66 research outputs found
Observations of Diffuse EUV Emission with the Cosmic Hot Interstellar Plasma Spectrometer (CHIPS)
The Cosmic Hot Interstellar Plasma Spectrometer (CHIPS) was designed to study
diffuse emission from hot gas in the local interstellar cavity in the
wavelength range 90 - 265 A. Between launch in January 2003 and early 2004, the
instrument was operated in narrow-slit mode, achieving a peak spectral
resolution of about 1.4 A FWHM. Observations were carried out preferentially at
high galactic latitudes; weighted by observing time, the mean absolute value of
the galactic latitude for all narrow-slit observations combined is about 45
degrees. The total integration time is about 13.2 Msec (74% day, 26% night). In
the context of a standard collisional ionization equilibrium plasma model, the
CHIPS data set tight constraints on the emission measure at temperatures
between 10^{5.55} K and 10^{6.4} K. At 10^{6.0} K, the 95% upper limit on the
emission measure is about 0.0004 cm^{-6} pc for solar abundance plasma with
foreground neutral hydrogen column of 2 x 10^{18} cm^{-2}. This constraint,
derived primarily from limits on the extreme ultraviolet emission lines of
highly ionized iron, is well below the range for the local hot bubble estimated
previously from soft X-ray studies. To support the emission measures inferred
previously from X-ray data would require depletions much higher than the
moderate values reported previously for hot gas.Comment: 13 pages, 4 figures, 1 tabl
A New Measurement of the Average FUV Extinction Curve
We have measured the extinction curve in the far-ultraviolet wavelength
region of (900 -- 1200 A) using spectra obtained with the Berkeley EUV/FUV
spectrometer during the ORFEUS-I and the ORFEUS-II missions in 1993 and 1996.
From the complete sample of early-type stars observed during these missions,
we have selected pairs of stars with the same spectral type but different
reddenings to measure the differential FUV extinction. We model the effects of
molecular hydrogen absorption and exclude affected regions of the spectrum to
determine the extinction from dust alone. We minimize errors from inaccuracies
in the cataloged spectral types of the stars by making our own determinations
of spectral types based on their IUE spectra. We find substantial scatter in
the curves of individual star pairs and present a detailed examination of the
uncertainties and their effects on each extinction curve. We find that, given
the potentially large uncertainties inherent in using the pair method at FUV
wavelengths, a careful analysis of measurement uncertainties is critical to
assessing the true dust extinction. We present a new measurement of the average
far-ultraviolet extinction curve to the Lyman limit; our new measurement is
consistent with an extrapolation of the standard extinction curve of Savage &
Mathis (1979).Comment: 13 pages text, 7 figures 4 tables. Sent as gzipped tar, with ms.tex
and 7 figure
A Search for EUV Emission from Comets with the Cosmic Hot Interstellar Plasma Spectrometer (CHIPS)
We have obtained EUV spectra between 90 and 255 \AA of the cometsC/2002 T7
(LINEAR), C/2001 Q4 (NEAT), and C/2004 Q2 (Machholz) near their perihelion
passages in 2004 with the Cosmic Hot Interstellar Plasma Spectrometer (CHIPS).
