Long-term light-curves of transient X-ray pulsars as a tool to study disk−magnetosphere interaction

X-ray pulsars are highly magnetized neutron stars in close binary systems accreting matter from a normal companion star. Their strong magnetic fields channel the accreting matter onto the magnetic poles of the neutron star, releasing an enormous amount of energy in the form of X-rays. If the matter accreted from the stellar companion carries a large amount of angular momentum, it will generally form an accretion disk around the neutron star. The strong magnetic field of the neutron star will effectively truncate the accretion disk at the magnetospheric radius, which defines the space around the X-ray pulsar known as the magnetosphere. The observed behavior of the X-ray pulsar will depend on several factors, including the rate at which mass is being accreted. At low mass accretion rates, the magnetosphere will be able to extend further out, and if the mass accretion rate drops below some critical value, accreting matter will be stopped by the centrifugal barrier created by the neutron star’s rapidly spinning magnetosphere. This is known as the propeller effect, because matter is basically flung out by the rapidly spinning magnetosphere. The propeller effect is generally used to explain the declining phases of the outbursts of transient X-ray pulsars into quiescence. Another phenomenon recently proposed for transient X-ray pulsars is the possibility of accretion from a cold accretion disk at low mass accretion rates. This is caused by a thermal-viscous instability developing in the accretion disk and is commonly invoked to explain the characteristic outbursts of dwarf novae, where the theory is encapsulated in the disk instability model (DIM). During the decay of dwarf nova outbursts, a propagating cooling front will appear in the accretion disk, and when this front reaches the inner disk radius, the entire disk will be in a cold state of neutral hydrogen. In this thesis, the data from observations made by the Swift observatory have been analyzed with the intent to test the possibility of the appearance of a propagating cooling front during the decaying phases of the outbursts of transient X-ray pulsars. The light-curves of three sources (SMC X-2, 4U 0115+63, V 0332+53) were fitted with a smoothed spline representing the observed behavior, which was subsequently compared to the modeled luminosity decay caused by the propagation of a cooling front. The result of the analysis is that by modeling the expected behavior of a cooling front propagating through the accretion disk, the luminosity decay of these transient X-ray pulsar’s outbursts can be well explained without the need to invoke the propeller effect. Additionally, the obtained αcold values are consistent with the values commonly used in the DIM

X-ray pulsar GRO J1008−-57 as an orthogonal rotator

X-ray polarimetry is a unique way to probe geometrical configuration of highly-magnetized accreting neutron stars (X-ray pulsars). GRO J1008$-$57 is the first transient X-ray pulsar observed at two different flux levels by the Imaging X-ray Polarimetry Explorer (IXPE) during its outburst in November 2022. The polarization properties were found to be independent of the source luminosity, with the polarization degree varying between non-detection to about 15% over the pulse phase. Fitting the phase-resolved spectro-polarimetric data with the rotating vector model allowed us to estimate the pulsar inclination (130 deg, which is in good agreement with the orbital inclination), the position angle (75 deg) of the pulsar spin axis, and the magnetic obliquity (74 deg). This makes GRO J1008$-$57 the first confidently identified X-ray pulsar as a nearly orthogonal rotator. The results are discussed in the context of the neutron star atmosphere models and theories of pulsars' axis alignment.Comment: 11 pages, 7 figures, submitted to A&A. arXiv admin note: text overlap with arXiv:2209.0244

IXPE Observations of the Quintessential Wind-accreting X-Ray Pulsar Vela X-1

The radiation from accreting X-ray pulsars was expected to be highly polarized, with some estimates for the polarization degree of up to 80%. However, phase-resolved and energy-resolved polarimetry of X-ray pulsars is required in order to test different models and to shed light on the emission processes and the geometry of the emission region. Here we present the first results of the observations of the accreting X-ray pulsar Vela X-1 performed with the Imaging X-ray Polarimetry Explorer. Vela X-1 is considered to be the archetypal example of a wind-accreting, high-mass X-ray binary system, consisting of a highly magnetized neutron star accreting matter from its supergiant stellar companion. The spectropolarimetric analysis of the phase-averaged data for Vela X-1 reveals a polarization degree (PD) of 2.3% ± 0.4% at the polarization angle (PA) of −47.°3 ± 5.°4. A low PD is consistent with the results obtained for other X-ray pulsars and is likely related to the inverse temperature structure of the neutron star atmosphere. The energy-resolved analysis shows the PD above 5 keV reaching 6%–10% and a ∼90° difference in the PA compared to the data in the 2–3 keV range. The phase-resolved spectropolarimetric analysis finds a PD in the range 0%–9% with the PA varying between −80° and 40°

