Probing isolated compact remnants with microlensing

Sartore, N.; Treves, A.

doi:10.1051/0004-6361/201015060

Cited by 13 publications

(12 citation statements)

References 44 publications

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“…If the MW halo were composed only from such lenses with mass of around 10 M⊙, such an optical depth would mean they contribute no more than 2 per cent of the total mass of the dark halo. This is in agreement with the expected mass fraction of black-holes in the total mass budget of the Galaxy varying from around 5 per cent (Sartore & Treves 2010) for all massive stellar remnants to 0.4 per cent for a standard initial mass function (e.g., Bastian et al 2010) integrated above 6 M⊙. It is also a much tighter limit than the limit of 40 per cent derived by the MACHO group on objects below 30 M⊙ (Alcock et al 2001), obtained based on a lack of long-term events.…”

Section: Discussionsupporting

confidence: 90%

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The OGLE view of microlensing towards the Magellanic Clouds - IV. OGLE-III SMC data and final conclusions on MACHOs★

Wyrzykowski

Skowron

Kozłowski

et al. 2011

Monthly Notices of the Royal Astronomical Society

185

180

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In this fourth part of the series presenting the Optical Gravitational Lensing Experiment (OGLE) microlensing studies of the dark matter halo compact objects (MACHOs), we describe results of the OGLE‐III monitoring of the Small Magellanic Cloud (SMC). Three sound candidates for microlensing events were found and yielded the optical depth τSMC‐OIII= 1.30 ± 1.01 × 10−7, consistent with the expected contribution from Galactic disc and SMC self‐lensing. We report that event OGLE‐SMC‐03 is most likely a thick‐disc lens candidate, the first of such type found towards the SMC. In this paper we also combined all OGLE Large Magellanic Cloud and SMC microlensing results in order to refine the conclusions on MACHOs. All but one of the OGLE events are most likely caused by the lensing by known populations of stars; therefore, we concluded that there is no need for introducing any special dark matter compact objects in order to explain the observed event rates. Potential black hole event indicates that similar lenses can contribute only about 2 per cent to the total mass of the halo, which is still in agreement with the expected number of such objects.

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Section: Discussionsupporting

confidence: 90%

“…The upper limit on MACHO abundance in the halo was set to 6–7 per cent by the EROS (Tisserand et al 2007) and OGLE groups (Wyrzykowski et al 2011) (see Moniez 2010, for review). The core of the detected microlensing signal seems to come from the SL events, as suggested already in Sahu (1994b, a).…”

Section: Introductionsupporting

confidence: 51%

The OGLE view of microlensing towards the Magellanic Clouds - IV. OGLE-III SMC data and final conclusions on MACHOs★

Wyrzykowski

Skowron

Kozłowski

et al. 2011

Monthly Notices of the Royal Astronomical Society

185

180

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“…The Galactic population of isolated compact objects – remnants of massive star evolution – is very large: about 10 9 (see e.g. Sartore & Treves , and references therein). It should be dominated by neutron stars, but the number of isolated black holes (IBHs) is also non‐negligible: their number is ≳10 8 (Agol & Kamionkowski ).…”

Section: Introductionmentioning

confidence: 99%

“…Such estimates are usually based on detailed calculations for isolated neutron stars and normalization based on the relative number of compact objects. The local isolated neutron star spatial density is estimated to be ∼3 × 10 −5 to 3 × 10 −4 pc −3 (Popov et al ; Ofek ; Sartore & Treves ). The relative number of BHs to neutron stars is about 1/3.…”

Section: Introductionmentioning

confidence: 99%

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Jets and gamma-ray emission from isolated accreting black holes

Barkov¹,

Khangulyan

Попов

2012

Monthly Notices of the Royal Astronomical Society

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The large number of isolated black holes (IBHs) in the Galaxy, estimated to be 10^8, implies a very high density of 10^-4 pc^-3 and an average distance between IBHs of 10 pc. Our study shows that the magnetic flux, accumulated on the horizon of an IBH because of accretion of interstellar matter, allows the Blandford-Znajeck mechanism to be activated. Thus, electron-positron jets can be launched. We have performed 2D numerical modelling which allowed the jet power to be estimated. Their inferred properties make such jets a feasible electron accelerator which, in molecular clouds, allows electron energy to be boosted up to 1 PeV. For the conditions expected in molecular clouds the radiative cooling time should be comparable to the escape time. Thus these sources can contribute both to the population of unidentified point-like sources and to the local cosmic ray (CR) electron spectrum. The impact of the generated electron CRs depends on the diffusion rate inside molecular clouds (MCs). If the diffusion regime in a MC is similar to Galactic diffusion, the produced electrons should rapidly escape the cloud and contribute to the Galactic CR population at very high energies >100 TeV. However, due to the modest jet luminosity (at the level of 10^35 erg s^-1) and low filling factor of MC, these sources cannot make a significant contribution to the spectrum of cosmic ray electrons at lower energies. On the other hand, if the diffusion within MCs operates at a rate close to the Bohm limit, the CR electrons escaping from the source should be confined in the cloud, significantly contributing to the local density of CRs. The IC emission of these locally-generated CRs may explain the variety of gamma ray spectra detected from nearby MCs.Comment: 6 pages, accepted by MNRA

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Matching microlensing events with X-ray sources

Sartore

Treves

2012

A&A

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Aims. The detection of old neutron stars and stellar mass black holes in isolation is one of the most sought after goals of compact object astrophysics. Microlensing surveys may help in achieving this aim because the lensing mechanism is independent of the emission properties of the lens. Several black hole candidates have indeed been detected by means of microlensing observations have been reported in the literature. The identification of counterparts, especially in the X-rays, would be a strong argument in favor of the compact nature of these lenses. Methods. We perform a cross-correlation between the catalogs of microlensing events produced by the OGLE, MACHO, and MOA teams, and those of X-rays sources from the data acquired by the XMM-Newton and Chandra satellites. On the basis of our previous work, we select only microlensing events with durations longer than one hundred days, which should contain a large fraction of lenses as compact objects. Our matching criterion takes into account the positional coincidence on the sky. Results. We find a single match between a microlensing event, OGLE-2004-BLG-081 (t E ∼ 103 days), and the X-ray source 2XMM J180540.5-273427. The angular separation is ∼0.5 arcsec, i.e. well within the 90% error box of the X-ray source. The hardness ratios reported in the 2XMM catalog imply that it has a hard spectrum with a peak between 2 keV and 4.5 keV or it has a softer but highly absorbed spectrum. Moreover, the microlensing event is not fully constrained, and other authors propose a possible association of the source star with either a flaring cataclysmic variable or a RS Canum Venaticorum-like star. Conclusions. The very small angular separation (within uncertainties) is a strong indicator that 2XMM J180540.5-273427 is the X-ray counterpart of the OGLE event. However, the uncertainties in the nature of both the lensed system and the lens itself challenge the interpretation of 2XMM J180540.5-273427 as the first confirmed isolated black hole identified so far. In any case, it verifies the diagnostic capacity of microlensing surveys and open the pathway for further identifications of black hole or neutron star candidates.

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Probing isolated compact remnants with microlensing

Cited by 13 publications

References 44 publications

The OGLE view of microlensing towards the Magellanic Clouds - IV. OGLE-III SMC data and final conclusions on MACHOs★

The OGLE view of microlensing towards the Magellanic Clouds - IV. OGLE-III SMC data and final conclusions on MACHOs★

Jets and gamma-ray emission from isolated accreting black holes

Matching microlensing events with X-ray sources

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