NGC 7679: an anomalous, composite Seyfert 1 galaxy whose X-ray luminous AGN vanishes at optical wavelengths

We present short-cadence data of the ultra-active star AB Dor measured by the Transiting Exoplanet Survey Satellite (TESS). In the TESS light curves of AB Dor, we found numerous flare events in addition to time-variable rotational modulation with an amplitude of up to 7%. We identified eight superflares (releasing more than 1034 erg) and studied their morphologies and energetics. We compared these flares to both the most energetic solar flare seen in total solar irradiance measurements as well as to a very energetic flare on AB Dor observed by XMM-Newton, the superflare nature of which we also demonstrate. The total energy of both the solar flare and the event on AB Dor emitted in the optical exceed their respective X-ray outputs possibly by an order of magnitude, suggesting that the dominant energy loss of such flares actually occurs at optical wavelengths. Superflares are found to take place on AB Dor at a rate of about one per week, and due to the star’s proximity and brightness can be studied in excruciating detail. Thus the TESS data offer a superb possibility to study the frequency and energetics of superflare events for stars in the solar neighborhood and at large.

Download Full-text

X-Ray Large Scale Structure and XMM

Symposium - International Astronomical Union ◽

10.1017/s0074180900114706 ◽

1998 ◽

Vol 188 ◽

pp. 177-180

Author(s):

M. Pierre

Keyword(s):

Large Scale ◽

Initial Conditions ◽

Data Set ◽

X Ray ◽

Large Scale Structures ◽

The Galaxy ◽

Optical Wavelengths ◽

Analytical Approaches ◽

The Universe ◽

Additional Constraints

The formation of Large Scale Structures (LSS) in the universe was first studied at optical wavelengths as the galaxy spatial distribution appeared to be far from homogeneous. Considerable effort has been invested in semi-analytical approaches and in numerical simulations (DM + hot gas) to explain the observed structures, given some set of initial conditions and using additional constraints provided by the COBE results. It is now clear however, that these two extreme data set are not sufficient to discriminate between the possible remaining cosmological scenarios. It is thus timely to investigate LSS at a much higher redshift than the present survey limits both in the optical and in other wavebands. In this context, the X-ray band will certainly become a hot field with the advent of the XMM observatory. The next section briefly summarizes what is known about LSS from optical wavelengths and simulations. Sect. 3 reviews the particular points that can be addressed in the X-ray band. Last section presents realistic prospects for mapping LSS with XMM.

Download Full-text

A New PG 1159-Type Central Star Discovered in the ROSAT XRT All Sky Survey: Non-LTE Analysis of X-Ray and Optical Spectra

Symposium - International Astronomical Union ◽

10.1017/s0074180900172298 ◽

1993 ◽

Vol 155 ◽

pp. 496-496

Author(s):

K. Werner ◽

C. Motch ◽

M. Pakull

Keyword(s):

Surface Brightness ◽

Central Star ◽

Model Atmosphere ◽

Complete Agreement ◽

Atmospheric Parameters ◽

Low Gravity ◽

X Ray ◽

Sky Survey ◽

Optical Wavelengths

We report on the discovery of a new PG 1159 star in the ROSAT XRT all sky survey and give results of a model atmosphere analysis. The X-ray source RX J2117.1+3412 is relatively faint (0.33 cnts−1) and extremely soft. Ground based optical follow-up spectroscopy (OHP, France) proofs its PG 1159 nature: It belongs to the “low gravity emission” spectral subtype. Optically, it is the second brightest PG1159 star. CCD [O III] imagery reveals that the star is surrounded by an old arc-shaped planetary nebula of faint surface brightness. The spectral analysis of the central star was performed with non-LTE line blanketed model atmospheres (Werner 1992). We find a complete agreement between the atmospheric parameters determined at optical wavelengths and in the ROSAT PSPC energy range.

Download Full-text

X-Ray Observations of Supernova Remnants from the Einstein Observatory

Publications of the Astronomical Society of Australia ◽

10.1017/s1323358000018579 ◽

1980 ◽

Vol 4 (1) ◽

pp. 4-8 ◽

Cited By ~ 1

Author(s):

Ian R. Tuohy

Keyword(s):

Supernova Remnants ◽

X Ray ◽

The Past ◽

Optical Wavelengths ◽

Einstein Observatory

The most extensive studies of supernova remnants (SNRs) in the past have taken place at radio and optical wavelengths.

