Equipment and Environment:

Constraint 2

Lets talk about the second first. I call my observing facility The Potomac Astrometric Observatory. Ideally, I would have placed it in a dark sky environment, and I would have done that were it not for my need to live in a place that supports my profession. Given that I live in light loving suburban Washington, and not somewhere else, there is the issue of my house and yard. My back yard is surrounded by tall trees, and is the lowest in elevation of any part of my property. My back yard is a bad choice for an observatory. My front yard is a much better prospect, but local zoning won’t permit a building in the front yard. I could move, but my location otherwise is excellent, and I like my house.

The upshot of all this is that I have no observatory building. My observatory is a state of mind, consisting of the open air, my telescope, and my camera equipment. One might say that in terms of money at least, I was able to live well within my second constraint. Someone else might say, yes and no. Serious observing here can be done, but only with non-modest investments in telescope equipment.

Constraint 1

The Gamma Ray Burst Transient Hunting Procedure is designed to permit rapid setup of equipment following a burst. The timeframe for capture is probably no greater than 2 hours following the report of the burst. In three hours, the afterglow has faded to past magnitude 18 and getting past this depth is difficult in my area. This has several implications. 1) I can’t drive to a dark site. That takes an hour and within one hour lost, I loose more magnitudes than I gain (See the Transient Decay Curve). I have to do this from home. 2) If I don’t have an observatory building, I have to set up my equipment in a very short period of time. 3) Burst reporting takes time. By the time we have a well-localized burst (we know good coordinates), more of the 3 hours has passed. 4) A large format telescope will be needed to recover some of this time so I can get deeper in less integration time. 5) A large pixel camera supports going deeper faster. Large pixels are more sensitive than small pixels. 6) Error boxes on a localization are often 20 arc-minutes in diameter. A large format camera grabs a larger chunk of sky with each exposure. 7) Since there is no building, the scope and the equipment must be portable, easy to set up and take down. This requirement limits the size and type of the telescope.

My Response to the requirements:

Telescope:

Aperture is important in this application. The burst transient will be fading rapidly. Larger aperture focuses more light on the detector. Getting to 18^th magnitude can be done with a 5-minute exposure. The 18 inch aperture of the NGT-18 is about as big as can be had on an equatorial base and still is movable by a single person. At 200 pounds, it comes with wheels and handles in a wheelbarrow like structure. I will have to do something even more than this to make the scope easier to move around

The telescope is an F/4.5 split ring equatorial Newtonian. It has excellent optics and a good tracking capability. The telescope can accept auto-guiding instructions from a camera. . The telescope has a measured focal length of 2022 mm.

Note: The reference to 18^th magnitude in 5 minutes references the ability of the scope to show stars to that magnitude in images. Photometry is not possible at that depth in that length of exposure. Stars at that depth have low signal-to-noise ratio. To achieve usable images for transient measurement purposes, as many as 4-5 images of this duration are likely needed. Astrometry can be done with unfiltered images. Photometry requires a minimum of the R filter.