197 research outputs found
Further Observations of the Intermediate Mass Black Hole Candidate ESO 243-49 HLX-1
The brightest Ultra-Luminous X-ray source HLX-1 in the galaxy ESO 243-49
currently provides strong evidence for the existence of intermediate mass black
holes. Here we present the latest multi-wavelength results on this intriguing
source in X-ray, UV and radio bands. We have refined the X-ray position to
sub-arcsecond accuracy. We also report the detection of UV emission that could
indicate ongoing star formation in the region around HLX-1. The lack of
detectable radio emission at the X-ray position strengthens the argument
against a background AGN.Comment: 4 pages, 2 figures. Accepted 11th of Feb 2010. Contributed talk to
appear in Proceedings of "X-ray Astronomy 2009: Present Status,
Multi-Wavelength Approach and Future Perspectives", Bologna, Italy, September
7-11, 2009, AIP, eds. A. Comastri, M. Cappi, and L. Angelin
Optical variability of the accretion disk around the intermediate mass black hole ESO 243-49 HLX-1 during the 2012 outburst
We present dedicated quasi-simultaneous X-ray (Swift) and optical (Very Large
Telescope (VLT), V- and R-band) observations of the intermediate mass black
hole candidate ESO 243-49 HLX-1 before and during the 2012 outburst. We show
that the V-band magnitudes vary with time, thus proving that a portion of the
observed emission originates in the accretion disk. Using the first quiescent
optical observations of HLX-1, we show that the stellar population surrounding
HLX-1 is fainter than V~25.1 and R~24.2. We show that the optical emission may
increase before the X-ray emission consistent with the scenario proposed by
Lasota et al. (2011) in which the regular outbursts could be related to the
passage at periastron of a star circling the intermediate mass black hole in an
eccentric orbit, which triggers mass transfer into a quasi-permanent accretion
disk around the black hole. Further, if there is indeed a delay in the X-ray
emission we estimate the mass-transfer delivery radius to be ~1e11 cm.Comment: 9 pages, 2 figures, accepted for publication in ApJ
A dwarf nova in the globular cluster M13
Dwarf novae in globular clusters seem to be rare with only 13 detections in
the 157 known Galactic globular clusters. We report the identification of a new
dwarf nova in M13, the 14th dwarf nova identified in a globular cluster to
date. Using the 2m Faulkes Telescope North, we conducted a search for stars in
M13 that show variability over a year (2005-2006) on timescales of days and
months. This led to the detection of one dwarf nova showing several outbursts.
A Chandra X-ray source is coincident with this dwarf nova and shows both a
spectrum and variability consistent with that expected from a dwarf nova, thus
supporting the identification. We searched for a counterpart in Hubble Space
Telescope ACS/WFC archived images and found at least 11 candidates, of which we
could characterize only the 7 brightest, including one with a 3 sigma H-alpha
excess and a faint blue star. The detection of one dwarf nova when more could
have been expected likely indicates that our knowledge of the global Galactic
population of cataclysmic variables is too limited. The proportion of dwarf
novae may be lower than found in catalogs, or they may have a much smaller duty
cycle in general as proposed by some population synthesis models and recent
observations in the field.Comment: Accepted for publication in ApJ, 12 pages, 12 figures, 5 tables (v2
contains corrections of the proofs
Spectroscopic Follow-up of X-ray Sources in the ChaMPlane Survey: Identification of a New Cataclysmic Variable
We present a multi-object optical spectroscopy follow-up study of X-ray
sources in a field along the Galactic Plane (l=327.42 deg, b=2.26 deg) which is
part of the Chandra Multi-wavelength Plane survey (ChaMPlane). We obtained
spectra for 46 stars, including 15 likely counterparts to X-ray sources, and
sources showing an H-alpha color excess. This has led to the identification of
a new cataclysmic variable (CV), CXOPS J154305.5-522709, also named ChaMPlane
Bright Source 7 (CBS~7), and we identified 8 X-ray sources in the field as
active late-type stars. CBS~7 was previously studied in X-rays and showed a
hard spectrum and two periods: 1.22+/-0.08 h and 2.43+/-0.26 h. We present here
clear evidence that the source is a CV through the detection of H, HeI and HeII
emission lines in its optical spectrum. The hard X-ray spectrum and the
presence of the HeII 4686 in emission with a large equivalent width suggest a
magnetic CV. The near-infrared counterpart is significantly variable, and we
found a period consistent with the longest X-ray period at 2.39+/-0.05 h but
not the shortest X-ray period. If this period is the orbital period, this would
place the system in the CV period gap. The possible orbital period suggests a
dM4+/-1 companion star. The distance is then estimated to be ~1 kpc. The system
could be a relatively hard and X-ray luminous polar or an intermediate polar,
possibly nearly-synchronous.Comment: accepted for publication in ApJ; 6 figures, 5 tables, 8 pages with
emulateapj styl
Investigating slim disk solutions for HLX-1 in ESO 243-49
The hyper luminous X-ray source HLX-1 in the galaxy ESO 243-49, currently the
best intermediate mass black hole candidate, displays spectral transitions
similar to those observed in Galactic black hole binaries, but with a
luminosity 100-1000 times higher. We investigated the X-ray properties of this
