X-Ray Synchrotron Emitting Fe-Rich Ejecta in SNR RCW 86

Supernova remnants may exhibit both thermal and nonthermal X-ray emission. We present Chandra observations of RCW 86. Striking differences in the morphology of X-rays below 1 keV and above 2 keV point to a different physical origin. Hard X-ray emission is correlated fairly well with the edges of regions of radio emission, suggesting that these are the locations of shock waves at which both short-lived X-ray emitting electrons, and longer-lived radio-emitting electrons, are accelerated. Soft X-rays are spatially well-correlated with optical emission from nonradiative shocks, which are almost certainly portions of the outer blast wave. These soft X-rays are well fit with simple thermal plane-shock models. Harder X-rays show Fe K alpha emission and are well described with a similar soft thermal component, but a much stronger synchrotron continuum dominating above 2 keV, and a strong Fe K alpha line. Quantitative analysis of this line and the surrounding continuum shows that it cannot be produced by thermal emission from a cosmic-abundance plasma; the ionization time is too short, as shown both by the low centroid energy (6.4 keV) and the absence of oxygen lines below 1 keV. Instead, a model of a plane shock into Fe-rich ejecta, with a synchrotron continuum, provides a natural explanation. This requires that reverse shocks into ejecta be accelerating electrons to energies of order 50 TeV. We show that maximum energies of this order can be produced by radiation-limited diffusive shock acceleration at the reverse shocks.Comment: ApJ, accepted; full resolution images in http://spider.ipac.caltech.edu/staff/rho/rcw86chandra.p

The Radio Continuum of the Metal-Deficient Blue Compact Dwarf Galaxy SBS0335-052

We present new Very Large Array observations at five frequencies, from 1.4 to 22GHz, of the extremely low-metallicity blue compact dwarf SBS0335-052. The radio spectrum shows considerable absorption at 1.49GHz, and a composite thermal+non-thermal slope. After fitting the data with a variety of models, we find the best-fitting geometry to be one with free-free absorption homogeneously intermixed with the emission of both thermal and non-thermal components. The best-fitting model gives an an emission measure EM ~ 8x10^7pc cm^{-6} and a diameter of the radio-emitting region D ~17pc. The inferred density is n_e ~ 2000 cm^{-3}. The thermal emission comes from an ensemble of \~9000 O7 stars, with a massive star-formation rate (>=5Msun) of 0.13-0.15 yr^{-1}, and a supernova rate of 0.006 yr^{-1}. We find evidence for ionized gas emission from stellar winds, since the observed Bralpha line flux significantly exceeds that inferred from the thermal radio emission. The non-thermal fraction at 5GHz is ~0.7, corresponding to a non-thermal luminosity of ~2x10^{20} W Hz^{-1}. We attribute the non-thermal radio emission to an ensemble of compact SN remnants expanding in a dense interstellar medium, and derive an equipartition magnetic field of ~0.6-1 mG, and a pressure of \~3x10^{-8}-1x10^{-7} dyne cm^{-2}. If the radio properties of SBS0335-052 are representative of star formation in extremely low-metallicity environments, derivations of the star formation rate from the radio continuum in high redshift primordial galaxies need to be reconsidered. Moreover, photometric redshifts inferred from ``standard'' spectral energy distributions could be incorrect.Comment: 25 pages, including 3 figures, accepted for publication in Ap

Thermal and Nonthermal X-Ray Emission in SNR RCW 86

Supernova remnants may exhibit both thermal and nonthermal X-ray emission. Such remnants can be distinguished by the weakness of their X-ray lines, because of the presence of a strong nonthermal X-ray continuum. RCW 86 is a remnant with weak lines, resulting in low and peculiar abundances when thermal models alone are used to interpret its X-ray spectrum. This indicates the presence of a strong nonthermal synchrotron continuum. We analyze ASCA X-ray spectra of RCW 86 with the help of both nonequilibrium ionization thermal models and nonthermal synchrotron models. A two-temperature thermal model and a simple nonthermal model with an exponential cutoff (plus interstellar absorption) give reasonable results. We obtain blast wave velocity of 800 km/s, the shock ionization age of 1-3x10^11 s/cm^3, and the break in nonthermal spectra at 2-4x10^16 Hz. The strength of nonthermal continuum correlates well with the radio brightness in the bright SW section of the remnant. This is convincing evidence for X-ray synchrotron emission in RCW 86.Comment: 14 pages, 11 figures, submitted to Astrophysical Journa

Finishing the euchromatic sequence of the human genome

The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead

X-ray synchrotron-emitting Fe-rich ejecta in supernova remnant RCW 86, Astrophys

Supernova remnants may exhibit both thermal and nonthermal X-ray emission. In a previous study with ASCA data, we found that the middle-aged supernova remnant RCW 86 showed evidence for both processes, and predicted that observations with much higher spatial resolution would distinguish harder X-rays, which we proposed were primarily synchrotron emission, from softer, thermal X-rays. Here we describe Chandra observations which amply confirm our predictions. Striking differences in the morphology of X-rays below 1 keV and above 2 keV point to a different physical origin. Hard X-ray emission is correlated fairly well with the edges of regions of radio emission, suggesting that these are the locations of shock waves at which both short-lived X-ray emitting electrons, and longer-lived radio-emitting electrons, are accelerated. Soft X-rays are spatially well-correlated with optical emission from nonradiative shocks, which are almost certainly portions of the outer blast wave. These soft X-rays are well fit with simple thermal plane-shock models. Harder X-rays show Fe Kα emissio

Genomic landscape of pediatric adrenocortical tumors

Pediatric adrenocortical carcinoma is a rare malignancy with poor prognosis. Here we analyze 37 adrenocortical tumors (ACTs) by whole genome, whole exome and/or transcriptome sequencing. Most cases (91%) show loss of heterozygosity (LOH) of chromosome 11p, with uniform selection against the maternal chromosome. IGF2 on chromosome 11p is overexpressed in 100% of the tumors. TP53 mutations and chromosome 17 LOH with selection against wild-type TP53 are observed in 28 ACTs (76%). Chromosomes 11p and 17 undergo copy-neutral LOH early during tumorigenesis, suggesting tumor-driver events. Additional genetic alterations include recurrent somatic mutations in ATRX and CTNNB1 and integration of human herpesvirus-6 in chromosome 11p. A dismal outcome is predicted by concomitant TP53 and ATRX mutations and associated genomic abnormalities, including massive structural variations and frequent background mutations. Collectively, these findings demonstrate the nature, timing and potential prognostic significance of key genetic alterations in pediatric ACT and outline a hypothetical model of pediatric adrenocortical tumorigenesis