Draft:Original research/Serpens X-1

Serpens X-1 is a more recent designation for an astronomical X-ray source (Serpens XR-1, 'XR' for X-ray) in the constellation Serpens Cauda. It is designated as the first X-ray source discovered overall in the constellation Serpens.

This learning resource is exploratory and experimental, in part, because many subsequent sounding rocket launches, balloon flights, and satellite X-ray scans have apparently found several locations for this early X-ray source.

The question is "Are any of these subsequent X-ray sources the original Serpens XR-1?"

The number of nearby X-ray sources detected as Serpens X-1 over time suggests that different X-ray sources are being detected by different probes and X-ray observatories. Depending upon the accuracy of location, strength of X-ray signal and possible variation over spectral, temporal, or spatial distributions, the original astronomical X-ray source appears to be missing. This search effort is ongoing so that anyone may enjoy contributing and discussing.

Notations
The astronomical X-number notation (X-#) for an astronomical X-ray source in a constellation has its start from the initial discoverers of an extrasolar X-ray source at the American Science and Engineering Company (ASE)-Massachusetts Institute of Technology (MIT). "[T]he constellation genitive (or an abbreviation) followed by X and a digit, such as SCO X-1 [is applied]." Researchers at the US Naval Research Laboratory suggested "XR" (for X-Ray) rather than "X". This would be SCO XR-1 for the first X-ray source discovered in the constellation Scorpius. "[I]t seems more logical to use this in the standard astronomical notation where the identification precedes the constellation, i.e., X-1 Scorpii." Among the first 17 catalogued astronomical X-ray sources are X1 Scorpii to X3 Scorpii, X1 and X2 Sagittarii, and X1 to X4 Cygni. X1 Serpentis is listed at RA 18h 45m Dec +5° 18'.

Later, the sources became simply the constellation (or an abbreviation) followed by X-#, e.g., Scorpius X-1 (Sco X-1).

Proof of concept for sources
"In some cases, source locations are suspect unless confirmed by two or more separate experimenters."

Theoretical Serpens XR-1
Here's a theoretical definition:

Def. source 'C', located at B 1950.0 RA 18h 45m Dec 05.3° with flux of 1.5 x 10-8 erg/cm2.s for a computed black body source with temperature of 2 x 107 K for the range in wavelength 0.15-0.8 nm, or 0.3 x 10-8 erg/cm2.s for a computed black body source with temperature of 5 x 106 K for the same wavelength range, from 16 June 1964, and 25 April 1965, is called Serpens XR-1.

Entities
Serpens is split into two non-contiguous parts, Serpens Caput (Serpent's Head) to the west and Serpens Cauda (Serpent's Tail) to the east. Between these two halves lies the constellation of Ophiuchus, the "Serpent-Bearer". ... Stars in the tail include [Zeta Serpentis] ζ, [Eta Serpentis] η, [Theta Serpentis] θ, [Nu Serpentis] ν, [Xi Serpentis] ξ, and [Omicron Serpentis] ο Serpentis.

The image at the left is of Serpens Cauda.

The image at the right is of Serpens Caput.

In the center is a combined image with Serpens Cauda on the left, skyward West, and Serpens Caput on the right.

Objects
TYC 460-624-1 is a rotationally variable star. It is X-ray source 1RXS J184510.6+062016.

Astronomical X-ray sources
On March 31, and April 2, 1966, two separate balloon flights detected an X-ray source at approximately B 1950.0 RA 19h ±30m Dec +5° ±10°, with a flux of about 5 x 10-8 ergs cm-2 sec-1, in the energy range from 20 to 180 keV.

"Possible fittings of our distribution, together with the evaluation of the NRL group for ... Ser X1, give an index of 1.6 for a power law and a temperature of 2 x 109 °K for an exponential law ... Independently of the mechanism invoked, a black-body source would appear to be excluded: the high energies involved will demand extraordinary conditions in the [source], such as strong magnetic fields and high electron energies or hot dense plasmas at quite unusual temperatures."

