28 research outputs found
Absorption Features in the X-ray Spectrum of an Ordinary Radio Pulsar
The vast majority of known non-accreting neutron stars (NSs) are
rotation-powered radio and/or gamma-ray pulsars. So far, their multiwavelength
spectra have all been described satisfactorily by thermal and non-thermal
continuum models, with no spectral lines. Spectral features have, however, been
found in a handful of exotic NSs and thought to be a manifestation of their
unique traits. Here we report the detection of absorption features in the X-ray
spectrum of an ordinary rotation-powered radio pulsar, J1740+1000. Our findings
bridge the gap between the spectra of pulsars and other, more exotic, NSs,
suggesting that the features are more common in the NS spectra than they have
been thought so far.Comment: 18 pages, 4 color figures, 1 Tabl
Spectroscopy of the brightest optical counterparts of X-ray sources in the direction of M~31 and M~33
Recent surveys of the Local Group spiral Galaxies M31 and M33 with XMM-Newton
yielded a large number of X-ray sources. As part of the effort to identify and
classify the objects responsible for this X-ray emission, we have obtained
optical spectra of the brightest optical counterparts of the identified X-ray
sources, using the 1.3m Skinakas Telescope. Most of these objects are
foreground star candidates. The purpose of the present study is to confirm this
identification and to explore the compatibility between the optical spectral
classification and the observed X-ray properties of the sources. We have
obtained optical spectra for the 14 brightest optical counterparts of X-ray
sources identified by XMM-Newton in the direction of M31 and for 21 optical
counterparts in the direction of M33, using the 1.3m Skinakas telescope in
Crete, Greece. All of the M31 sources and all but one of the M33 sources were
confirmed to be foreground stars, of spectral types between A and M. One of the
stars is a late M dwarf with H-alpha emission, a flare star, also displaying
strong X-ray variability. One of the M~33 sources (lying within the D25
ellipse) corresponds to a previously known background galaxy, LEDA 5899.Comment: 9 pages, 12 figures, accepted in A&
XMM-Newton Observations of Two Candidate Supernova Remnants
Candidate supernova remnants G23.5+0.1 and G25.5+0.0 were observed by
XMM-Newton in the course of a snap-shot survey of plerionic and composite SNRs
in the Galactic plane. In the field of G23.5+0.1, we detected an extended
source, ~3' in diameter, which we tentatively interpret as a pulsar-wind nebula
(PWN) of the middle-aged radio pulsar B1830-08. Our analysis suggests an
association between PSR B1830-08 and the surrounding diffuse radio emission. If
the radio emission is due to the SNR, then the pulsar must be significantly
younger than its characteristic age. Alternatively, the radio emission may come
from a relic PWN. In the field of G25.5+0.0, which contains the extended TeV
source HESS J1837-069, we detected the recently discovered young high-energy
pulsar J1838-0655 embedded in a PWN with extent of 1.3'. We also detected
another PWN candidate (AX J1837.3-0652) with an extent of 2' and unabsorbed
luminosity L_(2-10 keV) ~ 4 x 10^33 erg/s at d=7 kpc. The third X-ray source,
located within the extent of the HESS J1837-069, has a peculiar extended radio
counterpart, possibly a radio galaxy with a double nucleus or a microquasar. We
did not find any evidence of the SNR emission in the G25.5+0.0 field. We
provide detailed multiwavelength analysis and identifications of other field
sources and discuss robustness of the G25.5+0.0 and G23.5+0.1 classifications
as SNRs. (abstract abridged)Comment: 37 pages, 9 figures, submitted to Ap
X-ray Observations of Parsec-Scale Tails behind Two Middle-Aged Pulsars
Chandra and XMM-Newton resolved extremely long tails behind two middle-aged
pulsars, J1509-5850 and J1740+1000. The tail of PSR J1509-5850 is discernible
up to 5.6' from the pulsar (6.5 pc at a distance of 4 kpc), with a flux of
2*10^{-13} erg s^{-1} cm^{-2} in 0.5-8 keV. The tail spectrum fits an absorbed
power-law (PL) model with the photon index of 2.3\pm0.2, corresponding to the
0.5-8 keV luminosity of 1*10^{33} ergs s^{-1}, for n_H= 2.1*10^{22} cm^{-2}.
The tail of PSR J1740+1000 is firmly detected up to 5' (2 pc at a 1.4 kpc
distance), with a flux of 6*10^{-14} ergs cm^{-2} s^{-1} in 0.4-10 keV. The PL
fit yields photon index of 1.4-1.5 and n_H=1*10^{21} cm^{-2}. The large extent
of the tails suggests that the bulk flow in the tails starts as mildly
relativistic downstream of the termination shock, and then gradually
decelerates. Within the observed extent of the J1509-5850 tail, the average
flow speed exceeds 5,000 km s^{-1}, and the equipartition magnetic field is a
few times 10^{-5} G. For the J1740+1000 tail, the equipartition field is a
factor of a few lower. The harder spectrum of the J1740+1000 tail implies
either less efficient cooling or a harder spectrum of injected electrons. For
the high-latitude PSR J1740+1000, the orientation of the tail on the sky shows
that the pulsar is moving toward the Galactic plane, which means that it was
born from a halo-star progenitor. The comparison between the J1509 and J1740
tails and the X-ray tails of other pulsars shows that the X-ray radiation
efficiency correlates poorly with the pulsar spin-down luminosity or age. The
X-ray efficiencies of the ram-pressure confined pulsar wind nebulae (PWNe) are
systematically higher than those of PWNe around slowly moving pulsars with
similar spin-down parameters.Comment: 14 pages, 16 figures and 5 table
Deep XMM-Newton survey of M33
In an XMM-Newton raster observation of the bright local group spiral galaxy
M33 we study the population of X-ray sources (X-ray binaries, supernova
remnants, super-shells) down to a 0.5-10 keV luminosity of 10^35 erg s^-1 --
more than a factor of 10 deeper than earlier ROSAT observations. EPIC spectra
and hardness ratios are used to distinguish between different source classes.
