21 research outputs found
Tomography of X-ray Nova Muscae 1991: Evidence for ongoing mass transfer and stream-disc overflow
We present a spectroscopic analysis of the black hole binary Nova Muscae 1991
in quiescence using data obtained in 2009 with MagE on the Magellan Clay
telescope and in 2010 with IMACS on the Magellan Baade telescope at the Las
Campanas Observatory. Emission from the disc is observed in H alpha, H beta and
Ca II (8662 A). A prominent hotspot is observed in the Doppler maps of all
three emission lines. The existence of this spot establishes ongoing mass
transfer from the donor star in 2009-2010 and, given its absence in the
1993-1995 observations, demonstrates the presence of a variable hotspot in the
system. We find the radial distance to the hotspot from the black hole to be
consistent with the circularization radius. Our tomograms are suggestive of
stream-disc overflow in the system. We also detect possible Ca II (8662 A)
absorption from the donor star.Comment: 10 pages, 11 figures, 1 table. Accepted for publication in MNRA
The Complete Local Volume Groups Sample - I. Sample Selection and X-ray Properties of the High-Richness Subsample
We present the Complete Local-Volume Groups Sample (CLoGS), a statistically
complete optically-selected sample of 53 groups within 80 Mpc. Our goal is to
combine X-ray, radio and optical data to investigate the relationship between
member galaxies, their active nuclei, and the hot intra-group medium (IGM). We
describe sample selection, define a 26-group high-richness subsample of groups
containing at least 4 optically bright (log L_B>=10.2 LBsol) galaxies, and
report the results of XMM-Newton and Chandra observations of these systems. We
find that 14 of the 26 groups are X-ray bright, possessing a group-scale IGM
extending at least 65kpc and with luminosity >10^41 erg/s, while a further 3
groups host smaller galaxy-scale gas halos. The X-ray bright groups have masses
in the range M_500=0.5-5x10^13 Msol, based on system temperatures of 0.4-1.4
keV, and X-ray luminosities in the range 2-200x10^41 erg/s. We find that
~53-65% of the X-ray bright groups have cool cores, a somewhat lower fraction
than found by previous archival surveys. Approximately 30% of the X-ray bright
groups show evidence of recent dynamical interactions (mergers or sloshing),
and ~35% of their dominant early-type galaxies host AGN with radio jets. We
find no groups with unusually high central entropies, as predicted by some
simulations, and confirm that CLoGS is in principle capable of detecting such
systems. We identify three previously unrecognized groups, and find that they
are either faint (L_X,R500<10^42 erg/s) with no concentrated cool core, or
highly disturbed. This leads us to suggest that ~20% of X-ray bright groups in
the local universe may still be unidentified.Comment: Accepted for publication by MNRAS, 25 Manuscript pages with 6 tables
and 10 figures, plus 30 pages of appendices. v2 corrects minor typographical
errors identified at proof stag
Recurrent radio outbursts at the center of the NGC1407 galaxy group
We present deep Giant Metrewave Radio Telescope (GMRT) radio observations at
240, 330 and 610 MHz of the complex radio source at the center of the NGC1407
galaxy group. Previous GMRT observations at 240 MHz revealed faint, diffuse
emission enclosing the central twin-jet radio galaxy. This has been interpreted
as an indication of two possible radio outbursts occurring at different times.
Both the inner double and diffuse component are detected in the new GMRT images
at high levels of significance. Combining the GMRT observations with archival
Very Large Array data at 1.4 and 4.9 GHz, we derive the total spectrum of both
components. The inner double has a spectral index \alpha=0.7, typical for
active, extended radio galaxies, whereas the spectrum of the large-scale
emission is very steep, with \alpha=1.8 between 240 MHz and 1.4 GHz. The
radiative age of the large-scale component is very long, ~300 Myr, compared to
~30 Myr estimated for the central double, confirming that the diffuse component
was generated during a former cycle of activity of the central galaxy. The
current activity have so far released an energy which is nearly one order of
magnitude lower than that associated with the former outburst. The group X-ray
emission in the Chandra and XMM-Newton images and extended radio emission show
a similar swept-back morphology. We speculate that the two structures are both
affected by the motion of the group core, perhaps due to the core sloshing in
response to a recent encounter with the nearby elliptical galaxy NGC1400.Comment: 15 pages, 12 figures and 5 tables. Accepted for publication in Ap
A deep Chandra observation of the poor cluster AWM4 - II. The role of the radio jets in enriching the intra-cluster medium
We use a Chandra observation of the poor cluster AWM4 to map the temperature
and abundance of the intra-cluster medium, so as to examine the influence of
the central radio galaxy on its environment. While the cluster core is
generally enriched to near-solar abundances, we find evidence of super-solar
abundances correlated with the radio jets, extending ~35 kpc from the core of
the central dominant galaxy NGC 6051 along its minor axis. We conclude that the
enriched gas has been transported out of the central galaxy through the action
of the radio source. We estimate the excess mass of iron in the entrained gas
to be ~1.4x10^6 Msol, and find that this can be produced in the core of NGC
6051 within the timescale of the AGN outburst. The energy required to transport
this gas to its current location is ~4.5x10^57 erg, a significant fraction of
the estimated total mechanical energy output of the AGN, though this estimate
is dependent on the degree of enrichment of the uplifted gas. The larger
near-solar abundance region is also compatible with enrichment by metals mixed
outward from NGC 6051 over a much longer timescale.Comment: Accepted for publication in MNRAS, 11 pages, 6 figure
A combined low-radio frequency/X-ray study of galaxy groups I. Giant Metrewave Radio Telescope observations at 235 MHz and 610 MHz
We present new Giant Metrewave Radio Telescope observations at 235 MHz and
610 MHz of 18 X-ray bright galaxy groups. These observations are part of an
extended project, presented here and in future papers, which combines
low-frequency radio and X-ray data to investigate the interaction between
central active galactic nuclei (AGN) and the intra-group medium (IGM). The
radio images show a very diverse population of group-central radio sources,
varying widely in size, power, morphology and spectral index. Comparison of the
radio images with Chandra and XMM-Newton X-ray images shows that groups with
significant substructure in the X-ray band and marginal radio emission at >= 1
GHz host low-frequency radio structures that correlate with substructures in
IGM. Radio-filled X-ray cavities, the most evident form of AGN/IGM interaction
in our sample, are found in half of the systems, and are typically associated
with small, low- or mid-power double radio sources. Two systems, NGC5044 and
NGC4636, possess multiple cavities, which are isotropically distributed around
the group center, possibly due to group weather. In other systems the
radio/X-ray correlations are less evident. However, the AGN/IGM interaction can
manifest itself through the effects of the high-pressure medium on the
morphology, spectral properties and evolution of the radio-emitting plasma. In
particular, the IGM can confine fading radio lobes in old/dying radio galaxies
and prevent them from dissipating quickly. Evidence for radio emission produced
by former outbursts that coexist with current activity is found in six groups
of the sample.Comment: Accepted for publication in the Astrophysical Journal Supplement
Series, 26 pages, 18 figures. A version with high-quality figures is
http://www.astro.umd.edu/~simona/giacintucci_hr.pd