Another pulsar with strange companion in NGC 6440

SWIFT J1756.9-2508, a challenger appears...

Discovery of a 205.89 Hz accreting-millisecond X-ray pulsar in the globular cluster NGC 6440

Quote :

We report the discovery of the second accreting millisecond X-ray pulsar (AMXP) in the globularcluster NGC 6440. Pulsations with a frequency of 205.89 Hz were detected with the Rossi X-RayTiming Explorer on August 30th and October 1st, 2009, during the decay of . 4 days outburst of anewly X-ray transient source in NGC 6440. By studying the Doppler shift of the pulsation frequencywe find that the system is an ultra-compact binary with an orbital period of 57.3 minutes and aprojected semi-major axis of 6.22 light-milliseconds. Based on the mass function, we estimate a lowerlimit to the mass of the companion to be 0.0067 M_Sun (assuming a 1.4 M_Sun neutron star). This newpulsar shows the shortest outburst recurrence time among AMXPs ( 1 month). If this behavior doesnot cease, this AMXP has the potential to be one of the best sources in which to study how the binarysystem and the neutron star spin evolve. Furthermore, the characteristics of this new source indicatesthat there might exist a population of AMXPs undergoing weak outbursts which are undetected bycurrent all-sky X-ray monitors. NGC 6440 is the only globular cluster to host two known AMXPs,while no AMXPs have been detected in any other globular cluster.

Emphasis mine.

0.0067 M_Sunthis is mass accreting disk or planet ?

Borislav wrote:

0.0067 M_Sunthis is mass accreting disk or planet ?

It will probably be considered a star since it had more mass, but it was accreted by the neutron star.

This isn't really a planet in the usual sense of the term.

The article mentions this is more consistent with being a very low mass white dwarf donor, helium dominated.

Sure it is really an awkward astronomical object, since quite planetary mass.
I wonder how stellar processes may take place with such a low mass.

I could even accept this for a 30 Mj object, but nearly a 7 Jupiter mass one...

Well given the object was likely a white dwarf before it got down to that mass, it wasn't doing much in the way of stellar processing anyway.

Lazarus wrote:

Well given the object was likely a white dwarf before it got down to that mass, it wasn't doing much in the way of stellar processing anyway.

According to me it is turned off object. A vintage '80 black dwarf?? *lol*

Oh, look. Now listed at EPE, among unconfirmed objects:

http://exoplanet.eu/star.php?st=NGC+6440+X2

I don't get why they add this

Quote :

- NGC 6440 X2 Remarks :
	9 Nov. 2009: The planetary nature of this object is uncertain because beeing so close to an X-ray source it may be a short living object

The x-ray source its a neutron star , i get that , and eventually could torn apart whatever remains of a white dwarf there. What does the x-ray abundance of the radiation has to do with it? What i'm missing there?

I made some research about weird-object news released in the past and I found something interesting. The actual object's parameters are very similar to the ones of another object named SWIFT J1756.9-2508, discovered in 2007. I don't know if it's the same for you, but for me it's very weird...

Indeed. And if you look at first post in this thread you'll notice something...

Ah, okay, I didn't see, my apologies. In fact, I was aware of the object before you create the thread, so when I saw it, I skipped the first post without reading it.

No problem

ciceron wrote:

The x-ray source its a neutron star , i get that , and eventually could torn apart whatever remains of a white dwarf there. What does the x-ray abundance of the radiation has to do with it? What i'm missing there?

I think that x-ray sources indicate an accretion disk that is being heated to extremely high temperatures. If so, the accretion disk would come from the companion. Since the companion is being accreted into the neutron star, it may thus be a short-lived object.

Thank you , now i see it

Planet or degenerate companion around a 47 Tucanae Pulsar?

Further results from the timing of the millisecond pulsars in 47 Tucanae

Around PSR J0024-72I (NAME 47 TUC I) a 13 Mj companion with orbital period of roughly 0.23 d (a=0.0083 AUs?). Likely another helium dwarf or what else?

There are also other pulsars in 47 Tuc with low-mass companions (mass between 0.02-0.2 Msun).

NGC 6440 seems to be the "house of neutron stars with planet-mass secondaries":

Discoveries and Timing of Pulsars in NGC 6440

Quote :

Using the MeerKAT radio telescope, a series of observations have been conducted to time the known pulsars and search for new pulsars in the globular cluster NGC 6440. As a result, two pulsars have been discovered, NGC 6440G and NGC 6440H, one of which is isolated and the other a non-eclipsing (at frequencies above 962 MHz) "Black Widow", with a very low mass companion (Mc > 0.006 M⊙). It joins the other binary pulsars discovered so far in this cluster which all have low companion masses (Mc < 0.30 M⊙). We present the results of long-term timing solutions obtained using data from both Green Bank and MeerKAT telescopes for these two new pulsars and an analysis of the pulsars NGC 6440C and NGC 6440D. For the isolated pulsar NGC 6440C, we searched for planets using a Markov Chain Monte Carlo technique. We find evidence for significant unmodelled variations but they cannot be well modelled as planets nor as part of a power-law red-noise process. Studies of the eclipses of the "Redback" pulsar NGC 6440D at two different frequency bands reveal a frequency dependence with longer and asymmetric eclipses at lower frequencies (962-1283 MHz).