454 research outputs found
IR Monitoring of the Microquasar GRS 1915+105: Detection of Orbital and Superhump Signatures
We present the results of seven years of K-band monitoring of the low-mass
X-ray binary GRS 1915+105. Positive correlations between the infrared flux and
the X-ray flux and X-ray hardness are demonstrated. Analysis of the frequency
spectrum shows that the orbital period of the system is
days. The phase and amplitude of the orbital modulation suggests that the
modulation is due to the heating of the face of the secondary star. We also
report another periodic signature between 31.2 and 31.6 days, most likely due
to a superhump resonance. From the superhump period we then obtain a range on
the mass ratio of the system, .Comment: 16 pages, 6 figures; v2: minor change
M51 ULX-7: superorbital periodicity and constraints on the neutron star magnetic field
In this work, we explore the applicability of standard theoretical models of accretion to the observed properties of M51 ULX-7. The spin-up rate and observed X-ray luminosity are evidence of a neutron star with a surface magnetic field of 2-7 x 10(13) G, rotating near equilibrium. Analysis of the X-ray light curve of the system (Swift/XRT data) reveals the presence of a similar to 39 d superorbital period. We argue that the superorbital periodicity is due to disc precession, and that material is accreted on to the neutron star at a constant rate throughout it. Moreover, by attributing this modulation to the free precession of the neutron star we estimate a surface magnetic field strength of 3-4 x 10(13) G. The agreement of these two independent estimates provide strong constraints on the surface polar magnetic field strength of the NS
Can high-velocity stars reveal black holes in globular clusters?
We estimate the number of individual, fast-moving stars observable in
globular clusters under the assumption that the clusters contain massive
central black holes which follow the galactic black-hole mass vs. sigma
relationship. We find that radial velocity measurements are unlikely to detect
such stars, but that proper motion studies could reveal such stars, if they
exist, in the most likely clusters. Thus, HST proper motion studies can test
this hypothesis in a few nearby clusters.Comment: 10 pages, 1 figure in AASTeX v5.0. Accepted for publication in ApJ
Letter
HST Observations of the Central-Cusp Globular Cluster NGC 6752. The Effect of Binary Stars on the Luminosity Function in the Core
We consider the effect of binary stars on the main-sequence luminosity
functions observed in the core of globular clusters, with specific reference to
NGC 6752. We find that mass segregation results in an increased binary fraction
at fainter magnitudes along the main-sequence. If this effect is not taken into
account when analyzing luminosity functions, erroneous conclusions can be drawn
regarding the distribution of single stars, and the dynamical state of the
cluster. In the core of NGC 6752, our HST data reveal a flat luminosity
function, in agreement with previous results. However, when we correct for the
increasing binary fraction at faint magnitudes, the LF begins to fall
immediately below the turn-off. This effect appears to be confined to the inner
core radius of the cluster.Comment: 10 pages, 3 figures Accepted to ApJ Lett Vol 513 Number
The 2002 Outburst of the Black-Hole X-ray Binary 4U 1543-47: Optical and Infrared Light Curves
We have obtained simultaneous optical and near infrared observations of 4U
1543-47 during its 2002 outburst. The most striking feature of the outburst
light curve is the secondary maximum which appears after the object transitions
into the low-hard state. This secondary maximum is much stronger in the
infrared bands than optical. We suggest that the origin of the secondary
maximum flux may be synchrotron radiation associated with a jet. Close infrared
monitoring may lead to reliable triggers for simultaneous multiwavelength
campaigns to study jet formation processes.Comment: Accepted for publication in Ap
Discovery of a supernova associated with GRB 031203: SMARTS Optical-Infrared Lightcurves from 0.2 to 92 days
Optical and infrared monitoring of the afterglow site of gamma-ray burst
(GRB) 031203 has revealed a brightening source embedded in the host galaxy,
which we attribute to the presence of a supernova (SN) related to the GRB ("SN
031203"). We present details of the discovery and evolution of SN 031203 from
0.2 to 92 days after the GRB, derived from SMARTS consortium photometry in I
and J bands. A template type Ic lightcurve, constructed from SN 1998bw
photometry, is consistent with the peak brightness of SN 031203 although the
lightcurves are not identical. Differential astrometry reveals that the SN, and
hence the GRB, occurred less than 300 h_71^-1 pc (3-sigma) from the apparent
galaxy center. The peak of the supernova is brighter than the optical afterglow
suggesting that this source is intermediate between a strong GRB and a
supernova.Comment: 11 pages, 3 figures, submitted to ApJ Letter
Central Proper-Motion Kinematics of NGC 6752
We present proper motions derived from WFPC2 imaging for stars in the core of
the peculiar globular cluster NGC 6752. The central velocity dispersion in both
components of the proper motion is 12 km/s. We discuss the implications of this
result as well as the intrinsic difficulties in making such measurements. We
also give an alternative correction for the 34-row problem in the WFPC2 CCDs.Comment: 25 pages, 7 figures, 1 table included. Accepted for publication in A
Wind, jet, hybrid corona and hard X-ray flares: multiwavelength evolution of GRO J1655-40 during the 2005 outburst rise
We have investigated the complex multiwavelength evolution of GRO J1655-40
during the rise of its 2005 outburst. We detected two hard X-ray flares, the
first one during the transition from the soft state to the ultra-soft state,
and the second one in the ultra-soft state. The first X-ray flare coincided
with an optically thin radio flare. We also observed a hint of increased radio
emission during the second X-ray flare. To explain the hard flares without
invoking a secondary emission component, we fit the entire data set with the
eqpair model. This single, hybrid Comptonization model sufficiently fits the
data even during the hard X-ray flares if we allow reflection fractions greater
than unity. In this case, the hard X-ray flares correspond to a Comptonizing
corona dominated by non-thermal electrons. The fits also require absorption
features in the soft and ultra-soft state which are likely due to a wind. In
this work we show that the wind and the optically thin radio flare co-exist.
Finally, we have also investigated the radio to optical spectral energy
distribution, tracking the radio spectral evolution through the quenching of
the compact jet and rise of the optically thin flare, and interpreted all data
using state transition models.Comment: 16 pages, 11 figure
Optical-Infrared ANDICAM Observations of the Transient Associated with GRB 030329
We present photometry of the transient associated with GRB 030329 obtained
with the CTIO 1.3--meter telescope and the ANDICAM instrument, a dual
optical/infrared imager with a dichroic centered at one micron. Without the
need for light curve interpolation to produce snapshot broadband spectra, we
show that the transient spectrum remained statistically achromatic from day 2.7
to day 5.6, during a re-brightening episode. Associating the light in these
early epochs with the GRB afterglow, we infer a modest level of extinction due
to the host galaxy in the line--of--sight toward the GRB: A_V(host) = 0.30 +/-
0.03 mag for beta = -0.5 and A_V(host) < 0.4 mag (3 sigma) for any physically
plausible value of beta (with flux f_nu ~ lambda^-beta). We conclude that the
spectral slope of the afterglow component was more than beta = -0.8 between day
2.7-5.6 after the GRB, excluding the possibility that the synchrotron cooling
break passed through the optical/IR bandpass over that period. Taking
extinction into account, a decomposition of the light curve into an afterglow
and supernova component requires the presence of a supernova similar to that of
SN 1998bw, an afterglow that shows some evidence for a second break around day
8-10, and a fifth re-brightening event around day 15. Assuming an SN
1988bw-like evolution and a contemporaneous GRB and SN event, the peak SN
brightness was M_V = -19.8 +/- 0.4 - 5 log h_65 mag.Comment: Published in the Astronomical Journal, January 2004: see
http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004AJ....127..252
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