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In order to provide more precise GRB coordinates to search for counterparts, GCN has installed new triggers called LOCBURST and RXTE. These triggers utilize the best analysis performed by the BATSE team (involving an operator's interaction) and the RXTE satellite which uses the hard x-ray afterglow to localize the GRB position. The LOCBURST trigger error is ~0.2-2.0 degrees; and the RXTE trigger error is ~6-40 arcmin depending on the statistics. Although delayed (~15-35 min. for LOCBURST; ~3-5 hr. for RXTE triggers), the smaller error box enables a more conventional, deeper telescope (larger aperture but smaller field of view than LOTIS) to follow up on the GRBs. In addition, new state-of-the-art GRB detectors which will provide much more precise positions in real-time such as HETE-2 are scheduled to be launched in 1999. Since the bursts occur at random times and positions, this telescope will need to be dedicated and automated to always be ready for new triggers. In an attempt to make such observations, we are constructing a large aperture telescope system dedicated to this search.

Super-LOTIS Telescope Image 1 Super-LOTIS
Boller & Chivens 0.6 meter f/3.5 reflector telescope. After refurbishing, by adding computer controlled motors and installing a CCD camera, this automated system will be dedicated to the GRB optical counterpart search.


The telescope shown above is a Boller & Chivens 0.6 meter f/3.5 reflector. It has superb optical quality and mechanical structure; however, it is not yet equipped with computer controllable drives or an electro-optical imaging sensor. We are converting this telescope to Super-LOTIS by refurbishing the motor drive, installing a CCD camera, and placing it at a remote site for dedicated observation. We are installing a LOTIS CCD camera which utilizes a Loral 442A 2048 x 2048 CCD (15 x 15 micron pixels) with LLNL built readout electronics. The CCD is cooled with thermoelectric cooler (to -30 degrees C) which minimizes dark current and readout noise.

Super-LOTIS Telescope Image 2

Super-LOTIS will have 0.84 x 0.84 degree field-of-view (1.5 arcsec/pixel) which is sufficient for BATSE/RXTE trigger types distributed by the GCN. We plan to raster scan the GCN "Original" trigger coordinates which has only a 5 sec delay, but a large 15 degree error box. When we receive refined positions, i.e. LOCBURST or RXTE triggers, we will scan the region and stay at that location the remainder of the night. Our scanning strategy and automation will allow us to record GRB optical activity as early as a few minutes after the trigger.

Super-LOTIS Mirror 60 cm Mirror
The Super-LOTIS mirror has excellent optical quality. A CCD camera will be placed in the telescope tube at the focal plane of the primary mirror. A coma corrector is also being manufactured to minimize the off-axis spot size of the small f-number parabolic mirror.

The basic on-line software has already been written and has been operating on LOTIS. Very minimal modification to the existing software will be required for the entire data acquisition control.

Signal-to-Noise Plot
Super-LOTIS Sensitivity
Predicted signal-to-noise ratio vs. visual magnitude. Super-LOTIS will be able to detect V ~ 19 objects with 10 sec integration time and V ~ 21 with 60 sec integration time.

We have estimated the sensitivity of the Super-LOTIS system. The calculation includes the measured camera dark current at -30 degrees C, readout noise, typical sky background and shot noise. The figure above shows the resulting signal-to-noise ratio with 10 and 60 sec integration times vs. the visual magnitude. The calculation indicates that Super-LOTIS will detect V ~ 19 objects at a signal-to-noise ratio of 10 for a 10 sec integration time and V ~ 21 objects for 60 sec integration time.

Super-LOTIS Parameters
  • Aperture Diameter - 0.6 m
  • Optics Speed - f/3.5
  • Imaging Sensor - 2k x 2k CCD
  • Field-of-View - 0.84 x 0.84 deg
  • Resolution - < 1.5 arcsec
  • Sensitivity - V ~ 19 (10 s), V ~ 21 (60 s) at -30 deg C
  • Slew Speed - 5 deg/s

Super-LOTIS will be located on the former RMT () site at Kitt Peak National Observatory near Tucson, AZ. The system will be housed in a roll-off roof structure rather than a conventional dome to accomodate the the quick slew time of the telescope.

RMT; Super-LOTIS Site

Utilizing our successful experience in construction, operation, data handling, and data analysis of the GROCSE and LOTIS systems we expect Super-LOTIS to be constructed and operational within a year. Burst and afterglow emission are likely to probe different aspects of the GRB model (e.g. internal vs. external shocks.). Detection of optical emission (or stringent constraints on optical emission) at early times would provide a crucial link between the multiwavelength properties of the burst and its afterglow. Thus far only three optical afterglows have been detected and no optical detection simultaneous with or shortly after the gamma-ray burst has been made. The 90 minute delayed emission of high energy photons from GRB 940217 suggests that similar emissions in the optical wavelengths could accompany some bursts. Super-LOTIS would detect such a new spectral component of GRBs to a magnitude level of > V ~ 19. While upper limits will be useful for constraining the models, Super-LOTIS will establish the GRB light curves at early times providing crucial clues toward understanding GRB phenomenon.




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