By the end of 2023, we will have met 4 new “friends” outside the Milky Way!

Author: Fang Yangxuan, Zhao Jingyuan

Review | Zou Qianyi, Zhao Jingyuan, Zhang Mi, Li Shanshan

Edit|Please add your own

Unless otherwise specified, the time in the text is Beijing time, and the time in the picture is Coordinated Universal Time

As 2023 is coming to an end, the Public Supernova Search Project (PSP) has also ushered in a wave of discoveries. From the end of November to the beginning of December, PSP discovered four extragalactic novae in succession. Below, Xiaoxing will tell you about the process of these discoveries one by one.

AT 2023yoa

At about 6:00 am on November 28, PSP administrator Xu Jianlin discovered an extragalactic nova candidate in the PSP M31 raw image [taken by the Half Meter Telescope (HMT) in the early morning of the same day]. He then sent the candidate to the PSP administrator group. After further inspection and discussion, it was determined to be a real target with a brightness of about 16.2 magnitude (without filter). Administrator Zhang Mi immediately reported it to the Central Bureau of Astronomical Telegrams (CBAT) and the Temporary Name Service (TNS), and the candidate was immediately numbered AT 2023yoa and PNV J00430932+4115416, and internal number PSP23N.

A star can be seen in the central box of the discovery image of AT 2023yoa (left). There is no star in the corresponding position in the historical image of the Pan-STARRS survey project (right), and the star is located in the direction of the M31 galaxy. Considering the position and brightness, it is preliminarily judged to be a nova candidate.

No.: AT 2023yoa (= PSP23N) (= PNV J00430932+4115416)

Discovered by: Xu Jianlin, Zhang Mi, Tang Leiming, Zhou Wenjie, Zhao Jingyuan, Sun Guoyou, Ruan Jiangao, Gao Xing and PSP team

Brightness at Found: 16.2 mag (without filter)

Discovery time: 2023-11-28 03:56:16.800

TNS: https://www.wis-tns.org/object/2023yoa

CBAT:

http://www.cbat.eps.harvard.edu/unconf/followups/J00430932+4115416.html

After reporting, Zhang Mi noticed that the position of AT 2023yoa was very close to that of M31N 2013-10c, and suspected that it might be another outburst of M31N 2013-10c, so M31N 2013-10c might be a re-nova. However, Zhang Mi compared the positions of the two and noticed that they were 2.76 arc seconds apart, which did not conform to the hypothesis of a re-nova. However, considering the poor image quality of HMT in the early morning of that day, Zhang Mi reprocessed the image and measured the target coordinates again. By manually stacking and comparing the M31N 2013-10c discovery image with the HMT discovery image, it was found that the angular distance between the position of AT 2023yoa and M31N 2013-10c was very small and could be ignored, which made the administrators unanimously believe that AT 2023yoa was most likely another outburst of M31N 2013-10c.

On October 9, 2013, the Lick Observatory Supernova Search Project discovered the nova candidate M31N 2013-10c. Follow-up observations by the Intermediate Palomar Transient Factory (iPTF) showed that M31N 2013-10c has a peak brightness of 17.3 magnitude in the R band, and a t2 time (i.e., the time it takes to dim by 2 magnitudes from the peak brightness) of 10.4±0.4 days. There is no public spectroscopic observation record of M31N 2013-10c's outburst in 2013, but Czech astronomer Kamil Hornoch and others conducted photometric observations of it in the Hα band, and the results showed that M31N 2013-10c is likely to be a nova.

LOSS's M31N 2013-10c discovery image

Light curve of M31N 2013-10c obtained by iPTF

Since no spectrum was obtained in 2013, the outburst in 2023 needs to first be confirmed by spectroscopy to identify the type of AT 2023yoa, and then accurately compare the positions to confirm whether AT 2023yoa is related to M31N 2013-10c.

In the early morning of the 29th, Italian amateur astronomer Claudio Balcon used the FOSC-ES32 spectrometer and the 0.41-meter telescope to obtain a low-resolution spectrum of AT 2023yoa. Two hours later, he uploaded the spectrum to TNS and classified AT 2023yoa as a nova.

