Light Curve Timescale Research Articles

Introduction to gamma-ray burst data analysis algorithm and software tools for GECAM

The Gamma-Ray Burst (GRB) data analysis is of great importance for the research on Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM); therefore, a user-friendly software tool that covers all the requirements on GRB data analysis has been developed for users. In this paper, the framework and architectural design of GRB data analysis tools software has been described. Meanwhile, details design including the graphical user interface and command line interface were introduced, as well as its installation. The core algorithms of the GRB data analysis were clarified and outlined, including background analysis, calculations on statistical significance, duration and peak flux in given time scale of light curve, fit for deposited energy spectrum, the calculation for the association of GRBs and external trigger event, and a trigger classifier based on Native Bayesian Classification, which offers a rationale and sample for the forward GRB data analysis in GECAM.

Constraints on Earth-mass primordial black holes from OGLE 5-year microlensing events

We constrain the abundance of primordial black holes (PBH) using 2622 microlensing events obtained from 5-years observations of stars in the Galactic bulge by the Optical Gravitational Lensing Experiment (OGLE). The majority of microlensing events display a single or at least continuous population that has a peak around the light curve timescale $t_{\rm E}\simeq 20~{\rm days}$ and a wide distribution over the range $t_{\rm E}\simeq [1, 300]~{\rm days}$, while the data also indicates a second population of 6 ultrashort-timescale events in $t_{\rm E}\simeq [0.1,0.3]~{\rm days}$, which are advocated to be due to free-floating planets. We confirm that the main population of OGLE events can be well modeled by microlensing due to brown dwarfs, main sequence stars and stellar remnants (white dwarfs and neutron stars) in the standard Galactic bulge and disk models for their spatial and velocity distributions. Using the dark matter (DM) model for the Milky Way (MW) halo relative to the Galactic bulge/disk models, we obtain the tightest upper bound on the PBH abundance in the mass range $M_{\rm PBH}\simeq[10^{-6},10^{-3}]M_\odot$ (Earth-Jupiter mass range), if we employ null hypothesis that the OGLE data does not contain any PBH microlensing event. More interestingly, we also show that Earth-mass PBHs can well reproduce the 6 ultrashort-timescale events, without the need of free-floating planets, if the mass fraction of PBH to DM is at a per cent level, which is consistent with other constraints such as the microlensing search for Andromeda galaxy (M31) and the longer timescale OGLE events. Our result gives a hint of PBH existence, and can be confirmed or falsified by microlensing search for stars in M31, because M31 is towards the MW halo direction and should therefore contain a much less number of free-floating planets, even if exist, than the direction to the MW center.

Nebular-phase Spectra of Superluminous Supernovae: Physical Insights from Observational and Statistical Properties

Abstract We study the spectroscopic evolution of superluminous supernovae (SLSNe) later than 100 days after maximum light. We present new data for Gaia16apd and SN 2017egm and analyze these with a larger sample comprising 41 spectra of 12 events. The spectra become nebular within 2–4 e-folding times after light-curve peak, with the rate of spectroscopic evolution correlated to the light-curve timescale. Emission lines are identified with well-known transitions of oxygen, calcium, magnesium, sodium, and iron. SLSNe are differentiated from other SNe Ic by a prominent O i λ7774 line and higher ionization states of oxygen. The iron-dominated region around 5000 Å is more similar to broad-lined SNe Ic than to normal SNe Ic. Principal component analysis shows that five “eigenspectra” capture ≳70% of the variance, while a clustering analysis shows no clear evidence for multiple SLSN subclasses. Line velocities are 5000–8000 km s−1 and show stratification of the ejecta. O i λ7774 likely arises in a dense inner region that also produces calcium emission, while [O i] λ6300 comes from farther out until 300–400 days. The luminosities of O i λ7774 and Ca ii suggest significant clumping, in agreement with previous studies. Ratios of [Ca ii] λ7300/[O i] λ6300 favor progenitors with relatively massive helium cores, likely ≳6 , though more modeling is required here. SLSNe with broad light curves show the strongest [O i] λ6300, suggesting larger ejecta masses. We show how the inferred velocity, density, and ionization structure point to a central power source.

Timescale Stretch Parameterization of Type Ia SupernovaB‐Band Light Curves

R-band intensity measurements along the light curve of Type Ia supernovae discovered by the Cosmology Project (SCP) are fitted in brightness to templates allowing a free parameter the time-axis width factor w identically equal to s times (1+z). The data points are then individually aligned in the time-axis, normalized and K-corrected back to the rest frame, after which the nearly 1300 normalized intensity measurements are found to lie on a well-determined common rest-frame B-band curve which we call the composite curve. The same procedure is applied to 18 low-redshift Calan/Tololo SNe with Z < 0.11; these nearly 300 B-band photometry points are found to lie on the composite curve equally well. The SCP search technique produces several measurements before maximum light for each supernova. We demonstrate that the linear stretch factor, s, which parameterizes the light-curve timescale appears independent of z, and applies equally well to the declining and rising parts of the light curve. In fact, the B band template that best fits this composite curve fits the individual supernova photometry data when stretched by a factor s with chi 2/DoF ~;~; 1, thus as well as any parameterization can, given the current data sets. The measurement of the data of explosion, however, is model dependent and not tightly constrained by the current data. We also demonstrate the 1 + z light-cure time-axis broadening expected from cosmological expansion. This argues strongly against alternative explanations, such as tired light, for the redshift of distant objects.