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[show abstract]
[hide abstract]
ABSTRACT: We report on the present stage of SN 1987A as observed by the Chandra X-ray
Observatory. We reanalyze published Chandra observations and add three more
epochs of Chandra data to get a consistent picture of the evolution of the
X-ray fluxes in several energy bands. We discuss the implications of several
calibration issues for Chandra data. Using the most recent Chandra calibration
files, we find that the 0.5-2.0 keV band fluxes of SN 1987A have increased by
~6 x 10 ^-13 erg s^-1 cm^-2 per year since 2009. This is in contrast with our
previous result that the 0.5-2.0 keV light curve showed a sudden flattening in
2009. Based on our new analysis, we conclude that the forward shock is still in
full interaction with the equatorial ring.
12/2012;
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Y. Q. Xue,
B. Luo,
W. N. Brandt,
F. E. Bauer,
B. D. Lehmer, P. S. Broos,
D. P. Schneider,
D. M. Alexander,
M. Brusa,
A. Comastri, [......],
T. Liu,
V. Mainieri,
M. Paolillo,
D. A. Rafferty,
P. Rosati,
O. Shemmer,
J. D. Silverman,
I. Smail,
P. Tozzi,
and C. Vignali
[show abstract]
[hide abstract]
ABSTRACT: We present source catalogs for the 4 Ms Chandra Deep Field-South (CDF-S), which is the deepest Chandra survey to date and covers an area of 464.5 arcmin2. We provide a main Chandra source catalog, which contains 740 X-ray sources that are detected with WAVDETECT at a false-positive probability threshold of 10–5 in at least one of three X-ray bands (0.5-8 keV, full band; 0.5-2 keV, soft band; and 2-8 keV, hard band) and also satisfy a binomial-probability source-selection criterion of P < 0.004 (i.e., the probability of sources not being real is less than 0.004); this approach is designed to maximize the number of reliable sources detected. A total of 300 main-catalog sources are new compared to the previous 2 Ms CDF-S main-catalog sources. We determine X-ray source positions using centroid and matched-filter techniques and obtain a median positional uncertainty of 042. We also provide a supplementary catalog, which consists of 36 sources that are detected with WAVDETECT at a false-positive probability threshold of 10–5, satisfy the condition of 0.004 < P < 0.1, and have an optical counterpart with R < 24. Multiwavelength identifications, basic optical/infrared/radio photometry, and spectroscopic/photometric redshifts are provided for the X-ray sources in the main and supplementary catalogs. Seven hundred sixteen (97%) of the 740 main-catalog sources have multiwavelength counterparts, with 673 (94% of 716) having either spectroscopic or photometric redshifts. The 740 main-catalog sources span broad ranges of full-band flux and 0.5-8 keV luminosity; the 300 new main-catalog sources span similar ranges although they tend to be systematically lower. Basic analyses of the X-ray and multiwavelength properties of the sources indicate that >75% of the main-catalog sources are active galactic nuclei (AGNs); of the 300 new main-catalog sources, about 35% are likely normal and starburst galaxies, reflecting the rise of normal and starburst galaxies at the very faint flux levels uniquely accessible to the 4 Ms CDF-S. Near the center of the 4 Ms CDF-S (i.e., within an off-axis angle of 3'), the observed AGN and galaxy source densities have reached 9800+1300 – 1100 deg–2 and 6900+1100 – 900 deg–2, respectively. Simulations show that our main catalog is highly reliable and is reasonably complete. The mean backgrounds (corrected for vignetting and exposure-time variations) are 0.063 and 0.178 counts Ms–1 pixel–1 (for a pixel size of 0492) for the soft and hard bands, respectively; the majority of the pixels have zero background counts. The 4 Ms CDF-S reaches on-axis flux limits of 3.2 × 10–17, 9.1 × 10–18, and 5.5 × 10–17 erg cm–2 s–1 for the full, soft, and hard bands, respectively. An increase in the CDF-S exposure time by a factor of 2-2.5 would provide further significant gains and probe key unexplored discovery space.