Spectrum photographed by Claudio Balcon

TNS Page

Subsequently, the administrator Zhao Jingyuan contacted Professor Allen W. Shafter of the Department of Astronomy at San Diego State University and asked him to help confirm whether AT 2023yoa is related to M31N 2013-10c. After receiving the email, Professor Shafter quickly observed it using the 1-meter telescope of the Laguna Hills Observatory at San Diego State University on the afternoon of the 29th, and compared the obtained images with M31N 2013-10c. The results showed that the positions of the two targets were very consistent, so AT 2023yoa is indeed another outburst of M31N 2013-10c.

In the early morning of the 30th, Professor Shafter and others released Astronomer Telegram No. 16354 (ATel#16354), and all discoverers of AT 2023yoa were listed as co-authors. This ATel officially confirmed that M31N 2013-10c is a newly confirmed re-nova system, and AT 2023yoa is its second recorded outburst. The re-nova family has welcomed a new member.

ATel#16354 Original

Below is the full translation of ATel#16354 (translation: Fang Yangxuan):

M31N 2013-10c (= AT 2023yoa) is a recurrent nova in M31

ATel #16354; AW Shafter (San Diego State University), K. Hornoch (Institute of Astronomy, Czech Academy of Sciences), Xu Jianlin, Zhang Mi, Tang Leiming, Zhou Wenjie, Zhao Jingyuan, Sun Guoyou, Ruan Jiangao, Gao Xing (Xingming Observatory)

November 29, 2023 19:07 UTC

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Credibility certification: Allen W. Shafter

Topics: Optics, Nova, Transient Sources

On November 27.831, 2023 UT, Xu Jianlin et al. discovered the M31 nova AT 2023yoa = PNV J00430932+4115416 = PSP23N at the Xingming Observatory. Zhao Jingyuan reminded Allen W. Shafter that the object is located near the position of M31N 2013-10c and is likely to be the second outburst of this previous nova. The relatively fast evolution rate of M31N 2013-10c (t2 = 10.4 days; Soraisam et al. 2017, A&A, 599, A48) and the broad Hα emission lines observed from AT 2023yoa are consistent with this interpretation.

We made a follow-up observation of AT 2023yoa (which we cataloged as M31N 2023-11f) using the 40-inch reflecting telescope at San Diego State University's Laguna Hills Observatory (MLO) on November 29.151, 2023, R = 17.05 +/- 0.06. On November 26.094, 2023, the object was not visible in the Laguna Hills Observatory image, with an R-band limiting magnitude of 19.8.

To confirm the relationship between M31N 2023-11f and M31N 2013-10c, we aligned an image of M31N 2023-11f (taken by Laguna Hills Observatory on 29.151 UT 2023) with a historical Sloan r'-band image of M31N 2013-10c (taken by the 2.54-m Isaac Newton Telescope on 21.906 UT 2013 during the nova's fade) (see ATel #5503, which also confirmed that the object was likely a nova). As shown in the comparison images below, the nova is spatially consistent to better than 0.3 arc seconds.

Given the extremely remote possibility of the nova's location being a coincidence at such a great distance from the center of M31, we conclude that M31N 2023-11f is a follow-up outburst of the recently confirmed recurrent nova M31N 2013-10c.

More observations of this recent outburst of M31N 2013-10c are strongly recommended.

Compare images

AT 2023YPG and AT 2023YQT

PSP soon welcomed two more discoveries. On the evening of November 29, 2023, PSP participant Li Hualin discovered an extragalactic nova candidate in the M33.fts7 image. At about 7 a.m. the next morning, Xu Jianlin initially checked and judged the candidate as suspicious, and sent it to the administrator group for discussion. After checking the images recently taken by HMT and the 17-inch Photometric Auxiliary Telescope [abbreviated as PAT17, this is a survey project jointly conducted by Xingming Observatory and Xinjiang Astronomical Observatory, which is different from Xingming Observatory’s own Photometric Auxiliary Telescope (PAT)], the administrators unanimously agreed that the candidate was a real target. Zhang Mi immediately reported it to CBAT and TNS, and the candidate was given the numbers PNV J01325400+3021387, AT 2023ypg, and internal number PSP23O.

