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Tyler D. Desjardins,
Sarah C. Gallagher,
Panayiotis Tzanavaris,
John S. Mulchaey,
William N. Brandt,
Jane C. Charlton, Gordon P. Garmire,
Caryl Gronwall,
Ann E. Hornschemeier,
Kelsey E. Johnson,
Iraklis S. Konstantopoulos,
Ann I. Zabludoff
[show abstract]
[hide abstract]
ABSTRACT: Isolated compact groups of galaxies (CGs) present a range of dynamical
states, group velocity dispersions, and galaxy morphologies with which to study
galaxy evolution, particularly the properties of gas both within the galaxies
and in the intragroup medium. As part of a large, multiwavelength examination
of CGs, we present an archival study of diffuse X-ray emission in a subset of
nine Hickson compact groups observed with the Chandra X-ray Observatory. We
find that seven of the groups in our sample exhibit detectable diffuse
emission. However, unlike large-scale emission in galaxy clusters, the diffuse
features in the majority of the detected groups are linked to the individual
galaxies, in the form of both plumes and halos likely as a result of star
formation or AGN activity, as well as in emission from tidal features. Unlike
previous studies from earlier X-ray missions, HCGs 31, 42, 59, and 92 are found
to be consistent with the Lx-T relationship from clusters within the errors,
while HCGs 16 and 31 are consistent with the cluster Lx-sigma relation, though
this is likely coincidental given that the hot gas in these two systems is
largely due to star formation. We find that Lx increases with decreasing group
HI to dynamical-mass ratio with tentative evidence for a dependance in X-ray
luminosity on HI morphology whereby systems with intragroup HI indicative of
strong interactions are considerably more X-ray luminous than passively
evolving groups. We also find a gap in the Lx of groups as a function of the
total group specific star formation rate. Our findings suggest that the hot gas
in these groups is not in hydrostatic equilibrium and these systems are not
low-mass analogs of rich groups or clusters, with the possible exception of HCG
62.
12/2012;
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[show abstract]
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ABSTRACT: We analyze the long-term (rest-frame 3-30 yr) X-Ray variability of eleven
broad absorption line (BAL) quasars, mainly to constrain the variation
properties of the X-Ray absorbing shielding gas that is thought to play a
critical role in BAL wind launching. Our BAL quasar sample has coverage with
multiple X-ray observatories including Chandra, XMM-Newton, BeppoSAX, ASCA,
ROSAT, and Einstein; 3-11 observations are available for each source. For seven
of the eleven sources we have obtained and analyzed new Chandra observations
suitable for searching for any strong X-ray variability. We find highly
significant X-Ray variability in three sources (PG 1001+054, PG 1004+130, and
PG 2112+059). The maximum observed amplitude of the 2-8 keV variability is a
factor of $3.8\pm 1.3$, $1.5\pm 0.2$, and $9.9\pm 2.3$ for PG 1001+054, PG
1004+130, and PG 2112+059, respectively, and these sources show detectable
variability on rest-frame timescales down to 5.8, 1.4, and 0.5 yr. For PG
1004+130 and PG 2112+059 we also find significant X-Ray spectral variability
associated with the flux variability. Considering our sample as a whole, we do
not find that BAL quasars exhibit exceptional long-term X-Ray variability when
compared to the quasar population in general. We do not find evidence for
common strong changes in the shielding gas owing to physical rearrangement or
accretion-disk rotation, although some changes are found; this has implications
for modeling observed ultraviolet BAL variability. Finally, we report for the
first time an X-Ray detection of the highly polarized and well-studied BAL
quasar IRAS 14026+4341 in its new Chandra observation.
09/2012;
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[show abstract]
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ABSTRACT: Rich young stellar clusters produce HII regions whose expansion into the
nearby molecular cloud is thought to trigger the formation of new stars.
However, the importance of this mode of star formation is uncertain. This
investigation seeks to quantify triggered star formation (TSF) in IC 1396A
(a.k.a., the Elephant Trunk Nebula), a bright rimmed cloud (BRC) on the
periphery of the nearby giant HII region IC 1396 produced by the Trumpler 37
cluster. X-ray selection of young stars from Chandra X-ray Observatory data is
combined with existing optical and infrared surveys to give a more complete
census of the TSF population. Over 250 young stars in and around IC 1396A are
identified; this doubles the previously known population. A spatio-temporal
gradient of stars from the IC 1396A cloud toward the primary ionizing star HD
206267 is found. We argue that the TSF mechanism in IC 1396A is the
radiation-driven implosion process persisting over several million years.
