Skip to main content
New! Browse Circulars by Event, Advanced Search, Sample Codes, Schema Release. See news and announcements

GCN Circulars

GCN Circulars are rapid astronomical bulletins submitted by and distributed to community members worldwide. They are used to share discoveries, observations, quantitative near-term predictions, requests for follow-up observations, or future observing plans related to high-energy, multi-messenger, and variable or transient astrophysical events. See the documentation for help with subscribing to or submitting Circulars.

Search for Circulars by submitter, subject, or body text (e.g. 'Fermi GRB').
To navigate to a specific circular, enter the associated Circular ID (e.g. 'gcn123', 'Circular 123', or '123').
Advanced Search

To narrow the search results, use advanced search syntax. This allows for specifying which circular field to search (submitter, subject, and/or body). For additional information, refer to the advanced search documentation.

Advanced Search Examples (click to copy):

subject:"Swift"
body:"GRB"
submitter:"Judith Racusin"
  1. Swift GRB 250327A: Global MASTER-Net observations report
  2. GRB 250327A: DDOTI Optical Observations
  3. GRB 250327A: COLIBRÍ optical upper limit
  4. GRB 250327A: Swift detection of a burst
  5. GRB 250327A: Fermi GBM Final Real-time Localization
  6. Fermi trigger No 764700395: Global MASTER-Net observations report
  7. LIGO/Virgo/KAGRA S250326y: Updated Sky localization
  8. Konus-Wind detection of GRB 250322A (short)
  9. IPN triangulation of GRB 250322B
  10. LIGO/Virgo/KAGRA S250326y: Identification of a GW compact binary merger candidate
  11. EP250321a: Mondy AZT-33IK Continued Optical Observations
  12. Swift follow-up observations of FRB250316A and EP J120944.2+585060
  13. GRB 250322A: third epoch of NOT optical observations
  14. GRB 250322A: Swift-BAT refined analysis
  15. The EP-WXT trigger 01709133021 (designated as EP250324a) is not a real source
  16. GRB 250321B: ISON-Kitab RC-36 Optical Upper Limit
  17. FRB 250316A: NOT optical upper limit for the X ray source EP J120944.2+585060
  18. GRB 250322A: further NOT optical observations
  19. EP-WXT trigger 01709133021: Optical upper limit through Kinder observations
  20. GRB 250322A: Swift/UVOT Upper Limits
  21. EP250324A: COLIBRÍ/DDRAGO Optical Observations
  22. GRB 250322A: VLT/X-shooter redshift confirmation of the putative host galaxy
  23. FRB 250316A: COLIBRÍ/DDRAGO Optical follow up of the X ray source EP J120944.2+585060
  24. GRB 250322B: NuSTAR detection of the prompt emission and regular dips during the burst
  25. GRB 250321B: Swift-XRT observations
  26. GRB 250322A: Swift-XRT refined Analysis
  27. EP250321a: TNOT Observation of Optical Counterpart
  28. FRB 250316A: DDOTI Continued Optical Observations (Third Epoch)
  29. GRB 250322A: Gemini-North redshift of candidate host galaxy
  30. EP250304a: VLT/MUSE spectroscopic observation of its associated supernova SN 2025fhm
  31. SVOM/sb25032302: SVOM detection of a long X-ray transient
  32. GRB 250322A: AstroSat CZTI detection of a short burst
  33. GRB 250322B: AstroSat CZTI detection of a bright long burst
  34. GRB250322A: STEP/T80S optical limits
  35. GRB 250322A: Gemini-South optical observations
  36. GRB 250322A: VLT optical observations
  37. GRB 250322A: VLT near-infrared observations
  38. FRB 250316A: DDOTI Continued Optical Observations
  39. GRB 250322A: NOT optical upper limits
  40. GRB 250322A: Enhanced Swift-XRT position
  41. GRB 250321B: SVOM/COLIBRÍ (F-GFT) follow-up observations
  42. FRB 20250316A: Kinder optical upper limits of the Einstein Probe candidate X-ray source EP J120944.2+585060
