iv)  routine observations above -41 degrees declination, possibly
     down to -45 degrees under special circumstances.

The RFO should always include the following:

  1. The name(s) and institution(s) of the proposer(s).
  2. The names(s) and type(s) of radio source(s).
  3. Sky position(s) of arcsec accuracy (equinox B1950)
     together with uncertainty estimate(s).
  4. A brief description of the multiwavelength program, its scientific
     objectives, and duration of observation(s) with instrument(s)
     different from GBI.
  5. A brief statement about the known or expected radio properties of 
     the source(s). (Note the GBI limiting flux density at 2.3 GHz
     of 15-20 mJy).
  6. The proposed duration of the GBI monitoring (not to exceed 1 month
     for this program; extensions of this limit need to be strongly

  7. A justification for possible multiple GBI pointings per day.
Based upon the guidelines from the GBI-NASA steering committee,
the source may be scheduled as soon as practicable, possibly within
1-2 days, or in cases where it is not easy to do, the RFO may be
passed on to the GBI-NASA steering committee for a decision.  Either
the executive committee (Bob Hjellming, Elizabeth Waltman, Frank Ghigo)
or the Chair of the Steering Committee (Marco Tavani) will reply to
the RFO with regard to the scheduling of the source(s).

The primary sources for the GBI-NASA program occupy the 1300-0100 (=hhmm) range of right ascensions, with competition being most heavy for 1500-2300. Since the GBI is only a two-element interferometer operating simultaneously at 2.2 and 8.3 GHz, sources with largely unknown positions may need to be identified first at radio or optical wavelengths before they can feasibly be observed by the GBI. However, in the case of important new sources, positions good to a few arcminutes or less may be proposed, and the extraction of the radio source information can later be obtained from analysis of archived data after a position good to under one arcsecond is determined.

The initial GBI program to be used at GBI startup, which is expected before the middle of November 1996, and before the GBI-NASA RFO system is operating, includes the following sources. Comments on whether these, or other proposed sources, are objects of study in multi wavelength campaigns may determine whether they remain on the program and the time invested in their observations.

  GRO J1655-40 (XRN Sco 1994)
  GRS 1716-249 (XRN Oph 1993, GRO J1719-24)
  Sgr A*       (1742-289)
  SS433        (1909+048)
  Aql X-1      (1908+005)
  GRS 1915+105
  Cyg X-1      (1956+351)
  Cyg X-3      (2030+407)
  LSI+61 303   (0236+610)
  HR1099       (0334+004)
  Algol        (0304+408)
  0336-019     (CTA26)
  0851+202     (OJ287)
  1253-055     (3C279)
  Delta Lib    (1458-073)
                 The GBI-NASA Steering Committee:
                 Robin Corbet
                 Frank Ghigo
                 Eric Grove
                 Alan Harmon
                 Robert Hjellming
                 Chris Shrader,
                 Marco Tavani (Chair)
                 Elizabeth Waltman