Engineering topics

Marshall, H. L.

Publications and source records attributed to Marshall, H. L..

At least 19 records

NASA NTRS2004

Changes in the X-Ray Emission from the Magnetar Candidate 1E 2259+586 During its 2002 Outburst

An outburst of more than 80 individual bursts, similar to those seen from Soft Gamma Repeaters (SGRs), was detected from the anomalous X-ray pulsar (AXP) 1E 2259+586 in 2002 June. Coincident with this burst activity were gross changes in the pulsed flux, persistent flux, energy spectrum, pulse profile, and spin-down of the underlying X-ray source. We present Rossi X-Ray Timing Explorer and X-Ray Multi-Mirror Mission observations of 1E 2259+586 that show the evolution of the aforementioned source parameters during and following this episode and identify recovery timescales for each. Specifically, we observe an X-ray flux increase (pulsed and phase-averaged) by more than an order of magnitude having two distinct components. The first component is linked to the burst activity and decays within approx. 2 days, during which the energy spectrum is considerably harder than during the quiescent state of the source. The second component decays over the year following the glitch according to a power law in time with an exponent -0.22 +/- 0.01. The pulsed fraction decreased initially to approx. 15% rms but recovered rapidly to the preoutburst level of approx. 23% within the first 3 days. The pulse profile changed significantly during the outburst and recovered almost fully within 2 months of the outburst. A glitch of size Delta(sib (nu)max) = (4.24 +/- 0.11) x 10(exp -6) was observed in 1E 2259+586, which preceded the observed burst activity. The glitch could not be well fitted with a simple partial exponential recovery. An exponential rise of approx. 20% of the frequency jump with a timescale of approx. 14 days results in a significantly better fit to the data; however, contamination from a systematic drift in the phase of the pulse profile cannot be excluded. A fraction of the glitch (approx. 19%) was recovered in a quasi-exponential manner having a recovery timescale of approx. 16 days. The long-term postglitch spin-down rate decreased in magnitude relative to the preglitch value. The changes in the source properties of 1E 2259+586 during its 2002 outburst are shown to be qualitatively similar to changes seen during or following burst activity in two SGRs, thus further solidifying the common nature of SGRs and AXP's as magnetars. The changes in persistent emission properties of 1E 2259+586 suggest that the star underwent a plastic deformation of the crust that simultaneously impacted the superfluid interior (crustal and possibly core superfluid) and the magnetosphere. Finally, the changes in persistent emission properties coincident with burst activity in 1E 2259+586 enabled us to infer previous burst-active episodes from this and other AXP's. The nondetection of these outbursts by all-sky gamma-ray instruments suggests that the number of active magnetar candidates in our Galaxy is larger than previously thought.

Woods, P. M.↗

NASA NTRS2004

An Overview of the Performance of the Chandra X-ray Observatory

The Chandra X-ray Observatory is the X-ray component of NASA's Great Observatory Program which includes the recently launched Spitzer Infrared Telescope, the Hubble Space Telescope (HST) for observations in the visible, and the Compton Gamma-Ray Observatory (CGRO) which, after providing years of useful data has reentered the atmosphere. All these facilities provide, or provided, scientific data to the international astronomical community in response to peer-reviewed proposals for their use. The Chandra X-ray Observatory was the result of the efforts of many academic, commercial, and government organizations primarily in the United States but also in Europe. NASA s Marshall Space Flight Center (MSFC) manages the Project and provides Project Science; Northrop Grumman Space Technology (NGST - formerly TRW) served as prime contractor responsible for providing the spacecraft, the telescope, and assembling and testing the Observatory; and the Smithsonian Astrophysical Observatory (SAO) provides technical support and is responsible for ground operations including the Chandra X-ray Center (CXC). Telescope and instrument teams at SAO, the Massachusetts Institute of Technology (MIT), the Pennsylvania State University (PSU), the Space Research Institute of the Netherlands (SRON), the Max-Planck Institut fur extraterrestrische Physik (MPE), and the University of Kiel support also provide technical support to the Chandra Project. We present here a detailed description of the hardware, its on-orbit performance, and a brief overview of some of the remarkable discoveries that illustrate that performance.

