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The X-ray and Radio Loud Fast Blue Optical Transient AT2020mrf: Implications for an Emerging Class of Engine-Driven Massive Star Explosions

Yao, Yuhan and Ho, Anna Y. Q. and Medvedev, Pavel and AJ, Nayana and Perley, Daniel A. and Kulkarni, S. R. and Chandra, Poonam and Sazonov, Sergey and Gilfanov, Marat and Khorunzhev, Georgii and Khatami, David K. and Sunyaev, Rashid (2021) The X-ray and Radio Loud Fast Blue Optical Transient AT2020mrf: Implications for an Emerging Class of Engine-Driven Massive Star Explosions. . (Unpublished)

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We present AT2020mrf (SRGe J154754.2+443907), an extra-galactic (z = 0.1353) fast-rising (t_(g,rise) = 3.7 days) luminous (M_(g,peak) = −20.0) optical transient. Its optical spectrum around peak shows a broad (v ∼ 0.1c) emission feature on a blue continuum (T ∼ 2 × 10⁴ K), which bears a striking resemblance to AT2018cow. Its bright radio emission (ν_(Lν) = 1.2 × 10³⁹ erg s⁻¹; ν_(rest) = 7.4 GHz; 261 days) is similar to four other AT2018cow-like events, and can be explained by synchrotron radiation from the interaction between a sub-relativistic (≳ 0.07--0.08c) forward shock and a dense environment (M˙ ≲ 10⁻³ M_⊙ yr⁻¹ for v_w = 10³ km s⁻¹). AT2020mrf occurs in a galaxy with M∗ ∼ 10⁸ M_⊙ and specific star formation rate ∼10⁻¹⁰ yr⁻¹, supporting the idea that AT2018cow-like events are preferentially hosted by dwarf galaxies. The X-ray properties of AT2020mrf are unprecedented. At 35--37 days, SRG/eROSITA detected luminous (L_X ∼ 2 × 10⁴³ erg s⁻¹; 0.3--10 keV) X-ray emission. The X-ray spectral shape (f_ν ∝ ν^(−0.8)) and erratic intraday variability are reminiscent of AT2018cow, but the luminosity is a factor of ∼20 greater than AT2018cow. At 328 days, Chandra detected it at L_X ∼ 10⁴² erg s⁻¹, which is >200 times more luminous than AT2018cow and CSS161010. At the same time, the X-ray emission remains variable on the timescale of ∼1 day. We show that a central engine, probably a millisecond magnetar or an accreting black hole, is required to power the explosion. We predict the rates at which events like AT2018cow and AT2020mrf will be detected by present and future X-ray all-sky surveys, including SRG and Einstein Probe.

Item Type:Report or Paper (Discussion Paper)
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URLURL TypeDescription Paper
Yao, Yuhan0000-0001-6747-8509
Ho, Anna Y. Q.0000-0002-9017-3567
Medvedev, Pavel0000-0002-9380-8708
AJ, Nayana0000-0002-8070-5400
Perley, Daniel A.0000-0001-8472-1996
Kulkarni, S. R.0000-0001-5390-8563
Chandra, Poonam0000-0002-0844-6563
Gilfanov, Marat0000-0003-4029-6769
Khatami, David K.0000-0003-4307-0589
Sunyaev, Rashid0000-0002-2764-7192
Additional Information:Attribution 4.0 International (CC BY 4.0). We thank Patrick Slane for allocating DD time on Chandra. We thank the staff of Chandra, VLA, Keck, and GMRT that made these observations possible. We thank Jim Fuller, Mansi Kasliwal, Wenbin Lu, Tony Piro, and Eliot Quataert for helpful discussions. Y.Y. is supported in part by the Heising-Simons Foundation. Nayana A.J. would like to acknowledge DST-INSPIRE Faculty Fellowship (IFA20-PH-259) for supporting this research. P.C. acknowledges support of the Department of Atomic Energy, Government of India, under the project no. 12-R&D-TFR-5.02-0700. P.M., M.G., S.S., G.K. and R.S. acknowledge the partial support of this research by grant 21-12-00343 from the Russian Science Foundation. GMRT is run by the National Centre for Radio Astrophysics of the Tata Institute of Fundamental Research. This work is based on observations with the eROSITA telescope on board the SRG observatory. The SRG observatory was built by Roskosmos in the interests of the Russian Academy of Sciences represented by its Space Research Institute (IKI) in the framework of the Russian Federal Space Program, with the participation of the Deutsches Zentrum fur Luft- und Raumfahrt (DLR). The SRG/eROSITA X-ray telescope was built by a consortium of German Institutes led by MPE, and supported by DLR. The SRG spacecraft was designed, built, launched and is operated by the Lavochkin Association and its subcontractors. The science data are downlinked via the Deep Space Network Antennae in Bear Lakes, Ussurijsk, and Baykonur, funded by Roskosmos. The eROSITA data used in this work were processed using the eSASS software system developed by the German eROSITA consortium and proprietary data reduction and analysis software developed by the Russian eROSITA Consortium. The ZTF forced-photometry service was funded under the Heising-Simons Foundation grant #12540303 (PI: Graham). This work has made use of data from the ATLAS project, which is primarily funded to search for near earth asteroids through NASA grants NN12AR55G, 80NSSC18K0284, and 80NSSC18K1575; byproducts of the NEO search include images and catalogs from the survey area. This work was partially funded by Kepler/K2 grant J1944/80NSSC19K0112 and HST GO-15889, and STFC grants ST/T000198/1 and ST/S006109/1. The ATLAS science products have been made possible through the contributions of the University of Hawaii Institute for Astronomy, the Queen's University Belfast, the Space Telescope Science Institute, the South African Astronomical Observatory, and The Millennium Institute of Astrophysics (MAS), Chile. Software: astropy (Astropy Collaboration et al. 2013), CASA (v5.6.1; McMullin et al. 2007), CIAO (Fruscione et al. 2006), emcee (Foreman-Mackey et al. 2013), LPipe (Perley 2019), matplotlib (Hunter 2007), pandas (McKinney 2010), Prospector (Johnson et al. 2021), pyne2001 (Cordes & Lazio 2002), python-fsps (Foreman-Mackey et al. 2014), scipy (Virtanen et al. 2020). Facilities: CXO, XMM, PO:1.2m, Keck:I (LRIS), VLA, GMRT.
Group:Astronomy Department, Zwicky Transient Facility
Funding AgencyGrant Number
Heising-Simons Foundation12540303
Department of Science and Technology (India)IFA20-PH-259
Department of Atomic Energy (India)12-R&D-TFR-5.02-0700
Russian Science Foundation21-12-00343
Deutsches Zentrum für Luft- und Raumfahrt (DLR)UNSPECIFIED
Science and Technology Facilities Council (STFC)ST/T000198/1
Science and Technology Facilities Council (STFC)ST/S006109/1
Classification Code:X-ray transient sources (1852); Radio transient sources (2008); Supernovae (1668); Corecollapse supernovae (304); High energy astrophysics (739); Sky surveys (1464)
Record Number:CaltechAUTHORS:20220113-234528535
Persistent URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:112895
Deposited By: George Porter
Deposited On:14 Jan 2022 17:52
Last Modified:14 Jan 2022 17:52

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