Confined dense circumstellar material surrounding a regular type II supernova

TL;DR: In this article, the authors reported the discovery of the supernova iPTF 13dqy = SN 2013fs a mere 3'h after the explosion of a red supergiant.

Abstract: With the advent of new wide-field, high-cadence optical transient surveys, our understanding of the diversity of core-collapse supernovae has grown tremendously in the last decade. However, the pre-supernova evolution of massive stars, which sets the physical backdrop to these violent events, is theoretically not well understood and difficult to probe observationally. Here we report the discovery of the supernova iPTF 13dqy = SN 2013fs a mere ~3 h after explosion. Our rapid follow-up observations, which include multiwavelength photometry and extremely early (beginning at ~6 h post-explosion) spectra, map the distribution of material in the immediate environment (≲10^(15) cm) of the exploding star and establish that it was surrounded by circumstellar material (CSM) that was ejected during the final ~1 yr prior to explosion at a high rate, around 10^(−3) solar masses per year. The complete disappearance of flash-ionized emission lines within the first several days requires that the dense CSM be confined to within ≲10^(15) cm, consistent with radio non-detections at 70–100 days. The observations indicate that iPTF 13dqy was a regular type II supernova; thus, the finding that the probable red supergiant progenitor of this common explosion ejected material at a highly elevated rate just prior to its demise suggests that pre-supernova instabilities may be common among exploding massive stars.

Summary

Introduction

• A series of spectra, the earliest ever taken of a SN, were obtained using LRIS mounted on the 10 m Keck-I telescope to follow the evolution of flash-ionised emission lines (Fig. 2).
• This argues against a constant, high wind-like mass loss from the progenitor.
• Smith, N., Li, W., Filippenko, A. V. & Chornock, R. Observed fractions of core-collapse supernova types and initial masses of their single and binary progenitor stars.

1 Discovery

• The intermediate Palomar Transient Factory (iPTF35, which began operating in 2013 as a continuation of PTF33, 14), utilises the 48-inch Samuel Oschin telescope (P48) at Palomar Observatory, California, USA to monitor the transient sky.
• Fields are monitored with a short cadence (1–2 d), and at least two images are taken per field per night, separated by >∼ 30 min, to search for transient events.
• A shorter list of candidates is then vetted by human “scanners”43 who save the candidates of interest and assign prioritised follow-up observations.
• Following the second detection confirm- ing the discovery ∼ 50 min later (Oct. 6.279), it was automatically saved by a robotic process (internally referred to as “the treasurer”) on Oct. 6.365.

2 Photometry

• Shortly after the discovery with the P48, the authors initiated an extensive follow-up campaign; the multiband light curves are presented in Fig.
• Less than 3 hr after the first P48 detection, the authors began obtaining photometry with the Palomar 60-inch telescope (P60; ref. 44) in the g, r, and i filters.
• Magnitudes were measured using their custom pipeline performing point-spreadfunction (PSF) photometry on iPTF images after removing a reference image constructed from preexplosion data using image subtraction.
• All measurements were corrected for Galactic (Milky Way) extinction using the ref. 45 reddening law (assuming RV = 3.08).
• The Swift-XRT (ref. 48) observations, conducted between days 1 and 25 after explosion (with a roughly constant cadence of 1–2 d), were reduced using the tools of ref. 49, applying a 9′′ aperture radius centred on the SN position and correcting for 50% flux losses.

3 Spectroscopy

• All spectra were reduced using standard pipelines.
• A careful procedure was applied for subtracting the flux of the host from the four early-time Keck spectra, involving the subtraction of an offset H II region spectrum in each frame.
• Fig. 3 displays the later spectra, extending from day 8 through ∼ 2 months after explosion, revealing developed P-Cygni profiles typical of spectroscopically normal SNe II.
• All spectra and their accom- panying meta-data are publicly available via WISeREP32 (http://wiserep.weizmann.ac.il).

