- ID:
- ivo://CDS.VizieR/J/ApJS/255/7
- Title:
- X-ray monitoring of 1ES 1927+654
- Short Name:
- J/ApJS/255/7
- Date:
- 06 Dec 2021 19:56:23
- Publisher:
- CDS
- Description:
- 1ES 1927+654 is a nearby active galactic nucleus (AGN) that underwent a changing-look event in early 2018, developing prominent broad Balmer lines that were absent in previous observations. We have followed up this object in the X-rays with an ongoing campaign that started in 2018 May and that includes 265 NICER (for a total of 678ks) and 14 Swift/XRT (26ks) observations, as well as three simultaneous XMM-Newton/NuSTAR (158/169ks) exposures. In the X-rays, 1ES 1927+654 shows a behavior unlike any previously known AGN. The source is extremely variable both in spectral shape and flux and does not show any correlation between X-ray and UV flux on timescales of hours or weeks/months. After the outburst, the power-law component almost completely disappeared, and the source showed an extremely soft continuum dominated by a blackbody component. The temperature of the blackbody increases with the luminosity, going from kT~80eV (for a 0.3-2keV luminosity of L_0.3-2_~10^41.5^erg/s) to ~200eV (for L_0.3-2_~10^44^erg/s). The spectra show evidence of ionized outflows and of a prominent feature at ~1keV, which can be reproduced by a broad emission line. The unique characteristics of 1ES 1927+654 in the X-ray band suggest that it belongs to a new type of changing-look AGN. Future X-ray surveys might detect several more objects with similar properties.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/533/A52
- Title:
- X-ray monitoring of M31 novae
- Short Name:
- J/A+A/533/A52
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Context. Classical novae (CNe) represent the major class of supersoft X-ray sources (SSSs) in the central region of the galaxy M31. We performed a dedicated monitoring of the M31 central region with XMM-Newton and Chandra between Nov 2007 and Feb 2008 and between Nov 2008 and Feb 2009, respectively, to find SSS counterparts of CNe, determine the duration of their SSS phase, and derive physical outburst parameters. We systematically searched our data for X-ray counterparts of CNe, determined their X-ray light curves and characterised their spectra using blackbody fits and white dwarf (WD) atmosphere models. Additionally, we determined luminosity upper limits for all previously known X-ray emitting novae that are not detected any more and for all CNe in our field of view with optical outbursts between one year before the start of the X-ray monitoring (Oct 2006) and its end (Feb 2009).
- ID:
- ivo://CDS.VizieR/J/A+A/563/A2
- Title:
- X-ray monitoring of M31 novae
- Short Name:
- J/A+A/563/A2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Classical novae (CNe) represent the major class of supersoft X-ray sources (SSSs) in the central region of our neighbouring galaxy M 31. We performed a dedicated monitoring of the M 31 central region, which aimed to detect SSS counterparts of CNe, with XMM-Newton and Chandra between Nov and Mar of the years 2009/10, 2010/11, and 2011/12. We systematically searched our data for X-ray counterparts of CNe and determined their X-ray light curves and also their spectral properties in the case of XMM-Newton data. Additionally, we determined luminosity upper limits for all previously known X-ray emitting novae, which are not detected anymore, and for all CNe in our field of view with recent optical outbursts.
- ID:
- ivo://CDS.VizieR/J/A+A/465/375
- Title:
- X-ray monitoring of optical novae in M31
- Short Name:
- J/A+A/465/375
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Optical novae have recently been identified as the major class of supersoft X-ray sources in M 31 based on ROSAT and early XMM-Newton and Chandra observations. This paper reports on a search for X-ray counterparts of optical novae in M 31 based on archival Chandra HRC-I and ACIS-I as well as XMM-Newton observations of the galaxy center region obtained from July 2004 to February 2005. We systematically determine X-ray brightness or upper limit for counterparts of all known optical novae with outbursts between November 2003 to the end of the X-ray coverage. In addition, we determine the X-ray brightnesses for counterparts of four novae with earlier outbursts. For comparison with the X-ray data we created a catalogue of optical novae in M 31 based on our own nova search programs and on all novae reported in the literature. We collected all known properties and named the novae consistently following the CBAT scheme. We detect eleven out of 34 novae within a year after the optical outburst in X-rays. While for eleven novae we detect the end of the supersoft source phase, seven novae are still bright more than 1200, 1600, 1950, 2650, 3100, 3370 and 3380d after outburst. One nova is detected to turn on 50d, another 200d after outburst. Three novae unexpectedly showed short X-ray outbursts starting within 50d after the optical outburst and lasting only two to three months. The X-ray emission of several of the novae can be characterized as supersoft from hardness ratios and/or X-ray spectra or by comparing HRC-I count rates with ACIS-I count rates or upper limits. The number of detected optical novae at supersoft X-rays is much higher than previously estimated (>30%). We use the X-ray light curves to estimate the burned masses of the White Dwarf and of the ejecta.
- ID:
- ivo://CDS.VizieR/J/MNRAS/367/627
- Title:
- X-ray/NIR correlation for early-type galaxies
- Short Name:
- J/MNRAS/367/627
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The relation between X-ray luminosity and near-infrared (NIR) luminosity for early-type galaxies has been examined. NIR luminosities should provide a superior measure of stellar mass compared to optical luminosities used in previous studies, especially if there is significant star formation or dust present in the galaxies. However, we show that the X-ray-NIR relations are remarkably consistent with the X-ray-optical relations. This indicates that the large scatter of the relations is dominated by scatter in the X-ray properties of early-type galaxies, and is consistent with early-types consisting of old, quiescent stellar populations. We have investigated scatter in terms of environment, surface brightness profile, Mg2, H{beta}, H{gamma} line strength indices, spectroscopic age and nuclear H{alpha} emission.
