We present Chandra point-source catalogs for the Extended Chandra Deep Field-South (E-CDF-S) survey. The E-CDF-S consists of four contiguous 250 ks Chandra observations covering an approximately ...square region of total solid angle -0.3 deg super(2), which flank the existing -1 Ms Chandra Deep Field-South (CDF-S). The survey reaches sensitivity limits of -1.1 x 10 super(-16) and -6.7 x 10 super(-16) ergs cm super(-2) s super(-1) for the 0.5-2.0 and 2-8 keV bands, respectively. We detect 762 distinct X-ray point sources within the E-CDF-S exposure; 589 of these sources are new (i.e., not previously detected in the -1 Ms CDF-S). This brings the total number of X-ray point sources detected in the E-CDF-S region to 915 (via the E-CDF-S and -1 Ms CDF-S observations). Source positions are determined using matched-filter and centroiding techniques; the median positional uncertainty is -0.35. The basic X-ray and optical properties of these sources indicate a variety of source types, although absorbed active galactic nuclei (AGNs) seem to dominate. In addition to our main Chandra catalog, we constructed a supplementary source catalog containing 33 lower significance X-ray point sources that have bright optical counterparts (R < 23). These sources generally have X-ray-to-optical flux ratios expected for normal and starburst galaxies, which lack a strong AGN component. We present basic number-count results for our main Chandra catalog and find good agreement with the -1 Ms CDF-S for sources with 0.5-2.0 and 2-8 keV fluxes greater than 3 x 10 super(-16) and 1 x 10 super(-15) ergs cm super(-2) s super(-1), respectively. Furthermore, three extended sources are detected in the 0.5-2.0 keV band, which are found to be likely associated with galaxy groups or poor clusters at z - 0.1-0.7; these have typical rest-frame 0.5-2.0 keV luminosities of (1-5) x 10 super(42) ergs s super(-1).
ABSTRACT
We present deeper Chandra observations for weak-line quasars (WLQs) in a representative sample that previously had limited X-ray constraints, and perform X-ray photometric analyses to reveal ...the full range of X-ray properties of WLQs. Only 5 of the 32 WLQs included in this representative sample remain X-ray undetected after these observations, and a stacking analysis shows that these 5 have an average X-ray weakness factor of >85. One of the WLQs in the sample that was known to have extreme X-ray variability, SDSS J1539+3954, exhibited dramatic X-ray variability again: it changed from an X-ray normal state to an X-ray weak state within ≈3 months in the rest frame. This short time-scale for an X-ray flux variation by a factor of ≳9 further supports the thick disc and outflow (TDO) model proposed to explain the X-ray and multiwavelength properties of WLQs. The overall distribution of the X-ray-to-optical properties of WLQs suggests that the TDO has an average covering factor of the X-ray emitting region of ∼0.5, and the column density of the TDO can range from $N_{\rm H}\, \sim 10^{23-24}~{\rm cm}^{-2}$ to $N_{\rm H}\, \gtrsim 10^{24}~{\rm cm}^{-2}$, which leads to different levels of absorption and Compton reflection (and/or scattering) among WLQs.
Energetic flares are observed in the Galactic supermassive black hole Sagittarius A* from radio to X-ray wavelengths. On a few occasions, simultaneous flares have been detected in IR and X-ray ...observations, but clear counterparts at longer wavelengths have not been seen. We present a flare observed over several hours on 2006 July 17 with the Chandra X-Ray Observatory, the Keck II telescope, the Caltech Submillimeter Observatory, and the Submillimeter Array. All telescopes observed strong flare events, but the submillimeter peak is found to occur nearly 100 minutes after the X-ray peak. Submillimeter polarization data show linear polarization in the excess flare emission, increasing from 9% to 17% as the flare passes through its peak, consistent with a transition from optically thick to thin synchrotron emission. The temporal and spectral behavior of the flare require that the energetic electrons responsible for the emission cool faster than expected from their radiative output. This is consistent with adiabatic cooling in an expanding emission region, with X-rays produced through self-Compton scattering, although not consistent with the simplest model of such expansion. We also present a submillimeter flare that followed a bright IR flare on 2005 July 31. Compared to 2006, this event had a larger peak IR flux and similar submillimeter flux, but it lacked measurable X-ray emission. It also showed a shorter delay between the IR and submillimeter peaks. Based on these events we propose a synchrotron and self-Compton model to relate the submillimeter lag and the variable IR/X-ray luminosity ratio.
