Showing papers by "Gordon P. Garmire published in 2003"

The Chandra Deep Field North Survey. XIII. 2 Ms Point-Source Catalogs

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.

Advanced CCD imaging spectrometer (ACIS) instrument on the Chandra X-ray Observatory

Abstract: The ACIS instrument has been operating for three years in orbit, producing high quality scientific data on a wide variety of X-ray emitting astronomical objects. Except for a brief period at the very beginning of the mission when the CCDs were exposed to the radiation environment of the Outer van Allen Belts which resulted in substantial radiation damage to the front illuminated CCDs, the instrument has operated nearly flawlessly. The following report presents a description of the instrument, the current status of the instrument calibration and a few highlights of the scientific results obtained from the Guaranteed Observer Time.

Chandra X-Ray Spectroscopic Imaging of Sagittarius A* and the Central Parsec of the Galaxy

Abstract: We report the results of the first-epoch observation with the ACIS-I instrument on the Chandra X-Ray Observatory of Sagittarius A* (Sgr A*), the compact radio source associated with the supermassive black hole (SMBH) at the dynamical center of the Milky Way. This observation produced the first X-ray (0.5- 7 keV) spectroscopic image with arcsecond resolution of the central 17 0 � 17 0 (40 pc � 40 pc) of the Galaxy. We report the discovery of an X-ray source, CXOGC J174540.0� 290027, coincident with Sgr A* within 0>27 � 0>18. The probability of a false match is estimated to be d0.5%. The spectrum is well fitted either by an absorbed power law with photon index � � 2:7 or by an absorbed optically thin thermal plasma with kT � 1:9 keV and column density NH � 1 � 10 23 cm � 2 . The observed flux in the 2-10 keV band is � 1:3 � 10 � 13 ergs cm � 2 s � 1 , and the absorption-corrected luminosity is � 2:4 � 10 33 ergs s � 1 . The X-ray emission at the position of Sgr A* is extended, with an intrinsic size of � 1>4 (FWHM), consistent with the Bondi accretion radius for a 2:6 � 10 6 Mblack hole. A compact component within the source flared by up to a factor of 3 over a period of � 1 hr at the start of the observation. The search for Kline emission from iron was inconclusive, yielding an upper limit on the equivalent width of 2.2 keV. Several potential stellar origins for the X-ray emission at Sgr A* are considered, but we conclude that the various properties of the source favor accretion onto the SMBH as the origin for the bulk of the emission. These data are inconsistent with '' standard '' advection-dominated accretion flow (ADAF) models or Bondi models, unless the accretion rate from stellar winds is much lower than anticipated. The central parsec of the Galaxy contains an � 1.3 keV plasma with electron density ne � 26� � 1=2 f cm � 3 , wheref is the filling factor. This plasma should supply � 10 � 6 Myr � 1 of material to the accretion flow at the Bondi radius, whereas measurements of linear polar- ization at 150 GHz and above limit the accretion rate near the event horizon to d10 � 8 Myr � 1 , assuming an equipartition magnetic field. Taken together, the X-ray and radio results imply that outflows or convection are playing a role in ADAF models and subequipartition magnetic fields in Bondi models, or else the X-ray emission must be generated predominantly via the synchrotron self-Compton (SSC) process. The measured extent of the source and the detection of short timescale variability are evidence that the emission from Sgr A* contains both thermal and nonthermal emission components at comparable levels. We also discuss the complex structure of the X-ray emission from the Sgr A radio complex and along the Galactic plane. Mor- phological evidence is presented that Sgr A* and the H ii region Sgr A West lie within the hot plasma in the central cavity of Sgr A East, which we interpret as a supernova remnant that may have passed through the position of the SMBH, leading to a period of increased activity that ended within the past � 300 yr. Similarly, we have discovered bright clumps of X-ray emission located on opposite sides of the Galactic plane, along a line passing through the central parsec of the Galaxy. The arrangement of these lobes suggests that Sgr A* may have experienced an earlier period of increased activity lasting several thousand years during which it expelled hot gas in a bipolar outflow oriented roughly perpendicular to the Galactic plane. Additionally, we present an analysis of stellar emission within the central parsec of the Galaxy. Subject headings: accretion, accretion disks — black hole physics — galaxies: active — Galaxy: center — X-rays: ISM — X-rays: stars

Optical and Infrared Properties of the 2 Ms Chandra Deep Field North X-Ray Sources

