Pulsar-black hole binaries: prospects for new gravity tests with future radio telescopes

The anticipated discovery of a pulsar in orbit with a black hole is expected to provide a unique laboratory for black hole physics and gravity. In this context, the next generation of radio telescopes, like the Five-hundred-metre Aperture Spherical radio Telescope (FAST) and the Square Kilometre Array (SKA), with their unprecedented sensitivity, will play a key role. In this paper, we investigate the capability of future radio telescopes to probe the spacetime of a black hole and test gravity theories, by timing a pulsar orbiting a stellar-mass-black-hole (SBH). Based on mock data simulations, we show that a few years of timing observations of a sufficiently compact pulsar-SBH (PSR-SBH) system with future radio telescopes would allow precise measurements of the black hole mass and spin. A measurement precision of one per cent can be expected for the spin. Measuring the quadrupole moment of the black hole, needed to test GR's no-hair theorem, requires extreme system configurations with compact orbits and a large SBH mass. Additionally, we show that a PSR-SBH system can lead to greatly improved constraints on alternative gravity theories even if they predict black holes (practically) identical to GR's. This is demonstrated for a specific class of scalar-tensor theories. Finally, we investigate the requirements for searching for PSR-SBH systems. It is shown that the high sensitivity of the next generation of radio telescopes is key for discovering compact PSR-SBH systems, as it will allow for sufficiently short survey integration times.Comment: 20 pages, 11 figures, 1 table, accepted for publication in MNRA

Prospects for probing strong gravity with a pulsar-black hole system

The discovery of a pulsar (PSR) in orbit around a black hole (BH) is expected to provide a superb new probe of relativistic gravity and BH properties. Apart from a precise mass measurement for the BH, one could expect a clean verification of the dragging of space-time caused by the BH spin. In order to measure the quadrupole moment of the BH for testing the no-hair theorem of general relativity (GR), one has to hope for a sufficiently massive BH. In this respect, a PSR orbiting the super-massive BH in the center of our Galaxy would be the ultimate laboratory for gravity tests with PSRs. But even for gravity theories that predict the same properties for BHs as GR, a PSR-BH system would constitute an excellent test system, due to the high grade of asymmetry in the strong field properties of these two components. Here we highlight some of the potential gravity tests that one could expect from different PSR-BH systems, utilizing present and future radio telescopes, like FAST and SKA.Comment: Proceedings of IAUS 291 "Neutron Stars and Pulsars: Challenges and Opportunities after 80 years", J. van Leeuwen (ed.); 6 pages, 3 figure

Prospects for Probing the Spacetime of Sgr A* with Pulsars

The discovery of radio pulsars in compact orbits around Sgr A* would allow an unprecedented and detailed investigation of the spacetime of the supermassive black hole. This paper shows that pulsar timing, including that of a single pulsar, has the potential to provide novel tests of general relativity, in particular its cosmic censorship conjecture and no-hair theorem for rotating black holes. These experiments can be performed by timing observations with 100 micro-second precision, achievable with the Square Kilometre Array for a normal pulsar at frequency above 15 GHz. Based on the standard pulsar timing technique, we develop a method that allows the determination of the mass, spin, and quadrupole moment of Sgr A*, and provides a consistent covariance analysis of the measurement errors. Furthermore, we test this method in detailed mock data simulations. It seems likely that only for orbital periods below ~0.3 yr is there the possibility of having negligible external perturbations. For such orbits we expect a ~10^-3 test of the frame dragging and a ~10^-2 test of the no-hair theorem within 5 years, if Sgr A* is spinning rapidly. Our method is also capable of identifying perturbations caused by distributed mass around Sgr A*, thus providing high confidence in these gravity tests. Our analysis is not affected by uncertainties in our knowledge of the distance to the Galactic center, R0. A combination of pulsar timing with the astrometric results of stellar orbits would greatly improve the measurement precision of R0.Comment: 12 pages, 10 Figures, accepted for publication in Ap

Can we see pulsars around Sgr A*? - The latest searches with the Effelsberg telescope

Radio pulsars in relativistic binary systems are unique tools to study the curved space-time around massive compact objects. The discovery of a pulsar closely orbiting the super-massive black hole at the centre of our Galaxy, Sgr A*, would provide a superb test-bed for gravitational physics. To date, the absence of any radio pulsar discoveries within a few arc minutes of Sgr A* has been explained by one principal factor: extreme scattering of radio waves caused by inhomogeneities in the ionized component of the interstellar medium in the central 100 pc around Sgr A*. Scattering, which causes temporal broadening of pulses, can only be mitigated by observing at higher frequencies. Here we describe recent searches of the Galactic centre region performed at a frequency of 18.95 GHz with the Effelsberg radio telescope.Comment: 3 pages, 2 figures, Proceedings of IAUS 291 "Neutron Stars and Pulsars: Challenges and Opportunities after 80 years", 201

