The SWIRE/Chandra Survey: The X-ray Sources

We report a moderate-depth (70 ks), contiguous 0.7 deg^2 Chandra survey in the Lockman Hole Field of the Spitzer/SWIRE Legacy Survey coincident with a completed, ultra-deep VLA survey with deep optical and near-infrared imaging in-hand. The primary motivation is to distinguish starburst galaxies and active galactic nuclei (AGNs), including the significant, highly obscured (log N_H > 23) subset. Chandra has detected 775 X-ray sources to a limiting broadband (0.3-8 keV) flux ~4 × 10^(–16) erg cm^(–2) s^(–1). We present the X-ray catalog, fluxes, hardness ratios, and multi-wavelength fluxes. The log N versus log S agrees with those of previous surveys covering similar flux ranges. The Chandra and Spitzer flux limits are well matched: 771 (99%) of the X-ray sources have infrared (IR) or optical counterparts, and 333 have MIPS 24 μm detections. There are four optical-only X-ray sources and four with no visible optical/IR counterpart. The very deep (~2.7 μJy rms) VLA data yield 251 (>4σ) radio counterparts, 44% of the X-ray sources in the field. We confirm that the tendency for lower X-ray flux sources to be harder is primarily due to absorption. As expected, there is no correlation between observed IR and X-ray fluxes. Optically bright, type 1, and red AGNs lie in distinct regions of the IR versus X-ray flux plots, demonstrating the wide range of spectral energy distributions in this sample and providing the potential for classification/source selection. Many optically bright sources, which lie outside the AGN region in the optical versus X-ray plots (f_r /f_x >10), lie inside the region predicted for red AGNs in IR versus X-ray plots, consistent with the presence of an active nucleus. More than 40% of the X-ray sources in the VLA field are radio-loud using the classical definition, R_L . The majority of these are red and relatively faint in the optical so that the use of R_L to select those AGNs with the strongest radio emission becomes questionable. Using the 24 μm to radio flux ratio (q_(24)) instead results in 13 of the 147 AGNs with sufficient data being classified as radio-loud, in good agreement with the ~10% expected for broad-lined AGNs based on optical surveys. We conclude that q_(24) is a more reliable indicator of radio-loudness. Use of R_L should be confined to the optically selected type 1 AGN

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

Chandra and Spitzer unveil heavily obscured quasars in the SWIRE/Chandra Survey

Using the large multi-wavelength data set in the chandra/SWIRE Survey (0.6 square degrees in the Lockman Hole), we show evidence for the existence of highly obscured (Compton-thick) AGN, estimate a lower limit to their surface density and characterize their multi-wavelength properties. Two independent selection methods based on the X-ray and infrared spectral properties are presented. The two selected samples contain 1) 5 X-ray sources with hard X-ray spectra and column densities > 10^24 cm-2, and 2) 120 infrared sources with red and AGN-dominated infrared spectral energy distributions (SEDs). We estimate a surface density of at least 25 Compton-thick AGN per square degree detected in the infrared in the chandra/SWIRE field of which ~40% show distinct AGN signatures in their optical/near-infrared SEDs, the remainings being dominated by the host-galaxy emission. Only ~33% of all Compton-thick AGN are detected in the X-rays at our depth (F(0.3-8 keV)>10^-15 erg/cm2/s. We report the discovery of two sources in our sample of Compton-thick AGN, SWIRE_J104409.95+585224.8 (z=2.54) and SWIRE_J104406.30+583954.1 (z=2.43), which are the most luminous Compton-thick AGN 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.Comment: ApJ accepted (to appear in May 2006 issue, vol. 642, of ApJ) Figures 2, 3, and 14 have been degraded due to space consideration

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 “normal” 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 Mסּ) black holes

The X-ray point source population of spiral and star-forming galaxies

In this thesis, I study a sample of 11 nearby “normal” 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 Mסּ) black holes.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

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