| Supernovae,one of the most violent astrophysics phenomena in the universe,are the end of the evolution of some stars,meaning that a star completely collapses,with a peak luminosity comparable to that of an entire galaxy,and it would last for weeks or months before it disappears.As one of the supernovae,Type Ia supernovae(SNe Ia)have no hydrogen nor helium lines in their spectra.They are the producers of most of the iron group elements in the universe,driving the evolution of element abundance in galaxies.In addition,SNe Ia can be used as "standard candle" to measure the distance of extragalactic galaxies.In the early 2000 s,astronomers discovered the universe is expanding at an accelerating rate by using SN Ia and won the Nobel Prize in physics,spurring the need for a large sample of observations of SNe Ia.Current theories suggest that SNe Ia are triggered by a white dwarf,of which the mass has reached the Chandrasekhar mass limit,and the models are mainly single degenerate model and double degenerate model.The mechanism of SNe Ia and its progenitor star system are still controversial,which directly affects the accuracy of measuring the distance of distant objects in the universe.Different models and mechanisms of SNe Ia progenitor differ significantly in the early phase,and we expect to distinguish them by the photometry and the spectra of supernovae in the early phase.Therefore,we need to get more,earlier,and more accurate observations of SNe Ia.One of the important goals of the Si Tian Project promoted by National Astronomical Observatories,Chinese Academy of Sciences(NAOC)is to study the explosion mechanism of the SNe Ia.It requires high-frequency sampling to obtain the very early observation data of SNe Ia.As part of the pre-preparation project for the Si Tian Project,photometric and spectroscopic observations of the SNe Ia SN 2021 hpr,discovered on April 2,2021,were conducted.The spectroscopic observation was made with the 2.16 m telescope operated by the Xing Long Observatory,NAOC,and the photometric observation was conducted with the 60 cm telescope at Xing Long Observatory,NAOC.The observation,which began on April 4,2021,covers the phases from-14.37 days to + 63.68 days relative to the maximum luminosity in B-band,with photometric data of 26 nights and 6 spectra.The first spectrum we observed is the earliest one among all available spectra of SN 2021 hpr in public.Compared with the spectra of the typical SNe Ia SN2011 fe at the same phases,we find that the Si II ?6355 in the first spectrum of SN 2021 hpr we observed has a higher velocity,but the other spectra are similar to SN 2011 fe.Besides,the light curves of SN 2021 hpr are similar to other SNe Ia,and it can thus be inferred that SN 2021 hpr is a typical SNe Ia.SN 2021 hpr is located in one of the spiral arms of the host galaxy NGC3147 with redshift of 0.009346.In total,astronomers have observed 6supernovae in NGC 3147 between 1972 and 2022.Based on the estimates of the supernova explosion rate from its radio data,it shows that the supernova explosion rate in NGC 3147 in the last 50 years is slightly higher than that expected for SNe Ia,but lower for SNe Ibc and SNe II.The spectra show that the metal abundance around SN 2021 hpr is relatively rich,which is similar to that of the Sun.Finally,we calculate the maximum magnitude of SN 2021 hpr in B-band using the Phillips relation and obtain the distance modulus(m-M)of Galaxy NGC 3147(33.46 ± 0.11 mag)by a completely independent method.This result is close to those obtained by other people using different methods. |
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