5 Line Fluxes

• In addition to the other estimates of the mass-loss rate and the radius of the emitting (CSM) region, described in the main text, the authors can also obtain an order-of-magnitude estimate for the mass loss based on the measured Balmer Hα luminosity, following the expressions given by ref. 54.
• A basic underlying assumption is that the CSM around the progenitor has a spherical wind density profile of the form ρ = Kr−2, where r is the distance from the progenitor and K ≡ Ṁ/(4πvwind) is the mass-loading parameter (Ṁ being the mass-loss rate and vwind the wind expansion velocity).
• Additional lower limits on the mass-loss rate can be placed by analysis of the electron- scattering wings seen in the emission lines during the first several days.
• The Hα, Hβ, and He II lines first increase in flux, reaching a maximum around day 1 from explosion.

6 Emission-Line Spectra Models

• The authors performed detailed spectroscopic modeling of the early-time spectra of iPTF 13dqy using the radiative-transfer code CMFGEN34 and the same model assumptions as described by ref. 20.
• The free parameters are essentially the boundary of the inner radius (Rin) and the bolometric luminosity at this inner boundary (LSN).
• The resulting values described below were all obtained for models applying vwind = 100 km s−1.
• The best-fitting models were obtained for a He-enriched surface composition (Y = 0.49, X = 0.49, for the helium and hydrogen mass fractions, respectively); the rest of the abundances are consistent with solar.
• The fact that the strength of the N V line is extremely sensitive to the temperature, as well as the location on top of the strong, asymmetric electron-scattering wings of the He II λ4686 line, means that the nitrogen abundance can be consistent with the required He enhancement.

7 Radio Analysis

• The interaction between SN ejecta and surrounding material can produce synchrotron emission; thus, radio observations can provide powerful diagnostics of the CSM59, 60, 61, 62.
• The radio emission can be used to constrain physical properties such as the CSM density and the CSM shockwave radius and velocity.
• Data reduction was performed using the AIPS1 software63 with 3C 48 as a flux calibrator and J2330+11 as a phase calibrator.
• A second observation took place on 2014 Jan. 18 (with the same configuration and setup), resulting again in a null detection with an RMS of 12µJy and 10µJy in the C and K bands, respectively.
• Past studies have shown that the electron temperature at these distances can indeed be as high as 105–106 K (e.g., ref. 64).

8 Shock-Breakout Analysis

• The authors begin by considering the relevant timescales for the early observations.
• In such a case the continuum flux probably has a different origin than the recom- bination lines, such as coming from inside the stellar edge where the SBO occurs.
• The Palomar Transient Factory photometric catalog 1.0.

Figures

Figure 2 Early-time flash spectroscopy of iPTF 13dqy reveals flash-ionisation signatures during the first 2 d after explosion. High-ionisation oxygen emission lines (O VI λλ3811,

Figure 3 Spectra of iPTF 13dqy obtained between 8 and 57 days after explosion, showing P-Cygni profiles of the Balmer series and additional typical elements, confirm a regular Type II SN identification. The Balmer series, Ca II (the near-infrared triplet and the H&K lines), Fe II, and Mg I are marked for the specified expansion velocities. See the spectroscopic log (Table 1) for details of the spectra. All spectra presented in this study are publicly available via WISeREP32 (http://wiserep.weizmann.ac.il).

Figure 4 The best-fitting CMFGEN models to the observed early-time spectrum (6 hr post-explosion) of iPTF 13dqy reveal a temperature of the line forming region around

Figure 1 The early discovery of iPTF 13dqy and the prompt ensuing follow-up observations, multiband photometry and spectroscopy, enabled the direct probing and mapping of

Figure 6 The proposed CSM configuration surrounding the progenitor of iPTF 13dqy, resulting from our multiwavelength observations — a CSM density profile that is both nearby and confined. The figure summarises the CSM estimates we derive from analyses of the early-time spectra (at r ≈ 1014 cm) together with the region excluded by the later radio observations. The solid diagonal coloured lines denote constant mass-loss rates between 10−7 and 10−1 M yr−1 (following ρ = Ṁ/4πvwindr2, vwind = 100 km s−1) assuming an r−2 wind density profile. For an explanation of the lower limit on the mass-loss rate as obtained by measurement of the Hα luminosity, see Methods §5. The early-time