The Astrophysical Journal Supplement Series 06/2011; 195(1):10. · 13.46 Impact Factor
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Y Q Xue,
B Luo,
W N Brandt,
F E Bauer,
B D Lehmer, P S Broos,
D P Schneider,
D M Alexander,
M Brusa,
A Comastri,
A C Fabian,
R Gilli,
G Hasinger,
A E Hornschemeier
[show abstract]
[hide abstract]
ABSTRACT: We present source catalogs for the 4 Ms Chandra Deep Field-South (CDF-S), which is the deepest Chandra survey to date and covers an area of 464.5 arcmin 2 . We provide a main Chandra source catalog, which contains 740 X-ray sources that are detected with WAVDETECT at a false-positive probability threshold of 10 −5 in at least one of three X-ray bands (0.5–8 keV, full band; 0.5–2 keV, soft band; and 2–8 keV, hard band) and also satisfy a binomial-probability source-selection criterion of P < 0.004 (i.e., the probability of sources not being real is less than 0.004); this approach is designed to maximize the number of reliable sources detected. A total of 300 main-catalog sources are new compared to the previous 2 Ms CDF-S main-catalog sources. We determine X-ray source positions using centroid and matched-filter techniques and obtain a median positional uncertainty of ≈ 0.42 ′′ . We also provide a supplementary catalog, which consists of 36 sources that are detected with WAVDETECT at a false-positive probability threshold of 10 −5 , satisfy the condition of 0.004 < P < 0.1, and have an optical counterpart with R < 24. Multiwavelength identifications, basic optical/infrared/radio photometry, and spectroscopic/photometric redshifts are provided for the X-ray sources in the main and supplementary catalogs. 716 (≈ 97%) of the 740 main-catalog sources have multiwavelength counterparts, with 673 (≈ 94% of 716) having either spectroscopic or photometric redshifts. The 740 main-catalog sources span broad ranges of full-band flux and 0.5–8 keV luminosity; the 300 new main-catalog sources span similar ranges although they tend to be systematically lower. Basic analyses of the X-ray and multiwavelength properties of the sources indicate that > 75% of the main-catalog sources are AGNs; of the 300 new main-catalog sources, about 35% are likely normal and starburst galaxies, reflecting the rise of normal and starburst galaxies at the very faint flux levels uniquely accessible to the 4 Ms CDF-S. Near the center of the 4 Ms CDF-S (i.e., within an off-axis angle of 3 ′), the observed AGN and galaxy source densities have reached 9800 +1300 −1100 deg −2 and 6900 +1100 −900 deg −2 , respectively. Simulations show that our main catalog is highly reliable and is reasonably complete. The mean backgrounds (corrected for vignetting and exposure-time variations) are 0.063 and 0.178 count Ms −1 pixel −1 (for a pixel size of 0.492 ′′) for the soft and hard bands, respectively; the majority of the pixels have zero background counts. The 4 Ms CDF-S reaches on-axis flux limits of ≈ 3.2 × 10 −17 , 9.1 × 10 −18 , and 5.5 × 10 −17 erg cm −2 s −1 for the full, soft, and hard bands, respectively. An increase in the CDF-S exposure time by a factor of ≈ 2–2.5 would provide further significant gains and probe key unexplored discovery space.
04/2011; 13(19).
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[show abstract]
[hide abstract]
ABSTRACT: X-ray observations of the double-binary OB-star system QZ Car (HD 93206)
obtained with the Chandra X-ray Observatory over a period of roughly 2 years
are presented. The orbit of systems A (O9.7 I+b2 v, PA = 21 d) and B (O8 III+o9
v, PB = 6 d) are reasonably well sampled by the observations, allowing the
origin of the X-ray emission to be examined in detail. The X-ray spectra can be
well fitted by an attenuated three temperature thermal plasma model,
characterised by cool, moderate, and hot plasma components at kT ~ 0.2, 0.7,
and 2 keV, respectively, and a circumstellar absorption of ~ 0.2 x 10^22 cm-2.
Although the hot plasma component could be indicating the presence of wind-wind
collision shocks in the system, the model fluxes calculated from spectral fits,
with an average value of ~ 7 x 10^-13 erg s-1 cm-2, do not show a clear
correlation with the orbits of the two constituent binaries. A semi-analytical
model of QZ Car reveals that a stable momentum balance may not be established
in either system A or B. Yet, despite this, system B is expected to produce an
observed X-ray flux well in excess of the observations. If one considers the
wind of the O8 III star to be disrupted by mass transfer the model and
observations are in far better agreement, which lends support to the previous
suggestion of mass-transfer in the O8 III + o9 v binary. We conclude that the
X-ray emission from QZ Car can be reasonably well accounted for by a
combination of contributions mainly from the single stars and the mutual
wind-wind collision between systems A and B.
