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A new, faint population of X-ray transients

Bauer, Franz E.; Treister, Ezequiel; Schawinski, Kevin; Schulze, Steve; Luo, Bin; Alexander, David M.; Brandt, William N.; Comastri, Andrea; Forster, Francisco; Gilli, Roberto; Kann, David Alexander; Maeda, Keiichi; Nomoto, Ken'ichi; Paolillo, Maurizio; Ranalli, Piero; Schneider, Donald P.; Shemmer, Ohad; Tanaka, Masaomi; Tolstov, Alexey; Tominaga, Nozomu; Tozzi, Paolo; Vignali, Cristian; Wang, Junxian; Xue, Yongquan; Yang, Guang

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Franz E. Bauer

Ezequiel Treister

Kevin Schawinski

Steve Schulze

Bin Luo

William N. Brandt

Andrea Comastri

Francisco Forster

Roberto Gilli

David Alexander Kann

Keiichi Maeda

Ken'ichi Nomoto

Maurizio Paolillo

Piero Ranalli

Donald P. Schneider

Ohad Shemmer

Masaomi Tanaka

Alexey Tolstov

Nozomu Tominaga

Paolo Tozzi

Cristian Vignali

Junxian Wang

Yongquan Xue

Guang Yang


We report on the detection of a remarkable new fast high-energy transient found in the Chandra Deep Field-South, robustly associated with a faint (mR = 27.5 mag, zph ∼ 2.2) host in the CANDELS survey. The X-ray event is comprised of 115 +12−11 −11+12 net 0.3–7.0 keV counts, with a light curve characterized by an ≈100 s rise time, a peak 0.3–10 keV flux of ≈5 × 10−12 erg s−1 cm−2 and a power-law decay time slope of −1.53 ± 0.27. The average spectral slope is Γ=1.43+0.23−0.13 Γ=1.43−0.13+0.23 , with no clear spectral variations. The X-ray and multiwavelength properties effectively rule out the vast majority of previously observed high-energy transients. A few theoretical possibilities remain: an ‘orphan’ X-ray afterglow from an off-axis short-duration gamma-ray burst (GRB) with weak optical emission, a low-luminosity GRB at high redshift with no prompt emission below ∼20 keV rest frame, or a highly beamed tidal disruption event (TDE) involving an intermediate-mass black hole and a white dwarf with little variability. However, none of the above scenarios can completely explain all observed properties. Although large uncertainties exist, the implied rate of such events is comparable to those of orphan and low-luminosity GRBs as well as rare TDEs, implying the discovery of an untapped regime for a known transient class, or a new type of variable phenomena whose nature remains to be determined.


Bauer, F. E., Treister, E., Schawinski, K., Schulze, S., Luo, B., Alexander, D. M., …Yang, G. (2017). A new, faint population of X-ray transients. Monthly Notices of the Royal Astronomical Society, 467(4), 4841-4857.

Journal Article Type Article
Acceptance Date Feb 15, 2017
Online Publication Date Feb 20, 2017
Publication Date Jun 1, 2017
Deposit Date Jun 21, 2017
Publicly Available Date Jun 22, 2017
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Royal Astronomical Society
Peer Reviewed Peer Reviewed
Volume 467
Issue 4
Pages 4841-4857
Public URL


Published Journal Article (1.3 Mb)

Copyright Statement
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2017 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

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