New Models for X-Ray Synchrotron Radiation from the Remnant of Supernova 1006 AD

Galactic cosmic rays up to energies of around 10^15 eV are assumed to originate in supernova remnants (SNRs). The shock wave of a young SNR like SN 1006 AD can accelerate electrons to energies greater than 1 TeV, where they can produce synchrotron radiation in the X-ray band. A new model (SRESC) designed to model synchrotron X-rays from Type Ia supernovae can constrain values for the magnetic-field strength and electron scattering properties, with implications for the acceleration of the unseen ions which dominate the cosmic-ray energetics. New observations by ASCA, ROSAT, and RXTE have provided enormously improved data, which now extend to higher X-ray energies. These data allow much firmer constraints. We will describe model fits to these new data on SN 1006 AD, emphasizing the physical constraints that can be placed on SNRs and on the cosmic-ray acceleration process.Comment: 10 pages, 2 figures. to appear in "Cosmic Explosions", proceeding of the 10th Annual October Astrophysics Conference (ed. S.S. Holt and W. W. Zhang) LaTex aipproc.st

Searching for annihilation radiation from SN 1006 with SPI on INTEGRAL

Historical Type Ia supernovae are a leading candidate for the source of positrons observed through their diffuse annihilation emission in the Galaxy. However, search for annihilation emission from individual Type Ia supernovae has not been possible before the improved sensitivity of \integral. The total 511 keV annihilation flux from individual SNe Ia, as well as their contribution to the overall diffuse emission, depends critically on the escape fraction of positrons produced in $^{56}$Co decays. Late optical light curves suggest that this fraction may be as high as 5%. We searched for positron annihilation radiation from the historical Type Ia supernova SN 1006 using the SPI instrument on \integral. We did not detect significant 511 keV line emission, with a 3$\sigma$ flux upper limit of 0.59 x 10$^{-4}$ ergs cm^-2 s^-1 for \wsim 1 Msec exposure time, assuming a FWHM of 2.5 keV. This upper limit corresponds to a 7.5% escape fraction, 50% higher than the expected 5% escape scenario, and rules out the possibility that Type Ia supernovae produce all of the positrons in the Galaxy (~ 12% escape fraction), if the mean positron lifetime is less than 10$^{5}$ years. Future observations with \integral will provide stronger limits on the escape fraction of positrons, the mean positron lifetime, and the contribution of Type Ia supernovae to the overall positron content of the Galaxy.Comment: 3 pages, 2 figures, accepted for publication in ApJ

Apnea, bradycardia and desaturation spells in premature infants: impact of a protocol for the duration of 'spell-free' observation on interprovider variability and readmission rates.

ObjectiveTo study the impact of implementing a protocol to standardize the duration of observation in preterm infants with apnea/bradycardia/desaturation spells before hospital discharge on length of stay (LOS) and readmission rates.Study designA protocol to standardize the duration of in-hospital observation for preterm infants with apnea, bradycardia and desaturation spells who were otherwise ready for discharge was implemented in December 2013. We evaluated the impact of this protocol on the LOS and readmission rates of very low birth weight infants (VLBW). Data on readmission for apnea and an apparent life-threatening event (ALTE) within 30 days of discharge were collected. The pre-implementation epoch (2011 to 2013) was compared to the post-implementation period (2014 to 2016).ResultsThere were 426 and 368 VLBW discharges before and after initiation of the protocol during 2011 to 2013 and 2014 to 2016, respectively. The LOS did not change with protocol implementation (66±42 vs 64±42 days before and after implementation of the protocol, respectively). Interprovider variability on the duration of observation for apneic spells (F-8.8, P=0.04) and bradycardia spells (F-17.4, P<0.001) decreased after implementation of the protocol. The readmission rate for apnea/ALTE after the protocol decreased from 12.1 to 3.4% (P=0.01).ConclusionImplementing an institutional protocol for VLBW infants to determine the duration of apnea/bradycardia/ desaturation spell-free observation period as recommended by the American Academy of Pediatrics clinical report did not prolong the LOS but effectively reduced interprovider variability and readmission rates

On the lack of X-ray iron line reverberation in MCG-6-30-15: Implications for the black hole mass and accretion disk structure