Download Full-text

Dark Matter Determinations from Chandra Observations of Quadruply Lensed Quasars

Proceedings of the International Astronomical Union ◽

10.1017/s174392131000829x ◽

2009 ◽

Vol 5 (H15) ◽

pp. 76-76

Author(s):

David Pooley ◽

Jeffrey A. Blackburne ◽

Saul Rappaport ◽

Paul L. Schechter

Keyword(s):

Dark Matter ◽

Flux Ratio ◽

Source Size ◽

Point Sources ◽

Optical Data ◽

X Ray ◽

Optical Wavelengths

We present Chandra X-ray observations of 14 quadruply lensed quasars. The X-ray data reveal flux ratio anomalies which are more extreme than those seen at optical wavelengths, confirming the microlensing origin of the anomalies originally seen in the optical data. The reduction of the anomalies in the optical, as compared to X-ray, indicates that the sizes of the optical emitting regions of the quasars must be about 1/3 the size of the projected Einstein radii of the microlensing stars. The X-ray emitting regions are essentially point sources and therefore give a microlensing signal unencumbered by source size considerations. For each lensing galaxy, we determine the most likely ratio of smooth material (dark matter) to clumpy material (stars) to explain the X-ray flux ratios. The ensemble of Chandra-observed quads indicates that the amount of matter projected along the lines of sight to the images (at radial distances of several kpc from the centers of the lensing galaxies) is ~90% smooth dark matter and ~10% stars.

Download Full-text

Detection of the magnetar XTE J1810−197 at 150 and 260 GHz with the NIKA2 kinetic inductance detector camera

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038504 ◽

2020 ◽

Vol 640 ◽

pp. L2 ◽

Cited By ~ 3

Author(s):

P. Torne ◽

J. Macías-Pérez ◽

B. Ladjelate ◽

A. Ritacco ◽

M. Sánchez-Portal ◽

...

Keyword(s):

High Sensitivity ◽

Weather Conditions ◽

Kinetic Inductance Detector ◽

Kinetic Inductance ◽

X Ray ◽

Technical Requirements ◽

Optical Wavelengths ◽

The Stability ◽

Low Sensitivity ◽

First Time

Context. The investigation of pulsars between millimetre and optical wavelengths is challenging due to the faintness of the pulsar signals and the relative low sensitivity of the available facilities compared to 100 m class telescopes operating in the centimetre band. The kinetic inductance detector (KID) technology offers large instantaneous bandwidths and a high sensitivity that can help to increase the ability of existing observatories at short wavelengths substantially to detect pulsars and transient emission. Aims. To investigate whether pulsars can be detected with KIDs, we observed the anomalous X-ray pulsar XTE J1810−197 with the New IRAM KIDs Array-2 (NIKA2) camera installed at the IRAM 30 m telescope in Spain. Methods. Several short observations of XTE J1810−197 were made on 2019 March 25 under good weather conditions to verify the stability of the KIDs and to try to detect the expected broadband pulsations from the neutron star. Results. We detected the pulsations from the pulsar with NIKA2 at its two operating frequency bands, 150 and 260 GHz (λ = 2.0 and 1.15 mm, respectively). This is the first time that a pulsar is detected with a receiver based on KID technology in the millimetre band. In addition, this is the first report of short millimetre emission from XTE J1810−197 after its reactivation in December 2018, and it is the first time that the source is detected at 260 GHz, which gives us new insights into the radio emission process of the star. Conclusions. We demonstrate that KIDs can fulfil the technical requirements for detecting pulsed emission from neutron stars in the millimetre band. We show that the magnetar XTE J1810−197 is again emitting strong pulsations in the short millimetre band.

Download Full-text

The variable radio counterpart of Swift J1858.6-0814

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1704 ◽

2020 ◽

Vol 496 (4) ◽

pp. 4127-4140 ◽

Cited By ~ 2

Author(s):

J van den Eijnden ◽

N Degenaar ◽

T D Russell ◽

D J K Buisson ◽

D Altamirano ◽

...

Keyword(s):

Time Scales ◽

Radio Spectrum ◽

Electromagnetic Spectrum ◽

Very Large Array ◽

X Ray ◽

Geometric Origin ◽

Optical Wavelengths ◽

X Ray Binaries ◽

Variable Radio

ABSTRACT Swift J1858.6-0814 is a transient neutron star X-ray binary discovered in 2018 October. Multiwavelength follow-up observations across the electromagnetic spectrum revealed many interesting properties, such as erratic flaring on minute time-scales and evidence for wind outflows at both X-ray and optical wavelengths, strong and variable local absorption, and an anomalously hard X-ray spectrum. Here, we report on a detailed radio observing campaign consisting of one observation at 5.5/9 GHz with the Australia Telescope Compact Array, and nine observations at 4.5/7.5 GHz with the Karl G. Jansky Very Large Array. A radio counterpart with a flat to inverted radio spectrum is detected in all observations, consistent with a compact jet being launched from the system. Swift J1858.6-0814 is highly variable at radio wavelengths in most observations, showing significant variability when imaged on 3-to-5-min time-scales and changing up to factors of 8 within 20 min. The periods of brightest radio emission are not associated with steep radio spectra, implying they do not originate from the launching of discrete ejecta. We find that the radio variability is similarly unlikely to have a geometric origin, be due to scintillation, or be causally related to the observed X-ray flaring. Instead, we find that it is consistent with being driven by variations in the accretion flow propagating down the compact jet. We compare the radio properties of SwiftJ1858.6-0814 with those of Eddington-limited X-ray binaries with similar X-ray and optical characteristics, but fail to find a match in radio variability, spectrum, and luminosity.

