scholarly journals Chandra and HST studies of six millisecond pulsars in the globular cluster M13

2021 ◽  
Vol 502 (2) ◽  
pp. 1596-1604
Author(s):  
Jiaqi Zhao ◽  
Yue Zhao ◽  
Craig O Heinke
Keyword(s):  
Globular Cluster ◽  
White Dwarf ◽  
Hubble Space Telescope ◽  
X Rays ◽  
Power Law Model ◽  
Millisecond Pulsars ◽  
X Ray ◽  
V Band ◽  
Upper Limit ◽  
Single Power

ABSTRACT We analyse 55 ks of Chandra X-ray observations of the Galactic globular cluster (GC) M13. Using the latest radio timing positions of six known millisecond pulsars (MSPs) in M13 from Wang et al. (2020), we detect confident X-ray counterparts to five of the six MSPs at X-ray luminosities of LX(0.3–8 keV)∼3 × 1030–1031 erg s−1, including the newly discovered PSR J1641+3627F. There are limited X-ray counts at the position of PSR J1641+3627A, for which we obtain an upper limit LX < 1.3 × 1030 erg s−1. We analyse X-ray spectra of all six MSPs, which are well described by either a single blackbody (BB) or a single power-law model. We also incorporate optical/UV imaging observations from the Hubble Space Telescope (HST) and find optical counterparts to PSR J1641+3627D and J1641+3627F. Our colour–magnitude diagrams indicate the latter contains a white dwarf, consistent with the properties suggested by radio timing observations. The counterpart to J1641+3627D is only visible in the V band; however, we argue that the companion to J1641+3627D is also a white dwarf, since we see a BB-like X-ray spectrum, while MSPs with non-degenerate companions generally show non-thermal X-rays from shocks between the pulsar and companion winds. Our work increases the sample of known X-ray and optical counterparts of MSPs in GCs.

ROSAT Spectra of Quasars

1994 ◽  
Vol 159 ◽  
pp. 369-369
Author(s):  
P. Bühler ◽  
T.J.-L. Courvoisier ◽  
R. Staubert ◽  
H. Brunner ◽  
G. Lamer
Keyword(s):  
Power Law ◽  
Column Density ◽  
Soft Part ◽  
Black Body ◽  
Soft Component ◽  
X Rays ◽  
Power Law Model ◽  
X Ray ◽  
Power Law Index ◽  
Single Power

X–ray observations of AGN with Einstein, EXOSAT and Ginga have shown, that the spectra of quasars in the energy range 2 to 10 keV can be approximately described by a single power law model with a photon index of 1.7 to 2.0. They also suggested that a soft X-ray excess component (below ≈ 1 keV) is a common feature in many quasars. In order to investigate whether a soft excess is characteristic for a certain class of objects we analysed the data of the pointed ROSAT PSPC observations of the six radio-loud quasars PG0007+106, PKS0135-247, QSO0537-286, QSO0923+392, PG1225+317, 3C273 and the radio-quiet quasar PG0804+761. In a first step the observed spectra were fitted with an absorbed single power law model. The hydrogen column density was fixed to its galactic value and the normalisation at 1 keV and the spectral index α were the free fit parameters. In order to decide whether a soft component is present in a source, the resulting power law index was compared with the hard X-ray power law index (2–10 keV) determined in the past with other instruments. A steep ROSAT PSPC spectrum indicates the presence of an additional soft X–ray component. In four cases (PKS0135-247, PG0804+761, QSO0923+392, 3C273) we find that the spectra in the PSPC band are considerably steeper than the spectra above 2 keV and therefore suggest the presence of a soft excess. In order to quantify the contribution of the soft excess these spectra were successively fitted with a model containing a hard power law component and an additional soft component described either by a power law, thermal bremsstrahlung or black body model. For the other three members of our sample (0007+106, 0537-286, 1225+317) the fitted power law index is not enhanced. This means that no soft component has been detected, but not necessarily that it does not exist. There are two effects which render more difficult the detection of a soft component in ROSAT spectra, the absorption of photons by interstellar material and the shift of the spectra towards lower energies due to the redshift. Both processes have first an effect on the soft part of the observed spectrum and it is therefore evident, that this leads to a decrease of the sensitivity for soft X–rays of the emitted spectrum. For the three quasars in our sample, where no soft excess has been detected, either the column density (0007+106) or the redshift (0537-286, 1225+317) is especially large and therefore an eventually present soft component could have remained undetected. In these cases we calculated upper limits for the strength of such a soft component (P. Bühler et al., to be published in A&A.)

scholarly journals Discovery of an X-Ray Off-State in the Supersoft Source CAL 83

