17 research outputs found
Wide-Band X-Ray Spectra and Images of the Starburst Galaxy M82
The ASCA results of the starburst galaxy M82 are presented. The X-rays in the
0.5--10 keV band exhibit a thin thermal spectrum with emission lines from
highly ionized magnesium, silicon, and sulfur, as well as a hard tail extending
to higher than 10keV energy. The soft X-rays are spatially extended, while the
hard X-rays show an unresolved point-like structure with possible a long-term
flux variability. The flux ratio of the emission lines and the spatially
extended structure in the low-energy band indicate that at least
two-temperature thin thermal plasmas are present. The abundances of the oxygen,
neon, magnesium, silicon, sulfur, and iron in the thin thermal plasmas are
found to be significantly lower than the cosmic value. Neither type-Ia nor
type-II supernova explosions can reproduce the observed abundance ratio. The
origin of the unresolved hard X-rays is uncertain, but is probably an obscured
low-luminosity AGN.Comment: 25 pages, 8 figure
X-Ray Transients in the Advanced LIGO/Virgo Horizon
Advanced LIGO and Advanced Virgo will be all-sky monitors for merging compact objects within a few hundred megaparsecs. Finding the electromagnetic counterparts to these events will require an understanding of the transient sky at low redshift (z < 0.1). We performed a systematic search for extragalactic, low redshift, transient events in the XMM-Newton Slew Survey. In a flux limited sample, we found that highly variable objects comprised 10% of the sample, and that of these, 10% were spatially coincident with cataloged optical galaxies. This led to 4 Ă 10â4 transients per square degree above a flux threshold of 3 Ă 10^(â12) erg cm^â2 s^â1 (0.2â2 keV) which might be confused with LIGO/Virgo counterparts. This represents the first extragalactic measurement of the soft X-ray transient rate within the Advanced LIGO/Virgo horizon. Our search revealed six objects that were spatially coincident with previously cataloged galaxies, lacked evidence for optical active galactic nuclei, displayed high luminosities ~10^(43) erg s^â1, and varied in flux by more than a factor of 10 when compared with the ROSAT All-Sky Survey. At least four of these displayed properties consistent with previously observed tidal disruption events
Revealing the High Energy Emission from the Obscured Seyfert Galaxy MCG -5-23-16 with Suzaku
We report on a 100 ks Suzaku observation of the bright, nearby (z=0.008486)
Seyfert 1.9 galaxy MCG -5-23-16. The broad-band (0.4-100 keV) X-ray spectrum
allows us to determine the nature of the high energy emission with little
ambiguity. The X-ray continuum consists of a cutoff power-law of photon index
, absorbed through Compton-thin matter of column density cm. A soft excess is observed below 1 keV and is
likely a combination of emission from scattered continuum photons and distant
photoionized gas. The iron K line profile is complex, showing narrow neutral
iron K and K emission, as well as a broad line which can be
modeled by a moderately inclined accretion disk. The line profile shows either
the disk is truncated at a few tens of gravitational radii, or the disk
emissivity profile is relatively flat. A strong Compton reflection component is
detected above 10 keV, which is best modeled by a combination of reflection off
distant matter and the accretion disk. The reflection component does not appear
to vary. The overall picture is that this Seyfert 1.9 galaxy is viewed at
moderate (50 degrees) inclination through Compton-thin matter at the edge of a
Compton-thick torus covering steradians, consistent with unified models.Comment: 14 pages, inc 9 figures. Accepted for publication in PASJ (Suzaku
Special Issue
A search for AGN in the most extreme UV-selected starbursts using the European VLBI Network
We have used the European VLBI Network (EVN) to observe a sample of Lyman
Break Analogs (LBAs), nearby (z < 0.3) galaxies with properties similar to the
more distant Lyman Break Galaxies (LBGs). The study of LBGs may help define the
feed-back relationship between black holes (BHs) and their host galaxies.