Weisskopf, M. C.↗

NASA NTRS2003

Changes in the X-ray Emission from the Magnetar Candidate 1E 2259+586 during its 2002 Outburst

An outburst of more thm 80 individual bursts, similar to those see^ from Soft Gamma Repeaters (SGRs), was detected from the Anomalous X-ray Pulsar (AXP) 1E 2259+586 in 2002 June. Coincident with this burst activity were gross changes in the pulsed flux, persistent flux, energy spectrum, pulse profile and spin down of the underlying X-ray source. We present Rossa X-ray Tirnsng Explorer and X-ray Multi-Mirror Mission observations of 1E 2259+586 that show the evolution of the aforementioned source parameters during and following this episode and identify recovery time scales for each. Specifically, we observe an X-ray flux increase (pulsed and phase-averaged) by more than an order of magnitude having two distinct components. The first component is linked to the burst activity and decays within approx. 2 days during which the energy spectrum is considerably harder than during the quiescent state of the source. The second component decays over the year following the glitch according to a power law in time with an exponent -0.22+/-0.01. The pulsed fraction decreased initially to approx. 15% RMS, but recovered rapidly to the pre-outburst level of approx. 2 3 % within the first three days.

Woods, P. M.↗

NASA NTRS2000

Initial Results From The Chandra High Energy Transmission Grating Spectrometer

The High Energy Transmission Grating Spectrometer (HETGS) on the Chandra X-ray Observatory provides spectral resolving powers of 200-1000 over the range 0.4-8.0 keV (1.5-30 A) with effective area of 2-200 square centimeters. Initial observations during the activation and calibration phases of the mission show that the HETGS is performing as predicted prior to Chandra launch. The talk presented very preliminary results that illustrate the power of the HETGS for performing detailed studies of a wide range of celestial sources, including plasma diagnostics. This written version gives a brief summary of that talk with examples of preliminary spectra of Capella, the Crab pulsar, SS433 and the SNR E0102-72.

Canizares, C. R.↗

NASA NTRS2000

Discovery of Spatial and Spectral Structure in the X-Ray Emission from the Crab Nebula

The Chandra X-ray Observatory observed the Crab Nebula and Pulsar During orbital calibration. Zeroth-order images with the High-Energy Transmission Grating (HETG) read-out by the Advanced CCD Imaging Spectrometer spectroscopy array (ACIS-S) show a striking richness of X-ray structure, at a resolution comparable to that of the best ground-based visible-light observations. The HETG-ACIS-S images reveal, for the first time, an X-ray knots along the inner ring and (perhaps) along the inward extension of the X-ray jet. Although complicated by instrumental effects and the brightness of the Crab Nebula, the spectrometric analysis shows systematic variations of the X-ray spectrum throughout the Nebula.

Weisskopf, M.↗

NASA NTRS2000

Structure of the X-Ray Emission from the Jet of 3C 273

We present images from four Chandra observations of the quasar 3C 273. The zeroth order images from two grating observations using the AXAF CCD Imaging Spectrometer (ACIS-S) detector are used to examine the structure and spectrum of the jet. The jet has at least four distinct features which are not resolved in previous observations. Using jet feature nomenclature based on HST observations, we find that knot Al is very bright in X-rays. We have measured the X-ray spectrum of this X-ray knot for the first time, obtaining a photon index of 1.36 +/- 0.11 and a flux density of 37 +/- 4 nJy at 1 keV. Combining this measurement with lower frequency data shows that a pure synchrotron model can fit the spectrum of knot Al from 4 GHz to 5 keV (over nine decades in energy) without a change of spectral slope. Knot A2 is also detected and is somewhat blended with knot B1 but synchrotron emission is not likely to explain the X-ray emission due to the spectral turnover observed in the optical-UV band. No other knots are clearly detected but there is an indication of weak emission from the eastern portion of knot H3. near the "head," which is radio-bright. There is diffuse flux which extends from 14 arcsec to 20 arcsec which shows curvature that is comparable to the optical flux found by Bahcall, et al.