X-ray polarimetry of the accreting pulsar GX 301-2

The phase- and energy-resolved polarization measurements of accreting X-ray pulsars (XRPs) allow us to test different theoretical models of their emission, as well as to provide an avenue to determine the emission region geometry. We present the results of the observations of the XRP GX 301-2 performed with the Imaging X-ray Polarimetry Explorer (IXPE). GX 301-2 is a persistent XRP with one of the longest known spin periods of ~680 s. A massive hyper-giant companion star Wray 977 supplies mass to the neutron star via powerful stellar winds. We do not detect significant polarization in the phase-averaged data using spectro-polarimetric analysis, with the upper limit on the polarization degree (PD) of 2.3% (99% confidence level). Using the phase-resolved spectro-polarimetric analysis we get a significant detection of polarization (above 99% c.l.) in two out of nine phase bins and marginal detection in three bins, with a PD ranging between ~3% and ~10%, and a polarization angle varying in a very wide range from ~0 deg to ~160 deg. Using the rotating vector model we obtain constraints on the pulsar geometry using both phase-binned and unbinned analysis getting excellent agreement. Finally, we discuss possible reasons for a low observed polarization in GX 301-2.Comment: 10 pages, 10 figures, submitted to A&

A polarimetrically oriented X-ray stare at the accreting pulsar EXO 2030+375

Accreting X-ray pulsars (XRPs) are presumably ideal targets for polarization measurements, as their high magnetic field strength is expected to polarize the emission up to a polarization degree of ~80%. However, such expectations are being challenged by recent observations of XRPs with the Imaging X-ray Polarimeter Explorer (IXPE). Here we report on the results of yet another XRP, EXO 2030+375, observed with IXPE and contemporarily monitored with Insight-HXMT and SRG/ART-XC. In line with recent results obtained with IXPE for similar sources, analysis of the EXO 2030+375 data returns a low polarization degree of 0%-3% in the phase-averaged study and variation in the range 2%-7% in the phase-resolved study. Using the rotating vector model we constrain the geometry of the system and obtain a value for the magnetic obliquity of ~$60^{\circ}$. Considering also the estimated pulsar inclination of ~$130^{\circ}$, this indicates that the magnetic axis swings close to the observer line of sight. Our joint polarimetric, spectral and timing analysis hint to a complex accreting geometry where magnetic multipoles with asymmetric topology and gravitational light bending significantly affect the observed source behavior.Comment: A&A accepted. Proofs versio

Bloggare som marknadsförare : Trovärdigt eller ej?