Abstract: We present an optical and near-infrared catalog for the X-ray sources in the ?2 Ms Chandra observation of the Hubble Deep Field North region. We have high-quality multicolor imaging data for all 503 X-ray point sources in the X-ray?selected catalog and reliable spectroscopic redshifts for 284. We spectroscopically identify six high-redshift (z > 1) type II quasars (L2?8keV > 1044 ergs s-1) in our sample. Our spectroscopic completeness for the R ? 24 sources is 87%. The spectroscopic redshift distribution shows two broad redshift spikes that have clearly grown over those originally seen in the ?1 Ms exposure. The spectroscopically identified extragalactic sources already comprise 75% of the measured 2?8 keV light. Redshift slices versus 2?8 keV flux show that an impressive 54% of the measured 2?8 keV light arises from sources at z 5.7 that would classify them as extremely red objects (EROs). The photometric redshifts of these EROs are all between z ~ 1.5 and z ~ 2.5. We use our wide wavelength coverage to determine rest-frame colors for the X-ray sources with spectroscopic or photometric redshifts. We find that many of the X-ray sources have the rest-frame colors of evolved red galaxies and that there is very little evolution in these colors with redshift. We also determine absolute magnitudes and find that many of the non?broad-line sources are more luminous than M, even at high redshifts. We therefore infer that deep X-ray observations may provide an effective way of locating M* galaxies with colors similar to present-day early-type galaxies to high redshifts.

10 MK Gas in M17 and the Rosette Nebula: X-Ray Flows in Galactic H II Regions

Abstract: We present the first high spatial resolution X-ray images of two high-mass star forming regions, the Omega Nebula (M17) and the Rosette Nebula (NGC 2237-2246), obtained with the Chandra X-Ray Observatory Advanced CCD Imaging Spectrometer instrument. The massive clusters powering these H II regions are resolved at the arcsecond level into more than 900 (M17) 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 LX 3.4 × 1033 ergs s-1 in M17 with plasma energy components at kT 0.13 and 0.6 keV (1.5 and 7 MK), while in Rosette it has LX 6 × 1032 ergs s-1 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.

A Deep Chandra Catalog of X-Ray Point Sources toward the Galactic Center

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.

Ten Million Degree Gas in M 17 and the Rosette Nebula: X-ray Flows in Galactic H II Regions

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.

The Chandra Deep Field North Survey. XIV. X-Ray-detected Obscured AGNs and Starburst Galaxies in the Bright Submillimeter Source Population

Abstract: We provide X-ray constraints and perform the first X-ray spectral analyses for bright SCUBA sources (f850 μm ≥ 5 mJy; signal-to-noise ratio ≥4) in an 84 × 84 area of the 2 Ms Chandra Deep Field North survey containing the Hubble Deep Field North. X-ray emission is detected from seven of the 10 bright submillimeter sources in this region down to 0.5–8.0 keV fluxes of ≈1 × 10-16 ergs cm-2 s-1, corresponding to an X-ray–detected submillimeter source density of 360 deg-2; our analyses suggest that this equates to an X-ray–detected fraction of the bright submillimeter source population of 36%, although systematic effects may be present. Two of the X-ray–detected sources have nearby (within 3'') X-ray companions, suggesting merging/interacting sources or gravitational lensing effects, and three of the X-ray–detected sources lie within the approximate extent of the protocluster candidate CXOHDFN J123620.0+621554. Five of the X-ray–detected sources have flat effective X-ray spectral slopes (Γ 4) and could be either AGNs or starburst galaxies.

The Redshift Evolution of the 2-8 keV X-Ray Luminosity Function

Abstract: The high angular resolution and sensitivity of the Chandra X-Ray Observatory has yielded large numbers of faint X-ray sources with measured redshifts in the soft-energy (0.5-2 keV) and hard-energy (2-8 keV) bands. Many of these sources show few obvious optical signatures of active galactic nuclei (AGNs). We use Chandra observations of the Hubble Deep Field-North region, A370, and the Hawaii Survey fields SSA 13 and SSA 22, together with the ROSAT Ultra Deep Survey soft sample and the ASCA Large Sky Survey hard sample, to construct rest-frame 2-8 keV luminosity functions versus redshift for all the X-ray sources, regardless of their optical AGN characteristics. At z = 0.1-1, most of the 2-8 keV light density arises in sources with luminosities in the 1042-1044 ergs s-1 range. We show that the number density of sources in this luminosity range is rising, or is at least constant, with decreasing redshift. Broad-line AGNs are the dominant population at higher luminosities, and these sources show the well-known rapid positive evolution with increasing redshift to z ~ 3. We argue that the dominant supermassive black hole formation has occurred at recent times in objects with low accretion mass flow rates rather than at earlier times in more X-ray-luminous objects with high accretion mass flow rates.

