Supernova 2018aoq and a distance to Seyfert galaxy NGC 4151

TL;DR

This paper reports optical observations of SN 2018aoq, a Type II-P supernova in NGC 4151, and estimates the galaxy's distance using multiple methods, finding results consistent with geometric measurements.

Contribution

It provides detailed photometric and spectroscopic data of SN 2018aoq and applies two distance estimation methods to determine NGC 4151's distance.

Findings

Distance estimates of 20.0 ± 1.6 Mpc and 16.6 ± 1.1 Mpc from different methods.

Results are consistent with geometric distance measurements for NGC 4151.

SN 2018aoq exhibits typical Type II-P supernova features and intermediate brightness.

Abstract

We present optical photometric observations of SN 2018aoq from 2 to 100 days after explosion, and 7 spectra at epochs from 11 to 71 days. The light curves and spectra are typical for SNe II-P. As previously reported, SN 2018aoq appears to be of intermediate brightness between subluminous and normal SNe II-P. SN 2018aoq was discovered in Seyfert galaxy NGC 4151, for which the distance is uncertain. We utilised the Expanding Photosphere Method using three sets of filter combinations and velocities derived from the absorption minima of FeII lines and obtained a distance of 20.0 +-1.6 Mpc. The Standard Candle Method applied to SN 2018aoq yields a distance of 16.6 +-1.1 Mpc. Both values are consistent with the distance measurements for NGC 4151 based on geometric method.

Figures

Tables

Table 1. Table 1: The EPM quantities derived for SN 2018aoq. The uncertainties are in parentheses.

JD	Phase,	$v$(FeII$\lambda$5018)	$v$(FeII$\lambda$5169)	$T_{\mathrm{col}}\left(BVI\right)$	$\zeta$	$\theta$
2458200+	days	km s-1	km s-1	K		${10}^{-11}$ rad
34.36	26.4	3529 (140)	3893 (154)	7022 (225)	0.662	1.62 (0.11)
35.33	27.3	3529 (234)	3893 (231)	6968 (212)	0.667	1.63 (0.10)
46.35	38.4	3125 (185)	3083 (183)	6245 (181)	0.747	1.80 (0.12)
52.45	45.5	2707 (108)	2680 (106)	5975 (184)	0.786	1.88 (0.14)
56.40	48.4	2706 (108)	2666 (106)	5703 (187)	0.833	1.95 (0.17)
79.39	71.4	1903 (75)	1862 (90)	5365 (135)	0.905	1.94 (0.13)

Table 2. Table 2: The EPM distances for SN 2018aoq. The uncertainties are in parentheses.

Filter set	FeII line	$D$, Mpc	$t_0$, JD 2458000+
$BVI$	5018	21.4 (2.6)	200.3 (5.5)
$BVI$	5169	19.4 (1.7)	205.8 (3.2)
$BVI$	Average	20.2 (2.1)	203.5 (4.3)
$BV$	5018	19.9 (3.9)	203.3 (7.7)
$BV$	5169	19.7 (3.6)	204.3 (6.5)
$BV$	Average	20.0 (3.9)	203.3 (7.6)
$VI$	5018	21.0 (3.3)	199.2 (7.0)
$VI$	5169	19.1 (2.2)	204.6 (4.4)
$VI$	Average	19.8 (2.7)	202.4 (5.6)

Table 3. Table 3: U ​ B ​ V ​ R ​ I 𝑈 𝐵 𝑉 𝑅 𝐼 UBVRI magnitudes of local standard stars

$\alpha$(J2000)	$\delta$(J2000)	$U$	$B$	$V$	$R$	$I$	References
12:09:53.538	39:26:00.15	11.68	9.76	8.15			1
12:10:31.442	39:26:41.26	13.24	12.47	11.45	10.92	10.44	1,2,3
12:10:25.255	39:23:55.45		15.08	14.38	13.99	13.66	3
12:10:38.529	39:20:29.56	15.61	14.01	12.77	12.10	11.50	1,2