Discovery image of AT 2023ypg (left) and historical image of Pan-STARRS (right)

No.: AT 2023ypg (= PSP23O) (= PNV J01325400+3021387)

Discovered by: Li Hualin, Xu Jianlin, Zhang Mi, Tang Leiming, Zhou Wenjie, Zhao Jingyuan, Sun Guoyou, Ruan Jiangao, Gao Xing and PSP team

Found brightness: 18.2 magnitude (without filter)

Discovery time: November 29, 2023 22:36:57.600

TNS: https://www.wis-tns.org/object/2023ypg

CBAT:

http://www.cbat.eps.harvard.edu/unconf/followups/J01325400+3021387.html

Four days later, on the evening of December 3, Zhang Mi, Xu Jianlin and PSP participants Ren Yuqing, Ding Lanhe, Zhang Jiashuo and Yan Xiaochang successively discovered an extragalactic nova candidate in the PSP M31 original image (taken by HMT). After further inspection, Zhang Mi reported it to CBAT and TNS, and the candidate was numbered PNV J00422755+4111086, AT 2023yqt, and internally numbered PSP23Q.

The discovery image of AT 2023yqt (left) and the historical image of the Pan-STARRS survey project (right)

No.: AT 2023yqt (= PSP23Q) (= PNV J00422755+4111086)

Discovered by: Zhang Mi, Xu Jianlin, Ren Yuqing, Ding Lanhe, Zhang Jiashuo, Yan Xiaochang, Zhou Wenjie, Zhao Jingyuan, Sun Guoyou, Ruan Jiangao, Gao Xing and PSP team

Found brightness: 16.22 magnitude (without filter)

Discovery time: 20:21:16.992, December 3, 2023

TNS: https://www.wis-tns.org/object/2023yqt

CBAT:

http://www.cbat.eps.harvard.edu/unconf/followups/J00422755+4111086.html

PSP administrator Gao Xing obtained the spectra of AT 2023ypg and AT 2023yqt using the Ningbo Education Bureau-Xinjiang Astronomical Observatory Telescope (NEXT) on the evening of December 2 and December 5, respectively, and uploaded them to TNS after being processed by Zhao Jingyuan. The spectra of both candidates show strong Hα and β emission lines, so both are classified as novae.

Spectrum of AT 2023ypg

Spectrum of AT 2023yqt

M31N 2008-12a

The most important discoveries often come last, and this one was no exception.

M31N 2008-12a is a famous recurring nova. Since it was first discovered in December 2008, it has erupted again every year or so, without fail, making it the nova with the shortest eruption interval known so far. Due to its short eruption interval, it has attracted the attention of many nova hunters. In the second half of each year, a large number of astronomers and astronomy enthusiasts monitor the sky area where it is located, hoping to discover its eruption as early as possible and conduct follow-up observations in time to reveal the unique properties of this recurring nova.

Xingming Observatory also participated in the annual monitoring activities. Although it did not discover the outburst of M31N 2008-12a first in previous years due to various reasons, the large amount of data accumulated is still very valuable. Based on this, Xingming Observatory and astronomers have published several papers on M31N 2008-12a. With these experiences, the Xingming team believes that one day Xingming Observatory will also discover its outburst first.

On the evening of October 20, 2023, Xingming Observatory began this year's monitoring activities for M31N 2008-12a, and conducted special observations of the area where it is located on every clear night. At 21:13 on December 5, 2023, PSP administrator Sun Guoyou noticed that in the original image taken by HMT 8 minutes ago, there was an obvious star point at the position of M31N 2008-12a. He quickly sent a screenshot to the PSP administrator group and added the message that M31N 2008-12a "exploded".

The discovery image of AT 2023yvj (left) and the historical image of the Pan-STARRS survey project (right)

His speech attracted the interest of the administrators. After quickly confirming the authenticity of the candidate, the administrators divided the work and cooperated in an orderly manner. Soon, Zhang Mi reported the candidate to CBAT and TNS. The candidate was numbered PNV J00452890+4154100, AT 2023yvj, and the internal number PSP23R. Soon after, Zhao Jingyuan sent an email to the "M31N 2008-12a Monitoring" email group, reporting that Xingming Observatory had discovered the outbreak of M31N 2008-12a this year.

