14 research outputs found
Spectral Clustering for Optical Confirmation and Redshift Estimation of X-ray Selected Galaxy Cluster Candidates in the SDSS Stripe 82
We develop a galaxy cluster finding algorithm based on spectral clustering
technique to identify optical counterparts and estimate optical redshifts for
X-ray selected cluster candidates. As an application, we run our algorithm on a
sample of X-ray cluster candidates selected from the third XMM-Newton
serendipitous source catalog (3XMM-DR5) that are located in the Stripe 82 of
the Sloan Digital Sky Survey (SDSS). Our method works on galaxies described in
the color-magnitude feature space. We begin by examining 45 galaxy clusters
with published spectroscopic redshifts in the range of 0.1 to 0.8 with a median
of 0.36. As a result, we are able to identify their optical counterparts and
estimate their photometric redshifts, which have a typical accuracy of 0.025
and agree with the published ones. Then, we investigate another 40 X-ray
cluster candidates (from the same cluster survey) with no redshift information
in the literature and found that 12 candidates are considered as galaxy
clusters in the redshift range from 0.29 to 0.76 with a median of 0.57. These
systems are newly discovered clusters in X-rays and optical data. Among them 7
clusters have spectroscopic redshifts for at least one member galaxy.Comment: 15 pages, 7 figures, 3 tables, 1 appendix, Accepted by Journal of
"Astronomy and Computing
The 3XMM/SDSS Stripe 82 Galaxy Cluster Survey: Cluster catalogue and discovery of two merging cluster candidates
We present a galaxy cluster survey based on XMM-Newton observations that are
located in Stripe 82 of the Sloan Digital Sky Survey (SDSS). The survey covers
an area of 11.25 deg. The X-ray cluster candidates were selected as
serendipitously extended detected sources from the third XMM-Newton
serendipitous source catalogue (3XMM-DR5). A cross-correlation of the candidate
list that comprises 94 objects with recently published X-ray and optically
selected cluster catalogues provided optical confirmations and redshift
estimates for about half of the candidate sample. We present a catalogue of
X-ray cluster candidates previously known in X-ray and/or optical bands from
the matched catalogues or NED. The catalogue consists of 54 systems with
redshift measurements in the range of 0.05-1.19 with a median of 0.36. Of
these, 45 clusters have spectroscopic confirmations as stated in the matched
catalogues. We spectroscopically confirmed another 6 clusters from the
available spectroscopic redshifts in the SDSS-DR12. The cluster catalogue
includes 17 newly X-ray discovered clusters, while the remainder were detected
in previous XMM-Newton and/or ROSAT cluster surveys. Based on the available
redshifts and fluxes given in the 3XMM-DR5 catalogue, we estimated the X-ray
luminosities and masses for the cluster sample. We also present the list of the
remaining X-ray cluster candidates (40 objects) that have no redshift
information yet in the literature. Of these candidates, 25 sources are
considered as distant cluster candidates beyond a redshift of 0.6. We also
searched for galaxy cluster mergers in our cluster sample and found two strong
candidates for newly discovered cluster mergers at redshifts of 0.11 and 0.26.
The X-ray and optical properties of these systems are presented.Comment: 17 pages, 12 figures, accepted for publication in A&A, revised
version after language editin
Distant clusters of galaxies in the 2XMM/SDSS footprint: follow-up observations with the LBT
Context: Galaxy clusters at high redshift are important to test cosmological
models and models for the growth of structure. They are difficult to find in
wide-angle optical surveys, however, leaving dedicated follow-up of X-ray
selected candidates as one promising identification route. Aims: We aim to
increase the number of galaxy clusters beyond the SDSS-limit, z ~ 0.75.
Methods: We compiled a list of extended X-ray sources from the 2XMMp catalogue
within the footprint of the Sloan Digital Sky Survey. Fields without optical
counterpart were selected for further investigation. Deep optical imaging and
follow-up spectroscopy were obtained with the Large Binocular Telescope,
Arizona (LBT), of those candidates not known to the literature. Results: From
initially 19 candidates, selected by visually screening X-ray images of 478
XMM-Newton observations and the corresponding SDSS images, 6 clusters were
found in the literature. Imaging data through r,z filters were obtained for the
remaining candidates, and 7 were chosen for multi-object (MOS) spectroscopy.