Previous VLA observations have shown that the kpc-scale radio emission from
LBAs is dominated by starbursts. The main targets of this VLBI experiment were
selected because they possessed emission-line properties between starbursts and
Type 2 (obscured) AGN. Eight targets (three star-forming LBAs, four composite
LBAs, and one Type 1 AGN) were observed at 5 GHz, four of which were also
observed at 1.7 GHz. One star-forming LBA and one composite LBA were detected
above 5 \sigma at 1.7 GHz (only), while the AGN was detected at 5 GHz. In both
LBAs, the radio luminosity (LR) exceeds that expected from supernovae
(remnants) based on a comparison with Arp220, Arp229A and Mrk273, by factors of
2 - 8. The composite LBA exhibits a compact core emitting around 10% of the VLA
flux density. The high Tb of 3.5E7 K and excess core L_R with respect to the
L_R/L_X relation of radio-quiet AGN indicate that this LBA possesses an
obscured AGN (MBH ~ E5-E7 M_sun). While weak AGN may co-exist with the
starbursts as shown in at least one of the LBAs, their contribution to the
total radio flux is fairly minimal. Our results show that the detection of such
weak AGN presents a challenge at radio, X-ray and optical emission-line
wavelengths at z ~ 0.2, indicating the great difficulties that need to be
overcome in order to study similar processes at high redshift when these types
of galaxies were common.Comment: 10 pages, 4 figures, accepted for publication in MNRA
Local Lyman Break Galaxy Analogs: The Impact of Massive Star-forming Clumps on the Interstellar Medium and the Global Structure of Young, Forming Galaxies
We present HST UV/optical imaging, Spitzer mid-IR photometry, and optical
spectroscopy of a sample of 30 low-redshift (z=0.1-0.3) galaxies chosen from
SDSS/GALEX to be accurate local analogs of the high-z Lyman Break Galaxies. The
Lyman Break Analogs (LBAs) are similar in mass, metallicity, dust, SFR, size
and gas velocity dispersion, thus enabling a detailed investigation of
processes that are important at high-z. The optical emission line properties of
LBAs are also similar to those of LBGs, indicating comparable conditions in
their ISM. In the UV, LBAs are characterized by complexes of massive
star-forming "clumps", while in the optical they most often show evidence for
(post-)mergers/interactions. In 6 cases, we find an extremely massive (>10^9
Msun) compact (R~100 pc) dominant central object (DCO). The DCOs are
preferentially found in LBAs with the highest mid-IR luminosities and
correspondingly high SFRs (15-100 Msun/yr). We show that the massive SF clumps
(including the DCOs) have masses much larger than the nuclear super star
clusters seen in normal late type galaxies. However, the DCOs have masses,
sizes, and densities similar to the excess-light/central-cusps seen in typical
elliptical galaxies with masses similar to the LBA galaxies. We suggest that
the DCOs form in present-day examples of the dissipative mergers at high
redshift that are believed to have produced the central-cusps in local
ellipticals. More generally, the properties of the LBAs are consistent with the
idea that instabilities in a gas-rich disk lead to very massive star-forming
clumps that eventually coalesce to form a spheroid. We speculate that the DCOs
are too young at present to be growing a supermassive black hole because they
are still in a supernova-dominated outflow phase.Comment: The Astrophysical Journal, In Press (22 pages, 16 figures). For the
full version with high-resolution colour figures, see:
http://www.mpa-garching.mpg.de/~overzier/Overzier_LBApaper09.pd
The Athena X-ray Integral Field Unit: a consolidated design for the system requirement review of the preliminary definition phase
The Athena X-ray Integral Unit (X-IFU) is the high resolution X-ray
spectrometer, studied since 2015 for flying in the mid-30s on the Athena space
X-ray Observatory, a versatile observatory designed to address the Hot and
Energetic Universe science theme, selected in November 2013 by the Survey
Science Committee. Based on a large format array of Transition Edge Sensors
(TES), it aims to provide spatially resolved X-ray spectroscopy, with a
spectral resolution of 2.5 eV (up to 7 keV) over an hexagonal field of view of
5 arc minutes (equivalent diameter). The X-IFU entered its System Requirement
Review (SRR) in June 2022, at about the same time when ESA called for an
overall X-IFU redesign (including the X-IFU cryostat and the cooling chain),
due to an unanticipated cost overrun of Athena. In this paper, after
illustrating the breakthrough capabilities of the X-IFU, we describe the
instrument as presented at its SRR, browsing through all the subsystems and
associated requirements. We then show the instrument budgets, with a particular
emphasis on the anticipated budgets of some of its key performance parameters.