Analysis of the X-ray luminosity and initial mass functions indicates that >140
stars down to 0.1 Msun were formed by TSF. Considering other BRCs in the IC
1396 HII region, we estimate the TSF contribution for the entire HII region
exceeds 14-25% today, and may be higher over the lifetime of the HII region.
Such triggering on the periphery of HII regions may be a significant mode of
star formation in the Galaxy.
08/2012;
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Patrick S. Broos,
Leisa K. Townsley,
Eric D. Feigelson,
Konstantin V. Getman, Gordon P. Garmire,
Thomas Preibisch,
Nathan Smith,
Brian L. Babler,
Simon Hodgkin,
Rémy Indebetouw,
Mike Irwin,
Robert R. King,
Jim Lewis,
Steven R. Majewski,
Mark J. McCaughrean,
Marilyn R. Meade,
and Hans Zinnecker
[show abstract]
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ABSTRACT: We present a catalog of ~14,000 X-ray sources observed by the ACIS instrument on the Chandra X-ray Observatory within a 1.42 deg2 survey of the Great Nebula in Carina, known as the Chandra Carina Complex Project (CCCP). This study appears in a special issue devoted to the CCCP. Here, we describe the data reduction and analysis procedures performed on the X-ray observations, including calibration and cleaning of the X-ray event data, point-source detection, and source extraction. The catalog appears to be complete across most of the field to an absorption-corrected total-band luminosity of ~1030.7 erg s–1 for a typical low-mass pre-main-sequence star. Counterparts to the X-ray sources are identified in a variety of visual, near-infrared, and mid-infrared surveys. The X-ray and infrared source properties presented here form the basis of many CCCP studies of the young stellar populations in Carina.
The Astrophysical Journal Supplement Series 04/2011; 194(1):2. · 13.46 Impact Factor
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Leisa K. Townsley,
Patrick S. Broos,
You-Hua Chu,
Marc Gagné, Gordon P. Garmire,
Robert A. Gruendl,
Kenji Hamaguchi,
Mordecai-Mark Mac Low,
Thierry Montmerle,
Yaël Nazé,
M. S. Oey,
Sangwook Park,
Robert Petre,
and Julian M. Pittard
[show abstract]
[hide abstract]
ABSTRACT: We present a 1.42 deg2 mosaic of diffuse X-ray emission in the Great Nebula in Carina from the Chandra X-ray Observatory Advanced CCD Imaging Spectrometer camera. After removing >14,000 X-ray point sources from the field, we smooth the remaining unresolved emission, tessellate it into segments of similar apparent surface brightness, and perform X-ray spectral fitting on those tessellates to infer the intrinsic properties of the X-ray-emitting plasma. By modeling faint resolved point sources, we estimate the contribution to the extended X-ray emission from unresolved point sources and show that the vast majority of Carina's unresolved X-ray emission is truly diffuse. Line-like correlated residuals in the X-ray spectral fits suggest that substantial X-ray emission is generated by charge exchange at the interfaces between Carina's hot, rarefied plasma and its many cold neutral pillars, ridges, and clumps.
The Astrophysical Journal Supplement Series 04/2011; 194(1):15. · 13.46 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: LS 5039 is a high-mass binary with a period of 4 days, containing a compact
object and an O star, one of the few high-mass binaries detected in gamma-rays.
Our Chandra ACIS observation of LS 5039 provided a high-significance (~10sigma)
detection of extended emission clearly visible for up to 1' from the point
source. The spectrum of this emission can be described by an absorbed power-law
model with photon index Gamma=1.9pm0.3, somewhat softer than the point source
spectrum Gamma=1.44pm0.07, with the same absorption, N_H=(6.4pm0.6)e21 /cm2.
