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 January 2003 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 dataset on the X-ray emission of normal stars ever obtained in the history of X-ray astronomy.

No abstract

Most supermassive black holes (SMBHs) are accreting at very low levels and are difficult to distinguish from the galaxy centers where they reside. Our own Galaxy's SMBH provides a uniquely instructive exception, and we present a close-up view of its quiescent X-ray emission based on 3 mega-second of Chandra observations. Although the X-ray emission is elongated and aligns well with a surrounding disk of massive stars, we can rule out a concentration of low-mass coronally active stars as the origin of the 1 arXiv:1307.5845v2 [astro-ph.HE]

This paper reports measurements of Sgr A* made with NACO in L ′ -band (3.80 µm), Ks-band (2.12 µm) and H-band (1.66 µm) and with VISIR in N-band (11.88 µm) at the ESO VLT 1 , as well as with XMM-Newton at X-ray (2-10 keV) wavelengths. On 4 April, 2007, a very bright flare was observed from Sgr A* simultaneously at L ′ -band and X-ray wavelengths. No emission was detected 1 The Very Large Telescope (VLT) at the European Southern Observatory (ESO) on Paranal, Chile: Program IDs 179.B-0261(A) and Program ID: 079.B-0929(A).using VISIR. The resulting SED has a blue slope (β > 0 for νL ν ∝ ν β , consistent with νL ν ∝ ν 0.4 ) between 12 micron and 3.8 micron.For the first time our high quality data allow a detailed comparison of infrared and X-ray light curves with a resolution of a few minutes. The IR and X-ray flares are simultaneous to within 3 minutes. However the IR flare lasts significantly longer than the X-ray flare (both before and after the X-ray peak) and prominent substructures in the 3.8 micron light curve are clearly not seen in the X-ray data. From the shortest timescale variations in the L ′ -band lightcurve we find that the flaring region must be no more than 1.2 R S in size.The high X-ray to infrared flux ratio, blue νL ν slope MIR to L ′ -band, and the soft νL ν spectral index of the X-ray flare together place strong constraints on possible flare emission mechanisms. We find that it is quantitatively difficult to explain this bright X-ray flare with inverse Compton processes. A synchrotron emission scenario from an electron distribution with a cooling break is a more viable scenario.

Context. The Taurus Molecular Cloud (TMC) is the nearest large star-forming region, prototypical for the distributed mode of lowmass star formation. Pre-main sequence stars are luminous X-ray sources, probably mostly owing to magnetic energy release. Aims. The XMM-Newton Extended Survey of the Taurus Molecular Cloud (XEST) presented in this paper surveys the most populated ≈5 square degrees of the TMC, using the XMM-Newton X-ray observatory to study the thermal structure, variability, and long-term evolution of hot plasma, to investigate the magnetic dynamo, and to search for new potential members of the association. Many targets are also studied in the optical, and high-resolution X-ray grating spectroscopy has been obtained for selected bright sources. Methods. The X-ray spectra have been coherently analyzed with two different thermal models (2-component thermal model, and a continuous emission measure distribution model). We present overall correlations with fundamental stellar parameters that were derived from the previous literature. A few detections from Chandra observations have been added. Results. The present overview paper introduces the project and provides the basic results from the X-ray analysis of all sources detected in the XEST survey. Comprehensive tables summarize the stellar properties of all targets surveyed. The survey goes deeper than previous X-ray surveys of Taurus by about an order of magnitude and for the first time systematically accesses very faint and strongly absorbed TMC objects. We find a detection rate of 85% and 98% for classical and weak-line T Tau stars (CTTS resp. WTTS), and identify about half of the surveyed protostars and brown dwarfs. Overall, 136 out of 169 surveyed stellar systems are detected. We describe an X-ray luminosity vs. mass correlation, discuss the distribution of X-ray-to-bolometric luminosity ratios, and show evidence for lower X-ray luminosities in CTTS compared to WTTS. Detailed analysis (e.g., variability, rotation-activity relations, influence of accretion on X-rays) will be discussed in a series of accompanying papers.

