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Quasi-simultaneous INTEGRAL, SWIFT, and NuSTAR Observations of the New X-Ray Clocked Burster 1RXS J180408.9-342058

Fiocchi, M. and Bazzano, A. and Bruni, G. and Ludlam, R. and Natalucci, L. and Onori, F. and Ubertini, P. (2019) Quasi-simultaneous INTEGRAL, SWIFT, and NuSTAR Observations of the New X-Ray Clocked Burster 1RXS J180408.9-342058. Astrophysical Journal, 887 (1). Art. No. 30. ISSN 1538-4357.

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We report the quasi-simultaneous INTEGRAL, SWIFT, and NuSTAR observations showing spectral state transitions in the neutron star low-mass X-ray binary 1RXS J180408.9−342058 during its 2015 outburst. We present results of the analysis of high-quality broad energy band (0.8–200 keV) data in three different spectral states: high/soft, low/very-hard, and transitional state. The broadband spectra can be described in general as the sum of thermal Comptonization and reflection due to illumination of an optically thick accretion disk. During the high/soft state, blackbody emission is generated from the accretion disk and the surface of the neutron star. This emission, measured at a temperature of kT_(bb) ~ 1.2 keV, is then Comptonized by a thick corona with an electron temperature of ~2.5 keV. For the transitional and low/very-hard state, the spectra are successfully explained with emission from a double Comptonizing corona. The first component is described by thermal Comptonization of seed disk/neutron star photons (kT_(bb) ~ 1.2 keV) by a cold corona cloud with kT_e ~ 8–10 keV, while the second one originates from lower temperature blackbody photons (kT_(bb) ≤ 0.1 keV) Comptonized by a hot corona (kT_e ~ 35 keV). Finally, from NuSTAR observations, there is evidence that the source is a new clocked burster. The average time between two successive X-ray bursts corresponds to ~7.9 and ~4.0 ks when the persistent emission decreases by a factor of ~2, moving from a very hard to transitional state. The accretion rate (~4 x 10⁻⁹ M⊙ yr ⁻¹) and the decay time of the X-ray bursts longer than ~30 s suggest that the thermonuclear emission is due to mixed H/He burning triggered by thermally unstable He ignition.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Fiocchi, M.0000-0001-5697-6019
Bazzano, A.0000-0002-2017-4396
Bruni, G.0000-0002-5182-6289
Ludlam, R.0000-0002-8961-939X
Natalucci, L.0000-0002-6601-9543
Additional Information:© 2019 The American Astronomical Society. Received 2017 June 1; revised 2019 October 10; accepted 2019 October 11; published 2019 December. We thank Dr. N. Degenaar and J. van den Eijnden for suggestions and discussion, that improved our work. We acknowledge the ASI financial/programmatic support via contracts ASI-INAF agreement number 2013-025.R1 and ASI-INAF 2017-14-H.0. We acknowledge the use of public data from the SWIFT and NuSTAR data archive. This research has made use of data provided by the High Energy Astrophysics Science Archive Research Center (HEASARC), which is a service of the Astrophysics Science Division at NASA/GSFC and the High Energy Astrophysics Division of the Smithsonian Astrophysical Observatory. R.L. gratefully acknowledges funding through a NASA Earth and Space Sciences Fellowship and the support of NASA through Hubble Fellowship Program grant HST-HF2-51440.001. F.O. acknowledges the support of the H2020 European HEMERA program, grant agreement No. 730970.
Funding AgencyGrant Number
Agenzia Spaziale Italiana (ASI)2013-025.R1
Agenzia Spaziale Italiana (ASI)2017-14-H.0
NASA Earth and Space Science FellowshipUNSPECIFIED
NASA Hubble FellowshipHST-HF2-51440.001
European Research Council (ERC)730970
Subject Keywords:Binary stars; Low-mass X-ray binary stars; X-ray astronomy; Gamma-ray bursters; Gamma-ray astronomy
Issue or Number:1
Classification Code:Unified Astronomy Thesaurus concepts: Binary stars (154); Low-mass X-ray binary stars (939); X-ray astronomy (1810); Gamma-ray bursters (1878); Gamma-ray astronomy (628)
Record Number:CaltechAUTHORS:20191209-081753551
Persistent URL:
Official Citation:M. Fiocchi et al 2019 ApJ 887 30
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:100230
Deposited By: Tony Diaz
Deposited On:09 Dec 2019 18:03
Last Modified:09 Dec 2019 18:03

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