Download Full-text

Evidence for a 6 Year Periodicity in X Persei

Symposium - International Astronomical Union ◽

10.1017/s0074180900065153 ◽

1980 ◽

Vol 88 ◽

pp. 361-365

Author(s):

J. D. Dorren ◽

E. F. Guinan

Keyword(s):

Narrow Band ◽

High Energy ◽

Sufficient Evidence ◽

X Rays ◽

X Ray ◽

Hydrogen Emission ◽

Be Star ◽

Optical Wavelengths ◽

Photoelectric Observations ◽

Absorption Features

Intermediate and narrow-band photoelectric observations obtained at Biruni and Villanova Observatories from 1977 to the present, when combined with previous data, strongly suggest that light increases of about 0.5 mag occur at 6 year intervals. Possible explanations are considered.The X-ray pulsator X Persei (4U 0352+30) is an intriguing object at both X-ray and optical wavelengths. From the X-ray data a period of 13.9 minutes now appears well-established, but early suggestions of a 22.4 hour periodicity remain unconfirmed (White et al.,1976, Becker et al., 1979). The nature of the X-ray emission is unusual; the source is about 3 orders of magnitude weaker than other X-ray binary pulsars, and the spectrum contains a strong high-energy X-ray component (Mushotzky et al., 1977). Long known as an irregular variable, X Per has been classified as a Be star with an 09.5 (III-IV)e spectral type and showing broad hydrogen emission and absorption features (Brucato and Kristian 1972, Hutchings et al., 1975). A 581-day period is indicated by the radial velocity study of Hutchings et al., (1975). This has been variously interpreted as an orbital period (about a black hole) or an apsidal period, the models having in common accretion on to a neutron star as the source of the pulsed X-rays. In 1977 an increase in brightness of the star was observed by Kalv (1977) and Guinan et al., (1978), and by April 1979 we had accumulated sufficient evidence to suggest that X Per undergoes periodic (≃ 6-year) outbursts (Dorren et al., 1979a).

Download Full-text

A Catalogue of Galactic Supernova Remnants

Symposium - International Astronomical Union ◽

10.1017/s0074180900034495 ◽

1983 ◽

Vol 101 ◽

pp. 597-604 ◽

Cited By ~ 2

Author(s):

Sidney van den Bergh

Keyword(s):

Supernova Remnants ◽

X Rays ◽

True Nature ◽

X Ray ◽

The Galaxy ◽

Optical Wavelengths ◽

Optical Identifications

At this conference results have been presented on a number of individual galactic supernova remnants, but many others remain unstudied. It therefore seemed worthwhile to present a catalogue of all presently known SNR's in the Galaxy. Objects of which the true nature is not yet well established have, as far as possible, been omitted. Remnants which have been detected at optical wavelengths are marked by an asterisk in Table 1. Data on the optical identifications are from van den Bergh (1978), supplemented by recent results of Zealey, Elliot and Malin (1979), Reich, Kallas and Steube (1979), Downes, Pauls and Salter (1980), van den Bergh (1981) and Reich and Braunsfurth (1981). Also marked in the table are supernova remnants that have been detected in x-rays. These x-ray identifications are from miscellaneous sources.

Download Full-text

Tsinghua Center for Astrophysics and the Dark Universe

Asia Pacific Physics Newsletter ◽

10.1142/s2251158x14000368 ◽

2014 ◽

Vol 03 (02) ◽

pp. 63-70

Author(s):

Charling Tao

Keyword(s):

Gamma Rays ◽

Nuclear Physics ◽

Gamma Ray ◽

High Energy ◽

X Rays ◽

High Energy Astrophysics ◽

Research Directions ◽

X Ray ◽

Main Research ◽

Optical Wavelengths

The Tsinghua Center for Astrophysics (THCA) was founded in 2001 by Prof. Li Tipei and Shang Rencheng. A distinguishing characteristic of THCA's astrophysics program is its emphasis on space X-ray and gamma-ray instrumentation, by taking advantage of Tsinghua's strong programs on nuclear physics, nuclear engineering, space and aeronautics engineering, as well as electronics and information technology. The main research directions in THCA include high energy astrophysics and cosmology with space and ground observations in X-rays and gamma-rays, and more recently in optical wavelengths, radio-astronomy, gravitational waves, dark matter and dark energy analyses and projects.

Download Full-text