03/2011;
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Y. Naze, P. S. Broos,
L. Oskinova,
L. K. Townsley,
D. Cohen,
M. F. Corcoran,
N. R. Evans,
M. Gagne,
A. F. J. Moffat,
J. M. Pittard,
G. Rauw,
A. ud-Doula,
N. R. Walborn
[show abstract]
[hide abstract]
ABSTRACT: The key empirical property of the X-ray emission from O stars is a strong
correlation between the bolometric and X-ray luminosities. In the framework of
the Chandra Carina Complex Project, 129 O and B stars have been detected as
X-ray sources; 78 of those, all with spectral type earlier than B3, have enough
counts for at least a rough X-ray spectral characterization. This leads to an
estimate of the Lx/Lbol ratio for an exceptional number of 60 O stars belonging
to the same region and triples the number of Carina massive stars studied
spectroscopically in X-rays. The derived log(Lx/Lbol) is -7.26 for single
objects, with a dispersion of only 0.21dex. Using the properties of hot massive
stars listed in the literature, we compare the X-ray luminosities of different
types of objects. In the case of O stars, the Lx/Lbol ratios are similar for
bright and faint objects, as well as for stars of different luminosity classes
or spectral types. Binaries appear only slightly harder and slightly more
luminous in X-rays than single objects; the differences are not formally
significant (at the 1% level), except for the Lx/Lbol ratio in the medium
(1.0--2.5keV) energy band. Weak-wind objects have similar X-ray luminosities
but they display slightly softer spectra compared to "normal" O stars with the
same bolometric luminosity. Discarding three overluminous objects, we find a
very shallow trend of harder emission in brighter objects. The properties of
the few B stars bright enough to yield some spectral information appear to be
different overall (constant X-ray luminosities, harder spectra), hinting that
another mechanism for producing X-rays, besides wind shocks, might be at work.
However, it must be stressed that the earliest and X-ray brightest amongst
these few detected objects are similar to the latest O stars, suggesting a
possibly smooth transition between the two processes.
03/2011;
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M. P. Muno,
F. E. Bauer,
F. K. Baganoff,
R. M. Bandyopadhyay,
G. C. Bower,
W. N. Brandt, P. S. Broos,
A. Cotera,
S. S. Eikenberry,
G. P. Garmire, [......],
M. R. Morris,
T. Nagata,
S. Nishiyama,
S. Park,
S. V. Ramìrez,
S. R. Stolovy,
R. Wijnands,
Q. D. Wang,
Z. Wang,
and F. Yusef-Zadeh
[show abstract]
[hide abstract]
ABSTRACT: We present a catalog of 9017 X-ray sources identified in Chandra observations of a 2°× 08 field around the Galactic center. This enlarges the number of known X-ray sources in the region by a factor of 2.5. The catalog incorporates all of the ACIS-I observations as of 2007 August, which total 2.25 Ms of exposure. At the distance to the Galactic center (8 kpc), we are sensitive to sources with luminosities of 4 × 1032 erg s–1 (0.5-8.0 keV; 90% confidence) over an area of 1 deg2, and up to an order of magnitude more sensitive in the deepest exposure (1.0 Ms) around Sgr A*. The positions of 60% of our sources are accurate to <1 '' (95% confidence), and 20% have positions accurate to <05. We search for variable sources, and find that 3% exhibit flux variations within an observation, and 10% exhibit variations from observation-to-observation. We also find one source, CXOUGC J174622.7 – 285218, with a periodic 1745 s signal (1.4% chance probability), which is probably a magnetically accreting cataclysmic variable. We compare the spatial distribution of X-ray sources to a model for the stellar distribution, and find 2.8σ evidence for excesses in the numbers of X-ray sources in the region of recent star formation encompassed by the Arches, Quintuplet, and Galactic center star clusters. These excess sources are also seen in the luminosity distribution of the X-ray sources, which is flatter near the Arches and Quintuplet than elsewhere in the field. These excess point sources, along with a similar longitudinal asymmetry in the distribution of diffuse iron emission that has been reported by other authors, probably have their origin in the young stars that are prominent at l 01.
