Astrophys.J.631:1032-1038,2005 We present the results of a search for untriggered gamma-ray burst (GRB)
afterglows with the Robotic Optical Transient Search Experiment-III (ROTSE-III)
telescope ...array. This search covers observations from September 2003 to March
2005. We have an effective coverage of 1.74 deg^2 yr for rapidly fading
transients that remain brighter than ~ 17.5 magnitude for more than 30 minutes.
This search is the first large area survey to be able to detect typical
untriggered GRB afterglows. Our background rate is very low and purely
astrophysical. We have found 4 previously unknown cataclysmic variables (CVs)
and 1 new flare star. We have not detected any candidate afterglow events or
other unidentified transients. We can place an upper limit on the rate of
fading optical transients with quiescent counterparts dimmer than ~ 20th
magnitude at a rate of less than 1.9 deg^-2 yr-1 with 95% confidence. This
places limits on the optical characteristics of off-axis (orphan) GRB
afterglows. As a byproduct of this search, we have an effective ~ 52 deg^2 yr
of coverage for very slowly decaying transients, such as CVs. This implies an
overall rate of outbursts from high galactic latitude CVs of 0.1 deg^2 yr^-1.
Astrophys.J.638:L5-L8,2006 The ROTSE-IIIc telescope at the H.E.S.S. site, Namibia, obtained the earliest
detection of optical emission from a Gamma-Ray Burst (GRB), beginning only 21.8
s from the ...onset of Swift GRB 050801. The optical lightcurve does not fade or
brighten significantly over the first ~250 s, after which there is an
achromatic break and the lightcurve declines in typical power-law fashion. The
Swift/XRT also obtained early observations starting at 69 s after the burst
onset. The X-ray lightcurve shows the same features as the optical lightcurve.
These correlated variations in the early optical and X-ray emission imply a
common origin in space and time. This behavior is difficult to reconcile with
the standard models of early afterglow emission.
Astron.Lett.29:573-578,2003 We present the first results of the observations of the extremely bright
optical afterglow of gamma-ray burst (GRB) 030329 with the 1.5m Russian-Turkish
telescope RTT150 ...(TUBITAK National Observatory, Bakyrlytepe, Turkey). RTT150
was one of the first 1.5m-class telescopes pointed to the afterglow.
Observations were started approximately 6 hours after the burst. During the
first 5 hours of our observations the afterglow faded exactly as a power law
with index -1.19+-0.01 in each of the BVRI Bessel filters. After that, in all
BVRI filters simultaneously we observe a steepening of the power law light
curve. The power law decay index smoothly approaches the value ~= -1.9,
observed by other observatories later. This power law break occurs at t-t_0
=0.57 days and lasts for +-0.1 days. We observe no variability above the
gradual fading with the upper limits 10--1% on time scales 0.1--1000s. Spectral
flux distribution in four BVRI filters corresponds to the power law spectrum
with spectral index \alpha=0.66+-0.01. The change of the power law decay index
in the end of our observations can be interpreted as a signature of collimated
ultrarelativistic jet. The afterglow flux distribution in radio, optical and
x-rays is consistent with synchrotron spectrum. We continue our observations of
this unique object with RTT150.
Astrophys.J.636:959-966,2006 We present lightcurves of the afterglow of GRB050502A, including very early
data at t-t_{GRB} < 60s. The lightcurve is composed of unfiltered ROTSE-IIIb
optical ...observations from 44s to 6h post-burst, R-band MDM observations from
1.6 to 8.4h post-burst, and PAIRITEL J H K_s observations from 0.6 to 2.6h
post-burst. The optical lightcurve is fit by a broken power law, where
t^{alpha} steepens from alpha = -1.13 +- 0.02 to alpha = -1.44 +- 0.02 at
\~5700s. This steepening is consistent with the evolution expected for the
passage of the cooling frequency nu_c through the optical band. Even in our
earliest observation at 44s post-burst, there is no evidence that the optical
flux is brighter than a backward extrapolation of the later power law would
suggest. The observed decay indices and spectral index are consistent with
either an ISM or a Wind fireball model, but slightly favor the ISM
interpretation. The expected spectral index in the ISM interpretation is
consistent within 1 sigma with the observed spectral index beta = -0.8 +- 0.1;
the Wind interpretation would imply a slightly (~2 sigma) shallower spectral
index than observed. A small amount of dust extinction at the source redshift
could steepen an intrinsic spectrum sufficiently to account for the observed
value of beta. In this picture, the early optical decay, with the peak at or
below 4.7e14 Hz at 44s, requires very small electron and magnetic energy
partitions from the fireball.
