390 research outputs found
X-ray Pulsars in the Small Magellanic Cloud
XMM-Newton archival data for the Small Magellanic Cloud have been examined
for the presence of previously undetected X-ray pulsars. One such pulsar, with
a period of 202 s, is detected. Its position is consistent with an early B star
in the SMC and we identify it as a high mass X-ray binary (HMXB). In the course
of this study we determined the pulse period of the possible AXP CXOU
J010043.1-721134 to be 8.0 s, correcting an earlier report (Lamb et al 2002b)
of a 5.4 s period for this object. Pulse profiles and spectra for each of these
objects are presented as well as for a recently discovered (Haberl & Pietsch
2004) 263 s X-ray pulsar. Properties of an ensemble of 24 optically identified
HMXB pulsars from the SMC are investigated. The locations of the pulsars and an
additional 22 X-ray pulsars not yet identified as having high mass companions
are located predominately in the young (ages years) star
forming regions of the SMC as expected on the basis of binary evolution models.
We find no significant difference between the distribution of spin periods for
the HMXB pulsars of the SMC compared with that of the Milky Way. For those HMXB
pulsars which have Be companions we note an inverse correlation between spin
period and maximum X-ray flux density. (This anti-correlation has been
previously noted for all X-ray binary pulsars by Stella, White & Rosner 1986).
The anti-correlation for the Be binaries may be a reflection of the fact that
the spin periods and orbital periods of Be HMXBs are correlated. We note a
similar correlation between X-ray luminosity and spin period for the Be HMXB
pulsars of the Milky Way and speculate that exploitation of the correlation
could serve as a distance indicator.Comment: final version accepted in The Astrophysical Journa
Old and Young X-ray Point Source Populations in Nearby Galaxies
We analyzed 1441 Chandra X-ray point sources in 32 nearby galaxies. The total
point-source X-ray luminosity L_XP is well correlated with B, K, and FIR+UV
luminosities of spiral host galaxies, and with the B and K luminosities for
ellipticals. This suggests an intimate connection between L_XP and both the old
and young stellar populations, for which K and FIR+UV luminosities are proxies
for the galaxy mass M and star-formation rate SFR. We derive proportionality
constants 1.3E29 erg/s/Msol and 0.7E39 erg/s/(Msol/yr), which can be used to
estimate the old and young components from M and SFR, respectively. The
cumulative X-ray luminosity functions for the point sources have quite
different slopes for the spirals (gamma ~= 0.5-0.8) and ellipticals (gamma ~=
1.4), implying *the most luminous point sources dominate L_XP* for the spirals.
Most of the point sources have X-ray colors that are consistent with either
LMXBs or Ultraluminous X-ray sources (ULXs a.k.a. IXOs) and we rule out
classical HMXBs (e.g. neutron-star X-ray pulsars) as contributing much to L_XP.
Thus, for spirals, the ULXs dominate L_XP. We estimate that >~20% of all ULXs
found in spirals originate from the older (pop II) stellar populations,
indicating that many of the ULXs that have been found in spiral galaxies are in
fact pop II ULXs, like those in elliptical galaxies. The linear dependence of
L_XP on the SFR argues for either a steepening in the X-ray luminosity function
of the young (pop I) X-ray source population at L_X >~10^(38.5-39) erg/s, or a
decreasing efficiency for producing all types of young X-ray point sources as
the galaxy SFR increases.Comment: 33 pages AASTEX, ApJ accepted. Please download full version with
figures from http://www.pha.jhu.edu/~colbert/chps_accepted.p
Timing and spectral studies of the transient X-ray pulsar EXO 053109-6609.2 with ASCA and Beppo-SAX
We report timing and spectral properties of the transient Be X-ray pulsar EXO
053109--6609.2 studied using observations made with the ASCA and BeppoSAX
observatories. Though there must have been at least one spin-down episode of
the pulsar since its discovery, the new pulse period measurements show a
monotonic spin-up trend since 1996. The pulse profile is found to have marginal
energy dependence. There is also evidence for strong luminosity dependence of
the pulse profile, a single peaked profile at low luminosity that changes to a
double peaked profile at high luminosity. This suggests a change in the
accretion pattern at certain luminosity level. The X-ray spectrum is found to
consist of a simple power-law with photon index in the range of 0.4--0.8. At