The Astrophysical Journal Supplement Series 03/2009; 181(1):110. · 13.46 Impact Factor
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K. V. Getman,
E. Flaccomio, P. S. Broos,
N. Grosso,
M. Tsujimoto,
L. Townsley,
G. P. Garmire,
J. Kastner,
J. Li,
F. R. Harnden, [......],
M. J. McCaughrean,
G. Meeus,
F. Damiani,
G. Micela,
S. Sciortino,
J. Bally,
L. A. Hillenbrand,
W. Herbst,
T. Preibisch,
and E. D. Feigelson
[show abstract]
[hide abstract]
ABSTRACT: We present a description of the data reduction methods and the derived catalog of more than 1600 X-ray point sources from the exceptionally deep 2003 January Chandra X-Ray Observatory (Chandra) observation of the Orion Nebula Cluster and embedded populations around OMC-1. The observation was obtained with Chandra's Advanced CCD Imaging Spectrometer (ACIS) and has been nicknamed the Chandra Orion Ultradeep Project (COUP). With an 838 ks exposure made over a continuous period of 13.2 days, the COUP observation provides the most uniform and comprehensive data set on the X-ray emission of normal stars ever obtained in the history of X-ray astronomy.
The Astrophysical Journal Supplement Series 12/2008; 160(2):319. · 13.46 Impact Factor
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M. Tsujimoto,
E. D. Feigelson,
L. K. Townsley, P. S. Broos,
K. V. Getman,
J. Wang,
G. P. Garmire,
D. Baba,
T. Nagayama,
M. Tamura,
and E. B. Churchwell
[show abstract]
[hide abstract]
ABSTRACT: We present the results of a high-resolution X-ray imaging study of the stellar population in the Galactic massive star-forming region RCW 49 and its central OB association Westerlund 2. We obtained a ~40 ks X-ray image of a ~17' × 17' field using the Chandra X-Ray Observatory and deep NIR images using the Infrared Survey Facility in a concentric ~8.3' × 8.3' region. We detected 468 X-ray sources and identified optical, NIR, and Spitzer MIR counterparts for 379 of them. The unprecedented spatial resolution and sensitivity of the X-ray image, enhanced by optical and infrared imaging data, yielded the following results: (1) The central OB association Westerlund 2 is resolved for the first time in the X-ray band. X-ray emission is detected from all spectroscopically identified early-type stars in this region. (2) Most (~86%) X-ray sources with optical or infrared identifications are cluster members in comparison with a control field in the Galactic plane. (3) A loose constraint (2-5 kpc) for the distance to RCW 49 is derived from the mean X-ray luminosity of T Tauri stars. (4) The cluster X-ray population consists of low-mass pre-main-sequence and early-type stars as obtained from X-ray and NIR photometry. About 30 new OB star candidates are identified. (5) We estimate a cluster radius of 6'-7' based on the X-ray surface number density profiles. (6) A large fraction (~90%) of cluster members are identified individually using complimentary X-ray and MIR excess emission. (7) The brightest five X-ray sources, two Wolf-Rayet stars and three O stars, have hard thermal spectra.
The Astrophysical Journal 12/2008; 665(1):719. · 6.02 Impact Factor
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A. E. Hornschemeier,
W. N. Brandt,
G. P. Garmire,
D. P. Schneider, P. S. Broos,
L. K. Townsley,
M. W. Bautz,
D. N. Burrows,
G. Chartas,
E. D. Feigelson,
R. Griffiths,
D. Lumb,
J. A. Nousek,
and W. L. W. Sargent
[show abstract]
[hide abstract]
ABSTRACT: We present first results from an X-ray study of the Hubble Deep Field North (HDF-N) and its environs obtained using 166 ks of data collected by the Advanced CCD Imaging Spectrometer (ACIS) on board the Chandra X-Ray Observatory. This is the deepest X-ray observation ever reported, and in the HDF-N itself we detect six X-ray sources down to a 0.5-8 keV flux limit of ≈4 × 10-16 ergs cm-2 s-1. Comparing these sources with objects seen in multiwavelength HDF-N studies shows positional coincidences with the extremely red object NICMOS J123651.74+621221.4, an active galactic nucleus (AGN), three elliptical galaxies, and one nearby spiral galaxy. The X-ray emission from the ellipticals is consistent with that expected from a hot interstellar medium, and the spiral galaxy emission may arise from a "super-Eddington" X-ray binary or ultraluminous supernova remnant. Four of the X-ray sources have been detected at radio wavelengths. We also place X-ray upper limits on AGN candidates found in the HDF-N, and we present the tightest constraints yet on X-ray emission from the SCUBA submillimeter source population. None of the 10 high-significance submillimeter sources reported in the HDF-N and its vicinity is detected with the Chandra ACIS. These sources appear to be dominated by star formation or have AGNs with Compton-thick tori and little circumnuclear X-ray scattering.
