A method to constrain the neutron star magnetic field in Low Mass X-ray Binaries

We describe here a method to put an upper limit to the strength of the magnetic field of neutron stars in low mass X‐ray binaries for which the spin period and the X‐ray luminosity during X‐ray quiescent periods are known. This is obtained using simple considerations about the position of the magnetospheric radius during quiescent periods. We applied this method to the accreting millisecond pulsar SAX J1808.4‐3658, which shows coherent X‐ray pulsations at a frequency of ∼ 400 Hz and a quiescent X‐ray luminosity of ∼ 5 × 1031 ergs/s, and found that B ⩽ 5 × 108 Gauss in this source. Combined with the lower limit inferred from the presence of X‐ray pulsations, this constrains the SAX J1808.4‐3658 neutron star magnetic field in the quite narrow range (1 – 5) × 108 Gauss. Similar considerations applied to the case of Aql X‐1 and KS 1731‐260 give neutron star magnetic fields lower than ∼ 109 Gauss

A Complex Environment around Circinus X-1

We present the results of an archival 54 ks long Chandra observation of the peculiar source Cir X-1 during the phase passage 0.223-0.261. We focus on the study of detected emission and absorption features using the HETGS. A comparative analysis of X-ray spectra, selected at different flux levels of the source, allows us to distinguish between a very hard state, at a low count rate, and a brighter, softer, highly absorbed spectrum during episodes of flaring activity. The spectrum of the hard state clearly shows emission lines of highly ionized elements, while, during the flaring state, the spectrum also shows strong resonant absorption lines. The most intense and interesting feature in this latter state is present in the Fe K alpha region: a very broadened absorption line at energies similar to 6.5 keV that could result from a smeared blending of resonant absorption lines of moderately ionized iron ions (Fe XX-Fe XXIV). We also observe strong resonant absorption lines of Fe XXV and Fe XXVI, together with a smeared absorption edge above 7 keV. We argue that the emitting region during the quiescent/hard state is constituted of a purely photoionized medium, possibly present above an accretion disk, or of a photoionized plasma present in a beamed outflow. During the flaring states the source undergoes enhanced turbulent accretion that modifies both the accretion geometry and the optical depth of the gas surrounding the primary X- ray source

Spectral Evolution of Scorpio X-1 along its Color-Color Diagram

We analyze a large collection of RXTE archive data of the bright X-ray source Scorpius X-1 in order to study the broadband spectral evolution of the source for different values of the inferred mass accretion rate by selecting energy spectra from its Color-Color Diagram. We model the spectra with the combination of two absorbed components: a soft thermal component, which can be interpreted as thermal emission from an accretion disk, and a hybrid Comptonization component, which self-consistently includes the Fe Kα fluorescence line and the Compton reflected continuum. The presence of hard emission in Scorpius X-1 has been previously reported, however, without a clear relation with the accretion rate. We show, for the first time, that there exists a common trend in the spectral evolution of the source, where the spectral parameters change in correlation with the position of the source in the CD. Using a hybrid thermal/non-thermal Comptonization model (EQPAIR code), we show that the ratio of the power supplied to the non-thermal distribution to the total power injected into the Comptonizing plasma correlates with the accretion rate, being the highest at the lowest accretion rates. We discuss the physical implications derived from the results of our analysis, with a particular emphasis on the hardest part of the X-ray emission and its possible origin

Resolving the Fe XXV triplet with Chandra in Centaurus X-3

We present the results of a 45 ks Chandra observation of the high-mass X-ray binary Cen X-3 at orbital phases between 0.13 and 0.40 (in the eclipse post-egress phases). Here we concentrate on the study of discrete features in the energy spectrum at energies between 6 and 7 keV, that is, on the iron K alpha line region, using the High Energy Transmission Grating Spectrometer (HETGS) on board the Chandra satellite. We clearly see a K alpha neutral iron line at similar to 6.40 keV and were able to distinguish the three lines of the Fe xxv triplet at 6.61, 6.67, and 6.72 keV, with equivalent widths of 6, 9, and 5 eV, respectively. The equivalent width of the Ka neutral iron line is 13 eV, an order of magnitude lower than previous measures. We discuss the possibility that the small equivalent width is due to a decrease of the solid angle subtended by the reflector

The Zoo of emission lines in the spectrum of Cir X-1 observed by XMM-Newton

We present the preliminary analysis of a 10 ks XMM-Newton EPIC/pn observation of Cir X-1 immediately after the zero phase. The continuum emission is modeled using a blackbody component partially absorbed by neutral matter probably located around the binary system. We detect a forest of emission lines associated to highly ionized ions

General relativistic effects on the evolution of binary systems.

