ANISOTROPY OF COSMIC ACCELERATION

In this paper, we study the anisotropy of cosmic acceleration by dividing the Union2 Type Ia supernova (SNIa) dataset into 12 subsets according to their positions in Galactic coordinate system. In each region, we derive the deceleration parameter q0 as the diagnostic to quantify the anisotropy level in the corresponding direction, and construct q0 anisotropic maps by combining these q0 values. In addition to the monopole component, we find the significant dipole effect in the q0-maps with the amplitude [Formula: see text], which deviates from zero at more than 2-σ level. The direction of the best-fit dipole is (θ = 108.8°, ϕ = 187.0°) in Galactic system. Interesting enough, we find the direction of this dipole is nearly perpendicular to the CMB kinematic dipole, and the angle between them is 95.7°. The perpendicular relation is anomalous at the 1-in-10 level.

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ASASSN-18tb: a most unusual Type Ia supernova observed by TESS and SALT

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz1445 ◽

2019 ◽

Vol 487 (2) ◽

pp. 2372-2384 ◽

Cited By ~ 16

Author(s):

P J Vallely ◽

M Fausnaugh ◽

S W Jha ◽

M A Tucker ◽

Y Eweis ◽

...

Keyword(s):

Light Curve ◽

Power Law ◽

Type Ia Supernovae ◽

Normal Type ◽

Type Ia Supernova ◽

Type Ia ◽

Early Rise ◽

Ia Supernovae ◽

Best Fit ◽

Unusual Type

ABSTRACT We present photometric and spectroscopic observations of the unusual Type Ia supernova ASASSN-18tb, including a series of Southern African Large Telescope spectra obtained over the course of nearly six months and the first observations of a supernova by the Transiting Exoplanet Survey Satellite. We confirm a previous observation by Kollmeier et al. showing that ASASSN-18tb is the first relatively normal Type Ia supernova to exhibit clear broad (∼1000 km s−1) H α emission in its nebular-phase spectra. We find that this event is best explained as a sub-Chandrasekhar mass explosion producing $M_{\mathrm{ Ni}} \approx 0.3\,\, \rm {M}_\odot$. Despite the strong H α signature at late times, we find that the early rise of the supernova shows no evidence for deviations from a single-component power-law and is best fit with a moderately shallow power law of index 1.69 ± 0.04. We find that the H α luminosity remains approximately constant after its initial detection at phase +37 d, and that the H α velocity evolution does not trace that of the Fe iii λ4660 emission. These suggest that the H α emission arises from a circumstellar medium (CSM) rather than swept-up material from a non-degenerate companion. However, ASASSN-18tb is strikingly different from other known CSM-interacting Type Ia supernovae in a number of significant ways. Those objects typically show an H α luminosity two orders of magnitude higher than what is seen in ASASSN-18tb, pushing them away from the empirical light-curve relations that define ‘normal’ Type Ia supernovae. Conversely, ASASSN-18tb exhibits a fairly typical light curve and luminosity for an underluminous or transitional SN Ia, with MR ≈ −18.1 mag. Moreover, ASASSN-18tb is the only SN Ia showing H α from CSM interaction to be discovered in an early-type galaxy.

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Study of some parameters of modified Chaplygin gas in Galileon gravity theory from observational perspective

Canadian Journal of Physics ◽

10.1139/cjp-2014-0287 ◽

2014 ◽

Vol 92 (12) ◽

pp. 1667-1675 ◽

Cited By ~ 2

Author(s):

Chayan Ranjit ◽

Prabir Rudra ◽

Ujjal Debnath

Keyword(s):