The Astrophysical Journal 12/2008; 541(1):49. · 6.02 Impact Factor
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D. M. Alexander,
F. E. Bauer,
W. N. Brandt,
D. P. Schneider,
A. E. Hornschemeier,
C. Vignali,
A. J. Barger, P. S. Broos,
L. L. Cowie,
G. P. Garmire,
L. K. Townsley,
M. W. Bautz,
G. Chartas,
and W. L. W. Sargent
[show abstract]
[hide abstract]
ABSTRACT: We present point-source catalogs for the ≈2 Ms exposure of the Chandra Deep Field North, currently the deepest X-ray observation of the universe in the 0.5–8.0 keV band. Five hundred and three (503) X-ray sources are detected over an ≈448 arcmin2 area in up to seven X-ray bands. Twenty (20) of these X-ray sources lie in the central ≈5.3 arcmin2 Hubble Deep Field North (13,600 sources deg-2). The on-axis sensitivity limits are ≈2.5 × 10-17 ergs cm-2 s-1 (0.5–2.0 keV) and ≈1.4 × 10-16 ergs cm-2 s-1 (2–8 keV). Source positions are determined using matched-filter and centroiding techniques; the median positional uncertainty is ≈03. The X-ray colors of the detected sources indicate a broad variety of source types, although absorbed AGNs (including a small number of possible Compton-thick sources) are clearly the dominant type. We also match lower significance X-ray sources to optical counterparts and provide a list of 79 optically bright (R 23) lower significance Chandra sources. The majority of these sources appear to be starburst and normal galaxies. The average backgrounds in the 0.5–2.0 keV and 2–8 keV bands are 0.056 and 0.135 counts Ms-1 pixel-1, respectively. The background count distributions are very similar to Poisson distributions. We show that this ≈2 Ms exposure is approximately photon limited in all seven X-ray bands for regions close to the aim point, and we predict that exposures up to ≈25 Ms (0.5–2.0 keV) and ≈4 Ms (2–8 keV) should remain nearly photon limited. We demonstrate that this observation does not suffer from source confusion within ≈6' of the aim point, and future observations are unlikely to be source-confusion limited within ≈3' of the aim point even for source densities exceeding 100,000 deg-2. These analyses directly show that Chandra can achieve significantly higher sensitivities in an efficient, nearly photon-limited manner and be largely free of source confusion. To allow consistent comparisons, we have also produced point-source catalogs for the ≈1 Ms Chandra Deep Field South (CDF-S). Three hundred and twenty-six (326) X-ray sources are included in the main Chandra catalog, and an additional 42 optically bright X-ray sources are included in a lower significance Chandra catalog. We find good agreement with the photometry of the previously published CDF-S catalogs; however, we provide significantly improved positional accuracy.
The Astronomical Journal 12/2007; 126(2):539. · 4.03 Impact Factor
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W. N. Brandt,
D. M. Alexander,
A. E. Hornschemeier,
G. P. Garmire,
D. P. Schneider,
A. J. Barger,
F. E. Bauer, P. S. Broos,
L. L. Cowie,
L. K. Townsley,
D. N. Burrows,
G. Chartas,
E. D. Feigelson,
R. E. Griffiths,
J. A. Nousek,
and W. L. W. Sargent
[show abstract]
[hide abstract]
ABSTRACT: An extremely deep X-ray survey (≈1 Ms) of the Hubble Deep Field North (HDF-N) and its environs (≈450 arcmin2) has been performed with the Advanced CCD Imaging Spectrometer on board the Chandra X-Ray Observatory. This is one of the two deepest X-ray surveys ever performed; for point sources near the aim point, it reaches 0.5–2.0 and 2–8 keV flux limits of ≈3 × 10-17 and ≈2 × 10-16 ergs cm-2 s-1, respectively. Here we provide source catalogs, along with details of the observations, data reduction, and technical analysis. Observing conditions, such as background, were excellent for almost all of the exposure. We have detected 370 distinct point sources: 360 in the 0.5–8.0 keV band, 325 in the 0.5–2.0 keV band, 265 in the 2–8 keV band, and 145 in the 4–8 keV band. Two new Chandra sources in the HDF-N itself are reported and discussed. Source positions are accurate to within 06–17 (at ≈90% confidence), depending mainly on the off-axis angle. We also detect two highly significant extended X-ray sources and several other likely extended X-ray sources. We present basic number count results for sources located near the center of the field. Source densities of 7100 deg-2 (at 4.2 × 10-17 ergs cm-2 s-1) and 4200 deg-2 (at 3.8 × 10-16 ergs cm-2 s-1) are observed in the soft and hard bands, respectively.