Sociala medier blir allt större för var dag som går, och därmed måste företag kunna anpassa sig till förändringen och hitta på nya sätt att nå sina kunder på. Ett marknadsföringssätt som blivit allt större är att företaget kontaktar bloggare, som de sedan ber skriva ett inlägg om någon produkt eller tjänst gentemot lön i något format. Syftet med detta arbete är att ta reda på vad bloggläsarna anser om dessa reklaminlägg, och ge en idé över hur bloggare och företag kan förbättra sina samarbeten så att bloggarna inte tappar förtroendet hos sina läsare och företagen kan öka på sin kundkrets. Materialet till arbetet samlas in från böcker, analyser på nätet och med en undersökning i form av en enkät, vilken bloggläsare får svara på. Arbetet är uppdelat i tre delar. I första delen presenteras själva arbetet och syftet, samt hur det kommer att utföras. I del nummer två, teoridelen, diskuteras bland annat vad bloggar egentligen är samt etik och regler gällande bloggmarknadsföring, och en empiridel där resultatet av undersökningen presenteras och diskuteras.Sosiaalinen media kasvaa päivä päivältä ja on yhä tärkeämmässä roolissa markkinoinnin suhteen. Yritysten on pystyttävä soveltumaan tähän ja keksittävä uusia ratkaisuja miten lähestyä ja tavoittaa asiakkaitaan. Eräs menetelmä markkinoida, mikä on kasvanut yritysten kesken, on blogimarkkinointi, jolloin yritykset tavoittavat bloggaajia ja pyytävät heitä kirjoittamaan jostain tuotteesta tai palvelusta palkkaa vastaan. Tämän työn tarkoituksena onkin selvittää mitä lukijat tästä markkinointitavasta ajattelevat, ja antaa myös yrityksille ja bloggaajille ideanpoikasta miten voisivat kehittää yhteistyönsä niin, että molemmat hyötyvät siitä. Aineistoa työhön olen kerännyt kirjoista ja internetistä löytyneistä artikkeleista, sekä netissä kyselylomakkeen avulla johon eri blogien lukijat ovat saaneet vastata. Työ on jaettu kolmeen osaan. Ensimmäisessä osassa esitetään tarkemmin työn tarkoitus sekä miten se tullaan suorittaa. Toinen osa, eli teoreettinen osa, käsittelee muun muassa aihetta mitä blogit oikeasti ovat sekä etiikka ja säännöt kosken blogimarkkinointia. Kolmannessa osassa, empirissä, esitellään ja keskustellaan kyselylomakkeen tuloksia

IXPE Observations of the Quintessential Wind-accreting X-Ray Pulsar Vela X-1

Full list of authors: Forsblom, Sofia; Poutanen, Juri S.; Tsygankov, Sergey; Bachetti, Matteo; Marco, Alessandro Di; Doroshenko, Victor; Heyl, Jeremy; Monaca, Fabio La; Malacaria, Christian L.; Marshall, Herman; Muleri, Fabio A.; Mushtukov, Alexander; Pilia, Maura; Rogantini, Daniele F.; Suleimanov, Valery; Taverna, Roberto; Xie, Fei; Agudo, Ivan A.; Antonelli, Lucio; Baldini, Luca H.; Baumgartner, Wayne; Bellazzini, Ronaldo; Bianchi, Stefano D.; Bongiorno, Stephen; Bonino, Raffaella; Brez, Alessandro; Bucciantini, Niccolo; Capitanio, Fiamma; Castellano, Simone; Cavazzuti, Elisabetta; Chen, Chien-Ting; Ciprini, Stefano; Costa, Enrico; De Rosa, Alessandra; Del Monte, Ettore; Di Gesu, Laura; Di Lalla, Niccolo; Donnarumma, Immacolata; Dovciak, Michal R.; Ehlert, Steven; Enoto, Teruaki; Evangelista, Yuri; Fabiani, Sergio; Ferrazzoli, Riccardo A.; Garcia, Javier; Gunji, Shuichi; Hayashida, Kiyoshi; Iwakiri, Wataru G.; Jorstad, Svetlana; Kaaret, Philip; Karas, Vladimir; Kitaguchi, Takao J.; Kolodziejczak, Jeffery; Krawczynski, Henric; Latronico, Luca; Liodakis, Ioannis; Maldera, Simone; Manfreda, Alberto; Marin, Frederic; Marinucci, Andrea P.; Marscher, Alan; Matt, Giorgio; Mitsuishi, Ikuyuki; Mizuno, Tsunefumi; Negro, Michela; Ng, Chi-Yung L.; O'Dell, Stephen; Omodei, Nicola; Oppedisano, Chiara; Papitto, Alessandro G.; Pavlov, George L.; Peirson, Abel; Perri, Matteo; Pesce-Rollins, Melissa; Petrucci, Pierre-Olivier; Possenti, Andrea; Puccetti, Simonetta D.; Ramsey, Brian; Rankin, John; Ratheesh, Ajay J.; Roberts, Oliver W.; Romani, Roger; Sgro, Carmelo; Slane, Patrick; Soffitta, Paolo; Spandre, Gloria A.; Sunyaev, Rashid A.; Swartz, Douglas; Tamagawa, Toru; Tavecchio, Fabrizio; Tawara, Yuzuru F.; Tennant, Allyn E.; Thomas, Nicholas; Tombesi, Francesco; Trois, Alessio; Turolla, Roberto; Vink, Jacco C.; Weisskopf, Martin; Wu, Kinwah; Zane, Silvia; IXPE Collaboration.--This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.The radiation from accreting X-ray pulsars was expected to be highly polarized, with some estimates for the polarization degree of up to 80%. However, phase-resolved and energy-resolved polarimetry of X-ray pulsars is required in order to test different models and to shed light on the emission processes and the geometry of the emission region. Here we present the first results of the observations of the accreting X-ray pulsar Vela X-1 performed with the Imaging X-ray Polarimetry Explorer. Vela X-1 is considered to be the archetypal example of a wind-accreting, high-mass X-ray binary system, consisting of a highly magnetized neutron star accreting matter from its supergiant stellar companion. The spectropolarimetric analysis of the phase-averaged data for Vela X-1 reveals a polarization degree (PD) of 2.3% ± 0.4% at the polarization angle (PA) of −47fdg3 ± 5fdg4. A low PD is consistent with the results obtained for other X-ray pulsars and is likely related to the inverse temperature structure of the neutron star atmosphere. The energy-resolved analysis shows the PD above 5 keV reaching 6%–10% and a ∼90° difference in the PA compared to the data in the 2–3 keV range. The phase-resolved spectropolarimetric analysis finds a PD in the range 0%–9% with the PA varying between −80° and 40°. © 2023. The Author(s). Published by the American Astronomical Society.The Imaging X-ray Polarimetry Explorer (IXPE) is a joint US and Italian mission. The US contribution is supported by the National Aeronautics and Space Administration (NASA) and led and managed by its Marshall Space Flight Center (MSFC), with industry partner Ball Aerospace (contract NNM15AA18C). The Italian contribution is supported by the Italian Space Agency (Agenzia Spaziale Italiana, ASI) through contract ASI-OHBI-2017-12-I.0, agreements ASI-INAF-2017-12-H0 and ASI-INFN-2017.13-H0, and its Space Science Data Center (SSDC) with agreements ASI-INAF-2022-14-HH.0 and ASI-INFN 2021-43-HH.0, and by the Istituto Nazionale di Astrofisica (INAF) and the Istituto Nazionale di Fisica Nucleare (INFN) in Italy. This research used data products provided by the IXPE Team (MSFC, SSDC, INAF, and INFN) and distributed with additional software tools by the High-Energy Astrophysics Science Archive Research Center (HEASARC), at NASA Goddard Space Flight Center (GSFC). We acknowledge support from the RSF grant 19-12-00423 (SST), the Academy of Finland grants 333112, 349144, 349373, and 349906 (JP, SST), the German Academic Exchange Service (DAAD) travel grant 57525212 (VD, VFS), and the German Research Foundation (DFG) grant WE 1312/53-1 (VFS).With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2021-001131-S).Peer reviewe

