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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"

20175 results found.

  1. GRB 250903A: SVOM detection of a burst
  2. EP250903a: TRT optical observations
  3. EP250903a: Einstein Probe detection of an X-ray transient
  4. EP 250827B: Detection of supernova counterpart by LCO.
  5. GRB 250902B: SVOM/GRM observation
  6. EP250827b: SVOM/VT observation of AT 2025wkm
  7. LIGO/VIRGO/KAGRA S250818k: No evidence for radio variability of AT2025ulz in MeerKAT 3 GHz data
  8. GRB 250831A (SVOM trigger sb25083102): KAIT confirmation of stellar flare
  9. GRB 250901A: Swift/UVOT Upper Limit
  10. GRB 250830B: Swift-XRT afterglow detection
  11. GRB 250831A (SVOM trigger sb25083102): confirmation of a stellar flare by SVOM/VT
  12. GRB 250902A: SVOM/GRM observation
  13. EP250828a: Early near-infrared follow-up with MIRAGE on the MDM 1.3m telescope
  14. EP250901a: refined analysis of the EP-WXT and EP-FXT observations
  15. GRB 250901A: EP-FXT follow-up observation
  16. GRB 250901A: SVOM/VT optical afterglow with VHF data
  17. LIGO/Virgo/KAGRA S250830bp: DECam GW-MMADS candidates
  18. GRB 250901A: LCO optical upper limit
  19. LIGO/Virgo/KAGRA S250901cb: Identification of a GW compact binary merger candidate
  20. EP250831a: NOT optical observations and tentative afterglow candidate
  21. EP250827b: Contemporaneous detection of EP X-ray flare EP250827b and ZTF transient ZTF25abmpngy/AT2025wkm
  22. GRB 250901A: SVOM detection of a burst
  23. EP250901a: Mephisto optical upper limits
  24. GRB 250830C: AstroSat CZTI detection of a long burst
  25. EP250901a: Einstein Probe detection of an X-ray transient
  26. IceCube Alert 250831.75: Global MASTER-Net observations report
  27. EP250831a: EP-WXT detection of a fast X-ray transient
  28. GRB 250831A: Swift-XRT counterpart detection
  29. GRB 250831A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  30. GRB 250831A: SVOM/VT upper limit with VHF data
  31. GRB 250831A: SVOM detection of a soft burst
  32. EP250830a/GRB 250830B: Einstein Probe detection of an X-ray transient and Swift/XRT follow-up
  33. LIGO/Virgo/KAGRA S250830bp: Updated Sky localization, EM Bright Classification, and Source Classification
  34. LIGO/Virgo/KAGRA S250830bp: Identification of a GW compact binary merger candidate
  35. EP-WXT trigger 01709200994: Liverpool Telescope upper limits
  36. LIGO/Virgo/KAGRA S250830m: Identification of a GW compact binary merger candidate
  37. GRB 250828B: Swift-BAT refined analysis
  38. EP250821a: SOAR observations
  39. EP250827a: very early ATLAS detections, starting 43 sec after the EP trigger
  40. LIGO/Virgo/KAGRA S250725j: Observations with the NSF-DOE Vera C. Rubin Observatory
  41. LIGO/Virgo/KAGRA S250818k: MeerKAT detection of an increase in radio flux from AT2025ulz
  42. GRB 250808B: SVOM detection of a burst through offline search
  43. EP250828a: refined analysis of the EP-WXT and EP-FXT observations
  44. EP250828a: Optical counterpart detection with Kinder observations
  45. EP250828a: Liverpool Telescope upper limits
  46. EP-WXT trigger 01709200800 : KAIT optical observations
  47. EP250828a: KAIT optical upper limit
  48. EP250827a: Swift/UVOT Detection
  49. EP250828a: NOT optical counterpart confirmation
  50. EP250828a: SVOM/VT optical candidate
  51. EP250828a: Seimei/TriCCS optical counterpart detection
  52. EP250828a: Optical upper limit with Kinder observations
  53. LIGO/Virgo/KAGRA S250818k: uGMRT 1.3 GHz observations of AT2025ulz
  54. EP250828a: Einstein Probe detection of an X-ray transient
  55. EP250827a: Preliminary analysis of the EP-WXT and EP-FXT observations
  56. LIGO/Virgo/KAGRA S250827fo: Identification of a GW compact binary merger candidate
  57. EP250827a: confirmation of optical rebrightening with LCO
  58. EP250827a: GOTO observation of the optical afterglow
  59. GRB 250826A: SVOM/GRM observation
  60. EP250827A: An optical rebrightening was detected by LCO.
  61. EP250827a: TRT optical observations
  62. EP250827a: BOOTES-7 early optical dectection
  63. EP250827a: Las Cumbres independent detection of the optical counterpart
  64. EP250827a: Einstein Probe detection of an X-ray transient
  65. LIGO/Virgo/KAGRA S250827l: Identification of a GW compact binary merger candidate
  66. GRB 250806A: HiPERCAM/GTC limits on a possible supernova
  67. LIGO/Virgo/KAGRA S250818k: SAO RAS BTA z-band observations of AT2025ulz
  68. LIGO/Virgo/KAGRA S250818k: Continued Keck I LRIS spectroscopy of ZTF25abjmnps (AT2025ulz)
  69. LIGO/Virgo/KAGRA S250818k: MASTER predicovery limits of the AT2025ulz/ZTF25abjmnps KN candidate
  70. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of SN 2025ulz as a type II supernova
  71. EP250821a: MeerKAT radio counterpart
  72. GRB 250823A: COLIBRÍ optical observations
  73. GRB 250823A: SVOM/VT optical observation
  74. GRB 250823A: Swift/UVOT Detection
  75. LIGO/Virgo/KAGRA S250818k: COLIBRÍ confirmation of rebrightening of AT2025ulz
  76. GRB 250818B: MeerKAT Detection
  77. GRB 250823A: Enhanced Swift-XRT position
  78. GRB 250823A: LCOGT Optical Detection
  79. GRB 250823A: Liverpool Telescope optical detection
  80. GRB 250823A: Swift detection of a burst
  81. Konus-Wind detection of GRB 250821B
  82. LIGO/Virgo/KAGRA S250818k: HST nIR detection of AT 2025ulz
  83. LIGO/Virgo/KAGRA S250818k: J-GEM follow-up observation for AT2025ulz
  84. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz
  85. LIGO/Virgo/KAGRA S250818k: 3 GHz MeerKAT observations of AT2025ulz
  86. GRB 250821A: Kilonova-Catcher optical upper limits
  87. GRB 250821A: VLT/FORS2 Optical Observation
  88. GRB 250821B: SVOM/GRM observation
  89. EP250821a: SVOM/VT optical observation
  90. GRB 250821A: NOT z-band upper limit
  91. GRB 250821A: KAIT optical upper limit
  92. LIGO/Virgo/KAGRA S250818k: Continued fading and reddening of AT2025ulz from Keck/LRIS imaging observations
  93. GRB 250821A: Enhanced Swift-XRT position
  94. GRB 250821A: Swift/UVOT Upper Limits
  95. LIGO/Virgo/KAGRA S250818k: GOTO counterpart search and upper limits
  96. EP250821a: Preliminary analysis of the EP-WXT and EP-FXT observations
  97. GRB 250821A: LCOGT Optical Upper Limits
  98. GRB 250814A: CMO SAI and SAO RAS izJ observations.
  99. GRB 250821A: Swift detection of a burst
  100. LIGO/Virgo/KAGRA S250818k: WFST pre-discovery limits and follow-up observations of AT 2025ulz

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