Chandra spectra of the soft x-ray diffuse background

Abstract: We present an exploratory Chandra ACIS-S3 study of the diffuse component of the cosmic X-ray background (CXB) in the 0.3–7 keV band for four directions at high Galactic latitudes, with emphasis on details of the ACIS instrumental background modeling. Observations of the dark Moon are used to model the detector background. A comparison of the Moon data and the data obtained with ACIS stowed outside the focal area showed that the dark Moon does not emit significantly in our band. Point sources down to 3 � 10 � 16 ergs s � 1 cm � 2 in the 0.5–2 keV band are excluded in our two deepest observations. We estimate the contribution of fainter, undetected sources to be less than 20% of the remaining CXB flux in this band in all four pointings. In the 0.3–1 keV band, the diffuse signal varies strongly from field to field and contributes between 55% and 90% of the total CXB signal. It is dominated by emission lines that can be modeled by a kT ¼ 0:1 0:4 keV plasma. In particular, the two fields located away from bright Galactic features show a prominent line blend at E � 580 eV (O vii+O viii) and a possible line feature at E � 300 eV. The two pointings toward the North Polar Spur exhibit a brighter O blend and additional bright lines at 730–830 eV (Fe xvii). We measure the total 1–2 keV flux of 1:0 1:2 � 0:2 ðÞ �10 � 15 ergs s � 1 cm � 2 arcmin � 2 (mostly resolved) and the 2–7 keV flux of 4:0 4:5 � 1:5 ðÞ �10 � 15 ergs s � 1 cm � 2 arcmin � 2 .A tE > 2 keV, the diffuse emission is consistent with zero, to an accuracy limited by the short Moon exposure and systematic uncertainties of the S3 background. Assuming Galactic or local origin of the line emission, we put an upper limit of � 3 � 10 � 15 ergs s � 1 cm � 2 arcmin � 2 on the 0.3–1 keV extragalactic diffuse flux. Subject headings: intergalactic medium — ISM: general — methods: data analysis — X-rays: diffuse background — X-rays: ISM

X-rays in the orion nebula cluster: constraints on the origins of magnetic activity in pre-main-sequence stars

Abstract: A recent observation of the Orion Nebula Cluster with the ACIS instrument on board the Chandra X-Ray Observatory detected 1075 sources, 525 of which are pre-main-sequence (PMS) stars with measured bulk properties such as bolometric luminosities, masses, ages, and disk indicators. Nearly half of these stars have photometrically measured rotational periods. This provides a uniquely large and well-defined sample to study the dependence of magnetic activity on bulk properties for stars descending the Hayashi tracks. The following results are obtained: (1) X-ray luminosities Lt in the 0.5-8 keV band are strongly correlated with bolometric luminosity, with average ratio log L_t/L_(bol) = -3.8 for stars with masses 0.7 < M < 2 M_☉, an order of magnitude below the main-sequence saturation level; (2) the X-ray emission drops rapidly below this level in some stars with 2 < M < 3 M_☉; (3) the presence or absence of infrared circumstellar disks has no apparent relation to X-ray levels; and (4) X-ray luminosities exhibit a slight rise as rotational periods increase from 0.4 to 20 days. This last finding stands in dramatic contrast to the strong decline of X-ray emission with increasing period seen in main-sequence stars. The absence of a strong X-ray/rotation relationship in PMS stars, and particularly the high X-ray values seen in some very slowly rotating stars, is a clear indication that the mechanisms of magnetic field generation differ from those operating in main-sequence stars. The most promising possibility is a turbulent dynamo distributed throughout the deep convection zone, but other models, such as α-Ω dynamo with "supersaturation" or relic core fields, are not immediately excluded. The drop in magnetic activity in intermediate-mass stars may reflect the presence of a significant radiative core. The evidence does not support X-ray production in large-scale star-disk magnetic fields in T Tauri stars.

