399 research outputs found
PKS 0537-286, carrying the information of the environment of SMBHs in the early Universe
We present the results of a multifrequency campaign on the high-redshift (z =
3.1) blazar PKS 0537-286. The source was observed at different epochs from 2006
to 2008 with INTEGRAL and Swift, and nearly simultaneously with ground-based
near-IR/optical telescopes. The SEDs are compatible with a model based on
synchrotron radiation and external inverse Compton scattering. The campaign
gives an insight into the physical environment of the blazar.Comment: 8 pages, 5 figures, accepted for publication in A&
XMM-Newton and INTEGRAL observations of the black hole candidate XTE J1817-330
The galactic black hole candidate XTE J1817-330 was discovered in outburst by
RXTE in January 2006. We present here the results of an XMM-Newton Target of
opportunity observation (TOO), performed on 13 March 2006 (44 days after the
maximum), and an INTEGRAL observation performed on 15-18 February 2006 (18 days
after the maximum). The EPIC-pn camera on-board XMM-Newton was used in the fast
read-out Burst mode to avoid photon pile-up, while the RGSs were used in
Spectroscopy high count-rate mode. We fit both the XMM-Newton and the INTEGRAL
spectra with a two-component model consisting of a thermal accretion disk and a
comptonizing hot corona. The soft X-ray spectrum is dominated by an accretion
disk component, with a maximum temperature decreasing from 0.96+/-0.04 keV at
the time of the INTEGRAL observation to 0.70+/-m0.01 keV on 13 March. The
Optical Monitors on board INTEGRAL and XMM-Newton showed the source with
magnitudes V: 11.3-11.4, U:15.0-15.1 and UVW1:14.7-14.8. The soft X-ray
spectrum, together with the optical and UV data, show a low hydrogen column
density towards the source, and several absorption lines, most likely of
interstellar origin, are detected in the RGS spectrum: OI K-alpha, OI K-beta,
OII, OIII and OVII, which trace both cold and hot components of the ISM. The
soft X-ray spectrum indicates the presence of a black hole, with an estimate
for the upper limit of the mass of 6.0(+4.0/-2.5) Msun.Comment: Accepted for publication in A&
INTEGRAL observations of the blazar Mrk 421 in outburst (Results of a multi-wavelength campaign)
We report the results of a multi-wavelength campaign on the blazar Mrk 421
during outburst. We observed four strong flares at X-ray energies that were not
seen at other wavelengths (partially because of missing data). From the fastest
rise in the X-rays, an upper limit could be derived on the extension of the
emission region. A time lag between high-energy and low-energy X-rays was
observed, which allowed an estimation of the magnetic-field strength. The
spectral analysis of the X-rays revealed a slight spectral hardening of the
low-energy (3 - 43 keV) spectral index. The hardness-ratio analysis of the
Swift-XRT (0.2 - 10 keV) data indicated a small correlation with the intensity;
i. e., a hard-to-soft evolution was observed. At the energies of IBIS/ISGRI (20
- 150 keV), such correlations are less obvious. A multiwavelength spectrum was
composed and the X-ray and bolometric luminosities are calculated.Comment: 15 pages, 18 figures; accepted by Astronomy & Astrophysic
Multifrequency Observations of the Blazar 3C 279 in January 2006
We report first results of a multifrequency campaign from radio to hard X-ray
energies of the prominent gamma-ray blazar 3C 279, which was organised around
an INTEGRAL ToO observation in January 2006, and triggered on its optical
state. The variable blazar was observed at an intermediate optical state, and a
well-covered multifrequency spectrum from radio to hard X-ray energies could be
derived. The SED shows the typical two-hump shape, the signature of non-thermal
synchrotron and inverse-Compton (IC) emission from a relativistic jet. By the
significant exposure times of INTEGRAL and Chandra, the IC spectrum (0.3 - 100
keV) was most accurately measured, showing - for the first time - a possible
bending. A comparison of this 2006 SED to the one observed in 2003, also
centered on an INTEGRAL observation, during an optical low-state, reveals the
surprising fact that - despite a significant change at the high-energy
synchrotron emission (near-IR/optical/UV) - the rest of the SED remains
unchanged. In particular, the low-energy IC emission (X- and hard X-ray
energies) remains the same as in 2003, proving that the two emission components
do not vary simultaneously, and provides strong constraints on the modelling of
the overall emission of 3C 279.Comment: 4 pages, 6 figures; to be published in the Proc. of the 6th INTEGRAL