Table 4. Table 4: U ​ B ​ V ​ R ​ I 𝑈 𝐵 𝑉 𝑅 𝐼 UBVRI magnitudes of SN2018aoq

JD	Phase,	$U$	${\sigma }_U$	$B$	${\sigma }_B$	$V$	${\sigma }_V$	$R$	${\sigma }_R$	$I$	${\sigma }_I$	Telescope
2458000+	days
209.46	1.5			15.59	0.04	15.73	0.04	15.49	0.06	15.82	0.09	K70
213.30	5.3			15.51	0.06	15.44	0.08	15.28	0.05			M20
213.39	5.4			15.44	0.04	15.47	0.03	15.29	0.03	15.16	0.04	C50
213.42	5.4			15.30	0.04	15.43	0.04	15.23	0.08	15.22	0.05	C60
214.39	6.4			15.32	0.04	15.43	0.05	15.20	0.04	15.16	0.04	C60
215.32	7.3	14.52	0.05	15.28	0.04	15.40	0.04	15.19	0.04	15.15	0.04	C60
216.33	8.3	14.57	0.05	15.33	0.04	15.42	0.03	15.21	0.04	15.16	0.04	C60
217.32	9.3	14.58	0.07	15.45	0.05			15.26	0.03	15.21	0.04	C60
217.52	9.5	14.77	0.05	15.54	0.04	15.46	0.03	15.24	0.04	15.23	0.04	T60
218.36	10.4	14.79	0.05	15.44	0.04	15.46	0.04	15.25	0.04	15.20	0.04	C60
219.35	11.4	14.84	0.05	15.50	0.04	15.50	0.04	15.24	0.04	15.20	0.04	C60
220.27	12.3							15.26	0.05	15.25	0.09	M20
221.33	13.3	15.14	0.14	15.50	0.06	15.51	0.03	15.22	0.03	15.14	0.04	C60
222.34	14.3	15.20	0.13	15.55	0.05	15.53	0.03	15.16	0.05	15.17	0.03	C60
223.28	15.3					15.52	0.05	15.24	0.05	15.13	0.09	M20
224.31	16.3	15.36	0.05	15.67	0.04	15.52	0.03	15.22	0.03	15.15	0.03	C60
230.36	22.4	16.18	0.06	16.06	0.04	15.63	0.03	15.29	0.03	15.15	0.03	C60
231.36	23.4			16.17	0.04	15.68	0.03	15.32	0.04	15.17	0.03	C50
232.30	24.3			16.22	0.04	15.70	0.04	15.33	0.04	15.17	0.04	M70
232.34	24.3			16.25	0.04	15.68	0.03	15.33	0.04	15.18	0.03	C50
234.28	26.3					15.66	0.03			15.21	0.03	A60
235.25	27.2			16.34	0.07	15.67	0.03	15.37	0.03			A60
235.35	27.4			16.33	0.05	15.69	0.04	15.34	0.03	15.19	0.04	C50
236.29	28.3	16.70	0.06	16.32	0.04	15.67	0.04	15.33	0.03	15.19	0.04	T60
236.30	28.3			16.38	0.06	15.70	0.04	15.34	0.04	15.15	0.04	C50
236.47	28.5			16.35	0.04	15.70	0.03	15.35	0.03	15.13	0.04	M70
237.30	29.3			16.42	0.04	15.67	0.03	15.34	0.03	15.16	0.04	C50
240.31	32.3			16.42	0.05	15.72	0.04	15.29	0.05	15.14	0.05	C50
241.26	33.3					15.76	0.04	15.39	0.03	15.17	0.03	A60
241.34	33.3			16.49	0.04	15.70	0.03	15.35	0.03	15.13	0.03	C50
242.28	34.3			16.51	0.04	15.71	0.04	15.35	0.04	15.09	0.04	M70
242.32	34.3			16.50	0.04	15.72	0.03	15.33	0.03	15.13	0.03	C50
243.32	35.3			16.51	0.04	15.71	0.03	15.32	0.03	15.11	0.03	C50
245.34	37.3	17.05	0.06	16.56	0.04	15.69	0.04	15.32	0.04	15.10	0.05	C60
246.28	38.3			16.58	0.04	15.70	0.03	15.33	0.04	15.08	0.04	M70
246.41	38.4			16.66	0.06	15.73	0.04	15.29	0.04	15.11	0.04	A60
249.31	41.3			16.58	0.05	15.71	0.03	15.30	0.04	15.11	0.04	M70
249.38	41.4			16.61	0.04	15.70	0.04	15.29	0.03	15.10	0.04	T60
250.32	42.3			16.60	0.04	15.68	0.03	15.32	0.04	15.08	0.05	M70
253.37	45.4			16.66	0.04	15.74	0.06	15.32	0.05	15.02	0.04	A60
254.35	46.4			16.64	0.05	15.68	0.04	15.28	0.03	15.02	0.04	M70
255.42	47.4					15.72	0.05	15.33	0.05	15.11	0.03	A60
256.35	48.4			16.60	0.04	15.74	0.04	15.33	0.05	15.05	0.04	A60
257.36	49.4			16.68	0.03	15.78	0.04	15.36	0.04	15.03	0.04	A60
260.34	52.3			16.77	0.04	15.73	0.03	15.31	0.04	15.04	0.05	M70
262.30	54.3			16.86	0.05	15.73	0.04	15.31	0.04	15.05	0.04	M70
263.33	55.3			16.87	0.05	15.74	0.04	15.26	0.04	14.98	0.05	M70
264.32	56.3			16.79	0.05	15.74	0.03	15.30	0.03	15.05	0.04	M70
267.34	59.3			16.85	0.05	15.77	0.04	15.33	0.03	15.05	0.05	M70
271.31	63.3			16.98	0.05	15.78	0.04	15.32	0.03	15.07	0.05	M70
271.38	63.4			16.87	0.04	15.77	0.03	15.31	0.03	15.01	0.03	S100
272.31	64.3			16.93	0.04	15.79	0.05	15.32	0.05	15.05	0.04	S100
273.35	65.4			16.91	0.05	15.79	0.06	15.34	0.05	15.05	0.05	S100
275.27	67.3			16.88	0.05	15.81	0.07			15.02	0.03	A60
277.27	69.3			16.95	0.05	15.82	0.04	15.34	0.03	15.06	0.04	S100
278.30	70.3			16.97	0.05	15.85	0.05	15.37	0.05	15.09	0.04	S100
282.31	74.3			17.05	0.06	15.87	0.08	15.42	0.05	15.06	0.03	A60
283.29	75.3			17.02	0.04	15.83	0.04	15.36	0.04	15.05	0.04	S100
283.33	75.3					15.84	0.04	15.32	0.04	15.02	0.04	M70
284.29	76.3			16.94	0.05	15.84	0.04	15.37	0.04	15.07	0.05	S100
285.35	77.4			17.10	0.07	15.86	0.07	15.42	0.05	15.00	0.05	A60
285.37	77.4			17.05	0.06	15.80	0.03	15.32	0.03			M70
288.32	80.3					15.85	0.05	15.32	0.07	15.05	0.11	M70
290.32	82.3					15.87	0.06	15.36	0.06			M70
299.30	91.3			17.15	0.05	15.98	0.04	15.48	0.04	15.18	0.04	S100
308.44	100.4					15.97	0.12	15.50	0.05	15.11	0.11	S100