The "[b]alloon measurements ... observed ... [a flux] (20 to 180 kev) from Ser XR-1 [of] about 8 x 10-8 erg/cm2ˑsec".

On May 15, 1967, a balloon flight, designated 296-P, observed X-ray counts in the direction for Serpens XR-1 using the NRL coordinates. The flight used the same gondola and detector, a 56.3-cm2 NaI crystal and a collimator with 8.4° full-width-at-half-maximum (FWHM) field of view, as used in earlier and later balloon flights. In the energy range of 16.6 to 23.4 keV the detector registered < 0.075 counts/second source rate for Serpens XR-1. In the range 23.4-46.7 keV, the count rate was 0.124±0.130. For the same ranges the detector also observed Scorpius X-1 at 0.243 and 0.098 counts/second (cts/s), suggesting that the source emission ratios were < 0.309 and 1.27 of Scorpius X-1, respectively.

"A Hydra-Iris rocket was launched from the open ocean 500 miles off the coast of Baja California [on November 3, 1968, at 18h00m UTC], at latitude 27.4 N and longitude 125 W." Ser XR-1 was observed at a galactic longitude of 36.0°. Ser XR-2 was at 16.5° in galactic longitude. The galactic longitude for Ser XR-1 (NRL) is 37° 15' 05.7". The source observed on November 3, 1968, is just short of 2° from Ser XR-1.

"The strength of these sources [Ser XR-1 at 0.8 photons cm-2 sec-1 and Ser XR-2 at 2.1 photons cm-2 sec-1] is about the same as that observed by NRL on 1965 April 25 (Friedman et al. 1967). Ser XR-1 seems to be strongest at low energies and has a shape similar to that of the Crab Nebula. The background subtraction for Ser XR-2 is a bit uncertain because of the nearness of other sources. Nevertheless, our result is reasonably close to that of the 1965 October 11 experiment of Gorenstein et al. (1967). The 1965 September 30 experiment of Fisher et al. (1967) is similar in shape but lower in intensity."

Uhuru X-ray sources
The Uhuru satellite detected an X-ray source at 2U 1836+05. The exact position was listed as B 1950.0 RA 18 36 29 Dec +05 02 24. In an error box with corners: RA 18 36 51 Dec +05 02 24, RA 18 35 34 Dec +05 05 06, RA 18 35 34 Dec +05 03 00, and RA 18 36 48 Dec +04 59 24. The authors designated the 2U 1836+05 source as Ser XR-1. But this did not include the final position for this source at 4U 1837+04.

By December 5, 1977, at least five other positions, in epoch 1950.0 coordinates, for Serpens XR-1 are indicated
 * 1) RA 18h 37m 29.8s Dec +04° 59' 23",
 * 2) GX +36.3,
 * 3) 4U 1837+04,
 * 4) MXB 1837+049, and
 * 5) 2S 1837+049.

These have been observed by sounding rocket on
 * 1) November 25, 1964, over the range 0.15-0.8 nm,
 * 2) April 25, 1965, over the range 0.15-0.8 nm,
 * 3) September 30, 1965, over the range 0.4-0.8 nm,
 * 4) October 11, 1966, over the range 0.2-0.5 nm,
 * 5) September 24, 1970, over the range 0.12-1.6 nm, and
 * 6) May 25, 1971, over the range 0.2-0.6 nm.

Subsequent satellite observations are
 * 1) Uhuru, 1971-73, over the range 0.2-0.6 nm,
 * 2) Ariel, in November 1974, over the range 0.2-1.8 nm,
 * 3) SAS 3, October 4-7, 1975, over the range 0.2-2.4 nm,
 * 4) SAS 3, August 22-28, 1976, over the range 0.2-1.1 nm, and
 * 5) SAS 3, 1975-77, over the range 0.2-1.1 nm.

The SIMBAD astronomical database has Serpens XR-1 located at epoch 2000.0 RA 18h 39m 57.56s Dec +05° 02' 09.6".

The image at right is a celestial map of the astronomical sources within the 1.5° radius error circle around Serpens X-1, not Serpens XR-1. The other sources, or astronomical objects, within this error circle are stars (*), additional X-ray sources (X), a gamma-ray burst source (gammaBurst), and a dark nebula (DkNeb).