unique source fitting multi-epoch data collected by Swift, XMM-Newton & Chandra
with a disk model computing spectra for a wide range of sub- and
super-Eddington accretion rates assuming a non-spinning black hole and a
face-on disk (i = 0 deg). Under these assumptions we find that the black hole
in HLX-1 is in the intermediate mass range (~2 x 10^4 M_odot) and the accretion
flow is in the sub-Eddington regime. The disk radiation efficiency is eta =
0.11 +/-0.03. We also show that the source does follow the L_X ~ T^4 relation
for our mass estimate. At the outburst peaks, the source radiates near the
Eddington limit. The accretion rate then stays constant around 4 x 10^(-4)
M_odot yr^(-1) for several days and then decreases exponentially. Such
"plateaus" in the accretion rate could be evidence that enhanced mass transfer
rate is the driving outburst mechanism in HLX-1. We also report on the new
outburst observed in August 2011 by the Swift-X-ray Telescope. The time of this
new outburst further strengthens the ~1 year recurrence timescale.Comment: 24 pages, 10 figures, accepted for publication in Ap
Discovery of a red supergiant counterpart to RX J004722.4-252051, a ULX in NGC 253
We present two epochs of near-infrared spectroscopy of the candidate red supergiant counterpart to RX J004722.4â252051, a ULX in NGC 253. We measure radial velocities of the object and its approximate spectral type by cross-correlating our spectra with those of known red supergiants. Our VLT/X-shooter spectrum is best matched by that of early M-type supergiants, confirming the red supergiant nature of the candidate counterpart. The radial velocity of the spectrum, taken on 2014 August 23, is 417 ± 4 kmâsâ1. This is consistent with the radial velocity measured in our spectrum taken with Magellan/MMIRS on 2013 June 28, of 410 ± 70 kmâsâ1, although the large error on the latter implies that a radial velocity shift expected for a black hole of tens of Mâ can easily be hidden. Using nebular emission lines we find that the radial velocity due to the rotation of NGC 253 is 351 ± 4 kmâsâ1 at the position of the ULX. Thus the radial velocity of the counterpart confirms that the source is located in NGC 253, but also shows an offset with respect to the local bulk motion of the galaxy of 66 ± 6 kmâsâ1. We argue that the most likely origin for this displacement lies either in a SN kick, requiring a system containing a âł 50 Mâ black hole, and/or in orbital radial velocity variations in the ULX binary system, requiring a âł 100 Mâ black hole. We therefore conclude that RX J004722.4â252051 is a strong candidate for a ULX containing a massive stellar black hole
Data model issues in the Cherenkov Telescope Array project
The planned Cherenkov Telescope Array (CTA), a future ground-based
Very-High-Energy (VHE) gamma-ray observatory, will be the largest project of
its kind. It aims to provide an order of magnitude increase in sensitivity
compared to currently operating VHE experiments and open access to guest
observers. These features, together with the thirty years lifetime planned for
the installation, impose severe constraints on the data model currently being
developed for the project.
In this contribution we analyze the challenges faced by the CTA data model
development and present the requirements imposed to face them. While the full
data model is still not completed we show the organization of the work, status
of the design, and an overview of the prototyping efforts carried out so far.
We also show examples of specific aspects of the data model currently under
development.Comment: In Proceedings of the 34th International Cosmic Ray Conference
(ICRC2015), The Hague, The Netherlands. All CTA contributions at
arXiv:1508.0589
HI study of the environment around ESO 243-49, the host galaxy of an intermediate mass black hole
The lenticular galaxy ESO 243-49 hosts the ultraluminous X-ray source HLX-1,
the best candidate intermediate mass black hole (IMBH) currently known. The
environments of IMBHs remain unknown, however the proposed candidates include
the nuclei of dwarf galaxies or globular clusters. Evidence at optical
wavelengths points at HLX-1 being the remnant of an accreted dwarf galaxy. Here
we report the Australia Telescope Compact Array radio observations of HI
emission in and around ESO 243-49 searching for signatures of a recent merger
event. No HI line emission is detected in ESO 243-49 with a 5 upper
limit on the HI gas mass of a few . A likely reason for this
non-detection is the cluster environment depleting ESO 243-49's HI gas
reservoir. The upper limit is consistent with an interpretation of HLX-1 as a
dwarf satellite of ESO 243-49, however more sensitive observations are required
for a detection. We detect ~ of HI gas in the peculiar
spiral galaxy AM 0108-462, located at a projected distance of ~170 kpc from ESO
243-49. This amount of HI gas is ~10 times less than in spiral galaxies with
similar optical and near-infrared properties in the field, strengthening the
conclusion that the cluster environment indeed depletes the HI gas reservoir of
these two galaxies. Here we also report observations of AM 0108-462 in several
optical and near-infrared bands using the Magellan 6.5 m telescopes, and
archival X-ray and ultraviolet observations with XMM-Newton and Swift. These
data combined with the HI line data suggest it is likely that AM 0108-462 is
experiencing a merger event.Comment: 12 pages, 9 figures, accepted for publication in MNRA
- âŠ