The epsilon chamaeleontis young stellar group and the characterization of sparse stellar clusters

Abstract: We present the outcomes of a Chandra X-Ray Observatory snapshot study of five nearby Herbig Ae/Be (HAeBe) stars that are kinematically linked with the Oph-Sco-Cen association (OSCA). Optical photometric and spectroscopic follow-up was conducted for the HD 104237 field. The principal result is the discovery of a compact group of pre-main-sequence (PMS) stars associated with HD 104237 and its codistant, comoving B9 neighbor Chamaeleontis AB. We name the group after the most massive member. The group has five confirmed stellar systems ranging from spectral type B9 to M5, including a remarkably high degree of multiplicity for HD 104237 itself. The HD 104237 system is at least a quintet, with four low-mass PMS companions in nonhierarchical orbits within a projected separation of 1500 AU of the HAeBe primary. Two of the low-mass members of the group are actively accreting classical T Tauri stars. The Chandra observations also increase the census of companions for two of the other four HAeBe stars, HD 141569 and HD 150193, and identify several additional new members of the OSCA. We discuss this work in light of several theoretical issues: the origin of X-rays from HAeBe stars; the uneventful dynamical history of the high-multiplicity HD 104237 system; and the origin of the Cha group and other OSCA outlying groups in the context of turbulent giant molecular clouds. Together with the similar η Cha cluster, we paint a portrait of sparse stellar clusters dominated by intermediate-mass stars 5-10 Myr after their formation.

Very high redshift x-ray selected agn in the chandra deep field-north

Abstract: Deep Chandra X-ray exposures provide an efficient route for locating optically faint active galactic nuclei (AGN) at high redshifts. We use deep multicolor optical data to search for z > 5 AGN in the 2 Ms X-ray exposure of the Chandra Deep Field-North. Of the 423 X-ray sources bright enough (z ′ 6. The z > 5 object is spectroscopically confirmed at z = 5.19. Only 31 of the 77 sources with z ′ > 25.2 are undetected in the B or V bands at the 2� level and could lie at z > 5. There are too few moderate luminosity AGN at z = 5 6.5 to ionize the intergalactic medium. Subject headings: cosmology: observations — galaxies: active — galaxies: evolution — galaxies: formation — galaxies: distances and redshifts

The Chandra Deep Field North Survey. XV. Optically Bright, X-Ray-Faint Sources*

Abstract: We have analyzed optically bright, X-ray?faint [OBXF; i.e., log (fX/fR)-2] sources identified in an 178.9 arcmin2 area having high exposure (greater than 1500 ks) within the Chandra Deep Field North 2 Ms survey. We find 43 OBXF sources in this area, making up ?15% of the X-ray sources above a 0.5?2 keV flux of ?2.3 ? 10-17 ergs cm-2 s-1. We present spectroscopic identifications for 42 of the OBXF sources and optical spectra for 25, including five previously unpublished redshifts. Deep optical imaging data (either Hubble Space Telescope [HST] or ground-based) are presented for all the OBXF sources; we measure the optical morphologies of the 20 galaxies having HST imaging data. The OBXF population consists mainly of normal and starburst galaxies detected out to cosmologically significant distances (i.e., to a median redshift of z = 0.297 and a full redshift range z = 0.06?0.845). This is notable since these distances equate to look-back times of up to ?8 Gyr; we are thus provided with a window on the X-ray emission from galaxies at redshifts much closer to the cosmic star formation peak than was possible prior to the Chandra X-Ray Observatory. The X-ray luminosity distribution of OBXF sources extends to higher luminosity than does that of normal galaxies, indicating that a significant fraction are likely dominated by low-luminosity active galactic nuclei or vigorous star formation. The lowest redshift galaxies (z ? 0.06?0.2) have very low X-ray?to?optical flux ratios [i.e., log (fX/fR) -3], which are consistent with those of normal galaxies in the local universe. By combining the detected X-ray counts, we find the average OBXF X-ray spectrum to be consistent with a ? ? 2.0 power law. The 0.5?2 keV log N?log S for the OBXF galaxies is much steeper (? ? -1.7) than for the general X-ray source population. Indeed, the number of OBXF sources has doubled between the 1 and 2 Ms surveys, rising sharply in numbers at faint fluxes. The extragalactic OBXF sources are found to contribute ?1%?2% of the soft extragalactic X-ray background. We report on the discovery of five candidate off-nuclear ultraluminous X-ray sources (LX 1039 ergs s-1) with z ? 0.1?0.2 within the OBXF population. These sources are ultraluminous in that they are typically more X-ray luminous than, e.g., Eddington-limited accretion onto stellar-mass black holes; these sources are found to dominate the X-ray emission of their host galaxies.

