arXiv subjects

Jonathan McDowell

Publications and source records attributed to Jonathan McDowell.

23 records · Page 2Linked to original sources

arXiv2010

Scientific requirements of the VAO SED tool

This document describes the scientific requirements for the SED builder and analysis tool that will be designed and built by the US Virtual Astronomical Observatory (VAO). VAO is the VO effort based in the US, whose primary emphasis is to provide new scientific research capabilities to the astronomy community. The near-term goal of the VAO is to put useful and efficient tools in the hands of research astronomers as soon as possible. The VAO has identified eight major research initiatives that are of high priority, including the science obtained with the creation and analysis of the spectral energy distributions of astronomical sources. This document contains the high-level scientific requirements that will drive the design and implementation of the VAO SED tool.

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arXiv2009

A Vigorous Explorer Program

Explorers have made breakthroughs in many fields of astrophysics. The science from both these missions contributed to three Nobel Prizes - Giacconi (2002), Mather, and Smoot (2006). Explorers have: marked the definitive beginning of precision cosmology, discovered that short gamma-ray bursts are caused by compact star mergers and have measured metalicity to redshifts z>6. NASA Explorers do cutting-edge science that cannot be done by facility-class instruments. The Explorer program provides a rapid response to changing science and technology, to enable cutting-edge science at moderate cost. Explorers also enable innovation, and engage & train scientists, managers and engineers, adding human capital to NASA and the nation. The astrophysics Explorer launch rate now being achieved is 1 per 3 years, and budget projections are in the $150M/year range for the next five years. A newly Vigorous Explorer Program should be created to: 1. Reach the long-stated goal of annual astrophysics launches; 2. Find additional launch options for Explorers and actively encourage cost savings in launchers and spacecraft, such as new commercial vehicles and innovative partnerships. 3. Mitigate risk via stronger technical development and sub-orbital programs, and through longer, more thorough, Phase A programs, potentially reducing the need for a 30% contingency; 4. Strive to protect the funding for missions that have reached Phase B, to prevent significant launch slips and cancellations, with a goal of 4 to 5 years from Phase B to launch; 5. Review the project management procedures and requirements to seek cost reductions, including the risk management strategy and the review and reporting process; 6. Review and possibly modify the cost caps for all Explorer classes to optimize scientific returns per dollar. [ABRIDGED]

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arXiv2003

Chandra Observations of the Dwarf Nova WX Hyi in Quiescence

We report Chandra observations of the dwarf nova WX Hyi in quiescence. The X-ray spectrum displays strong and narrow emission lines of N, O, Mg, Ne, Si, S and Fe. The various ionization states implied by the lines suggest that the emission is produced within a flow spanning a wide temperature range, from T ~ 10^6 K to T >~ 10^8 K. Line diagnostics indicate that most of the radiation originates from a very dense region, with n ~ 10^{13}-10^{14} cm^{-3}. The Chandra data allow the first tests of specific models proposed in the literature for the X-ray emission in quiescent dwarf novae. We have computed the spectra for a set of models ranging from hot boundary layers, to hot settling flows solutions, to X-ray emitting coronae. WX Hyi differs from other dwarf novae observed at minimum in having much stronger low temperature lines, which prove difficult to fit with existing models, and possibly a very strong, broad O VII line, perhaps produced in a wind moving at a few x 10^3 km/s. The accretion rate inferred from the X-rays is lower than the value inferred from the UV. The presence of high-velocity mass ejection could account for this discrepancy while at the same time explaining the presence of the broad O VII line. If this interpretation is correct, it would provide the first detection of a wind from a dwarf nova in quiescence.

astro-ph↗

arXiv2001

150 keV Emission from PKS2149-306 with BeppoSAX

A BeppoSAX observation of the z=2.34 quasar PKS2149-306 produced a strong signal in the high energy PDS instrument up to a maximum observed energy of nearly 50 keV, 150 keV in the quasar frame. The Beppo-SAX spectrum spans almost 3 decades (0.3-150 keV, quasar frame) and shows an extremely hard (alpha=0.4+/-0.05) X-ray spectrum above 3 keV (comparable to the X-ray background slope), and either a softer (alpha=1.0(+0.6, -0.3)) low energy component, or an ionized absorber at zero redshift. No evidence is seen of an Fe-K emission line (EW<167 eV at 6.5 keV quasar frame) or a Compton hump (R<0.3). A bremsstrahlung fit gives kT(rest)=46(+32, -16) keV, similar to the X-ray background value, and a high energy cut-off power law requires E(cut)>120 keV (quasar frame). The SED of PKS 2149-306 shows two peaks at ~ 10(12+/-0.5}Hz and \~10(21+/-1.0)Hz (~ 0.3 mm and ~ 4 MeV), strongly resembling a low energy cutoff BL~Lac object (LBL). The ratio of the two peaks shows an extreme Compton dominance (C_D=1.4+/- 0.4), as in flat spectrum radio quasars (FSRQs). The presence of an additional `optical/UV big bump' component may provide photons that cool the jet, suppressing the radio emission.

astro-ph↗

arXiv1998

The U.S. ISO Key Project on Quasars

Observations for the U.S. key project on quasars using ISO were completed in April when the satellite's cryogen supply expired. This proceeding presents an update of the project, including information on the final sample, a discussion of some of the data reduction challenges and current efforts to meet them, plus a comparison of preliminary results with IRAS fluxes.

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