XMM-Newton sources
The image at the top right is a graph of the XMM-Newton spectral signature from superheated iron atoms at the inner edge of the accretion disk orbiting the neutron star in Serpens X-1. Normally, the line would be a symmetrical peak, but it exhibits the classic features of distortion due to relativistic effects. The extremely fast motion of the iron-rich gas causes the line to spread out. The entire line has been shifted to longer wavelengths (left, red) because of the neutron star's powerful gravity. The line is brighter toward shorter wavelengths (right, blue) because Einstein's special theory of relativity predicts that a high-speed source beamed toward Earth will appear brighter than the same source moving away from Earth.

As of August 27, 2007 discoveries concerning asymmetric iron line broadening and their implications for relativity have been a topic of much excitement. With respect to the asymmetric iron line broadening, "We're seeing the gas whipping around just outside the neutron star's surface. And since the inner part of the disk obviously can't orbit any closer than the neutron star's surface, these measurements give us a maximum size of the neutron star's diameter. The neutron stars can be no larger than 18 to 20.5 miles across, results that agree with other types of measurements."

"We've seen these asymmetric lines from many black holes, but this is the first confirmation that neutron stars can produce them as well. It shows that the way neutron stars accrete matter is not very different from that of black holes, and it gives us a new tool to probe Einstein's theory."

"This is fundamental physics. There could be exotic kinds of particles or states of matter, such as quark matter, in the centers of neutron stars, but it's impossible to create them in the lab. The only way to find out is to understand neutron stars."

Serpens X-1, which contains a neutron star and a stellar companion, was observed using XMM-Newton and Suzaku's superb spectral capabilities to survey Serpens X-1. The Suzaku data confirmed the XMM-Newton result regarding the iron line in Serpens X-1.

The observations of the iron line asymmetric broadening using XMM-Newton of a Serpens X-1 (the LMXB) as reported in 2007 do not contain coordinates for the X-ray source.

MM Serpentis
B1950 coordinates are RA 18 37 29.55 Dec +04 59 21.0. Other designations: 3A 1837+049, GPS 1838+047, 1H 1837+049, INTEGRAL1 98, 1M 1837+049, 1RXS J183956.9+050203, 2S 1837+049, SWIFT J1840.0+0501, 2U 1836+05, 	3U 1837+04, 4U 1837+04, XB 1837+049, [BM83] X1837+049, and [KRL2007b] 331.

J2000 coordinates are RA 18 39 57.56 Dec +05 02 09.6.

"NuSTAR observed Serpens X-1 twice on 12 and 13 July, 2013 (Sequence IDs 30001013002 and 30001013004). The data were screened and processed using the NuSTAR Data Analysis Software (NuSTARDAS) version 1.1.1, resulting in a total of 43.4 ks of on-target time. The source is relatively bright, so the net exposure after instrumental deadtime is taken into account is 30.4 ks. Spectra from the FPMA and FPMB detectors were extracted from 120” regions centered on the source position, using the “nuproducts” FTOOL. Corresponding response files appropriate for the pointing type (on-axis), source type (point), and extraction regions were also created. Backgrounds were created using the “nusky-bgd” tool, which self-consistently accounts for background variations across the face of the detector."

"Serpens X-1 is known to exhibit Type-1 X-ray bursts at a rate of approximately 0.1 per hour (Galloway et al. 2008)."

"Owing to the abilities of NuSTAR, an Fe K line in the spectrum is revealed to be skewed at a high level of statistical confidence, and the Compton back-scattering "hump" expected in disk reflection scenarios is detected in a neutron star X-ray binary for the first time. Both findings are robust since the FPMA and FPMB detectors do not suffer from flux distortions due to effects such as photon pile-up. Clearly, broad Fe K lines in at least some neutron star X-ray binaries arise in the inner disk, and can be used to probe the stellar properties and inner accretion flow."

Hypotheses

 * 1) The first source believed to be Serpens X-1 is probably not as exciting as the currently accepted source.