Another pulsar with strange companion in NGC 6440

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Another pulsar with strange companion in NGC 6440

Post by Edasich on 4th November 2009, 5:28 am

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

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

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 MSun (assuming a 1.4 MSun 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.
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Re: Another pulsar with strange companion in NGC 6440

Post by Borislav on 4th November 2009, 7:19 am

0.0067 MSunthis is mass accreting disk or planet ?

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Re: Another pulsar with strange companion in NGC 6440

Post by Sirius_Alpha on 4th November 2009, 9:03 am

Borislav wrote:0.0067 MSunthis 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.

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Re: Another pulsar with strange companion in NGC 6440

Post by Lazarus on 4th November 2009, 1:54 pm

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.
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Re: Another pulsar with strange companion in NGC 6440

Post by Edasich on 4th November 2009, 4:13 pm

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...
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Re: Another pulsar with strange companion in NGC 6440

Post by Lazarus on 4th November 2009, 4:15 pm

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. Smile
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Re: Another pulsar with strange companion in NGC 6440

Post by Edasich on 4th November 2009, 6:42 pm

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. Smile

According to me it is turned off object. A vintage '80 black dwarf?? *lol*
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Re: Another pulsar with strange companion in NGC 6440

Post by Edasich on 4th December 2009, 5:21 pm

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

http://exoplanet.eu/star.php?st=NGC+6440+X2
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Re: Another pulsar with strange companion in NGC 6440

Post by ciceron on 4th December 2009, 6:16 pm

I don't get why they add this


- 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?


Last edited by ciceron on 4th December 2009, 6:16 pm; edited 1 time in total (Reason for editing : little spell check)

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Re: Another pulsar with strange companion in NGC 6440

Post by Sedna on 5th December 2009, 2:32 pm

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...

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Re: Another pulsar with strange companion in NGC 6440

Post by Edasich on 5th December 2009, 2:56 pm

Indeed. And if you look at first post in this thread you'll notice something... Laughing
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Re: Another pulsar with strange companion in NGC 6440

Post by Sedna on 5th December 2009, 6:42 pm

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.

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Re: Another pulsar with strange companion in NGC 6440

Post by Edasich on 6th December 2009, 5:28 am

No problem Wink
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Re: Another pulsar with strange companion in NGC 6440

Post by Sirius_Alpha on 7th December 2009, 4:18 am

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.

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Re: Another pulsar with strange companion in NGC 6440

Post by ciceron on 7th December 2009, 9:37 am

Thank you , now i see it Smile

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Re: Another pulsar with strange companion in NGC 6440

Post by Edasich on 13th December 2009, 1:53 pm

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).
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