14 research outputs found
The Distances of the Galactic Novae
Utilising the unique location of red clump giants on colour-magnitude
diagrams obtained from various near-IR surveys, we derived specific
reddening-distance relations towards 119 Galactic novae for which independent
reddening measurements are available. Using the derived distance-extinction
relation and the independent measurements of reddening we calculated the most
likely distances for each system. We present the details of our distance
measurement technique and the results of this analysis, which yielded the
distances of 73 Galactic novae and allowed us to set lower limits on the
distances of 46 systems. We also present the reddening-distance relations
derived for each nova, which may be useful to analyze the different Galactic
components present in the line of sight.Comment: Published in MNRAS (24 pages, 12 figures, 4 tables), Minor typo
correction. For the catalogue which has all reddening-distance relations, see
http://highenergyastro.istanbul.edu.tr/novae_cat/index.php,
2016MNRAS.461.1177
Investigation on the Orbital Period Variations of NN Ser: Implications for the Hypothetical Planets, the Applegate Mechanism and the Orbital Stability
We present 36 new mid-eclipse times obtained between 2017 and 2023 using the
T100 telescope in Turkey, extending the time span of the diagram to 25
years. Once again, these new observations show significant deviations from
previous published models that were able to explain the observed variations of
the binary period. We investigate two plausible explanations for this
variability: the LTT effect due to the presence of one or two invisible
low-mass (planetary) companion(s) in distant circumbinary orbits; other
mechanisms, like e.g. the Applegate mechanism, associated with the magnetic
cycles of the M-dwarf component of the WD+dM binary. Through MCMC analyzes, we
demonstrate that the observed variability can be explained by the
presence of a planet with a minimum mass of . This circumbinary
planet orbits around the binary system with a period of about 19.5 years,
maintaining a stable orbit for a timeline of 10 Myr. By adding a weak LTT
signal from a secondary hypothetical planet we achieve statistically better
results. However, the orbits of the bodies in a two-planet system remain stable
only for a small range of the parameter space. The energy required to power the
Applegate and other Applegate-like mechanisms is too high to explain the period
variations observed. Thus, on the one hand there is substantial evidence
supporting the existence of a planet in the NN Ser system, but on the other
hand there are also compelling indications that cast doubt on the existence of
a second hypothetical planet.Comment: 8 pages, 6 figures, 4 tables. Published in MNRAS on October 202
A New Catalogue of Galactic Novae: Investigation of the MMRD relation & Spatial Distribution
In this study, a new Galactic novae catalogue is introduced collecting
important parameters of these sources such as their light curve parameters,
classifications, full width half maximum (FWHM) of H line, distances
and interstellar reddening estimates. The catalogue is also published on a
website with a search option via a SQL query and an online tool to re-calculate
the distance/reddening of a nova from the derived reddening-distance relations.
Using the novae in the catalogue, the existence of a maximum magnitude-rate of
decline (MMRD) relation in the Galaxy is investigated. Although an MMRD
relation was obtained, a significant scattering in the resulting MMRD
distribution still exists. We suggest that the MMRD relation likely depends on
other parameters in addition to the decline time, as FWHM H, the light
curve shapes. Using two different samples depending on the distances in the
catalogue and from the derived MMRD relation, the spatial distributions of
Galactic novae as a function of their spectral and speed classes were studied.
The investigation on the Galactic model parameters implies that best estimates
for the local outburst density are 3.6 and 4.2 pc
yr with a scale height of 148 and 175 pc, while the space density
changes in the range of pc. The local
outburst density and scale height obtained in this study infer that the disk
nova rate in the Galaxy is in the range of to yr with
an average estimate yr.Comment: 24 pages, 9 figures, 6 tables; Accepted for publication in MNRAS on
13 Feb 201
Characterizing the optical nature of the blazar S5 1803+784 during its 2020 flare
We report the results from our study of the blazar S5 1803+784 carried out
using the quasi-simultaneous , , , and observations from May 2020
to July 2021 on 122 nights. Our observing campaign detected the historically
bright optical flare during MJD 59063.5MJD 59120.5. We also found the source
in its brightest (= 13.617) and faintest (= 15.888) states
till date. On 13 nights, covering both flaring and non-flaring periods, we
searched for the intraday variability using the power-enhanced test and the
nested ANOVA test. We found significant variability in 2 out of these 13
nights. However, no such variability was detected during the flaring period.