Table 5. Table 5: Journal of spectroscopic observations of SN 2018aoq

JD 2458200+	Phase	Exp. time (s)	CCD binning
19.34	11.3	900	8x8
34.36	26.4	3600	4x4
35.33	27.3	1200	8x8
46.35	38.4	1800	8x8
52.45	44.5	3600	4x4
56.40	48.4	3600	4x4
79.39	71.4	3600	4x4

Full text

††pubyear: 2019††pagerange: Supernova 2018aoq and a distance to Seyfert galaxy NGC 4151–5

1 Introduction

NGC 4151 is well-known Seyfert 1 galaxy, one of the nearest galaxies with active nucleus.

NGC 4151 is one of the rare objects for which there exist two independent dynamical measurements for the mass of the central black hole. To first order, the black hole mass derived by the stellar dynamical modeling depends linearly on the assumed distance to the galaxy (Onken et al., 2014).

However, the actual distance to the galaxy is rather uncertain.

The Extragalactic Distance Database (Tully et al., 2009) presents distance measurements based on the Tully-Fisher relation: the individual estimate for NGC 4151 is 3.9$\pm$0.4 Mpc, and the group-average distance is 11.2$\pm$1.1 Mpc. The reability of these distance estimates are doubtful, as discussed by Onken et al. (2014).

