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Post Info TOPIC: 1RXS J141256.0+792204
Blobrana


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Calvera
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Title: Is Calvera a Gamma-ray Pulsar?
Authors: J.P. Halpern

Originally selected as a neutron star (NS) candidate in the ROSAT All-Sky Survey, 1RXS J141256.0+792204 ("Calvera") was discovered to be a 59 ms X-ray pulsar in a pair of XMM-Newton observations (Zane et al. 2011). Surprisingly, their claimed detection of this pulsar in Fermi gamma-ray data requires no period derivative, severely restricting its dipole magnetic field strength, spin-down luminosity, and distance to small values. This implies that the cooling age of Calvera is much younger than its characteristic spin-down age. If so, it could be a mildly recycled pulsar, or the first "orphaned" central compact object (CCO). Here we show that the published Fermi ephemeris fails to align the pulse phases of the two X-ray observations with each other, which indicates that the Fermi detection is almost certainly spurious. Analysis of additional Fermi data also does not confirm the gamma-ray detection. This leaves the spin-down rate of Calvera less constrained, and its place among the families of NSs uncertain. It could still be either a normal pulsar, a mildly recycled pulsar, or an orphaned CCO.

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Blobrana


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1RXS J141256.0+792204
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Title: Chandra Observations of 1RXS J141256.0+792204 (Calvera)
Authors: Andrew S. H. Shevchuk, Derek B. Fox, Robert E. Rutledge

We report the results of a 30 ks Chandra ACIS-S observation of the isolated compact object 1RXS J141256.0+792204 (Calvera). The X-ray spectrum is adequately described by an absorbed neutron star hydrogen atmosphere model with an effective temperature at infinity of 88.3 ±0.8 eV and radiation radius at infinity of 4.1 ±0.1 km/kpc. The best-fit blackbody spectrum yields parameters consistent with previous measurements; although the fit itself is not statistically acceptable, systematic uncertainties in the pile-up correction may contribute to this. We find marginal evidence for narrow spectral features in the X-ray spectrum between 0.3 and 1.0 keV. In one interpretation, we find evidence at 81%-confidence for an absorption edge at 0.64 (+0.08) (-0.06) keV with an equivalent width of ~70 eV; if this feature is real, it is reminiscent of features seen in the isolated neutron stars RX J1605.3+3249, RX J0720.4-3125, and 1RXS J130848.6+212708 (RBS 1223). In an alternative approach, we find evidence at 88%-confidence for an unresolved emission line at energy 0.53 ±0.02 keV, with an equivalent width of ~28 eV; the interpretation of this feature, if real, is uncertain. We search for coherent pulsations up to the Nyquist frequency of 1.13 Hz and set an upper limit of 8.0% rms on the strength of any such modulation. We derive an improved position for the source and set the most rigorous limits to-date on any associated extended emission on arcsecond scales. Our analysis confirms the basic picture of Calvera as the first isolated compact object in the ROSAT/Bright Source Catalogue discovered in six years, the hottest such object known, and an intriguing target for multiwavelength study.

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Blobrana


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Astronomers have spotted a space oddity in Earth's neighbourhood: a dead star with some unusual characteristics.
The object - known as a neutron star - was studied using space telescopes and ground-based observatories.
But this one, located in the constellation Ursa Minor, seems to lack some key characteristics found in other neutron stars.

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Blobrana


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Using NASA's Swift satellite, McGill University and Penn State University astronomers have identified an object that is likely one of the closest neutron stars to Earth -- and possibly the closest.
The object, located in the constellation Ursa Minor, is nicknamed Calvera, after the villain in the movie "The Magnificent Seven." If confirmed, it would be only the eighth known "isolated neutron star" -- meaning a neutron star that does not have an associated supernova remnant, binary companion, or radio pulsations.

"The seven previously known isolated neutron stars are known collectively as 'The Magnificent Seven' within the community and so the name Calvera is a bit of an inside joke on our part" - Derek Fox of Penn State, co-discoverer.

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Title: Discovery of an Isolated Compact Object at High Galactic Latitude
Authors: R. E. Rutledge, D. B. Fox, & A. H. Shevchuk

We report discovery of Calvera,  a compact object at high Galactic latitude. We initially identified Calvera as a ROSAT All-Sky Survey Bright Source Catalogue X-ray source, 1RXS J141256.0+792204, statistically likely to possess a high X-ray to optical flux ratio. Further observations using Swift, Gemini-North, and the Chandra X-ray Observatory refined the source position and confirmed the absence of any optical counterpart to an X-ray to optical flux ratio of FX(0.12.4 keV)/FV > 5100 (3). Interpretation of Calvera as a typical Xray-dim isolated neutron star would place it at z = 6.7 kpc above the Galactic disk in the Galactic halo implying that it either has an extreme space velocity (vz = > 6700 kms^1) or has failed to cool according to theoretical predictions. Interpretations as a persistent anomalous X-ray pulsar, or a compact central object present conflicts with these classes typical properties. We conclude the properties of Calvera are most consistent with those of a nearby (150 to 560 pc) radio pulsar, similar to the radio millisecond pulsars of 47 Tuc, with further observations required to confirm this classification. If it is a millisecond pulsar, it would be among the X-ray brightest millisecond pulsars, and only the third northern hemisphere millisecond pulsar at such close distance, making it an interesting target for X-ray-study, a radio pulsar timing array, and LIGO.

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