The University of Wyoming

1
The University of Wyoming GRB Afterglow
Follow-Up Program S. L. Savage1,2, M. Pierce1, R.
Canterna1, A. S. Kutyrev2, J. P. Norris2 1
University of Wyoming, 2 NASA GSFC
WIRO INSTRUMENTATION
Red Buttes Observatory
Abstract As the Swift era approaches, the
University of Wyoming in Laramie has been
preparing its two research observatories for an
extensive GRB afterglow follow-up program. The
2.3-m telescope at Wyoming Infrared Observatory
(WIRO) is located on Jelm Mt. (2944-m elevation)
in a semi-arid atmosphere, 40 km west of Laramie.
On dry, cold winter nights, WIRO's sensitivity
rivals that of 4-m class telescopes at more
temperate sites. Three instruments are currently
in use at the observatory WIRO-Prime, WIRO-Spec,
and the Goddard IR camera. WIRO-Prime is a 20482
prime-focus CCD camera with a 20 arcmin diameter
FOV (f/2.1). A 5-minute exposure reaches point
sources as faint as 24th magnitude in V in
1-arcsec seeing. WIRO-Spec is an integral field,
holographic spectrometer which utilizes
Volume-Phase-Holographic gratings with a 20482
CCD detector. A 15 X 20 array of 1 arcsec
optical fibers will allow simultaneous
spectroscopy over an equivalent region on the sky
for rapid follow-up spectroscopy of GRB
afterglows. The high system efficiency ( 40)
should enable us to reach S/N 10 for a 20th mag
point source in a 10-min exposure with a typical
resolution of 5 Angstrom. The Goddard IR
Camera is a 2562 InSb camera (FOV 108 arc sec)
mounted at Cassegrain and operated at 15K.
Available filters for GRB observations include R,
I, J, H, and K. Red Buttes Observatory (RBO)
features a 0.6-m f/8 Cassegrain telescope, 19 km
south of Laramie. RBO's 10242 CCD camera has a
limiting magnitude of 20 in a 5-minute exposure
and an 18 arc minute FOV, sufficiently large for
BAT localizations. At WIRO we plan to pursue
afterglows with whichever instrument is in use at
the time of an alert and hope to obtain a
response time of 120 s, comparable to Swifts
slew timescale. Together, these facilities
should significantly enhance the current
capabilities for rapid follow-up response to GRB
events and thereby provide valuable optical and
near-IR photometry and spectroscopy of the
afterglows.
WIRO-Prime

• 20482 13.5-um pixel CCD
• 0.55 arcsec / pixel
• Prime-focus mount
• 20 arcmin diameter FOV (f/2.1)
• 5 minute exposure ? 24th V mag with 1 arcsec
  seeing
• 400 1000 nm

RBO is located 19 km south of Laramie on a dark
site which, combined with the dry, thin
atmosphere ( 2200-m elevation), enables
relatively deep imaging with its Apogee AP8p
10242 CCD camera mounted to a 0.6-m Cassegrain
DFM reflector. Ten-minute exposures can yield
typical limiting magnitudes of 19.5 (19) for V
and R (B). The large 18-arcmin FOV is sufficient
for rapidly acquiring and imaging Swifts BAT
error regions ( 4 arcmin radius) and relaying
the locations to WIRO for deeper imaging in the
IR and spectroscopy. Demands on RBO by the U.
Wyoming Physics and Astronomy Department have
greatly increased for various scientific
endeavors in addition to GRB afterglow follow-up
study. To realize rapid response and to
modernize the facility, RBO has been extensively
renovated and upgraded. Among the upgrades are
refurbishment of the telescope platform and
facility, acquisition of faster computers,
establishment of a microwave link, and
installation of a GPS clock, flat-field
lights/screen, a weather station, and an all-sky
camera for local weather monitoring. All of the
improvements were commensurate with the goal of
realizing a completely automated GRB afterglow
response. Current follow-up operations require
human intervention however, total automation is
planned for the near future.
WIRO-Prime is pictured mounted at prime focus.
The above galaxy is a scaled, color image of M101
taken with WIRO-Prime using B (10-min), V
(5-min), and R (5-min). Note The older CCD
used to obtain this image had a 10242 24-um pixel
CCD and 18 arcmin FOV. The new CCD has better
spatial sampling with a similar FOV (see above).
WIRO-Spec

• 20482 CCD detector
• Volume-Phase-Holographic (VPH) gratings
• 293 fiber optical cables
• 1 fiber 1 arcsec
• 15 20 fiber array
• Fibers connect Cassegrain mount to stationary
  spectrometer
• 400 1000 nm