We obtained contemporaneous data on Comet NEAT Q4 with the X-ray
Observatory ACIS instrument, marking the first simultaneous EUV and X-ray
spectral observations of a comet. The total CHIPS/EUV observing times were 337
ks for Q4, 234 ks for T7, and 483 ks for Machholz and for both CHIPS and
we calculate we have captured all the comet flux in the instrument
field of view. We set upper limits on solar wind charge exchange emission lines
of O, C, N, Ne and Fe occurring in the spectral bandpass of CHIPS. The spectrum
of Q4 obtained with can be reproduced by modeling emission lines of
C, N O, Mg, Fe, Si, S, and Ne solar wind ions. The measured X-ray emission line
intensities are consistent with our predictions from a solar wind charge
exchange model. The model predictions for the EUV emission line intensities are
determined from the intensity ratios of the cascading X-ray and EUV photons
arising in the charge exchange processes. They are compatible with the measured
limits on the intensities of the EUV lines. For comet Q4, we measured a total
X-ray flux of 3.7 ergs cm s, and derive from
model predictions a total EUV flux of 1.5 erg cm
s. The CHIPS observations occurred predominantly while the satellite was
on the dayside of Earth. For much of the observing time, CHIPS performed
observations at smaller solar angles than it was designed for and EUV emission
from the Sun scattered into the instrument limited the sensitivity of the EUV
measurements.Comment: 28 pages total, 4 tables, 7 figures. Accepted by The Astrophysical
Journa
Spectral Observations of Diffuse Far-Ultraviolet Emission from the Hot Phase of the Interstellar Medium with the Diffuse Ultraviolet Experiment
One of the keys to interpreting the character and evolution of interstellar
matter in the galaxy is understanding the distribution of the low density hot
(10^5 K -10^6 K) phase of the interstellar medium (ISM). This phase is much
more difficult to observe than the cooler high density components of the ISM
because of its low density and lack of easily observable tracers. Because gas
of this temperature emits mainly in the far ultraviolet (912 angstrom - 1800
angstroms) and extreme ultraviolet (80 angstrom - 912 angstrom), and (for gas
hotter than 10^6 K) X-rays, observations in these bands can provide important
constraints to the distribution of this gas. Because of interstellar opacity at
EUV wavelengths, only FUV and X-ray observations can provide clues to the
properties of hot gas from distant regions. We present results from a search
for FUV emission from the diffuse ISM conducted with an orbital FUV
spectrometer, DUVE, which was launched in July, 1992. The DUVE spectrometer,
which covers the band from 950 angstrom to 1080 angstrom with 3.2 angstrom
resolution, observed a region of low neutral hydrogen column density near the
south galactic pole for a total effective integration time of 1583 seconds. The
only emission line detected was a geocoronal hydrogen line at 1025 angstrom. We
are able to place upper limits to several expected emission features that
provide constraints on interstellar plasma parameters. We are also able to
place limits on the continuum emission throughout the bandpass. We compare
these limits and other diffuse observations with several models of the
structure of the interstellar medium and discuss the ramifications.Comment: 23 pages, LaTeX, 10 eps figures, uses aaspp4.sty and Psfig/TeX
Release 1.2, Minor editorial change
Detection of Pulsed X-ray Emission from XMM-Newton Observations of PSR J0538+2817
We report on the XMM-Newton observations of the 143 ms pulsar PSR J0538+2817.
We present evidence for the first detections of pulsed X-rays from the source
at a frequency which is consistent with the predicted radio frequency. The
pulse profile is broad and asymmetric, with a pulse fraction of 18 +/- 3%. We
find that the spectrum of the source is well-fit with a blackbody with
T^{infty} = (2.12^{+0.04}_{-0.03}) x 10^6 K and N_{H} = 2.5 x 10^21 cm^{-2}.
The radius determined from the model fit of 1.68 +/- 0.05 km suggests that the
emission is from a heated polar cap. A fit to the spectrum with an atmospheric
model reduces the inferred temperature and hence increases the radius of the
emitting region, however the pulsar distance determined from the fit is then
smaller than the dispersion distance.Comment: 24 pages, 6 figures, 3 tables, accepted for publication in ApJ. Error
in radius calculation corrected, discussion and conclusions remain unchange
LOTIS Upper Limits and the Prompt OT from GRB 990123
GRB 990123 established the existence of prompt optical emission from
gamma-ray bursts (GRBs). The Livermore Optical Transient Imaging System (LOTIS)
has been conducting a fully automated search for this kind of simultaneous low
energy emission from GRBs since October 1996. Although LOTIS has obtained
simultaneous, or near simultaneous, coverage of the error boxes obtained with
BATSE, IPN, XTE, and BeppoSAX for several GRBs, image analysis resulted in only
upper limits. The unique gamma-ray properties of GRB 990123, such as very large
fluence (top 0.4%) and hard spectrum, complicate comparisons with more typical
bursts. We scale and compare gamma-ray properties, and in some cases afterglow
properties, from the best LOTIS events to those of GRB 990123 in an attempt to
determine whether the prompt optical emission of this event is representative
of all GRBs. Furthermore, using LOTIS upper limits in conjunction with the
relativistic blast wave model, we weakly constrain the GRB and afterglow
parameters such as density of the circumburster medium and bulk Lorentz factor
of the ejecta.Comment: 5 pages, 2 figures, To appear in Proceedings of the 5th Huntsville
Gamma-Ray Burst Symposiu
XMM-Newton Observations of PSR B1706-44
We report on the XMM-Newton observations of the young, 102 ms pulsar PSR
B1706-44. We have found that both a blackbody plus power-law and a magnetized
atmospheric model plus power-law provide an excellent fit to the EPIC spectra.