The Astronomical Journal 12/2007; 122(6):2810. · 4.03 Impact Factor
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M Tsujimoto,
E. D. Feigelson,
L. K. Townsley, P. S. Broos,
K. V. Getman,
J. Wang,
G. P. Garmire,
D. Baba,
T Nagayama,
M Tamura,
E. B. Churchwell
[show abstract]
[hide abstract]
ABSTRACT: We present the results of a high-resolution X-ray imaging study of the stellar population in the Galactic massive star-forming region RCW49 and its central OB association Westerlund 2. We obtained a 40 ks X-ray image of a 17'x17' field using the Chandra X-ray Observatory and deep NIR images using the Infrared Survey Facility in a concentric 8'3x8'3 region. We detected 468 X-ray sources and identified optical, NIR, and Spitzer Space Telescope MIR counterparts for 379 of them. The unprecedented spatial resolution and sensitivity of the X-ray image, enhanced by optical and infrared imaging data, yielded the following results: (1) The central OB association Westerlund 2 is resolved for the first time in the X-ray band. X-ray emission is detected from all spectroscopically-identified early-type stars in this region. (2) Most (86%) X-ray sources with optical or infrared identifications are cluster members in comparison with a control field in the Galactic Plane. (3) A loose constraint (2--5 kpc) for the distance to RCW49 is derived from the mean X-ray luminosity of T Tauri stars. (4) The cluster X-ray population consists of low-mass pre--main-sequence and early-type stars as obtained from X-ray and NIR photometry. About 30 new OB star candidates are identified. (5) We estimate a cluster radius of 6'--7' based on the X-ray surface number density profiles. (6) A large fraction (90%) of cluster members are identified individually using complimentary X-ray and MIR excess emission. (7) The brightest five X-ray sources, two Wolf-Rayet stars and three O stars, have hard thermal spectra. Comment: 19 pages, 17 figures, 4 tables. ApJ in press
05/2007;
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[show abstract]
[hide abstract]
ABSTRACT: We report the Chandra detection of hard X-ray emission from the Welch ring in W49A, an organized structure of ultra-compact (UC) HII regions containing a dozen nascent early-type stars. Two UC HII regions are associated with hard X-ray emission in a deep Advanced CCD Imaging Spectrometer image exposed for 96.7 ks. One of the two X-ray sources has no near-infrared counterpart and is extended by ~5 arcsec, or ~0.3 pc, at a distance of ~11.4 kpc, which is spatially aligned with the cometary radio continuum emission associated with the UC HII region. The X-ray spectrum of the emission, when fit with a thermal model, indicates a heavily absorbed plasma with extinction of \~5x10^{23}/cm^{2}, temperature of ~7 keV, and X-ray luminosity in the 3.0-8.0 keV band of ~3x10^{33} ergs/s. Both the luminosity and the size of the emission resemble the extended hard emission found in UC HII regions in Sagittarius B2, yet they are smaller by an order of magnitude than the emission found in massive star clusters such as NGC 3603. Three possibilities are discussed for the cause of the hard extended emission in the Welch ring: an ensemble of unresolved point sources, shocked interacting winds of the young O stars, and a wind-blown bubble interacting with ambient cold matter.