high intensity level the spectrum also shows presence of weak iron emission
line.Comment: 12 pages, 8 figures, Accepted for publication in Ap
Discovery of a new pulsating X-ray source with a 1549.1-s period, AX J183220-0840
A new pulsating X-ray source, AX J183220-0840, with a 1549.1-s period was
discovered at R.A.= 18h32m20s and Dec.=-8d40'30'' (J2000,
uncertainty=0.6degree) during an ASCA observation on the Galactic plane. The
source was observed two times, in 1997 and in 1999. A phase-averaged X-ray flux
of 1.1E-11 ergs cm-2 s-1 and pulsation period of 1549.1+/-0.4 s were
consistently obtained from these two observations. The X-ray spectrum was
represented by a flat absorbed power-law with a photon-index of =~0.8 and an
absorption column density of =~1.3E22 cm-2. Also, a signature of iron K-shell
line emission with a centroid of 6.7 keV and an equivalent width of
approximately 450 eV was detected. From the pulsation period and the iron-line
feature, AX J183220-0840 is likely to be a magnetic white dwarf binary with a
complexly absorbed thermal spectrum with a temperature of about 10 keV.Comment: 13 pages, 4 figures, accepted for publication in ApJ Letter
A Study of the Populations of X-ray Sources in the Small Magellanic Cloud with ASCA
The Advanced Satellite for Cosmology and Astrophysics (ASCA) has made
multiple observations of the Small Magellanic Cloud (SMC). X-ray mosaic images
in the soft (0.7--2.0 keV) and hard (2.0--7.0 keV) bands are separately
constructed, and the latter provides the first hard X-ray view of the SMC. We
extract 39 sources from the two-band images with a criterion of S/N>5, and
conduct timing and spectral analyses for all of these sources. Coherent
pulsations are detected from 12 X-ray sources; five of which are new
discoveries. Most of the 12 X-ray pulsars are found to exhibit long-term flux
variabilities, hence they are likely to be X-ray binary pulsars (XBPs). On the
other hand, we classify four supernova remnants (SNRs) as thermal SNRs, because
their spectra exhibit emission lines from highly ionized atoms. We find that
XBPs and thermal SNRs in the SMC can be clearly separated by their hardness
ratio (the ratio of the count rate between the hard and soft bands). Using this
empirical grouping, we find many XBP candidates in the SMC, although no
pulsations have yet been detected from these sources. Possible implications on
the star-formation history and evolution of the SMC are presented by a
comparison of the source populations in the SMC and our Galaxy.Comment: 11 pages, 39 Figures, to be published in ApJ Supplement. Tables (body
and figures also) are available at
http://www-cr.scphys.kyoto-u.ac.jp/member/jun/job
X-ray observations of Be/X-ray binaries in the SMC
(shortened) Fifteen Be/X-ray binaries and candidates in the SMC were observed
serendipitously with the EPIC instruments of XMM-Newton during two observations
of SNR 0047-73.5 and SNR 0103-72.6 in October 2000. A total of twelve of those
sources are detected. For eleven of them an accurate position and in part
detection of X-ray pulsations support the proposed identification as Be/X-ray
binaries. The detection of pulsations (172.2 s, 320.1 s and 751 s) from three
hard X-ray sources with periods known from ASCA observations confirm their
proposed identifications with ROSAT sources and their optical Be star
counterparts. In addition, pulsations with a period of 263.6 s were found from
XMMUJ004723.7-731226=RXJ0047.3-7312. For SAXJ0103.2-7209 a pulse period of
341.20.5 s was determined, continuing the large spin-up seen with ASCA,
BeppoSAX and Chandra between 1996 and 1999 with a period derivative of 1.6 s
yr covering now 4.5 years. The 0.3-10.0 keV EPIC spectra of all eleven
Be/X-ray binaries and candidates are consistent with power-law energy
distributions with derived photon indices strongly peaked at 1.00 with a
standard deviation of 0.16. No pulsations are detected from RXJ0049.2-7311 and
RXJ0049.5-7310 (both near the 9 s pulsar AXJ0049-732) and RXJ0105.1-7211 (near
AXJ0105-722, which may pulsate with 3.3 s), leaving the identification of the
ASCA sources with ROSAT and corresponding XMM-Newton objects still unclear. We
present an updated list of high mass X-ray binaries (HMXBs) and candidates in
the SMC incorporating improved X-ray positions obtained from Chandra and
XMM-Newton observations. Including the results from this work and recent
publications the SMC HMXB catalogue comprises 65 objects with at least 37