RESULTS EXPECTATIONS
Motivation
Because of the transient nature of bursts, GRB
follow-up research must be performed on a
target-of-opportunity basis. Both observatories,
within an hour of Laramie, are owned by the
university making rapid and numerous prompt
observations as well as long-term follow-up
monitoring more feasible. Short bursts have yet
to be associated with optical counterparts due to
their predicted steep light curves and
intrinsically low initial brightness.3 Acquiring
light curves for short bursts with the rapid
reaction capabilities of RBO would be a
significant contribution. In addition to imaging
and photometry, spectroscopy is available for
determining redshifts of high z burst sources a
necessary ingredient for modeling. GRBs are
predicted to occur at considerable rates beyond z
5, thus making them primary candidates as
probes for cosmology in the study of the Lyman-a
forest, the epoch of reionization, the evolution
of metallicity, and large-scale, high-redshift
structure.1,2 Prior to the involvement of WIRO
in the GRB program, RBO collected data on several
GRBs in collaboration with the Follow-Up Network
(FUN) GRB group in primary affiliation with Dan
Reichart of the University of North Carolina,
Chapel Hill. Eight GCN notices have been
archived from the University of Wyoming with
detection or magnitude contributions. WIRO will
continue the lightcurve analysis to deeper
magnitudes than RBO, add infrared capability (J,
H, and K bands), and spectroscopy for
determination of high redshift burst afterglows.
To complement the GRB response from Swift, the
combined efforts of the two research
observatories at the University of Wyoming, WIRO
and RBO, will enable rapid reaction to burst
alerts, offer a large FOV for targeting bursts,
and provide wavelength coverage ranging from
optical through near-infrared. RBOs automated
response, with a slewing rate comparable to
Swifts, coupled with a large 18-arcmin FOV
assures targeting a burst in its early afterglow
stages and possibly detecting the elusive
afterglow of short bursts a feat yet to be
accomplished. The large collecting power of the
2.3-m WIRO telescope and infrared optimization
ensure deep imaging in wavelengths not accessible
by Swift. WIRO and RBO will also be able to
overlap with Swifts coverage in the optical.
WIRO-Spec is pictured from above inside its
stationary freezer. The fibers are connected to
a Cassegrain platform. The above solar spectra
are taken via the moons reflection. The
curvature of the lines is an optical artifact and
are straightened using software and comparison
spectra. The spectra collected from individual
fibers run vertically and a spectral feature
(i.e., a given spectral line) run horizontally.
Each fiber looks at a different area of the 15
20 FOV. Due to its high efficiency ( 40), a
10-min exposure typically yields a S/N 10 with
a resolution of 5 Angstrom for a 20th magnitude
point source.
WIRO-Goddard IR Camera

• 2562 InSb detector
• Operates at 15K
• Cassegrain mount
• 108 arcsec FOV
• R, I, J, H, K

Wyoming Infrared Observatory
To left are pictures of the WIRO-Goddard IR
camera. It must be vacuum-pumped and cooled to
15K with liquid nitrogen and liquid helium for
operation. The false color image of Jupiter at
right was composed using the IR camera under
heavy cloud with three filters (J, K, and Br?).
WIRO, situated at 2944 m, 40 km southwest of
Laramie in semi-arid conditions, is an optimal
site for optical and infrared observations. The
2.3-m telescope is one of the largest with
extensive availability to afterglow follow-up
research. WIROs intermediate size allows fast
acquisition strategies in comparison with larger
telescopes. WIRO is currently undergoing
renovations which include new and upgraded
instruments as well as facility improvements.
Recent additions are WIROs three primary
instruments WIRO-Prime, WIRO-Spec, and the
WIRO-Goddard IR camera. Beyond GRB targets of
opportunity, WIRO is primarily dedicated to
on-going observing programs by the faculty, new
graduate students, and visiting astronomers with
scientific emphasis on quasars, cataclysmic
variables, globular clusters, etc. For speed of
acquisition the instrument in use at the time of
a burst alert will be utilized to promptly pursue
afterglows with photometry or spectroscopy.


Above left are images taken from RBO of the
brightest and one of the closest bursts
GRB030329. Below, its lightcurve is shown as
measured by RBO. The results of RBO monitoring
have contributed eight GCN notices to date.
References 1Bromm, V. Loeb, A. 2002 ApJ, 575,
111 2Lamb, D.Q. Reichart, D.E. 2000 ApJ,
536, 1 3Panaitescu, A., Kumar,
P., Narayan, R. 2001 ApJ, 561, L171
Acknowledgements This research has been
supported by NSF grant AST 00-97356, NASA EPSCoR
grant NCC5-578, and NASA grant NAG5-11191.