J/ApJ/949/23 SN 2017egm spectroscopic & photometric obs. (Zhu+, 2023)
SN 2017egm: a helium-rich superluminous supernova with multiple bumps in the
light curves.
Zhu J., Jiang N., Dong S., Filippenko A.V., Rudy R.J., Pastorello A.,
Ashall C., Bose S., Post R.S., Bersier D., Benetti S., Brink T.G.,
Chen P., Dou L., Elias-Rosa N., Lundqvist P., Mattila S., Russell R.W.,
Sitko M.L., Somero A., Stritzinger M.D., Wang T., Brown P.J.,
Cappellaro E., Fraser M., Kankare E., Moran S., Prentice S., Pursimo T.,
Reynolds T.M., Zheng W.
<Astrophys. J., 949, 23 (2023)>
=2023ApJ...949...23Z 2023ApJ...949...23Z
ADC_Keywords: Supernovae; Photometry, ultraviolet; Photometry, ugriz;
Spectra, optical; Spectra, infrared; X-ray sources
Keywords: Supernovae
Abstract:
When discovered, SN 2017egm was the closest (redshift z=0.03)
hydrogen-poor superluminous supernova (SLSN-I) and a rare case that
exploded in a massive and metal-rich galaxy. Thus, it has since been
extensively observed and studied. We report spectroscopic data showing
strong emission at around HeIλ10830 and four HeI absorption
lines in the optical. Consequently, we classify SN 2017egm as a member
of an emerging population of helium-rich SLSNe-I (i.e., SLSNe-Ib). We
also present our late-time photometric observations. By combining them
with archival data, we analyze high-cadence ultraviolet, optical, and
near-infrared light curves spanning from early pre- peak (~-20days) to
late phases (~+300 days). We obtain its most complete bolometric light
curve, in which multiple bumps are identified. None of the previously
proposed models can satisfactorily explain all main light-curve
features, while multiple interactions between the ejecta and
circumstellar material (CSM) may explain the undulating features. The
prominent infrared excess with a blackbody luminosity of
107-108L☉ detected in SN 2017egm could originate from the
emission of either an echo of a pre-existing dust shell or newly
formed dust, offering an additional piece of evidence supporting the
ejecta-CSM interaction model. Moreover, our analysis of deep Chandra
observations yields the tightest-ever constraint on the X-ray emission
of an SLSN-I, amounting to an X-ray-to-optical luminosity ratio
≲10-3 at late phases (∼100-200 days), which could help explore its
close environment and central engine.
Description:
Multiband photometry from UV to mid-infrared (MIR) wavelengths, as
well as optical spectra spanning ∼300 days since the discovery of
SN2017egm, were taken by us or gathered from publicly available
archives.
We obtained late-time multiband images with a set of ground-based
instruments. Optical data in the BVgriz bands were taken with 0.6m
telescopes at Post Observatory (PO) at the Sierra Remote Observatories
(SRO; CA, USA), the 2.0m Las Cumbres Observatory Global Telescope
network (LCOGT), the 2.0m Liverpool Telescope (LT) at La Palma, and
the ALFOSC mounted on the 2.6m Nordic Optical Telescope (NOT). The JHK
near-infrared (NIR) images were obtained with the NIR Camera mounted
on the NOT (NOTCam) and the NIR Wide-Field Camera mounted on the
United Kingdom Infrared Telescope (UKIRT).
UV images were obtained with the Neil Gehrels Swift Observatory with
the Ultraviolet Optical Telescope (UVOT). The Swift/UVOT data covered
∼140 days of NUV data after discovery.
To acquire high-S/N measurements, we choose to perform photometry on
the time-resolved WISE/NEOWISE coadds. See Section 2.3.
Four epochs of X-ray observations of SN 2017egm (PI R. Margutti) were
obtained with the Chandra X-ray Observatory on 2017 June 26 (24ks
exposure), 2017 September 17 (25ks), 2017 November 9 (25ks), and
2018 May 21 (24ks); they correspond to +4, +85, +136, and +323 days
since the optical peak. See Section 2.4.
Optical spectra from +84 to +261 days were obtained using the Kast
Spectrograph mounted on the 3m Shane telescope at Lick Observatory
(CA, USA), the Double Spectrograph for the Palomar 200 inch Hale
telescope (P200), the MODS1 multiobject double spectrographs mounted
at the Large Binocular Telescope Observatory (LBT), and the OSIRIS
instrument located in the Gran Telescopio CANARIAS (GTC). We also
obtained spectra of SN 2017egm in the NIR at +105 days using the
Aerospace Corporation's Visible and Near-Infrared Imaging Spectrograph
(VNIRIS) mounted on the Shane telescope and +143 days using the Spex
medium-resolution spectrograph (0.7-5.3um) on the NASA Infrared
Telescope Facility (IRTF).