We confirmed the 3.45 d orbital light curve of the X-ray binary M33 X7,
detected a transient super-soft source in M33, and searched for short term
variability of the brighter sources. We characterize the diffuse X-ray
component that is correlated with the inner disk and spiral arms. We will
compare the results with other nearby galaxies.Comment: Proceedings of the "X-ray surveys, in the light of the new
observatories" workshop, Astronomische Nachrichten, in the press (4 pages, 5
figures, uses an.cls
The spectral energy distribution of PKS 2004-447: a compact steep-spectrum source and possible radio-loud narrow-line Seyfert 1 galaxy
(abridged) The spectral energy distribution (SED) of the compact steep
spectrum (CSS) source and possible radio-loud narrow-line Seyfert 1 galaxy
(NLS1), PKS2004-447, is presented. Five out of six well studied RL NLS1 share
this dual classification (optically defined as a NLS1 with radio definition of
a CSS or giga-hertz peaked spectrum (GPS) source). The SED is created from
simultaneous observations at radio (ATCA), optical/NIR (Siding Spring) and
UV/X-ray (XMM-Newton) wavelengths. The X-ray data show evidence of short-term
variability, a possible soft excess, and negligible absorption. Together with
the rest of the SED, the X-ray emission is excessive in comparison to
synchrotron plus synchrotron self-Compton (SSC) models. The SED can be
described with a two component model consisting of extended synchrotron/SSC
emission with Comptonisation in the X-rays, though SSC models with a very high
electron-to-magnetic energy density ratio cannot be excluded either. The peak
emission in the SED appears to be in the near infrared, which can be attributed
to thermal emission from a dusty torus. Analysis of a non-contemporaneous, low
resolution optical spectrum suggests that the narrow-line region (NLR) is much
more reddened than the X-ray emitting region suggesting that the gas-to-dust
ratio in PKS2004-447 may be very different then in our own Galaxy. Long-term
radio monitoring of PKS2004-447 shows a rather constant light curve over nearly
a six month period with the exception of one outburst when the 6.65GHz flux
increased by ~35% over 19 days. In comparison to general samples of GPS
sources, which appear to be X-ray weak, NLS1-CSS/GPS sources possess stronger
X-ray emission relative to radio, and lower intrinsic absorption than GPS
sources of similar X-ray luminosity.Comment: 10 pages, 8 figures. Accepted for publication in MNRA
The eclipsing massive X-ray binary M33 X-7: New X-ray observations and optical identification
The eclipsing X-ray binary M33 X-7 was in the field of view during several
observations of our XMM-Newton M33 survey and in the archival Chanfdra
observation 1730 which cover a large part of the 3.45 d orbital period. We
detect emission of M33 X-7 during eclipse and a soft X-ray spectrum of the
source out of eclipse that can best be described by bremsstrahlung or disk
blackbody models. No significant regular pulsations of the source in the range
0.25-1000 s were found. The average source luminosity out of eclipse is 5E37
erg/s (0.5-4.5 keV). In a special analysis of DIRECT observations we identify
as optical counterpart a B0I to O7I star of 18.89 mag in V which shows the
ellipsoidal heating light curve of a high mass X-ray binary with the M33 X-7
binary period. The location of the X-ray eclipse and the optical minima allow
us to determine an improved binary period and ephemeris of mid-eclipse as HJD
(2451760.61+-0.09)+- N * (3.45376+-0.00021). The mass of the compact object
derived from orbital parameters and the optical companion mass, the lack of
pulsations, and the X-ray spectrum of M33 X-7 may indicate that the compact
object in the system is a black hole. M33 X-7 would be the first detected
eclipsing high mass black hole X-ray binary.Comment: 9 pages including 6 figures, A&A accepte
XMM-Newton survey of the Local Group galaxy M 33
In an XMM-Newton raster observation of the bright Local Group spiral galaxy M
33 we study the population of X-ray sources (X-ray binaries, supernova
remnants) down to a 0.2--4.5 keV luminosity of 10^35 erg/s -- more than a
factor of 10 deeper than earlier ROSAT observations. EPIC hardness ratios and
optical and radio information are used to distinguish between different source
classes. The survey detects 408 sources in an area of 0.80 square degree. We
correlate these newly detected sources with earlier M 33 X-ray catalogues and
information from optical, infra-red and radio wavelengths. As M 33 sources we
detect 21 supernova remnants (SNR) and 23 SNR candidates, 5 super-soft sources,
and 2 X-ray binaries (XRBs). There are 267 sources classified as hard, which
may either be XRBs or Crab-like SNRs in M 33 or background AGN. The 44
confirmed and candidate SNRs more than double the number of X-ray detected SNRs
in M 33. 16 of these are proposed as SNR candidates from the X-ray data for the
first time. On the other hand, there are several sources not connected to M 33:
five foreground stars, 30 foreground star candidates, 12 active galactic
nucleus candidates, one background galaxy and one background galaxy candidate.
Extrapolating from deep field observations we would expect 175 to 210
background sources in this field. This indicates that about half of the sources
detected are sources within M 33.Comment: 14 pages, 6 figures, accepted for publication in A&A, the images of
Figs. 1,2,3,4,6 are available in jpg format, a full version of the paper is
available at ftp://ftp.xray.mpe.mpg.de/people/fwh/docs/M33_AA0068.p