Very High Redshift X-Ray-selected Active Galactic Nuclei in the Chandra Deep Field-North

Abstract: Deep Chandra X-ray exposures provide an efficient route for locating optically faint active galactic nuclei (AGNs) at high redshifts. We use deep multicolor optical data to search for z > 5 AGNs in the 2 Ms X-ray exposure of the Chandra Deep Field-North. Of the 423 X-ray sources bright enough (z' 6. The one z > 5 object is spectroscopically confirmed at z = 5.19. Only 31 of the 77 sources with z' > 25.2 are undetected in the B or V bands at the 2 ? level and could lie at z > 5. There are too few moderate-luminosity AGNs at z = 5-6.5 to ionize the intergalactic medium.

Chandra Observations of QSO 2237+0305

Abstract: We present the observations of the gravitationally lensed system QSO 2237+0305 (Einstein Cross) performed with the Advanced CCD Imaging Spectrometer on board the Chandra X-Ray Observatory on 2000 September 6 and on 2001 December 8 for 30.3 and 9.5 ks, respectively. Imaging analysis resolves the four X-ray images of the Einstein Cross. A possible fifth image is detected; however, the poor signal-to-noise ratio of this image combined with contamination produced by a nearby brighter image make this detection less certain. We investigate possible origins of the additional image. Fits to the combined spectrum of all images of the Einstein Cross assuming a simple power law with Galactic and intervening absorption at the lensing galaxy yields a photon index of 1.90 consistent with the range of Γ measured for large samples of radio-quiet quasars. For the first Chandra observation of the Einstein Cross this spectral model yields a 0.4-8.0 keV X-ray flux of 4.6 × 10-13 ergs cm-2 s-1 and a 0.4-8.0 keV lensed luminosity of 1.0 × 1046 ergs s-1. The source exhibits variability over both long and short timescales. The X-ray flux has dropped by 20% between the two observations, and the Kolmogorov-Smirnov test showed that image A is variable at the 97% confidence level within the first observation. Furthermore, a possible time delay of 2.7 hr between images A and B with image A leading is detected in the first Chandra observation. The X-ray flux ratios of the images are consistent with the optical flux ratios that are affected by microlensing, suggesting that the X-ray emission is also microlensed. A comparison between our measured column densities and those inferred from extinction measurements suggests a higher dust-to-gas ratio in the lensing galaxy than the average value of our Galaxy. Finally, we report the detection at the 99.99% confidence level of a broad emission feature near the redshifted energy of the Fe Kα line in only the spectrum of image A. The rest frame energy, width, and equivalent width of this feature are Eline = 5.7 keV, σline = 0.87 keV, and EW = 1200 eV, respectively.

The radial structure of supernova remnant n103b

Abstract: We report on the results from a Chandra ACIS observation of the young, compact, supernova remnant N103B. The unprecedented spatial resolution of Chandra reveals subarcsecond structure, in both the brightness and spectral variations. Underlying these small-scale variations is a surprisingly simple radial structure in the equivalent widths of the strong Si and S emission lines. We investigate these radial variations through spatially resolved spectroscopy, using a plane-parallel, nonequilibrium ionization model with multiple components. The majority of the emission arises from components with a temperature of 1 keV: a fully ionized hydrogen component; a high ionization timescale (net > 1012 s cm-3) component containing Si, S, Ar, Ca, and Fe; and a low ionization timescale (net ~ 1011 s cm-3) O, Ne, and Mg component. To reproduce the strong Fe Kα line, it is necessary to include additional Fe in a hot (> 2 keV), low ionization timescale (net ~ 1010.8 s cm-3) component. This hot Fe might be in the form of hot Fe bubbles, formed in the radioactive decay of clumps of 56Ni. We find no radial variation in the ionization timescales or temperatures of the various components. Rather, the Si and S equivalent widths increase at large radii because these lines, as well as those of Ar and Ca, are formed in a shell occupying the outer half of the remnant. A shell of hot Fe is located interior to this, but there is a large region of overlap between these two shells. In the inner 30% of the remnant, there is a core of cooler, 1 keV Fe. We find that the distribution of the ejecta and the yields of the intermediate-mass species are consistent with model prediction for Type Ia events.

