TY - JOUR
T1 - The Peculiar X-Ray Transient Swift J0840.7-3516
T2 - An Unusual Low-mass X-Ray Binary or a Tidal Disruption Event?
AU - Shidatsu, Megumi
AU - Iwakiri, Wataru
AU - Negoro, Hitoshi
AU - Mihara, Tatehiro
AU - Ueda, Yoshihiro
AU - Kawai, Nobuyuki
AU - Nakahira, Satoshi
AU - Kennea, Jamie A.
AU - Evans, Phil A.
AU - Gendreau, Keith C.
AU - Enoto, Teruaki
AU - Tombesi, Francesco
N1 - Publisher Copyright:
© 2021. The American Astronomical Society. All rights reserved.
PY - 2021/4/1
Y1 - 2021/4/1
N2 - We report on the X-ray properties of the new transient Swift J0840.7-3516, discovered with Swift/BAT in 2020 February, using extensive data from Swift, MAXI, NICER, and NuSTAR. The source flux increased for ∼103 s after the discovery, decayed rapidly over ∼5 orders of magnitude in five days, and then remained almost constant over nine months. Large-amplitude short-term variations on timescales of 1-104 s were observed throughout the decay. In the initial flux rise, the source showed a hard power-law-shaped spectrum with a photon index of ∼1.0 extending up to ∼30 keV, above which an exponential cutoff was present. The photon index increased in the following rapid decay and became ∼2 at the end of the decay. A spectral absorption feature at 3-4 keV was detected in the decay. It is not straightforward to explain all the observed properties by any known class of X-ray sources. We discuss the possible nature of the source, including a Galactic low-mass X-ray binary with multiple extreme properties and a tidal disruption event by a supermassive black hole or a Galactic neutron star.
AB - We report on the X-ray properties of the new transient Swift J0840.7-3516, discovered with Swift/BAT in 2020 February, using extensive data from Swift, MAXI, NICER, and NuSTAR. The source flux increased for ∼103 s after the discovery, decayed rapidly over ∼5 orders of magnitude in five days, and then remained almost constant over nine months. Large-amplitude short-term variations on timescales of 1-104 s were observed throughout the decay. In the initial flux rise, the source showed a hard power-law-shaped spectrum with a photon index of ∼1.0 extending up to ∼30 keV, above which an exponential cutoff was present. The photon index increased in the following rapid decay and became ∼2 at the end of the decay. A spectral absorption feature at 3-4 keV was detected in the decay. It is not straightforward to explain all the observed properties by any known class of X-ray sources. We discuss the possible nature of the source, including a Galactic low-mass X-ray binary with multiple extreme properties and a tidal disruption event by a supermassive black hole or a Galactic neutron star.
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U2 - 10.3847/1538-4357/abe6a1
DO - 10.3847/1538-4357/abe6a1
M3 - Article
AN - SCOPUS:85104680690
SN - 0004-637X
VL - 910
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
M1 - 144
ER -