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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"

24668 results found.

  1. EP250831a: Global MASTER-Net observations report
  2. EP250831a: EP-WXT detection of a fast X-ray transient
  3. GRB 250831A (SVOM trigger sb25083102) is likely an outburst from star G 272-61
  4. GRB 250831A: Swift-XRT counterpart detection
  5. GRB 250831A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  6. GRB 250831A: SVOM detection of a soft burst
  7. EP250830a: Global MASTER-Net observations report
  8. EP250830a/GRB 250830B: Einstein Probe detection of an X-ray transient and Swift/XRT follow-up
  9. LIGO/Virgo/KAGRA S250830bp: Coverage and upper limits from MAXI/GSC observations
  10. EP-WXT trigger 01709200994: Liverpool Telescope upper limits
  11. EP-WXT trigger 01709200994: confirmation of a stellar flare by BOOTES-6
  12. The EP-WXT trigger 01709200994 is likely a flaring star
  13. GRB 250828B: Swift-BAT refined analysis
  14. EP250821a: SOAR observations
  15. EP250827a: very early ATLAS detections, starting 43 sec after the EP trigger
  16. LIGO/Virgo/KAGRA S250818k: MeerKAT detection of an increase in radio flux from AT2025ulz
  17. GRB 250808B: SVOM detection of a burst through offline search
  18. EP250828a: Optical counterpart detection with Kinder observations
  19. EP250828a: Liverpool Telescope upper limits
  20. Swift GRB 250828B: Global MASTER-Net observations report
  21. EP250828a: Global MASTER-Net observations report
  22. EP-WXT trigger 01709200800 : KAIT optical observations
  23. EP250827a: Swift/UVOT Detection
  24. EP250828a: NOT optical counterpart confirmation
  25. EP250828a: SVOM/VT optical candidate
  26. GRB 250828B: Swift detection of a burst
  27. EP250827a: STEP/T80S Confirmation of fading optical counterpart
  28. EP250828a: Optical upper limit with Kinder observations
  29. LIGO/Virgo/KAGRA S250818k: uGMRT 1.3 GHz observations of AT2025ulz
  30. EP250827a: LCO observations show fading optical counterpart
  31. GRB 250828A: Fermi GBM Final Localization
  32. Fermi GRB 250827A: Global MASTER-Net observations report
  33. EP250827a: confirmation of optical rebrightening with LCO
  34. EP250827a: GOTO observation of the optical afterglow
  35. GRB 250827A: Fermi GBM Final Real-time Localization
  36. EP250827A: An optical rebrightening was detected by LCO.
  37. EP250827a: Swift-XRT counterpart detection
  38. The EP-WXT trigger 01709200800 is likely a flaring star
  39. EP250827a: TRT optical observations
  40. EP250827a: BOOTES-7 early optical dectection
  41. EP250827a: Gemini-South redshift z = 1.613
  42. EP250827a: Global MASTER-Net observations report
  43. EP250827a: Gemini-South optical counterpart detection
  44. Fermi GRB 250826A: Global MASTER-Net observations report
  45. LIGO/Virgo/KAGRA S250818k: SAO RAS BTA z-band observations of AT2025ulz
  46. Fermi trigger No 777883624: Global MASTER-Net observations report
  47. Fermi Gamma-ray Burst Monitor trigger 777883624/250826283 is not a GRB
  48. GRB 250826A: Fermi GBM Final Real-time Localization
  49. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Confirmation of Rebrightening of AT2025ulz
  50. Fermi GRB 250824B: Global MASTER-Net observations report
  51. LIGO/Virgo/KAGRA S250818k: VLA upper limits on AT2025ulz
  52. LIGO/Virgo/KAGRA S250818k: Pan-STARRS imaging confirms re-brightening of SN2025ulz
  53. GRB 250823A: Swift-BAT refined analysis
  54. LIGO/Virgo/KAGRA S250818k: MASTER predicovery limits of the AT2025ulz/ZTF25abjmnps KN candidate
  55. GRB 250823A: Swift-XRT refined Analysis
  56. EP triggers 01709200706 and 01709200707: GOTO confirmation of flaring stars
  57. LIGO/Virgo/KAGRA S250818k: Swift Observations of AT 2025ulz - Second Epoch
  58. GRB 250824B: Fermi GBM Final Real-time Localization
  59. The EP-WXT trigger 01709200707 is likely a flaring star
  60. GRB 250823A: COLIBRÍ optical observations
  61. The EP-WXT trigger 01709200706 is likely a flaring star
  62. GRB 250823A: SVOM/VT optical observation
  63. GRB 250824A: Fermi GBM Final Real-time Localization
  64. GRB 250823A: Swift/UVOT Detection
  65. GRB 250823A: NOT optical observations
  66. LIGO/Virgo/KAGRA S250818k: COLIBRÍ confirmation of rebrightening of AT2025ulz
  67. GRB 250823A: Fermi GBM Observation
  68. GRB 250823A: LCOGT Optical Detection
  69. GRB 250823A: BOOTES6/DPRT early optical detection
  70. GRB 250823A: Liverpool Telescope optical detection
  71. GRB 250823A: Swift detection of a burst
  72. GRB 250823A: Fermi GBM Final Real-time Localization
  73. Swift GRB250823.84: Global MASTER-Net observations report
  74. LIGO/Virgo/KAGRA S250818k: PRIME nIR observations of AT2025ulz
  75. LIGO/Virgo/KAGRA S250818k: JinShan optical observations of AT2025ulz
  76. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz
  77. LIGO/Virgo/Kagra S250818k: STEP/T80N upper limits on 2025ulz
  78. LIGO/Virgo/KAGRA S250818k: 3 GHz MeerKAT observations of AT2025ulz
  79. IPN triangulation of GRB 250821B (long/bright)
  80. GRB 250821A: Kilonova-Catcher optical upper limits
  81. GRB 250821A: Swift-BAT refined analysis
  82. LIGO/Virgo/KAGRA S250818k: NOT optical observations of AT2025ulz
  83. EP250821a: VLT X-shooter spectroscopic redshift z = 0.577
  84. GRB 250821A: VLT/FORS2 Optical Observation
  85. GRB 250821A: GECAM-B detection
  86. EP250821a: SVOM/VT optical observation
  87. Fermi GRB 250821B: Global MASTER-Net observations report
  88. GRB 250821A: NOT z-band upper limit
  89. GRB 250821C: Fermi GBM Final Real-time Localization
  90. GRB 250821A: Swift-XRT refined Analysis
  91. Swift GRB 250821A: Global MASTER-Net observations report
  92. GRB 250821B: Fermi GBM Detection
  93. GRB 250821B: BALROG localization (Fermi Trigger / GRB 250821672)
  94. GRB 250821B: Fermi GBM Final Localization of a Bright Burst
  95. GRB 250821A: Swift/UVOT Upper Limits
  96. EP250821a: Rapidly fading optical source detected in Las Cumbres followup
  97. EP250821a: Swift XRT and UVOT counterpart detection
  98. LIGO/Virgo/KAGRA S250818k: GOTO counterpart search and upper limits
  99. GRB 250821A: LCOGT Optical Upper Limits
  100. GRB 250814A: CMO SAI and SAO RAS izJ observations.

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