Chaplygin Gas ◽

Cosmic Acceleration ◽

Joint Analysis ◽

Type Ia Supernovae ◽

Distance Modulus ◽

Modified Chaplygin Gas ◽

Data Set ◽

Type Ia ◽

Ia Supernovae ◽

Best Fit

We have assumed the Friedmann–Robertson–Walker model of the universe in Galileon gravity, which is filled with dark matter and modified Chaplygin gas (MCG) type dark energy. We present the Hubble parameter in terms of some unknown parameters and observational parameters with the redshift z. Some cosmological parameters are reconstructed and plots are generated to study the nature of the model and its viability. It is seen that the model is perfectly consistent with the present cosmic acceleration. From observed Hubble data (OHD) set or Stern data set of 12 points, we have obtained the bounds of the arbitrary parameters (A, B) and (A, C) by minimizing the χ2 test. Next because of joint analysis of OHD + baryonic acoustic oscillation (BAO) and OHD+BAO+CMB observations, we have also obtained the best fit values and the bounds of the parameters (A, B) and (A, C) by fixing some other parameters. The best-fit values and bounds of the parameters are obtained with 66%, 90%, and 99% confidence levels for OHD, OHD+BAO, and OHD+BAO+CMB joint analysis. Next we have also taken type Ia supernovae data set (union2 data set with 557 data points). The distance modulus μ(z) against redshift z for our theoretical MCG model in Galileon gravity have been tested for the best fit values of the parameters and the observed type Ia supernovae union2 data sample and from this, we have concluded that our model is in agreement with the union2 sample data.

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Cosmographic Evaluation of the Deceleration Parameter Using Type Ia Supernova Data

The Astrophysical Journal ◽

10.1086/423365 ◽

2004 ◽

Vol 614 (1) ◽

pp. 1-5 ◽

Cited By ~ 70

Author(s):

Moncy V. John

Keyword(s):

Deceleration Parameter ◽

Type Ia Supernova ◽

Type Ia

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Evidence for Cosmic Acceleration Is Robust to Observed Correlations between Type Ia Supernova Luminosity and Stellar Age

The Astrophysical Journal ◽

10.3847/2041-8213/ab94ad ◽

2020 ◽

Vol 896 (1) ◽

pp. L4 ◽

Cited By ~ 2

Author(s):

B. M. Rose ◽

D. Rubin ◽

A. Cikota ◽

S. E. Deustua ◽

S. Dixon ◽

...

Keyword(s):

Cosmic Acceleration ◽

Type Ia Supernova ◽

Type Ia

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Discovery and progenitor constraints on the Type Ia supernova 2013gy

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834389 ◽

2019 ◽

Vol 627 ◽

pp. A174 ◽

Cited By ~ 11

Author(s):

S. Holmbo ◽

M. D. Stritzinger ◽

B. J. Shappee ◽

M. A. Tucker ◽

W. Zheng ◽

...

Keyword(s):

Light Curve ◽

Early Time ◽

Natural System ◽

Doppler Velocity ◽

Photometric System ◽

System A ◽

Type Ia Supernova ◽

Type Ia ◽

Power Law Function ◽

Best Fit

We present an early-phase g-band light curve and visual-wavelength spectra of the normal Type Ia supernova (SN) 2013gy. The light curve is constructed by determining the appropriate S-corrections to transform KAIT natural-system B- and V-band photometry and Carnegie Supernova Project natural-system g-band photometry to the Pan-STARRS1 g-band natural photometric system. A Markov chain Monte Carlo calculation provides a best-fit single power-law function to the first ten epochs of photometry described by an exponent of 2.16+0.06−0.06 and a time of first light of MJD 56629.4+0.1−0.1, which is 1.93+0.12−0.13 days (i.e., < 48 h) before the discovery date (2013 December 4.84 UT) and −19.10+0.12−0.13 days before the time of B-band maximum (MJD 56648.5 ± 0.1). The estimate of the time of first light is consistent with the explosion time inferred from the evolution of the Si IIλ6355 Doppler velocity. Furthermore, discovery photometry and previous nondetection limits enable us to constrain the companion radius down to Rc ≤ 4 R⊙. In addition to our early-time constraints, we used a deep +235 day nebular-phase spectrum from Magellan/IMACS to place a stripped H-mass limit of < 0.018 M⊙. Combined, these limits effectively rule out H-rich nondegenerate companions.

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