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- ID:
- ivo://CDS.VizieR/J/A+A/589/A116
- Title:
- Multiwavelength study of Sgr A*
- Short Name:
- J/A+A/589/A116
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of the multiwavelength study of the flaring activity of the supermassive black hole named Sgr A* is located at the dynamical center of the Milky Way. We detected two X-ray flares on 2014 Mar. 10 and Apr. 2 with XMM-Newton, three near-infrared (NIR) flares with HST on 2014 Mar. 10 and Apr. 2, and two NIR flares on 2014 Apr. 3 and 4 with VLT. The X-ray flare on 2014 Mar. 10 is characterized by a long rise and a rapid decay. Its total duration is one of the longest detected so far in X-rays. Its NIR counterpart peaked well before the X-ray maximum, implying a dramatic change in the X-ray-to-NIR flux ratio during this event. This NIR/X-ray flare is interpreted as either a single flare where variation in the X-ray-to-NIR flux ratio is explained by the adiabatic compression of a plasmon, or two distinct flaring components separated by 1.2h with simultaneous peaks in X-rays and NIR. We identified an increase in the rising radio flux density at 13.37GHz on 2014 Mar. 10 with the VLA that could be the delayed radio emission from a NIR/X-ray flare that occurred before the start of our observation. The X-ray flare on 2014 Apr. 2 occurred for HST during the occultation of Sgr A* by the Earth, therefore we only observed the start of its NIR counterpart. With NIR synchrotron emission from accelerated electrons and assuming X-rays from synchrotron self-Compton emission, the region of this NIR/X-ray flare has a size of 0.03-7 times the Schwarzschild radius and an electron density of 10^8.5-10^10.2cm^-3^, assuming a synchrotron spectral index of 0.3-1.5. When Sgr A* reappeared to the HST view, we observed the decay phase of a distinct bright NIR flare with no detectable counterpart in X-rays. On 2014 Apr. 3, two 95GHz flares were observed with CARMA, where the first may be the delayed emission of a NIR flare observed with VLT.
- ID:
- ivo://CDS.VizieR/J/MNRAS/425/1215
- Title:
- Multiwavelength survey of AGNs
- Short Name:
- J/MNRAS/425/1215
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We aim to study the effect of environment on the presence and fuelling of active galactic nuclei (AGNs) in massive galaxy clusters. We explore the use of different AGN detection techniques with the goal of selecting AGN across a broad range of luminosities, AGN/host galaxy flux ratios and obscuration levels. From a sample of 12 galaxy clusters at redshifts 0.5<z<0.9, we identify AGN candidates using optical variability from multi-epoch Hubble Space Telescope imaging, X-ray point sources in Chandra images and mid-infrared (IR) spectral energy distribution power-law fits through the Spitzer Infrared Array Camera channels. We find 178 optical variables, 74 X-ray point sources and 64 IR power-law sources, resulting in an average of ~25 AGN per cluster.
- ID:
- ivo://CDS.VizieR/J/A+A/647/A88
- Title:
- Multi-wavelength variability of Mrk 421
- Short Name:
- J/A+A/647/A88
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The origin of the gamma-ray emission of the blazar Mrk 421 is still a matter of debate. We used 5.5 years of unbiased observing campaign data, obtained using the FACT telescope and the Fermi LAT detector at TeV and GeV energies, the longest and densest so far, together with contemporaneous multi-wavelength observations, to characterise the variability of Mrk 421 and to constrain the underlying physical mechanisms. We studied and correlated light curves obtained by ten different instruments and found two significant results. The TeV and X-ray light curves are very well correlated with a lag of <0.6 days. The GeV and radio (15GHz band) light curves are widely and strongly correlated. Variations of the GeV light curve lead those in the radio. Lepto-hadronic and purely hadronic models in the frame of shock acceleration predict proton acceleration or cooling timescales that are ruled out by the short variability timescales and delays observed in Mrk 421. Instead the observations match the predictions of leptonic models.
- ID:
- ivo://CDS.VizieR/J/A+A/539/A149
- Title:
- Multiwavelength view of blazar PKS 2155-304
- Short Name:
- J/A+A/539/A149
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Multiwavelength (MWL) observations of the blazar PKS 2155-304 during two weeks in July and August 2006, the period when two exceptional flares at very high energies (VHE, E>=100GeV) occurred, provide a detailed picture of the evolution of its emission. The complete data set from this campaign is presented, including observations in VHE gamma-rays (H.E.S.S.), X-rays (RXTE, CHANDRA, SWIFT XRT), optical (SWIFT UVOT, Bronberg, Watcher, ROTSE), and in the radio band (NRT, HartRAO, ATCA). Optical and radio light curves from 2004 to 2008 are compared to the available VHE data from this period, to put the 2006 campaign into the context of the long-term evolution of the source. The data set offers a close view of the evolution of the source on different time scales and yields new insights into the properties of the emission process. The predictions of synchrotron self-Compton (SSC) scenarios are compared to the MWL data, with the aim of describing the dominant features in the data down to the hour time scale. The spectral variability in the X-ray and VHE bands is explored and correlations between the integral fluxes at different wavelengths are evaluated. SSC modelling is used to interpret the general trends of the varying spectral energy distribution.