The methods based on the reprocessing of the emission of the active nucleus provided much larger distances: 19 Mpc (Cackett et al., 2007) and 29 Mpc (Yoshii et al., 2014). Hönig et al. (2014) applied a geometric method, measuring the size of region of hot dust emission as determined from time-delays and infrared interferometry, which yielded 19.0$\pm$2.5 Mpc.

The discovery of a type II-P supernova (SN) 2018aoq in NGC 4151 presents a new possibility to obtain an independent estimate of the distance to the galaxy.

The optical transient Kait-18P=2018aoq was discovered on 2018-04-01.4316 by the Lick Observatory Supernova Search at the unfiltered magnitude of 15.3 at a distance of 73″ from the center of NGC 4151. Spectroscopic observations with the 1.5-m Kanata telescope classified the transient as a Type II supernova111https://wis-tns.weizmann.ac.il/search.

Observations of type II-P SNe can be used to determine distances to their host galaxies using the Expanding Photosphere Method (EPM), which was first developed by Kirshner & Kwan (1974). The method is based on measuring the angular radius of the photosphere from photometric data and comparing the resulting expansion rate to the velocity extracted from the spectral data. The EPM provides estimates of distance independent of extragalactic distance ladder. The method requires high-quality spectroscopic and photometric monitoring of SNe and was applied mostly to nearby objects (e.g., Hamuy et al., 2001; Takáts & Vinkó, 2006; Jones et al., 2009; Bose & Kumar, 2014), although recently it became possible to perform the EPM on SNe at cosmologically significant redshifts (e.g., Gall et al., 2016; Gall et al., 2018). The other method for distance determinations using SNe II-P is the Standardized Candle Method (SCM) (Hamuy & Pinto, 2002), based on a correlation between the luminosity and the expansion velocity of SNe during the plateau phase. This method relies on the local distance calibrators and yields distances that are in reasonable agreement with the EPM (e.g., Nugent et al., 2006; Poznanski et al., 2009; Olivares E. et al., 2010; Gall et al., 2018).

2 Observations

Photometric $UBVRI$ CCD observations of SN 2018aoq were carried out at the 60-cm and 50-cm telescopes of Crimean Observatory of Sternberg Astronomical Institute (SAI), the 70-cm and 20-cm telescopes of Moscow Observatory of SAI, the 1-m telescope of Institute of Astronomy of Russian Academy of Science (INASAN) at Simeiz Observatory, the 60-cm telescope of Stará Lesná Observatory of the Astronomical Institute of Slovak Academy of Science, and the 60-cm telescope of Shamakhy Astrophysical Observatory.

The standard image reductions and photometry were made using the IRAF222IRAF is distributed by the National Optical Astronomy Observatory, which is operated by AURA under cooperative agreement with the National Science Foundation..

The magnitudes of the SN were derived by a PSF-fitting relatively to a sequence of local standard stars, which were calibrated by Lyutyi (1973), Doroshenko et al. (2005), and Roberts & Rumstay (2012). The photometry was transformed to standard Johnson-Cousins $UBVRI$ magnitudes by means of instrumental colour-terms.

The surface brightness of the host galaxy at the location of the SN is not very high, nevertheless we checked if the galaxy background affects the photometry. We used the images obtained before SN outburst at the Shamakhy Observatory for galaxy subtraction. We found that for most of the images the effect of galaxy background does not exceed the errors of magnitudes, but for the 50-cm telescope of SAI it may amount to 0.05-0.1 mag. We applied galaxy subtraction for all images obtained with this telescope.

The magnitudes of standard stars are presented in Table  3, the photometric data are presented in Table LABEL:tab:photometry.

Prediscovery observations were reported by Nazarov et al. (2018). We carried out photometry on their images, using our local standard stars and applying galaxy subtraction, and obtained new magnitude estimates, which are also reported in Table LABEL:tab:photometry. The light curves are shown in Fig. 1

The shape of the light curves is typical for SNe II-P. The first observations were obtained on the rising part of the light curves, and we can determine the epoch when the SN reached the plateau phase as JD 2458215$\pm$1 (April 6). Yamanaka et al. (2018) obtained images of NGC 4151 on JD 2458209.0 (March 31.5) and derived an upper limit of 17.5 mag in the $R$-band, O’Neill et al. (2019) reported that the SN was fainter than 18.89 mag in the ’orange’ ATLAS filter on JD 2458206.97 (March 29). We used a polynomial fit to the $R$-band magnitudes on the rise and found that the best estimate for the epoch of explosion is JD 2458208$\pm$1, 7 days before start of the plateau. This value of rise time is in agreement with the average rise time for SNe II-P reported by Gall et al. (2015).