Message sent to the "M31N 2008-12a Monitoring" mailing list

Then, Zhao Jingyuan completed the draft of ATel to announce the discovery and contacted Professor Matt Darnley of the Institute of Astrophysics at Liverpool John Moores University in the UK, asking him to help publish ATel. At 22:47, ATel#16361 was officially released, and all PSP administrators who participated in the discovery were listed as co-authors.

ATel#16361 Original

No.: AT 2023yvj (= PSP23R) (= PNV J00452890+4154100)

Discovered by: Sun Guoyou, Xu Jianlin, Zhang Mi, Zhou Wenjie, Zhao Jingyuan, Ruan Jiangao, Gao Xing and PSP team

Found brightness: 18.63 magnitude (without filter)

Discovery time: 21:06:29.088, December 5, 2023

TNS: https://www.wis-tns.org/object/2023yvj

CBAT:

http://www.cbat.eps.harvard.edu/unconf/followups/J00452890+4154100.html

The following is the full translation of ATel#16361 (translation: Zhao Jingyuan):

Re-nova M31N 2008-12a: The 2023 outburst was discovered using the half-meter telescope at the Xingming Observatory

ATel#16361; Sun Guoyou, Xu Jianlin, Zhang Mi, Zhou Wenjie, Zhao Jingyuan, Ruan Jiangao, Gao Xing (Xingming Observatory)

December 5, 2023 14:47 UTC

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Credibility Certification: Matt Darnley

Topics: Optics, Request for observation, Nova, Transient sources

We report the discovery of a recurrent nova, M31N 2008-12a, in 2023.

The nova is clearly visible in this 120-second exposure, unfiltered image taken on 2023-12-05.54617 UTC using a 0.5-meter f/4 half-meter telescope in the Observatory Room 2 of the Xingming Observatory.

We measured its unfiltered brightness to be 18.63 ± 0.14 magnitude.

On December 05.54775, 2023 UTC, we obtained another image using the same instrument, in which the transient source is also visible, with an unfiltered brightness of 18.79±0.13 magnitude. However, in the historical image taken on December 04.83536, 2023 UTC using Xinjiang Astronomical Observatory PAT17, no celestial body can be seen at this position (r' band limiting magnitude 19.5).

We have also reported this transient source to CBAT and TNS, where it was assigned the designations PNV J00452890+4154100 and AT 2023yvj.

We strongly encourage follow-up photometric and spectral observations.

In the early morning of December 7, Italian amateur astronomer Claudio Balcon used the FOSC-ES32 spectrometer and the 0.41-meter telescope to obtain a low-resolution spectrum of the candidate, which showed broad and strong Hα emission lines. One hour later, he uploaded the spectrum to TNS and classified the candidate as a nova.

Spectrum photographed by Claudio Balcon

However, the signal-to-noise ratio of Balcon's spectrum is very low and cannot be compared with the spectrum of previous outbursts. Fortunately, on the afternoon of December 7, Judhajeet Basu, a doctoral student from the Indian Institute of Astrophysics, and others released ATel#16367, reporting their spectral observations and pointing out that its spectrum is similar to previous outbursts, indicating that the Xingming Observatory has finally taken the lead in discovering the outburst of M31N 2008-12a this year!

ATel#16367 Original

The following is the full translation of ATel#16367 (translation: Zhao Jingyuan):

Spectral confirmation of the outburst of M31N 2008-12a in 2023

ATel #16367; Judhajeet Basu, Sudhanshu Barway, GC Anupama, Shatakshi Chamoli, S. Pramod Kumar (Indian Institute of Astrophysics)

December 7, 2023 07:57 UTC

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Credibility certification: Sudhanshu Barway

Topics: Optics, Nova

We have acquired the optical spectrum of the 2023 outburst of the re-emerging nova M31N 2008-12a (see ATel#16365, ATel#16364, ATel#16362, ATel#16361, AT 2023yvj) using the Hanle Faint Object Spectrograph Camera (HFOSC) mounted on the 2-m Himalayan Chandra Telescope (HCT) at the Indian Astronomical Observatory (IAO) in Hanle. The spectrum was acquired on 2023-12-06.582 UT in the wavelength range of 3500-7500 Å with an exposure time of 2700 s.