workshop "The Obscured Universe" (Moscow, July 2-8, 2006), eds. S. Grebenev,
R. Sunyaev, C. Winkler, ESA SP 622 (2006
Draft genome sequence of Lactobacillus crispatus EM-LC1, an isolate with antimicrobial activity cultured from an elderly subject
Here we report the 1.86-Mb draft genome sequence of Lactobacillus crispatus EM-LC1, a fecal isolate with antimicrobial activity. This genome sequence is expected to provide insights into the antimicrobial activity of L. crispatus and improve our knowledge of its potential probiotic traits
Riboflavin Biosynthesis and Overproduction by a Derivative of the Human Gut Commensal Bifidobacterium longum subsp. infantis ATCC 15697
Riboflavin or vitamin B2 is the precursor of the essential coenzymes flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD). Despite increased interest in microbial synthesis of this water-soluble vitamin, the metabolic pathway for riboflavin biosynthesis has been characterized in just a handful of bacteria. Here, comparative genome analysis identified the genes involved in the de novo biosynthetic pathway of riboflavin in certain bifidobacterial species, including the human gut commensal Bifidobacterium longum subsp. infantis (B. infantis) ATCC 15697. Using comparative genomics and phylogenomic analysis, we investigated the evolutionary acquisition route of the riboflavin biosynthesis or rib gene cluster in Bifidobacterium and the distribution of riboflavin biosynthesis-associated genes across the genus. Using B. infantis ATCC 15697 as model organism for this pathway, we isolated spontaneous riboflavin overproducers, which had lost transcriptional regulation of the genes required for riboflavin biosynthesis. Among them, one mutant was shown to allow riboflavin release into the medium to a concentration of 60.8 ng mL–1. This mutant increased vitamin B2 concentration in a fecal fermentation system, thus providing promising data for application of this isolate as a functional food ingredient
BL Lacertae objects beyond redshift 1.3 - UV-to-NIR photometry and photometric redshift for Fermi/LAT blazars
Observations of the gamma-ray sky with Fermi led to significant advances
towards understanding blazars, the most extreme class of Active Galactic
Nuclei. A large fraction of the population detected by Fermi is formed by BL
Lacertae (BL Lac) objects, whose sample has always suffered from a severe
redshift incompleteness due to the quasi-featureless optical spectra. Our goal
is to provide a significant increase of the number of confirmed high-redshift
BL Lac objects contained in the 2 LAC Fermi/LAT catalog. For 103 Fermi/LAT
blazars, photometric redshifts using spectral energy distribution fitting have
been obtained. The photometry includes 13 broad-band filters from the far
ultraviolet to the near-IR observed with Swift/UVOT and the multi-channel
imager GROND at the MPG/ESO 2.2m telescope. Data have been taken
quasi-simultaneously and the remaining source-intrinsic variability has been
corrected for. We release the UV-to-near-IR 13-band photometry for all 103
sources and provide redshift constraints for 75 sources without previously
known redshift. Out of those, eight have reliable photometric redshifts at
z>1.3, while for the other 67 sources we provide upper limits. Six of the
former eight are BL Lac objects, which quadruples the sample of confirmed
high-redshift BL Lac. This includes three sources with redshifts higher than
the previous record for BL Lac, including CRATES J0402-2615 with the best-fit
solution at z~1.9.Comment: Uploaded correct Fig 4. Changed counterpart name for 2FGLJ0537.7-5716
from PKS 0541-834 (different source) to SUMSS J053748-57182
INTEGRAL and Multiwavelength Observations of the Blazar Mrk 421 during an Active Phase
A ToO observation of the TeV-emitting blazar Mrk 421 with INTEGRAL was
triggered in June 2006 by an increase of the RXTE count rate to more than 30
mCrab. The source was then observed with all INTEGRAL instruments with the
exception of the spectrometer SPI for a total exposure of 829 ks. During this
time several outbursts were observed by IBIS and JEM-X. Multiwavelength
observations were immediately triggered and the source was observed at radio,
optical and X-ray wavelengths up to TeV energies. The data obtained during
these observations are analysed with respect to spectral evolution and
correlated variability. Preliminary results of the analysis are presented in
this poster.Comment: 2 pages, 3 figures; to appear in the Proc. of the First Int. GLAST
Symp. (Stanford, Feb. 5-8, 2007), eds. S.Ritz, P.F.Michelson, and C.Meegan,
AIP Conf. Pro
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