Marshall, H. L.↗

NASA NTRS2000

Analysis of the PKS0637-752 X-Ray Jet System

The X-ray jet emitted from the quasar PKS0637-752 is the largest and most luminous detected to date. It extends 10 arcsec west of the nucleus, and is coincident with GHz radio jet emission in this region. If the individual X-ray/optical/radio knots in this jet were detected as isolated objects, they might be classified as BL Lac objects or quasars. We present a detailed analysis of the Chandra observations of this system, including a search for an intra-cluster medium to confine the jet, and limits to X-ray emission from the eastern radio knot and past the bend of the radio jet to the northwest. The projection in the plane of the sky implies that the X-ray jet is an aligned extension of the pc-scale jet, for which VLBI/VSOP observations show super-luminal motion with an apparent velocity of 11c. In this case, the X-ray jet is of order 1 Mpc in length, and explaining the X-ray emission mechanism presents new challenges.

Schwartz, D. A.↗

NASA NTRS1999

The Soft X-Ray Variability and Spectrum of 1H0419-577 from a Long EUVE Observation

The active galaxy associated with the hard X-ray source 1H0419-577 was observed with EUVE (Extreme Ultraviolet Explorer Satellite) for about 25 days to obtain a long, contiguous light curve and an EUV spectrum. An EUV source was detected which was about as bright as the AGN (Active Galactic Nuclei) and was later identified as an AM Her type system. The AGN showed variations as large as a factor of two over 5-10 day time scales and occasionally varied by 20-30% in less than 0.5day. The spectrum is dominated by a continuum that is poorly fit by a simple power law. There are possible emission lines without positive identifications but the lines are likely to be spurious.

Marshall, H. L.↗

NASA NTRS1999

The Soft X-Ray Variability and Spectrum of 1H0419-577 from a Long EUVE Observation

The active galaxy associated with the hard X-ray source 1H0419-577 was observed with Extreme Ultraviolet Explorer Satellite (EUVE) for about 25 days to obtain a long, contiguous light curve and an Extreme Ultraviolet Radiation (EUV) spectrum. An EUV source was detected which was about as bright as the AGN and was later identified as an AM Her type system. The AGN showed variations as large as a factor of two over 5-10 day time scales and occasionally varied by 20-30% in less than 0.5day. The spectrum is dominated by a continuum that is poorly fit by a simple power law. There are possible emission lines without positive identifications but the lines are likely to be spurious.

Marshall, H. L.↗

NASA NTRS1998

ROSAT and ASCA Observations of the Seyfert Galaxy 1H0419-577-577, Identified with LB 1727

We discuss the properties of the Seyfert 1.5 galaxy LB 1727 based upon the analysis of two ASCA observations, a two-month Rosat monitoring campaign, and optical data. The target is identified with the HEAO-A1 source 1H0419-577, so it has been observed by ASCA and ROSAT in order to obtain better X-ray variability and spectra data. Only modest (20%) variability is observed within or between ASCA and BeppoSAX observations in the approximately 2 - 10 keV band. However, the soft X-ray flux increased by a factor of 3 over a period of 2 months, while it was monitored daily by the ROSAT HRI instrument. The hard X-ray continuum can be parameterized as a power-law of slope Gamma approximately 1.5 - 1.6 across 0.7 - 11 keV in the rest-frame. We also report the first detection of an iron K(alpha) line in this source, consistent with emission from neutral material. The X-ray spectrum steepens sharply below 0.7 keV yielding a power-law of slope Gamma approximately 3.2. There is no evidence for absorption by neutral material, intrinsic to the nucleus. If the nucleus is unattenuated, then the break energy between the soft-excess and hard component is 0.7+/-0.08 keV. An ionized absorber may produce some turn-up in the spectrum at low energies, but a steepening of the underlying continuum is also required to explain the simultaneous ASCA and HRI data. We cannot rule out the possibility that a significant column of ionized material exists in the line-of-sight, if that is true, then the continuum break-energy can only be constrained to lie within the approximately 0.1 - 0.7 keV band.