The spectrum shows prominent hydrogen Balmer lines and 5876 angstrom He I lines. The full width at half maximum of the Hα line indicates a velocity of 3000 km/s. The spectrum is similar to previous bursts.

We will continue to monitor this nova using facilities at the Indian Astronomical Observatory.

We thank the observers at HCT for taking the time to perform the Target of Opportunity observations. The Indian Astronomical Observatory is operated by the Indian Institute of Astrophysics, Bangalore, India.

Finally, let's briefly review the history of M31N 2008-12a and understand its unique properties. On December 26, 2008, Japanese amateur astronomers Koichi Nishiyama and Fujio Kashima first discovered M31N 2008-12a in the northeast of M31. Because of the unusually rapid dimming, there was no spectrum for the 2008 outburst. However, to the astronomers' surprise, about three years later, on October 22, 2011, Russian amateur astronomers Stanislav Korotkiy and Leonid Elenin discovered a transient source at the location of M31N 2008-12a using a 0.45-meter telescope at the International Optical Monitoring Network's New Mexico Observatory. These two discoveries made astronomers begin to think that M31N 2008-12a might be a recurring nova with a very short interval between outbursts, but since there is no spectrum, other possibilities cannot be ruled out. Fortunately, a year later, the opportunity to obtain a spectrum came. Koichi Nishiyama and Fujio Kashima discovered another transient source at this location on October 18, 2012. Professor Shafter and others subsequently obtained a spectrum and confirmed that it was a He/N-type nova. Due to its short interval between outbursts, astronomers still cannot confidently determine that it is a recurring nova, but they have realized that if M31N 2008-12a is a recurring nova, then the nova system must have a white dwarf with a high accretion rate, and its mass is close to the Chandrasekhar limit. Under the influence of M31N 2008-12a, some astronomers began to explore the relationship between the mass and accretion rate of white dwarfs and the length of the interval between nova outbursts. At the same time, in 2013, Steven Williams, a doctoral student at Liverpool John Moores University in the UK, and others found the progenitor of M31N 2008-12a in the data of the Hubble Space Telescope. The brightness of the B band is 24.12, and it is obviously blue, which may indicate that the nova system has a high accretion rate. Finally, in early 2014, astronomers confidently determined that M31N 2008-12a is indeed a re-emerging nova and may be a candidate for the progenitor of a Type Ia supernova. This conclusion has made astronomers very interested in the nova system, and they have used a large number of facilities to monitor its annual outbursts. In 2013 and 2015, astronomers found the outbursts in 2009 and 2010 respectively from historical data; in 2014, astronomers found the X-ray counterparts of the outbursts in 1992, 1993 and 2001 from historical data of the Roentgen X-ray Observatory and the Chandra X-ray Observatory. In early 2019, Professor Darnley and others discovered a huge nova remnant around M31N 2008-12a, which was produced by the frequent explosions of the nova system. The latest research believes that the nova system contains a white dwarf with a mass greater than 1.36 times that of the sun. The white dwarf increases its mass by accreting matter from a companion star. At the same time, the mass of matter ejected by the nova explosion of this white dwarf is smaller than the mass of matter accreted, so it may explode as a Type Ia supernova or collapse into a neutron star within hundreds of thousands of years. Since 2011, observers around the world have promptly reported every explosion of M31N 2008-12a and obtained a large amount of valuable data. The explosions over the years are listed in the following table.

M31N 2008-12a eruption summary

Conclusion

PSP discovered 4 extragalactic novae in just 8 days, which is a very inspiring event. Among them, 3 novae have special significance:

1. PSP discovered the second recorded outburst of M31N 2013-10c, making it the latest confirmed re-emitted nova in M31.

2. PSP discovered the first nova in M33 - AT 2023ypg;

3. In recent years, Xingming Observatory has been at the forefront of the world in the search for new stars in M31, but there was one unfulfilled wish, which was M31N 2008-12a. This time, the wish was finally fulfilled, which was both a pleasant surprise and well deserved.

