268 research outputs found
Blazar surveys with WMAP and Swift
We present the preliminary results from two new surveys of blazars that have
direct implications on the GLAST detection of extragalactic sources from two
different perspectives: microwave selection and a combined deep X-ray/radio
selection. The first one is a 41 GHz flux-limited sample extracted from the
WMAP 3-yr catalog of microwave point sources. This is a statistically well
defined sample of about 200 blazars and radio galaxies, most of which are
expected to be detected by GLAST. The second one is a new deep survey of
Blazars selected among the radio sources that are spatially coincident with
serendipitous sources detected in deep X-ray images (0.3-10 keV) centered on
the Gamma Ray Bursts (GRB) discovered by the Swift satellite. This sample is
particularly interesting from a statistical viewpoint since a) it is unbiased
as GRBs explode at random positions in the sky, b) it is very deep in the X-ray
band (\fx \simgt \ergs) with a position accuracy of a few
arc-seconds, c) it will cover a fairly large (20-30 square deg.) area of sky,
d) it includes all blazars with radio flux (1.4 GHz) larger than 10 mJy, making
it approximately two orders of magnitude deeper than the WMAP sample and about
one order of magnitude deeper than the deepest existing complete samples of
radio selected blazars, and e) it can be used to estimate the amount of
unresolved GLAST high latitude gamma-ray background and its anisotropy
spectrum.Comment: 3 pages, 3 figures, to appear in Proc. of the 1st GLAST Symposium,
Feb 5-8, 2007, Stanford, AIP, Eds. S. Ritz, P. F. Michelson, and C. Meega
Browsing the sky through the ASI Science Data Centre Data Explorer Tool
We present here the Data Explorer tool developed at the ASI Science Data
Center (ASDC). This tool is designed to provide an efficient and user-friendly
way to display information residing in several catalogs stored in the ASDC
servers, to cross-correlate this information and to download/analyze data via
our scientific tools and/or external services. Our database includes GRB
catalogs (such as Swift and Beppo-SAX), which can be queried through the Data
Explorer. The GRB fields can be viewed in multiwavelength and the data can be
analyzed or retrieved.Comment: 3 pages, 2 .ps figures, to appear in "Deciphering the Ancient
Universe with GRBs" conference proceeding
Timing accuracy of the Swift X-Ray Telescope in WT mode
The X-Ray Telescope (XRT) on board Swift was mainly designed to provide
detailed position, timing and spectroscopic information on Gamma-Ray Burst
(GRB) afterglows. During the mission lifetime the fraction of observing time
allocated to other types of source has been steadily increased. In this paper,
we report on the results of the in-flight calibration of the timing
capabilities of the XRT in Windowed Timing read-out mode. We use observations
of the Crab pulsar to evaluate the accuracy of the pulse period determination
by comparing the values obtained by the XRT timing analysis with the values
derived from radio monitoring. We also check the absolute time reconstruction
measuring the phase position of the main peak in the Crab profile and comparing
it both with the value reported in literature and with the result that we
obtain from a simultaneous Rossi X-Ray Timing Explorer (RXTE) observation. We
find that the accuracy in period determination for the Crab pulsar is of the
order of a few picoseconds for the observation with the largest data time span.
The absolute time reconstruction, measured using the position of the Crab main
peak, shows that the main peak anticipates the phase of the position reported
in literature for RXTE by ~270 microseconds on average (~150 microseconds when
data are reduced with the attitude file corrected with the UVOT data). The
analysis of the simultaneous Swift-XRT and RXTE Proportional Counter Array
(PCA) observations confirms that the XRT Crab profile leads the PCA profile by
~200 microseconds. The analysis of XRT Photodiode mode data and BAT event data
shows a main peak position in good agreement with the RXTE, suggesting the
discrepancy observed in XRT data in Windowed Timing mode is likely due to a
systematic offset in the time assignment for this XRT read out mode.Comment: 6 pages, 4 figures. Accepted for publication on
Astronomy&Astrophysic
Testing the gamma-ray burst variability/peak luminosity correlation on a Swift homogeneous sample
We test the gamma-ray burst correlation between temporal variability and peak
luminosity of the -ray profile on a homogeneous sample of 36 Swift/BAT
GRBs with firm redshift determination. This is the first time that this
correlation can be tested on a homogeneous data sample. The correlation is
confirmed, as long as the 6 GRBs with low luminosity (<5x10^{50} erg s^{-1} in
the rest-frame 100-1000 keV energy band) are ignored. We confirm that the
considerable scatter of the correlation already known is not due to the
combination of data from different instruments with different energy bands, but
it is intrinsic to the correlation itself. Thanks to the unprecedented
sensitivity of Swift/BAT, the variability/peak luminosity correlation is tested
on low-luminosity GRBs. Our results show that these GRBs are definite outliers.Comment: Accepted for Publication in MNRAS. 10 pages, 5 figures, 3 table
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
A BeppoSAX observation of MKN6
We have used the BeppoSAX satellite to study the broad band (0.5-100 keV)
X-ray spectrum of the Seyfert 1.5 galaxy MKN6. The source is characterized by a
power law of Gamma=1.7 [+0.08, -0.07] and there is no strong evidence for
either a reflection bump or a high energy cut-off. We have detected a narrow
iron line at 6.4 keV (rest frame) with an equivalent width of 98 [+33, -35] eV.
MKN6 also exhibits strong and complex absorption. At least two components (NH_1
=1.34 [+0.4,-0.4] x 10^(22) cm^(-2) and NH_2 = 4.18 [+2.2, -1.3] x 10^(22)
cm^(-2)) are present and they both partially cover the source with covering
fractions of ~90% and ~50% respectively. Comparison with a previous ASCA
observation indicates that in both absorbing columns the NH is variable over a
2 year timescale, while the covering fractions are constant over the same
amount of time. The state of each absorber is cold or mildly photoionized. The
Broad Line Region (BLR) is suggested as the possible location for this complex
absorption.Comment: 5 pages, 5 figures, to be published in A&
The 26 year-long X-ray light curve and the X-ray spectrum of the BL Lac Object 1E 1207.9+3945 in its brightest state
We studied the temporal and spectral evolution of the synchrotron emission
from the high energy peaked BL Lac object 1E 1207.9+3945. Two recent
observations have been performed by the XMM-Newton and Swift satellites; we
carried out X-ray spectral analysis for both of them, and photometry in
optical-ultraviolet filters for the Swift one. Combining the results thus
obtained with archival data we built the long-term X-ray light curve, spanning
a time interval of 26 years, and the Spectral Energy Distribution (SED) of this
source. The light curve shows a large flux increasing, about a factor of six,
in a time interval of a few years. After reaching its maximum in coincidence
with the XMM-Newton pointing in December 2000 the flux decreased in later
years, as revealed by Swift. The very good statistics available in the 0.5-10
keV XMM-Newton X-ray spectrum points out a highly significant deviation from a
single power law. A log-parabolic model with a best fit curvature parameter of
0.25 and a peak energy at ~1 keV describes well the spectral shape of the
synchrotron emission. The simultaneous fit of Swift UVOT and XRT data provides
a milder curvature (b~0.1) and a peak at higher energies (~15 keV), suggesting
a different state of source activity. In both cases UVOT data support the
scenario of a single synchrotron emission component extending from the
optical/UV to the X-ray band. New X-ray observations are important to monitor
the temporal and spectral evolution of the source; new generation gamma-ray
telescopes like AGILE and GLAST could for the first time detect its inverse
Compton emission.Comment: 7 pages, 6 figures, accepted for publication in A&
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