We present the first systematic analysis of the X-ray variability of Sgr A * during the Chandra Xray Observatory's 2012 Sgr A * X-ray Visionary Project (XVP). With 38 High Energy Transmission Grating Spectrometer (HETGS) observations spaced an average of 7 days apart, this unprecedented campaign enables detailed study of the X-ray emission from this supermassive black hole at high spatial, spectral and timing resolution. In 3 Ms of observations, we detect 39 X-ray flares from Sgr A * , lasting from a few hundred seconds to approximately 8 ks, and ranging in 2 − 10 keV luminosity from ∼ 10 34 erg s −1 to 2 × 10 35 erg s −1 . Despite tentative evidence for a gap in the distribution of flare peak count rates, there is no evidence for X-ray color differences between faint and bright flares. Our preliminary X-ray flare luminosity distribution dN/dL is consistent with a power law with index −1.9 +0.3 −0.4 ; this is similar to some estimates of Sgr A * 's NIR flux distribution. The observed flares contribute one-third of the total X-ray output of Sgr A * during the campaign, and as much as 10% of the quiescent X-ray emission could be comprised of weak, undetected flares, which may also contribute high-frequency variability. We argue that flares may be the only source of X-ray emission from the inner accretion flow.

We report on the properties of pre-main-sequence objects in the Taurus molecular clouds as observed in 7 mid-and far-infrared bands with the Spitzer Space Telescope. There are 215 previously-identified members of the Taurus star-forming region in our ∼44 square degree map; these members exhibit a range of Spitzer colors that we take to define young stars still surrounded by circumstellar dust (noting that ∼20% of the bonafide Taurus members exhibit no detectable dust excesses). We looked for new objects in the survey field with similar Spitzer properties, aided -2by extensive optical, X-ray, and ultraviolet imaging, and found 148 candidate new members of Taurus. We have obtained follow-up spectroscopy for about half the candidate sample, thus far confirming 34 new members, 3 probable new members, and 10 possible new members, an increase of 15-20% in Taurus members. Of the objects for which we have spectroscopy, 7 are now confirmed extragalactic objects, and one is a background Be star. The remaining 93 candidate objects await additional analysis and/or data to be confirmed or rejected as Taurus members. Most of the new members are Class II M stars and are located along the same cloud filaments as the previously-identified Taurus members. Among non-members with Spitzer colors similar to young, dusty stars are evolved Be stars, planetary nebulae, carbon stars, galaxies, and AGN.Subject headings: stars: formation -stars: circumstellar matter -stars: pre-main sequenceinfrared: starswhere m is the reported magnitude (and F ν the flux density) for a given object, Z = 18.259, 17.204, and 14.837, and f = 1.94×10 −16 , 4.76×10 −16 , and 5.71×10 −15 ergs cm −2 s −1Å−1 counts −1 sec for U , UVW1, and UVW2 (respectively). In the equation, λ is in units ofÅ, and c is 3×10 18Å s −1 The effective wavelengths are 0.344, 0.291, and 0.212 µm for U , UVW1, and UVW2. There are ∼1600 objects with XMM-Newton OM flux densities in our catalog (0.2% of the entire catalog).We note that many of the X-ray detected XEST sources are likely background galaxies (see Güdel et al. 2007) and that XEST included regions not covered by our map, such as L1551.The XEST team assembled a catalog of supporting data from the literature, such as optical photometric measurements, for all of the previously-identified Taurus members (see §3.1.1 below); we have included these photometric points in our database, converting Johnson magnitudes to flux densities using zero-points available in the literature (e.g., Cox 2001 and references therein).The SEDs presented in this paper use all of these supporting data where available (except for the X-ray fluxes), and are presented as λF λ in cgs units (erg s −1 cm −2 ), against λ in microns.2 In SDSS, a "maggy" is the ratio of the flux density of the object to a standard flux density. The Sloan magnitudes are AB magnitudes, as opposed to Vega magnitudes. In the AB system, a flat spectrum object with 3631 Jy at each band should have every magnitude equal to zero, and all maggies equal to one. Flux densities returned by th...

Abstract. We report the high S/N observation on October 3, 2002 with XMM-Newton of the brightest X-ray flare detected so far from Sgr A* with a duration shorter than one hour (∼2.7 ks). The light curve is almost symmetrical with respect to the peak flare, and no significant difference between the soft and hard X-ray range is detected. The overall flare spectrum is well represented by an absorbed power-law with a soft photon spectral index of Γ = 2.5 ± 0.3, and a peak 2-10 keV luminosity of 3.6 +0.3 −0.4 × 10 35 erg s −1 , i.e. a factor 160 higher than the Sgr A* quiescent value. No significant spectral change during the flare is observed. This X-ray flare is very different from other bright flares reported so far: it is much brighter and softer. The present accurate determination of the flare characteristics challenge the current interpretation of the physical processes occuring inside the very close environment of Sgr A* by bringing very strong constraints for the theoretical flare models.