Spectroscopic redshifts, optical magnitudes, and X-ray parameters (flux,
temperature, and luminosity) are presented for the clusters with spectroscopic
redshifts. The distant clusters studied here constitute one additional redshift
bin for studies of the L-T relation, which does not seem to evolve from high to
low redshifts. ...Comment: This is a abridged version of the paper. The full version can be
downloaded at the following URL:
https://cloud.aip.de/index.php/s/2Btv7ST1KTLHfT
The 3XMM/SDSS Stripe 82 Galaxy Cluster Survey II. X-ray and optical properties of the cluster sample
We present X-ray and optical properties of the optically confirmed galaxy
cluster sample from the 3XMM/SDSS Stripe 82 cluster survey. The sample includes
54 galaxy clusters in the redshift range of 0.05-1.2, with a median redshift of
0.36. We first present the X-ray temperature and luminosity measurements that
are used to investigate the X-ray luminosity-temperature relation. The slope
and intercept of the relation are consistent with those published in the
literature. Then, we investigate the optical properties of the cluster galaxies
including their morphological analysis and the galaxy luminosity functions. The
morphological content of cluster galaxies is investigated as a function of
cluster mass and distance from the cluster center. No strong variation of the
fraction of early and late type galaxies with cluster mass is observed. The
fraction of early type galaxies as a function of cluster radius varies as
expected. The individual galaxy luminosity functions (GLFs) of red sequence
galaxies were studied in the five ugriz bands for 48 clusters. The GLFs were
then stacked in three mass bins and two redshift bins. Twenty clusters of the
present sample are studied for the first time in X-rays, and all are studied
for the first time in the optical range. Altogether, our sample appears to have
X-ray and optical properties typical of average cluster properties.Comment: accepted for publications in MNRA
Photometric and Spectroscopic Analysis of the SX Phe Star BL Cam
In the present paper, we report the photometric and spectroscopic
observations obtained by the 1.88 m telescope at the Kottamia astronomical
observatory of the pulsating star BL Cam. Fourier analysis of the light curves
reveals that the fundamental mode has two harmonics. The O-C method is used to
establish the period changes. So far, the analysis has been very successful in
mapping the pulsation amplitude of the star across the instability strip. By
using the formalism of Eddington and Plakidis (1929), we found significant
results and strong indications of the evolutionary period change. A total of 55
new maximum light timings are reported. New values of (1/P) dP/dt are estimated
using the O-C diagram based on all newly obtained times of maximum light
combined with those taken from the literature, assuming the periods are
decreasing and changing smoothly. To compute the effective temperature and
surface gravity of the star, we performed model atmosphere analysis on its
spectra. The physical parameters of the star are calculated and compared with
the evolutionary models
SN 2018gj: A Short-plateau Type II Supernova with Persistent Blue-shifted H-alpha Emission
We present an extensive, panchromatic photometric (UV, Optical, and NIR) and
low-resolution optical spectroscopic coverage of a Type IIP supernova SN 2018gj
that occurred on the outskirts of the host galaxy NGC 6217. From the V-band
light curve, we estimate the plateau length to be ~ 70 +- 2 d, placing it among
the very few well-sampled short plateau supernovae (SNe). With V-band peak
absolute magnitude Mv < -17.0 +- 0.1 mag, it falls in the middle of the
luminosity distribution of the Type II SNe. The colour evolution is typical to
other Type II SNe except for an early elbow-like feature in the evolution of
V-R colour owing to its early transition from the plateau to the nebular phase.
Using the expanding photospheric method, we present an independent estimate of
the distance to SN 2018gj. We report the spectral evolution to be typical of a
Type II SNe. However, we see a persistent blue shift in emission lines until
the late nebular phase, not ordinarily observed in Type II SNe. The amount of
radioactive nickel (56Ni) yield in the explosion was estimated to be 0.026 +-
0.007 Msol. We infer from semi-analytical modelling, nebular spectrum, and 1-D
hydrodynamical modelling that the probable progenitor was a red supergiant with
a zero-age-main-sequence mass < 13 Msol. In the simulated hydrodynamical model
light curves, reproducing the early optical bolometric light curve required an
additional radiation source, which could be the interaction with the proximal
circumstellar matter (CSM).Comment: Accepted for publication in ApJ (31 pages, 23 figures and 7 tables
Optical intra-day variability of the blazar S5 0716+714
We present an extensive recent multi-band optical photometric observations of
the blazar S5 0716+714 carried out over 53 nights with two telescopes in India,
two in Bulgaria, one in Serbia, and one in Egypt during 2019 November -- 2022
December. We collected 1401, 689, 14726, and 165 photometric image frames in B,
V, R, and I bands, respectively. We montiored the blazar quasi-simultaneously
during 3 nights in B, V, R, and I bands; 4 nights in B, V, and R; 2 nights in
V, R, and I; 5 nights in B and R; and 2 nights in V and R bands. We also took
37 nights of data only in R band. Single band data are used to study intraday
flux variability and two or more bands quasi-simultaneous observations allow us
to search for colour variation in the source. We employ the power-enhanced
F-test and the nested ANOVA test to search for genuine flux and color
variations in the light curves of the blazar on intraday timescales. Out of 12,
11, 53, and 5 nights observations, intraday variations with amplitudes between
~3% and ~20% are detected in 9, 8, 31 and 3 nights in B, V, R, and I bands,
respectively, corresponding to duty cycles of 75%, 73%, 58% and 60%. These duty
cycles are lower than those typically measured at earlier times. On these
timescales color variations with both bluer-when-brighter and
redder-when-brighter are seen, though nights with no measurable colour
variation are also present. We briefly discuss possible explanations for this
observed intraday variability.Comment: 19 pages, 5 figures, 4 tables, Accepted for Publication in MNRA
DISCOVERY OF DRAMATIC OPTICAL VARIABILITY IN SDSS J1100+4421: A PECULIAR RADIO-LOUD NARROW-LINE SEYFERT 1 GALAXY?
We present our discovery of dramatic variability in SDSS J1100+4421 by the high-cadence transient survey Kiso Supernova Survey (KISS). The source brightened in the optical by at least a factor of three within about half a day. Spectroscopic observations suggest that this object is likely a narrow-line Seyfert 1 galaxy (NLS1) at z=0.840, however with unusually strong narrow emission lines. The estimated black hole mass of ~ 10^7 Msun implies bolometric nuclear luminosity close to the Eddington limit. SDSS J1100+4421 is also extremely radio-loud, with a radio loudness parameter of R ~ 4 x 10^2 - 3 x 10^3, which implies the presence of relativistic jets. Rapid and large-amplitude optical variability of the target, reminiscent of that found in a few radio- and gamma-ray loud NLS1s, is therefore produced most likely in a blazar-like core. The 1.4 GHz radio image of the source shows an extended structure with a linear size of about 100 kpc. If SDSS J1100+4421 is a genuine NLS1, as suggested here, this radio structure would then be the largest ever discovered in this type of active galaxie