THE 70 MONTH SWIFT-BAT ALL-SKY HARD X-RAY SURVEY Baumgartner, W. H.; Tueller, J.; Markwardt, C. B. ...
The Astrophysical journal. Supplement series,
08/2013, Letnik:
207, Številka:
2
Journal Article
Recenzirano
Odprti dostop
ABSTRACTWe present the catalog of sources detected in 70 months of observations with the Burst Alert Telescope (BAT) hard X-ray detector on the Swift gamma-ray burst observatory. The Swift-BAT 70 ...month survey has detected 1171 hard X-ray sources (more than twice as many sources as the previous 22 month survey) in the 14-195 keV band down to a significance level of 4.8σ, associated with 1210 counterparts. The 70 month Swift-BAT survey is the most sensitive and uniform hard X-ray all-sky survey and reaches a flux level of 1.03 × 10−11 erg s−1 cm−2 over 50% of the sky and 1.34 × 10−11 erg s−1 cm−2 over 90% of the sky. The majority of new sources in the 70 month survey continue to be active galactic nuclei, with over 700 in the catalog. As part of this new edition of the Swift-BAT catalog, we also make available eight-channel spectra and monthly sampled light curves for each object detected in the survey in the online journal and at the Swift-BAT 70 month Web site.
Aims. Variability at all observed wavelengths is a distinctive property of active galactic nuclei (AGN). Hard X-rays provide us with a view of the innermost regions of AGN, mostly unbiased by ...absorption along the line of sight. Characterizing the intrinsic hard X-ray variability of a large AGN sample and comparing it to the results obtained at lower X-ray energies can significantly contribute to our understanding of the mechanisms underlying the high-energy radiation. Methods. Swift/BAT provides us with the unique opportunity to follow, on time scales of days to years and with regular sampling, the 14–195 keV emission of the largest AGN sample available up to date for this kind of investigation. As a continuation of an early work using the first 9 months of BAT data, we study the amplitude of the variations and their dependence on subclass and on energy, for a sample of 110 radio quiet and radio loud AGN selected from the BAT 58-month survey. Results. About 80% of the AGN in the sample are found to exhibit significant variability on month-to-year time scales. In particular, radio loud sources are the most variable, and Seyfert 1.5−2 galaxies are slightly more variable than Seyfert 1, while absorbed and unabsorbed objects show similar timing properties. The amplitude of the variations and their energy dependence are incompatible with variability being driven at hard X-rays by changes in the absorption column density. In general, the variations in the 14–24 and 35–100 keV bands are correlated well, suggesting a common origin to the variability across the BAT energy band. However, radio quiet AGN display on average 10% larger variations at 14–24 keV than at 35–100 keV, and a softer-when-brighter behavior for most of the Seyfert galaxies with detectable spectral variability on a time scale of a month. In addition, sources with harder spectra are found to be more variable than softer ones, unlike what it is observed below 10 keV. These properties are generally consistent with a variable, in flux and shape, power law continuum, pivoting at energies ≳ 50 keV, to which a constant reflection component is superposed. When the same time scales are considered, the timing properties of AGN at hard X-rays are comparable to those at lower energies, with at least some of the differences possibly ascribable to components contributing differently in the two energy domains (e.g., reflection, absorption).