From the correlation analysis, we observed that the emission in all optical
bands were strongly correlated with a time lag of 0 days. To get
insights into its dominant emission mechanisms, we generated the optical
spectral energy distributions of the source on 79 nights and estimated the
spectral indices by fitting the simple power law. Spectral index varied from
1.392 to 1.911 and showed significant variations with time and band
magnitude. We have detected a mild bluer-when-brighter trend (BWB) during the
whole monitoring period while a much stronger BWB trend during the flare. We
also carried out a periodicity search using four different methods and found no
significant periodicity during our observation duration. Based on the analysis
during the flaring state of the source one can say that the emissions most
likely originate from the jet rather than the accretion disk.Comment: 17 pages, 8 figures, 7 tables, accepted for publication in The
Astrophysical Journal (ApJ
Multi-wavelength study of TeV blazar 1ES 1218+304 using gamma-ray, X-ray and optical observations
We report the multi-wavelength study for a high-synchrotron-peaked BL Lac 1ES
1218+304 using near-simultaneous data obtained during the period from January
1, 2018, to May 31, 2021 (MJD 58119-59365) from various instruments including
Fermi-LAT, Swift-XRT, AstroSat, and optical from Swift-UVOT TUBITAK
observatory in Turkey. The source was reported to be flaring in TeV
-ray band during 2019, but no significant variation is observed with
Fermi-LAT. A sub-hour variability is seen in the SXT light curve, suggesting a
compact emission region for their variability. However, hour scale variability
is observed in the -ray light curve. A "softer-when-brighter" trend is
observed in -rays, and an opposite trend is seen in X-rays suggesting
both emissions are produced via two different processes as expected from an HBL
source. We have chosen the two epochs in January 2019 to study and compare
their physical parameters. A joint fit of SXT and LAXPC provides a constraint
on the synchrotron peak, roughly estimated to be 1.6 keV. A clear shift
in the synchrotron peak is observed from 1 keV to above 10 keV revealing
its extreme nature or behaving like an EHBL-type source. The optical
observation provides color-index variation as "blue-when-brighter". The
broadband SED is fitted with a single-zone SSC model, and their parameters are
discussed in the context of a TeV blazar and the possible mechanism behind the
broadband emission.Comment: 13 pages, 10 figures, 5 tables, Accepted for publication in MNRA
Multiband optical variability of 3C 279 on diverse time-scales
We have monitored the flat spectrum radio quasar, 3C 279, in the optical B, V, R, and I passbands from 2018 February to 2018 July for 24 nights, with a total of 716 frames, to study flux, colour, and spectral variability on diverse time-scales. 3C 279 was observed using seven different telescopes: two in India, two in Argentina, two in Bulgaria, and one in Turkey to understand the nature of the source in optical regime. The source was found to be active during the whole monitoring period and displayed significant flux variations in B, V, R, and I passbands. Variability amplitudes on intraday basis varied from 5.20 to 17.9 per cent. A close inspection of variability patterns during our observation cycle reveals simultaneity among optical emissions from all passbands. During the complete monitoring period, progressive increase in the amplitude of variability with frequency was detected for our target. The amplitudes of variability in B, V, R, and I passbands have been estimated to be 177 per cent, 172 per cent, 171 per cent, and 158 per cent, respectively. Using the structure function technique, we found intraday time-scales ranging from ∼23 min to about 115 min. We also studied colour–magnitude relationship and found indications of mild bluer-when-brighter trend on shorter time-scales. Spectral