Optical and near-infrared observations of Type Ia SN 2018gv from early phase
Yun JeUng, Koji S. Kawabata, Masayuki Yamanaka, Miho Kawabata, Tatsuya Nakaoka(Hiroshima University)

1. Introduction
It is widely known that type Ia supernovae (SNe Ia) areused to measure the distances of their host galaxies.
However, It is still lack to understand the detail of theprogenitor systems and explosion mechanisms, as well
as how differences in initial conditions create the diversity
in observed properties of SNe Ia. To solve theseproblems, and others, detailed multi-band observations ofmany hundreds of SNe Ia are required.
Recently, diversities of the color evolution in early phaseof SNe Ia were reported (Jiang et al. 2018; Stritzinger etal. 2018). Near-infrared properties of SNe Ia are still
ambiguous (Yamanaka et al. 2016, but see also Li et al.
2019). In this poster, we present light curve, color
evolution, and spectra of Type Ia SN2018gv, andcompare with other SNe Ia.
From these information, we mention multi-band (BVRIJHKs-bands) and spectra properties of the SN2018gv fromIts early phase.
Reference :http://www.k-itagaki.jp/
https://wis-tns.weizmann.ac.il/object

2. Color evolution comparison
Filled circles : SN2018gv
Open circles : SN2011fe• The overall shape of color evolution of theSN2018gv and the SN2011fe seems to be similar.
• In the case of V-I color evolution, the slope ofSN2018gv is quite steeper than the slope ofSN2011fe after 40days from B-band maximum.
• It is very interesting that SNe show the samecolor evolution although there is the diversity in therising time of the light curve. We think that thisphenomenon should be related to explosion model(For example, the 56Ni distribution is strongly
mixed up, but the mixing is rather predicted fromthe double-detonation model, not consistent withthe standard delayed detonation.)• The period of inclination change in the V-I color
evolution is same with the time when the third
peaks is appeared in the near-infrared wavelength.
• In the Yang et al. 2019, the r-i color evolution
also shows a peculiar bump during the third peak
period.
• The steep V-I color inclination and peculiar
bumps are appeared in SN2000cx which is aluminous and peculiar type Ia supernova.
Therefore, we guess the third peaks are also
appeared in the type Ia supernova which shows
peculiar color evolution such as SN 2000cx.

Fig 1. PSN2018gv
RA : 08:05:34.610
DEC : -11:26:16.30
Redshift : 0.0053
Discovery date : 2018 January 15
Discovery Magnitude : 16.5
Discoverer : Koichi Itagaki

2. Research method

Fig 5. Color evolution comparison

3. Spectral evolution• After the maximum light, Fe II 5169Å begins todevelop. Fe II 5169Å is narrow rather than SN
2011fe. After 2 weeks later from the maximum light,Fe II 6500Å shows broad emission in the SN2018gv.
• Based on the EW of Si lines, the SN 2018gv islocated near the boundary between SS and CNsubclass. The CN subclass indicates normal typeIa supernova. Moreover, luminous type Ia
supernovae such as SN 1999T and SN 1999aa
belong to SS subclass.
• In the result of the Si II 6355Å velocity gradientversus ∆m15(B), the SN 2018gv belong to lowvelocity-gradient (LVG) sub-group.
• The result of SI line depth ratio compared to∆m15(B) shows that the SN 2018gv is located near
the SN 1991T which is luminous type Ia supernova.
As a result, the SN 2018gv is LVG sub-groip typeIa supernova, and it shows very similar silicon line
properties with luminous type Ia supernova like SN1991T.

1. Observation• We observed the SN2018gv through 1.5m-Kanata
telescope from 2018 January 17th to May 14th.
• We got BVRIJHKs-bands and optical spectra.
• Resolution of the 1.5m-Kanata telescope is R=400 andcoverage is 4500-9000A.

2. Light curve• We got light curves through processes of PSF photometryand sigma clipping in IRAF.
• We used reference star magnitudes from the AAVSO andthe 2MASS catalogues to calibrate the magnitude.

Fig 2. 1.5m - Kanata telescope
3. Spectra• We performed the data reduction according to the standard
procedure using IRAF.
• Due to the red shift effect of host galaxy, we have to convert theobserved wavelength into the rest wavelength.
Reference : http://hasc.hiroshima-u.ac.jp/telescope/kanatatel-e.html

Fig 6. Spectral evolution

Fig 7. Sub-class of type Ia supernova
4. Third peaks in the near-infrared• The third peaks in the near-infrared wavelengthappear after 50 days from B-band maximum.
When I matched data from Hubble Space
Telescope (HST) to my light curves, the data show
similar tendency. Because the HST is very
powerful telescope and less affected byatmosphere, this is one of the strong evidence thatthe third peak is real.
• According to the Wood-Vasey et al. 2008, theinclination of light curves do not change after thesecond peak. However, the inclination of my light
curve is changed after the third peaks.
• When I combined UV and NIR data, themagnitude shows quite constant tendency.
Because UV re-brightening in NIR, this result isreasonable.

3. Results & Discussion
1. Light curve of SN2018gv
Filled circles : SN2018gv
Open circles : SN2011fe• The decline rates of the B and V-bands maximum
are ∆m15(B) ∼0.97, and ∆m15(V) ∼0.7.
• There are prominent first and second peaks inI,J,H,Ks bands.
• Magnitudes of H and Ks-bands increase around60~70 days.
→ This increased magnitude suggest that the thirdpeaks are existed in the near-infrared wavelength.
•The second peaks of the I, J, H, and Ks-bands are
25days, 35days, 27days, and 24days after B-band
maximum respectively.
• The absolute magnitude of SN 2018gv is 19,006±0.05mag.
• Through the Phillips relations, we can estimate theabsolute magnitude from Å Å ∼0.97. The estimatedabsolute magnitude is -19.3±0.15mag. Thus, the SN
2018gv shows a little bit faint absolute magnitude.
• Although the overall light curve shapes of SN2018gv
and SN2011fe seem to be similar around the B-band
maximum date, the magnitudes show somedifferences in the late phase.
→ The SN2011fe is one of the most famous typicaltype Ia supernova. Although the SN 2018gv shows
similar light curve shapes in the maximum date, theSN 2018gv shows some differences in the late phase.
Thus, we suggest that SN2018gv is a transient type Ia
supernova.
• We successfully derived very long coverage nearinfrared light curves.
• The time between first and second peaks is
proportional to the luminosity. Thus, the SN 2018gv
shows features of luminous type Ia supernova.

Fig 8. Inclination change

4. Conclusion

Fig 3. Light curve comparison• The absolute magnitude of SN 2018gv is -19,006 mag. This value is different with the estimatedabsolute magnitude from ∆m15(B) by using the Phillips relation,• From the light curve data such as color evolution, time between first and second peak in the nearinfrared light curves, the SN 2018gv shows some features of luminous type Ia supernova.
• In the spectrum data such as subclass which is located between SS (bright group) and CN (normalgroup), ratio of EW of Si II 5972 and 6355, the SN 2018gv shows normal and luminous type Iasupernova features.
a• We successfully derived very long coverage light curves in the near-infrared wavelength. Moreover,
we observed third peaks in the near-infrared wavelength which are expected only in theoreticalresearch.
• Various telescopes (Kanata, HST, Swift, and LCO network) shows similar tendency for the thirdpeaks. Besides, light curves changes also prove that the third peaks are real.

Fig 4. Near-infrared light curve• The third peaks may be observed from 02es-like SN or SN which has peculiar color evolution suchas SN 2000cx.