showing X-ray pulsations.Comment: 10 pages, 7 figures, accepted for publication in A&
AGN in the XMM-Newton first-light image as probes for the interstellar medium in the LMC
The XMM-Newton first-light image revealed X-ray point sources which show
heavily absorbed power-law spectra. The spectral indices and the probable
identification of a radio counterpart for the brightest source suggest AGN
shining through the interstellar gas of the Large Magellanic Cloud (LMC). The
column densities derived from the X-ray spectra in combination with HI
measurements will allow to draw conclusions on HI to H_2 ratios in the LMC and
compare these with values found for the galactic plane.Comment: 4 pages, LaTex, 4 figures, Accepted for publication in A&A Letter
XMM-Newton observations of the Small Magellanic Cloud: Be/X-ray binary pulsars active between October 2006 and June 2007
(abridged) We analysed eight XMM-Newton observations toward the Small
Magellanic Cloud (SMC), performed between October 2006 and June 2007, to
investigate high mass X-ray binary systems. We found new X-ray binary pulsars
with periods of 202 s (XMMU J005929.0-723703), 342 s (XMMU J005403.8-722632),
645 s (XMMU J005535.2-722906) and 325 s (XMMU J005252.1-721715), in the latter
case confirming the independent discovery in Chandra data. In addition we
detected sixteen known Be/X-ray binary pulsars and six ROSAT-classified
candidate high mass X-ray binaries. From one of the candidates, RX
J0058.2-7231, we discovered X-ray pulsations with a period of 291 s which makes
it the likely counterpart of XTE J0051-727. From the known pulsars, we revise
the pulse period of CXOU J010206.6-714115 to 967 s, and we detected the 18.37 s
pulsar XTE J0055-727 (= XMM J004911.4-724939) in outburst, which allowed us to
localise the source. The pulse profiles of the X-ray pulsars show a large
variety of shapes from smooth to highly structured patterns and differing
energy dependence. For all the candidate high mass X-ray binaries optical
counterparts can be identified with magnitudes and colours consistent with Be
stars. Twenty of the Be/X-ray binaries were detected with X-ray luminosities in
the range 1.5x10^35 erg/s - 5.5x10^36 erg/s. The majority of the spectra is
well represented by an absorbed power-law with an average power-law index of
0.93. The absorption (in addition to the Galactic foreground value) varies over
a wide range between a few 10^20 H cm^-2 and several 10^22 H cm^-2. An overall
correlation of the absorption with the total SMC HI column density suggests
that the absorption seen in the X-ray spectra is often largely caused by
interstellar gas.Comment: Accepted for publication in A&A, 22 pages, 12 figure
Where Are Be/black-hole Binaries?
We apply the tidal truncation model proposed by Negueruela & Okazaki(2001) to
arbitrary Be/compact star binaries to study the truncation efficiency
dependance on the binary parameters. We find that the viscous decretion disks
around the Be stars could be truncated very effectively in narrow systems.
Combining this with the population synthesis results of Podsiadlowski,
Rappaport and Han (2003) that binary black holes are most likely to be born in
systems with orbital periods less than about 30 days, we suggest that most of
the Be/black-hole binaries may be transient systems with very long quiescent
states. This could explain the lack of observed Be/black-hole X-ray binaries.
We also discuss the evolution of the Be/black-hole binaries and their possible
observational features.Comment: 14 pages,3 figures, ApJ accepte
Discovery of a new Transient X-ray Pulsar in the Small Magellanic Cloud
Rossi X-Ray Timing Explorer observations of the Small Magellanic Cloud have
revealed a previously unknown transient X-ray pulsar with a pulse period of
95s. Provisionally designated XTE SMC95, the pulsar was detected in three
Proportional Counter Array observations during an outburst spanning 4 weeks in
March/April 1999. The pulse profile is double peaked reaching a pulse fraction
\~0.8. The source is proposed as a Be/neutron star system on the basis of its
pulsations, transient nature and characteristically hard X-ray spectrum. The
2-10 keV X-ray luminosity implied by our observations is > 2x10^37 erg/s which
is consistent with that of normal outbursts seen in Galactic systems. This
discovery adds to the emerging picture of the SMC as containing an extremely
dense population of transient high mass X-ray binaries.Comment: Accepted by A&A. 7 pages, 6 figure
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