When a radio pulsar brakes down due to magnetodipole emission,its gravitational mass decreases accordingly. If the pulsar is hosted in a binary system, this mass loss will Increase the orbital period of the system. We show that this relativistic effect can be indeed observable if the neutron star is fast and magnetized enough and that, if observed, it will help to put tight constraints to the equation of state of ultradense matter. Moreover, in Low Mass X-ray Binaries that evolve towards short periods, the neutron star lights up as a radio pulsar during the "period gap". As the effect we consider contrasts the orbital period decay, the system spends a longer time in this phase. As a consequence, the neutron star can survive this phase only if it is non-supramassive, Since in such bianries similar to 0.84M(circle dot) can be accreted onto the neutron star, short period (P <= 2 h) millisecond Xray pulsars like SAX J1808.4-3658 can be formed only if either a large part of the accreting matter has been ejected from the system, or the equation of state of ultradense matter is very stiff

The BeppoSAX 0.1 - 18 keV Spectrum of the Bright Atoll Source GX 9+1: an Indication of the Source Distance

We report the results of a long, 350 ks, BeppoSAX observation of the bright atoll source GX 9+1 in the 0.12 - 18 keV energy range. During this observation GX 9+1 showed a large count rate variability in its lightcurve. From its color - color diagram we selected six zones and extracted the source energy spectrum from each zone. We find that the model, composed of a blackbody plus a Comptonized component absorbed by an equivalent hydrogen column of similar to 1.4 x 10(22) cm(-2), fits the spectra in the energy range 1 - 18 keV well; however, below 1 keV a soft excess is present. We find that the spectrum of GX 9+1, in the 0.12 - 18 keV energy range, is well fitted by the model above, if we use an equivalent hydrogen column of similar to 0.8 x 10(22) cm(-2), together with several absorption edges from ionized matter ( O VII, O VIII, Ne IX, Ar XVII, and Ca XX) and an absorption line from Si XIV. From the study of these features we deduce that the electron density of the plasma and the equivalent hydrogen column density associated with the ionized matter is similar to 10(12) cm(-3) and similar to 10(23) cm(-2), respectively, at a distance from the central object of r similar to 10(11) cm, while at larger distances the equivalent hydrogen column density associated to the ionized matter decreases down to similar to 10(22) cm(-2)

High resolution Spectroscopy of 4U 1728-34 from a Simultaneous Chandra-RXTE Observation.

We report on a simultaneous Chandra and RossiXTE observation of the LMXB atoll bursting source 4U 1728-34 performed on 2002 March 3-5. We fitted the 1.2-35 keV continuum spectrum with a blackbody plus a Comptonized component. An overabundance of Si by a factor of ~2 with respect to Solar abundance is required for a satisfactory fit. Large residuals at 6-10 keV can be fitted by a broad (FWHM ~ 1.6 keV) Gaussian emission line, or, alternatively, by absorption edges associated with Fe I and Fe XXV at ~7.1 keV and ~9 keV, respectively. In this interpretation, we find no evidence of a broad, or narrow Fe Kalpha line, between 6 and 7 keV. We tested our alternative modeling of the iron Kalpha region by reanalyzing a previous BeppoSAX observation of 4U 1728-34, finding a general agreement with our new spectral model

Salaria fluviatilis: a Mediterranean, endangered, freshwater blenny

The Mediterranean freshwater ichthyofauna includes many interesting but poorly known species, because of little interest for sport fishing and culinary purposes. Salaria fluviatilis is the most widespread freshwater blenny of the Mediterranean. This species is found in rivers, brooks and low altitude lakes rich in branches and with stone bottom. Average lifespan is up to 5 years; larvae are planktonic until the size of about 1.5 cm and live in quiet waters. They reach a size of 12 cm on average and males are larger than females, and have a small ridge on the head. S. fluviatilis feeds on benthic organisms like small snails and shrimps, on fish and all kinds of insect larvae; it is itself prey of birds (migratory and resident), tortoise (e.g. Emys orbicularis) and snakes (e.g. Natrix spp). The population is very fragmented, and few data are available due to the difficulties to catch or to observe this fish; consequently, it is difficult to know its conservation status. It is included in Annex III of the Bern Convention and is considered a locally endangered species, listed by the IUCN Red List. The species is included in the overall plan of action for the conservation of freshwater Italian fishes. In South Italy, the main threat factors are water pollution, habitat destruction (gravel extraction, damming, canalization of rivers, etc.) and introduction of non-native predatory fish species like catfish (Ameiurus melas), bluegill (Lepomis macrochirus) and largemouth bass (Micropterus salmoides), of two allochthonous decapod crustaceans (Procambarus clarkii and Orconectes limosus) and two Testudines (Trachemys spp.). Due to their important ecological and trophic role of connection between benthic invertebrates, migratory birds and reptiles, we started a monitoring scientific program, capture of breeding animals, setting up of dedicated mesocosms and reproduction as well as rearing of juveniles for, local or in larger scale, restocking purpose allowed by the low genetic divergence of the species

Secreted miR-210-3p as non-invasive biomarker in clear cell renal cell carcinoma

The most common subtype of renal cell carcinoma (RCC) is clear cell RCC (ccRCC). It accounts for 70-80% of all renal malignancies representing the third most common urological cancer after prostate and bladder cancer. The identification of non-invasive biomarkers for the diagnosis and responsiveness to therapy of ccRCC may represent a relevant step-forward in ccRCC management. The aim of this study is to evaluate whether specific miRNAs deregulated in ccRCC tissues present altered levels also in urine specimens. To this end we first assessed that miR-21-5p, miR-210-3p and miR-221-3p resulted upregulated in ccRCC fresh frozen tissues compared to matched normal counterparts. Next, we evidenced that miR-210-3p resulted significantly upregulated in 38 urine specimens collected from two independent cohorts of ccRCC patients at the time of surgery compared to healthy donors samples. Of note, miR- 210-3p levels resulted significantly reduced in follow-up samples. These results point to miR-210-3p as a potential non-invasive biomarker useful not only for diagnosis but also for the assessment of complete resection or response to treatment in ccRCC management