The observed 0.5-8 keV flux of the extended emission is 8.8e-14 erg/s/cm2, or
5% of the point source flux; the latter is a factor of ~2 lower than the lowest
flux detected so far. Fainter extended emission with comparable flux and a
softer (Gamma~3) spectrum is detected at even greater radii (up to 2'). Two
possible interpretations of the extended emission are a dust scattering halo
and a synchrotron nebula powered by energetic particles escaping the binary. We
discuss both of these scenarios and favor the nebula interpretation, although
some dust contribution is possible. We have also found transient sources
located within a narrow stripe south of LS 5039. We discuss the likelihood of
these sources to be related to LS 5039.
03/2011;
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Eric D. Feigelson,
Konstantin V. Getman,
Leisa K. Townsley,
Patrick S. Broos,
Matthew S. Povich, Gordon P. Garmire,
Robert R. King,
Thierry Montmerle,
Thomas Preibisch,
Nathan Smith,
Keivan G. Stassun,
Junfeng Wang,
Scott Wolk,
Hans Zinnecker
[show abstract]
[hide abstract]
ABSTRACT: The distribution of young stars found in the Chandra Carina Complex Project
(CCCP) is examined for clustering structure. X-ray surveys are advantageous for
identifying young stellar populations compared to optical and infrared surveys
in suffering less contamination from nebular emission and Galactic field stars.
The analysis is based on smoothed maps of a spatially complete subsample of
about 3000 brighter X-ray sources classified as Carina members, and about
10,000 stars from the full CCCP sample. The principal known clusters are
recovered, and some additional smaller groups are identified. No rich embedded
clusters are present, although a number of sparse groups are found. The CCCP
reveals considerable complexity in clustering properties. The Trumpler 14 and
15 clusters have rich stellar populations in unimodal, centrally concentrated
structures several parsecs across. Non-spherical internal structure is seen,
and large-scale low surface density distributions surround these rich clusters.
Trumpler 16, in contrast, is comprised of several smaller clusters within a
circular boundary. Collinder 228 is a third type of cluster which extends over
tens of parsecs with many sparse compact groups likely arising from triggered
star formation processes. A widely dispersed, but highly populous, distribution
of X-ray stars across the about 50 pc CCCP mosaic supports a model of past
generations of star formation in the region. Collinder 234, a group of massive
stars without an associated cluster of pre-main sequence stars, may be part of
this dispersed population.
03/2011;
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[show abstract]
[hide abstract]
ABSTRACT: The Chandra Carina Complex Project (CCCP) provides a sensitive X-ray survey
of a nearby starburst region over >1 square degree in extent. Thousands of
faint X-ray sources are found, many concentrated into rich young stellar
clusters. However, significant contamination from unrelated Galactic and
extragalactic sources is present in the X-ray catalog. We describe the use of a
naive Bayes classifier to assign membership probabilities to individual
sources, based on source location, X-ray properties, and visual/infrared
properties. For the particular membership decision rule adopted, 75% of CCCP
sources are classified as members, 11% are classified as contaminants, and 14%
remain unclassified. The resulting sample of stars likely to be Carina members
is used in several other studies, which appear in a Special Issue of the ApJS
devoted to the CCCP.
02/2011;
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[show abstract]
[hide abstract]
ABSTRACT: We describe detailed simulations of X-ray-emitting populations to evaluate
the levels of contamination by both Galactic and extragalactic X-ray sources
unrelated to a star-forming region under study. For Galactic contaminations, we
consider contribution from main-sequence stars and giants (not including
cataclysmic variables and other classes of accretion-driven X-ray binary
systems) as they make the dominant contribution at the position of the Carina
Nebula. The simulations take into consideration a variety of technical factors
involving a Galactic population synthesis model, stellar X-ray luminosity
functions, Chandra telescope response, source detection methodology, and
possible spatial variations in the X-ray background and absorption through
molecular clouds. When applied to the 1.42 square-degree field of the Chandra
Carina Complex Project (CCCP), the simulations predict ~5000 contaminating
sources (1 source per square arcminute of the survey), evenly distributed
across the field. The results of the simulations are further employed in a
companion CCCP study to assign membership probabilities to individual sources.