1997 ◽  
Vol 163 ◽  
pp. 730-731
Author(s):  
P. Kahabka
Keyword(s):  
White Dwarf ◽  
Accretion Rate ◽  
X Rays ◽  
X Ray ◽  
Mass Accretion Rate ◽  
Upper Limit ◽  
Linear Decline

AbstractAn X-ray off state of CAL 83 has been observed in April 1996 with the ROSAT HRI three weeks after a normal on state. An upper limit for a linear decline time of the observed flux of ~20 days (and of an efolding decline time of ~6 days) is deduced. This decline may be due to the response of the white dwarf envelope to a temporary increased mass accretion rate giving rise to an envelope expansion. CAL 83 may resemble the recurrent supersoft LMC transient RX J0513.9–6951 with episodes of disappearance in X-rays.

Improving x-ray map resolution with image restoration techniques

1996 ◽  
Vol 54 ◽  
pp. 598-599
Author(s):  
Richard B. Mott ◽  
John J. Friel ◽  
Charles G. Waldman
Keyword(s):  
Image Restoration ◽  
Hubble Space Telescope ◽  
Extensive Literature ◽  
Small Object ◽  
X Rays ◽  
X Ray ◽  
Mapping Parameters ◽  
The Matrix ◽  
The 1960S ◽  
Map Resolution

X-rays are emitted from a relatively large volume in bulk samples, limiting the smallest features which are visible in X-ray maps. Beam spreading also hampers attempts to make geometric measurements of features based on their boundaries in X-ray maps. This has prompted recent interest in using low voltages, and consequently mapping L or M lines, in order to minimize the blurring of the maps.An alternative strategy draws on the extensive work in image restoration (deblurring) developed in space science and astronomy since the 1960s. A recent example is the restoration of images from the Hubble Space Telescope prior to its new optics. Extensive literature exists on the theory of image restoration. The simplest case and its correspondence with X-ray mapping parameters is shown in Figures 1 and 2.Using pixels much smaller than the X-ray volume, a small object of differing composition from the matrix generates a broad, low response. This shape corresponds to the point spread function (PSF). The observed X-ray map can be modeled as an “ideal” map, with an X-ray volume of zero, convolved with the PSF. Figure 2a shows the 1-dimensional case of a line profile across a thin layer. Figure 2b shows an idealized noise-free profile which is then convolved with the PSF to give the blurred profile of Figure 2c.

scholarly journals A Chandra look at the X-ray faint millisecond pulsars in the globular cluster NGC 6752

2014 ◽  
Vol 441 (1) ◽  
pp. 757-768 ◽  
Author(s):  
L. M. Forestell ◽  
C. O. Heinke ◽  
H. N. Cohn ◽  
P. M. Lugger ◽  
G. R. Sivakoff ◽  
...  
Keyword(s):  
Globular Cluster ◽  
Millisecond Pulsars ◽  
X Ray

scholarly journals The HST large programme on NGC 6752 – III. Detection of the peak of the white dwarf luminosity function

2019 ◽  
Vol 488 (3) ◽  
pp. 3857-3865
Author(s):  
L R Bedin ◽  
M Salaris ◽  
J Anderson ◽  
M Libralato ◽  
D Apai ◽  
...  
Keyword(s):  
Globular Cluster ◽  
White Dwarf ◽  
Luminosity Function ◽  
Main Sequence ◽  
Hubble Space Telescope ◽  
Horizontal Branch ◽  
Space Telescope

ABSTRACT We report on the white dwarf (WD) cooling sequence of the old globular cluster NGC 6752, which is chemically complex and hosts a blue horizontal branch. This is one of the last globular cluster WD cooling sequences accessible to imaging by the Hubble Space Telescope. Our photometry and completeness tests show that we have reached the peak of the luminosity function of the WD cooling sequence, at a magnitude mF606W  = 29.4 ± 0.1, which is consistent with a formal age of ∼14 Gyr. This age is also consistent with the age from fits to the main-sequence turn-off (13–14 Gyr), reinforcing our conclusion that we observe the expected accumulation of WDs along the cooling sequence.