The X-Ray Polarimetry View of the Accreting Pulsar Cen X-3

International audienceThe first X-ray pulsar, Cen X-3, was discovered 50 yr ago. Radiation from such objects is expected to be highly polarized due to birefringence of plasma and vacuum associated with propagation of photons in the presence of the strong magnetic field. Here we present results of the observations of Cen X-3 performed with the Imaging X-ray Polarimetry Explorer. The source exhibited significant flux variability and was observed in two states different by a factor of ~20 in flux. In the low-luminosity state, no significant polarization was found in either pulse phase-averaged (with a 3σ upper limit of 12%) or phase-resolved (the 3σ upper limits are 20%-30%) data. In the bright state, the polarization degree of 5.8% ± 0.3% and polarization angle of 49.°6 ± 1.°5 with a significance of about 20σ were measured from the spectropolarimetric analysis of the phase-averaged data. The phase-resolved analysis showed a significant anticorrelation between the flux and the polarization degree, as well as strong variations of the polarization angle. The fit with the rotating vector model indicates a position angle of the pulsar spin axis of about 49° and a magnetic obliquity of 17°. The detected relatively low polarization can be explained if the upper layers of the neutron star surface are overheated by the accreted matter and the conversion of the polarization modes occurs within the transition region between the upper hot layer and a cooler underlying atmosphere. A fraction of polarization signal can also be produced by reflection of radiation from the neutron star surface and the accretion curtain