02/2011;
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Leisa K. Townsley,
Patrick S. Broos,
Michael F. Corcoran,
Eric D. Feigelson,
Marc Gagné,
Thierry Montmerle,
M. S. Oey,
Nathan Smith, Gordon P. Garmire,
Konstantin V. Getman, [......],
L. M. Oskinova,
Julian M. Pittard,
Keivan G. Stassun,
Asif ud-Doula,
Nolan R. Walborn,
Wayne L. Waldron,
Ed Churchwell,
J. S. Nichols,
Stanley P. Owocki,
N. S. Schulz
[show abstract]
[hide abstract]
ABSTRACT: The Great Nebula in Carina provides an exceptional view into the violent
massive star formation and feedback that typifies giant HII regions and
starburst galaxies. We have mapped the Carina star-forming complex in X-rays,
using archival Chandra data and a mosaic of 20 new 60ks pointings using the
Chandra X-ray Observatory's Advanced CCD Imaging Spectrometer, as a testbed for
understanding recent and ongoing star formation and to probe Carina's regions
of bright diffuse X-ray emission. This study has yielded a catalog of
properties of >14,000 X-ray point sources; >9800 of them have multiwavelength
counterparts. Using Chandra's unsurpassed X-ray spatial resolution, we have
separated these point sources from the extensive, spatially-complex diffuse
emission that pervades the region; X-ray properties of this diffuse emission
suggest that it traces feedback from Carina's massive stars. In this
introductory paper, we motivate the survey design, describe the Chandra
observations, and present some simple results, providing a foundation for the
15 papers that follow in this Special Issue and that present detailed catalogs,
methods, and science results.
02/2011;
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[show abstract]
[hide abstract]
ABSTRACT: The young high-eccentricity binary DQ Tau exhibits powerful recurring
millimeter-band (mm) flaring attributed to collisions between the two stellar
magnetospheres near periastron, when the stars are separated by only ~8Rstar.
These magnetospheric interactions are expected to have scales and magnetic
field strengths comparable to those of large X-ray flares from single
pre-main-sequence (PMS) stars observed in the Chandra Orion Ultradeep Project
(COUP). To search for X-rays arising from processes associated with colliding
magnetospheres, we performed simultaneous X-ray and mm observations of DQ Tau
near periastron phase. We report here several results. 1) As anticipated, DQ
Tau was caught in a flare state in both mm and X-rays. A single long X-ray
flare spanned the entire 16.5 hour Chandra exposure. 2) The inferred
morphology, duration, and plasma temperature of the X-ray flare are typical of
those of large flares from COUP stars. 3) However, our study provides three
lines of evidence that this X-ray flare likely arises from colliding
magnetospheres: the chance of capturing a large COUP-like flare within the span
of our observation is small; the relative timing of the X-ray and mm flares
indicates the Neupert effect and is consistent with a common coronal structure;
the size of the emitting coronal structure (4-5Rstar) inferred from our
analysis (which is admittedly model-dependent and should be considered with
caution) is comparable to half the binary separation. 4) The peak flare X-ray
luminosity is in agreement with an estimate of the power dissipated by magnetic
reconnection within the framework of a simple model of interacting
magnetospheres.
