Mereghetti, S;
Rigoselli, M;
Taverna, R;
Baldeschi, L;
Crestan, S;
Turolla, R;
Zane, S;
(2021)
NICER Study of Pulsed Thermal X-Rays from Calvera: A Neutron Star Born in the Galactic Halo?
The Astrophysical Journal
, 922
(2)
, Article 253. 10.3847/1538-4357/ac34f2.
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Abstract
Calvera (1RXS J141256.0+792204) is an isolated neutron star detected only through its thermal X-ray emission. Its location at high Galactic latitude (b=+37∘) is unusual if Calvera is a relatively young pulsar, as suggested by its spin period (59 ms) and period derivative (3.2×10−15 Hz s−1). Using the Neutron Star Interior Composition Explorer (NICER), we obtained a phase-connected timing solution spanning four years which allowed us to measure the second derivative of the frequency ν¨=−2.5×10−23 Hz s−2 and to reveal timing noise consistent with that of normal radio pulsars. A magnetized hydrogen atmosphere model, covering the entire star surface, provides a good description of the phase-resolved spectra and energy-dependent pulsed fraction. However, we find that a temperature map more anisotropic than that produced by a dipole field is required, with a hotter zone concentrated towards the poles. By adding two small polar caps, we find that the surface effective temperature and that of the caps are ~0.1 and ~0.36 keV, respectively. The inferred distance is ~3.3 kpc. We confirm the presence of an absorption line at 0.7 keV associated to the emission from the whole star surface, difficult to interpret as a cyclotron feature and more likely originating from atomic transitions. We searched for pulsed γ-ray emission by folding seven years of Fermi-LAT data using the X-ray ephemeris, but no evidence for pulsations was found. Our results favour the hypothesis that Calvera is a normal rotation-powered pulsar, with the only peculiarity of being born at a large height above the Galactic disk
| Type: | Article |
|---|---|
| Title: | NICER Study of Pulsed Thermal X-Rays from Calvera: A Neutron Star Born in the Galactic Halo? |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.3847/1538-4357/ac34f2 |
| Publisher version: | https://doi.org/10.3847/1538-4357/ac34f2 |
| Language: | English |
| Additional information: | Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence (http://creativecommons.org/licenses/by/4.0/). Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10139302 |
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