We use the method of Press, Rybicki & Hewitt (1992) to search for time lags and time leads between different energy bands of the RXTE data for MCG-6-30-15. We tailor our search in order to probe any reverberation signatures of the fluorescent iron Kalpha line that is thought to arise from the inner regions of the black hole accretion disk. In essence, an optimal reconstruction algorithm is applied to the continuum band (2-4keV) light curve which smoothes out noise and interpolates across the data gaps. The reconstructed continuum band light curve can then be folded through trial transfer functions in an attempt to find lags or leads between the continuum band and the iron line band (5-7keV). We find reduced fractional variability in the line band. The spectral analysis of Lee et al. (1999) reveals this to be due to a combination of an apparently constant iron line flux (at least on timescales of few x 10^4s), and flux correlated changes in the photon index. We also find no evidence for iron line reverberation and exclude reverberation delays in the range 0.5-50ksec. This extends the conclusions of Lee et al. and suggests that the iron line flux remains constant on timescales as short as 0.5ksec. The large black hole mass (>10^8Msun) naively suggested by the constancy of the iron line flux is rejected on other grounds. We suggest that the black hole in MCG-6-30-15 has a mass of M_BH~10^6-10^7Msun and that changes in the ionization state of the disk may produce the puzzling spectral variability. Finally, it is found that the 8-15keV band lags the 2-4keV band by 50-100s. This result is used to place constraints on the size and geometry of the Comptonizing medium responsible for the hard X-ray power-law in this AGN.Comment: 11 pages, 13 postscript figures. Accepted for publication in Ap

Occultation Mapping of the Central Engine in the Active Galaxy MCG -6-30-15

The colossal power output of active galactic nuclei (AGN) is believed to be fueled by the accretion of matter onto a supermassive black hole. This central accreting region of AGN has hitherto been spatially unresolved and its structure therefore unknown. Here we propose that a previously reported `deep minimum' in the X-ray intensity of the AGN MCG-6-30-15, was due to a unique X-ray occultation event and that it probes structure of the central engine on scales < 1e14 cm, or 1.4e-7 arcseconds. The data are consistent with a bright central source surrounded by a less intense ring, which we identify with the inner edge of an accretion disk. These may be the first direct measurements of the spatial structure and geometry of the accreting black-hole system in an active galaxy.If the ring of X-ray emission is identified with the inner edge of an accretion disk, upper limits on the BH mass can be derived. Our occultation interpretation is controversial in the sense that X-ray variability in AGNs is normally attributed to intrinsic physical changes in the X-ray emission region, such as disk or coronal instabilities.Comment: 15 pages, 2 Figures. Latex with separate postscript figure files. Accepted for publication in ApJ Letter

On The Reddening in X-ray Absorbed Seyfert 1 Galaxies

There are several Seyfert galaxies for which there is a discrepancy between the small column of neutral hydrogen deduced from X-ray observations and the much greater column derived from the reddening of the optical/UV emission lines and continuum. The standard paradigm has the dust within the highly ionized gas which produces O~VII and O~VIII absorption edges (i.e., a ``dusty warm absorber''). We present an alternative model in which the dust exists in a component of gas in which hydrogen has been stripped, but which is at too low an ionization state to possess significant columns of O~VII and O~VIII (i.e, a ``lukewarm absorber''). The lukewarm absorber is at sufficient radial distance to encompass much of the narrow emission-line region, and thus accounts for the narrow-line reddening, unlike the dusty warm absorber. We test the model by using a combination of photoionization models and absorption edge fits to analyze the combined ROSAT/ASCA dataset for the Seyfert 1.5 galaxy, NGC 3227. We show that the data are well fit by a combination of the lukewarm absorber and a more highly ionized component similar to that suggested in earlier studies. We predict that the lukewarm absorber will produce strong UV absorption lines of N V, C IV, Si IV and Mg II. Finally, these results illustrate that singly ionized helium is an important, and often overlooked, source of opacity in the soft X-ray band (100 - 500 eV).Comment: 17 pages, Latex, includes 1 figure (encapsulated postscript), one additional table in Latex (landscape format), to appear in the Astrophysical Journa

The viscosity of Miranda

Voyager 2 images of Miranda revealed a significant history of geological activity. Overlying an apparently ancient cratered terrain are assemblages of concentric ridges, scarps, and dark banded material. The problems that evolutionary thermal and structural modes of Miranda must face, to provide a convincing explanation for such topographic complexity, are examined

Searching for additional heating - [OII] emission in the diffuse ionized gas of NGC891, NGC4631 and NGC3079

We present spectroscopic data of ionized gas in the disk--halo regions of three edge-on galaxies, NGC 891, NGC 4631 and NGC 3079, covering a wavelength range from [\ion{O}{2}] $\lambda$3727\AA to [\ion{S}{2}] $\lambda$6716.4\AA. The inclusion of the [\ion{O}{2}] emission provides new constraints on the properties of the diffuse ionized gas (DIG), in particular, the origin of the observed spatial variations in the line intensity ratios. We used three different methods to derive electron temperatures, abundances and ionization fractions along the slit. The increase in the [\ion{O}{2}]/H$\alpha$ line ratio towards the halo in all three galaxies requires an increase either in electron temperature or in oxygen abundance. Keeping the oxygen abundance constant yields the most reasonable results for temperature, abundances, and ionization fractions. Since a constant oxygen abundance seems to require an increase in temperature towards the halo, we conclude that gradients in the electron temperature play a significant role in the observed variations in the optical line ratios from extraplanar DIG in these three spiral galaxies.Comment: 43 pages, 29 figure