We present the second Swift Burst Alert Telescope (BAT) catalog of gamma-ray bursts (GRBs), which contains 476 bursts detected by the BAT between 2004 December 19 and 2009 December 21. This catalog ...(hereafter the BAT2 catalog) presents burst trigger time, location, 90% error radius, duration, fluence, peak flux, time-averaged spectral parameters, and time-resolved spectral parameters measured by the BAT. In the correlation study of various observed parameters extracted from the BAT prompt emission data, we distinguish among long-duration GRBs (L-GRBs), short-duration GRBs (S-GRBs), and short-duration GRBs with extended emission (S-GRBs with E.E.) to investigate differences in the prompt emission properties. The fraction of L-GRBs, S-GRBs, and S-GRBs with E.E. in the catalog are 89%, 8%, and 2%, respectively. We compare the BAT prompt emission properties with the BATSE, BeppoSAX, and HETE-2 GRB samples. We also correlate the observed prompt emission properties with the redshifts for the GRBs with known redshift. The BAT T 90 and T 50 durations peak at 70 s and 30 s, respectively. We confirm that the spectra of the BAT S-GRBs are generally harder than those of the L-GRBs. The time-averaged spectra of the BAT S-GRBs with E.E. are similar to those of the L-GRBs. Whereas, the spectra of the initial short spikes of the S-GRBs with E.E. are similar to those of the S-GRBs. We show that the BAT GRB samples are significantly softer than the BATSE bright GRBs and that the time-averaged E obs peak of the BAT GRBs peaks at 80 keV, which is significantly lower energy than those of the BATSE sample, which peak at 320 keV. The time-averaged spectral properties of the BAT GRB sample are similar to those of the HETE-2 GRB samples. By time-resolved spectral analysis, we find that only 10% of the BAT observed photon indices are outside the allowed region of the synchrotron shock model. We see no obvious observed trend in the BAT T 90 and the observed spectra with redshifts. The T 90 and T 50 distributions measured at the 140-220 keV band in the GRB rest frame from the BAT known redshift GRBs peak at 19 s and 8 s, respectively. We also provide an update on the status of the on-orbit BAT calibrations.
Swift BAT Survey of AGNs Tueller, J; Mushotzky, R. F; Barthelmy, S ...
The Astrophysical journal,
07/2008, Letnik:
681, Številka:
1
Journal Article
Recenzirano
We present the results of the analysis of the first 9 months of data of the Swift BAT survey of AGNs in the 14-195 keV band. Using archival X-ray data or follow-up Swift XRT observations, we have ...identified 129 (103 AGNs) of 130 objects detected at image and with significance >4.8 capital sigma . One source remains unidentified. These same X-ray data have allowed measurement of the X-ray properties of the objects. We fit a power law to the image distribution, and find the slope to be image. Characterizing the differential luminosity function data as a broken power law, we find a break luminosity image (erg s super(-1)) = 43.85 +/- 0.26, a low-luminosity power law slope image, and a high-luminosity power law slope image, similar to the values that have been reported based on INTEGRAL data. We obtain a mean photon index 1.98 in the 14-195 keV band, with an rms spread of 0.27. Integration of our luminosity function gives a local volume density of AGNs above image erg simage of image Mpcimage, which is about 10% of the total luminous local galaxy density above image. We have obtained X-ray spectra from the literature and from Swift XRT follow-up observations. These show that the distribution of image is essentially flat from image to image cmimage, with 50% of the objects having column densities of less than image cmimage. BAT Seyfert galaxies have a median redshift of 0.03, a maximum image luminosity of 45.1, and approximately half have image.
We use Swift BAT Earth occultation data at different geomagnetic latitudes to derive a sensitive measurement of the cosmic X-ray background (CXB) and of the Earth albedo emission in the 15-200 keV ...band. We compare our CXB spectrum with recent (INTEGRAL, BeppoSAX) and past results (HEAO-1) and find good agreement. Using an independent measurement of the CXB spectrum we are able to confirm our results. This study shows that the BAT CXB spectrum has a normalization image larger than the HEAO-1 measurement. The BAT accurate Earth albedo spectrum can be used to predict the level of photon background for satellites in low Earth and mid inclination orbits.
Context.
Hard X-ray properties of beamed active galactic nuclei have been published in the 105-month
Swift
/BAT catalog, but there have not been any studies carried out so far on a well-defined, ...radio-selected sample of low-peaked blazars in the hard X-ray band.
Aims.
Using the statistically complete MOJAVE-1 sample, we aim to determine the hard X-ray properties of radio-selected blazars, including the enigmatic group of gamma-ray-faint blazars. Additionally, we aim to determine the contribution of radio-selected low-peaked blazars to the diffuse cosmic X-ray background (CXB).