Figure 5 Radio non-detections rule out an extended dense wind structure around the progenitor of iPTF 13dqy. The plotted coloured curves display theoretical light curves of radio emission originating from the interaction of SN ejecta with an extended CSM. These extended CSM structures are assumed to be a result of a constant mass-loss rate through stellar winds. Our measured limits (triangles) on the late-time radio emission (at ∼ 70, 100d) rule out a wide range of mass-loss rates. In particular, our limits show that the mass-loss rate estimate required to explain the early optical data could not have been sustained over long periods. Otherwise, an extended CSM structure would have formed with sufficiently high density to be detected in the radio at late times (up to a

Full text

Confined Dense Circumstellar Material Surrounding a Regular Type II
Supernova
Yaron, O., Perley, D. A., Gal-Yam, A., Groh, J. H., Horesh, A., Ofek, E. O., Kulkarni, S. R., Sollerman, J.,
Fransson, C., Rubin, M. A., Szabo, P., Sapir, N., Taddia, F., Cenko, S. B., Arcavi, I., Howell, D. A., Kasliwal, M.
M., Vreeswijk, P. M., Khazov, D., ... Soumagnac, M. T. (2017). Confined Dense Circumstellar Material
Surrounding a Regular Type II Supernova.
Nature Physics
, 510-521. https://doi.org/10.1038/NPHYS4025
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Nature Physics
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Peer reviewed version
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Download date:09. Aug. 2022

Confined Dense Circumstellar Material Surrounding
a Regular Type II Supernova: The Unique Flash-
Spectroscopy Event - SN 2013fs
O. Yaron
1
, D. A. Perley
2,3
, A. Gal-Yam
1
, J. H. Groh
4
, A. Horesh
5,1
, E. O. Ofek
1
, S. R. Kulkarni
2
,
J. Sollerman
6
, C. Fransson
6
, A. Rubin
1
, P. Szabo
1
, N. Sapir
1,7
, F. Taddia
6
, S. B. Cenko
8,9
, S. Valenti
10
,
I. Arcavi
11,12
, D. A. Howell
11,12
, M. M. Kasliwal
2
, P. M. Vreeswijk
1
, D. Khazov
1
, O. D. Fox
13
,
Y. Cao
2
, O. Gnat
5
, P. L. Kelly
13
, P. E. Nugent
13,14
, A. V. Filippenko
13
, R. R. Laher
15
, P. R. Wozniak
16
,
W. H. Lee
17
, U. D. Rebbapragada
18
, K. Maguire
19
, M. Sullivan
20
, M. T. Soumagnac
1
1
Department of Particle Physics and Astrophysics, Weizmann Institute of Science, Rehovot 76100,
Israel.
2
Division of Physics, Math and Astronomy, California Institute of Technology, 1200 E. California
Boulevard, Pasadena, CA 91125, USA.
3
Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen Juliane Maries Vej 30,
2100 Copenhagen Ø, Denmark.
4
School of Physics, Trinity College Dublin, Dublin 2, Ireland.
5
Racah Institute of Physics, Hebrew University, Jerusalem 91904, Israel.
6
The Oskar Klein Centre, Department of Astronomy, Stockholm University, AlbaNova, 10691
Stockholm, Sweden.
7
Plasma Physics Department, Soreq Nuclear Research Center, Yavne 81800, Israel.
8
Astrophysics Science Division, NASA Goddard Space Flight Center, Mail Code 661, Greenbelt,
MD 20771, USA.
1
arXiv:1701.02596v2 [astro-ph.HE] 16 Feb 2017

9
Joint Space-Science Institute, University of Maryland, College Park, MD 20742, USA.
10
Department of Physics, University of California, 1 Shields Ave, Davis, CA 95616-5270, USA
11
Las Cumbres Observatory, 6740 Cortona Drive, Suite 102,Goleta, CA 93117, USA.
12
Department of Physics, University of California, Santa Barbara, CA 93106-9530, USA.
13
Department of Astronomy, University of California, Berkeley, CA 94720-3411, USA.
14
Computational Research Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road
MS 50B-4206, Berkeley, CA 94720, USA.
15
Spitzer Science Center, California Institute of Technology, Pasadena, CA 91125, USA.
16
Los Alamos National Laboratory, Mail Stop B244, Los Alamos, NM 87545, USA.
17
Instituto de Astronom
´
ıa, Universidad Nacional Auton
´
oma de M
´
exico, Apdo. Postal 70-264,
04510 M
´
exico DF, M
´
exico.
18
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA.
19
Astrophysics Research Centre, School of Mathematics and Physics, Queens University Belfast,
Belfast BT7 1NN, UK.
20
School of Physics and Astronomy, University of Southampton, Southampton, SO17 1BJ, UK.
2