Observing Radio Pulsars in the Galactic Centre with the Square Kilometre Array

The discovery and timing of radio pulsars within the Galactic centre is a fundamental aspect of the SKA Science Case, responding to the topic of "Strong Field Tests of Gravity with Pulsars and Black Holes" (Kramer et al. 2004; Cordes et al. 2004). Pulsars have in many ways proven to be excellent tools for testing the General theory of Relativity and alternative gravity theories (see Wex (2014) for a recent review). Timing a pulsar in orbit around a companion, provides a unique way of probing the relativistic dynamics and spacetime of such a system. The strictest tests of gravity, in strong field conditions, are expected to come from a pulsar orbiting a black hole. In this sense, a pulsar in a close orbit ($P_{\rm orb}$ < 1 yr) around our nearest supermassive black hole candidate, Sagittarius A* - at a distance of ~8.3 kpc in the Galactic centre (Gillessen et al. 2009a) - would be the ideal tool. Given the size of the orbit and the relativistic effects associated with it, even a slowly spinning pulsar would allow the black hole spacetime to be explored in great detail (Liu et al. 2012). For example, measurement of the frame dragging caused by the rotation of the supermassive black hole, would allow a test of the "cosmic censorship conjecture." The "no-hair theorem" can be tested by measuring the quadrupole moment of the black hole. These are two of the prime examples for the fundamental studies of gravity one could do with a pulsar around Sagittarius A*. As will be shown here, SKA1-MID and ultimately the SKA will provide the opportunity to begin to find and time the pulsars in this extreme environment.Comment: 14 pages, 5 figures, to be published in: "Advancing Astrophysics with the Square Kilometre Array", Proceedings of Science, PoS(AASKA14)04

Pulsar J1411+2551: A Low Mass New Double Neutron Star System

In this work, we report the discovery and characterization of PSR J1411+2551, a new binary pulsar discovered in the Arecibo 327 MHz Drift Pulsar Survey. Our timing observations of the radio pulsar in the system span a period of about 2.5 years. This timing campaign allowed a precise measurement of its spin period (62.4 ms) and its derivative (9.6 $\pm$ 0.7) $\times 10^{-20}\, \rm s\, s^{-1}$; from these, we derive a characteristic age of $\sim 10\,$Gyr and a surface magnetic field strength of 2.5 $\times 10^{9}$ G. These numbers indicate that this pulsar was mildly recycled by accretion of matter from the progenitor of the companion star. The system has an eccentric ($e\, = \, 0.17$) 2.61 day orbit. This eccentricity allows a highly significant measurement of the rate of advance of periastron, $\dot{\omega} = 0.07686 \pm 0.00046 ^{\circ}~{\rm yr}^{-1}$. Assuming general relativity accurately models the orbital motion, this implies a total system mass M = $2.538 \pm 0.022 M_{\odot}$. The minimum companion mass is $0.92\, M_{\odot}$ and the maximum pulsar mass is $1.62\, M_{\odot}$. The large companion mass and the orbital eccentricity suggest that PSR J1411+2551 is a double neutron star system; the lightest known to date including the DNS merger GW 170817. Furthermore, the relatively low orbital eccentricity and small proper motion limits suggest that the second supernova had a relatively small associated kick; this and the low system mass suggest that it was an ultra-stripped supernova.Comment: Accepted for publication in APJ letter

Mucosal Progranulin expression is induced by H. pylori, but independent of Secretory Leukocyte Protease Inhibitor (SLPI) expression

<p>Abstract</p> <p>Background</p> <p>Mucosal levels of Secretory Leukocyte Protease Inhibitor (SLPI) are specifically reduced in relation to <it>H. pylori</it>-induced gastritis. Progranulin is an epithelial growth factor that is proteolytically degraded into fragments by elastase (the main target of SLPI). Considering the role of SLPI for regulating the activity of elastase, we studied whether the <it>H. pylori</it>-induced reduction of SLPI and the resulting increase of elastase-derived activity would reduce the Progranulin protein levels both <it>ex vivo </it>and <it>in vitro</it>.</p> <p>Methods</p> <p>The expression of Progranulin was studied in biopsies of <it>H. pylori</it>-positive, -negative and -eradicated subjects as well as in the gastric tumor cell line AGS by ELISA, immunohistochemistry and real-time RT-PCR.</p> <p>Results</p> <p><it>H. pylori</it>-infected subjects had about 2-fold increased antral Progranulin expression compared to <it>H. pylori</it>-negative and -eradicated subjects (P < 0.05). Overall, no correlations between mucosal Progranulin and SLPI levels were identified. Immunohistochemical analysis confirmed the upregulation of Progranulin in relation to <it>H. pylori </it>infection; both epithelial and infiltrating immune cells contributed to the higher Progranulin expression levels. The <it>H. pylori</it>-induced upregulation of Progranulin was verified in AGS cells infected by <it>H. pylori</it>. The down-regulation of endogenous SLPI expression in AGS cells by siRNA methodology did not affect the Progranulin expression independent of the infection by <it>H. pylori</it>.</p> <p>Conclusions</p> <p>Taken together, Progranulin was identified as novel molecule that is upregulated in context to <it>H. pylori </it>infection. In contrast to other diseases, SLPI seems not to have a regulatory role for Progranulin in <it>H. pylori</it>-mediated gastritis.</p

Leukotriene receptor expression in esophageal squamous cell cancer and non-transformed esophageal epithelium: a matched case control study

Study questionnaire. (DOC 21 kb

Discovery of 10 pulsars in an Arecibo drift-scan survey

We present the results of a 430-MHz survey for pulsars conducted during the upgrade to the 305-m Arecibo radio telescope. Our survey covered a total of 1147 square degrees of sky using a drift-scan technique. We detected 33 pulsars, 10 of which were not known prior to the survey observations. The highlight of the new discoveries is PSR J0407+1607, which has a spin period of 25.7 ms, a characteristic age of 1.5 Gyr and is in a 1.8-yr orbit about a low-mass (>0.2 Msun) companion. The long orbital period and small eccentricity (e = 0.0009) make the binary system an important new addition to the ensemble of binary pulsars suitable to test for violations of the strong equivalence principle. We also report on our initially unsuccessful attempts to detect optically the companion to J0407+1607 which imply that its absolute visual magnitude is > 12.1. If, as expected on evolutionary grounds, the companion is an He white dwarf, our non-detection imples a cooling age of least 1 Gyr.Comment: 8 pages, 3 figures, accepted for publication in MNRA