Turner, T. J.↗

NASA NTRS1998

ROSAT and ASCA Observations of the Seyfert Galaxy 1H0419-577, Identified with LB 1727

We discuss the properties of the Seyfert 1.5 galaxy LB 1727 based upon the analysis of two ASCA observations, a two-month Rosat monitoring campaign, and optical data. The target is identified with the HEAO-A1 source 1H0419-577, so it has been observed by ASCA and ROSAT in order to obtain better X-ray variability and spectra data. Only modest (20%) variability is observed within or between ASCA and BeppoSAX observations in the approximately 2 - 10 keV band. However, the soft X-ray flux increased by a factor of 3 over a period of 2 months, while it was monitored daily by the ROSAT HRI instrument. The hard X-ray continuum can be parameterized as a power-law of slope Gamma approximately 1.5 - 1.6 across 9.7 - 11 keV in the rest-frame. We also report the first detection of an iron K(alpha) line in this source, consistent with emission from neutral material. The X-ray spectrum steepens sharply below 0.7 keV yielding a power-law of slope Gamma approximately 3.2. There is no evidence for absorption by neutral material, instrinsic to the nucleus. If the nucleus is unattenuated, then the break energy between the soft-excess and hard component is 0.7+/-0.08 keV. An ionized absorber may produce some tum-up in the spectrum at low energies, but a steepening of the underlying continuum is also required to explain the simultaneous ASCA and HRI data. We cannot rule out the possibility that a significant column of ionized material exists in the line-of-sight, if that is true, then the continuum break-energy can only be constrained to lie within the approximately 0.1 - -0.7 keV band.

Turner, T. J.↗

NASA NTRS1995

Active galaxies observed during the Extreme Ultraviolet Explorer all-sky survey

We present observations of active galactic nuclei (AGNs) obtained with the Extreme Ultraviolet Explorer (EUVE) during the all-sky survey. A total of 13 sources were detected at a significance of 2.5 sigma or better: seven Seyfert galaxies, five BL Lac objects, and one quasar. The fraction of BL Lac objects is higher in our sample than in hard X-ray surveys but is consistent with the soft X-ray Einstein Slew Survey, indicating that the main reason for the large number of BL Lac objects in the extreme ulktraviolet (EUV) and soft X-ray bands is their steeper X-ray spectra. We show that the number of AGNs observed in both the EUVE and ROSAT Wide Field Camera surveys can readily be explained by modelling the EUV spectra with a simple power law in the case of BL Lac objects and with an additional EUV excess in the case of Seyferts and quasars. Allowing for cold matter absorption in Seyfert galaxy hosts drive up the inferred average continuum slope to 2.0 +/- 0.5 (at 90% confidence), compared to a slope of 1.0 usually found from soft X-ray data. If Seyfert galaxies without EUV excesses form a significant fraction of the population, then the average spectrum of those with bumps should be even steeper. We place a conservative limit on neutral gas in BL Lac objects: N(sub H) less than 10(exp 20)/sq cm.

Marshall, H. L.↗

NASA NTRS1993

Observations of PKS 2155-304 with the Extreme Ultraviolet Explorer

We present a high-accuracy light curve for the BL Lac object PKS 2155-304, observed with the Extreme Ultraviolet Explorer. The light curve shows variations of about 10 percent over a 1.3 d observing period. The observed EUV flux is a factor of 1.7 fainter than when PKS 2155-304 was observed by the ROSAT Wide Field Camera (WFC) during the EUV survey. The optical flux during our observations is about a factor of 2 fainter than during the WFC observations, so we conclude that the overall spectral shape is invariant as the flux varies. These observations support the model in which the spectrum from the optical to the X-ray band is given by a synchrotron spectrum. Extrapolating an X-ray power-law spectrum with an energy index of 1.66 into the EUV only slightly overpredicts the observed EUV count rates so that changing any one of several spectral parameters within the uncertainties gives an acceptable model.