The blue colour of SN 2018aoq at maximum and the absence of detectable interstellar lines in the spectra allows to conclude that the absorption in the host galaxy was negligible. The galactic extinction is small $E(B-V)_{gal}=0.02$ mag (Schlafly & Finkbeiner, 2011). O’Neill et al. (2019) compared the colour curves of SN 2018aoq to those of type II-P SNe for which the extinction is well-known, and derived the total extinction for SN 2018aoq $E(B-V)_{tot}=0.04$ mag, only slightly larger than $E(B-V)_{gal}$. We used $E(B-V)_{tot}=0.04$ for all further calculations.

Spectroscopic observations were obtained at the 2-m telescope of Shamakhy Astrophysical Observatory. The modified Universal Astronomical Grating Spectrograph provided the wavelength range of 3900 – 7000 Å with a dispersion of 115Å mm*-1*, which corresponds to 4.1 or 8.2 Å pixel*-1* for different CCD binning. The journal of spectroscopic observations is presented in Table 5, the spectra are shown in Fig. 2.

We continue the observations of SN 2018aoq, the complete set of data and its analysis will be presented in a separate paper.

3 The EPM distance

The Expanding Photosphere Method (EPM) (Kirshner & Kwan, 1974) determines a distance $D$ to the SN from the relation $\theta=R/D$, where $\theta$ is the angular radius of photosphere, $R$ is its linear radius.

The method can be applied if the ejecta is spherically symmetric, the envelope undergoes free expansion, so that the velocity of matter $v$ and the radial distance $r$ are connected by $v=r/(t-t_{0})$, where $t_{0}$ is the zero-point time, which might be offset from the true moment of explosion.

The photospheric flux of SN is described by a modified Planck spectrum $F_{\nu}(R)=\zeta^{2}\pi B_{\nu}(T_{\rm col})$, where $\zeta$ is the correction factor, $T_{\rm col}$ is the colour temperature, $B_{\nu}(T_{\rm col})$ is the Planck function.

The description of the EPM is presented in a number of papers, (e.g., Hamuy et al., 2001; Takáts & Vinkó, 2006; Jones et al., 2009; Gall et al., 2018). We applied the EPM following the prescriptions of Hamuy et al. (2001).

The correction factor $\zeta$ cannot be determined from observations. The empirical relations between $\zeta$ and $T_{\rm col}$ were established by Eastman et al. (1996) and Dessart & Hillier (2005). We used the relation by Dessart & Hillier (2005), which is confirmed by our research (Baklanov, in prep.) and by Vogl et al. (2018).

We used three sets of filter combinations to derive the temperature and angular radius of SN photosphere. The errors in quantities $\theta$ and $T_{\rm col}$ were estimated using Monte Carlo technique. Samples of data points were drawn from normal distributions of uncertainty in the photometric fluxes.

The velocity of matter at the photosphere $v_{\rm ph}$ can be measured by the blueshift of weak absorption lines, the lines of FeII $\lambda$5018Å  and $\lambda$5169Å  are used more often (Takáts & Vinkó, 2012). The observed spectra were corrected for the redshift of the galaxy $z=0.00332$333https://ned.ipac.caltech.edu/ and continuum subtracted, using polynome fitting with the SNID package (Blondin & Tonry, 2007). The spectra were smoothed with a Savitzky-Golay filter (Savitzky & Golay, 1964) and wavelengths of absorption minima were determined. The uncertainties of velocity measurements were estimated to be in the range of 4–6%, depending on the spectral resolution and photon statistics of the detector.

The computations were carried out for three sets of filter combinations: $BVI$, $BV$, and $VI$, for the velocities derived from the lines FeII$\lambda$5018, $\lambda$5169 and for the average velocities.

Table  1 presents the basic EPM quantities. $T_{\rm col}$, $\zeta$ and $\theta$ are given only for the $BVI$ filter set, for other sets they are similar.