Objects:
----------------------------------------------------------
RA (ICRS) DE Designation(s)
----------------------------------------------------------
10 19 05.62 +46 27 14.0 SN 2017egm = Gaia 17biu
----------------------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 68 561 Photometry of SN 2017egm
table2.dat 143 15 Summary of late-time spectroscopic observations
of SN 2017egm
table3.dat 38 71 Best-fit blackbody parameters
fig5.dat 37 6 MIR light curves of SN 2017egm
sp/* . 16 Optical and NIR spectra in MRT format
(Data behind Figures 6 and 7)
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See also:
B/chandra : The Chandra Archive Log (CXC, 1999-2014)
B/swift : Swift Master Catalog (HEASARC, 2004-)
J/ApJ/690/1358 : Spectra of unusual optical transient SCP 06F6 (Barbary+, 2009)
J/ApJ/750/99 : The Pan-STARRS1 photometric system (Tonry+, 2012)
J/ApJ/792/30 : NEOWISE magnitudes for near-Earth objects (Mainzer+, 2014)
J/ApJ/852/81 : 17 PS1 superluminous SNe LCs + classif. sp. (Lunnan+, 2018)
J/ApJ/864/45 : X-ray emission from superluminous SNe survey (Margutti+, 2018)
J/ApJ/901/61 : LCs of 4 superluminous SNe from the ZTF survey (Lunnan+, 2020)
J/ApJ/902/6 : UV to visible-light obs. of SN 2018fif (Soumagnac+, 2020)
J/ApJ/902/L8 : Optical & NIR spectra of ZTF19aawfbtg (SN2019hge) (Yan+, 2020)
J/ApJ/933/14 : LC analysis of type I superluminous SNe (Hosseinzadeh+, 2022)
J/ApJ/943/42 : Hydrogen-poor superluminous SNe from ZTF P1. II. (Chen+, 2023)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 F8.2 d MJD [57904.9/58293.2] Modified Julian Date
(JD-2400000.5)
10- 15 F6.2 d Time [-20.3/356.5] Rest-frame time from g-band peak
at JD=2457926.3
17- 20 A4 --- Filt Filter
22- 22 A1 --- l_omag [> ] Limit flag on omag
24- 28 F5.2 mag omag [14.4/21.8] Observed magnitude in Filter (1)
30- 33 F4.2 mag e_omag [0.01/1]? Uncertainty in omag
35- 48 A14 --- Tel Telescope/Instrument used (2)
50- 68 A19 --- Ref Reference for photometry (3)
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Note (1): Swift/UVOT and optical griz photometric data were
calibrated for the AB magnitude system while BVJHK for the Vega
magnitude system.
Note (2): The abbreviations of telescope/instrument used are:
LT = 2.0m Liverpool Telescope;
PO = 0.6m telescopes of Post Observatory;
LCOGT = Las Cumbres Observatory Global Telescope Network;
AF = ALFOSC mounted on 2.0m NOT telescope;
KeplerCam = KeplerCam mounted on 1.2m telescope at
Fred Lawrence Whipple Observatory (FLWO)
NC = NotCAM IR imager on 2.0m NOT telescope;
UKIRT = NIR Wide-Field Camera mounted on the United Kingdom
Infrared Telescope;
UVOT = Ultraviolet Optical Telescope onboard Swift satellite.
Note (3): References as follows:
2018ApJ...853...57B 2018ApJ...853...57B = Bose et al. reprocessed using the same procedure
with this work;
2022ApJ...933...14H 2022ApJ...933...14H = Hosseinzadeh et al.
This work = This work.
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Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 13 A13 "Y/M/D" Date UT date of observation
15- 20 F6.2 d JD [13/195.5] Julian Date; JD-2458000
22- 26 F5.1 d Time [84/261.2] Rest-frame time from g-band peak
at JD=2457926.3
28- 35 A8 s Exp Exposure time
37- 39 F3.1 --- Airmass [1/2.9] Airmass
41- 56 A16 --- Tel Telescope / Instrument
58-101 A44 --- FileName1 File identifier in the "sp" subdirectory
(in MRT format); column added by CDS
103-143 A41 --- FileName2 Name of a second file if any;
column added by CDS
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Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 F6.2 d Time [-19.1/249] Rest-frame time from g-band peak
at JD=2457926.3
8- 12 F5.2 10+3K Tbb [4.78/17.4] black-body Temperature (1)
14- 17 F4.2 10+3K e_Tbb [0.05/1.5] Uncertainty in Tbb (1)
19- 22 F4.2 10+15cm Rbb [0.59/4] black-body radius (1)
24- 27 F4.2 10+15cm e_Rbb [0.01/0.6] Uncertainty in Rbb (1)
29- 33 F5.2 [10-7J] logLbb [41.8/44.3] log, black-body Luminosity (1)
35- 38 F4.2 [10-7J] e_logLbb [0.01/0.3] Uncertainty in logLbb (1)
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Note (1): For Time >148d blackbody fitting is performed without NUV photometry.
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Byte-by-byte Description of file: fig5.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 F9.3 d MJD [57863.26/58797.5] Modified Julian Date of WISE
data
11 A1 --- l_W1mag Limit flag on W1mag
13- 17 F5.3 mJy W1mag [0.028/0.08] WISE/NEOWISE 3.4um band flux
19- 23 F5.3 mJy e_W1mag [0.014/0.015]? Uncertainty in W1mag
25 A1 --- l_W2mag Limit flag on W2mag
27- 31 F5.3 mJy W2mag [0.05/0.17] WISE/NEOWISE 4.6um band flux
33- 37 F5.3 mJy e_W2mag [0.016/0.02]? Uncertainty in W2mag
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 14-May-2025