01/2011;
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[show abstract]
[hide abstract]
ABSTRACT: X-ray sources with very few counts can be identified with low-noise X-ray detectors such as ACIS onboard the Chandra X-ray Observatory. These sources are often too faint for parametric spectral modeling using well-established methods such as fitting with XSPEC. We discuss the estimation of apparent and intrinsic broad-band X-ray fluxes and soft X-ray absorption from gas along the line of sight to these sources, using nonparametric methods. Apparent flux is estimated from the ratio of the source count rate to the instrumental effective area averaged over the chosen band. Absorption, intrinsic flux, and errors on these quantities are estimated from comparison of source photometric quantities with those of high S/N spectra that were simulated using spectral models characteristic of the class of astrophysical sources under study. The concept of this method is similar to the long-standing use of color-magnitude diagrams in optical and infrared astronomy, with X-ray median energy replacing color index and X-ray source counts replacing magnitude. Our nonparametric method is tested against the apparent spectra of 2000 faint sources in the Chandra observation of the rich young stellar cluster in the M17 HII region. We show that the intrinsic X-ray properties can be determined with little bias and reasonable accuracy using these observable photometric quantities without employing often uncertain and time-consuming methods of non-linear parametric spectral modeling. Our method is calibrated for thermal spectra characteristic of stars in young stellar clusters, but recalibration should be possible for some other classes of faint X-ray sources such as extragalactic AGN. Comment: Accepted for publication in The Astrophysical Journal. 39 pages, 15 figures
12/2009;
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[hide abstract]
ABSTRACT: We present the evolution of the radial expansion of SNR 1987A as measured using Chandra X-ray observations taken over the last 10 years. To characterize the complex structure of the remnant and isolate the expansion measurement, we fit the images to several empirical models including: a simple circular torus, a torus with bilateral lobes, and a torus with four tangentially extended lobes. We discuss the results of this measure in the context of the overall evolution of the supernova remnant, for which we believe we have measured the end of the free expansion phase and its transition to the adiabatic phase (at least along the equatorial ring). The timing of this event is in agreement with early predictions of the remnant evolution. Comment: Accepted for publication in ApJ, 21 pages, 4 figures, 3 tables
The Astrophysical Journal 08/2009; · 6.02 Impact Factor
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ABSTRACT: The full stellar population of NGC 6334, one of the most spectacular regions of massive star formation in the nearby Galaxy, have not been well-sampled in past studies. We analyze here a mosaic of two Chandra X-ray Observatory images of the region using sensitive data analysis methods, giving a list of 1607 faint X-ray sources with arcsecond positions and approximate line-of-sight absorption. About 95 percent of these are expected to be cluster members, most lower mass pre-main sequence stars. Extrapolating to low X-ray levels, the total stellar population is estimated to be 20-30,000 pre-main sequence stars. The X-ray sources show a complicated spatial pattern with about 10 distinct star clusters. The heavily-obscured clusters are mostly associated with previously known far-infrared sources and radio HII regions. The lightly-obscured clusters are mostly newly identified in the X-ray images. Dozens of likely OB stars are found, both in clusters and dispersed throughout the region, suggesting that star formation in the complex has proceeded over millions of years. A number of extraordinarily heavily absorbed X-ray sources are associated with the active regions of star formation. Comment: To appear in the Astronomical Journal. A version with high-quality figures appears at http://www.astro.psu.edu/users/edf/NGC6334.pdf
05/2009;
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[show abstract]
[hide abstract]
ABSTRACT: We present X-ray spectral analysis of five Chandra and XMM-Newton obser-vations of the gravitationally-lensed blazar PKS 1830−211 from 2000 to 2004. We show that the X-ray absorption toward PKS 1830−211 is variable, and the variable absorption is most likely to be intrinsic with amplitudes of ∼ 2 × 10 22 – 30 × 10 22 cm −2 depending on whether or not the absorber is partially covering the X-ray source. Our results confirm the variable absorption observed previ-ously, although interpreted differently, in a sequence of ASCA observations. This large variation in the absorption column density can be interpreted as outflows from the central engine in the polar direction, consistent with recent numerical models of inflow/outflows in AGNs. In addition, it could possibly be caused by the interaction between the blazar jet and its environment, or the variation from the geometric configuration of the jet. While the spectra can also be fitted with a variable absorption at the lens redshift, we show that this model is unlikely. We also rule out the simple microlensing interpretation of variability which was previously suggested.
03/2009;
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[show abstract]
[hide abstract]
ABSTRACT: The supernova remnant (SNR) N49 in the Large Magellanic Cloud has been observed with the Advanced CCD Imaging Spectrometer (ACIS) on board the Chandra X-Ray Observatory. The superb angular resolution of the Chandra/ACIS images resolves a point source, the likely X-ray counterpart of soft gamma-ray repeater SGR 0526-66, and the diffuse filaments and knots across the SNR. These filamentary features represent the blast wave sweeping through the ambient interstellar medium and nearby dense molecular clouds. We detect metal-rich ejecta beyond the main blast wave shock boundary in the southwest of the SNR, which appear to be explosion fragments, or "bullets," ejected from the progenitor star. The detection of strong H-like Si line emission in the eastern side of the SNR requires multiphase shocks in order to describe the observed X-ray spectrum, whereas such a multiphase plasma is not evident in the western side. This complex spectral structure of N49 suggests that the postshock regions toward the east of the SNR might have been reheated by the reverse shock off the dense molecular clouds while the blast wave shock front has decelerated as it propagates into the dense clouds. The X-ray spectrum of the detected pointlike source is continuum-dominated and can be described with a power law of Γ ~ 3. This provides a confirmation that this pointlike X-ray source is the counterpart of SGR 0526-66 in the quiescent state.