Congratulations to all the discoverers. Special thanks to Mr. Claudio Balcon, Professor Allen W. Shafter, Professor Matt Darnley, and the Indian Institute of Astrophysics team for their help in discovering all 4 extragalactic novae.

At present, PSP has discovered 135 candidate objects, of which 28 supernovae, 24 extragalactic novae (including 6 recurrent novae), 1 cataclysmic variable star, and 1 active galactic nucleus have been spectrally confirmed, and another 55 variable stars of various types have been included and clearly classified in the International Variable Star Index (VSX).

Open https://nadc.china-vo.org/psp/ and join us. You may be the next discoverer of a new celestial body.

References

1. AT 2023yoa, Transient Name Server, https://www.wis-tns.org/object/2023yoa

2. PNV J00430932+4115416, Central Bureau for Astronomical Telegrams, http://www.cbat.eps.harvard.edu/unconf/followups/J00430932+4115416.html

3. PSP23N, Xingming Observatory official website, http://xjltp.china-vo.org/psp23n.html

4. PNV J00430954+4115399 (= M31N 2013-10c), Central Bureau for Astronomical Telegrams, http://www.cbat.eps.harvard.edu/unconf/followups/J00430954+4115399.html

5. A novel method for transient detection in high-cadence optical surveys: Its application for a systematic search for novae in M31, Astronomy & Astrophysics, https://www.aanda.org/articles/aa/full_html/2017/03/aa29368-16/aa29368-16.html

6. ATel#5503: H-alpha Confirmation of Six Novae in M31, The Astronomer's Telegram, https://www.astronomerstelegram.org/?read=5503

7. ATel#16354: M31N 2013-10c (= AT 2023yoa) is a Recurrent Nova in M31, The Astronomer's Telegram, https://www.astronomerstelegram.org/?read=16354

8. AT 2023ypg, Transient Name Server, https://www.wis-tns.org/object/2023ypg

9. PNV J01325400+3021387, Central Bureau for Astronomical Telegrams, http://www.cbat.eps.harvard.edu/unconf/followups/J01325400+3021387.html

10. PSP23O, Xingming Observatory official website, http://xjltp.china-vo.org/psp23o.html

11. AT 2023yqt, Transient Name Server, https://www.wis-tns.org/object/2023yqt

12. PNV J00422755+4111086, Central Bureau for Astronomical Telegrams, http://www.cbat.eps.harvard.edu/unconf/followups/J00422755+4111086.html

13. PSP23Q, Xingming Observatory official website, http://xjltp.china-vo.org/psp23q.html

14. AT 2023yvj, Transient Name Server, https://www.wis-tns.org/object/2023yvj

15. PNV J00452890+4154100, Central Bureau for Astronomical Telegrams, http://www.cbat.eps.harvard.edu/unconf/followups/J00452890+4154100.html

16. PSP23R, Xingming Observatory official website, http://xjltp.china-vo.org/psp23r.html

17. ATel#16361: Recurrent Nova M31N 2008-12a: discovery of the 2023 eruption with Half Meter Telescope at Xingming Observatory, The Astronomer's Telegram, https://www.astronomerstelegram.org/?read=16361

18. ATel#16367: Spectroscopic confirmation of the 2023 outburst of M31N 2008-12a, The Astronomer's Telegram, https://www.astronomerstelegram.org/?read=16367

19. Extragalactic Novae: A historical perspective, IOPscience, https://iopscience.iop.org/book/mono/978-0-7503-1296-7

20. M31N 2008-12a - the remarkable recurrent nova in M31: Panchromatic observations of the 2015 eruption, The Astrophysical Journal, https://iopscience.iop.org/article/10.3847/1538-4357/833/2/149

21. Multi-wavelength observations of multiple eruptions of the recurrent nova M31N 2008-12a, arXiv, https://arxiv.org/abs/2310.06586

22. A recurrent nova super-remnant in the Andromeda galaxy, Nature, https://www.nature.com/articles/s41586-018-0825-4

23. M31’s new star, 1 year’s 16th chapter’s new star burst, confirmed, AstroArts, https://www.astroarts.co.jp/article/hl/a/13377_nova_m31

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