12/2006;
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[show abstract]
[hide abstract]
ABSTRACT: We have studied the X-ray point source population of the 30 Doradus star-forming complex in the Large Magellanic Cloud using high-spatial-resolution X-ray images and spatially-resolved spectra obtained with the Advanced CCD Imaging Spectrometer (ACIS) aboard the Chandra X-ray Observatory. Here we describe the X-ray sources in a 17' x 17' field centered on R136, the massive star cluster at the center of the main 30 Dor nebula. We detect 20 of the 32 Wolf-Rayet stars in the ACIS field. R136 is resolved at the subarcsecond level into almost 100 X-ray sources, including many typical O3--O5 stars as well as a few bright X-ray sources previously reported. Over two orders of magnitude of scatter in L_X is seen among R136 O stars, suggesting that X-ray emission in the most massive stars depends critically on the details of wind properties and binarity of each system, rather than reflecting the widely-reported characteristic value L_X/L_bol ~ 10^{-7}. Such a canonical ratio may exist for single massive stars in R136, but our data are too shallow to confirm this relationship. Through this and future X-ray studies of 30 Doradus, the complete life cycle of a massive stellar cluster can be revealed. Comment: 31 pages, 6 bitmapped figures, 5 tables; accepted to AJ
01/2006;
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P. W. A. Roming,
T. E. Kennedy,
K. O. Mason,
J. A. Nousek,
L. Ahr,
R. E. Bingham, P. S. Broos,
M. J. Carter,
B. K. Hancock,
H. E. Huckle, [......],
K. Smith,
P. J. Smith,
J. C. Soto,
P. T. Boyd,
A. A. Breeveld,
S. T. Holland,
M. Ivanushkina,
M. S. Pryzby,
M. D. Still,
J. Stock
[show abstract]
[hide abstract]
ABSTRACT: The UV/Optical Telescope (UVOT) is one of three instruments flying aboard the
Swift Gamma-ray Observatory. It is designed to capture the early (approximately
1 minute) UV and optical photons from the afterglow of gamma-ray bursts in the
170-600 nm band as well as long term observations of these afterglows. This is
accomplished through the use of UV and optical broadband filters and grisms.
The UVOT has a modified Ritchey-Chretien design with micro-channel plate
intensified charged-coupled device detectors that record the arrival time of
individual photons and provide sub-arcsecond positioning of sources. We discuss
some of the science to be pursued by the UVOT and the overall design of the
instrument.
Space Science Reviews 07/2005; 120(3). · 3.61 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: The Chandra X-ray Observatory is providing remarkable new views of massive star-forming regions, revealing all stages in the life cycle of high-mass stars and their effects on their surroundings. We present a Chandra tour of several high-mass star-forming regions, highlighting physical processes that characterize the life of a cluster of high-mass stars, from deeply-embedded cores too young to have established an HII region to superbubbles so large that they shape our views of galaxies. Along the way we see that X-ray observations reveal hundreds of stellar sources powering great HII region complexes, suffused by both hard and soft diffuse X-ray structures caused by fast O-star winds thermalized in wind-wind collisions or by termination shocks against the surrounding media. Finally, we examine the effects of the deaths of high-mass stars that remained close to their birthplaces, exploding as supernovae within the superbubbles that these clusters created. We present new X-ray results on W51 IRS2E and 30 Doradus and we introduce new data on Trumpler 14 in Carina and the W3 HII region complexes W3 Main and W3(OH). Comment: 6 pages, 3 figures, to appear in the proceedings of IAU Symposium 227,"Massive Star Birth - A Crossroads of Astrophysics," eds. R. Cesaroni, E. Churchwell, M. Felli, and C.M. Walmsley
06/2005;
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ABSTRACT: We examine the X-ray spectra and variability of the sample of X-ray sources with L_X = 10^{31}-10^{33} erg s^{-1} identified within the inner 9' of the Galaxy. Very few of the sources exhibit intra-day or inter-month variations. We find that the spectra of the point sources near the Galactic center are very hard between 2--8 keV, even after accounting for absorption. When modeled as power laws the median photon index is Gamma=0.7, while when modeled as thermal plasma we can only obtain lower limits to the temperature of kT>8 keV. The combined spectra of the point sources is similarly hard, with a photon index of Gamma=0.8. Strong line emission is observed from low-ionization, He-like, and H-like Fe, both in the average spectra and in the brightest individual sources. The line ratios of the highly-ionized Fe in the average spectra are consistent with emission from a plasma in thermal equilibrium. This line emission is observed whether average spectra are examined as a function of the count rate from the source, or as a function of the hardness ratios of individual sources. This suggests that the hardness of the spectra may in fact to due local absorption that partially-covers the X-ray emitting regions in the Galactic center systems. We suggest that most of these sources are intermediate polars, which (1) often exhibit hard spectra with prominent Fe lines, (2) rarely exhibit either flares on short time scales or changes in their mean X-ray flux on long time scales, and (3) are the most numerous hard X-ray sources with comparable luminosities in the Galaxy. Comment: 27 pages, including 13 figures. To appear in ApJ, 1 October 2004, v613 issue. An electronic version of table 2 is on http://astro.ucla.edu/~mmuno/sgra/table2_electronic.txt and reduced data files for each source are available on http://www.astro.psu.edu/users/niel/galcen-xray-data/galcen-xray-data.html
03/2004;
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ABSTRACT: We present a catalog of 2357 point sources detected during 620 ks of Chandra observations of the 17 × 17 arcminutes field around Sgr A*. This field encompasses a physical area of 40 × 40 parsecs at 8 kpc. The completeness limit of the sample at the Galactic Center is ≈1031 erg s−1 (2–8 keV), while the detection limit is an order of magnitude lower. We estimate that 20–100 of the observed sources are background AGN. The spectra of the majority of the Galactic Center sources are very hard and are best described by a power law (E−Γ) with photon index Γ < 1. Such hard spectra are only seen from magnetically accreting white dwarfs (polars and intermediate polars) and neutron stars (pulsars). The spatial density of the Galactic Center X-ray sources falls off as R−2, similar to that of the infrared stars in the field. This highlights the possibility that these X-ray sources can be used to study the history of star formation at the Galactic Center. The log(N) − log(S) distribution of the Galactic Center sources is extremely steep, such that point sources could account for all of the previously reported diffuse emission if the number counts extend down to 1029 erg s−1 with the same slope. However, there are numerous fllamentary structures in the field that also contribute to the total flux, which implies that the luminosity distribution between 2–8 keV must turn over below our completeness limit.