The nuclei of most galaxies are now believed to harbour supermassive black holes. The motions of stars in the central few light years of our Milky Way Galaxy indicate the presence of a dark object ...with a mass of about 2.6 × 106 solar masses (refs 2, 3). This object is spatially coincident with the compact radio source Sagittarius A* (Sgr A*) at the dynamical centre of the Galaxy, and the radio emission is thought to be powered by the gravitational potential energy released by matter as it accretes onto a supermassive black hole. Sgr A* is, however, much fainter than expected at all wavelengths, especially in X-rays, which has cast some doubt on this model. The first strong evidence for X-ray emission was found only recently. Here we report the discovery of rapid X-ray flaring from the direction of Sgr A*, which, together with the previously reported steady X-ray emission, provides compelling evidence that the emission is coming from the accretion of gas onto a supermassive black hole at the Galactic Centre.
We present a catalog of 9017 X-ray sources identified in Chandra observations of a 2°X 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 X 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 2.8s 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.
We report on two Chandra observations of the 3 Myr old pulsar B1929+10, which reveal a faint compact (image9 super(image ) x 5 super(image )) nebula elongated in the direction perpendicular to the ...pulsar's proper motion, two patchy wings, and a possible short (image3 super(image )) jet emerging from the pulsar. In addition, we detect a tail extending up to at least image in the direction opposite to the pulsar's proper motion, aligned with the image15 super(image ) long tail detected in ROSAT and XMM-Newton observations. The overall morphology of the nebula suggests that the shocked pulsar wind is confined by the ram pressure due to the pulsar's supersonic speed. The shape of the compact nebula in the immediate vicinity of the pulsar seems to be consistent with the current MHD models. However, since these models do not account yet for the change of the flow velocity at larger distances from the pulsar, they are not able to constrain the extent of the long pulsar tail. The luminosity of the whole nebula as seen by Chandra is image ergs simage in the 0.3-8 keV band, for the distance of 361 pc. Using the Chandra and XMM-Newton data, we found that the pulsar spectrum is composed of nonthermal (magnetospheric) and thermal components. The nonthermal component can be described by a power-law model with photon index image and luminosity image ergs simage in the 0.3-10 keV band. The blackbody fit for the thermal component, which presumably emerges from hot polar caps, gives the temperature image keV and projected emitting area image m super(2), corresponding to the bolometric luminosity image ergs simage.
Chandra and XMM-Newton resolved extremely long tails behind two middle-aged pulsars, J1509-5850 and J1740+1000. The tail of PSR J1509-5850 is discernible up to 5.6 super(image ) from the pulsar, ...which corresponds to the projected length image pc, where image kpc is the distance to the pulsar. The observed tail flux is image ergs s super(-1) cm super(-2) in the 0.5-8 keV band. The tail spectrum fits an absorbed power law (PL) with the photon index image and 0.5-8 keV luminosity of image ergs s super(-1), for image cm super(- 2). The tail of PSR J1740+1000 is firmly detected up to 5 super(image ) (image pc), with a flux of image ergs cm super(-2) s super(-1) in the 0.4-10 keV band. The PL fit yields image -1.5, image cm super(-2), and an 0.4-10 keV luminosity of image ergs s super(-1). The large extent of the tails suggests that the bulk flow in the tails starts as mildly relativistic downstream of the termination shock and then gradually decelerates. Within the observed extent of the J1509-5850 tail, the average flow speed exceeds 5000 km s super(- 1), and the equipartition magnetic field is a few x 10 super(-5) G. For the J1740+1000 tail, the equipartition field is a factor of a few lower. For the high-latitude PSR J1740+1000, the orientation of the tail suggests that the pulsar was born from a halo-star progenitor. The X-ray efficiencies of the ram pressure-confined pulsar wind nebulae (PWNe) correlate poorly with the pulsar spin-down luminosities or ages. The efficiencies are systematically higher than those of PWNe around slowly moving pulsars with similar spin-down parameters.
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