We report observations of PSR's 0740-28, 1737-30, 1822-09, 1915+13 and 1916+14 with ROSAT. In the 0.1-2.1 keV range upper limits to luminosity are derived for power law and blackbody spectra, using a ...range of \(N_{H}\) estimates. The upper limit to the blackbody luminosity from PSR1822-09 turns out to be consistent with standard cooling curves. For the other pulsars the upper limits are not restrictive as they are much larger than the luminosities predicted by the models.
The ROSAT HRI was used to monitor X-ray emission from the Vela Pulsar. Six observations span 2-1/2 years and 3 glitches. The summed data yield a determination of the pulse shape, and X-ray emission ...from the pulsar is found to be 12 % pulsed with one broad and two narrow peaks. One observation occurred 15 days after a large glitch. No change in pulse structure was observed and any change in X-ray luminosity, if present, was less than 3 %. Implications for neutron star structure are discussed.
Using the archival ROSAT observation of TT Ari, X-ray energy spectra in
different orbital phases and power spectra of the intensity time series are
presented. Spectral fits show that the source gets ...brighter during the
observation. The orbital modulation of the X-ray counting rate and
bremsstrahlung temperature suggests that soft X-ray emission peaks in the
orbital phase interval 0.75-0.90, when an outer disk hot spot is near the line
of sight. This correlates with the orbital modulation of C IV($\lambda$1549)
absorption. Timing analysis indicates that while the source gets brighter, the
frequency of the 1mHz oscillation is not correlated with X-ray intensity. This
implies that in the X-rays from TT Ari, the beat frequency model is not
appropriate for explaining the changes in the 1mHz oscillations.
\keywords{Accretion discs - stars: TT Ari - stars: cataclysmic variables -
X-ray: binaries - X-rays
Using the archival ROSAT observation of TT Ari, X-ray energy spectra in different orbital phases and power spectra of the intensity time series are presented. Spectral fits show that the source gets ...brighter during the observation. The orbital modulation of the X-ray counting rate and bremsstrahlung temperature suggests that soft X-ray emission peaks in the orbital phase interval 0.75-0.90, when an outer disk hot spot is near the line of sight. This correlates with the orbital modulation of C IV(\(\lambda\)1549) absorption. Timing analysis indicates that while the source gets brighter, the frequency of the 1mHz oscillation is not correlated with X-ray intensity. This implies that in the X-rays from TT Ari, the beat frequency model is not appropriate for explaining the changes in the 1mHz oscillations. \keywords{Accretion discs - stars: TT Ari - stars: cataclysmic variables - X-ray: binaries - X-rays
The ROTSE-IIIa telescope at Siding Spring Observatory, Australia, detected prompt optical emission from Swift GRB 050401. In this letter, we present observations of the early optical afterglow, first ...detected by the ROTSE-IIIa telescope 33 s after the start of gamma-ray emission, contemporaneous with the brightest peak of this emission. This GRB was neither exceptionally long nor bright. This is the first prompt optical detection of a GRB of typical duration and luminosity. We find that the early afterglow decay does not deviate significantly from the power-law decay observable at later times, and is uncorrelated with the prompt gamma-ray emission. We compare this detection with the other two GRBs with prompt observations, GRB 990123 and GRB 041219a. All three bursts exhibit quite different behavior at early times.
We present the first results of the observations of the extremely bright optical afterglow of gamma-ray burst (GRB) 030329 with the 1.5m Russian-Turkish telescope RTT150 (TUBITAK National ...Observatory, Bakyrlytepe, Turkey). RTT150 was one of the first 1.5m-class telescopes pointed to the afterglow. Observations were started approximately 6 hours after the burst. During the first 5 hours of our observations the afterglow faded exactly as a power law with index -1.19+-0.01 in each of the BVRI Bessel filters. After that, in all BVRI filters simultaneously we observe a steepening of the power law light curve. The power law decay index smoothly approaches the value ~= -1.9, observed by other observatories later. This power law break occurs at t-t_0 =0.57 days and lasts for +-0.1 days. We observe no variability above the gradual fading with the upper limits 10--1% on time scales 0.1--1000s. Spectral flux distribution in four BVRI filters corresponds to the power law spectrum with spectral index \alpha=0.66+-0.01. The change of the power law decay index in the end of our observations can be interpreted as a signature of collimated ultrarelativistic jet. The afterglow flux distribution in radio, optical and x-rays is consistent with synchrotron spectrum. We continue our observations of this unique object with RTT150.