Astronomische Nachrichten 10/2003; 324(S1):33 - 39. · 1.01 Impact Factor
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ABSTRACT: We present the first high-spatial-resolution X-ray images of two high-mass star forming regions, the Omega Nebula (M 17) and the Rosette Nebula (NGC 2237--2246), obtained with the Chandra X-ray Observatory Advanced CCD Imaging Spectrometer (ACIS) instrument. The massive clusters powering these H II regions are resolved at the arcsecond level into >900 (M 17) and >300 (Rosette) stellar sources similar to those seen in closer young stellar clusters. However, we also detect soft diffuse X-ray emission on parsec scales that is spatially and spectrally distinct from the point source population. The diffuse emission has luminosity L_x ~ 3.4e33 ergs/s in M~17 with plasma energy components at kT ~0.13 and ~0.6 keV (1.5 and 7 MK), while in Rosette it has L_x \~6e32 ergs/s with plasma energy components at kT ~0.06 and ~0.8 keV (0.7 and 9 MK). This extended emission most likely arises from the fast O-star winds thermalized either by wind-wind collisions or by a termination shock against the surrounding media. We establish that only a small portion of the wind energy and mass appears in the observed diffuse X-ray plasma; in these blister H II regions, we suspect that most of it flows without cooling into the low-density interstellar medium. These data provide compelling observational evidence that strong wind shocks are present in H II regions. Comment: 35 pages, including 11 figures; to appear in ApJ, August 20, 2003. A version with high-resolution figures is available at ftp://ftp.astro.psu.edu/pub/townsley/diffuse.ps.gz
05/2003;
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ABSTRACT: (abridged) We present a catalog of 2357 point sources detected during 590 ks of Chandra observations of the 17-by-17 arcminute field around Sgr A*. This field encompasses a physical area of 40 by 40 pc at a distance of 8 kpc. The completeness limit of the sample at the Galactic center is 10^{31} erg s^{-1} (2.0--8.0 keV), while the detection limit is an order of magnitude lower. The 281 sources detected below 1.5 keV are mainly in the foreground of the Galactic center, while comparisons to the Chandra deep fields at high Galactic latitudes suggest that only about 100 of the observed sources are background AGN. The surface density of absorbed sources (not detected below 1.5 keV) falls off as 1/theta away from Sgr A*, in agreement with the distribution of stars in infrared surveys. Point sources brighter than our completeness limit produce 10% of the flux previously attributed to diffuse emission. The log(N)-log(S) distribution of the Galactic center sources is extremely steep (power-law slope alpha = 1.7). If this distribution extends down to a flux of 10^{-17} erg cm^{-1} s^{-1} (10^{29} erg s^{-1} at 8 kpc, 2.0--8.0 keV) with the same slope, then point sources would account for all of the previously reported diffuse emission. Therefore, the 2.0--8.0 keV luminosity distribution must flatten between 10^{29} - 10^{31} erg s^{-1}. Finally, the spectra of more than half of the Galactic center sources are very hard, and can be described by a power law ($E^{-Gamma}) with photon index Gamma < 1. Such hard spectra have been seen previously only from magnetically accreting white dwarfs and wind-accreting neutron stars, suggesting that there are large numbers of these systems in our field.
02/2003;