596. M83 X-ray sources
- ID:
- ivo://CDS.VizieR/J/A+A/410/53
- Title:
- M83 X-ray sources
- Short Name:
- J/A+A/410/53
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have identified 127 discrete sources in a Chandra ACIS observation of M 83, with a detection limit of ~3x10^36^erg/s in the 0.3-8.0keV band.
- ID:
- ivo://CDS.VizieR/J/MNRAS/414/1329
- Title:
- M82 X-ray sources long-term variability
- Short Name:
- J/MNRAS/414/1329
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the long-term variability exhibited by the X-ray point sources in the starburst galaxy M82. By combining nine Chandra observations taken between 1999 and 2007, we detect 58 X-ray point sources within the D_25_ isophote of M82 down to a luminosity of ~10^37^erg/s. Of these 58 sources, we identify three supernova remnant candidates and one supersoft source. 26 sources in M82 exhibit long-term (i.e. days to years) flux variability and three show long-term spectral variability. Furthermore, we classify 26 sources as variables and 10 as persistent sources. Among the total 26 variables, 17 varied by a flux ratio of >3 and six are transient candidates. By comparing with other nearby galaxies, M82 shows extremely strong long-term X-ray variability that 47 per cent of the X-ray sources are variables with a flux ratio of >3. The strong X-ray variability of M82 suggests that the population is dominated by X-ray binaries.
- ID:
- ivo://CDS.VizieR/J/ApJ/833/193
- Title:
- MYStIX candidate protostars
- Short Name:
- J/ApJ/833/193
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Massive Young Star-Forming Complex in Infrared and X-ray (MYStIX) project provides a new census on stellar members of massive star-forming regions within 4kpc. Here the MYStIX Infrared Excess catalog and Chandra-based X-ray photometric catalogs are mined to obtain high-quality samples of Class I protostars using criteria designed to reduce extragalactic and Galactic field star contamination. A total of 1109 MYStIX Candidate Protostars (MCPs) are found in 14 star-forming regions. Most are selected from protoplanetary disk infrared excess emission, but 20% are found from their ultrahard X-ray spectra from heavily absorbed magnetospheric flare emission. Two-thirds of the MCP sample is newly reported here. The resulting samples are strongly spatially associated with molecular cores and filaments on Herschel far-infrared maps. This spatial agreement and other evidence indicate that the MCP sample has high reliability with relatively few "false positives" from contaminating populations. But the limited sensitivity and sparse overlap among the infrared and X-ray subsamples indicate that the sample is very incomplete with many "false negatives." Maps, tables, and source descriptions are provided to guide further study of star formation in these regions. In particular, the nature of ultrahard X-ray protostellar candidates without known infrared counterparts needs to be elucidated.
- ID:
- ivo://CDS.VizieR/J/ApJS/209/30
- Title:
- MYStIX project: Bayesian matching
- Short Name:
- J/ApJS/209/30
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Identifying the infrared counterparts of X-ray sources in Galactic plane fields such as those of the MYStIX project presents particular difficulties due to the high density of infrared sources. This high stellar density makes it inevitable that a large fraction of X-ray positions will have a faint field star close to them, which standard matching techniques may incorrectly take to be the counterpart. Instead we use the infrared data to create a model of both the field star and counterpart magnitude distributions, which we then combine with a Bayesian technique to yield a probability that any star is the counterpart of an X-ray source. In our more crowded fields, between 10% and 20% of counterparts that would be identified on the grounds of being the closest star to an X-ray position within a 99% confidence error circle are instead identified by the Bayesian technique as field stars. These stars are preferentially concentrated at faint magnitudes. Equally importantly the technique also gives a probability that the true counterpart to the X-ray source falls beneath the magnitude limit of the infrared catalog. In deriving our method, we place it in the context of other procedures for matching astronomical catalogs.
- ID:
- ivo://CDS.VizieR/J/ApJS/209/27
- Title:
- MYStIX: the Chandra X-ray sources
- Short Name:
- J/ApJS/209/27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Massive Young star-forming complex Study in Infrared and X-ray (MYStIX) uses data from the Chandra X-Ray Observatory to identify and characterize the young stellar populations in 20 Galactic (d<4kpc) massive star-forming regions. Here, the X-ray analysis for Chandra ACIS-I observations of 10 of the MYStIX fields is described, and a catalog of >10000 X-ray sources is presented. In comparison to other published Chandra source lists for the same regions, the number of MYStIX-detected faint X-ray sources in a region is often doubled. While the higher catalog sensitivity increases the chance of false detections, it also increases the number of matches to infrared stars. X-ray emitting contaminants include foreground stars, background stars, and extragalactic sources. The X-ray properties of sources in these classes are discussed.