Methods.
We determined photon indices, fluxes, and luminosities in the range of 20 keV–100 keV of the X-ray spectra of blazars and other extragalactic jets from the MOJAVE-1 sample, derived from the 105-month
Swift
/BAT survey. We calculated log
N
–log
S
distributions and determined the luminosity functions.
Results.
The majority of the MOJAVE-1 blazars are found to be hard X-ray emitters albeit many at low count rates. The log
N
–log
S
distribution for the hard X-ray emission of radio-selected blazars is clearly non-Euclidean, in contrast to the radio flux density distribution. Approximately 0.2% of the CXB in the 20 keV–100 keV band can be resolved into MOJAVE-1 blazars.
Conclusions.
The peculiar log
N
–log
S
distribution disparity might be attributed to different evolutionary paths in the X-ray and radio bands, as tested by luminosity-function modeling. X-ray variability can be ruled out as the dominant contributor. Low-peaked blazars constitute an intrinsically different source population in terms of CXB contribution compared to similar studies of X-ray-selected blazars. The hard X-ray flux and spectral index can serve as a good proxy for the gamma-ray detection probability of individual sources. Future observations combining deep X-ray survey, for example, with eROSITA, and targeted gamma-ray observations with CTA can benefit strongly from the tight connection between these high-energy bands for the different blazar sub-classes.
We use 3 years of data from the Swift/BAT survey to select a complete sample of X-ray blazars above 15 keV. This sample comprises 26 Flat-Spectrum Radio Quasars (FSRQs) and 12 BL Lac objects detected ...over a redshift range of 0.03 < z < 4.0. We use this sample to determine, for the first time in the 15-55 keV band, the evolution of blazars. We find that, contrary to the Seyfert-like AGNs detected by BAT, the population of blazars shows strong positive evolution. This evolution is comparable to the evolution of luminous optical QSOs and luminous X-ray selected AGNs. We also find evidence for an epoch-dependence of the evolution as determined previously for radio-quiet AGNs. We interpret both these findings as a strong link between accretion and jet activity. In our sample, the FSRQs evolve strongly, while our best-fit shows that BL Lacs might not evolve at all. The blazar population accounts for 10-20% (depending on the evolution of the BL Lacs) of the Cosmic X-ray background (CXB) in the 15-55 keV band. We find that FSRQs can explain the entire CXB emission for energies above 500 keV solving the mystery of the generation of the MeV background. The evolution of luminous FSRQs shows a peak in redshift (z{sub c} = 4.3 {+-} 0.5) which is larger than the one observed in QSOs and X-ray selected AGNs. We argue that FSRQs can be used as tracers of massive elliptical galaxies in the early Universe.
The 22 Month Swift-BAT All-Sky Hard X-ray Survey Tueller, J; Baumgartner, W. H; Markwardt, C. B ...
The Astrophysical journal. Supplement series,
02/2010, Letnik:
186, Številka:
2
Journal Article
We report the detection of 10 clusters of galaxies in the ongoing Swift/Burst Alert Telescope (BAT) all-sky survey. This sample, which mostly comprises merging clusters, was serendipitously detected ...in the 15-55 keV band. We use the BAT sample to investigate the presence of excess hard X-rays above the thermal emission. The BAT clusters do not show significant (e.g., >=2 sigma ) nonthermal hard X-ray emission. The only exception is represented by Perseus whose high-energy emission is likely due to NGC 1275. Using XMM-Newton, Swift/XRT, Chandra and BAT data, we are able to produce upper limits of the inverse Compton (IC) emission mechanism which are in disagreement with most of the previously-claimed hard X-ray excesses. The coupling of the X-ray upper limits of the IC mechanism to radio data shows that, in some clusters, the magnetic field might be larger than 0.5 is a subset of G. We also derive the first log N-log S and luminosity function distributions of galaxy clusters above 15 keV.
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