indices ranged from 2.3 to 3.0 with no clear trend on long-term basis. We have also generated spectral energy distributions for 3C 279 in optical B, V, R, and I passbands for 17 nights. Finally, possible emission mechanisms causing variability in blazars are discussed briefly.Fil: Agarwal, Aditi. Indian Institute of Astrophysics; IndiaFil: Cellone, Sergio Aldo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Complejo Astronómico "El Leoncito". Universidad Nacional de Córdoba. Complejo Astronómico "El Leoncito". Universidad Nacional de la Plata. Complejo Astronómico "El Leoncito". Universidad Nacional de San Juan. Complejo Astronómico "El Leoncito"; ArgentinaFil: Andruchow, Ileana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Mammana, Luis Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Complejo Astronómico "El Leoncito". Universidad Nacional de Córdoba. Complejo Astronómico "El Leoncito". Universidad Nacional de la Plata. Complejo Astronómico "El Leoncito". Universidad Nacional de San Juan. Complejo Astronómico "El Leoncito"; ArgentinaFil: Singh, Mridweeka. Aryabhatta Research Institute of Observational Sciences; IndiaFil: Anupama, G. C.. Indian Institute of Astrophysics; IndiaFil: Mihov, B.. Bulgarian Academy of Sciences; BulgariaFil: Raj, Ashish. Indian Institute of Astrophysics; IndiaFil: Slavcheva Mihova, L.. Bulgarian Academy of Sciences; BulgariaFil: Özdönmez, Aykut. Tübİtak National Observatory; TurquíaFil: Ege, Ergün. Istanbul University; Turquí
Gaia Çağında Bilinen Kataklismik Değişenlerin Galaksimizdeki Dağılımları ve HR Diyagramındaki Konumları
Bu çalışmada literatürde kataklismik değişen olarak sınıflandırılmış yıldız sistemlerinin Gaia DR2 kataloğundan derlenen trigonometrik paralaksları kullanılarak, doğrusal ve geometrik yöntemler ile elde edilmiş uzaklıkları belirlenmiştir. Kataklismik değişenlerin Güneş merkezli Galaktik koordinat sistemindeki uzay dağılımları elde edilmiş ve Gaia renklerinden oluşturulan Hertzsprung-Russell (HR) diyagramındaki konumları tartışılmıştır. Galaktik düzlemden dik uzaklıkları hesaplanan kataklismik değişenler için yükseklik ölçekleri Gaia DR2’nin duyarlı astrometrik verilerinden elde edilmiştir
Optical flux and spectral characterization of the blazar PG 1553 + 113 based on the past 15 years of data
We study flux and spectral variability of the high energy peaked TeV blazar PG 1553 + 113 on diverse timescales using the data collected from 2005 to 2019 which also includes the intensive intra-night monitoring of the target. Additionally, we recorded the brightest flare of the blazar PG 1553 + 113 during April 2019 when the source attained an R-band magnitude of 13.2. Analyzing the spectral evolution of the source during the flare gave a clockwise spectral hysteresis loop and a time lag with V-band variations leading to the R-band ones. Various statistical tests, fitting procedures and cross-correlation techniques are applied to search for periodicity and examine the color-magnitude relationship. We find a median period of (2.21 ± 0.04) years along with the secondary period of about 210 days. Finally, we briefly discuss various physical mechanisms which are capable of explaining our findings.Fil: Agarwal, Aditi. Raman Research Institute; IndiaFil: Mihov, B.. Bulgarian Academy of Sciences; BulgariaFil: Andruchow, Ileana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Cellone, Sergio Aldo. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Complejo Astronómico "El Leoncito". Universidad Nacional de Córdoba. Complejo Astronómico "El Leoncito". Universidad Nacional de la Plata. Complejo Astronómico "El Leoncito". Universidad Nacional de San Juan. Complejo Astronómico "El Leoncito"; ArgentinaFil: Anupama, G. C.. Indian Institute of Astrophysics; IndiaFil: Agrawal, V.. Rmz Ecoworld; IndiaFil: Zola, S.. Jagiellonian University; PoloniaFil: Özdönmez, Aykut. Ataturk University; TurquíaFil: Ege, Ergün. Istanbul University; Turquí