With the advent of new wide-field, high-cadence optical transient surveys, our understand-
ing of the diversity of core-collapse supernovae has grown tremendously in the last decade.
However, the pre-supernova evolution of massive stars, that sets the physical backdrop to
these violent events, is theoretically not well understood and difficult to probe observation-
ally. Here we report the discovery of the supernova iPTF 13dqy = SN 2013fs a mere ∼ 3 hr
after explosion. Our rapid follow-up observations, which include multiwavelength photome-
try and extremely early (beginning at ∼ 6 hr post-explosion) spectra, map the distribution of
material in the immediate environment (
<
∼
10
15
cm) of the exploding star and establish that
it was surrounded by circumstellar material (CSM) that was ejected during the final ∼ 1 yr
prior to explosion at a high rate, around 10
−3
solar masses per year. The complete disap-
pearance of flash-ionised emission lines within the first several days requires that the dense
CSM be confined to within
<
∼
10
15
cm, consistent with radio non-detections at 70–100 days.
The observations indicate that iPTF 13dqy was a regular Type II SN; thus, the finding that
the probable red supergiant (RSG) progenitor of this common explosion ejected material at
a highly elevated rate just prior to its demise suggests that pre-supernova instabilities may
be common among exploding massive stars.
Why and how massive stars explode as supernovae is one of the outstanding open questions
in astrophysics. Massive stars fuse light elements into heavier ones in their core. During the
final years of their (relatively short, a few 10
6
–10
7
yr) lifetime, these stars burn heavy fuel, the
fusion products of hydrogen and helium, until an iron core grows and ultimately collapses. Stellar
evolution in these final years, which sets the initial conditions for the final collapse and explosion
3

of such stars as supernovae (SNe), is poorly understood
1
. Direct observations of these processes is
challenging, as stars in these brief final stages are rare. Statistically, it is very likely that not even
a single star that is within 1 yr of explosion currently exists in our Galaxy.
Recently, growing observational evidence has suggested the existence of pre-explosion el-
evated mass loss and eruptions
2, 3, 4, 5
. Accommodating these findings, a handful of theoretical
studies
6, 7, 8, 9
were carried out exploring possible pathways by which massive stars may become
unstable during their terminal years, leading to the observable signatures of increased mass loss,
variability, and eruptive episodes prior to the terminal explosion. Material ejected by the star in the
year prior to its demise may imprint unique signatures on the emission observed from the young
SN event, but as this material will be quickly swept away by the expanding explosion debris, such
detections require rapid observations to be secured within a few days of explosion
2, 10
. A handful
of recent observations provide evidence for enhanced mass loss and eruptive episodes during the
terminal years prior to explosion, but mainly for rare subclasses of SNe which comprise at most
a few percent of the population. The observations presented here of iPTF 13dqy indicate that it
was a fairly regular Type II SN, similar to ∼ 50%
11
of exploding massive stars, and thus may
strengthen the hypothesis that the ultimate collapse of the core and the preceding vigorous ejection
of mass from the outer envelope are causally coupled. In addition, the structure of the outer enve-
lope of massive stars during the very late stages of evolution may significantly differ from what is
predicted by stellar evolution models
12, 13
.
On 2013 Oct. 6.245 (UTC dates are used throughout this paper), a new transient source with
4

Frequently asked questions

Q1. What contributions have the authors mentioned in the paper "Confined dense circumstellar material surrounding a regular type ii supernova" ?

Yaron, O., Perley, D. this paper, Gal-Yam, A., Groh, J. H., Horesh, A, Ofek, E. O., Kulkarni, S. A., Kasliwal, M. M., Khazov, D., ... Soumagnac, M., Szabo, P., Sapir, N., Taddia, F., Cenko, S.,