Finally we briefly discuss on the ongoing key technology demonstration
activities, the calibration and the activities foreseen in the X-IFU Instrument
Science Center, and touch on communication and outreach activities, the
consortium organisation, and finally on the life cycle assessment of X-IFU
aiming at minimising the environmental footprint, associated with the
development of the instrument. Thanks to the studies conducted so far on X-IFU,
it is expected that along the design-to-cost exercise requested by ESA, the
X-IFU will maintain flagship capabilities in spatially resolved high resolution
X-ray spectroscopy, enabling most of the original X-IFU related scientific
objectives of the Athena mission to be retained. (abridged).Comment: 48 pages, 29 figures, Accepted for publication in Experimental
Astronomy with minor editin
The Athena X-ray Integral Field Unit: a consolidated design for the system requirement review of the preliminary definition phase
The Athena X-ray Integral Unit (X-IFU) is the high resolution X-ray spectrometer studied since 2015 for flying in the mid-30s on the Athena space X-ray Observatory. Athena is a versatile observatory designed to address the Hot and Energetic Universe science theme, as selected in November 2013 by the Survey Science Committee. Based on a large format array of Transition Edge Sensors (TES), X-IFU aims to provide spatially resolved X-ray spectroscopy, with a spectral resolution of 2.5 eV (up to 7 keV) over a hexagonal field of view of 5 arc minutes (equivalent diameter). The X-IFU entered its System Requirement Review (SRR) in June 2022, at about the same time when ESA called for an overall X-IFU redesign (including the X-IFU cryostat and the cooling chain), due to an unanticipated cost overrun of Athena. In this paper, after illustrating the breakthrough capabilities of the X-IFU, we describe the instrument as presented at its SRR (i.e. in the course of its preliminary definition phase, so-called B1), browsing through all the subsystems and associated requirements. We then show the instrument budgets, with a particular emphasis on the anticipated budgets of some of its key performance parameters, such as the instrument efficiency, spectral resolution, energy scale knowledge, count rate capability, non X-ray background and target of opportunity efficiency. Finally, we briefly discuss the ongoing key technology demonstration activities, the calibration and the activities foreseen in the X-IFU Instrument Science Center, touch on communication and outreach activities, the consortium organisation and the life cycle assessment of X-IFU aiming at minimising the environmental footprint, associated with the development of the instrument. Thanks to the studies conducted so far on X-IFU, it is expected that along the design-to-cost exercise requested by ESA, the X-IFU will maintain flagship capabilities in spatially resolved high resolution X-ray spectroscopy, enabling most of the original X-IFU related scientific objectives of the Athena mission to be retained. The X-IFU will be provided by an international consortium led by France, The Netherlands and Italy, with ESA member state contributions from Belgium, Czech Republic, Finland, Germany, Poland, Spain, Switzerland, with additional contributions from the United States and Japan.The French contribution to X-IFU is funded by CNES, CNRS and CEA. This work has been also supported by ASI (Italian Space Agency) through the Contract 2019-27-HH.0, and by the ESA (European Space Agency) Core Technology Program (CTP) Contract No. 4000114932/15/NL/BW and the AREMBES - ESA CTP No.4000116655/16/NL/BW. This publication is part of grant RTI2018-096686-B-C21 funded by MCIN/AEI/10.13039/501100011033 and by âERDF A way of making Europeâ. This publication is part of grant RTI2018-096686-B-C21 and PID2020-115325GB-C31 funded by MCIN/AEI/10.13039/501100011033