9 research outputs found
The Redshift of the Optical Transient Associated with GRB 010222
The gamma-ray burst (GRB) 010222 is the brightest GRB detected to date by the
BeppoSAX satellite. Prompt identification of the associated optical transient
(OT) allowed for spectroscopy with the Tillinghast 1.5m telescope at F. L.
Whipple Observatory while the source was still relatively bright (R ~ 18.6
mag), within five hours of the burst. The OT shows a blue continuum with many
superimposed absorption features corresponding to metal lines at z = 1.477,
1.157, and possibly also at 0.928. The redshift of GRB 010222 is therefore
unambiguously placed at z >= 1.477. The high number of Mg II absorbers and
especially the large equivalent widths of the Mg II, Mg I, and Fe II absorption
lines in the z = 1.477 system further argue either for a very small impact
parameter or that the z = 1.477 system is the GRB host galaxy itself. The
spectral index of the OT is relatively steep, beta = 0.89 +/- 0.03, and this
cannot be caused by dust with a standard Galactic extinction law in the z =
1.477 absorption system. This spectroscopic identification of the redshift of
GRB 010222 shows that prompt and well-coordinated followup of bright GRBs can
be successful even with telescopes of modest aperture.Comment: 12 pages, 3 figures; ApJ Letters accepted version, only minor change
Rapid UBVRI Follow-up of the Highly Collimated Optical Afterglow of GRB010222
(Abridged) We present the earliest optical observations of the optical
counterpart to the GRB 010222, obtained with the FLWO 1.2-m telescope in UBVRI
passbands, starting 3.64 hours after the burst. We also present late R-band
observations of the afterglow obtained with the 1.8-m VATT ~25 days after the
burst. The temporal analysis of our data joined with published data indicates a
steepening decay, independent of wavelength, asymptotically approaching
t^{-0.80+/-0.05} at early times (t << 1 day) and t^{-1.30+/-0.05} at late
times, with a sharp break at t_b=0.72+/-0.1 days. This is the second earliest
observed break of any afterglow (after GRB 980519), which clearly indicates the
importance of rapid multi-band follow-up for GRB afterglow research. The
optical spectral energy distribution, corrected for small Galactic reddening,
can be fit fairly well by a single power-law with a slope of -1.07+/-0.09.
However, when we fit using our BVRI data only, we obtain a shallower slope of
-0.88+/- 0.1, in excellent agreement with the slope derived from our
low-resolution spectrum (-0.89 +/- 0.03). The spectral slope and light curve
decay slopes we derive are not consistent with a jet model despite the presence
of a temporal break. Significant host dust extinction with a star-burst
reddening law would flatten the spectral index to match jet predictions and
still be consistent with the observed spectral energy distribution. We derive
an opening angle of 2.1 deg, smaller than any listed in the recent compilation
of Frail et al. The total beamed energy corrected for the jet geometry is
4x10^50 erg, very close to the ``standard'' value of 5x10^50 erg found by Frail
et al. for a number of other bursts with light-curve breaks.Comment: revised version (minor changes only) to be published in the ApJ Part
1, 12 pages, 4 figures; all data used for the fits and our CCD frames
available at ftp://cfa-ftp.harvard.edu/pub/kstanek/GRB010222/ and through WWW
at http://cfa-www.harvard.edu/cfa/oir/Research/GRB
Analysis of two methods of isometric muscle contractions during the anti-G straining maneuver
This study investigated the difference in Mean Arterial Pressure (MAP) and Cardiac Output (CO) between two methods of isometric muscle contractions during the Anti-G Straining Maneuver (AGSM). 12 subjects (ages 18 to 38 yrs, height 176.8 +/- 7.4 cm, body mass 78.8 +/- 15.6 kg, percent body fat 14.3 +/- 6.6%) participated in the study. The study was a one-way within-subject design with test conditions counterbalanced. Two methods of isometric muscle contractions lasting 30 seconds each were assessed; an isometric push contraction and an isometric muscle tensing contraction. The dependent parameters were MAP and CO. The average MAP during the push contraction was 123 mmHg, SD +/- 11 and for tense was 118 mmHg, SD +/- 8. CO was 7.6 L/min, SD +/- 1.6 for push and 7.9 L/min, SD +/- 2.0 for tense method. Dependent t-tests revealed t(11) = 1.517, p = 0.157 for MAP and t(11) = 0.875, p = 0.400 for CO. This study demonstrated that the two methods of isometric muscle contractions were not statistically different with regards to MAP and CO. Therefore, both forms of isometric contractions may be potentially useful when performing the muscle contraction portion of the AGSM
The X-ray point source population of spiral and star-forming galaxies
In this thesis, I study a sample of 11 nearby ânormalâ spiral galaxies and one starburst galaxy with the Chandra X-ray Observatory and supporting ground-based telescopes, with particular emphasis on the characterisation of the discrete X-ray point source population. Emission from discrete point sources dominates the X-ray flux from spiral galaxies. This survey spans the Hubble sequence for spirals and, hence, a range in star formation, allowing insights into the X-ray source population of many diverse systems. The inclusion of M82, the prototypical starburst galaxy in the nearby universe, allows for comparison with a system at the extreme of star formation. Presented here is a detailed catalogue of the source population of these galaxies. For each source, I have derived fluxes, luminosities, X-ray colours, and variability properties. I have also searched for optical and radio counterparts. For the most luminous sources, detailed spectral and temporal analyses have been performed. For galaxies as a whole, I have examined X-ray point source luminosity functions and how these relate to star formation of those galaxies. I have also devised a strategy for initial classification of X-ray sources based upon their position within a colour-colour diagram. The luminosity function analysis has then been performed on each class of sources, showing 1) that the method of classification appears to be robust to the first order, and 2) that the old and young (i.e. low-mass X-ray binary and high-mass X-ray binary) populations can be segregated, providing insight into the star formation history of each individual galaxy. I have also studied the environments in which the sources fall within their host galaxies and what this can tell us about the nature of the sources. I have included a discussion of the enigmatic ultraluminous X-ray sources (ULXs), which may be candidates for intermediate mass (100-10,000 Mï) black holes.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
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Chandra and Spitzer Unveil Heavily Obscured Quasars in the Chandra /SWIRE Survey
Using the large multiwavelength data set in the Chandra/SWIRE Survey (0.6 deg2 in the Lockman Hole), we show evidence for the existence of highly obscured (Compton-thick) AGNs, estimate a lower limit to their surface density, and characterize their multiwavelength properties. Two independent selection methods based on the X-ray and infrared spectral properties are presented. The two selected samples contain (1) five X-ray sources with hard X-ray spectra and column densities gsim1024 cm-2 and (2) 120 infrared sources with red and AGN-dominated infrared SEDs. We estimate a surface density of at least 25 Compton-thick AGNs deg-2 detected in the infrared in the Chandra/SWIRE field, of which ~40% show distinct AGN signatures in their optical/near-infrared SEDs, the remaining being dominated by the host galaxy emission. Only ~33% of all Compton-thick AGNs are detected in the X-rays at our depth [F(0.3-8 keV) > 10-15 ergs cm-2 s-1]. We report the discovery of two sources in our sample of Compton-thick AGNs, SWIRE J104409.95+585224.8 (z = 2.54) and SWIRE J104406.30+583954.1 (z = 2.43), which are the most luminous Compton-thick AGNs at high z currently known. The properties of these two sources are discussed in detail with an analysis of their spectra, SEDs, luminosities, and black hole masses.Astronom