J/ApJ/926/142 UV, optical and X-ray evolution of ASASSN-14ko (Payne+, 2022)
The rapid X-ray and UV evolution of ASASSN-14ko.
Payne A.V., Shappee B.J., Hinkle J.T., Holoien T.W.-S., Auchettl K.,
Kochanek C.S., Stanek K.Z., Thompson T.A., Tucker M.A., Armstrong J.D.,
Boyd P.T., Brimacombe J., Cornect R., Huber M.E., Jha S.W., Lin C.-C.
<Astrophys. J., 926, 142 (2022)>
=2022ApJ...926..142P 2022ApJ...926..142P
ADC_Keywords: Transient; Photometry, ultraviolet; X-ray sources;
Spectra, optical
Keywords: Active galaxies ; Black holes ; Galaxy nuclei ; High energy
astrophysics
Abstract:
ASASSN-14ko is a recently discovered periodically flaring transient at
the center of the active galactic nucleus (AGN) ESO 253-G003 with a
slowly decreasing period. Here, we show that the flares originate from
the northern, brighter nucleus in this dual-AGN, post-merger system.
The light curves for the two flares that occurred in 2020 May and
September are nearly identical over all wavelengths. For both events,
Swift observations showed that the UV and optical wavelengths
brightened in unison. The effective temperature of the UV/optical
emission rises and falls with the increase and subsequent decline in
the luminosity. The X-ray flux, by contrast, first rapidly drops over
∼2.6 days, rises for ∼5.8 days, drops again over ∼4.3 days, and then
recovers. The X-ray spectral evolution of the two flares differ,
however. During the 2020 May peak the spectrum softened with increases
in the X-ray luminosity, while we observed the reverse for the
2020 September peak. We found a small change in the period derivative,
which seems to indicate that the system does not have a static period
derivative and there is some stochasticity in its evolution.
Description:
ASAS-SN is an ongoing all-sky survey to discover supernovae and other
transient phenomena. The 20 robotic telescopes at five sites in both
the Northern and Southern Hemispheres are hosted by the Las Cumbres
Observatory Global Telescope (LCOGT). All telescopes obtain data in
the g band. See Section 2.1.
Using our prediction of the optical peak time and the expected
multiwavelength trend based on the 2020 May flare, we requested Swift
UltraViolet/Optical Telescope (UVOT) target-of-opportunity (ToO)
observations (ToO ID: 14389, 14488, PI: Payne). The UVOT data were
obtained in six filters: V (5425Å), B (4350Å), U (3467Å),
UVW1 (2581Å), UVM2 (2246Å), and UVW2 (2055Å). See Section 2.2.
We obtained photometric observations from the LCOGT using the 1m
telescope at Siding Spring Observatory in New South Wales, Australia.
The data consisted of B, V, g', and r' observations. See Section 2.3.
There were 28 epochs of ASASSN-14ko Pan-STARRS1 data between 2014 and
2020. See Section 2.4.
We used the 10m Southern African Large Telescope (SALT) with the
Robert Stobie Spectrograph (RSS) to obtain optical spectra during the
flare. The data were obtained with the 1.5" slit on UT 2020-09-04 and
UT 2020-09-16, which corresponded to ∼1day prior and ∼11days after the
measured optical g-band peak, respectively.
Amateur astronomer photometry data were collected using a 41cm
telescope at Savannah Skies Observatory from Queensland, Australia.
The 180s exposures were obtained using the B, V, and RC filters, and
the data were bias and dark subtracted. Data were also taken at
Moondyne Observatory located east of Perth, Australia, using a 0.4m
telescope with AOX adaptive optics. See Section 2.6.
Objects:
----------------------------------------------------------
RA (ICRS) DE Designation(s)
----------------------------------------------------------
05 25 18.13 -46 00 20.3 ASASSN-14ko = ASASSN -14ko
----------------------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 53 407 Light curve data of ASASSN-14ko used in this analysis
fig4.dat 24 7775 The SALT ASASSN-14ko spectra
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See also:
II/294 : The SDSS Photometric Catalog, Release 7 (Adelman-McCarthy+, 2009)
J/ApJ/613/682 : AGN central masses & broad-line region sizes (Peterson+, 2004)
J/ApJ/687/1201 : SN and LGRB locations in their host galaxies (Kelly+, 2008)
J/ApJ/750/99 : The Pan-STARRS1 photometric system (Tonry+, 2012)
J/ApJ/788/48 : X-ray through NIR photometry of NGC 2617 (Shappee+, 2014)
J/A+A/594/A116 : HI4PI spectra and column density maps (HI4PI team+, 2016)
J/MNRAS/455/2918 : Phot. & line luminosities for ASASSN-14li (Holoien+, 2016)
J/MNRAS/463/3813 : ASASSN-15oi UBVI M2W1W2 light curves (Holoien+, 2016)
J/ApJ/883/94 : Optical and UV follow-up of 1ES 1927+654 (Trakhtenbrot+, 2019)
J/ApJ/898/161 : 500days of ASASSN-18pg multiwavelength obs. (Holoien+, 2020)
J/ApJ/910/83 : Swift phot. recomputed for 38 transients (Hinkle+, 2021)
J/ApJ/910/125 : Follow-up photometry of ASASSN-14ko (Payne+, 2021)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 11 F11.3 d JD [2448102.27/2459113.72] Julian Date
13- 17 A5 --- Band Observational passband
19- 31 A13 --- n_Band Description of Band (1)
33 A1 --- l_Lum Upper limit flag on Lum
34- 43 E10.4 10-7W Lum ? Luminosity in Band; erg/s
45- 53 E9.4 10-7W e_Lum ? Uncertainty in Lum
55 A1 --- l_HR Upper limit flag on HR
56- 65 E10.5 --- HR [-0.7/0.61]? Hardness ratio: HR=(H-S)/(H+S) (2)
67- 75 E9.4 --- e_HR [0.002/0.8]? Uncertainty in Lum
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Note (1): Where the X-ray band is in keV and the UV/Optical are the central
wavelengths of the filter.
Note (2): The hardness ratio is defined as HR=(H-S)/(H+S) where
H=2-10keV and S=0.3-2keV.
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Byte-by-byte Description of file: fig4.dat
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Bytes Format Units Label Explanations
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1 I1 --- Obs [1/2] Spectrum identifier (1)
3- 13 E11.5 0.1nm lambda [3493.1/7258.3] Wavelength; Angstroms
15- 24 E10.3 cW/m2/nm Flux [9.7e-16/1.1e-14] Flux; erg/s/cm2/Å
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Note (1): Spectrum identifier as follows:
1 = Obtained on UT 2020-09-04 (3890 occurrences);
2 = Obtained on UT 2020-09-16 (3885 occurrences).
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 31-Oct-2023