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A new, faint population of X-ray transients.

Bauer, Franz E. and Treister, Ezequiel and Schawinski, Kevin and Schulze, Steve and Luo, Bin and Alexander, David M. and Brandt, William N. and Comastri, Andrea and Forster, Francisco and Gilli, Roberto and Kann, David Alexander and Maeda, Keiichi and Nomoto, Ken'ichi and Paolillo, Maurizio and Ranalli, Piero and Schneider, Donald P. and Shemmer, Ohad and Tanaka, Masaomi and Tolstov, Alexey and Tominaga, Nozomu and Tozzi, Paolo and Vignali, Cristian and Wang, Junxian and Xue, Yongquan and Yang, Guang (2017) 'A new, faint population of X-ray transients.', Monthly notices of the Royal Astronomical Society., 467 (4). pp. 4841-4857.

Abstract

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.

Item Type:Article
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Status:Peer-reviewed
Publisher Web site:https://doi.org/10.1093/mnras/stx417
Publisher 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.
Date accepted:15 February 2017
Date deposited:22 June 2017
Date of first online publication:20 February 2017
Date first made open access:22 June 2017

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