- ID:
- ivo://CDS.VizieR/J/ApJ/809/161
- Title:
- X-ray obs. and membership probabilities of M37
- Short Name:
- J/ApJ/809/161
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Empirical calibrations of the stellar age-rotation-activity relation (ARAR) rely on observations of the co-eval populations of stars in open clusters. We used the Chandra X-ray Observatory to study M37, a 500-Myr-old open cluster that has been extensively surveyed for rotation periods (P_rot_). M37 was observed almost continuously for five days, for a total of 440.5ks, to measure stellar X-ray luminosities (L_X_), a proxy for coronal activity, across a wide range of masses. The cluster's membership catalog was revisited to calculate updated membership probabilities from photometric data and each star's distance to the cluster center. The result is a comprehensive sample of 1699 M37 members: 426 with P_rot_, 278 with X-ray detections, and 76 with both. We calculate Rossby numbers, R_0_=P_rot_/{tau}, where {tau} is the convective turnover time, and ratios of the X-ray-to-bolometric luminosity, L_X_/L_bol_, to minimize mass dependencies in our characterization of the rotation-coronal activity relation at 500Myr. We find that fast rotators, for which R_0_<0.09+/-0.01, show saturated levels of activity, with log(L_X_/L_bol_)=-3.06+/-0.04. For R_0_>=0.09+/-0.01, activity is unsaturated and follows a power law of the form R_0_^{beta}^, where {beta}=-2.03^+0.17^_-1.14_. This is the largest sample available for analyzing the dependence of coronal emission on rotation for a single-aged population, covering stellar masses in the range 0.4-1.3M_{sun}_, P_rot_ in the range 0.4-12.8 days, and L_X_ in the range 10^28.4-30.5^erg/s. Our results make M37 a new benchmark open cluster for calibrating the ARAR at ages of ~500Myr.
21767. X-ray observations of CG 12
- ID:
- ivo://CDS.VizieR/J/ApJ/673/331
- Title:
- X-ray observations of CG 12
- Short Name:
- J/ApJ/673/331
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The mysterious high Galactic latitude cometary globule CG 12 has been observed with the ACIS detector on board the Chandra X-Ray Observatory. We detect 128 X-ray sources, of which half are likely young stars formed within the globule's head. This new population of >~50 T Tauri stars and one new embedded protostar is far larger than the previously reported few intermediate-mass and two protostellar members of the cloud.
- ID:
- ivo://CDS.VizieR/J/ApJS/73/781
- Title:
- X-ray observations of galactic Supernova Remnants
- Short Name:
- J/ApJS/73/781
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper summarizes the observations of Galactic supernova remnants with the imaging detectors of the Einstein Observatory. X-ray surface brightness contours of 47 remnants are shown together with gray-scale pictures. Count rates for these remnants have been derived and are listed for the HRI, IPC, and MPC detectors.
- ID:
- ivo://CDS.VizieR/J/ApJ/817/95
- Title:
- X-ray observations of HCG galaxies
- Short Name:
- J/ApJ/817/95
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We obtain total galaxy X-ray luminosities, L_X_, originating from individually detected point sources in a sample of 47 galaxies in 15 compact groups of galaxies (CGs). For the great majority of our galaxies, we find that the detected point sources most likely are local to their associated galaxy, and are thus extragalactic X-ray binaries (XRBs) or nuclear active galactic nuclei (AGNs). For spiral and irregular galaxies, we find that, after accounting for AGNs and nuclear sources, most CG galaxies are either within the +/-1{sigma} scatter of the Mineo et al. L_X_-star formation rate (SFR) correlation or have higher L_X_ than predicted by this correlation for their SFR. We discuss how these "excesses" may be due to low metallicities and high interaction levels. For elliptical and S0 galaxies, after accounting for AGNs and nuclear sources, most CG galaxies are consistent with the Boroson et al. L_X_-stellar mass correlation for low-mass XRBs, with larger scatter, likely due to residual effects such as AGN activity or hot gas. Assuming non-nuclear sources are low- or high-mass XRBs, we use appropriate XRB luminosity functions to estimate the probability that stochastic effects can lead to such extreme L_X_ values. We find that, although stochastic effects do not in general appear to be important, for some galaxies there is a significant probability that high L_X_ values can be observed due to strong XRB variability.
- ID:
- ivo://CDS.VizieR/J/AJ/134/999
- Title:
- X-ray observations of NGC 2264
- Short Name:
- J/AJ/134/999
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from an X-ray imaging survey of the young cluster NGC 2264, carried out with the European Photon Imaging Cameras (EPIC) on board the XMM-Newton spacecraft. The X-ray data are merged with extant optical and near-infrared photometry, spectral classifications, Halpha emission strengths, and rotation periods to examine the interrelationships between coronal and chromospheric activity, rotation, stellar mass, and internal structure for a statistically significant sample of pre-main-sequence stars. A total of 300 distinct X-ray sources can be identified with optical or near-infrared counterparts. The sources are concentrated within three regions of the cluster: in the vicinity of S Mon, within the large emission/reflection nebulosity southwest of S Mon, and along the broad ridge of molecular gas that extends from the Cone Nebula to the NGC 2264 IRS 2 field.