The ratio $\theta/v$ as a function of time for the filter sets $BVI$, $BV$, and $VI$ is presented in Fig. 3.

We determined $t_{0}$ and $D$ using the Markov Chain Monte Carlo method in the EMCEE software package (Foreman-Mackey et al., 2013).

The results are presented in Table 2.

4 The SCM distance

The Standardized Candle Method (SCM) (Hamuy & Pinto, 2002) is based on a correlation between the absolute brightness of SNe II-P and the expansion velocities derived from the minimum of the FeII P-Cygni feature observed during the plateau phase.

We used our estimates of expansion velocity from the shift of FeII$\lambda 5169$ line and photometry in the $VI$ bands and applied the SCM using the calibration by Polshaw et al. (2015), based on the Cepheid distances to well-observed SNe II-P. We obtain distance estimates $D_{V}=16.7\pm 1.4$ Mpc, $D_{I}=16.5\pm 1.3$ Mpc, and the average $D=16.6\pm 1.1$ Mpc.

5 Discussion

All distance estimates presented in Table 2 are consistent with each other, and we may accept the average value $D=20.0\pm 1.6$ Mpc as the EPM distance for SN 2018aoq and NGC 4151, which is in good agreement with the result of Hönig et al. (2014).

The estimates of $t_{0}$ are earlier than the explosion epoch derived from photometry, but for most of the data the difference does not exceed the uncertainties. We should note that the epoch $t_{0}$ from the EPM fit may be offset from the explosion date (Takáts & Vinkó, 2006).

Recently O’Neill et al. (2019) utilised the SCM method for SN 2018aoq as calibrated by Polshaw et al. (2015) to obtain a distance of $18.2\pm 1.2$ Mpc. Our SCM distance is about 9% shorter than the result of O’Neill et al. (2019), because of small differences in the observational data.

The expansion velocity of SN 2018aoq is low, about 2600 km s*-1* at 50 days past explosion. The luminosity at the plateau is $M_{I}=-16.4$ mag for the EPM distance, and $M_{I}=-16.0$ mag for the SCM distance. SN 2018aoq appears to be an intermediate object between subluminous and normal SNe II-P, as was suggested by O’Neill et al. (2019).

The distance measurements by the EPM and SCM may have systematic errors, for the EPM they result from the adopted values of dilution factor $\zeta$, which may also be a function of chemical composition and density structure of the envelope. Other reasons for uncertainty are the difference of photospheric velocity from that derived from the FeII lines and absence of spherical symmetry of the ejecta. The major sources of errors for the SCM are the calibration process and the internal diversity of the properties of SNe II-P.

In the case of SN 2018aoq the SCM distance is about 18% shorter than the EPM distance, but both values are consistent with the most reliable distance estimate for the host galaxy $D=19.0\pm 2.5$ Mpc, based on geometric technique (Hönig et al., 2014).

We may conclude that these results confirm the applicability of SNe II-P for distance measurements.

Acknowledgements

The work of D.Tsvetkov and P.Baklanov was partly supported by the Russian Science Foundation Grant No. 16-12-10519. The work of S.Shugarov was partially supported by Grants VEGA 2/0008/17 and APVV-15-0458. The work of I.Volkov was supported by the scholarship of the Slovak Academic Information Agency (SAIA), by the Russian Science Foundation Grant No. 14-12-00146 and Russian Foundation for Basic Research Grant No. 18-502-12025. The work on photospheric velocity determination was done by M.Sh.Potashov and was supported by the Russian Science Foundation Grant No. 19-12-00229. We thank the anonymous referee for constructive suggestions which helped to improve the paper.

Appendix A Data tables

A60 = 60-cm reflector of Shamakhy Observatory, C60 = 60-cm reflector of Crimean Observatory of SAI, C50 = 50-cm meniscus telescope of Crimean Observatory of SAI, T60 = 60-cm reflector of Stará Lesná Observatory, S100 = 1-m reflector at Simeiz Observatory, M70 = 70-cm reflector of Moscow Observatory of SAI, M20 = 20-cm meniscus telescope of Moscow Observatory of SAI, K70 = 70-cm reflector of Crimean Astrophysical Observatory (reprocessing of data by Nazarov et al. (2018))