  43. GRB 250322A: MASTER optical observation
  44. EP250321a: Liverpool Telescope optical follow-up
  45. EP250321a: Mondy AZT-33IK Optical Observations
  46. GRB 250322A: Swift detection of a short burst
  47. FRB 20250316A: detection of a candidate associated X-ray source EP J120944.2+585060 by Einstein Probe
  48. EP250321a: refined analysis of the EP-WXT and EP-FXT observations
  49. EP250321a: KAIT optical observations
  50. EP250321A: COLIBRÍ Continuing Optical Observations
  51. GRB 250225B: GECAM-A detection
  52. GRB 250312A: GECAM-A detection
  53. GRB 250321B: Swift ToO observations
  54. EP250321a: WFST optical observations
  55. GRB 250320B: NuSTAR detection of the prompt emission from two broad bursts and preliminary analysis
  56. GRB 250321C: Fermi GBM Final Real-time Localization
  57. GRB 250320A: NuSTAR Detection of the Prompt Emission and Preliminary Results
  58. GRB 250320B: Fermi GBM Observation
  59. EP250321a: Xinglong 216 decaying optical observations
  60. GRB 250321A: Swift-BAT refined analysis
  61. GRB 250321A: Swift-XRT refined Analysis
  62. GRB 250320B: Fermi-LAT detection
  63. GRB 250321B: SVOM detection of a sub-threshold transient event
  64. EP250321a: SVOM/VT optical observation
  65. EP 250321A: Optical counterpart detection by LCO.
  66. EP250321a: Kinder optical follow-up observations
  67. GRB 250321A: Swift/UVOT Upper Limits
  68. GRB 250320B: SVOM/GRM observation of a long burst
  69. EP250321a: LCO optical counterpart detection
  70. EP250321a: Swift-XRT detection of an X-ray source
  71. EP250321A: COLIBRÍ Optical Observations
  72. EP250321a: VLT/X-shooter redshift z = 4.368
  73. GRB 250320B: AstroSat CZTI detection
  74. EP250321a: REM optical/NIR afterglow detection
  75. Fermi GRB 250320B: Global MASTER-Net observations report
  76. EP250321a: BOOTES-5/JGT optical afterglow detection
  77. EP250321a: TRT optical counterpart detection
  78. EP250321a: Global MASTER-Net observations report
  79. Swift GRB 250321A: Global MASTER-Net observations report
  80. Fermi GRB 250321A: Global MASTER-Net observations report
  81. EP250321a: Einstein Probe detection of an X-ray transient
  82. GRB 250321A: GOTO optical upper limits
  83. GRB 250321A: Swift-XRT localisation
  84. GRB 250314A: Keck/NIRC2 J-band upper limit
  85. EP250226a/GRB 250226A: KAIT optical observations
  86. GRB 250321A: Fermi GBM Observation
  87. GRB 250321A: Swift detection of a burst
  88. GRB 250321A: Fermi GBM Final Real-time Localization
  89. GRB 250320B: Fermi GBM Final Real-time Localization
  90. GRB 250309B: Proof-of-concept for Joint ZTF+EP Experiment
  91. GRB 250317B: Mondy AZT-33IK Continued Optical Observations
  92. GRB 250320A: Fermi GBM Final Real-time Localization
  93. Fermi GRB 250319B: Global MASTER-Net observations report
  94. FRB 20250316A: Upper limits for gamma-ray transient from Insight-HXMT/HE observations
  95. GRB 250313A: GRBAlpha detection
  96. LIGO/Virgo/KAGRA S250206dm: LIGHETR followup observations of AT2025azn
  97. GRB 250317B: SVOM/COLIBRI (F-GFT) follow-up observations
  98. GRB 250319B: Fermi GBM Final Localization
  99. GRB 250319A: Fermi GBM Final Localization
  100. GRB 250317D: EIRSAT-1 GMOD Detection

Advanced

Download all Circulars as a .tar.gz archive:
Questions or comments?
Contact GCN directly.
Have you found a bug in GCN?
Open an issue.
Want to contribute code to GCN?
Get involved on GitHub.

gcn.nasa.gov

A service of the Astrophysics Science Division at NASA Goddard Space Flight Center

Looking for U.S. government information and services? Visit USA.gov