Sigma upper limits to the hard X-ray/soft gamma-ray emission from the millisecond pulsars of the nearby globular cluster 47 Tucunae

1993 ◽  
Vol 405 ◽  
pp. L59 ◽  
Author(s):  
D. Barret ◽  
P. Mandrou ◽  
M. Denis ◽  
J. F. Olive ◽  
P. Laurent ◽  
...  
Keyword(s):  
Globular Cluster ◽  
Gamma Ray ◽  
Millisecond Pulsars ◽  
X Ray ◽  
Upper Limits ◽  
Gamma Ray Emission

scholarly journals The X-ray Spectra of High Redshift Quasars

1989 ◽  
Vol 134 ◽  
pp. 161-166
Author(s):  
Claude R. Canizares ◽  
Julia L. White
Keyword(s):  
High Redshift ◽  
Radio Spectrum ◽  
Clear Correlation ◽  
X Rays ◽  
Spectral Parameters ◽  
X Ray ◽  
Systematic Uncertainties ◽  
Two Component ◽  
X Ray Background ◽  
Single Power

We present mean spectral parameters for various ensembles of quasars observed with the Einstein Observatory Imaging Proportional Counter (IPC). Our sample contains 71 optically or radio selected quasars with 0.1 < z < 3.5, Galactic NH < 1021 cm−2, total counts of 30 −500, and IPC gain < 19. Quasars are grouped into ensembles according to radio properties (Flat Radio Spectrum [FRS], Steep Radio Spectrum [SRS] or Radio Quiet [RQ]), and either redshift or X-ray luminosity, lx. We find a clear correlation between radio properties and α. FRS quasars have α∼0.4, SRS quasars have α∼0.7 and RQ quasars have α ∼1–1.4. There is no evidence for a dependence of α on z nor, for the FRS and SRS ensembles, on lx over nearly three decades. FRS quasars with 2.0 < z < 3.5 have just as flat mean spectra as those with low z, implying that a single power law, which is flatter than the canonical one with α ∼ 0.65, continues into the 1–10 keV band (in which the observed softer X-rays were emitted). Unfortunately, the results for high redshift and high lx RQ quasars are ambiguous because of systematic uncertainties in the ensemble means. Thus we cannot test the two-component spectral hypothesis of Wilkes and Elvis for these objects. SRS X-ray spectra could be steeper than FRS spectra because of the mixing of two components, although a single intrinsically steeper spectrum is easier to reconcile with the absence of z dependence. The uncertainty in a for RQ quasars with high z leaves open the important question of their contribution to the cosmic X-ray background.

scholarly journals Searching for optical companions to four binary millisecond pulsars with the Gran Telescopio Canarias

2020 ◽  
Vol 492 (2) ◽  
pp. 3032-3040 ◽  
Author(s):  
A Yu Kirichenko ◽  
A V Karpova ◽  
D A Zyuzin ◽  
S V Zharikov ◽  
E A López ◽  
...  
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Optical Data ◽  
Pure Hydrogen ◽  
Millisecond Pulsars ◽  
Upper Limit ◽  
Photometric Observations ◽  
Low Mass

ABSTRACT We report on multiband photometric observations of four binary millisecond pulsars with the Gran Telescopio Canarias. The observations led to detection of binary companions to PSRs J1630+3734, J1741+1351, and J2042+0246 in the Sloan g′, r′, and i′ bands. Their magnitudes in the r′ band are ≈24.4, 24.4, and 24.0, respectively. We also set a 3σ upper limit on the brightness of the PSR J0557+1550 companion in the r′ band of ≈25.6 mag. Combining the optical data with the radio timing measurements and white dwarf cooling models, we show that the detected companions are cool low-mass white dwarfs with temperatures and ages in the respective ranges of (4–7) × 103 K and 2–5 Gyr. All the detected white dwarfs are found to likely have either pure hydrogen or mixed helium–hydrogen atmospheres.

scholarly journals An ASCA Observation of the Eclipsing Dwarf Nova HT Cas

1996 ◽  
Vol 158 ◽  
pp. 269-272
Author(s):  
K. Mukai ◽  
E. M. Schlegel ◽  
J. H. Swank ◽  
T. Naylor ◽  
Janet H. Wood
Keyword(s):  
Boundary Layer ◽  
White Dwarf ◽  
X Rays ◽  
X Ray ◽  
Dwarf Nova

AbstractWe report on a 1-day ASCA observation of the eclipsing dwarf nova HT Cas. We confirm the presence of an X-ray eclipse, which is narrow and deep. The data are consistent with the X-rays originating entirely from the immediate neighborhood of the white dwarf. We draw some preliminary conclusions on the boundary layer and other relevant issues.

scholarly journals Study of Hubble Space Telescope counterparts to Chandra X-ray sources in the globular cluster M 71

2010 ◽  
Vol 513 ◽  
pp. A16 ◽  
Author(s):  
R. H. H. Huang ◽  
W. Becker ◽  
P. D. Edmonds ◽  
R. F. Elsner ◽  
C. O. Heinke ◽  
...  
Keyword(s):  
Globular Cluster ◽  
Hubble Space Telescope ◽  
Space Telescope ◽  
X Ray
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