Characteristics of Diffuse X-Ray Line Emission within 20 pc of the Galactic Center

Abstract: Over the last 3 yrs, the Galactic center (GC) region has been monitored with the Chandra X-Ray Observatory. With 11 Chandra observations through 2002 June, the total effective exposure reaches ~590 ks, providing significant photon statistics on the faint, filamentary, diffuse X-ray emission. The true-color X-ray image and the equivalent width (EW) images for the detected elemental species demonstrate that the diffuse X-ray features have a broad range of spatio-spectral properties. Enhancements of the low-ionization-state, or ``neutral'' Fe line emission (E~6.4 keV) to the northeast of Sgr A* can be interpreted as fluorescence within the dense ISM resulting from irradiation by hard, external X-ray sources. They may also be explained by emission induced by the bombardments by high energy particles on the ISM, such as unresolved supernova (SN) ejecta intruding into dense ISM. The detection of molecular cloud counterparts to the 6.4 keV Fe line features indicates that these Fe line features are associated with dense GC clouds and/or active star-forming regions, which supports the X-ray reflection and/or SN ejecta origins for the Fe line emission. We detect highly ionized S and Si lines which are generally coincident with the neutral Fe line emission and the dense molecular clouds in the northeast of Sgr A*. These hot plasmas are likely produced by massive star-forming activities and/or SNRs. In contrast, we find that highly ionized He-like Fe line emission (E~6.7 keV) is primarily distributed along the plane instead of being concentrated in the northeast of Sgr A*. The implied high temperature and the alignment along the plane are consistent with the magnetic confinement model.

X-Ray Emission from Multiphase Shock in the Large Magellanic Cloud Supernova Remnant N49

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.

X-Ray Lighthouses of the High-Redshift Universe: Probing the Most Luminous z>4 Palomar Digital Sky Survey Quasars with Chandra

Abstract: We present the results from exploratory Chandra observations of nine high-redshift (z = 4.09–4.51) optically selected quasars. These quasars, taken from the Palomar Digital Sky Survey (DPOSS), are among the optically brightest and most luminous z > 4 quasars known (MB ≈ -28.4 to -30.2). All have been detected by Chandra in exposure times of ≈5–6 ks, tripling the number of highly luminous quasars (MB 4. These quasars' average broadband spectral energy distributions are characterized by steeper (more negative) αox values (αox = -1.81 ± 0.03) than those of lower luminosity, lower redshift samples of quasars. We confirm the presence of a significant correlation between the ultraviolet magnitude and soft X-ray flux previously found for z > 4 quasars. The joint ≈2–30 keV rest-frame X-ray spectrum of the nine quasars is well parameterized by a simple power-law model whose photon index, Γ ≈ 2.0 ± 0.2, is consistent with those of lower redshift quasars. No evidence for significant amounts of intrinsic absorption has been found (NH 8.8 × 1021 cm-2 at 90% confidence). In general, our results show that z ≈ 4.1–4.5 quasars and local quasars have reasonably similar X-ray and broadband spectra (once luminosity effects are taken into account), suggesting that the accretion mechanisms in these objects are similar. We also present near-simultaneous optical spectra for these quasars obtained with the Hobby-Eberly Telescope; this is the first time optical spectra have been published for seven of these objects. The objects presented in this paper are among the best z > 4 targets for X-ray spectroscopy with XMM-Newton and next-generation, large-area X-ray telescopes. These will detect or constrain iron Kα emission lines down to rest-frame equivalent widths of ≈50 eV and intrinsic column densities down to NH values roughly a few times 1021 cm-2 at z ≈ 4. We also present 45 new ROSAT upper limits for z ≥ 4 quasars and a likely (3 σ) HRI detection of the blazar GB 1713+2148 at z = 4.01.

Coronal X-Ray Emission from an Intermediate-Age Brown Dwarf

Abstract: We report the X-ray detection of the brown dwarf (BD) companion TWA 5B in an 12 Myr old pre-main-sequence binary system. We clearly resolve the faint companion (35 photons) separated from the X-ray luminous primary by 2'' in a Chandra ACIS image. TWA 5B shows a soft X-ray spectrum with a low plasma temperature of only 0.3 keV and a constant flux during the 3 hr observation, of which the characteristics are commonly seen in the solar corona. The X-ray luminosity is 4 ? 1027 ergs s-1 (0.1-10 keV band) or log = -3.4. Comparing these properties to both younger and older BDs, we discuss the evolution of the X-ray emission in BDs. During their first few megayears, they exhibit high levels of X-ray activity, as seen in higher mass pre-main-sequence stars. The level in TWA 5B is still high at t 12 Myr in log LX/Lbol, while kT has already substantially cooled.