The two scenarios are therefore indistinguishable on a statistical basis,
although we are inclined to prefer the latter on physical grounds. In this
case, assuming a source distance of ~2.3 kpc, the size of the region
responsible for the thermal emission is R~13 km, compatible with the surface of
a neutron star. A comparison of the surface temperature of PSR B1706-44
obtained from this fit with cooling curves favor a medium mass neutron star
with M~1.45 solar masses or M~1.59 solar masses, depending on two different
models of proton superfluidity in the interior. The large collecting area of
XMM-Newton allows us to resolve a substructure in the broad soft X-ray
modulation detected by Chandra, revealing the presence of two separate peaks
with pulsed fractions of 7 +/- 4% and 15 +/- 3%, respectively.Comment: 21 pages, 5 figures, 2 tables, accepted for publication in Ap
X-ray and optical properties of X-ray sources in the 13hr XMM-Newton/Chandra deep survey
The 13hr XMM-Newton/Chandra deep survey is the first of two extremely deep
XMM-Newton fields observed by the XMM-OM consortium. A 120 ks Chandra mosaic,
covering 0.2 square degrees, provides sensitive, confusion-free point source
detection with sub-arcsecond positions, while the 200 ks XMM-Newton observation
provides high quality X-ray spectroscopy over the same sky area. We have
optical spectroscopic identifications for 70 X-ray sources. Of these, 42 are
broad emission-line AGN with a wide range of redshifts. The optical
counterparts of a further 23 sources are narrow emission line galaxies and
absorption line galaxies. These 23 sources all lie at z < 1 and typically have
lower X-ray luminosities than the broad-line AGN. About half of them show
significant X-ray absorption and are almost certainly intrinsically absorbed
AGN. However some of them have unabsorbed, AGN-like, power-law components in
their X-ray spectra, but do not show broad emission lines in their optical
spectra. These sources may be weak, unobscured AGN in bright galaxies and their
existence at low redshifts could be a consequence of the strong cosmological
evolution of AGN characteristic luminosities.Comment: Proceedings of the "X-ray surveys, in the light of the new
observatories" workshop, Astronomische Nachrichten, in press (4 pages, 4
figures
Radio observations of the XMM-Newton/Chandra 13hr deep survey field
Our VLA observations of the XMM-Newton/Chandra 13hr deep survey field (see
Page et al., this proceedings) result in one of the two deepest 1.4GHz radio
maps ever made. Within the 15' radius field covered by the deep X-ray data
(0.19 sq deg), a total of 556 radio sources are detected, down to a 4 sigma
flux limit of 28uJy. Of the 214 Chandra sources, 55 have radio counterparts.
The sub-arcsecond accuracy of the VLA and Chandra positions enable us to
determine with high confidence the sources common to both surveys. Here we
present the relationship between the X-ray and radio source populations at the
faintest radio flux limits yet probed by such a study. We discuss how the
X-ray/radio relationship differs as a function of optical morphology, ie
between unresolved `stellar' objects and well resolved galaxies. We then
discuss the origin of the X-ray and radio emission, ie AGN, starburst or a
mixture of both, in these two classes of object.Comment: Astronomische Nachrichten, in press (Feb 2003). Proceedings of "X-ray
Surveys, in the Light of New Observatories", 4-6 September, Santander, Spai
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