G. Novara

An accreting pulsar with extreme properties drives an ultraluminous x-ray source in NGC 5907

Spinning up an extragalactic neutron star Ultraluminous x-ray sources (ULXs) are strange objects in other galaxies that cannot be explained by conventional accretion onto stellar-mass objects. This has led to exotic interpretations, such as the long-sought intermediate-mass black holes. Israel et al. observed a ULX in the nearby galaxy NGC 5907 and found that it is instead a neutron star. The spinning neutron star is accreting material so fast that its spin period is quickly accelerating. The only way that it can consume enough material to explain these properties is if it has a strong multipolar magnetic field. Science, this issue p. 817 An ultraluminous x-ray source in NGC 5907 is a spinning neutron star with a complex magnetic field. Ultraluminous x-ray sources (ULXs) in nearby galaxies shine brighter than any x-ray source in our Galaxy. ULXs are usually modeled as stellar-mass black holes (BHs) accreting at very high rates or intermediate-mass BHs. We present observations showing that NGC 5907 ULX is instead an x-ray accreting neutron star (NS) with a spin period evolving from 1.43 seconds in 2003 to 1.13 seconds in 2014. It has an isotropic peak luminosity of ~1000 times the Eddington limit for a NS at 17.1 megaparsec. Standard accretion models fail to explain its luminosity, even assuming beamed emission, but a strong multipolar magnetic field can describe its properties. These findings suggest that other extreme ULXs (x-ray luminosity ≥ 1041 erg second−1) might harbor NSs.

MULTIWAVELENGTH OBSERVATIONS OF 3C 454.3. I. THE AGILE 2007 NOVEMBER CAMPAIGN ON THE “CRAZY DIAMOND”

We report on a multiwavelength observation of the blazar 3C 454.3 (which we dubbedcrazydiamond) carried out on November 2007 by means of the astrophysical satellitesAGILE,InternationalGamma-RayAstrophysicsLaboratory (INTEGRAL), Swift, the Whole Earth Blazar Telescope (WEBT) Consortium, and the optical–NIR telescope Rapid Eye Mount (REM). Thanks to the wide field of view of theAGILE satellite and its prompt alert dissemination to other observatories, we obtained a long (three weeks), almost continuous γ -ray coverage of the blazar 3C 454.3 across 14 decades of energy. This broadband monitoring allows us to study in great detail light curves, correlations, time lags, and spectral energy distributions (SEDs) during different physical states. Gamma-ray data were collected during an AGILE pointing toward the Cygnus Region. Target of Opportunity (ToO) observations were performed to follow up the γ -ray observations in the soft and hard X-ray energy bands. Optical data were acquired continuously by means of a preplanned WEBT campaign and through an REM ToO repointing. 3C 454.3 is detected at a ∼19σ level during the three-week observing period, with an average flux above 100 MeV of FE>100 MeV = (170 ± 13) × 10 −8 photons cm −2 s −1 .T heγ -ray spectrum can be fitted with a single power law with photon index ΓGRID = 1.73 ± 0.16 between 100 MeV and 1 GeV. We detect significant day-by-day variability of the γ -ray emission during our observations, and we can exclude that the fluxes are constant at the 99.6% (∼ 2.9σ ) level. The source was detected typically around 40 deg off-axis, and it was substantially off–axis in the field of view of the AGILE hard X-ray imager. However, a five-day long ToO observation by INTEGRAL detected 3C 454.3 at an average flux of about F20–200 keV = 1.49 × 10 −3 photons cm −2 s −1 with an average photon index of ΓIBIS = 1.75 ± 0.24 between 20– 200 keV. Swift also detected 3C 454.3 with a flux in the 0.3–10 keV energy band in the range (1.23–1.40) × 10 −2 photons cm −2 s −1 and a photon index in the range ΓXRT = 1.56–1.73. In the optical band, both WEBT and REM show an extremely variable behavior in the R band. A correlation analysis based on the entire data set is consistent with no time lags between the γ -ray and the optical flux variations. Our simultaneous multifrequency observations strongly indicate that the dominant emission mechanism between 30 MeV and 30 GeV is dominated by inverse Compton scattering of relativistic electrons in the jet on the external photons from the broad line region.

Highly absorbed X-ray binaries in the Small Magellanic Cloud

Many of the high mass X-ray binaries (HMXRBs) discovered in recent years in our Galaxy are characterized by a high absorption, most likely intrinsic to the system, that can impede their detection at the softest X-ray energies. Exploiting the good coverage obtained with sensitive XMM-Newtonobservations, we have undertaken a search for highly absorbed X-ray sources in the Small Magellanic Cloud (SMC), which is known to contain a large number of HMXRBs. After a systematic analysis of 62 XMM-NewtonSMC observations, we obtained a sample of 30 sources with evidence of an equivalent hydrogen column density larger than 3×10 23 cm 2 . Five of these sources are clearly identified as HMXRBs, four being previously known (including three X-ray pulsars) and one, XMMU J005605.8-720012, being reported here for the first time. For the latter, we present optical spectroscopy confirming the asso ciation with a Be star in the SMC. The other sources in our sample have optical counterparts fainter than magnitude ∼16 in the V band, and many have possible NIR counterparts consistent with highly reddened early-type stars in the SMC. While their number is broadly consistent with the expected population of background highly absorbed active galactic nuclei, a few of them could be HMXRBs in which an early-type companion is severely reddened by local material.

XMM–Newton and Swift observations prove GRB 090709A to be a distant, standard, long GRB

GRB 090709A is a long gamma-ray burst (GRB) discovered by Swift, featuring a bright X-ray afterglow as well as a faint infrared transient with very red and peculiar colours. The burst attracted a large interest because of a possible quasi-periodicity at P = 8.1 s in the prompt emission, suggesting that it could have a different origin with respect to standard, long GRBs. In order to understand the nature of this burst, we obtained a target of opportunity observation with XMM-Newton. X-ray spectroscopy, based on XMM-Newton and Swift data, allowed us to model the significant excess in photoelectric absorption with respect to the Galactic value as due to a large column density (~6.5 x 10 22 cm -2 ) in the GRB host, located at z ~ 4.2. Such a picture is also consistent with the infrared transients properties. Re-analysis of the prompt emission, based on International Gamma-Ray Astrophysics Laboratory and on Swift data, excludes any significant modulation at P = 8.1 s. Thus, we conclude that GRB 090709A is a distant, standard, long GRB.

EXTraS discovery of an 1.2-s X-ray pulsar in M 31

During a search for coherent signals in the X-ray archival data of XMM-Newton, we discovered a modulation at 1.2 s in 3XMM J004301.4+413017 (3X J0043), a source lying in the direction of an external arm of M 31. This short period indicates a neutron star (NS). Between 2000 and 2013, the position of 3X J0043 was imaged by public XMM-Newton observations 35 times. The analysis of these data allowed us to detect an orbital modulation at 1.27 d and study the long-term properties of the source. The emission of the pulsar was rather hard (most spectra are described by a power law with

Results from DROXO - IV. EXTraS discovery of an X-ray flare from the Class I protostar candidate ISO-Oph 85

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Follow-up observations of X-ray emitting hot subdwarf stars: the He-rich sdO BD +37° 1977

) and, assuming the distance to M 31, the 0.3-10 keV luminosity was variable, from

EXTraS discovery of two pulsators in the direction of the LMC: a Be/X-ray binary pulsar in the LMC and a candidate double-degenerate polar in the foreground

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A new ultraluminous X-ray source in the galaxy NGC 5907

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