X-Ray Source Population in the Elliptical Galaxy NGC 720 with Chandra

Abstract: With a Chandra ACIS-S3 observation, we detect 42 X-ray point sources in the elliptical galaxy NGC 720, including a possible central source. Most of these sources will be low-mass X-ray binaries, and 12 are located within 2'' of globular cluster candidates. We investigate both the hardness ratios and combined spectra of the sources. They exhibit a distribution of X-ray colors similar to those seen in other early-type galaxies. We find that there is a population of highly absorbed sources located at large distances from the center of the galaxy. The overall spatial distribution of sources is consistent with the ellipticity and position angle of the galaxy, but the sources appear to form several arcs. NGC 720 contains nine ultraluminous sources (ULXs; LX ≥ 1039 ergs s-1). This number is more than have previously been detected in an early-type galaxy but similar to the number seen in the Antennae merger system. The ratio LULX/LB for NGC 720 is more than double the ratio for the S0 galaxy NGC 1553 and a factor of 7 higher than for the elliptical galaxy NGC 4697, although uncertainties in the distance and the source spectral properties could bring these ratios into agreement. The X-ray source luminosity function is also nearly as flat as those seen in disk and merger systems. The large number of ULXs in NGC 720 and its relatively flat X-ray luminosity function may provide evidence against the association of all ULXs with young stars. We also see a possible high-luminosity break in the luminosity function at 2 × 1039h ergs s-1.

0103-72.6: A new oxygen-rich supernova remnant in the small magellanic cloud

Abstract: 0103-72.6, the second brightest X-ray supernova remnant (SNR) in the Small Magellanic Cloud (SMC), has been observed with the Chandra X-Ray Observatory. Our Chandra observation unambiguously resolves the X-ray emission into a nearly complete, remarkably circular shell surrounding bright clumpy emission in the center of the remnant. The observed X-ray spectrum for the central region is evidently dominated by emission from reverse-shock-heated metal-rich ejecta. Elemental abundances in this ejecta material are particularly enhanced in oxygen and neon, while less prominent in the heavier elements Si, S, and Fe. We thus propose that 0103-72.6 is a new "oxygen-rich" SNR, making it only the second member of the class in the SMC. The outer shell is the limb-brightened soft X-ray emission from the swept-up SMC interstellar medium. The presence of O-rich ejecta and the SNR's location within an H II region attest to a massive star core-collapse origin for 0103-72.6. The elemental abundance ratios derived from the ejecta suggest an ~18 M☉ progenitor star.

Detection of Magnesium-rich Ejecta in the Middle-aged Supernova Remnant N49B

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.

Detection of Magnesium-Rich Ejecta in the Middle-Aged Supernova Remnant N49B

Abstract: The middle-aged supernova remnant (SNR) N49B in the Large Magellanic Cloud has been observed with the {\it Chandra X-Ray Observatory}. The superb angular resolution of {\it 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 for either point-like 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 $\sim$$2\times 10^{33}$ ergs s$^{-1}$ on the 0.5 $-$ 5 keV band X-ray luminosity of any embedded compact object.

0103-72.6: A New Oxygen-Rich Supernova Remnant in the Small Magellanic Cloud

Abstract: 0103$-$72.6, the second brightest X-ray supernova remnant (SNR) in the Small Magellanic Cloud (SMC), has been observed with the {\it Chandra X-Ray Observatory}. Our {\it Chandra} observation unambiguously resolves the X-ray emission into a nearly complete, remarkably circular shell surrounding bright clumpy emission in the center of the remnant. The observed X-ray spectrum for the central region is evidently dominated by emission from reverse shock-heated metal-rich ejecta. Elemental abundances in this ejecta material are particularly enhanced in oxygen and neon, while less prominent in the heavier elements Si, S, and Fe. We thus propose that 0103$-$72.6 is a new ``oxygen-rich'' SNR, making it only the second member of the class in the SMC. The outer shell is the limb-brightened, soft X-ray emission from the swept-up SMC interstellar medium. The presence of O-rich ejecta and the SNR's location within an H{\small II} region attest to a massive star core-collapse origin for 0103$-$72.6. The elemental abundance ratios derived from the ejecta suggest an $\sim$18 M$_{\odot}$ progenitor star.

