An XMM-Newton look at the strongly variable radio-weak BL Lac Fermi J1544-0639

F. Ursini, L. Bassani, F. Panessa, E. Pian, G. Bruni, A. Bazzano, N. Masetti, K. Sokolovsky, P. Ubertini

Research output: Contribution to journalArticle

Abstract

Context. Fermi J1544-0639/ASASSN-17gs/AT2017egv was identified as a gamma-ray/optical transient on May 15, 2017. Subsequent multiwavelength observations suggest that this source may belong to the new class of radio-weak BL Lacs. Aims. We studied the X-ray spectral properties and short-term variability of Fermi J1544-0639 to constrain the X-ray continuum emission mechanism of this peculiar source. Methods. We present the analysis of an XMM-Newton observation, 56 ks in length, performed on February 21, 2018. Results. The source exhibits strong X-ray variability, both in flux and spectral shape, on timescales of ∼10 ks, with a harder-when-brighter behaviour typical of BL Lacs. The X-ray spectrum is nicely described by a variable broken power law, with a break energy of around 2.7 keV consistent with radiative cooling due to Comptonization of broad-line region photons. We find evidence for a "soft excess", nicely described by a blackbody with a temperature of ∼0.2 keV, consistent with being produced by bulk Comptonization along the jet.

Original languageEnglish
Article numberA116
JournalAstronomy and Astrophysics
Volume622
DOIs
Publication statusPublished - 6 Feb 2019

Fingerprint

XMM-Newton telescope
newton
radio
x rays
power law
gamma rays
continuums
cooling
timescale
photons
energy
temperature

Keywords

  • BL Lacertae objects: general
  • Quasars: general
  • Radiation mechanisms: non-thermal
  • X-rays: galaxies

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Ursini, F., Bassani, L., Panessa, F., Pian, E., Bruni, G., Bazzano, A., ... Ubertini, P. (2019). An XMM-Newton look at the strongly variable radio-weak BL Lac Fermi J1544-0639. Astronomy and Astrophysics, 622, [A116]. https://doi.org/10.1051/0004-6361/201834662
Ursini, F. ; Bassani, L. ; Panessa, F. ; Pian, E. ; Bruni, G. ; Bazzano, A. ; Masetti, N. ; Sokolovsky, K. ; Ubertini, P. / An XMM-Newton look at the strongly variable radio-weak BL Lac Fermi J1544-0639. In: Astronomy and Astrophysics. 2019 ; Vol. 622.
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Ursini, F, Bassani, L, Panessa, F, Pian, E, Bruni, G, Bazzano, A, Masetti, N, Sokolovsky, K & Ubertini, P 2019, 'An XMM-Newton look at the strongly variable radio-weak BL Lac Fermi J1544-0639', Astronomy and Astrophysics, vol. 622, A116. https://doi.org/10.1051/0004-6361/201834662

An XMM-Newton look at the strongly variable radio-weak BL Lac Fermi J1544-0639. / Ursini, F.; Bassani, L.; Panessa, F.; Pian, E.; Bruni, G.; Bazzano, A.; Masetti, N.; Sokolovsky, K.; Ubertini, P.

In: Astronomy and Astrophysics, Vol. 622, A116, 06.02.2019.

Research output: Contribution to journalArticle

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T1 - An XMM-Newton look at the strongly variable radio-weak BL Lac Fermi J1544-0639

AU - Ursini, F.

AU - Bassani, L.

AU - Panessa, F.

AU - Pian, E.

AU - Bruni, G.

AU - Bazzano, A.

AU - Masetti, N.

AU - Sokolovsky, K.

AU - Ubertini, P.

PY - 2019/2/6

Y1 - 2019/2/6

N2 - Context. Fermi J1544-0639/ASASSN-17gs/AT2017egv was identified as a gamma-ray/optical transient on May 15, 2017. Subsequent multiwavelength observations suggest that this source may belong to the new class of radio-weak BL Lacs. Aims. We studied the X-ray spectral properties and short-term variability of Fermi J1544-0639 to constrain the X-ray continuum emission mechanism of this peculiar source. Methods. We present the analysis of an XMM-Newton observation, 56 ks in length, performed on February 21, 2018. Results. The source exhibits strong X-ray variability, both in flux and spectral shape, on timescales of ∼10 ks, with a harder-when-brighter behaviour typical of BL Lacs. The X-ray spectrum is nicely described by a variable broken power law, with a break energy of around 2.7 keV consistent with radiative cooling due to Comptonization of broad-line region photons. We find evidence for a "soft excess", nicely described by a blackbody with a temperature of ∼0.2 keV, consistent with being produced by bulk Comptonization along the jet.

AB - Context. Fermi J1544-0639/ASASSN-17gs/AT2017egv was identified as a gamma-ray/optical transient on May 15, 2017. Subsequent multiwavelength observations suggest that this source may belong to the new class of radio-weak BL Lacs. Aims. We studied the X-ray spectral properties and short-term variability of Fermi J1544-0639 to constrain the X-ray continuum emission mechanism of this peculiar source. Methods. We present the analysis of an XMM-Newton observation, 56 ks in length, performed on February 21, 2018. Results. The source exhibits strong X-ray variability, both in flux and spectral shape, on timescales of ∼10 ks, with a harder-when-brighter behaviour typical of BL Lacs. The X-ray spectrum is nicely described by a variable broken power law, with a break energy of around 2.7 keV consistent with radiative cooling due to Comptonization of broad-line region photons. We find evidence for a "soft excess", nicely described by a blackbody with a temperature of ∼0.2 keV, consistent with being produced by bulk Comptonization along the jet.

KW - BL Lacertae objects: general

KW - Quasars: general

KW - Radiation mechanisms: non-thermal

KW - X-rays: galaxies

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