The Astrophysical Journal 12/2008; 586(1):210. · 6.02 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We report here results from a Chandra ACIS observation of the stellar populations in and around the M17 H II region. The field reveals 886 sources with observed X-ray luminosities (uncorrected for absorption) between ~ 29.3 ergs s-1 < log LX < 32.8 ergs s-1, 771 of which have stellar counterparts in infrared images. In addition to comprehensive tables of X-ray source properties, several results are presented:
The Astrophysical Journal Supplement Series 12/2008; 169(2):353. · 13.46 Impact Factor
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Ronald F. Elsner,
G. Randall Gladstone,
J. Hunter Waite,
Frank J. Crary,
Robert R. Howell,
Robert E. Johnson,
Peter G. Ford,
Albert E. Metzger,
Kevin C. Hurley,
Eric D. Feigelson, Gordon P. Garmire,
Anil Bhardwaj,
Denis C. Grodent,
Tariq Majeed,
Allyn F. Tennant,
and Martin C. Weisskopf
[show abstract]
[hide abstract]
ABSTRACT: We report the discovery of soft (0.25-2 keV) X-ray emission from the Galilean satellites Io and Europa, probably Ganymede, and from the Io Plasma Torus (IPT). Bombardment by energetic (greater than 10 keV) H, O, and S ions from the region of the IPT seems to be the likely source of the X-ray emission from the Galilean satellites. According to our estimates, fluorescent X-ray emission excited by solar X-rays, even during flares from the active Sun, charge-exchange processes, previously invoked to explain Jupiter's X-ray aurora and cometary X-ray emission, and ion stripping by dust grains fail to account for the observed emission. On the other hand, bremsstrahlung emission of soft X-rays from nonthermal electrons in the few hundred to few thousand eV range may account for a substantial fraction of the observed X-ray flux from the IPT.
The Astrophysical Journal 12/2008; 572(2):1077. · 6.02 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: The middle-aged supernova remnant (SNR) N49B in the Large Magellanic Cloud has been observed with the Chandra X-Ray Observatory. The superb angular resolution of Chandra resolves the complex structure of X-ray-emitting filaments across the SNR. All observed features are soft (E < 3 keV), and we find no evidence of either pointlike or extended hard emission within the SNR. Spectral lines from O, Ne, Mg, Si, S, and Fe are present. Equivalent width images for the detected elemental species and spatially resolved spectral analysis reveal the presence of Mg-rich ejecta within the SNR. We find no such enrichment in O or Ne, which may reflect details of the nucleosynthesis process or the heating and cooling of the ejecta as it evolved. The bright circumferential filaments are emission from the shocked dense interstellar medium (ISM). We detect faint diffuse X-ray emission that extends beyond the X-ray-bright filaments toward the west and southeast. These features appear to be the blast wave shock front expanding into lower density portions of the ISM seen in projection. We set an upper limit of ~2 × 1033 ergs s-1 on the 0.5-5 keV band X-ray luminosity of any embedded compact object.
The Astrophysical Journal 12/2008; 592(1):L41. · 6.02 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We present high-resolution Chandra observations of the remnant of SN 1987A in the Large Magellanic Cloud. The high angular resolution of the Chandra X-Ray Observatory permits us to resolve the X-ray remnant. We find that the remnant is shell-like in morphology, with X-ray peaks associated with some of the optical hot spots seen in Hubble Space Telescope images. The X-ray light curve has deviated from the linear flux increase observed by ROSAT, with a 0.5-2.0 keV luminosity of 1.5 × 1035 ergs s-1 in 2000 January. We set an upper limit of 2.3 × 1034 ergs s-1 on the observed luminosity of any embedded central source (0.5-2 keV). We also present a high-resolution spectrum and show that the X-ray emission is thermal in origin and is dominated by highly ionized species of O, Ne, Mg, and Si.
The Astrophysical Journal 12/2008; 543(2):L149. · 6.02 Impact Factor