X-Ray Sources with Periodic Variability in a Deep Chandra Image of the Galactic Center

Abstract: We report the discovery of eight X-ray sources with periodic variability in 487 ks of observations of the Galactic center with Chandra. The sources are identified from a sample of 285 objects detected with 100-4200 net counts. Their periods range from 300 s to 4.5 hr, with amplitudes between 40% and 70% rms. They have luminosities of (1-5) × 1032 ergs s-1 (2-8 keV at 8 kpc). The spectra of seven of the eight sources are consistent with Γ ≈ 0 power laws absorbed by gas and dust with a column density equal to or higher than that toward the Galactic center (6 × 1022 cm-2). Four of these sources also exhibit emission lines near 6.7 keV from He-like Fe, with equivalent widths of 600-1000 eV. These properties are consistent with both magnetically accreting cataclysmic variables and wind-accreting neutron stars in high-mass X-ray binaries. The eighth source has an absorbing column of 5 × 1021 cm-2 that places it in the foreground. Its spectrum is consistent with either a Γ = 1.4 power law or kT = 25 keV bremsstrahlung emission. Its period-folded flux profile clearly identifies it as an eclipsing polar. We place an approximate upper limit of i' > 23 mag on the optical counterpart to this source using a 5 minute exposure obtained with the Magellan Instant Camera on the Clay telescope (Magellan II) at Las Campanas.

X-ray Sources with Periodic Variability in a Deep Chandra Image of the Galactic Center

Abstract: We report the discovery of eight X-ray sources with periodic variability in 487 ks of observations of the Galactic center with Chandra. The sources are identified from a sample of 285 objects detected with 100-4200 net counts. Their periods range from 300 s to 4.5 h with amplitudes between 40% and 70% rms. They have luminosities of (1 - 5) \times 10^{32} erg/sec (2--8 keV at 8 kpc). The spectra of seven of the eight sources are consistent with Gamma = 0 power laws absorbed by gas and dust with a column density equal to or higher than that toward the Galactic Center (6 times 10^{22} cm^{-2}). Four of these sources also exhibit emission lines near 6.7 keV from He-like Fe, with equivalent widths of 600-1000 eV. These properties are consistent with both magnetically accreting cataclysmic variables and wind-accreting neutron stars in high-mass X-ray binaries. The eighth source has an absorbing column of 5 \times 10^{21} cm^{-2} that places it in the foreground. Its spectrum is consistent with either a Gamma = 1.4 power law or kT = 25 keV bremsstrahlung emission. Its period-folded flux profile clearly identifies it as an eclipsing polar. We place an approximate upper limit of i^\prime > 23 magnitude on the optical counterpart to this source using a 5 min exposure obtained with the MagIC camera on the Clay telescope (Magellan II) at Las Campanas.

Deep X‐Ray Imaging of the Central 20 Parsecs of the Galaxy with Chandra

Abstract: A deep observation toward the Galactic center with the Chandra X-Ray Observatory revealed a number of extended features, in addition to Sgr A* and SgrA East. Here, we focus on two curious, extended X-ray structures: large-scale (∼10 pc) bipolar lobes centered on Sgr A* and a bright cometary source located 0.3 pc from Sgr A*, CXOGC J174539.7-290020. The bipolar lobes consist of a number of emission clumps oriented along a line perpendicular to the Galactic plane, suggesting that a series of ejections has taken place on characteristic time scales of hundreds to thousands of years. The clumps are embedded in a low-intensity, edge-brightened lobe which is most evident in a flux ratio map. At two locations along the lobe, nonthermal linear features are present, suggesting that relativistic electrons may be impinging on the compressed, magnetic wall of this structure. The cometary X-ray source has no counterpart at other wavelengths; its orientation is consistent with a high-velocity neutron star ejected from the grouping of stars at IRS13, but there are problems with that hypothesis, and other models warrant consideration.

The AGN source population in the Chandra Deep Field-North Survey: Constraints from X-ray spectroscopy and variability

Abstract: With the 0.5-10.0 keV background nearly resolved (e.g., Giacconi et al. 2000; Cowie et al. 2002), the emphasis has shifted towards understanding the nature of the faint X-ray population — a clear necessity if we wish to understand the formation and evolution of active galactic nuclei (AGN). Here we report on preliminary spectral and temporal Xray studies of AGN in the 2 Ms Chandra Deep Field-North Survey (CDF-N; D.M. Alexander et al. in prep). Our sample is comprised of 136 CDF-N sources with > 200 net counts (∼30% of the total CDF-N sample), spanning (0.014– 2)× 10 ergs cm s; 72 sources have known redshifts.