Marshall, H. L.↗

NASA NTRS1984

1300 + 361 A,B is not a gravitational lens

Spectroscopic observations toward 1300 + 361 B obtained at 320-940 nm using a double spectrograph with CCD detectors on the 5-m Hale telescope (resolution about 7 A at 470-940 nm and 10-12 A at 320-470 nm on April 4-5, 1984, are reported. Two objects with magnitude 20 and spectral characteristics resembling those of an interacting pair of metal-poor H II regions at redshift 0.107 are observed, separated by about 10.6 arcsec and with a velocity difference of less than 80 km/s. It is considered unlikely that these objects form a gravitational-lens system. The ratio of the dereddened flux of the 5007-A forbidden line of O III to that of H-beta is found to be 5.03 for 1300 + 361 A and 3.67 for 1300 + 361 B; the difference is attributed to the presence of star-forming regions in the interacting system.

Halpern, J. P.↗

NASA NTRS1984

A complete sample of quasars at B = 19.80

A quasar candidate spectroscopic UV-excess survey with B less than 19.80 has yielded 35 quasars in the 1.75 sq deg region studied. The X-ray data for the 35 quasars are used to show that quasars with B lower than 19.80 and z lower than 2.2 constitute 24 + 10, -8 percent of the observed X-ray background at 2 keV. This sample is combined with one containing 22 quasars with B values lower than 18.25, and it is noted that fits of evolution and luminosity functions are substantially similar to previous results, although the confidence limits for the model parameters are reduced by a factor of 2. Pure luminosity evolution models are found to produce very good fits to the observed N(less than B) data, and are used to estimate the overall contribution of quasars to the X-ray background.

Marshall, H. L.↗

NASA NTRS1983

Analysis of complete quasar samples to obtain parameters of luminosity and evolution functions

A parametric likelihood analysis of the joint redshift-luminosity distribution is presented for a composite, complete sample of 32 quasars with B between 17.0 and 19.2 selected on the basis of ultraviolet excess. Best estimates and joint confidence regions are determined for the parameters of several models of the quasar optical luminosity and evolution function. These models are also tested explicitly for their acceptability. A steeper luminosity function is found than was found for previous samples. A model invoking pure density evolution is rejected on the basis of its extrapolation to fainter magnitudes through comparisons with the optical number counts and independently with the observed 2 keV X-ray background. Assuming an average value for L(x)/L(opt), the contribution of quasars to the X-ray background at 2 keV is discussed.

Marshall, H. L.↗

NASA NTRS1983

Optical and X-ray observations of faint quasars in an optically selected sample

The confirmation of six quasars from spectrographic observations made in 1981 using the Multiple Mirror Telescope, and the characterization of 10 quasars from 1980 Einstein-Observatory X-ray observations (using both imaging proportional counter and high-resolution imager), are reported. The candidates had been selected by Formiggini et al. (1980) in a 1.72-sq-deg region centered on 13h 6 deg, on the basis of ultraviolet excess and a limiting B magnitude of 19.20. A total sample of 10 UV-excess quasars of this magnitude has now been confirmed, for an integral surface density of 5.8 + or - 1.8 per sq deg. Confirmation of three objects from another sample with B less than 18.25 as quasars yielded a surface density of 0./59 + or - 0.13 per sq deg at that magnitude. Data from the complete samples were used to compute the number-flux relation, found to be described by a power law with a 2.25 index for quasars with B between 17.0 and 19.2. From the X-ray observations it was determined that quasars with z less than 2.2 and B less than 19.20 contribute about 15 percent to the cosmic 2-keV background.

Marshall, H. L.↗

NASA NTRS1980

Time-resolved imaging and spectral studies of an X-ray burst from the globular cluster Terzan

The first image of an X-ray burst was recorded with the HRI detector at the Einstein Observatory while observing the globular cluster Terzan 2. The burst was coincident with a persistent X-ray source located near the center of the cluster (thus confirming an earlier suggested identification) and reached a peak luminosity exceeding 5 x 10 to the 38th (d/10 kpc) squared. After a rapid rise to peak luminosity, a double-peaked spectral variation was observed over the next approximately 20 s with anticorrelated changes in the apparent emission region radius and temperature derived from blackbody (and modified blackbody) spectral fits. A shell or disk geometry, which undergoes adiabatic expansion and contraction, may be implied for the burst emission region. Alternatively, Comptonization is required. It is also shown that the peak burst luminosity must exceed the Eddington limit.

Grindlay, J. E.↗